https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109967
Bug ID: 109967
Summary: Wrong code at -O2 on x86_64-linux-gnu
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: shaohua.li at inf dot ethz.ch
Target Milestone: ---
For the following code, gcc trunk at -O2 emits the wrong code. This seems to be
a long latent bug since GCC-7 (I tried gcc-7.4 on compiler explorer, which
still emits the wrong result.)
Compiler explorer: https://godbolt.org/z/YGeWedWq7
$ cat a.c
int printf(const char *, ...);
int a, c;
int main() {
long f[2];
int e = 0;
for (; e < 2; e++) {
{
char g[20];
char *b = g;
int d = 48, e = 0;
while (d && e < 5)
b[e++] = d /= 10;
c = e;
}
f[c - 2 + e] = 1;
}
a = f[0];
printf("%d\n", a);
}
$
$ gcc-tk -O0 a.c && ./a.out
1
$ gcc-tk -O2 a.c && ./a.out
4
$
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=gcc-tk
COLLECT_LTO_WRAPPER=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f050dabbf6dd3b992c3b46661848dbcf30d9e/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../configure --disable-multilib --disable-bootstrap
--enable-languages=c,c++
--prefix=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-8d5f050dabbf6dd3b992c3b46661848dbcf30d9e
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230523 (experimental) (GCC)
$
