https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116488
Bug ID: 116488
Summary: wrong code at -O{s,2,3} with "-fno-forward-propagate"
on x86_64-linux-gnu
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhendong.su at inf dot ethz.ch
Target Milestone: ---
It appears to be a recent regression as it doesn't reproduce with 14.2 and
earlier. It might be related to PR 116420.
Compiler Explorer: https://godbolt.org/z/Y9hjoxb3n
[605] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/suz-local/software/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/15.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-trunk/configure --disable-bootstrap
--enable-checking=yes --prefix=/local/suz-local/software/local/gcc-trunk
--enable-sanitizers --enable-languages=c,c++ --disable-werror --enable-multilib
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240826 (experimental) (GCC)
[606] %
[606] % gcctk -O3 small.c; ./a.out
0
-1
[607] % gcctk -fno-forward-propagate -O3 small.c
[608] % ./a.out
0
0
[609] % cat small.c
int printf(const char *, ...);
int a, b;
char c, e;
unsigned char d;
void f(int g, short h) {
for (; a < 2; a++) {
b = h >> 16;
e = b * h;
printf("%d\n", b);
d = h;
h = c = d % g;
}
}
int main() { f(129, 128); }
