[Bug tree-optimization/126044] New: Possible Missed Optimization at O3

[apowenq at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126044

            Bug ID: 126044
           Summary: Possible Missed Optimization at O3
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: apowenq at gmail dot com
  Target Milestone: ---

cat prog.c
int src(int v3_i8, int v5_i8) {
  if (!((0 <= v3_i8) && (v3_i8 <= 1))) __builtin_unreachable();
  if (!((-127 <= v5_i8) && (v5_i8 <= -64))) __builtin_unreachable();
  int i0_i8 = v3_i8 % v5_i8;
  return i0_i8;
}

GCC truck at O3 cannot optimize the C program (not a regression), but Clang
truck at O3 can.
Reproducer: https://godbolt.org/z/5anax4e4e

GCC at O3:
"src":
        mov     eax, edi
        cdq
        idiv    esi
        mov     eax, edx
        ret

LLVM at O3:
src:
        mov     eax, edi
        ret