[Bug tree-optimization/125813] New: Possible Missed Optimization at O3

[apowenq at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125813

            Bug ID: 125813
           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 v4_i8) {
  if (!((1 <= v3_i8) && (v3_i8 <= 8))) __builtin_unreachable();
  if (!((-128 <= v4_i8) && (v4_i8 <= -127))) __builtin_unreachable();
  int i0_i8 = v4_i8 / v3_i8;
  int i1_i8 = v3_i8 % i0_i8;
  return i1_i8;
}

GCC truck at O3 cannot optimize the C program (not a regression), but Clang
truck at O3 can.
Reproducer: https://godbolt.org/z/8McT1sGzK

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

Clang at O3:
src:
        mov     eax, edi
        ret