[Bug tree-optimization/116420] New: wrong code at -O{2,3} with "-fno-forward-propagate -fno-tree-ch" on x86_64-linux-gnu

[zhendong.su at inf dot ethz.ch via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116420

            Bug ID: 116420
           Summary: wrong code at -O{2,3} with "-fno-forward-propagate
                    -fno-tree-ch" 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: ---

It appears to be a recent regression as it doesn't reproduce with 14.* and
earlier. 

Compiler Explorer: https://godbolt.org/z/zfssY8K95


[524] % 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 20240819 (experimental) (GCC) 
[525] % 
[525] % gcctk -O2 small.c; ./a.out
[526] % 
[526] % gcctk -O2 -fno-forward-propagate -fno-tree-ch small.c
[527] % ./a.out
Aborted
[528] % cat small.c
int a, d, e;
char b = -1, c, f;
int main() {
  int g;
  for (; d < 1; d++) {
    g = b;
    for (; c; c = g)
      ;
  }
  f = g;
  for (; e < 1; e++)
    if (g >= a)
      __builtin_abort();
  return 0;
}