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GNU Info File | 1993-06-12 | 51KB | 900 lines

This is Info file gcc.info, produced by Makeinfo-1.47 from the input file gcc.tex. This file documents the use and the internals of the GNU compiler. Copyright (C) 1988, 1989, 1992 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the sections entitled "GNU General Public License" and "Protect Your Freedom--Fight `Look And Feel'" are included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the sections entitled "GNU General Public License" and "Protect Your Freedom--Fight `Look And Feel'", and this permission notice, may be included in translations approved by the Free Software Foundation instead of in the original English. File: gcc.info, Node: Instruction Output, Next: Dispatch Tables, Prev: Macros for Initialization, Up: Assembler Format 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 structures containing a name and a register number. This macro defines additional names for hard registers, thus allowing the `asm' option in declarations to refer to registers using alternate names. `ASM_OUTPUT_OPCODE (STREAM, PTR)' Define this macro if you are using an unusual assembler 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 opcode name in its "internal" form--the form that is written in the machine description. The definition should output the opcode name to STREAM, performing any translation you desire, and increment 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 opcode 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 instruction is output in the usual way. `FINAL_PRESCAN_INSN (INSN, OPVEC, NOPERANDS)' If defined, a C statement to be executed just prior to the output of assembler code for INSN, to modify the extracted operands so they will be output 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 contents of the vector. This macro is useful when various assembler syntaxes share a single file of instruction patterns; by defining this macro differently, you can cause a large class of instructions to be output differently (such as with rearranged operands). Naturally, variations in assembler syntax affecting individual insn patterns ought to be handled by writing conditional output routines in those patterns. 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 differently depending on the context. CODE comes from the `%' specification that was used to request printing 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 array `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 character), 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 address 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. *Note Assembler Format::. `DBR_OUTPUT_SEQEND(FILE)' A C statement, to be executed after all slot-filler instructions have been output. If necessary, 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 being output as part of a sequence (i.e. when the scheduling pass is not run, or when no slot fillers 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 assembler 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. File: gcc.info, Node: Dispatch Tables, Next: Alignment Output, Prev: Instruction Output, Up: Assembler Format 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 output 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 output at the end of a jump-table. The definition 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. File: gcc.info, Node: Alignment Output, Prev: Dispatch Tables, Up: Assembler Format Assembler Commands for Alignment -------------------------------- `ASM_OUTPUT_ALIGN_CODE (FILE)' A C expression to output text to align the location 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 location 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'. File: gcc.info, Node: Debugging Info, Next: Cross-compilation, Prev: Assembler Format, Up: Target Macros Controlling Debugging Information Format ======================================== * Menu: * All Debuggers:: Macros that affect all debugging formats uniformly. * DBX Options:: Macros enabling specific options in DBX format. * DBX Hooks:: Hook macros for varying DBX format. * File Names and DBX:: Macros controlling output of file names in DBX format. * SDB and DWARF:: Macros for SDB (COFF) and DWARF formats. File: gcc.info, Node: All Debuggers, Next: DBX Options, Up: Debugging Info Macros Affecting All Debugging Formats -------------------------------------- `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 registers 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. `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 assumes 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 expression). The nominal offset is OFFSET. File: gcc.info, Node: DBX Options, Next: DBX Hooks, Prev: All Debuggers, Up: Debugging Info Specific Options for DBX Output ------------------------------- `DBX_DEBUGGING_INFO' Define this macro if GNU CC should produce debugging output for DBX in response to the `-g' option. `XCOFF_DEBUGGING_INFO' Define this macro if GNU CC should produce XCOFF format debugging output in response to the `-g' option. This is a variant of DBX format. `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 debugging information is enabled at all). If you don't define the macro, the default is 1: always generate the extended information if there is any occasion to. `DEBUG_SYMS_TEXT' Define this macro if all `.stabs' commands should be output while in the text section. `ASM_STABS_OP' A C string constant naming the assembler pseudo op to use instead of `.stabs' to define an ordinary debugging 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. `DBX_NO_XREFS' Define this macro if DBX on your system does not support the construct `xsTAGNAME'. On some systems, 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 inhibit splitting by defining this macro with the value zero. You can override the default splitting-length by defining this macro as an expression 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 character instead, define this macro as a character constant 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_TYPE_DECL_STABS_CODE' The value to use in the "code" field of the `.stabs' directive for a typedef. The default is `N_LSYM'. `DBX_STATIC_CONST_VAR_CODE' The value to use in the "code" field of the `.stabs' directive for a static variable located in the text section. DBX format does not provide any "right" way to do this. The default is `N_FUN'. `DBX_REGPARM_STABS_CODE' The value to use in the "code" field of the `.stabs' directive for a parameter passed in registers. DBX format does not provide any "right" way to do this. The default is `N_RSYM'. `DBX_REGPARM_STABS_LETTER' The letter to use in DBX symbol data to identify a symbol as a parameter passed in registers. DBX format does not customarily provide any way to do this. The default is `'P''. `DBX_MEMPARM_STABS_LETTER' The letter to use in DBX symbol data to identify a symbol as a stack parameter. The default is `'p''. `DBX_FUNCTION_FIRST' Define this macro if the DBX information for a function and its arguments should precede the assembler code for the function. Normally, in DBX format, the debugging information entirely follows the assembler code. `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. File: gcc.info, Node: DBX Hooks, Next: File Names and DBX, Prev: DBX Options, Up: Debugging Info Open-Ended Hooks for DBX Format ------------------------------- `DBX_OUTPUT_LBRAC (STREAM, NAME)' Define this macro to say how to output to STREAM the debugging information for the start of a scope level for variable names. The argument NAME is the name of an assembler symbol (for use with `assemble_name') whose value is the address where the scope begins. `DBX_OUTPUT_RBRAC (STREAM, NAME)' Like `DBX_OUTPUT_LBRAC', but for the end of a scope level. `DBX_OUTPUT_ENUM (STREAM, TYPE)' Define this macro if the target machine requires special handling to output an enumeration type. The definition should be a C statement (sans semicolon) to output the appropriate information to STREAM for the type TYPE. `DBX_OUTPUT_FUNCTION_END (STREAM, FUNCTION)' Define this macro if the target machine requires special output at the end of the debugging information for a function. The definition should be a C statement (sans semicolon) to output the appropriate 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 beginning of compilation. The argument SYMS is a `tree' which is a chain of all the predefined global symbols, 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 different 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 afterward 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 exist. 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. Here is another way of finding a particular type: { tree decl; for (decl = syms; decl; decl = TREE_CHAIN (decl)) if (TREE_CODE (decl) == TYPE_DECL && TREE_CODE (TREE_TYPE (decl)) == INTEGER_CST && TYPE_PRECISION (TREE_TYPE (decl)) == 16 && TYPE_UNSIGNED (TREE_TYPE (decl))) /* This must be `unsigned short'. */ dbxout_symbol (decl); ... } File: gcc.info, Node: File Names and DBX, Next: SDB and DWARF, Prev: DBX Hooks, Up: Debugging Info File Names in DBX Format ------------------------ `DBX_WORKING_DIRECTORY' Define this if DBX wants to have the current directory recorded in each object file. Note that the working directory is always recorded if GDB extensions are enabled. `DBX_OUTPUT_MAIN_SOURCE_FILENAME (STREAM, NAME)' A C statement to output DBX debugging information to the stdio stream STREAM which indicates 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 information to the stdio stream STREAM which indicates that the current directory during compilation 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 information at the end of compilation of the main source file NAME. If you don't define this macro, nothing special 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 information to the stdio stream STREAM which indicates that file NAME is the current source file. This output is generated each time input 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. File: gcc.info, Node: SDB and DWARF, Prev: File Names and DBX, Up: Debugging Info Macros for SDB and DWARF Output ------------------------------- `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. `PUT_SDB_...' Define these macros to override the assembler syntax 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 delimiter 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 information. `SDB_ALLOW_UNKNOWN_REFERENCES' Define this macro to allow references to unknown structure, union, or enumeration tags to be emitted. 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 structure, 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. File: gcc.info, Node: Cross-compilation, Next: Misc, Prev: Debugging Info, Up: Target Macros Cross Compilation and Floating Point Format =========================================== While all modern machines use 2's complement representation 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 different amounts of range and precision, the cross compiler cannot safely use the host machine's floating point arithmetic. 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 format. 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 convert 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 convert 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 convert 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 convert 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 representation. The value has type `REAL_VALUE_TYPE'. `REAL_INFINITY' Define this macro if infinity is a possible floating point value, and therefore division by 0 is legitimate. `REAL_VALUE_ISINF (X)' A macro for a C expression which determines whether 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 whether 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 compiling. 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 arithmetic 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 `return 0;', which indicates the inability to perform the arithmetic operation requested. `REAL_VALUE_NEGATE (X)' A macro for a C expression which returns the negative 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 operation. `REAL_VALUE_TRUNCATE (MODE, X)' A macro for a C expression which converts the floating point value X to mode MODE. 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 output properly as a floating constant whose precision accords with mode MODE. 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 floating point value X into a double-precision integer which is then stored into LOW and HIGH, two variables 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. File: gcc.info, Node: Misc, Prev: Cross-compilation, Up: Target Macros Miscellaneous Parameters ======================== `PREDICATE_CODES' Optionally define this if you have added predicates 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 array of rtl codes. For each predicate, list all rtl codes that can be in expressions matched by the predicate. 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 generated code (however, incorrect definitions that omit an rtl code that may be matched by the predicate can cause the compiler to malfunction). Instead, it allows the table built by `genrecog' to be more compact and efficient, 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 contain 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 actually ignored by the `case' insn proper. `CASE_VALUES_THRESHOLD' Define this to be the smallest number of different values for which it is best to use a jump-table instead of a tree of conditional branches. The default is four for machines with a `casesi' instruction and five otherwise. This is best for most machines. `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. `BYTE_LOADS_SIGN_EXTEND' Define this macro if an instruction to load a value narrower than a word from memory into a register also sign-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 integer. `EASY_DIV_EXPR' is used when it is permissible 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 instruction 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, which may include `bit test' instructions, defining `SHIFT_COUNT_TRUNCATED' also enables deletion of truncations of the values that serve as arguments to bitfield instructions. If both types of instructions truncate the count (for shifts) and position (for bitfield operations), or if no variable-position bitfield instructions exist, you should define this macro. However, on some machines, such as the 80386 and the 680x0, truncation only applies to shift operations and not the (real or pretended) bitfield operations. Do not define `SHIFT_COUNT_TRUNCATED' on such machines. Instead, add patterns to the `md' file that include the implied truncation of the shift instructions. `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 with an integral mode and stored by a store-flag instruction (`sCOND') when the condition is true. This description must apply to *all* the `sCOND' patterns and all the comparison operators whose results have a `MODE_INT' mode. 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. Otherwise, the value indicates which bits of the result are guaranteed to be 1 when the comparison 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. Presently, 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 operations 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 always 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 instruction to perform a logical-and of the result with 1 in the pattern for the comparison operators and let us know (*note Bug Reporting::.). Often, a machine will have multiple instructions 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: * Use the shortest sequence that yields a valid definition for `STORE_FLAG_VALUE'. It is more efficient 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. * 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. * 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. * Otherwise, use a value of `0x80000000'. You need not define `STORE_FLAG_VALUE' if the machine has no store-flag instructions. `FLOAT_STORE_FLAG_VALUE' A C expression that gives a non-zero floating point value that is returned when comparison operators with floating-point results are true. Define this macro on machine that have comparison operations that return floating-point values. If there are no such operations, do not define this macro. `Pmode' An alias for the machine mode for pointers. Normally 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 instructions 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 statement 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. `DOLLARS_IN_IDENTIFIERS' Define this macro to control use of the character `$' in identifier names. The value should be 0, 1, or 2. 0 means `$' is not allowed by default; 1 means it is allowed by default 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. `NO_DOLLAR_IN_LABEL' Define this macro if the assembler does not accept the character `$' in label names. By default constructors and destructors in G++ have `$' in the identifiers. If this macro is defined, `.' is used instead. `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 instructions. 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 defined. File: gcc.info, Node: Config, Next: Index, Prev: Target Macros, Up: Top The Configuration File ********************** The configuration file `xm-MACHINE.h' contains macro definitions that describe the machine and system on which the compiler is running, unlike the definitions in `MACHINE.h', which describe the machine for which the compiler is producing output. Most of the values in `xm-MACHINE.h' are actually the same on all machines that GNU CC runs on, so large parts of all configuration files are identical. But there are some macros that vary: `USG' Define this macro if the host system is System V. `VMS' Define this macro if the host system is VMS. `FAILURE_EXIT_CODE' A C expression for the status code to be returned when the compiler exits after serious errors. `SUCCESS_EXIT_CODE' A C expression for the status code to be returned when the compiler exits without serious errors. `HOST_WORDS_BIG_ENDIAN' Defined if the host machine stores words of multi-word values in big-endian order. (GNU CC does not depend on the host byte ordering within a word.) `HOST_FLOAT_FORMAT' A numeric code distinguishing the floating point format for the host machine. See `TARGET_FLOAT_FORMAT' in *Note Storage Layout:: for the alternatives and default. `HOST_BITS_PER_CHAR' A C expression for the number of bits in `char' on the host machine. `HOST_BITS_PER_SHORT' A C expression for the number of bits in `short' on the host machine. `HOST_BITS_PER_INT' A C expression for the number of bits in `int' on the host machine. `HOST_BITS_PER_LONG' A C expression for the number of bits in `long' on the host machine. `ONLY_INT_FIELDS' Define this macro to indicate that the host compiler only supports `int' bit fields, rather than other integral types, including `enum', as do most C compilers. `EXECUTABLE_SUFFIX' Define this macro if the host system uses a naming convention for executable files that involves a common suffix (such as, in some systems, `.exe') that must be mentioned explicitly when you run the program. `OBSTACK_CHUNK_SIZE' A C expression for the size of ordinary obstack chunks. If you don't define this, a usually-reasonable default is used. `OBSTACK_CHUNK_ALLOC' The function used to allocate obstack chunks. If you don't define this, `xmalloc' is used. `OBSTACK_CHUNK_FREE' The function used to free obstack chunks. If you don't define this, `free' is used. `USE_C_ALLOCA' Define this macro to indicate that the compiler is running with the `alloca' implemented in C. This version of `alloca' can be found in the file `alloca.c'; to use it, you must also alter the `Makefile' variable `ALLOCA'. (This is done automatically for the systems on which we know it is needed.) If you do define this macro, you should probably do it as follows: #ifndef __GNUC__ #define USE_C_ALLOCA #else #define alloca __builtin_alloca #endif so that when the compiler is compiled with GNU CC it uses the more efficient built-in `alloca' function. `FUNCTION_CONVERSION_BUG' Define this macro to indicate that the host compiler does not properly handle converting a function value to a pointer-to-function when it is used in an expression. `HAVE_VPRINTF' Define this if the library function `vprintf' is available on your system. `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. `HAVE_PUTENV' Define this if the library function `putenv' is available on your system. `NO_SYS_SIGLIST' Define this if your system *does not* provide the variable `sys_siglist'. `USE_PROTOTYPES' Define this to be 1 if you know that the host compiler supports prototypes, even if it doesn't define __STDC__, or define it to be 0 if you do not want any prototypes used in compiling GNU CC. If `USE_PROTOTYPES' is not defined, it will be determined automatically whether your compiler supports prototypes by checking if `__STDC__' is defined. `NO_MD_PROTOTYPES' Define this if you wish suppression of prototypes generated from the machine description file, but to use other prototypes within GNU CC. If `USE_PROTOTYPES' is defined to be 0, or the host compiler does not support prototypes, this macro has no effect. `MD_CALL_PROTOTYPES' Define this if you wish to generate prototypes for the `gen_call' or `gen_call_value' functions generated from the machine description file. If `USE_PROTOTYPES' is defined to be 0, or the host compiler does not support prototypes, or `NO_MD_PROTOTYPES' is defined, this macro has no effect. As soon as all of the machine descriptions are modified to have the appropriate number of arguments, this macro will be removed. Some systems do provide this variable, but with a different name such as `_sys_siglist'. On these systems, you can define `sys_siglist' as a macro which expands into the name actually provided. `NO_STAB_H' Define this if your system does not have the include file `stab.h'. If `USG' is defined, `NO_STAB_H' is assumed. In addition, configuration files for system V define `bcopy', `bzero' and `bcmp' as aliases. Some files define `alloca' as a macro when compiled with GNU CC, in order to take advantage of the benefit of GNU CC's built-in `alloca'.