Bug#179712: marked as done (gcc-3.2 -O2 miscompilation (i386))
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From: Marko Kreen <marko@l-t.ee>
To: Debian Bug Tracking System <submit@bugs.debian.org>
Subject: gcc-3.2 -O2 miscompilation (i386)
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Package: gcc-3.2
Version: 1:3.2.2-0pre8
Severity: normal
gcc-3.2 -O2 miscompiles following program:
---------------------------------------------
extern int write(int fd, void *buf, int len);
extern int toupper(int c);
void strupr (char *s)
{
while (*s)
*s++ = toupper(*s);
}
int main(int argc, char *argv[])
{
char s[] = "foo";
strupr(s);
write(1, s, 3);
write(1, "\n", 1);
return 0;
}
---------------------------------------------
$ gcc-3.2 -Wall -O2 -o test test.c
test.c: In function `strupr':
test.c:7: warning: operation on `s' may be undefined
$ ./test
OO
$
---------------------------------------------
gcc-2.95 compiles it correctly, also gcc-3.2 when optimizing
less than -O2. When the "toupper(*s)" is replaced with "*s & 0x5f"
gcc-3.2 -O2 also works and without warning.
found the error when tried to compile glheretic.
-- System Information:
Debian Release: testing/unstable
Architecture: i386
Kernel: Linux snoopy 2.4.20 #1 SMP Mon Jan 13 17:12:00 EET 2003 i686
Locale: LANG=C, LC_CTYPE=C
Versions of packages gcc-3.2 depends on:
ii binutils 2.13.90.0.16-1 The GNU assembler, linker and bina
ii cpp-3.2 1:3.2.2-0pre8 The GNU C preprocessor
ii gcc-3.2-base 1:3.2.2-0pre8 The GNU Compiler Collection (base
ii libc6 2.3.1-10 GNU C Library: Shared libraries an
ii libgcc1 1:3.2.2-0pre8 GCC support library
-- no debconf information
---------------------------------------
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>From doko@cs.tu-berlin.de Sun Jul 06 04:55:36 2003
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From: Matthias Klose <doko@cs.tu-berlin.de>
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Message-ID: <16135.61934.101701.81516@gargle.gargle.HOWL>
Date: Sun, 6 Jul 2003 11:54:54 +0200
To: Daniel Jacobowitz <dan@debian.org>, 179712-done@bugs.debian.org
Cc: Marko Kreen <marko@l-t.ee>
Subject: Re: Bug#179712: gcc-3.2 -O2 miscompilation (i386)
In-Reply-To: <20030204143640.GA30193@nevyn.them.org>
References: <20030204030210.AC6AD15182@snoopy.l-t.ee>
<20030204143640.GA30193@nevyn.them.org>
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Daniel Jacobowitz writes:
> On Tue, Feb 04, 2003 at 05:02:10AM +0200, Marko Kreen wrote:
> > Package: gcc-3.2
> > Version: 1:3.2.2-0pre8
> > Severity: normal
> >
> >
> > gcc-3.2 -O2 miscompiles following program:
> >
> > ---------------------------------------------
> > extern int write(int fd, void *buf, int len);
> > extern int toupper(int c);
> >
> > void strupr (char *s)
> > {
> > while (*s)
> > *s++ = toupper(*s);
> > }
> >
> > int main(int argc, char *argv[])
> > {
> > char s[] = "foo";
> > strupr(s);
> > write(1, s, 3);
> > write(1, "\n", 1);
> > return 0;
> > }
> >
> > ---------------------------------------------
> > $ gcc-3.2 -Wall -O2 -o test test.c
> > test.c: In function `strupr':
> > test.c:7: warning: operation on `s' may be undefined
> > $ ./test
> > OO
> > $
> > ---------------------------------------------
> >
> > gcc-2.95 compiles it correctly, also gcc-3.2 when optimizing
> > less than -O2. When the "toupper(*s)" is replaced with "*s & 0x5f"
> > gcc-3.2 -O2 also works and without warning.
>
> I think the lack of warning in that case is actually the bug, but I'm
> not sure. C doesn't guarantee order-of-operation across an equals
> sign; it's not a sequence point. The function call is a sequence point
> but it isn't specified which side of the sequence point the increment
> will happen on.
closing the report. the warning is printed by the default gcc (3.3) in our
current testing/unstable distribution.
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