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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/54954] malloc optimizations not disabled by -fno-builtin
Date: Thu, 21 Nov 2013 12:05:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54954

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|INVALID                     |WORKSFORME

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
I said it works for me because it works with -fno-builtin-malloc.

Andrew, you are wrong - the malloc attribute itself does not tell us
that the malloc call may not clobber global memory.

I've massaged the testcase to build w/o warnings:

m.c:
#include <string.h>
#include <stdio.h>

void *__libc_malloc(size_t size);

void *malloc(size_t size)
{
    increment_count();
    return (void*)__libc_malloc(size);
}

t.c:
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>

static int count = 0;

void increment_count(void)
{
        count++;
}

int main (void)
{
        char *ptr;
        count = 0;
        ptr = malloc(1);
        assert(ptr);
        assert(count);
        printf("%p\n", ptr);
        free(ptr);
        return 0;
}

rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.7.0/bin/gcc -o t t.c m.c
-O2 -fno-builtin-malloc
rguenther@murzim:/tmp> ./t
0x1127010
rguenther@murzim:/tmp> /space/rguenther/install/gcc-4.7.0/bin/gcc -o t t.c m.c
-O2  
rguenther@murzim:/tmp> ./t
t: t.c:18: main: Assertion `count' failed.
Aborted


Works with all GCC versions I tried.  I tried on x86_64-linux (just in case
RTL optimizers break this in which case the target architecture may be
important).