https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109925
Bug ID: 109925
Summary: Wrong code at -O2 on x86_64-linux-gnu since GCC-12
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 emits wrong code at -O2.
Compiler explorer: https://godbolt.org/z/hcnaxoPaP
$ cat a.c
int printf(const char *, ...);
int a, c, f;
int main() {
int g[2];
c = 0;
for (; c < 2; c++) {
{
char h[20];
char *b = h;
int d = 48, e = 0;
while (d && e < 5)
b[e++] = d /= 10;
f = e;
}
g[f - 2 + c] = 0;
}
for (;;) {
for (; a <= 4; a++)
if (g[0])
break;
break;
}
printf("%d\n", a);
}
$
$ gcc-tk -O0 a.c && ./a.out
5
$ gcc-tk -O2 a.c && ./a.out
0
$ gcc-tk -v
Using built-in specs.
COLLECT_GCC=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-f211757f6fa9515e3fd1a4f66f1a8b48e500c9de/bin/gcc
COLLECT_LTO_WRAPPER=/zdata/shaoli/compilers/ccbuilder-compilers/gcc-f211757f6fa9515e3fd1a4f66f1a8b48e500c9de/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-f211757f6fa9515e3fd1a4f66f1a8b48e500c9de
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 14.0.0 20230521 (experimental) (GCC)
$
