[Bug tree-optimization/120341] New: wrong code at -O1 and above with "-fallow-store-data-races" on x86_64-linux-gnu

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120341

            Bug ID: 120341
           Summary: wrong code at -O1 and above with
                    "-fallow-store-data-races" 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/PK19PqYjq

It appears to be a regression from 14.2, and affects 15.1 and later. 

[561] % gcctk -v
Using built-in specs.
COLLECT_GCC=gcctk
COLLECT_LTO_WRAPPER=/local/home/suz/suz-local/software/local/gcc-trunk/bin/../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 20250518 (experimental) (GCC) 
[562] % 
[562] % gcctk -O1 small.c; ./a.out
[563] % 
[563] % gcctk -O1 -fallow-store-data-races small.c
[564] % ./a.out
Segmentation fault
[565] % 
[565] % cat small.c
char a, *b;
int main() {
  b = "0";
  if (a)
    b[0]++;
  return 0;
}