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INTERNALS 1. Machine Description Macros In addition to the file `machine.md', a machine description includes a C header file conventionally given the name `machine.h'. This header file defines numerous macros that convey the information about the target machine that does not fit into the scheme of the `.md' file. The file `tm.h' should be a link to `machine.h'. The header file `config.h' includes `tm.h' and most compiler source files include `config.h'. 1.1. Controlling the Compilation Driver, `gcc' SWITCH_TAKES_ARG (char) A C expression which determines whether the option `-char' takes arguments. The value should be the number of arguments that option takes--zero, for many options. By default, this macro is defined to handle the standard options properly. You need not define it unless you wish to add additional options which take arguments. WORD_SWITCH_TAKES_ARG (name) A C expression which determines whether the option `-name' takes arguments. The value should be the number of arguments that option takes--zero, for many options. This macro rather than SWITCH_TAKES_ARG is used for multi-character op- tion names. By default, this macro is defined to handle the standard options properly. You need not define it unless you wish to add additional options which take arguments. SWITCHES_NEED_SPACES A string-valued C expression which is nonempty if the linker needs a space between the `-L' or `-o' option and its argument. If this macro is not defined, the default value is 0. CPP_SPEC A C string constant that tells the GNU CC driver program options to pass to CPP. It can also specify how to translate options you give to GNU CC into options for GNU CC to pass to the CPP. Do not define this macro if it does not need to do anything. SIGNED_CHAR_SPEC A C string constant that tells the GNU CC driver program options to pass to CPP. By default, this macro is defined to pass the option `- D__CHAR_UNSIGNED__' to CPP if char will be treated as unsigned char by cc1. Do not define this macro unless you need to over- ride the default definition. CC1_SPEC A C string constant that tells the GNU CC driver program options to pass to cc1. It can also specify how to translate options you give to GNU CC into options for GNU CC to pass to the cc1. Do not define this macro if it does not need to do anything. CC1PLUS_SPEC A C string constant that tells the GNU CC driver program options to pass to cc1plus. It can also specify how to translate options you give to GNU CC into options for GNU CC to pass to the cc1plus. Do not define this macro if it does not need to do anything. ASM_SPEC A C string constant that tells the GNU CC driver program options to pass to the assembler. It can also specify how to translate options you give to GNU CC into options for GNU CC to pass to the as- sembler. See the file `sun3.h' for an example of this. Do not define this macro if it does not need to do anything. ASM_FINAL_SPEC A C string constant that tells the GNU CC driver program how to run any programs which cleanup after the normal assembler. Normally, this is not needed. See the file `mips.h' for an example of this. Do not define this macro if it does not need to do anything. LINK_SPEC A C string constant that tells the GNU CC driver program options to pass to the linker. It can also specify how to translate options you give to GNU CC into options for GNU CC to pass to the linker. Do not define this macro if it does not need to do anything. LIB_SPEC Another C string constant used much like LINK_SPEC. The difference between the two is that LIB_SPEC is used at the end of the command given to the linker. If this macro is not defined, a default is provid- ed that loads the standard C library from the usu- al place. See `gcc.c'. STARTFILE_SPEC Another C string constant used much like LINK_SPEC. The difference between the two is that STARTFILE_SPEC is used at the very beginning of the command given to the linker. If this macro is not defined, a default is provid- ed that loads the standard C startup file from the usual place. See `gcc.c'. ENDFILE_SPEC Another C string constant used much like LINK_SPEC. The difference between the two is that ENDFILE_SPEC is used at the very end of the com- mand given to the linker. Do not define this macro if it does not need to do anything. LINK_LIBGCC_SPECIAL Define this macro meaning that gcc should find the library `libgcc.a' by hand, rather than passing the argument `-lgcc' to tell the linker to do the search. RELATIVE_PREFIX_NOT_LINKDIR Define this macro to tell gcc that it should only translate a `-B' prefix into a `-L' linker option if the prefix indicates an absolute file name. STANDARD_EXEC_PREFIX Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/lib/gcc/' as the default prefix to try when searching for the executable files of the compiler. MD_EXEC_PREFIX If defined, this macro is an additional prefix to try after STANDARD_EXEC_PREFIX. MD_EXEC_PREFIX is not searched when the `-b' option is used, or the compiler is built as a cross compiler. STANDARD_STARTFILE_PREFIX Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/lib/gcc/' as the default prefix to try when searching for startup files such as `crt0.o'. MD_STARTFILE_PREFIX If defined, this macro supplies an additional pre- fix to try after the standard prefixes. MD_EXEC_PREFIX is not searched when the `-b' op- tion is used, or the compiler is built as a cross compiler. LOCAL_INCLUDE_DIR Define this macro as a C string constant if you wish to override the standard choice of `/usr/local/include' as the default prefix to try when searching for local header files. LOCAL_INCLUDE_DIR comes before SYSTEM_INCLUDE_DIR in the search order. Cross compilers do not use this macro and do not search either `/usr/local/include' or its replace- ment. SYSTEM_INCLUDE_DIR Define this macro as a C string constant if you wish to specify a system-specific directory to search for header files before the standard direc- tory. SYSTEM_INCLUDE_DIR comes before STANDARD_INCLUDE_DIR in the search order. Cross compilers do not use this macro and do not search the directory specified. STANDARD_INCLUDE_DIR Define this macro as a C string constant if you wish to override the standard choice of `/usr/include' as the default prefix to try when searching for header files. Cross compilers do not use this macro and do not search either `/usr/include' or its replacement. INCLUDE_DEFAULTS Define this macro if you wish to override the en- tire default search path for include files. The default search path includes GPLUSPLUS_INCLUDE_DIR, GCC_INCLUDE_DIR, LOCAL_INCLUDE_DIR, SYSTEM_INCLUDE_DIR, and STANDARD_INCLUDE_DIR. In addition, the macros GPLUSPLUS_INCLUDE_DIR and GCC_INCLUDE_DIR are de- fined automatically by `Makefile', and specify private search areas for GCC. The directory GPLUSPLUS_INCLUDE_DIR is used only for C++ pro- grams. The definition should be an initializer for an ar- ray of structures. Each array element should have two elements: the directory name (a string con- stant) and a flag for C++-only directories. Mark the end of the array with a null element. For ex- ample, here is the definition used for VMS: #define INCLUDE_DEFAULTS \ { \ { "GNU_GXX_INCLUDE:", 1}, \ { "GNU_CC_INCLUDE:", 0}, \ { "SYS$SYSROOT:[SYSLIB.]", 0}, \ { ".", 0}, \ { 0, 0} \ } Here is the order of prefixes tried for exec files: 1. Any prefixes specified by the user with `-B'. 2. The environment variable GCC_EXEC_PREFIX, if any. 3. The directories specified by the environment vari- able COMPILER_PATH. 4. The macro STANDARD_EXEC_PREFIX. 5. `/usr/lib/gcc/'. 6. The macro MD_EXEC_PREFIX, if any. Here is the order of prefixes tried for startfiles: 1. Any prefixes specified by the user with `-B'. 2. The environment variable GCC_EXEC_PREFIX, if any. 3. The directories specified by the environment vari- able LIBRARY_PATH. 4. The macro STANDARD_EXEC_PREFIX. 5. `/usr/lib/gcc/'. 6. The macro MD_EXEC_PREFIX, if any. 7. The macro MD_STARTFILE_PREFIX, if any. 8. The macro STANDARD_STARTFILE_PREFIX. 9. `/lib/'. 10. `/usr/lib/'. 1.2. Run-time Target Specification CPP_PREDEFINES Define this to be a string constant containing `- D' options to define the predefined macros that identify this machine and system. These macros will be predefined unless the `-ansi' option is specified. In addition, a parallel set of macros are prede- fined, whose names are made by appending `__' at the beginning and at the end. These `__' macros are permitted by the ANSI standard, so they are predefined regardless of whether `-ansi' is speci- fied. For example, on the Sun, one can use the following value: "-Dmc68000 -Dsun -Dunix" The result is to define the macros __mc68000__, __sun__ and __unix__ uncondition- ally, and the macros mc68000, sun and unix provided `-ansi' is not specified. STDC_VALUE Define the value to be assigned to the built- in macro __STDC__. The default is the value `1'. extern int target_flags; This declaration should be present. TARGET_... This series of macros is to allow compiler command arguments to enable or disable the use of optional features of the target machine. For example, one machine description serves both the 68000 and the 68020; a command argu- ment tells the compiler whether it should use 68020-only instructions or not. This command argument works by means of a macro TAR- GET_68020 that tests a bit in target_flags. Define a macro TARGET_featurename for each such option. Its definition should test a bit in target_flags; for example: #define TARGET_68020 (target_flags & 1) One place where these macros are used is in the condition-expressions of instruction pat- terns. Note how TARGET_68020 appears fre- quently in the 68000 machine description file, `m68k.md'. Another place they are used is in the definitions of the other macros in the `machine.h' file. TARGET_SWITCHES This macro defines names of command options to set and clear bits in target_flags. Its de- finition is an initializer with a subgrouping for each command option. Each subgrouping contains a string constant, that defines the option name, and a number, which contains the bits to set in target_flags. A negative number says to clear bits instead; the negative of the number is which bits to clear. The actual option name is made by appending `-m' to the specified name. One of the subgroupings should have a null string. The number in this grouping is the default value for target_flags. Any target options act starting with that value. Here is an example which defines `-m68000' and `-m68020' with opposite meanings, and picks the latter as the default: #define TARGET_SWITCHES \ { { "68020", 1}, \ { "68000", -1}, \ { "", 1}} TARGET_OPTIONS This macro is similar to TARGET_SWITCHES but defines names of command options that have values. Its definition is an initializer with a subgrouping for each command option. Each subgrouping contains a string constant, that defines the fixed part of the option name, and the address of a variable. The variable, type char *, is set to the variable part of the given option if the fixed part matches. The actual option name is made by appending `-m' to the specified name. Here is an example which defines `-mshort- data-number'. If the given option is `- mshort-data-512', the variable m88k_short_data will be set to the string "512". extern char *m88k_short_data; #define TARGET_OPTIONS { { "short-data-", &m88k_short_data } } TARGET_VERSION This macro is a C statement to print on stderr a string describing the particular machine description choice. Every machine description should define TARGET_VERSION. For example: #ifdef MOTOROLA #define TARGET_VERSION fprintf (stderr, " (68k, Motorola syntax)"); #else #define TARGET_VERSION fprintf (stderr, " (68k, MIT syntax)"); #endif OVERRIDE_OPTIONS Sometimes certain combinations of command op- tions do not make sense on a particular target machine. You can define a macro OVERRIDE_OPTIONS to take account of this. This macro, if defined, is executed once just after all the command options have been parsed. Don't use this macro to turn on various extra optimizations for `-O'. That is what OPTIMIZATION_OPTIONS is for. OPTIMIZATION_OPTIONS (level) Some machines may desire to change what optim- izations are performed for various optimiza- tion levels. This macro, if defined, is exe- cuted once just after the optimization level is determined and before the remainder of the command options have been parsed. Values set in this macro are used as the default values for the other command line options. level is the optimization level specified; 2 if -O2 is specified, 1 if -O is specified, and 0 if neither is specified. Do not examine write_symbols in this macro! The debugging options are not supposed to alter the generated code. 1.3. Storage Layout Note that the definitions of the macros in this table which are sizes or alignments measured in bits do not need to be constant. They can be C expressions that refer to static variables, such as the target_flags. See section Run-time Target. BITS_BIG_ENDIAN Define this macro to be the value 1 if the most significant bit in a byte has the lowest number; otherwise define it to be the value zero. This means that bit-field instructions count from the most significant bit. If the machine has no bit- field instructions, this macro is irrelevant. This macro does not affect the way structure fields are packed into bytes or words; that is controlled by BYTES_BIG_ENDIAN. BYTES_BIG_ENDIAN Define this macro to be 1 if the most significant byte in a word has the lowest number. WORDS_BIG_ENDIAN Define this macro to be 1 if, in a multiword ob- ject, the most significant word has the lowest number. BITS_PER_UNIT Number of bits in an addressable storage unit (byte); normally 8. BITS_PER_WORD Number of bits in a word; normally 32. MAX_BITS_PER_WORD Maximum number of bits in a word. If this is un- defined, the default is BITS_PER_WORD. Otherwise, it is the constant value that is the largest value that BITS_PER_WORD can have at run-time. UNITS_PER_WORD Number of storage units in a word; normally 4. POINTER_SIZE Width of a pointer, in bits. PARM_BOUNDARY Normal alignment required for function parameters on the stack, in bits. All stack parameters re- ceive least this much alignment regardless of data type. On most machines, this is the same as the size of an integer. STACK_BOUNDARY Define this macro if you wish to preserve a cer- tain alignment for the stack pointer. The defini- tion is a C expression for the desired alignment (measured in bits). If PUSH_ROUNDING is not defined, the stack will always be aligned to the specified boundary. If PUSH_ROUNDING is defined and specifies a less strict alignment than STACK_BOUNDARY, the stack may be momentarily unaligned while pushing argu- ments. FUNCTION_BOUNDARY Alignment required for a function entry point, in bits. BIGGEST_ALIGNMENT Biggest alignment that any data type can require on this machine, in bits. BIGGEST_FIELD_ALIGNMENT Biggest alignment that any structure field can re- quire on this machine, in bits. MAX_OFILE_ALIGNMENT Biggest alignment supported by the object file format of this machine. Use this macro to limit the alignment which can be specified using the __attribute__ ((aligned (n))) construct. If not defined, the default value is BIGGEST_ALIGNMENT. DATA_ALIGNMENT (type, basic-align) If defined, a C expression to compute the align- ment for a static variable. type is the data type, and basic-align is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. If this macro is not defined, then basic-align is used. One use of this macro is to increase alignment of medium-size data to make it all fit in fewer cache lines. Another is to cause character arrays to be word-aligned so that strcpy calls that copy con- stants to character arrays can be done inline. CONSTANT_ALIGNMENT (constant, basic-align) If defined, a C expression to compute the align- ment given to a constant that is being placed in memory. constant is the constant and basic-align is the alignment that the object would ordinarily have. The value of this macro is used instead of that alignment to align the object. If this macro is not defined, then basic-align is used. The typical use of this macro is to increase alignment for string constants to be word aligned so that strcpy calls that copy constants can be done inline. EMPTY_FIELD_BOUNDARY Alignment in bits to be given to a structure bit field that follows an empty field such as int : 0;. STRUCTURE_SIZE_BOUNDARY Number of bits which any structure or union's size must be a multiple of. Each structure or union's size is rounded up to a multiple of this. If you do not define this macro, the default is the same as BITS_PER_UNIT. STRICT_ALIGNMENT Define this if instructions will fail to work if given data not on the nominal alignment. If in- structions will merely go slower in that case, do not define this macro. PCC_BITFIELD_TYPE_MATTERS Define this if you wish to imitate the way many other C compilers handle alignment of bitfields and the structures that contain them. The behavior is that the type written for a bit- field (int, short, or other integer type) imposes an alignment for the entire structure, as if the structure really did contain an ordinary field of that type. In addition, the bitfield is placed within the structure so that it would fit within such a field, not crossing a boundary for it. Thus, on most machines, a bitfield whose type is written as int would not cross a four-byte boun- dary, and would force four-byte alignment for the whole structure. (The alignment used may not be four bytes; it is controlled by the other align- ment parameters.) If the macro is defined, its definition should be a C expression; a nonzero value for the expression enables this behavior. Note that if this macro is not defined, or its value is zero, some bitfields may cross more than one alignment boundary. The compiler can support such references if there are `insv', `extv', and `extzv' insns that can directly reference memory. The other known way of making bitfields work is to define STRUCTURE_SIZE_BOUNDARY as large as BIGGEST_ALIGNMENT. Then every structure can be accessed with fullwords. Unless the machine has bitfield instructions or you define STRUCTURE_SIZE_BOUNDARY that way, you must define PCC_BITFIELD_TYPE_MATTERS to have a nonzero value. BITFIELD_NBYTES_LIMITED Like PCC_BITFIELD_TYPE_MATTERS except that its ef- fect is limited to aligning a bitfield within the structure. ROUND_TYPE_SIZE (struct, size, align) Define this macro as an expression for the overall size of a structure (given by struct as a tree node) when the size computed from the fields is size and the alignment is align. The default is to round size up to a multiple of align. ROUND_TYPE_ALIGN (struct, computed, specified) Define this macro as an expression for the align- ment of a structure (given by struct as a tree node) if the alignment computed in the usual way is computed and the alignment explicitly specified was specified. The default is to use specified if it is larger; otherwise, use the smaller of computed and BIGGEST_ALIGNMENT MAX_FIXED_MODE_SIZE An integer expression for the size in bits of the largest integer machine mode that should actually be used. All integer machine modes of this size or smaller can be used for structures and unions with the appropriate sizes. If this macro is un- defined, GET_MODE_BITSIZE (DImode) is assumed. CHECK_FLOAT_VALUE (mode, value) A C statement to validate the value value (of type double) for mode mode. This means that you check whether value fits within the possible range of values for mode mode on this target machine. The mode mode is always SFmode or DFmode. If value is not valid, you should call error to print an error message and then assign some valid value to value. Allowing an invalid value to go through the compiler can produce incorrect assem- bler code which may even cause Unix assemblers to crash. This macro need not be defined if there is no work for it to do. TARGET_FLOAT_FORMAT A code distinguishing the floating point format of the target machine. There are three defined values: IEEE_FLOAT_FORMAT This code indicates IEEE floating point. It is the default; there is no need to define this macro when the format is IEEE. VAX_FLOAT_FORMAT This code indicates the peculiar format used on the Vax. UNKNOWN_FLOAT_FORMAT This code indicates any other format. The value of this macro is compared with HOST_FLOAT_FORMAT (see section Config) to deter- mine whether the target machine has the same for- mat as the host machine. If any other formats are actually in use on supported machines, new codes should be defined for them. 1.4. Layout of Source Language Data Types These macros define the sizes and other characteristics of the standard basic data types used in programs being com- piled. Unlike the macros in the previous section, these apply to specific features of C and related languages, rather than to fundamental aspects of storage layout. INT_TYPE_SIZE A C expression for the size in bits of the type int on the target machine. If you don't define this, the default is one word. SHORT_TYPE_SIZE A C expression for the size in bits of the type short on the target machine. If you don't define this, the default is half a word. (If this would be less than one storage unit, it is rounded up to one unit.) LONG_TYPE_SIZE A C expression for the size in bits of the type long on the target machine. If you don't define this, the default is one word. LONG_LONG_TYPE_SIZE A C expression for the size in bits of the type long long on the target machine. If you don't de- fine this, the default is two words. CHAR_TYPE_SIZE A C expression for the size in bits of the type char on the target machine. If you don't define this, the default is one quarter of a word. (If this would be less than one storage unit, it is rounded up to one unit.) FLOAT_TYPE_SIZE A C expression for the size in bits of the type float on the target machine. If you don't define this, the default is one word. DOUBLE_TYPE_SIZE A C expression for the size in bits of the type double on the target machine. If you don't define this, the default is two words. LONG_DOUBLE_TYPE_SIZE A C expression for the size in bits of the type long double on the target machine. If you don't define this, the default is two words. DEFAULT_SIGNED_CHAR An expression whose value is 1 or 0, according to whether the type char should be signed or unsigned by default. The user can always override this de- fault with the options `-fsigned-char' and `- funsigned-char'. DEFAULT_SHORT_ENUMS A C expression to determine whether to give an enum type only as many bytes as it takes to represent the range of possible values of that type. A nonzero value means to do that; a zero value means all enum types should be allocated like int. If you don't define the macro, the default is 0. SIZE_TYPE A C expression for a string describing the name of the data type to use for size values. The typedef name size_t is defined using the contents of the string. The string can contain more than one keyword. If so, separate them with spaces, and write first any length keyword, then unsigned if appropriate, and finally int. The string must exactly match one of the data type names defined in the function init_decl_processing in the file `c-decl.c'. You may not omit int or change the order---that would cause the compiler to crash on startup. If you don't define this macro, the default is "long unsigned int". PTRDIFF_TYPE A C expression for a string describing the name of the data type to use for the result of subtracting two pointers. The typedef name ptrdiff_t is de- fined using the contents of the string. See SIZE_TYPE above for more information. If you don't define this macro, the default is "long int". WCHAR_TYPE A C expression for a string describing the name of the data type to use for wide characters. The typedef name wchar_t is defined using the contents of the string. See SIZE_TYPE above for more in- formation. If you don't define this macro, the default is "int". WCHAR_TYPE_SIZE A C expression for the size in bits of the data type for wide characters. This is used in cpp, which cannot make use of WCHAR_TYPE. OBJC_INT_SELECTORS Define this macro if the type of Objective C selectors should be int. If this macro is not defined, then selectors should have the type struct objc_selector *. OBJC_NONUNIQUE_SELECTORS Define this macro if Objective C selector- references will be made unique by the linker (this is the default). In this case, each selector- reference will be given a separate assembler la- bel. Otherwise, the selector-references will be gathered into an array with a single assembler la- bel. MULTIBYTE_CHARS Define this macro to enable support for multibyte characters in the input to GNU CC. This requires that the host system support the ANSI C library functions for converting multibyte characters to wide characters. TARGET_BELL A C constant expression for the integer value for escape sequence `\a'. TARGET_BS TARGET_TAB TARGET_NEWLINE C constant expressions for the integer values for escape sequences `\b', `\t' and `\n'. TARGET_VT TARGET_FF TARGET_CR C constant expressions for the integer values for escape sequences `\v', `\f' and `\r'. 1.5. Register Usage This section explains how to describe what registers the target machine has, and how (in general) they can be used. The description of which registers a specific instruc- tion can use is done with register classes; see `Register Classes'. For information on using registers to access a stack frame, see `Frame Registers'. For passing values in registers, see `Register Arguments'. For returning values in registers, see `Scalar Return'. 1.5.1. Basic Characteristics of Registers FIRST_PSEUDO_REGISTER Number of hardware registers known to the com- piler. They receive numbers 0 through FIRST_PSEUDO_REGISTER-1; thus, the first pseudo register's number really is assigned the number FIRST_PSEUDO_REGISTER. FIXED_REGISTERS An initializer that says which registers are used for fixed purposes all throughout the compiled code and are therefore not available for general allocation. These would include the stack pointer, the frame pointer (except on machines where that can be used as a general register when no frame pointer is needed), the program counter on machines where that is considered one of the addressable registers, and any other numbered re- gister with a standard use. This information is expressed as a sequence of numbers, separated by commas and surrounded by braces. The nth number is 1 if register n is fixed, 0 otherwise. The table initialized from this macro, and the table initialized by the following one, may be overridden at run time either automatically, by the actions of the macro CONDITIONAL_REGISTER_USAGE, or by the user with the command options `-ffixed-reg', `-fcall-used- reg' and `-fcall-saved-reg'. CALL_USED_REGISTERS Like FIXED_REGISTERS but has 1 for each register that is clobbered (in general) by function calls as well as for fixed registers. This macro there- fore identifies the registers that are not avail- able for general allocation of values that must live across function calls. If a register has 0 in CALL_USED_REGISTERS, the compiler automatically saves it on function entry and restores it on function exit, if the register is used within the function. CONDITIONAL_REGISTER_USAGE Zero or more C statements that may conditionally modify two variables fixed_regs and call_used_regs (both of type char []) after they have been ini- tialized from the two preceding macros. This is necessary in case the fixed or call- clobbered registers depend on target flags. You need not define this macro if it has no work to do. If the usage of an entire class of registers depends on the target flags, you may indicate this to GCC by using this macro to modify fixed_regs and call_used_regs to 1 for each of the registers in the classes which should not be used by GCC. Also define the macro REG_CLASS_FROM_LETTER to re- turn NO_REGS if it is called with a letter for a class that shouldn't be used. (However, if this class is not included in GENERAL_REGS and all of the insn patterns whose constraints permit this class are controlled by target switches, then GCC will automatically avoid using these registers when the target switches are opposed to them.) NON_SAVING_SETJMP If this macro is defined and has a nonzero value, it means that setjmp and related functions fail to save the registers, or that longjmp fails to re- store them. To compensate, the compiler avoids putting variables in registers in functions that use setjmp. 1.5.2. Order of Allocation of Registers REG_ALLOC_ORDER If defined, an initializer for a vector of in- tegers, containing the numbers of hard registers in the order in which GNU CC should prefer to use them (from most preferred to least). If this macro is not defined, registers are used lowest numbered first (all else being equal). One use of this macro is on machines where the highest numbered registers must always be saved and the save-multiple-registers instruction sup- ports only sequences of consecutive registers. On such machines, define REG_ALLOC_ORDER to be an in- itializer that lists the highest numbered allocat- able register first. ORDER_REGS_FOR_LOCAL_ALLOC A C statement (sans semicolon) to choose the order in which to allocate hard registers for pseudo- registers local to a basic block. Store the desired order of registers in the array reg_alloc_order. Element 0 should be the register to allocate first; element 1, the next register; and so on. The macro body should not assume anything about the contents of reg_alloc_order before execution of the macro. On most machines, it is not necessary to define this macro. 1.5.3. How Values Fit in Registers This section discusses the macros that describe which kinds of values (specifically, which machine modes) each register can hold, and how many consecutive registers are needed for a given mode. HARD_REGNO_NREGS (regno, mode) A C expression for the number of consecutive hard registers, starting at register number regno, re- quired to hold a value of mode mode. On a machine where all registers are exactly one word, a suitable definition of this macro is #define HARD_REGNO_NREGS(REGNO, MODE) \ ((GET_MODE_SIZE (MODE) + UNITS_PER_WORD - 1) \ / UNITS_PER_WORD)) HARD_REGNO_MODE_OK (regno, mode) A C expression that is nonzero if it is per- missible to store a value of mode mode in hard register number regno (or in several registers starting with that one). For a machine where all registers are equivalent, a suitable de- finition is #define HARD_REGNO_MODE_OK(REGNO, MODE) 1 It is not necessary for this macro to check for the numbers of fixed registers, because the allocation mechanism considers them to be always occupied. On some machines, double-precision values must be kept in even/odd register pairs. The way to implement that is to define this macro to reject odd register numbers for such modes. The minimum requirement for a mode to be OK in a register is that the `movmode' instruction pattern support moves between the register and any other hard register for which the mode is OK; and that moving a value into the register and back out not alter it. Since the same instruction used to move SImode will work for all narrower integer modes, it is not necessary on any machine for HARD_REGNO_MODE_OK to distinguish between these modes, provided you define patterns `movhi', etc., to take advantage of this. This is useful because of the interaction between HARD_REGNO_MODE_OK and MODES_TIEABLE_P; it is very desirable for all integer modes to be tieable. Many machines have special registers for floating point arithmetic. Often people as- sume that floating point machine modes are al- lowed only in floating point registers. This is not true. Any registers that can hold in- tegers can safely hold a floating point machine mode, whether or not floating arith- metic can be done on it in those registers. Integer move instructions can be used to move the values. On some machines, though, the converse is true: fixed-point machine modes may not go in floating registers. This is true if the floating registers normalize any value stored in them, because storing a non-floating value there would garble it. In this case, HARD_REGNO_MODE_OK should reject fixed-point machine modes in floating registers. But if the floating registers do not automatically normalize, if you can store any bit pattern in one and retrieve it unchanged without a trap, then any machine mode may go in a floating re- gister and this macro should say so. The primary significance of special floating registers is rather that they are the regis- ters acceptable in floating point arithmetic instructions. However, this is of no concern to HARD_REGNO_MODE_OK. You handle it by writ- ing the proper constraints for those instruc- tions. On some machines, the floating registers are especially slow to access, so that it is better to store a value in a stack frame than in such a register if floating point arithmet- ic is not being done. As long as the floating registers are not in class GENERAL_REGS, they will not be used unless some pattern's con- straint asks for one. MODES_TIEABLE_P (mode1, mode2) A C expression that is nonzero if it is desir- able to choose register allocation so as to avoid move instructions between a value of mode mode1 and a value of mode mode2. If HARD_REGNO_MODE_OK (r, mode1) and HARD_REGNO_MODE_OK (r, mode2) are ever dif- ferent for any r, then MODES_TIEABLE_P (mode1, mode2) must be zero. 1.5.4. Handling Leaf Functions On some machines, a leaf function (i.e., one which make no calls) can run more efficiently if it does not make its own register window. Often this means it is required to receive its arguments in the registers where they are passed by the caller, instead of the registers where they would normally arrive. Also, the leaf function may use only those registers for its own variables and temporaries. GNU CC assigns register numbers before it knows whether the function is suitable for leaf function treatment. So it needs to renumber the registers in order to output a leaf function. The following macros accomplish this. LEAF_REGISTERS A C initializer for a vector, indexed by hard re- gister number, which contains 1 for a register that is allowable in a candidate for leaf function treatment. If leaf function treatment involves renumbering the registers, then the registers marked here should be the ones before renumbering---those that GNU CC would ordinarily allocate. The registers which will actually be used in the assembler code, after renumbering, should not be marked with 1 in this vector. Define this macro only if the target machine offers a way to optimize the treatment of leaf functions. LEAF_REG_REMAP (regno) A C expression whose value is the register number to which regno should be renumbered, when a func- tion is treated as a leaf function. If regno is a register number which should not ap- pear in a leaf function before renumbering, then the expression should yield -1, which will cause the compiler to abort. Define this macro only if the target machine offers a way to optimize the treatment of leaf functions, and registers need to be renumbered to do this. REG_LEAF_ALLOC_ORDER If defined, an initializer for a vector of in- tegers, containing the numbers of hard registers in the order in which the GNU CC should prefer to use them (from most preferred to least) in a leaf function. If this macro is not defined, REG_ALLOC_ORDER is used for both non-leaf and leaf-functions. Normally, it is necessary for FUNCTION_PROLOGUE and FUNCTION_EPILOGUE to treat leaf functions specially. The C variable leaf_function is nonzero for such a function. 1.5.5. Registers That Form a Stack There are special features to handle computers where some of the ``registers'' form a stack, as in the 80387 coprocessor for the 80386. Stack registers are normally written by pushing onto the stack, and are numbered relative to the top of the stack. Currently, GNU CC can only handle one group of stack- like registers, and they must be consecutively numbered. STACK_REGS Define this if the machine has any stack-like re- gisters. FIRST_STACK_REG The number of the first stack-like register. This one is the top of the stack. LAST_STACK_REG The number of the last stack-like register. This one is the bottom of the stack. 1.5.6. Obsolete Macros for Controlling Register Usage These features do not work very well. They exist because they used to be required to generate correct code for the 80387 coprocessor of the 80386. They are no longer used by that machine description and may be removed in a later version of the compiler. Don't use them! OVERLAPPING_REGNO_P (regno) If defined, this is a C expression whose value is nonzero if hard register number regno is an over- lapping register. This means a hard register which overlaps a hard register with a different number. (Such overlap is undesirable, but occa- sionally it allows a machine to be supported which otherwise could not be.) This macro must return nonzero for all the registers which overlap each other. GNU CC can use an overlapping register only in certain limited ways. It can be used for allocation within a basic block, and may be spilled for reloading; that is all. If this macro is not defined, it means that none of the hard registers overlap each other. This is the usual situation. INSN_CLOBBERS_REGNO_P (insn, regno) If defined, this is a C expression whose value should be nonzero if the insn insn has the effect of mysteriously clobbering the contents of hard register number regno. By ``mysterious'' we mean that the insn's RTL expression doesn't describe such an effect. If this macro is not defined, it means that no insn clobbers registers mysteriously. This is the usual situation; all else being equal, it is best for the RTL expression to show all the activity. PRESERVE_DEATH_INFO_REGNO_P (regno) If defined, this is a C expression whose value is nonzero if accurate REG_DEAD notes are needed for hard register number regno at the time of output- ting the assembler code. When this is so, a few optimizations that take place after register allo- cation and could invalidate the death notes are not done when this register is involved. You would arrange to preserve death info for a re- gister when some of the code in the machine description which is executed to write the assem- bler code looks at the death notes. This is necessary only when the actual hardware feature which GNU CC thinks of as a register is not actu- ally a register of the usual sort. (It might, for example, be a hardware stack.) If this macro is not defined, it means that no death notes need to be preserved. This is the usual situation. 1.6. Register Classes On many machines, the numbered registers are not all equivalent. For example, certain registers may not be allowed for indexed addressing; certain registers may not be allowed in some instructions. These machine restrictions are described to the compiler using register classes. You define a number of register classes, giving each one a name and saying which of the registers belong to it. Then you can specify register classes that are allowed as operands to particular instruction patterns. In general, each register will belong to several classes. In fact, one class must be named ALL_REGS and con- tain all the registers. Another class must be named NO_REGS and contain no registers. Often the union of two classes will be another class; however, this is not required. One of the classes must be named GENERAL_REGS. There is nothing terribly special about the name, but the operand constraint letters `r' and `g' specify this class. If GENERAL_REGS is the same as ALL_REGS, just define it as a macro which expands to ALL_REGS. Order the classes so that if class x is contained in class y then x has a lower class number than y. The way classes other than GENERAL_REGS are specified in operand constraints is through machine-dependent operand constraint letters. You can define such letters to correspond to various classes, then use them in operand con- straints. You should define a class for the union of two classes whenever some instruction allows both classes. For example, if an instruction allows either a floating point (coproces- sor) register or a general register for a certain operand, you should define a class FLOAT_OR_GENERAL_REGS which includes both of them. Otherwise you will get suboptimal code. You must also specify certain redundant information about the register classes: for each class, which classes contain it and which ones are contained in it; for each pair of classes, the largest class contained in their union. When a value occupying several consecutive registers is expected in a certain class, all the registers used must belong to that class. Therefore, register classes cannot be used to enforce a requirement for a register pair to start with an even-numbered register. The way to specify this requirement is with HARD_REGNO_MODE_OK. Register classes used for input-operands of bitwise-and or shift instructions have a special requirement: each such class must have, for each fixed-point machine mode, a sub- class whose registers can transfer that mode to or from memory. For example, on some machines, the operations for single-byte values (QImode) are limited to certain regis- ters. When this is so, each register class that is used in a bitwise-and or shift instruction must have a subclass con- sisting of registers from which single-byte values can be loaded or stored. This is so that PREFERRED_RELOAD_CLASS can always have a possible value to return. enum reg_class An enumeral type that must be defined with all the register class names as enumeral values. NO_REGS must be first. ALL_REGS must be the last register class, followed by one more enumeral value, LIM_REG_CLASSES, which is not a register class but rather tells how many classes there are. Each register class has a number, which is the value of casting the class name to type int. The number serves as an index in many of the tables described below. N_REG_CLASSES The number of distinct register classes, defined as follows: #define N_REG_CLASSES (int) LIM_REG_CLASSES REG_CLASS_NAMES An initializer containing the names of the re- gister classes as C string constants. These names are used in writing some of the debug- ging dumps. REG_CLASS_CONTENTS An initializer containing the contents of the register classes, as integers which are bit masks. The nth integer specifies the contents of class n. The way the integer mask is in- terpreted is that register r is in the class if mask & (1 << r) is 1. When the machine has more than 32 registers, an integer does not suffice. Then the in- tegers are replaced by sub-initializers, braced groupings containing several integers. Each sub-initializer must be suitable as an initializer for the type HARD_REG_SET which is defined in `hard-reg-set.h'. REGNO_REG_CLASS (regno) A C expression whose value is a register class containing hard register regno. In general there is more that one such class; choose a class which is minimal, meaning that no small- er class also contains the register. BASE_REG_CLASS A macro whose definition is the name of the class to which a valid base register must be- long. A base register is one used in an ad- dress which is the register value plus a dis- placement. INDEX_REG_CLASS A macro whose definition is the name of the class to which a valid index register must be- long. An index register is one used in an ad- dress where its value is either multiplied by a scale factor or added to another register (as well as added to a displacement). REG_CLASS_FROM_LETTER (char) A C expression which defines the machine- dependent operand constraint letters for re- gister classes. If char is such a letter, the value should be the register class correspond- ing to it. Otherwise, the value should be NO_REGS. REGNO_OK_FOR_BASE_P (num) A C expression which is nonzero if register number num is suitable for use as a base re- gister in operand addresses. It may be either a suitable hard register or a pseudo register that has been allocated such a hard register. REGNO_OK_FOR_INDEX_P (num) A C expression which is nonzero if register number num is suitable for use as an index re- gister in operand addresses. It may be either a suitable hard register or a pseudo register that has been allocated such a hard register. The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two registers, neither one of them scaled, then either one may be labeled the ``base'' and the other the ``index''; but whichever la- beling is used must fit the machine's con- straints of which registers may serve in each capacity. The compiler will try both label- ings, looking for one that is valid, and will reload one or both registers only if neither labeling works. PREFERRED_RELOAD_CLASS (x, class) A C expression that places additional restric- tions on the register class to use when it is necessary to copy value x into a register in class class. The value is a register class; perhaps class, or perhaps another, smaller class. On many machines, the definition #define PREFERRED_RELOAD_CLASS(X,CLASS) CLASS is safe. Sometimes returning a more restrictive class makes better code. For example, on the 68000, when x is an integer constant that is in range for a `moveq' instruction, the value of this macro is always DATA_REGS as long as class in- cludes the data registers. Requiring a data register guarantees that a `moveq' will be used. If x is a const_double, by returning NO_REGS you can force x into a memory constant. This is useful on certain machines where immediate floating values cannot be loaded into certain kinds of registers. LIMIT_RELOAD_CLASS (mode, class) A C expression that places additional restric- tions on the register class to use when it is necessary to be able to hold a value of mode mode in a reload register for which class class would ordinarily be used. Unlike PREFERRED_RELOAD_CLASS, this macro should be used when there are certain modes that simply can't go in certain reload classes. The value is a register class; perhaps class, or perhaps another, smaller class. Don't define this macro unless the target machine has limitations which require the mac- ro to do something nontrivial. SECONDARY_RELOAD_CLASS (class, mode, x) SECONDARY_INPUT_RELOAD_CLASS (class, mode, x) SECONDARY_OUTPUT_RELOAD_CLASS (class, mode, x) Many machines have some registers that cannot be copied directly to or from memory or even from other types of registers. An example is the `MQ' register, which on most machines, can only be copied to or from general registers, but not memory. Some machines allow copying all registers to and from memory, but require a scratch register for stores to some memory locations (e.g., those with symbolic address on the RT, and those with certain symbolic ad- dress on the Sparc when compiling PIC). In some cases, both an intermediate and a scratch register are required. You should define these macros to indicate to the reload phase that it may need to allocate at least one register for a reload in addition to the register to contain the data. Specifi- cally, if copying x to a register class in mode requires an intermediate register, you should define SECONDARY_INPUT_RELOAD_CLASS to return the largest register class all of whose registers can be used as intermediate regis- ters or scratch registers. If copying a register class in mode to x re- quires an intermediate or scratch register, you should define SECONDARY_OUTPUT_RELOAD_CLASS to return the largest register class required. If the re- quirements for input and output reloads are the same, the macro SECONDARY_RELOAD_CLASS should be used instead of defining both macros identically. The values returned by these macros are often GENERAL_REGS. Return NO_REGS if no spare re- gister is needed; i.e., if x can be directly copied to or from a register of class in mode without requiring a scratch register. Do not define this macro if it would always return NO_REGS. If a scratch register is required (either with or without an intermediate register), you should define patterns for `reload_inm' or `reload_outm', as required (see section Stan- dard Names. These patterns, which will nor- mally be implemented with a define_expand, should be similar to the `movm' patterns, ex- cept that operand 2 is the scratch register. Define constraints for the reload register and scratch register that contain a single regis- ter class. If the original reload register (whose class is class) can meet the constraint given in the pattern, the value returned by these macros is used for the class of the scratch register. Otherwise, two additional reload registers are required. Their classes are obtained from the constraints in the insn pattern. x might be a pseudo-register or a subreg of a pseudo-register, which could either be in a hard register or in memory. Use true_regnum to find out; it will return -1 if the pseudo is in memory and the hard register number if it is in a register. These macros should not be used in the case where a particular class of registers can only be copied to memory and not to another class of registers. In that case, secondary reload registers are not needed and would not be helpful. Instead, a stack location must be used to perform the copy and the movm pattern should use memory as a intermediate storage. This case often occurs between floating-point and general registers. SMALL_REGISTER_CLASSES Normally the compiler will avoid choosing spill registers from registers that have been explicitly mentioned in the rtl (these regis- ters are normally those used to pass parame- ters and return values). However, some machines have so few registers of certain classes that there would not be enough regis- ters to use as spill registers if this were done. On those machines, you should define SMALL_REGISTER_CLASSES. When it is defined, the compiler allows registers explicitly used in the rtl to be used as spill registers but prevents the compiler from extending the life- time of these registers. Defining this macro is always safe, but un- necessarily defining this macro will reduce the amount of optimizations that can be per- formed in some cases. If this macro is not defined but needs to be, the compiler will run out of reload registers and print a fatal er- ror message. For most machines, this macro should not be defined. CLASS_MAX_NREGS (class, mode) A C expression for the maximum number of con- secutive registers of class class needed to hold a value of mode mode. This is closely related to the macro HARD_REGNO_NREGS. In fact, the value of the macro CLASS_MAX_NREGS (class, mode) should be the maximum value of HARD_REGNO_NREGS (regno, mode) for all regno values in the class class. This macro helps control the handling of multiple-word values in the reload pass. Three other special macros describe which operands fit which constraint letters. CONST_OK_FOR_LETTER_P (value, c) A C expression that defines the machine-dependent operand constraint letters that specify particular ranges of integer values. If c is one of those letters, the expression should check that value, an integer, is in the appropriate range and return 1 if so, 0 otherwise. If c is not one of those letters, the value should be 0 regardless of value. CONST_DOUBLE_OK_FOR_LETTER_P (value, c) A C expression that defines the machine-dependent operand constraint letters that specify particular ranges of const_double values. If c is one of those letters, the expression should check that value, an RTX of code const_double, is in the appropriate range and re- turn 1 if so, 0 otherwise. If c is not one of those letters, the value should be 0 regardless of value. const_double is used for all floating-point con- stants and for DImode fixed-point constants. A given letter can accept either or both kinds of values. It can use GET_MODE to distinguish between these kinds. EXTRA_CONSTRAINT (value, c) A C expression that defines the optional machine- dependent constraint letters that can be used to segregate specific types of operands, usually memory references, for the target machine. Nor- mally this macro will not be defined. If it is required for a particular target machine, it should return 1 if value corresponds to the operand type represented by the constraint letter c. If c is not defined as an extra constraint, the value returned should be 0 regardless of value. For example, on the ROMP, load instructions cannot have their output in r0 if the memory reference contains a symbolic address. Constraint letter `Q' is defined as representing a memory address that does not contain a symbolic address. An al- ternative is specified with a `Q' constraint on the input and `r' on the output. The next alter- native specifies `m' on the input and a register class that does not include r0 on the output. 1.7. Describing Stack Layout and Calling Conventions 1.7.1. Basic Stack Layout STACK_GROWS_DOWNWARD Define this macro if pushing a word onto the stack moves the stack pointer to a smaller address. When we say, ``define this macro if ...,'' it means that the compiler checks this macro only with #ifdef so the precise definition used does not matter. FRAME_GROWS_DOWNWARD Define this macro if the addresses of local vari- able slots are at negative offsets from the frame pointer. ARGS_GROW_DOWNWARD Define this macro if successive arguments to a function occupy decreasing addresses on the stack. STARTING_FRAME_OFFSET Offset from the frame pointer to the first local variable slot to be allocated. If FRAME_GROWS_DOWNWARD, the next slot's offset is found by subtracting the length of the first slot from STARTING_FRAME_OFFSET. Otherwise, it is found by adding the length of the first slot to the value STARTING_FRAME_OFFSET. STACK_POINTER_OFFSET Offset from the stack pointer register to the first location at which outgoing arguments are placed. If not specified, the default value of zero is used. This is the proper value for most machines. If ARGS_GROW_DOWNWARD, this is the offset to the location above the first location at which outgo- ing arguments are placed. FIRST_PARM_OFFSET (fundecl) Offset from the argument pointer register to the first argument's address. On some machines it may depend on the data type of the function. If ARGS_GROW_DOWNWARD, this is the offset to the location above the first argument's address. STACK_DYNAMIC_OFFSET (fundecl) Offset from the stack pointer register to an item dynamically allocated on the stack, e.g., by allo- ca. The default value for this macro is STACK_POINTER_OFFSET plus the length of the outgo- ing arguments. The default is correct for most machines. See `function.c' for details. DYNAMIC_CHAIN_ADDRESS (frameaddr) A C expression whose value is RTL representing the address in a stack frame where the pointer to the caller's frame is stored. Assume that frameaddr is an RTL expression for the address of the stack frame itself. If you don't define this macro, the default is to return the value of frameaddr---that is, the stack frame address is also the address of the stack word that points to the previous frame. 1.7.2. Registers That Address the Stack Frame STACK_POINTER_REGNUM The register number of the stack pointer register, which must also be a fixed register according to FIXED_REGISTERS. On most machines, the hardware determines which register this is. FRAME_POINTER_REGNUM The register number of the frame pointer register, which is used to access automatic variables in the stack frame. On some machines, the hardware determines which register this is. On other machines, you can choose any register you wish for this purpose. ARG_POINTER_REGNUM The register number of the arg pointer register, which is used to access the function's argument list. On some machines, this is the same as the frame pointer register. On some machines, the hardware determines which register this is. On other machines, you can choose any register you wish for this purpose. If this is not the same register as the frame pointer register, then you must mark it as a fixed register according to FIXED_REGISTERS, or arrange to be able to elim- inate it (see section Elimination). STATIC_CHAIN_REGNUM STATIC_CHAIN_INCOMING_REGNUM Register numbers used for passing a function's static chain pointer. If register windows are used, STATIC_CHAIN_INCOMING_REGNUM is the register number as seen by the called function, while STATIC_CHAIN_REGNUM is the register number as seen by the calling function. If these registers are the same, STATIC_CHAIN_INCOMING_REGNUM need not be defined. The static chain register need not be a fixed re- gister. If the static chain is passed in memory, these macros should not be defined; instead, the next two macros should be defined. STATIC_CHAIN STATIC_CHAIN_INCOMING If the static chain is passed in memory, these macros provide rtx giving mem expressions that denote where they are stored. STATIC_CHAIN and STATIC_CHAIN_INCOMING give the locations as seen by the calling and called functions, respectively. Often the former will be at an offset from the stack pointer and the latter at an offset from the frame pointer. The variables stack_pointer_rtx, frame_pointer_rtx, and arg_pointer_rtx will have been initialized prior to the use of these macros and should be used to refer to those items. If the static chain is passed in a register, the two previous macros should be defined instead. 1.7.3. Eliminating Frame Pointer and Arg Pointer FRAME_POINTER_REQUIRED A C expression which is nonzero if a function must have and use a frame pointer. This expression is evaluated in the reload pass. If its value is nonzero the function will have a frame pointer. The expression can in principle examine the current function and decide according to the facts, but on most machines the constant 0 or the constant 1 suffices. Use 0 when the machine al- lows code to be generated with no frame pointer, and doing so saves some time or space. Use 1 when there is no possible advantage to avoiding a frame pointer. In certain cases, the compiler does not know how to produce valid code without a frame pointer. The compiler recognizes those cases and automati- cally gives the function a frame pointer regard- less of what FRAME_POINTER_REQUIRED says. You don't need to worry about them. In a function that does not require a frame pointer, the frame pointer register can be allo- cated for ordinary usage, unless you mark it as a fixed register. See FIXED_REGISTERS for more in- formation. This macro is ignored and need not be defined if ELIMINABLE_REGS is defined. INITIAL_FRAME_POINTER_OFFSET (depth-var) A C statement to store in the variable depth-var the difference between the frame pointer and the stack pointer values immediately after the func- tion prologue. The value would be computed from information such as the result of get_frame_size () and the tables of registers regs_ever_live and call_used_regs. If ELIMINABLE_REGS is defined, this macro will be not be used and need not be defined. Otherwise, it must be defined even if FRAME_POINTER_REQUIRED is defined to always be true; in that case, you may set depth-var to anything. ELIMINABLE_REGS If defined, this macro specifies a table of regis- ter pairs used to eliminate unneeded registers that point into the stack frame. If it is not de- fined, the only elimination attempted by the com- piler is to replace references to the frame pointer with references to the stack pointer. The definition of this macro is a list of struc- ture initializations, each of which specifies an original and replacement register. On some machines, the position of the argument pointer is not known until the compilation is com- pleted. In such a case, a separate hard register must be used for the argument pointer. This re- gister can be eliminated by replacing it with ei- ther the frame pointer or the argument pointer, depending on whether or not the frame pointer has been eliminated. In this case, you might specify: #define ELIMINABLE_REGS \ {{ARG_POINTER_REGNUM, STACK_POINTER_REGNUM}, \ {ARG_POINTER_REGNUM, FRAME_POINTER_REGNUM}, \ {FRAME_POINTER_REGNUM, STACK_POINTER_REGNUM}} Note that the elimination of the argument pointer with the stack pointer is specified first since that is the preferred elimination. CAN_ELIMINATE (from-reg, to-reg) A C expression that returns non-zero if the compiler is allowed to try to replace register number from-reg with register number to-reg. This macro need only be defined if ELIMINABLE_REGS is defined, and will usually be the constant 1, since most of the cases preventing register elimination are things that the compiler already knows about. INITIAL_ELIMINATION_OFFSET (from-reg, to- reg, offset-var) This macro is similar to INITIAL_FRAME_POINTER_OFFSET. It specifies the initial difference between the specified pair of registers. This macro must be defined if ELIMINABLE_REGS is defined. LONGJMP_RESTORE_FROM_STACK Define this macro if the longjmp function re- stores registers from the stack frames, rather than from those saved specifically by setjmp. Certain quantities must not be kept in regis- ters across a call to setjmp on such machines. 1.7.4. Passing Function Arguments on the Stack The macros in this section control how arguments are passed on the stack. See the following section for other macros that control passing certain arguments in registers. PROMOTE_PROTOTYPES Define this macro if an argument declared as char or short in a prototype should actually be passed as an int. In addition to avoiding errors in cer- tain cases of mismatch, it also makes for better code on certain machines. PUSH_ROUNDING (npushed) A C expression that is the number of bytes actual- ly pushed onto the stack when an instruction at- tempts to push npushed bytes. If the target machine does not have a push in- struction, do not define this macro. That directs GNU CC to use an alternate strategy: to allocate the entire argument block and then store the argu- ments into it. On some machines, the definition #define PUSH_ROUNDING(BYTES) (BYTES) will suffice. But on other machines, instructions that appear to push one byte actually push two bytes in an attempt to maintain alignment. Then the definition should be #define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1) ACCUMULATE_OUTGOING_ARGS If defined, the maximum amount of space re- quired for outgoing arguments will be computed and placed into the variable current_function_outgoing_args_size. No space will be pushed onto the stack for each call; instead, the function prologue should increase the stack frame size by this amount. It is not proper to define both PUSH_ROUNDING and ACCUMULATE_OUTGOING_ARGS. REG_PARM_STACK_SPACE Define this macro if functions should assume that stack space has been allocated for argu- ments even when their values are passed in re- gisters. The value of this macro is the size, in bytes, of the area reserved for arguments passed in registers. This space can either be allocated by the caller or be a part of the machine-dependent stack frame: OUTGOING_REG_PARM_STACK_SPACE says which. OUTGOING_REG_PARM_STACK_SPACE Define this if it is the responsibility of the caller to allocate the area reserved for argu- ments passed in registers. If ACCUMULATE_OUTGOING_ARGS is defined, this macro controls whether the space for these ar- guments counts in the value of current_function_outgoing_args_size. STACK_PARMS_IN_REG_PARM_AREA Define this macro if REG_PARM_STACK_SPACE is defined but stack parameters don't skip the area specified by REG_PARM_STACK_SPACE. Normally, when a parameter is not passed in registers, it is placed on the stack beyond the REG_PARM_STACK_SPACE area. Defining this macro suppresses this behavior and causes the parameter to be passed on the stack in its na- tural location. RETURN_POPS_ARGS (funtype, stack-size) A C expression that should indicate the number of bytes of its own arguments that a function pops on returning, or 0 if the function pops no arguments and the caller must therefore pop them all after the function returns. funtype is a C variable whose value is a tree node that describes the function in question. Normally it is a node of type FUNCTION_TYPE that describes the data type of the function. From this it is possible to obtain the data types of the value and arguments (if known). When a call to a library function is being considered, funtype will contain an identifier node for the library function. Thus, if you need to distinguish among various library functions, you can do so by their names. Note that ``library function'' in this context means a function used to perform arithmetic, whose name is known specially in the compiler and was not mentioned in the C code being com- piled. stack-size is the number of bytes of arguments passed on the stack. If a variable number of bytes is passed, it is zero, and argument pop- ping will always be the responsibility of the calling function. On the Vax, all functions always pop their ar- guments, so the definition of this macro is stack-size. On the 68000, using the standard calling convention, no functions pop their ar- guments, so the value of the macro is always 0 in this case. But an alternative calling con- vention is available in which functions that take a fixed number of arguments pop them but other functions (such as printf) pop nothing (the caller pops all). When this convention is in use, funtype is examined to determine whether a function takes a fixed number of ar- guments. 1.7.5. Passing Arguments in Registers This section describes the macros which let you control how various types of arguments are passed in registers or how they are arranged in the stack. FUNCTION_ARG (cum, mode, type, named) A C expression that controls whether a function argument is passed in a register, and which regis- ter. The arguments are cum, which summarizes all the previous arguments; mode, the machine mode of the argument; type, the data type of the argument as a tree node or 0 if that is not known (which happens for C support library functions); and named, which is 1 for an ordinary argument and 0 for nameless arguments that correspond to `...' in the called function's prototype. The value of the expression should either be a reg RTX for the hard register in which to pass the ar- gument, or zero to pass the argument on the stack. For machines like the Vax and 68000, where normal- ly all arguments are pushed, zero suffices as a definition. The usual way to make the ANSI library `stdarg.h' work on a machine where some arguments are usually passed in registers, is to cause nameless argu- ments to be passed on the stack instead. This is done by making FUNCTION_ARG return 0 whenever named is 0. You may use the macro MUST_PASS_IN_STACK (mode, type) in the definition of this macro to determine if this argument is of a type that must be passed in the stack. If REG_PARM_STACK_SPACE is not de- fined and FUNCTION_ARG returns non-zero for such an argument, the compiler will abort. If REG_PARM_STACK_SPACE is defined, the argument will be computed in the stack and then loaded into a register. FUNCTION_INCOMING_ARG (cum, mode, type, named) Define this macro if the target machine has ``re- gister windows'', so that the register in which a function sees an arguments is not necessarily the same as the one in which the caller passed the ar- gument. For such machines, FUNCTION_ARG computes the re- gister in which the caller passes the value, and FUNCTION_INCOMING_ARG should be defined in a simi- lar fashion to tell the function being called where the arguments will arrive. If FUNCTION_INCOMING_ARG is not defined, FUNCTION_ARG serves both purposes. FUNCTION_ARG_PARTIAL_NREGS (cum, mode, type, named) A C expression for the number of words, at the be- ginning of an argument, must be put in registers. The value must be zero for arguments that are passed entirely in registers or that are entirely pushed on the stack. On some machines, certain arguments must be passed partially in registers and partially in memory. On these machines, typically the first n words of arguments are passed in registers, and the rest on the stack. If a multi-word argument (a double or a structure) crosses that boundary, its first few words must be passed in registers and the rest must be pushed. This macro tells the compiler when this occurs, and how many of the words should go in registers. FUNCTION_ARG for these arguments should return the first register to be used by the caller for this argument; likewise FUNCTION_INCOMING_ARG, for the called function. FUNCTION_ARG_PASS_BY_REFERENCE (cum, mode, type, named) A C expression that indicates when an argument must be passed by reference. If nonzero for an argument, a copy of that argument is made in memory and a pointer to the argument is passed in- stead of the argument itself. The pointer is passed in whatever way is appropriate for passing a pointer to that type. On machines where REG_PARM_STACK_SPACE is not de- fined, a suitable definition of this macro might be #define FUNCTION_ARG_PASS_BY_REFERENCE(CUM, MODE, TYPE, NAMED) \ MUST_PASS_IN_STACK (MODE, TYPE) CUMULATIVE_ARGS A C type for declaring a variable that is used as the first argument of FUNCTION_ARG and oth- er related values. For some target machines, the type int suffices and can hold the number of bytes of argument so far. There is no need to record in CUMULATIVE_ARGS anything about the arguments that have been passed on the stack. The compiler has other variables to keep track of that. For target machines on which all arguments are passed on the stack, there is no need to store anything in CUMULATIVE_ARGS; however, the data struc- ture must exist and should not be empty, so use int. INIT_CUMULATIVE_ARGS (cum, fntype, libname) A C statement (sans semicolon) for initializ- ing the variable cum for the state at the be- ginning of the argument list. The variable has type CUMULATIVE_ARGS. The value of fntype is the tree node for the data type of the function which will receive the args, or 0 if the args are to a compiler support library function. When processing a call to a compiler support library function, libname identifies which one. It is a symbol_ref rtx which contains the name of the function, as a string. lib- name is 0 when an ordinary C function call is being processed. Thus, each time this macro is called, either libname or fntype is nonzero, but never both of them at once. INIT_CUMULATIVE_INCOMING_ARGS (cum, fntype, libname) Like INIT_CUMULATIVE_ARGS but overrides it for the purposes of finding the arguments for the function being compiled. If this macro is un- defined, INIT_CUMULATIVE_ARGS is used instead. The argument libname exists for symmetry with INIT_CUMULATIVE_ARGS. The value passed for libname is always 0, since library routines with special calling conventions are never compiled with GNU CC. FUNCTION_ARG_ADVANCE (cum, mode, type, named) A C statement (sans semicolon) to update the summarizer variable cum to advance past an ar- gument in the argument list. The values mode, type and named describe that argument. Once this is done, the variable cum is suitable for analyzing the following argument with FUNCTION_ARG, etc. This macro need not do anything if the argu- ment in question was passed on the stack. The compiler knows how to track the amount of stack space used for arguments without any special help. FUNCTION_ARG_PADDING (mode, type) If defined, a C expression which determines whether, and in which direction, to pad out an argument with extra space. The value should be of type enum direction: either upward to pad above the argument, downward to pad below, or none to inhibit padding. This macro does not control the amount of pad- ding; that is always just enough to reach the next multiple of FUNCTION_ARG_BOUNDARY. This macro has a default definition which is right for most systems. For little-endian machines, the default is to pad upward. For big-endian machines, the default is to pad downward for an argument of constant size shorter than an int, and upward otherwise. FUNCTION_ARG_BOUNDARY (mode, type) If defined, a C expression that gives the alignment boundary, in bits, of an argument with the specified mode and type. If it is not defined, PARM_BOUNDARY is used for all ar- guments. FUNCTION_ARG_REGNO_P (regno) A C expression that is nonzero if regno is the number of a hard register in which function arguments are sometimes passed. This does not include implicit arguments such as the static chain and the structure-value address. On many machines, no registers can be used for this purpose since all function arguments are pushed on the stack. 1.7.6. How Scalar Function Values Are Returned This section discusses the macros that control return- ing scalars as values---values that can fit in registers. TRADITIONAL_RETURN_FLOAT Define this macro if `-traditional' should not cause functions declared to return float to con- vert the value to double. FUNCTION_VALUE (valtype, func) A C expression to create an RTX representing the place where a function returns a value of data type valtype. valtype is a tree node representing a data type. Write TYPE_MODE (valtype) to get the machine mode used to represent that type. On many machines, only the mode is relevant. (Actually, on most machines, scalar values are returned in the same place regardless of mode). If the precise function being called is known, func is a tree node (FUNCTION_DECL) for it; other- wise, func is a null pointer. This makes it pos- sible to use a different value-returning conven- tion for specific functions when all their calls are known. FUNCTION_VALUE is not used for return vales with aggregate data types, because these are returned in another way. See STRUCT_VALUE_REGNUM and re- lated macros, below. FUNCTION_OUTGOING_VALUE (valtype, func) Define this macro if the target machine has ``re- gister windows'' so that the register in which a function returns its value is not the same as the one in which the caller sees the value. For such machines, FUNCTION_VALUE computes the re- gister in which the caller will see the value, and FUNCTION_OUTGOING_VALUE should be defined in a similar fashion to tell the function where to put the value. If FUNCTION_OUTGOING_VALUE is not defined, FUNCTION_VALUE serves both purposes. FUNCTION_OUTGOING_VALUE is not used for return vales with aggregate data types, because these are returned in another way. See STRUCT_VALUE_REGNUM and related macros, below. LIBCALL_VALUE (mode) A C expression to create an RTX representing the place where a library function returns a value of mode mode. If the precise function being called is known, func is a tree node (FUNCTION_DECL) for it; otherwise, func is a null pointer. This makes it possible to use a different value-returning convention for specific functions when all their calls are known. Note that ``library function'' in this context means a compiler support routine, used to perform arithmetic, whose name is known specially by the compiler and was not mentioned in the C code being compiled. The definition of LIBRARY_VALUE need not be con- cerned aggregate data types, because none of the library functions returns such types. FUNCTION_VALUE_REGNO_P (regno) A C expression that is nonzero if regno is the number of a hard register in which the values of called function may come back. A register whose use for returning values is lim- ited to serving as the second of a pair (for a value of type double, say) need not be recognized by this macro. So for most machines, this defini- tion suffices: #define FUNCTION_VALUE_REGNO_P(N) ((N) == 0) If the machine has register windows, so that the caller and the called function use dif- ferent registers for the return value, this macro should recognize only the caller's re- gister numbers. 1.7.7. How Large Values Are Returnd When a function value's mode is BLKmode (and in some other cases), the value is not returned according to FUNCTION_VALUE (see section Scalar Return). Instead, the caller passes the address of a block of memory in which the value should be stored. This address is called the struc- ture value address. This section describes how to control returning struc- ture values in memory. RETURN_IN_MEMORY (type) A C expression which can inhibit the returning of certain function values in registers, based on the type of value. A nonzero value says to return the function value in memory, just as large structures are always returned. Here type will be a C ex- pression of type tree, representing the data type of the value. Note that values of mode BLKmode are returned in memory regardless of this macro. Also, the option `-fpcc-struct-return' takes effect regardless of this macro. On most systems, it is possible to leave the macro undefined; this causes a default definition to be used, whose value is the constant 0. STRUCT_VALUE_REGNUM If the structure value address is passed in a re- gister, then STRUCT_VALUE_REGNUM should be the number of that register. STRUCT_VALUE If the structure value address is not passed in a register, define STRUCT_VALUE as an expression re- turning an RTX for the place where the address is passed. If it returns 0, the address is passed as an ``invisible'' first argument. STRUCT_VALUE_INCOMING_REGNUM On some architectures the place where the struc- ture value address is found by the called function is not the same place that the caller put it. This can be due to register windows, or it could be because the function prologue moves it to a different place. If the incoming location of the structure value address is in a register, define this macro as the register number. STRUCT_VALUE_INCOMING If the incoming location is not a register, define STRUCT_VALUE_INCOMING as an expression for an RTX for where the called function should find the value. If it should find the value on the stack, define this to create a mem which refers to the frame pointer. A definition of 0 means that the address is passed as an ``invisible'' first argu- ment. PCC_STATIC_STRUCT_RETURN Define this macro if the usual system convention on the target machine for returning structures and unions is for the called function to return the address of a static variable containing the value. GNU CC does not normally use this convention, even if it is the usual one, but does use it if `- fpcc-struct-value' is specified. Do not define this if the usual system convention is for the caller to pass an address to the sub- routine. 1.7.8. Caller-Saves Register Allocation If you enable it, GNU CC can save registers around function calls. This makes it possible to use call- clobbered registers to hold variables that must live across calls. DEFAULT_CALLER_SAVES Define this macro if function calls on the target machine do not preserve any registers; in other words, if CALL_USED_REGISTERS has 1 for all regis- ters. This macro enables `-fcaller-saves' by de- fault. Eventually that option will be enabled by default on all machines and both the option and this macro will be eliminated. CALLER_SAVE_PROFITABLE (refs, calls) A C expression to determine whether it is worthwhile to consider placing a pseudo-register in a call-clobbered hard register and saving and restoring it around each function call. The ex- pression should be 1 when this is worth doing, and 0 otherwise. If you don't define this macro, a default is used which is good on most machines: 4 * calls < refs. 1.7.9. Function Entry and Exit This section describes the macros that output function entry (prologue) and exit (epilogue) code. FUNCTION_PROLOGUE (file, size) A C compound statement that outputs the assembler code for entry to a function. The prologue is responsible for setting up the stack frame, ini- tializing the frame pointer register, saving re- gisters that must be saved, and allocating size additional bytes of storage for the local vari- ables. size is an integer. file is a stdio stream to which the assembler code should be out- put. The label for the beginning of the function need not be output by this macro. That has already been done when the macro is run. To determine which registers to save, the macro can refer to the array regs_ever_live: element r is nonzero if hard register r is used anywhere within the function. This implies the function prologue should save register r, provided it is not one of the call-used registers. (FUNCTION_EPILOGUE must likewise use regs_ever_live.) On machines that have ``register windows'', the function entry code does not save on the stack the registers that are in the windows, even if they are supposed to be preserved by function calls; instead it takes appropriate steps to ``push'' the register stack, if any non-call-used registers are used in the function. On machines where functions may or may not have frame-pointers, the function entry code must vary accordingly; it must set up the frame pointer if one is wanted, and not otherwise. To determine whether a frame pointer is in wanted, the macro can refer to the variable frame_pointer_needed. The variable's value will be 1 at run time in a function that needs a frame pointer. See section Elimination. The function entry code is responsible for allo- cating any stack space required for the function. This stack space consists of the regions listed below. In most cases, these regions are allocated in the order listed, with the last listed region closest to the top of the stack (the lowest ad- dress if STACK_GROWS_DOWNWARD is defined, and the highest address if it is not defined). You can use a different order for a machine if doing so is more convenient or required for compatibility rea- sons. Except in cases where required by standard or by a debugger, there is no reason why the stack layout used by GCC need agree with that used by other compilers for a machine. o+ A region of current_function_pretend_args_size bytes of uninitialized space just underneath the first argument arriving on the stack. (This may not be at the very start of the allocated stack region if the calling sequence has pushed anything else since pushing the stack arguments. But usually, on such machines, nothing else has been pushed yet, because the function prologue itself does all the push- ing.) This region is used on machines where an argument may be passed partly in registers and partly in memory, and, in some cases to support the features in `varargs.h' and `stdargs.h'. o+ An area of memory used to save certain regis- ters used by the function. The size of this area, which may also include space for such things as the return address and pointers to previous stack frames, is machine-specific and usually depends on which registers have been used in the function. Machines with re- gister windows often do not require a save area. o+ A region of at least size bytes, possibly rounded up to an allocation boundary, to con- tain the local variables of the function. On some machines, this region and the save area may occur in the opposite order, with the save area closer to the top of the stack. o+ Optionally, in the case that ACCUMULATE_OUTGOING_ARGS is defined, a region of current_function_outgoing_args_size bytes to be used for outgoing argument lists of the function. See section Stack Arguments. Normally, it is necessary for FUNCTION_PROLOGUE and FUNCTION_EPILOGUE to treat leaf functions spe- cially. The C variable leaf_function is nonzero for such a function. EXIT_IGNORE_STACK Define this macro as a C expression that is nonzero if the return instruction or the function epilogue ignores the value of the stack pointer; in other words, if it is safe to delete an in- struction to adjust the stack pointer before a re- turn from the function. Note that this macro's value is relevant only for functions for which frame pointers are maintained. It is never safe to delete a final stack adjust- ment in a function that has no frame pointer, and the compiler knows this regardless of EXIT_IGNORE_STACK. FUNCTION_EPILOGUE (file, size) A C compound statement that outputs the assembler code for exit from a function. The epilogue is responsible for restoring the saved registers and stack pointer to their values when the function was called, and returning control to the caller. This macro takes the same arguments as the macro FUNCTION_PROLOGUE, and the registers to restore are determined from regs_ever_live and CALL_USED_REGISTERS in the same way. On some machines, there is a single instruction that does all the work of returning from the func- tion. On these machines, give that instruction the name `return' and do not define the macro FUNCTION_EPILOGUE at all. Do not define a pattern named `return' if you want the FUNCTION_EPILOGUE to be used. If you want the target switches to control whether return instruc- tions or epilogues are used, define a `return' pattern with a validity condition that tests the target switches appropriately. If the `return' pattern's validity condition is false, epilogues will be used. On machines where functions may or may not have frame-pointers, the function exit code must vary accordingly. Sometimes the code for these two cases is completely different. To determine whether a frame pointer is in wanted, the macro can refer to the variable frame_pointer_needed. The variable's value will be 1 at run time in a function that needs a frame pointer. Normally, it is necessary for FUNCTION_PROLOGUE and FUNCTION_EPILOGUE to treat leaf functions spe- cially. The C variable leaf_function is nonzero for such a function. See section Leaf Functions. On some machines, some functions pop their argu- ments on exit while others leave that for the caller to do. For example, the 68020 when given `-mrtd' pops arguments in functions that take a fixed number of arguments. Your definition of the macro RETURN_POPS_ARGS de- cides which functions pop their own arguments. FUNCTION_EPILOGUE needs to know what was decided. The variable current_function_pops_args is the number of bytes of its arguments that a function should pop. See section Scalar Return. DELAY_SLOTS_FOR_EPILOGUE Define this macro if the function epilogue con- tains delay slots to which instructions from the rest of the function can be ``moved''. The defin- ition should be a C expression whose value is an integer representing the number of delay slots there. ELIGIBLE_FOR_EPILOGUE_DELAY (insn, n) A C expression that returns 1 if insn can be placed in delay slot number n of the epilogue. The argument n is an integer which identifies the delay slot now being considered (since different slots may have different rules of eligibility). It is never negative and is always less than the number of epilogue delay slots (what DELAY_SLOTS_FOR_EPILOGUE returns). If you reject a particular insn for a given delay slot, in prin- ciple, it may be reconsidered for a subsequent de- lay slot. Also, other insns may (at least in principle) be considered for the so far unfilled delay slot. The insns accepted to fill the epilogue delay slots are put in an RTL list made with insn_list objects, stored in the variable current_function_epilogue_delay_list. The insn for the first delay slot comes first in the list. Your definition of the macro FUNCTION_EPILOGUE should fill the delay slots by outputting the insns in this list, usually by calling final_scan_insn. You need not define this macro if you did not de- fine DELAY_SLOTS_FOR_EPILOGUE. 1.7.10. Generating Code for Profiling FUNCTION_PROFILER (file, labelno) A C statement or compound statement to output to file some assembler code to call the profiling subroutine mcount. Before calling, the assembler code must load the address of a counter variable into a register where mcount expects to find the address. The name of this variable is `LP' fol- lowed by the number labelno, so you would generate the name using `LP%d' in a fprintf. The details of how the address should be passed to mcount are determined by your operating system en- vironment, not by GNU CC. To figure them out, compile a small program for profiling using the system's installed C compiler and look at the as- sembler code that results. PROFILE_BEFORE_PROLOGUE Define this macro if the code for function profil- ing should come before the function prologue. Normally, the profiling code comes after. FUNCTION_BLOCK_PROFILER (file, labelno) A C statement or compound statement to output to file some assembler code to initialize basic-block profiling for the current object module. This code should call the subroutine __bb_init_func once per object module, passing it as its sole ar- gument the address of a block allocated in the ob- ject module. The name of the block is a local symbol made with this statement: ASM_GENERATE_INTERNAL_LABEL (buffer, "LPBX", 0); Of course, since you are writing the defini- tion of ASM_GENERATE_INTERNAL_LABEL as well as that of this macro, you can take a short cut in the definition of this macro and use the name that you know will result. The first word of this block is a flag which will be nonzero if the object module has al- ready been initialized. So test this word first, and do not call __bb_init_func if the flag is nonzero. BLOCK_PROFILER (file, blockno) A C statement or compound statement to incre- ment the count associated with the basic block number blockno. Basic blocks are numbered separately from zero within each compilation. The count associated with block number blockno is at index blockno in a vector of words; the name of this array is a local symbol made with this statement: ASM_GENERATE_INTERNAL_LABEL (buffer, "LPBX", 2); Of course, since you are writing the defini- tion of ASM_GENERATE_INTERNAL_LABEL as well as that of this macro, you can take a short cut in the definition of this macro and use the name that you know will result. 1.8. Implementing the Varargs Macros GNU CC comes with an implementation of `varargs.h' and `stdarg.h' that work without change on machines that pass arguments on the stack. Other machines require their own implementations of varargs, and the two machine independent header files must have conditionals to include it. ANSI `stdarg.h' differs from traditional `varargs.h' mainly in the calling convention for va_start. The tradi- tional implementation takes just one argument, which is the variable in which to store the argument pointer. The ANSI implementation takes an additional first argument, which is the last named argument of the function. However, it should not use this argument. The way to find the end of the named arguments is with the built-in functions described below. __builtin_saveregs () Use this built-in function to save the argument registers in memory so that the varargs mechanism can access them. Both ANSI and traditional ver- sions of va_start must use __builtin_saveregs, un- less you use SETUP_INCOMING_VARARGS (see below) instead. On some machines, __builtin_saveregs is open-coded under the control of the macro EXPAND_BUILTIN_SAVEREGS. On other machines, it calls a routine written in assembler language, found in `libgcc2.c'. Regardless of what code is generated for the call to __builtin_saveregs, it appears at the beginning of the function, not where the call to __builtin_saveregs is written. This is because the registers must be saved before the function starts to use them for its own purposes. __builtin_args_info (category) Use this built-in function to find the first anonymous arguments in registers. In general, a machine may have several categories of registers used for arguments, each for a par- ticular category of data types. (For example, on some machines, floating-point registers are used for floating-point arguments while other arguments are passed in the general registers.) To make non-varargs functions use the proper calling con- vention, you have defined the CUMULATIVE_ARGS data type to record how many registers in each category have been used so far __builtin_args_info accesses the same data struc- ture of type CUMULATIVE_ARGS after the ordinary argument layout is finished with it, with category specifying which word to access. Thus, the value indicates the first unused register in a given category. Normally, you would use __builtin_args_info in the implementation of va_start, accessing each category just once and storing the value in the va_list object. This is because va_list will have to update the values, and there is no way to alter the values accessed by __builtin_args_info. __builtin_next_arg () This is the equivalent of __builtin_args_info, for stack arguments. It returns the address of the first anonymous stack argument, as type void *. If ARGS_GROW_DOWNWARD, it returns the address of the location above the first anonymous stack argument. Use it in va_start to initialize the pointer for fetching arguments from the stack. __builtin_classify_type (object) Since each machine has its own conventions for which data types are passed in which kind of re- gister, your implementation of va_arg has to em- body these conventions. The easiest way to categorize the specified data type is to use __builtin_classify_type together with sizeof and __alignof__. __builtin_classify_type ignores the value of ob- ject, considering only its data type. It returns an integer describing what kind of type that is-- -integer, floating, pointer, structure, and so on. The file `typeclass.h' defines an enumeration that you can use to interpret the values of __builtin_classify_type. These machine description macros help implement varargs: EXPAND_BUILTIN_SAVEREGS (args) If defined, is a C expression that produces the machine-specific code for a call to __builtin_saveregs. This code will be moved to the very beginning of the function, before any parameter access are made. The return value of this function should be an RTX that contains the value to use as the return of __builtin_saveregs. The argument args is a tree_list containing the arguments that were passed to __builtin_saveregs. If this macro is not defined, the compiler will output an ordinary call to the library function `__builtin_saveregs'. SETUP_INCOMING_VARARGS (args_so_far, mode, type, pretend_args_size, second_time) This macro offers an alternative to using __builtin_saveregs and defining the macro EXPAND_BUILTIN_SAVEREGS. Use it to store the anonymous register arguments into the stack so that all the arguments appear to have been passed consecutively on the stack. Once this is done, you can use the standard implementation of varargs that works for machines that pass all their argu- ments on the stack. The argument args_so_far is the CUMULATIVE_ARGS data structure, containing the values that obtain after processing of the named arguments. The ar- guments mode and type describe the last named argument---its machine mode and its data type as a tree node. The macro implementation should do two things: first, push onto the stack all the argument regis- ters not used for the named arguments, and second, store the size of the data thus pushed into the int-valued variable whose name is supplied as the argument pretend_args_size. The value that you store here will serve as additional offset for setting up the stack frame. Because you must generate code to push the anonymous arguments at compile time without know- ing their data types, SETUP_INCOMING_VARARGS is only useful on machines that have just a single category of argument register and use it uniformly for all data types. If the argument second_time is nonzero, it means that the arguments of the function are being analyzed for the second time. This happens for an inline function, which is not actually compiled until the end of the source file. The macro SETUP_INCOMING_VARARGS should not generate any in- structions in this case. 1.9. Trampolines for Nested Functions A trampoline is a small piece of code that is created at run time when the address of a nested function is taken. It normally resides on the stack, in the stack frame of the containing function. These macros tell GNU CC how to generate code to allocate and initialize a trampoline. The instructions in the trampoline must do two things: load a constant address into the static chain register, and jump to the real address of the nested function. On CISC machines such as the m68k, this requires two instructions, a move immediate and a jump. Then the two addresses exist in the trampoline as word-long immediate operands. On RISC machines, it is often necessary to load each address into a register in two parts. Then pieces of each address form separate immediate operands. The code generated to initialize the trampoline must store the variable parts---the static chain value and the function address---into the immediate operands of the instructions. On a CISC machine, this is simply a matter of copying each address to a memory reference at the proper offset from the start of the trampoline. On a RISC machine, it may be necessary to take out pieces of the address and store them separately. TRAMPOLINE_TEMPLATE (file) A C statement to output, on the stream file, as- sembler code for a block of data that contains the constant parts of a trampoline. This code should not include a label---the label is taken care of automatically. TRAMPOLINE_SIZE A C expression for the size in bytes of the tram- poline, as an integer. TRAMPOLINE_ALIGNMENT Alignment required for trampolines, in bits. If you don't define this macro, the value of BIGGEST_ALIGNMENT is used for aligning trampo- lines. INITIALIZE_TRAMPOLINE (addr, fnaddr, static_chain) A C statement to initialize the variable parts of a trampoline. addr is an RTX for the address of the trampoline; fnaddr is an RTX for the address of the nested function; static_chain is an RTX for the static chain value that should be passed to the function when it is called. ALLOCATE_TRAMPOLINE (fp) A C expression to allocate run-time space for a trampoline. The expression value should be an RTX representing a memory reference to the space for the trampoline. If this macro is not defined, by default the tram- poline is allocated as a stack slot. This default is right for most machines. The exceptions are machines where it is impossible to execute in- structions in the stack area. On such machines, you may have to implement a separate stack, using this macro in conjunction with FUNCTION_PROLOGUE and FUNCTION_EPILOGUE. fp points to a data structure, a struct function, which describes the compilation status of the im- mediate containing function of the function which the trampoline is for. Normally (when ALLOCATE_TRAMPOLINE is not defined), the stack slot for the trampoline is in the stack frame of this containing function. Other allocation stra- tegies probably must do something analogous with this information. Implementing trampolines is difficult on many machines because they have separate instruction and data caches. Writing into a stack location fails to clear the memory in the instruction cache, so when the program jumps to that location, it executes the old contents. Here are two possible solutions. One is to clear the relevant parts of the instruction cache whenever a trampo- line is set up. The other is to make all trampolines ident- ical, by having them jump to a standard subroutine. The former technique makes trampoline execution faster; the latter makes initialization faster. To clear the instruction cache when a trampoline is initialized, define the following macros which describe the shape of the cache. INSN_CACHE_SIZE The total size in bytes of the cache. INSN_CACHE_LINE_WIDTH The length in bytes of each cache line. The cache is divided into cache lines which are disjoint slots, each holding a contiguous chunk of data fetched from memory. Each time data is brought into the cache, an entire line is read at once. The data loaded into a cache line is always aligned on a boundary equal to the line size. INSN_CACHE_DEPTH The number of alternative cache lines that can hold any particular memory location. To use a standard subroutine, define the following macro. In addition, you must make sure that the instruc- tions in a trampoline fill an entire cache line with identi- cal instructions, or else ensure that the beginning of the trampoline code is always aligned at the same point in its cache line. Look in `m68k.h' as a guide. TRANSFER_FROM_TRAMPOLINE Define this macro if trampolines need a special subroutine to do their work. The macro should ex- pand to a series of asm statements which will be compiled with GNU CC. They go in a library func- tion named __transfer_from_trampoline. If you need to avoid executing the ordinary prolo- gue code of a compiled C function when you jump to the subroutine, you can do so by placing a special label of your own in the assembler code. Use one asm statement to generate an assembler label, and another to make the label global. Then trampo- lines can use that label to jump directly to your special assembler code. 1.10. Implicit Calls to Library Routines MULSI3_LIBCALL A C string constant giving the name of the func- tion to call for multiplication of one signed full-word by another. If you do not define this macro, the default name is used, which is __mul- si3, a function defined in `libgcc.a'. DIVSI3_LIBCALL A C string constant giving the name of the func- tion to call for division of one signed full-word by another. If you do not define this macro, the default name is used, which is __divsi3, a func- tion defined in `libgcc.a'. UDIVSI3_LIBCALL A C string constant giving the name of the func- tion to call for division of one unsigned full- word by another. If you do not define this macro, the default name is used, which is __udivsi3, a function defined in `libgcc.a'. MODSI3_LIBCALL A C string constant giving the name of the func- tion to call for the remainder in division of one signed full-word by another. If you do not define this macro, the default name is used, which is __modsi3, a function defined in `libgcc.a'. UMODSI3_LIBCALL A C string constant giving the name of the func- tion to call for the remainder in division of one unsigned full-word by another. If you do not de- fine this macro, the default name is used, which is __umodsi3, a function defined in `libgcc.a'. MULDI3_LIBCALL A C string constant giving the name of the func- tion to call for multiplication of one signed double-word by another. If you do not define this macro, the default name is used, which is __mul- di3, a function defined in `libgcc.a'. DIVDI3_LIBCALL A C string constant giving the name of the func- tion to call for division of one signed double- word by another. If you do not define this macro, the default name is used, which is __divdi3, a function defined in `libgcc.a'. UDIVDI3_LIBCALL A C string constant giving the name of the func- tion to call for division of one unsigned full- word by another. If you do not define this macro, the default name is used, which is __udivdi3, a function defined in `libgcc.a'. MODDI3_LIBCALL A C string constant giving the name of the func- tion to call for the remainder in division of one signed double-word by another. If you do not de- fine this macro, the default name is used, which is __moddi3, a function defined in `libgcc.a'. UMODDI3_LIBCALL A C string constant giving the name of the func- tion to call for the remainder in division of one unsigned full-word by another. If you do not de- fine this macro, the default name is used, which is __umoddi3, a function defined in `libgcc.a'. TARGET_MEM_FUNCTIONS Define this macro if GNU CC should generate calls to the System V (and ANSI C) library functions memcpy and memset rather than the BSD functions bcopy and bzero. LIBGCC_NEEDS_DOUBLE Define this macro if only float arguments cannot be passed to library routines (so they must be converted to double). This macro affects both how library calls are generated and how the library routines in `libgcc1.c' accept their arguments. It is useful on machines where floating and fixed point arguments are passed differently, such as the i860. FLOAT_ARG_TYPE Define this macro to override the type used by the library routines to pick up arguments of type float. (By default, they use a union of float and int.) The obvious choice would be float---but that won't work with traditional C compilers that expect all arguments declared as float to arrive as double. To avoid this conversion, the library routines ask for the value as some other type and then treat it as a float. On some systems, no other type will work for this. For these systems, you must use LIBGCC_NEEDS_DOUBLE instead, to force conversion of the values double before they are passed. FLOATIFY (passed-value) Define this macro to override the way library rou- tines redesignate a float argument as a float in- stead of the type it was passed as. The default is an expression which takes the float field of the union. FLOAT_VALUE_TYPE Define this macro to override the type used by the library routines to return values that ought to have type float. (By default, they use int.) The obvious choice would be float---but that won't work with traditional C compilers gratuitously convert values declared as float into double. INTIFY (float-value) Define this macro to override the way the value of a float-returning library routine should be pack- aged in order to return it. These functions are actually declared to return type FLOAT_VALUE_TYPE (normally int). These values can't be returned as type float be- cause traditional C compilers would gratuitously convert the value to a double. A local variable named intify is always available when the macro INTIFY is used. It is a union of a float field named f and a field named i whose type is FLOAT_VALUE_TYPE or int. If you don't define this macro, the default defin- ition works by copying the value through that un- ion. SItype Define this macro as the name of the data type corresponding to SImode in the system's own C com- piler. You need not define this macro if that type is int, as it usually is. perform_... Define these macros to supply explicit C state- ments to carry out various arithmetic operations on types float and double in the library routines in `libgcc1.c'. See that file for a full list of these macros and their arguments. On most machines, you don't need to define any of these macros, because the C compiler that comes with the system takes care of doing them. NEXT_OBJC_RUNTIME Define this macro to generate code for Objective C message sending using the calling convention of the NeXT system. This calling convention involves passing the object, the selector and the method arguments all at once to the method-lookup library function. The default calling convention passes just the ob- ject and the selector to the lookup function, which returns a pointer to the method. 1.11. Addressing Modes HAVE_POST_INCREMENT Define this macro if the machine supports post- increment addressing. HAVE_PRE_INCREMENT HAVE_POST_DECREMENT HAVE_PRE_DECREMENT Similar for other kinds of addressing. CONSTANT_ADDRESS_P (x) A C expression that is 1 if the RTX x is a con- stant which is a valid address. On most machines, this can be defined as CONSTANT_P (x), but a few machines are more restrictive in which constant addresses are supported. CONSTANT_P accepts integer-values expressions whose values are not explicitly known, such as symbol_ref, label_ref, and high expressions and const arithmetic expressions, in addition to const_int and const_double expressions. MAX_REGS_PER_ADDRESS A number, the maximum number of registers that can appear in a valid memory address. Note that it is up to you to specify a value equal to the maximum number that GO_IF_LEGITIMATE_ADDRESS would ever accept. GO_IF_LEGITIMATE_ADDRESS (mode, x, label) A C compound statement with a conditional goto la- bel; executed if x (an RTX) is a legitimate memory address on the target machine for a memory operand of mode mode. It usually pays to define several simpler macros to serve as subroutines for this one. Otherwise it may be too complicated to understand. This macro must exist in two variants: a strict variant and a non-strict one. The strict variant is used in the reload pass. It must be defined so that any pseudo-register that has not been allo- cated a hard register is considered a memory reference. In contexts where some kind of regis- ter is required, a pseudo-register with no hard register must be rejected. The non-strict variant is used in other passes. It must be defined to accept all pseudo-registers in every context where some kind of register is required. Compiler source files that want to use the strict variant of this macro define the macro REG_OK_STRICT. You should use an #ifdef REG_OK_STRICT conditional to define the strict variant in that case and the non-strict variant otherwise. Typically among the subroutines used to define GO_IF_LEGITIMATE_ADDRESS are subroutines to check for acceptable registers for various purposes (one for base registers, one for index registers, and so on). Then only these subroutine macros need have two variants; the higher levels of macros may be the same whether strict or not. Normally, constant addresses which are the sum of a symbol_ref and an integer are stored inside a const RTX to mark them as constant. Therefore, there is no need to recognize such sums specifi- cally as legitimate addresses. Normally you would simply recognize any const as legitimate. Usually PRINT_OPERAND_ADDRESS is not prepared to handle constant sums that are not marked with const. It assumes that a naked plus indicates in- dexing. If so, then you must reject such naked constant sums as illegitimate addresses, so that none of them will be given to PRINT_OPERAND_ADDRESS. On some machines, whether a symbolic address is legitimate depends on the section that the address refers to. On these machines, define the macro ENCODE_SECTION_INFO to store the information into the symbol_ref, and then check for it here. When you see a const, you will have to look inside it to find the symbol_ref in order to determine the section. See section Assembler Format. The best way to modify the name string is by ad- ding text to the beginning, with suitable punctua- tion to prevent any ambiguity. Allocate the new name in saveable_obstack. You will have to modify ASM_OUTPUT_LABELREF to remove and decode the added text and output the name accordingly. You can check the information stored here into the symbol_ref in the definitions of GO_IF_LEGITIMATE_ADDRESS and PRINT_OPERAND_ADDRESS. REG_OK_FOR_BASE_P (x) A C expression that is nonzero if x (assumed to be a reg RTX) is valid for use as a base register. For hard registers, it should always accept those which the hardware permits and reject the others. Whether the macro accepts or rejects pseudo regis- ters must be controlled by REG_OK_STRICT as described above. This usually requires two vari- ant definitions, of which REG_OK_STRICT controls the one actually used. REG_OK_FOR_INDEX_P (x) A C expression that is nonzero if x (assumed to be a reg RTX) is valid for use as an index register. The difference between an index register and a base register is that the index register may be scaled. If an address involves the sum of two re- gisters, neither one of them scaled, then either one may be labeled the ``base'' and the other the ``index''; but whichever labeling is used must fit the machine's constraints of which registers may serve in each capacity. The compiler will try both labelings, looking for one that is valid, and will reload one or both registers only if neither labeling works. LEGITIMIZE_ADDRESS (x, oldx, mode, win) A C compound statement that attempts to replace x with a valid memory address for an operand of mode mode. win will be a C statement label elsewhere in the code; the macro definition may use GO_IF_LEGITIMATE_ADDRESS (mode, x, win); to avoid further processing if the address has be- come legitimate. x will always be the result of a call to break_out_memory_refs, and oldx will be the operand that was given to that function to produce x. The code generated by this macro should not alter the substructure of x. If it transforms x into a more legitimate form, it should as- sign x (which will always be a C variable) a new value. It is not necessary for this macro to come up with a legitimate address. The compiler has standard ways of doing so in all cases. In fact, it is safe for this macro to do nothing. But often a machine-dependent strategy can generate better code. GO_IF_MODE_DEPENDENT_ADDRESS (addr, label) A C statement or compound statement with a conditional goto label; executed if memory ad- dress x (an RTX) can have different meanings depending on the machine mode of the memory reference it is used for. Autoincrement and autodecrement addresses typ- ically have mode-dependent effects because the amount of the increment or decrement is the size of the operand being addressed. Some machines have other mode-dependent addresses. Many RISC machines have no mode-dependent ad- dresses. You may assume that addr is a valid address for the machine. LEGITIMATE_CONSTANT_P (x) A C expression that is nonzero if x is a legi- timate constant for an immediate operand on the target machine. You can assume that x sa- tisfies CONSTANT_P, so you need not check this. In fact, `1' is a suitable definition for this macro on machines where anything CONSTANT_P is valid. LEGITIMATE_PIC_OPERAND_P (x) A C expression that is nonzero if x is a legi- timate immediate operand on the target machine when generating position independent code. You can assume that x satisfies CONSTANT_P, so you need not check this. You can also assume flag_pic is true, so you need not check it ei- ther. You need not define this macro if all constants (including SYMBOL_REF) can be im- mediate operands when generating position in- dependent code. 1.12. Condition Code Status The file `conditions.h' defines a variable cc_status to describe how the condition code was computed (in case the interpretation of the condition code depends on the instruc- tion that it was set by). This variable contains the RTL expressions on which the condition code is currently based, and several standard flags. Sometimes additional machine-specific flags must be defined in the machine description header file. It can also add additional machine-specific information by defining CC_STATUS_MDEP. CC_STATUS_MDEP C code for a data type which is used for declaring the mdep component of cc_status. It defaults to int. This macro is not used on machines that do not use cc0. CC_STATUS_MDEP_INIT A C expression to initialize the mdep field to ``empty''. The default definition does nothing, since most machines don't use the field anyway. If you want to use the field, you should probably define this macro to initialize it. This macro is not used on machines that do not use cc0. NOTICE_UPDATE_CC (exp, insn) A C compound statement to set the components of cc_status appropriately for an insn insn whose body is exp. It is this macro's responsibility to recognize insns that set the condition code as a byproduct of other activity as well as those that explicitly set (cc0). This macro is not used on machines that do not use cc0. If there are insns that do not set the condition code but do alter other machine registers, this macro must check to see whether they invalidate the expressions that the condition code is record- ed as reflecting. For example, on the 68000, insns that store in address registers do not set the condition code, which means that usually NOTICE_UPDATE_CC can leave cc_status unaltered for such insns. But suppose that the previous insn set the condition code based on location `a4@(102)' and the current insn stores a new value in `a4'. Although the condition code is not changed by this, it will no longer be true that it reflects the contents of `a4@(102)'. Therefore, NOTICE_UPDATE_CC must alter cc_status in this case to say that nothing is known about the condition code value. The definition of NOTICE_UPDATE_CC must be prepared to deal with the results of peephole op- timization: insns whose patterns are parallel RTXs containing various reg, mem or constants which are just the operands. The RTL structure of these insns is not sufficient to indicate what the insns actually do. What NOTICE_UPDATE_CC should do when it sees one is just to run CC_STATUS_INIT. A possible definition of NOTICE_UPDATE_CC is to call a function that looks at an attribute (see section Insn Attributes) named, for example, `cc'. This avoids having detailed information about patterns in two places, the `md' file and in NOTICE_UPDATE_CC. EXTRA_CC_MODES A list of names to be used for additional modes for condition code values in registers (see sec- tion Jump Patterns). These names are added to enum machine_mode and all have class MODE_CC. By convention, they should start with `CC' and end with `mode'. You should only define this macro if your machine does not use cc0 and only if additional modes are required. EXTRA_CC_NAMES A list of C strings giving the names for the modes listed in EXTRA_CC_MODES. For example, the Sparc defines this macro and EXTRA_CC_MODES as #define EXTRA_CC_MODES CC_NOOVmode, CCFPmode #define EXTRA_CC_NAMES "CC_NOOV", "CCFP" This macro is not required if EXTRA_CC_MODES is not defined. SELECT_CC_MODE (op, x) Returns a mode from class MODE_CC to be used when comparison operation code op is applied to rtx x. For example, on the Sparc, SELECT_CC_MODE is defined as (see see section Jump Patterns for a description of the reason for this definition) #define SELECT_CC_MODE(OP,X) \ (GET_MODE_CLASS (GET_MODE (X)) == MODE_FLOAT ? CCFPmode \ : (GET_CODE (X) == PLUS || GET_CODE (X) == MINUS \ || GET_CODE (X) == NEG) \ ? CC_NOOVmode : CCmode) This macro is not required if EXTRA_CC_MODES is not defined. 1.13. Describing Relative Costs of Operations These macros let you describe the relative speed of various operations on the target machine. CONST_COSTS (x, code) A part of a C switch statement that describes the relative costs of constant RTL expressions. It must contain case labels for expression codes const_int, const, symbol_ref, label_ref and const_double. Each case must ultimately reach a return statement to return the relative cost of the use of that kind of constant value in an ex- pression. The cost may depend on the precise value of the constant, which is available for ex- amination in x. code is the expression code---redundant, since it can be obtained with GET_CODE (x). RTX_COSTS (x, code) Like CONST_COSTS but applies to nonconstant RTL expressions. This can be used, for example, to indicate how costly a multiply instruction is. In writing this macro, you can use the construct COSTS_N_INSNS (n) to specify a cost equal to n fast instructions. This macro is optional; do not define it if the default cost assumptions are adequate for the tar- get machine. ADDRESS_COST (address) An expression giving the cost of an addressing mode that contains address. If not defined, the cost is computed from the address expression and the CONST_COSTS values. For most CISC machines, the default cost is a good approximation of the true cost of the addressing mode. However, on RISC machines, all instructions normally have the same length and execution time. Hence all addresses will have equal costs. In cases where more than one form of an address is known, the form with the lowest cost will be used. If multiple forms have the same, lowest, cost, the one that is the most complex will be used. For example, suppose an address that is equal to the sum of a register and a constant is used twice in the same basic block. When this macro is not defined, the address will be computed in a regis- ter and memory references will be indirect through that register. On machines where the cost of the addressing mode containing the sum is no higher than that of a simple indirect reference, this will produce an additional instruction and possi- bly require an additional register. Proper specification of this macro eliminates this over- head for such machines. Similar use of this macro is made in strength reduction of loops. address need not be valid as an address. In such a case, the cost is not relevant and can be any value; invalid addresses need not be assigned a different cost. On machines where an address involving more than one register is as cheap as an address computation involving only one register, defining ADDRESS_COST to reflect this can cause two registers to be live over a region of code where only one would have been if ADDRESS_COST were not defined in that manner. This effect should be considered in the definition of this macro. Equivalent costs should probably only be given to addresses with different numbers of registers on machines with lots of re- gisters. This macro will normally either not be defined or be defined as a constant. REGISTER_MOVE_COST (from, to) A C expression for the cost of moving data from a register in class from to one in class to. The classes are expressed using the enumeration values such as GENERAL_REGS. A value of 2 is the de- fault; other values are interpreted relative to that. It is not required that the cost always equal 2 when from is the same as to; on some machines it is expensive to move between registers if they are not general registers. If reload sees an insn consisting of a single set between two hard registers, and if REGISTER_MOVE_COST applied to their classes re- turns a value of 2, reload does not check to en- sure that the constraints of the insn are met. Setting a cost of other than 2 will allow reload to verify that the constraints are met. You should do this if the `movm' pattern's constraints do not allow such copying. MEMORY_MOVE_COST (m) A C expression for the cost of moving data of mode m between a register and memory. A value of 2 is the default; this cost is relative to those in REGISTER_MOVE_COST. If moving between registers and memory is more ex- pensive than between two registers, you should de- fine this macro to express the relative cost. BRANCH_COST A C expression for the cost of a branch instruc- tion. A value of 1 is the default; other values are interpreted relative to that. Here are additional macros which do not specify precise relative costs, but only that certain actions are more expensive than GNU CC would ordinarily expect. SLOW_BYTE_ACCESS Define this macro as a C expression which is nonzero if accessing less than a word of memory (i.e. a char or a short) is no faster than access- ing a word of memory, i.e., if such access require more than one instruction or if there is no difference in cost between byte and (aligned) word loads. When this macro is not defined, the compiler will access a field by finding the smallest containing object; when it is defined, a fullword load will be used if alignment permits. Unless bytes accesses are faster than word accesses, using word accesses is preferable since it may eliminate sub- sequent memory access if subsequent accesses occur to other fields in the same word of the structure, but to different bytes. SLOW_ZERO_EXTEND Define this macro if zero-extension (of a char or short to an int) can be done faster if the desti- nation is a register that is known to be zero. If you define this macro, you must have instruc- tion patterns that recognize RTL structures like this: (set (strict_low_part (subreg:QI (reg:SI ...) 0)) ...) and likewise for HImode. SLOW_UNALIGNED_ACCESS Define this macro if unaligned accesses have a cost many times greater than aligned accesses, for example if they are emulated in a trap handler. When this macro is defined, the compiler will act as if STRICT_ALIGNMENT were defined when generating code for block moves. This can cause significantly more instructions to be produced. Therefore, do not define this macro if unaligned accesses only add a cycle or two to the time for a memory access. DONT_REDUCE_ADDR Define this macro to inhibit strength reduc- tion of memory addresses. (On some machines, such strength reduction seems to do harm rath- er than good.) MOVE_RATIO The number of scalar move insns which should be generated instead of a string move insn or a library call. Increasing the value will al- ways make code faster, but eventually incurs high cost in increased code size. If you don't define this, a reasonable default is used. NO_FUNCTION_CSE Define this macro if it is as good or better to call a constant function address than to call an address kept in a register. NO_RECURSIVE_FUNCTION_CSE Define this macro if it is as good or better for a function to call itself with an explicit address than to call an address kept in a re- gister. 1.14. Dividing the Output into Sections (Texts, Data, ...) An object file is divided into sections containing dif- ferent types of data. In the most common case, there are three sections: the text section, which holds instructions and read-only data; the data section, which holds initialized writable data; and the bss section, which holds uninitialized data. Some systems have other kinds of sec- tions. The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections. TEXT_SECTION_ASM_OP A C string constant for the assembler operation that should precede instructions and read-only data. Normally ".text" is right. DATA_SECTION_ASM_OP A C string constant for the assembler operation to identify the following data as writable initial- ized data. Normally ".data" is right. SHARED_SECTION_ASM_OP If defined, a C string constant for the assembler operation to identify the following data as shared data. If not defined, DATA_SECTION_ASM_OP will be used. INIT_SECTION_ASM_OP If defined, a C string constant for the assembler operation to identify the following data as ini- tialization code. If not defined, GNU CC will as- sume such a section does not exist. EXTRA_SECTIONS A list of names for sections other than the stan- dard two, which are in_text and in_data. You need not define this macro on a system with no other sections (that GCC needs to use). EXTRA_SECTION_FUNCTIONS One or more functions to be defined in `varasm.c'. These functions should do jobs analogous to those of text_section and data_section, for your addi- tional sections. Do not define this macro if you do not define EXTRA_SECTIONS. READONLY_DATA_SECTION On most machines, read-only variables, constants, and jump tables are placed in the text section. If this is not the case on your machine, this mac- ro should be defined to be the name of a function (either data_section or a function defined in EXTRA_SECTIONS) that switches to the section to be used for read-only items. If these items should be placed in the text sec- tion, this macro should not be defined. SELECT_SECTION (exp, reloc) A C statement or statements to switch to the ap- propriate section for output of exp. You can as- sume that exp is either a VAR_DECL node or a con- stant of some sort. reloc indicates whether the initial value of exp requires link-time reloca- tions. Select the section by calling text_section or one of the alternatives for other sections. Do not define this macro if you put all read-only variables and constants in the read-only data sec- tion (usually the text section). SELECT_RTX_SECTION (mode, rtx) A C statement or statements to switch to the ap- propriate section for output of rtx in mode mode. You can assume that rtx is some kind of constant in RTL. The argument mode is redundant except in the case of a const_int rtx. Select the section by calling text_section or one of the alternatives for other sections. Do not define this macro if you put all constants in the read-only data section. JUMP_TABLES_IN_TEXT_SECTION Define this macro if jump tables (for tablejump insns) should be output in the text section, along with the assembler instructions. Otherwise, the readonly data section is used. This macro is irrelevant if there is no separate readonly data section. ENCODE_SECTION_INFO (decl) Define this macro if references to a symbol must be treated differently depending on something about the variable or function named by the symbol (such as what section it is in). The macro definition, if any, is executed immedi- ately after the rtl for decl has been created and stored in DECL_RTL (decl). The value of the rtl will be a mem whose address is a symbol_ref. The usual thing for this macro to do is to record a flag in the symbol_ref (such as SYMBOL_REF_FLAG) or to store a modified name string in the symbol_ref (if one bit is not enough information). 1.15. Position Independent Code This section describes macros that help implement gen- eration of position independent code. Simply defining these macros is not enough to generate valid PIC; you must also add support to the macros GO_IF_LEGITIMATE_ADDRESS and LEGITIMIZE_ADDRESS, and PRINT_OPERAND_ADDRESS as well. You must modify the definition of `movsi' to do something appropriate when the source operand contains a symbolic address. You may also need to alter the handling of switch statements so that they use relative addresses. PIC_OFFSET_TABLE_REGNUM The register number of the register used to ad- dress a table of static data addresses in memory. In some cases this register is defined by a processor's ``application binary interface'' (ABI). When this macro is defined, RTL is gen- erated for this register once, as with the stack pointer and frame pointer registers. If this mac- ro is not defined, it is up to the machine- dependent files to allocate such a register (if necessary). FINALIZE_PIC By generating position-independent code, when two different programs (A and B) share a common li- brary (libC.a), the text of the library can be shared whether or not the library is linked at the same address for both programs. In some of these environments, position-independent code requires not only the use of different addressing modes, but also special code to enable the use of these addressing modes. The FINALIZE_PIC macro serves as a hook to emit these special codes once the function is being compiled into assembly code, but not before. (It is not done before, because in the case of compil- ing an inline function, it would lead to multiple PIC prologues being included in functions which used inline functions and were compiled to assem- bly language.) 1.16. Defining the Output Assembler Language This section describes macros whose principal purpose is to describe how to write instructions in assembler language--rather than what the instructions do. 1.16.1. The Overall Framework of an Assembler File ASM_FILE_START (stream) A C expression which outputs to the stdio stream stream some appropriate text to go at the start of an assembler file. Normally this macro is defined to output a line containing `#NO_APP', which is a comment that has no effect on most assemblers but tells the GNU as- sembler that it can save time by not checking for certain assembler constructs. On systems that use SDB, it is necessary to output certain commands; see `attasm.h'. ASM_FILE_END (stream) A C expression which outputs to the stdio stream stream some appropriate text to go at the end of an assembler file. If this macro is not defined, the default is to output nothing special at the end of the file. Most systems don't require any definition. On systems that use SDB, it is necessary to output certain commands; see `attasm.h'. ASM_IDENTIFY_GCC (file) A C statement to output assembler commands which will identify the object file as having been com- piled with GNU CC (or another GNU compiler). If you don't define this macro, the string `gcc_compiled.:' is output. This string is calcu- lated to define a symbol which, on BSD systems, will never be defined for any other reason. GDB checks for the presence of this symbol when read- ing the symbol table of an executable. On non-BSD systems, you must arrange communication with GDB in some other fashion. If GDB is not used on your system, you can define this macro with an empty body. ASM_COMMENT_START A C string constant describing how to begin a com- ment in the target assembler language. The com- piler assumes that the comment will end at the end of the line. ASM_APP_ON A C string constant for text to be output before each asm statement or group of consecutive ones. Normally this is "#APP", which is a comment that has no effect on most assemblers but tells the GNU assembler that it must check the lines that follow for all valid assembler constructs. ASM_APP_OFF A C string constant for text to be output after each asm statement or group of consecutive ones. Normally this is "#NO_APP", which tells the GNU assembler to resume making the time-saving assump- tions that are valid for ordinary compiler output. ASM_OUTPUT_SOURCE_FILENAME (stream, name) A C statement to output COFF information or DWARF debugging information which indicates that filename name is the current source file to the stdio stream stream. This macro need not be defined if the standard form of output for the file format in use is ap- propriate. ASM_OUTPUT_SOURCE_LINE (stream, line) A C statement to output DBX or SDB debugging in- formation before code for line number line of the current source file to the stdio stream stream. This macro need not be defined if the standard form of debugging information for the debugger in use is appropriate. ASM_OUTPUT_IDENT (stream, string) A C statement to output something to the assembler file to handle a `#ident' directive containing the text string. If this macro is not defined, noth- ing is output for a `#ident' directive. OBJC_PROLOGUE A C statement to output any assembler statements which are required to precede any Objective C ob- ject definitions or message sending. The state- ment is executed only when compiling an Objective C program. 1.16.2. Output of Data ASM_OUTPUT_LONG_DOUBLE (stream, value) ASM_OUTPUT_DOUBLE (stream, value) ASM_OUTPUT_FLOAT (stream, value) A C statement to output to the stdio stream stream an assembler instruction to assemble a floating- point constant of TFmode, DFmode or SFmode, respectively, whose value is value. value will be a C expression of type REAL_VALUE__TYPE, usually double. ASM_OUTPUT_QUADRUPLE_INT (stream, exp) ASM_OUTPUT_DOUBLE_INT (stream, exp) ASM_OUTPUT_INT (stream, exp) ASM_OUTPUT_SHORT (stream, exp) ASM_OUTPUT_CHAR (stream, exp) A C statement to output to the stdio stream stream an assembler instruction to assemble an integer of 16, 8, 4, 2 or 1 bytes, respectively, whose value is value. The argument exp will be an RTL expres- sion which represents a constant value. Use `output_addr_const (stream, exp)' to output this value as an assembler expression. For sizes larger than UNITS_PER_WORD, if the ac- tion of a macro would be identical to repeatedly calling the macro corresponding to a size of UNITS_PER_WORD, once for each word, you need not define the macro. ASM_OUTPUT_BYTE (stream, value) A C statement to output to the stdio stream stream an assembler instruction to assemble a single byte containing the number value. ASM_BYTE_OP A C string constant giving the pseudo-op to use for a sequence of single-byte constants. If this macro is not defined, the default is "byte". ASM_OUTPUT_ASCII (stream, ptr, len) A C statement to output to the stdio stream stream an assembler instruction to assemble a string con- stant containing the len bytes at ptr. ptr will be a C expression of type char * and len a C ex- pression of type int. If the assembler has a .ascii pseudo-op as found in the Berkeley Unix assembler, do not define the macro ASM_OUTPUT_ASCII. ASM_OUTPUT_POOL_PROLOGUE (file funname fundecl size) A C statement to output assembler commands to de- fine the start of the constant pool for a func- tion. funname is a string giving the name of the function. Should the return type of the function be required, it can be obtained via fundecl. size is the size, in bytes, of the constant pool that will be written immediately after this call. If no constant-pool prefix is required, the usual case, this macro need not be defined. ASM_OUTPUT_SPECIAL_POOL_ENTRY (file, x, mode, align, labelno, jumpto) A C statement (with or without semicolon) to out- put a constant in the constant pool, if it needs special treatment. (This macro need not do any- thing for RTL expressions that can be output nor- mally.) The argument file is the standard I/O stream to output the assembler code on. x is the RTL ex- pression for the constant to output, and mode is the machine mode (in case x is a `const_int'). align is the required alignment for the value x; you should output an assembler directive to force this much alignment. The argument labelno is a number to use in an internal label for the address of this pool entry. The definition of this macro is responsible for outputting the label definition at the proper place. Here is how to do this: ASM_OUTPUT_INTERNAL_LABEL (file, "LC", labelno); When you output a pool entry specially, you should end with a goto to the label jumpto. This will prevent the same pool entry from be- ing output a second time in the usual manner. You need not define this macro if it would do nothing. ASM_OPEN_PAREN ASM_CLOSE_PAREN These macros are defined as C string constant, describing the syntax in the assembler for grouping arithmetic expressions. The follow- ing definitions are correct for most assem- blers: #define ASM_OPEN_PAREN "(" #define ASM_CLOSE_PAREN ")" 1.16.3. Output of Uninitialized Variables Each of the macros in this section is used to do the whole job of outputting a single uninitialized variable. ASM_OUTPUT_COMMON (stream, name, size, rounded) A C statement (sans semicolon) to output to the stdio stream stream the assembler definition of a common-label named name whose size is size bytes. The variable rounded is the size rounded up to whatever alignment the caller wants. Use the expression assemble_name (stream, name) to output the name itself; before and after that, output the additional assembler syntax for defin- ing the name, and a newline. This macro controls how the assembler definitions of uninitialized global variables are output. ASM_OUTPUT_ALIGNED_COMMON (stream, name, size, alignment) Like ASM_OUTPUT_COMMON except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of ASM_OUTPUT_COMMON, and gives you more flexibility in handling the required alignment of the vari- able. ASM_OUTPUT_SHARED_COMMON (stream, name, size, rounded) If defined, it is similar to ASM_OUTPUT_COMMON, except that it is used when name is shared. If not defined, ASM_OUTPUT_COMMON will be used. ASM_OUTPUT_LOCAL (stream, name, size, rounded) A C statement (sans semicolon) to output to the stdio stream stream the assembler definition of a local-common-label named name whose size is size bytes. The variable rounded is the size rounded up to whatever alignment the caller wants. Use the expression assemble_name (stream, name) to output the name itself; before and after that, output the additional assembler syntax for defin- ing the name, and a newline. This macro controls how the assembler definitions of uninitialized static variables are output. ASM_OUTPUT_ALIGNED_LOCAL (stream, name, size, alignment) Like ASM_OUTPUT_LOCAL except takes the required alignment as a separate, explicit argument. If you define this macro, it is used in place of ASM_OUTPUT_LOCAL, and gives you more flexibility in handling the required alignment of the vari- able. ASM_OUTPUT_SHARED_LOCAL (stream, name, size, rounded) If defined, it is similar to ASM_OUTPUT_LOCAL, ex- cept that it is used when name is shared. If not defined, ASM_OUTPUT_LOCAL will be used. 1.16.4. Output and Generation of Labels ASM_OUTPUT_LABEL (stream, name) A C statement (sans semicolon) to output to the stdio stream stream the assembler definition of a label named name. Use the expression assemble_name (stream, name) to output the name itself; before and after that, output the addi- tional assembler syntax for defining the name, and a newline. ASM_DECLARE_FUNCTION_NAME (stream, name, decl) A C statement (sans semicolon) to output to the stdio stream stream any text necessary for declar- ing the name name of a function which is being de- fined. This macro is responsible for outputting the label definition (perhaps using ASM_OUTPUT_LABEL). The argument decl is the FUNCTION_DECL tree node representing the function. If this macro is not defined, then the function name is defined in the usual manner as a label (by means of ASM_OUTPUT_LABEL). ASM_DECLARE_FUNCTION_SIZE (stream, name, decl) A C statement (sans semicolon) to output to the stdio stream stream any text necessary for declar- ing the size of a function which is being defined. The argument name is the name of the function. The argument decl is the FUNCTION_DECL tree node representing the function. If this macro is not defined, then the function size is not defined. ASM_DECLARE_OBJECT_NAME (stream, name, decl) A C statement (sans semicolon) to output to the stdio stream stream any text necessary for declar- ing the name name of an initialized variable which is being defined. This macro must output the la- bel definition (perhaps using ASM_OUTPUT_LABEL). The argument decl is the VAR_DECL tree node representing the variable. If this macro is not defined, then the variable name is defined in the usual manner as a label (by means of ASM_OUTPUT_LABEL). ASM_GLOBALIZE_LABEL (stream, name) A C statement (sans semicolon) to output to the stdio stream stream some commands that will make the label name global; that is, available for reference from other files. Use the expression assemble_name (stream, name) to output the name itself; before and after that, output the addi- tional assembler syntax for making that name glo- bal, and a newline. ASM_OUTPUT_EXTERNAL (stream, decl, name) A C statement (sans semicolon) to output to the stdio stream stream any text necessary for declar- ing the name of an external symbol named name which is referenced in this compilation but not defined. The value of decl is the tree node for the declaration. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. ASM_OUTPUT_EXTERNAL_LIBCALL (stream, symref) A C statement (sans semicolon) to output on stream an assembler pseudo-op to declare a library func- tion name external. The name of the library func- tion is given by symref, which has type rtx and is a symbol_ref. This macro need not be defined if it does not need to output anything. The GNU assembler and most Unix assemblers don't require anything. ASM_OUTPUT_LABELREF (stream, name) A C statement (sans semicolon) to output to the stdio stream stream a reference in assembler syn- tax to a label named name. This should add `_' to the front of the name, if that is customary on your operating system, as it is in most Berkeley Unix systems. This macro is used in assemble_name. ASM_OUTPUT_LABELREF_AS_INT (file, label) Define this macro for systems that use the program collect2. The definition should be a C statement to output a word containing a reference to the la- bel label. ASM_GENERATE_INTERNAL_LABEL (string, prefix, num) A C statement to store into the string string a label whose name is made from the string prefix and the number num. This string, when output subsequently by ASM_OUTPUT_LABELREF, should produce the same out- put that ASM_OUTPUT_INTERNAL_LABEL would produce with the same prefix and num. ASM_OUTPUT_INTERNAL_LABEL (stream, prefix, num) A C statement to output to the stdio stream stream a label whose name is made from the string prefix and the number num. These labels are used for internal purposes, and there is no reason for them to appear in the symbol table of the object file. On many systems, the letter `L' at the beginning of a label has this effect. The usual definition of this macro is as follows: fprintf (stream, "L%s%d:\n", prefix, num) ASM_FORMAT_PRIVATE_NAME (outvar, name, number) A C expression to assign to outvar (which is a variable of type char *) a newly allocated string made from the string name and the number number, with some suitable punctuation added. Use alloca to get space for the string. This string will be used as the argument to ASM_OUTPUT_LABELREF to produce an assembler label for an internal static variable whose name is name. Therefore, the string must be such as to result in valid assembler code. The argument number is different each time this macro is executed; it prevents conflicts between similarly-named internal static vari- ables in different scopes. Ideally this string should not be a valid C identifier, to prevent any conflict with the user's own symbols. Most assemblers allow periods or percent signs in assembler symbols; putting at least one of these between the name and the number will suffice. OBJC_GEN_METHOD_LABEL (buf, is_inst, class_name, cat_name, sel_name) Define this macro to override the default as- sembler names used for Objective C methods. The default name is a unique method number followed by the name of the class (e.g. `_1_Foo'). For methods in categories, the name of the category is also included in the assembler name (e.g. `_1_Foo_Bar'). These names are safe on most systems, but make debugging difficult since the method's selec- tor is not present in the name. Therefore, particular systems define other ways of com- puting names. buf is a buffer in which to store the name (256 chars max); is_inst specifies whether the method is an instance method or a class method; class_name is the name of the class; cat_name is the name of the category (or NULL if the method is not in a category); and sel_name is the name of the selector. On systems where the assembler can handle quoted names, you can use this macro to pro- vide more human-readable names. 1.16.5. Output of Initialization Routines The compiled code for certain languages includes con- structors (also called initialization routines)---functions to initialize data in the program when the program is started. These functions need to be called before the pro- gram is ``started''---that is to say, before main is called. Compiling some languages generates destructors (also called termination routines) that should be called when the program terminates. To make the initialization and termination functions work, the compiler must output something in the assembler code to cause those functions to be called at the appropri- ate time. When you port the compiler to a new system, you need to specify what assembler code is needed to do this. Here are the two macros you should define if necessary: ASM_OUTPUT_CONSTRUCTOR (stream, name) Define this macro as a C statement to output on the stream stream the assembler code to arrange to call the function named name at initialization time. Assume that name is the name of a C function gen- erated automatically by the compiler. This func- tion takes no arguments. Use the function assemble_name to output the name name; this per- forms any system-specific syntactic transforma- tions such as adding an underscore. If you don't define this macro, nothing special is output to arrange to call the function. This is correct when the function will be called in some other manner---for example, by means of the col- lect program, which looks through the symbol table to find these functions by their names. If you want to use collect, then you need to arrange for it to be built and installed and used on your sys- tem. ASM_OUTPUT_DESTRUCTOR (stream, name) This is like ASM_OUTPUT_CONSTRUCTOR but used for termination functions rather than initialization functions. 1.16.6. Output of Assembler Instructions REGISTER_NAMES A C initializer containing the assembler's names for the machine registers, each one as a C string constant. This is what translates register numbers in the compiler into assembler language. ADDITIONAL_REGISTER_NAMES If defined, a C initializer for an array of struc- tures containing a name and a register number. This macro defines additional names for hard re- gisters, thus allowing the asm option in declara- tions to refer to registers using alternate names. ASM_OUTPUT_OPCODE (stream, ptr) Define this macro if you are using an unusual as- sembler that requires different names for the machine instructions. The definition is a C statement or statements which output an assembler instruction opcode to the stdio stream stream. The macro-operand ptr is a variable of type char * which points to the op- code name in its ``internal'' form---the form that is written in the machine description. The defin- ition should output the opcode name to stream, performing any translation you desire, and incre- ment the variable ptr to point at the end of the opcode so that it will not be output twice. In fact, your macro definition may process less than the entire opcode name, or more than the op- code name; but if you want to process text that includes `%'-sequences to substitute operands, you must take care of the substitution yourself. Just be sure to increment ptr over whatever text should not be output normally. If you need to look at the operand values, they can be found as the elements of recog_operand. If the macro definition does nothing, the instruc- tion is output in the usual way. FINAL_PRESCAN_INSN (insn, opvec, noperands) If defined, a C statement to be executed just pri- or to the output of assembler code for insn, to modify the extracted operands so they will be out- put differently. Here the argument opvec is the vector containing the operands extracted from insn, and noperands is the number of elements of the vector which contain meaningful data for this insn. The contents of this vector are what will be used to convert the insn template into assembler code, so you can change the assembler output by changing the con- tents of the vector. This macro is useful when various assembler syn- taxes share a single file of instruction patterns; by defining this macro differently, you can cause a large class of instructions to be output dif- ferently (such as with rearranged operands). Na- turally, variations in assembler syntax affecting individual insn patterns ought to be handled by writing conditional output routines in those pat- terns. If this macro is not defined, it is equivalent to a null statement. PRINT_OPERAND (stream, x, code) A C compound statement to output to stdio stream stream the assembler syntax for an instruction operand x. x is an RTL expression. code is a value that can be used to specify one of several ways of printing the operand. It is used when identical operands must be printed different- ly depending on the context. code comes from the `%' specification that was used to request print- ing of the operand. If the specification was just `%digit' then code is 0; if the specification was `%ltr digit' then code is the ASCII code for ltr. If x is a register, this macro should print the register's name. The names can be found in an ar- ray reg_names whose type is char *[]. reg_names is initialized from REGISTER_NAMES. When the machine description has a specification `%punct' (a `%' followed by a punctuation charac- ter), this macro is called with a null pointer for x and the punctuation character for code. PRINT_OPERAND_PUNCT_VALID_P (code) A C expression which evaluates to true if code is a valid punctuation character for use in the PRINT_OPERAND macro. If PRINT_OPERAND_PUNCT_VALID_P is not defined, it means that no punctuation characters (except for the standard one, `%') are used in this way. PRINT_OPERAND_ADDRESS (stream, x) A C compound statement to output to stdio stream stream the assembler syntax for an instruction operand that is a memory reference whose address is x. x is an RTL expression. On some machines, the syntax for a symbolic ad- dress depends on the section that the address refers to. On these machines, define the macro ENCODE_SECTION_INFO to store the information into the symbol_ref, and then check for it here. See section Assembler Format. DBR_OUTPUT_SEQEND(file) A C statement, to be executed after all slot- filler instructions have been output. If neces- sary, call dbr_sequence_length to determine the number of slots filled in a sequence (zero if not currently outputting a sequence), to decide how many no-ops to output, or whatever. Don't define this macro if it has nothing to do, but it is helpful in reading assembly output if the extent of the delay sequence is made explicit (e.g. with white space). Note that output routines for instructions with delay slots must be prepared to deal with not be- ing output as part of a sequence (i.e. when the scheduling pass is not run, or when no slot fill- ers could be found.) The variable final_sequence is null when not processing a sequence, otherwise it contains the sequence rtx being output. REGISTER_PREFIX LOCAL_LABEL_PREFIX USER_LABEL_PREFIX IMMEDIATE_PREFIX If defined, C string expressions to be used for the `%R', `%L', `%U', and `%I' options of asm_fprintf (see `final.c'). These are useful when a single `md' file must support multiple as- sembler formats. In that case, the various `tm.h' files can define these macros differently. ASM_OUTPUT_REG_PUSH (stream, regno) A C expression to output to stream some assembler code which will push hard register number regno onto the stack. The code need not be optimal, since this macro is used only when profiling. ASM_OUTPUT_REG_POP (stream, regno) A C expression to output to stream some assembler code which will pop hard register number regno off of the stack. The code need not be optimal, since this macro is used only when profiling. 1.16.7. Output of Dispatch Tables ASM_OUTPUT_ADDR_DIFF_ELT (stream, value, rel) This macro should be provided on machines where the addresses in a dispatch table are relative to the table's own address. The definition should be a C statement to output to the stdio stream stream an assembler pseudo- instruction to generate a difference between two labels. value and rel are the numbers of two internal labels. The definitions of these labels are output using ASM_OUTPUT_INTERNAL_LABEL, and they must be printed in the same way here. For example, fprintf (stream, "\t.word L%d-L%d\n", value, rel) ASM_OUTPUT_ADDR_VEC_ELT (stream, value) This macro should be provided on machines where the addresses in a dispatch table are absolute. The definition should be a C statement to out- put to the stdio stream stream an assembler pseudo-instruction to generate a reference to a label. value is the number of an internal label whose definition is output using ASM_OUTPUT_INTERNAL_LABEL. For example, fprintf (stream, "\t.word L%d\n", value) ASM_OUTPUT_CASE_LABEL (stream, prefix, num, table) Define this if the label before a jump-table needs to be output specially. The first three arguments are the same as for ASM_OUTPUT_INTERNAL_LABEL; the fourth argument is the jump-table which follows (a jump_insn containing an addr_vec or addr_diff_vec). This feature is used on system V to output a swbeg statement for the table. If this macro is not defined, these labels are output with ASM_OUTPUT_INTERNAL_LABEL. ASM_OUTPUT_CASE_END (stream, num, table) Define this if something special must be out- put at the end of a jump-table. The defini- tion should be a C statement to be executed after the assembler code for the table is written. It should write the appropriate code to stdio stream stream. The argument table is the jump-table insn, and num is the label- number of the preceding label. If this macro is not defined, nothing special is output at the end of the jump-table. 1.16.8. Assembler Commands for Alignment ASM_OUTPUT_ALIGN_CODE (file) A C expression to output text to align the loca- tion counter in the way that is desirable at a point in the code that is reached only by jumping. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. ASM_OUTPUT_LOOP_ALIGN (file) A C expression to output text to align the loca- tion counter in the way that is desirable at the beginning of a loop. This macro need not be defined if you don't want any special alignment to be done at such a time. Most machine descriptions do not currently define the macro. ASM_OUTPUT_SKIP (stream, nbytes) A C statement to output to the stdio stream stream an assembler instruction to advance the location counter by nbytes bytes. Those bytes should be zero when loaded. nbytes will be a C expression of type int. ASM_NO_SKIP_IN_TEXT Define this macro if ASM_OUTPUT_SKIP should not be used in the text section because it fails put zeros in the bytes that are skipped. This is true on many Unix systems, where the pseudo--op to skip bytes produces no-op instructions rather than zeros when used in the text section. ASM_OUTPUT_ALIGN (stream, power) A C statement to output to the stdio stream stream an assembler command to advance the location counter to a multiple of 2 to the power bytes. power will be a C expression of type int. 1.17. Controlling Debugging Information Format DBX_REGISTER_NUMBER (regno) A C expression that returns the DBX register number for the compiler register number regno. In simple cases, the value of this expression may be regno itself. But sometimes there are some regis- ters that the compiler knows about and DBX does not, or vice versa. In such cases, some register may need to have one number in the compiler and another for DBX. If two registers have consecutive numbers inside GNU CC, and they can be used as a pair to hold a multiword value, then they must have consecutive numbers after renumbering with DBX_REGISTER_NUMBER. Otherwise, debuggers will be unable to access such a pair, because they expect register pairs to be consecutive in their own numbering scheme. If you find yourself defining DBX_REGISTER_NUMBER in way that does not preserve register pairs, then what you must do instead is redefine the actual register numbering scheme. DBX_DEBUGGING_INFO Define this macro if GNU CC should produce debug- ging output for DBX in response to the `-g' op- tion. SDB_DEBUGGING_INFO Define this macro if GNU CC should produce COFF- style debugging output for SDB in response to the `-g' option. DWARF_DEBUGGING_INFO Define this macro if GNU CC should produce dwarf format debugging output in response to the `-g' option. DEFAULT_GDB_EXTENSIONS Define this macro to control whether GNU CC should by default generate GDB's extended version of DBX debugging information (assuming DBX-format debug- ging information is enabled at all). If you don't define the macro, the default is 1: always gen- erate the extended information. DEBUG_SYMS_TEXT Define this macro if all .stabs commands should be output while in the text section. DEBUGGER_AUTO_OFFSET (x) A C expression that returns the integer offset value for an automatic variable having address x (an RTL expression). The default computation as- sumes that x is based on the frame-pointer and gives the offset from the frame-pointer. This is required for targets that produce debugging output for DBX or COFF-style debugging output for SDB and allow the frame-pointer to be eliminated when the `-g' options is used. DEBUGGER_ARG_OFFSET (offset, x) A C expression that returns the integer offset value for an argument having address x (an RTL ex- pression). The nominal offset is offset. ASM_STABS_OP A C string constant naming the assembler pseudo op to use instead of .stabs to define an ordinary de- bugging symbol. If you don't define this macro, .stabs is used. This macro applies only to DBX debugging information format. ASM_STABD_OP A C string constant naming the assembler pseudo op to use instead of .stabd to define a debugging symbol whose value is the current location. If you don't define this macro, .stabd is used. This macro applies only to DBX debugging information format. ASM_STABN_OP A C string constant naming the assembler pseudo op to use instead of .stabn to define a debugging symbol with no name. If you don't define this macro, .stabn is used. This macro applies only to DBX debugging information format. PUT_SDB_... Define these macros to override the assembler syn- tax for the special SDB assembler directives. See `sdbout.c' for a list of these macros and their arguments. If the standard syntax is used, you need not define them yourself. SDB_DELIM Some assemblers do not support a semicolon as a delimiter, even between SDB assembler directives. In that case, define this macro to be the delim- iter to use (usually `\n'). It is not necessary to define a new set of PUT_SDB_op macros if this is the only change required. SDB_GENERATE_FAKE Define this macro to override the usual method of constructing a dummy name for anonymous structure and union types. See `sdbout.c' for more informa- tion. SDB_ALLOW_UNKNOWN_REFERENCES Define this macro to allow references to unknown structure, union, or enumeration tags to be emit- ted. Standard COFF does not allow handling of unknown references, MIPS ECOFF has support for it. SDB_ALLOW_FORWARD_REFERENCES Define this macro to allow references to struc- ture, union, or enumeration tags that have not yet been seen to be handled. Some assemblers choke if forward tags are used, while some require it. DBX_NO_XREFS Define this macro if DBX on your system does not support the construct `xstagname'. On some sys- tems, this construct is used to describe a forward reference to a structure named tagname. On other systems, this construct is not supported at all. DBX_CONTIN_LENGTH A symbol name in DBX-format debugging information is normally continued (split into two separate .stabs directives) when it exceeds a certain length (by default, 80 characters). On some operating systems, DBX requires this splitting; on others, splitting must not be done. You can inhi- bit splitting by defining this macro with the value zero. You can override the default splitting-length by defining this macro as an ex- pression for the length you desire. DBX_CONTIN_CHAR Normally continuation is indicated by adding a `\' character to the end of a .stabs string when a continuation follows. To use a different charac- ter instead, define this macro as a character con- stant for the character you want to use. Do not define this macro if backslash is correct for your system. DBX_STATIC_STAB_DATA_SECTION Define this macro if it is necessary to go to the data section before outputting the `.stabs' pseudo-op for a non-global static variable. DBX_LBRAC_FIRST Define this macro if the N_LBRAC symbol for a block should precede the debugging information for variables and functions defined in that block. Normally, in DBX format, the N_LBRAC symbol comes first. DBX_FUNCTION_FIRST Define this macro if the DBX information for a function and its arguments should precede the as- sembler code for the function. Normally, in DBX format, the debugging information entirely follows the assembler code. DBX_OUTPUT_FUNCTION_END (stream, function) Define this macro if the target machine requires special output at the end of the debugging infor- mation for a function. The definition should be a C statement (sans semicolon) to output the ap- propriate information to stream. function is the FUNCTION_DECL node for the function. DBX_OUTPUT_STANDARD_TYPES (syms) Define this macro if you need to control the order of output of the standard data types at the begin- ning of compilation. The argument syms is a tree which is a chain of all the predefined global sym- bols, including names of data types. Normally, DBX output starts with definitions of the types for integers and characters, followed by all the other predefined types of the particular language in no particular order. On some machines, it is necessary to output dif- ferent particular types first. To do this, define DBX_OUTPUT_STANDARD_TYPES to output those symbols in the necessary order. Any predefined types that you don't explicitly output will be output after- ward in no particular order. Be careful not to define this macro so that it works only for C. There are no global variables to access most of the built-in types, because another language may have another set of types. The way to output a particular type is to look through syms to see if you can find it. Here is an example: { tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (!strcmp (IDENTIFIER_POINTER (DECL_NAME (decl)), "long int")) dbxout_symbol (decl); ... } This does nothing if the expected type does not ex- ist. See the function init_decl_processing in source file `c-decl.c' to find the names to use for all the built-in C types. DBX_OUTPUT_MAIN_SOURCE_FILENAME (stream, name) A C statement to output DBX debugging informa- tion to the stdio stream stream which indi- cates that file name is the main source file- --the file specified as the input file for compilation. This macro is called only once, at the beginning of compilation. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. DBX_OUTPUT_MAIN_SOURCE_DIRECTORY (stream, name) A C statement to output DBX debugging informa- tion to the stdio stream stream which indi- cates that the current directory during compi- lation is named name. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. DBX_OUTPUT_MAIN_SOURCE_FILE_END (stream, name) A C statement to output DBX debugging informa- tion at the end of compilation of the main source file name. If you don't define this macro, nothing spe- cial is output at the end of compilation, which is correct for most machines. DBX_OUTPUT_SOURCE_FILENAME (stream, name) A C statement to output DBX debugging informa- tion to the stdio stream stream which indi- cates that file name is the current source file. This output is generated each time in- put shifts to a different source file as a result of `#include', the end of an included file, or a `#line' command. This macro need not be defined if the standard form of output for DBX debugging information is appropriate. 1.18. Cross Compilation and Floating Point Format While all modern machines use 2's complement represen- tation for integers, there are a variety of representations for floating point numbers. This means that in a cross- compiler the representation of floating point numbers in the compiled program may be different from that used in the machine doing the compilation. Because different representation systems may offer dif- ferent amounts of range and precision, the cross compiler cannot safely use the host machine's floating point arith- metic. Therefore, floating point constants must be represented in the target machine's format. This means that the cross compiler cannot use atof to parse a floating point constant; it must have its own special routine to use instead. Also, constant folding must emulate the target machine's arithmetic (or must not be done at all). The macros in the following table should be defined only if you are cross compiling between different floating point formats. Otherwise, don't define them. Then default definitions will be set up which use double as the data type, == to test for equality, etc. You don't need to worry about how many times you use an operand of any of these macros. The compiler never uses operands which have side effects. REAL_VALUE_TYPE A macro for the C data type to be used to hold a floating point value in the target machine's for- mat. Typically this would be a struct containing an array of int. REAL_VALUES_EQUAL (x, y) A macro for a C expression which compares for equality the two values, x and y, both of type REAL_VALUE_TYPE. REAL_VALUES_LESS (x, y) A macro for a C expression which tests whether x is less than y, both values being of type REAL_VALUE_TYPE and interpreted as floating point numbers in the target machine's representation. REAL_VALUE_LDEXP (x, scale) A macro for a C expression which performs the standard library function ldexp, but using the target machine's floating point representation. Both x and the value of the expression have type REAL_VALUE_TYPE. The second argument, scale, is an integer. REAL_VALUE_FIX (x) A macro whose definition is a C expression to con- vert the target-machine floating point value x to a signed integer. x has type REAL_VALUE_TYPE. REAL_VALUE_UNSIGNED_FIX (x) A macro whose definition is a C expression to con- vert the target-machine floating point value x to an unsigned integer. x has type REAL_VALUE_TYPE. REAL_VALUE_FIX_TRUNCATE (x) A macro whose definition is a C expression to con- vert the target-machine floating point value x to a signed integer, rounding toward 0. x has type REAL_VALUE_TYPE. REAL_VALUE_UNSIGNED_FIX_TRUNCATE (x) A macro whose definition is a C expression to con- vert the target-machine floating point value x to an unsigned integer, rounding toward 0. x has type REAL_VALUE_TYPE. REAL_VALUE_ATOF (string) A macro for a C expression which converts string, an expression of type char *, into a floating point number in the target machine's representa- tion. The value has type REAL_VALUE_TYPE. REAL_INFINITY Define this macro if infinity is a possible float- ing point value, and therefore division by 0 is legitimate. REAL_VALUE_ISINF (x) A macro for a C expression which determines wheth- er x, a floating point value, is infinity. The value has type int. By default, this is defined to call isinf. REAL_VALUE_ISNAN (x) A macro for a C expression which determines wheth- er x, a floating point value, is a ``nan'' (not- a-number). The value has type int. By default, this is defined to call isnan. Define the following additional macros if you want to make floating point constant folding work while cross com- piling. If you don't define them, cross compilation is still possible, but constant folding will not happen for floating point values. REAL_ARITHMETIC (output, code, x, y) A macro for a C statement which calculates an ar- ithmetic operation of the two floating point values x and y, both of type REAL_VALUE_TYPE in the target machine's representation, to produce a result of the same type and representation which is stored in output (which will be a variable). The operation to be performed is specified by code, a tree code which will always be one of the following: PLUS_EXPR, MINUS_EXPR, MULT_EXPR, RDIV_EXPR, MAX_EXPR, MIN_EXPR. The expansion of this macro is responsible for checking for overflow. If overflow happens, the macro expansion should execute the statement re- turn 0;, which indicates the inability to perform the arithmetic operation requested. REAL_VALUE_NEGATE (x) A macro for a C expression which returns the nega- tive of the floating point value x. Both x and the value of the expression have type REAL_VALUE_TYPE and are in the target machine's floating point representation. There is no way for this macro to report overflow, since overflow can't happen in the negation opera- tion. REAL_VALUE_TRUNCATE (x) A macro for a C expression which converts the double-precision floating point value x to single-precision. Both x and the value of the expression have type REAL_VALUE_TYPE and are in the target machine's floating point representation. However, the value should have an appropriate bit pattern to be out- put properly as a single-precision floating con- stant. There is no way for this macro to report overflow. REAL_VALUE_TO_INT (low, high, x) A macro for a C expression which converts a float- ing point value x into a double-precision integer which is then stored into low and high, two vari- ables of type int. REAL_VALUE_FROM_INT (x, low, high) A macro for a C expression which converts a double-precision integer found in low and high, two variables of type int, into a floating point value which is then stored into x. 1.19. Miscellaneous Parameters PREDICATE_CODES Optionally define this if you have added predi- cates to `machine.c'. This macro is called within an initializer of an array of structures. The first field in the structure is the name of a predicate and the second field is an arrary of rtl codes. For each predicate, list all rtl codes that can be in expressions matched by the predi- cate. The list should have a trailing comma. Here is an example of two entries in the list for a typical RISC machine: #define PREDICATE_CODES \ {"gen_reg_rtx_operand", {SUBREG, REG}}, \ {"reg_or_short_cint_operand", {SUBREG, REG, CONST_INT}}, Defining this macro does not affect the gen- erated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to mal- function). Instead, it allows the table built by `genrecog' to be more compact and effi- cient, thus speeding up the compiler. The most important predicates to include in the list specified by this macro are thoses used in the most insn patterns. CASE_VECTOR_MODE An alias for a machine mode name. This is the machine mode that elements of a jump-table should have. CASE_VECTOR_PC_RELATIVE Define this macro if jump-tables should con- tain relative addresses. CASE_DROPS_THROUGH Define this if control falls through a case insn when the index value is out of range. This means the specified default-label is ac- tually ignored by the case insn proper. BYTE_LOADS_ZERO_EXTEND Define this macro if an instruction to load a value narrower than a word from memory into a register also zero-extends the value to the whole register. IMPLICIT_FIX_EXPR An alias for a tree code that should be used by default for conversion of floating point values to fixed point. Normally, FIX_ROUND_EXPR is used. FIXUNS_TRUNC_LIKE_FIX_TRUNC Define this macro if the same instructions that convert a floating point number to a signed fixed point number also convert validly to an unsigned one. EASY_DIV_EXPR An alias for a tree code that is the easiest kind of division to compile code for in the general case. It may be TRUNC_DIV_EXPR, FLOOR_DIV_EXPR, CEIL_DIV_EXPR or ROUND_DIV_EXPR. These four division operators differ in how they round the result to an in- teger. EASY_DIV_EXPR is used when it is per- missible to use any of those kinds of division and the choice should be made on the basis of efficiency. MOVE_MAX The maximum number of bytes that a single in- struction can move quickly from memory to memory. SHIFT_COUNT_TRUNCATED Defining this macro causes the compiler to omit a sign-extend, zero-extend, or bitwise `and' instruction that truncates the count of a shift operation to a width equal to the number of bits needed to represent the size of the object being shifted. On machines that have instructions that act on bitfields at variable positions, including `bit test' in- structions, defining SHIFT_COUNT_TRUNCATED also causes truncation not to be applied to these instructions. If both types of instructions truncate the count (for shifts) and position (for bitfield operations), or if no variable-position bit- field instructions exist, you should define this macro. However, on some machines, such as the 80386, truncation only applies to shift operations and not bitfield operations. Do not define SHIFT_COUNT_TRUNCATED on such machines. In- stead, add patterns to the `md' file that in- clude the implied truncation of the shift in- structions. TRULY_NOOP_TRUNCATION (outprec, inprec) A C expression which is nonzero if on this machine it is safe to ``convert'' an integer of inprec bits to one of outprec bits (where outprec is smaller than inprec) by merely operating on it as if it had only outprec bits. On many machines, this expression can be 1. It is reported that suboptimal code can result when TRULY_NOOP_TRUNCATION returns 1 for a pair of sizes for modes for which MODES_TIEABLE_P is 0. If this is the case, making TRULY_NOOP_TRUNCATION return 0 in such cases may improve things. STORE_FLAG_VALUE A C expression describing the value returned by a comparison operator and stored by a store-flag instruction (`scond') when the con- dition is true. This description must apply to all the `scond' patterns and all the com- parison operators. A value of 1 or -1 means that the instruction implementing the comparison operator returns exactly 1 or -1 when the comparison is true and 0 when the comparison is false. Other- wise, the value indicates which bits of the result are guaranteed to be 1 when the com- parison is true. This value is interpreted in the mode of the comparison operation, which is given by the mode of the first operand in the `scond' pattern. Either the low bit or the sign bit of STORE_FLAG_VALUE be on. Present- ly, only those bits are used by the compiler. If STORE_FLAG_VALUE is neither 1 or -1, the compiler will generate code that depends only on the specified bits. It can also replace comparison operators with equivalent opera- tions if they cause the required bits to be set, even if the remaining bits are undefined. For example, on a machine whose comparison operators return an SImode value and where STORE_FLAG_VALUE is defined as `0x80000000', saying that just the sign bit is relevant, the expression (ne:SI (and:SI x (const_int power-of-2)) (const_int 0)) can be converted to (ashift:SI x (const_int n)) where n is the appropriate shift count to move the bit being tested into the sign bit. There is no way to describe a machine that al- ways sets the low-order bit for a true value, but does not guarantee the value of any other bits, but we do not know of any machine that has such an instruction. If you are trying to port GNU CC to such a machine, include an in- struction to perform a logical-and of the result with 1 in the pattern for the comparis- on operators and let us know (see section Bug Reporting). Often, a machine will have multiple instruc- tions that obtain a value from a comparison (or the condition codes). Here are rules to guide the choice of value for STORE_FLAG_VALUE, and hence the instructions to be used: o+ Use the shortest sequence that yields a valid definition for STORE_FLAG_VALUE. It is more efficent for the compiler to ``normalize'' the value (convert it to, e.g., 1 or 0) than for the comparison operators to do so because there may be opportunities to combine the normalization with other operations. o+ For equal-length sequences, use a value of 1 or -1, with -1 being slightly preferred on machines with expensive jumps and 1 preferred on other machines. o+ As a second choice, choose a value of `0x80000001' if instructions exist that set both the sign and low-order bits but do not define the others. o+ Otherwise, use a value of `0x80000000'. You need not define STORE_FLAG_VALUE if the machine has no store-flag instructions. Pmode An alias for the machine mode for pointers. Nor- mally the definition can be #define Pmode SImode FUNCTION_MODE An alias for the machine mode used for memory references to functions being called, in call RTL expressions. On most machines this should be QImode. INTEGRATE_THRESHOLD (decl) A C expression for the maximum number of in- structions above which the function decl should not be inlined. decl is a FUNCTION_DECL node. The default definition of this macro is 64 plus 8 times the number of arguments that the function accepts. Some people think a larger threshold should be used on RISC machines. SCCS_DIRECTIVE Define this if the preprocessor should ignore #sccs directives and print no error message. HANDLE_PRAGMA (stream) Define this macro if you want to implement any pragmas. If defined, it should be a C state- ment to be executed when #pragma is seen. The argument stream is the stdio input stream from which the source text can be read. It is generally a bad idea to implement new uses of #pragma. The only reason to define this macro is for compatibility with other compilers that do support #pragma for the sake of any user programs which already use it. HAVE_VPRINTF Define this if the library function vprintf is available on your system. DOLLARS_IN_IDENTIFIERS Define this macro to control use of the char- acter `$' in identifier names. The value should be 0, 1, or 2. 0 means `$' is not al- lowed by default; 1 means it is allowed by de- fault if `-traditional' is used; 2 means it is allowed by default provided `-ansi' is not used. 1 is the default; there is no need to define this macro in that case. DEFAULT_MAIN_RETURN Define this macro if the target system expects every program's main function to return a standard ``success'' value by default (if no other value is explicitly returned). The definition should be a C statement (sans semicolon) to generate the appropriate rtl in- structions. It is used only when compiling the end of main. HAVE_ATEXIT Define this if the target system supports the function atexit from the ANSI C standard. If this is not defined, and INIT_SECTION_ASM_OP is not defined, a default exit function will be provided to support C++. EXIT_BODY Define this if your exit function needs to do something besides calling an external function _cleanup before terminating with _exit. The EXIT_BODY macro is only needed if netiher HAVE_ATEXIT nor INIT_SECTION_ASM_OP are de- fined.