** Description changed:
Binary package hint: gcc-4.1
- When compiling this code with -O2 flags the result is different than
- when compiled with -O.
+ When compiling this code with the -O2 flag the result is different than
+ when compiling with -O, or when disabling tree-pre or strict-aliasing
+ optimizations.
$ gcc -v
Using built-in specs.
Target: i486-linux-gnu
Configured with: ../src/configure -v
--enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
--enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/include/c++/4.1.3 --program-suffix=-4.1
--enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug
--enable-mpfr --enable-checking=release i486-linux-gnu
Thread model: posix
gcc version 4.1.3 20070929 (prerelease) (Ubuntu 4.1.2-16ubuntu2)
$ gcc -O test.c ; ./a.out
$ gcc -O2 test.c ; ./a.out
Ohhh
+ $ gcc -O2 -fno-tree-pre test.c ; ./a.out
+ $ gcc -O2 -fno-strict-aliasing test.c ; ./a.out
$ cat test.c
#include <stdlib.h>
#include <stdio.h>
int bmemcmp(void *a1, void *a2, unsigned len)
{
int dwlen = len / 4;
while (dwlen)
{
int res = *(int *)a1 - *(int *)a2;
if (res)
return res;
--dwlen;
++*(int **)&a1;
++*(int **)&a2;
}
return 0;
}
int main(int argc, char *argv[])
{
int *p1 = (int*)calloc(sizeof(int), 1024 * 1024 * 4);
int *p2 = (int*)calloc(sizeof(int), 1024 * 1024 * 4);
p1[3] = 1;
if (bmemcmp(p1, p2, 1024 * 1024 * 4) == 0)
printf("Ohhh\n");
return 0;
}
--
gcc -O2 generates wrong code
https://bugs.launchpad.net/bugs/158799
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