[Bug target/120356] New: [16 Regression] RISC-V: Miscompile at -O[23]

[ewlu at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120356

            Bug ID: 120356
           Summary: [16 Regression] RISC-V: Miscompile at -O[23]
           Product: gcc
           Version: 16.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ewlu at rivosinc dot com
  Target Milestone: ---

Testcase:
unsigned char a = 5;
signed char b[8][18][18][18];
long long c[18];
long long aj;
char e = 9;
short g = 60;
unsigned q = 143;
char s = 119;
int u = 2;
void d(char e, short g, unsigned q, char s, int u) {
  for (short i = 0; i < g; i += 65413)
    for (signed j = 0; j < 5; j++)
      for (short k = 0; k < 18; k++)
        if (e) {
          for (unsigned l = 0; l < 18; l++) {
            b[4][j][k][l] = 0;
            if (g ? u : e)
              a *= 0 > e ? 0 : q;
          }
          for (char l = 0; l < 8; l++)
            for (int m = 0; m < 18; m++)
              c[m] = 0;
        }
}
int main() {
  d(e, g, q, s, u);
  aj ^= a;
  for (int am = 0; am < 8; ++am)
    aj ^= c[am];
  __builtin_printf("%llu\n", aj);
}


Commands:
# -O3
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv_zvl256b -flto -O3 -mrvv-vector-bits=zvl red.c -o 
> user-config.out -fsigned-char -fno-strict-aliasing -fwrapv
> QEMU_CPU=rv64,vlen=256,rvv_ta_all_1s=true,rvv_ma_all_1s=true,v=true,vext_spec=v1.0,zve32f=true,zve64f=true
>  timeout --verbose -k 0.1 4 
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 user-config.out 
> 1
5

# -O2
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv_zvl256b -flto -O2 -mrvv-vector-bits=zvl red.c -o 
> user-config.out -fsigned-char -fno-strict-aliasing -fwrapv
> QEMU_CPU=rv64,vlen=256,rvv_ta_all_1s=true,rvv_ma_all_1s=true,v=true,vext_spec=v1.0,zve32f=true,zve64f=true
>  timeout --verbose -k 0.1 4 
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 user-config.out 
> 1
5

# -O1
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv_zvl256b -flto -O1 -mrvv-vector-bits=zvl red.c -o 
> user-config.out -fsigned-char -fno-strict-aliasing -fwrapv
> QEMU_CPU=rv64,vlen=256,rvv_ta_all_1s=true,rvv_ma_all_1s=true,v=true,vext_spec=v1.0,zve32f=true,zve64f=true
>  timeout --verbose -k 0.1 4 
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 user-config.out 
> 1
69

bisected to r15-6881-g7b815107f40 as the first bad commit

Found via fuzzer.