NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/sys/hp/10030

Text File | 1992-09-03 | 2.2 KB | 60 lines

Path: sparky!uunet!wupost!uwm.edu!rutgers!psinntp!psinntp!rsi!prcrs!paul
From: [e-mail] (Paul Hite)
Newsgroups: comp.sys.hp
Subject: Re: that HPUX cc compiler
Message-ID: <[e-mail]>
Date: 2 Sep 92 15:14:42 GMT
References: <[e-mail]>
Organization: PRC Realty Systems, McLean, VA
Lines: 49


HP gets a lot of grief from the behavior of their c optimizer.  I'm sure
that some of it is valid.  But a lot of the posts basicly say something
like:
    I've got a program that works without the optimizer and fails
    when I optimize it.  Therefore HP's optimizer is broken.

Here's a real live counter-example to that argument.  I wrote a replacement
to w and it worked without the optimizer and failed when I optimized it.
I reduced the program to a tiny example that also failed with the optimizer.
The complete program is below my signature, but here is the important part:
    struct utmp entry;
    while(fread(entry, sizeof entry, 1, u)) {
        bogus = entry.ut_time;
With the optimizer, bogus always had the same value.  Without the optimizer
various correct values are printed.  The problem is the fread.  It should be:
    while(fread(&entry, sizeof entry, 1, u)) {
                ^
And the optimizer works fine on the corrected program.  Actually it's amazing
that the program works at all the first way.  All of this is on an 847, those
of you on other platforms may get different results with the buggy program.
(Indeed, Steinar Haug found the bug for me as he struggled to get my program
working on a 425!)

But my point is that the existence of a program like mine that fails when
optimized does not necessarily prove that the optimizer is broken.  It may
be that the program is broken.

Paul Hite   PRC Realty Systems  McLean,Va   [e-mail]    [phone]
    "We are trying to bring up an Air Traffic Control display on an X window
      terminal and there seems to be some problems." -- from comp.windows.x
--------------
#include <stdio.h>
#include <sys/stat.h>
#include <utmp.h>
#include <time.h>
time_t bogus;
main ()
{
    FILE *u;
    struct utmp entry;
    u = fopen("/etc/utmp","r");
    while(fread(entry, sizeof entry, 1, u)) {
        bogus = entry.ut_time;
        printf("bogus = %d\n");
    }
    fclose(u);
    exit(0);
}