From: hjl@lucon.org (H.J. Lu)
To: florian@suse.de (Florian La Roche)
Cc: paubert@iram.es, egcs@cygnus.com
Subject: Re: egcs-problem 1.0.2
Date: Sat, 04 Apr 1998 20:05:00 -0000 [thread overview]
Message-ID: <m0yLfGJ-00058xC@ocean.lucon.org> (raw)
In-Reply-To: <19980331132837.33334@knorke.saar.de>
> On Wed, 25 Feb 1998, Jeffrey A Law wrote:
>
> > I think the best way to proceed is for someone to give me a hunk of
> > code that I can feed the compiler that will show a case where a
> > clobber is being used for input addressing. That way I can debug
> > the compiler and see what's really happening.
>
> I can't keep up with the weekly updates, so my GCC currently is:
> gcc version egcs-2.91.06 980122 (gcc-2.8.0 release)
>
> The following code breaks when compiled with -fno-strength-reduce, but
> independantly of -O2/-O3, -fomit-frame-pointer, and -m[345]86:
>
> ===============================================================================
> #include <linux/string.h>
Please don't use anything from <linux/> or <asm/> directly in
the user codes unless it it is absolutely necessary.
>
> int count_substring_matches(char **haystacks, char **needles)
> {
> int hits=0, i, j;
> for(i=0; haystacks[i]; i++) {
> for(j=0; needles[j]; j++) {
> if (strstr(haystacks[i], needles[j])) hits++;
> }
> }
> return hits;
> }
> ===============================================================================
>
> generates for the strstr function:
>
> ===============================================================================
> #APP
> cld
> movl (%ebx,%edx,4),%edi
> repne
> scasb
> notl %ecx
> decl %ecx
> movl %ecx,%edx
> 1: movl (%ebx,%edx,4),%edi
> movl %esi,%eax
> movl %edx,%ecx
> repe
> cmpsb
> je 2f
> xchgl %eax,%esi
> incl %esi
> cmpb $0,-1(%eax)
> jne 1b
> xorl %eax,%eax
> 2:
> #NO_APP
> ===============================================================================
>
> in this precise case the problem is with %edx. Other compilers/versions
> used %edi in the address computation. Note that it generates correct code
> when I exchange the order of the nested loops !
>
> If I add -fpic the addressing mode is even able to use two
> clobbered registers and becomes (%edx,%edi,4), and only -fstrength-reduce
> -fomit-frame-pointer generates correct pic code. Otherwise the compiler
> sometimes reloads %edi with movl (%edx),%edi.
>
>
>
# gcc -O2 -fno-strength-reduce foo.c
# a.out
zsh: 2924 segmentation fault ./a.out
I am not sure if it is a bug or not. The problem is when an asm
statement marks a register as clobber, how can egcs safely use it
for the asm statement? I think when a register is marked as clobber,
egcs cannot use it inside the asm statement via %0, %1, %2, .... Is
there a fix for that? The bug may be in combine.
Thanks.
H.J.
---foo.c--
extern inline char * strstr(const char * cs,const char * ct)
{
register char * __res;
__asm__ __volatile__(
"cld\n\t" \
"movl %4,%%edi\n\t"
"repne\n\t"
"scasb\n\t"
"notl %%ecx\n\t"
"decl %%ecx\n\t"
"movl %%ecx,%%edx\n"
"1:\tmovl %4,%%edi\n\t"
"movl %%esi,%%eax\n\t"
"movl %%edx,%%ecx\n\t"
"repe\n\t"
"cmpsb\n\t"
"je 2f\n\t"
"xchgl %%eax,%%esi\n\t"
"incl %%esi\n\t"
"cmpb $0,-1(%%eax)\n\t"
"jne 1b\n\t"
"xorl %%eax,%%eax\n\t"
"2:"
:"=a" (__res):"0" (0),"c" (0xffffffff),"S" (cs),"g" (ct)
:"cx","dx","di","si");
return __res;
}
int count_substring_matches(char **haystacks, char **needles)
{
int hits=0, i, j;
for(i=0; haystacks[i]; i++) {
for(j=0; needles[j]; j++) {
if (strstr(haystacks[i], needles[j])) hits++;
}
}
return hits;
}
main ()
{
char * haystacks [] = {"foobar", 0};
char * needles [] = {"foo", 0};
if (count_substring_matches (haystacks, needles ) != 1)
abort ();
return 0;
}
next parent reply other threads:[~1998-04-04 20:05 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <19980331132837.33334@knorke.saar.de>
1998-04-04 20:05 ` H.J. Lu [this message]
1998-04-05 21:29 ` Jeffrey A Law
1998-04-05 21:29 ` H.J. Lu
1998-04-05 17:27 ` Jeffrey A Law
1998-04-05 17:27 ` H.J. Lu
1998-04-05 21:29 ` Jeffrey A Law
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