https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120046
Bug ID: 120046
Summary: wrong code at -O{s,2} with "-fno-tree-ccp
-fno-tree-dominator-opts -fno-tree-fre
-fno-expensive-optimizations -fno-gcse" on
x86_64-linux-gnu
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: zhendong.su at inf dot ethz.ch
Target Milestone: ---
Compiler Explorer: https://godbolt.org/z/4hsdEKM4v
It appears to be a recent regression, and affects 15.1 and later.
[553] % 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/16.0.0/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 16.0.0 20250430 (experimental) (GCC)
[554] %
[554] % gcctk -O2 small.c; ./a.out
0
[555] % gcctk -O2 -fno-tree-ccp -fno-tree-dominator-opts -fno-tree-fre
-fno-expensive-optimizations -fno-gcse small.c
[556] % ./a.out
0
Aborted
[557] %
[557] % cat small.c
int printf(const char *, ...);
struct a {
long b;
} d, g, *f = &d;
int c, h;
volatile int e;
struct a i() {
struct a j = {5000000000}, *k = &j;
printf("0\n");
l:
if (j.b)
return j;
if (h) {
if (c)
goto l;
return g;
}
printf("%d", e);
struct a *m, **n = &m;
*n = k;
return *m;
}
int main() {
*f = i();
if (d.b != 5000000000)
__builtin_abort();
return 0;
}
