[Bug target/120297] New: [16 Regression] RISC-V: Miscompile at -O3

[ewlu at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120297

            Bug ID: 120297
           Summary: [16 Regression] RISC-V: Miscompile at -O3
           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 a;
short c;
char d;
unsigned long e;
_Bool f[10][10];
unsigned g[10];
long long ak;
char i = 7;
long long t[10];
short x[10][10][10][10];
short y[10][10][10][10];
void h(char i, long long t[], short x[][10][10][10], short y[][10][10][10],
_Bool aa) {
  for (int j = 2; j < 8; j += 2) {
    for (short k = 0; k < 10; k++) {
      for (int l = 3; l < 8; l += 2)
        a = x[1][j][k][l];
      c = x[c][1][1][c];
    }
    for (int k = 0; k < 10; k++) {
      f[2][k] |= (_Bool)t[c];
      g[c] = t[c + 1];
      d += y[j][1][k][k];
      e = e > i ? e : i;
    }
  }
}
int main() {
  t[c] = 1;
  h(i, t, x, y, a);
  for (int j = 0; j < 10; ++j)
    for (int k = 0; k < 10; ++k)
      ak ^= f[j][k] + 238516665 + (ak >> 2);
  ak ^= g[c] + 238516665 + (ak >> 2);
  __builtin_printf("%llu\n", ak);
}

Commands:
# -O3
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -flto -O3 red.c -o user-config.out -fsigned-char 
> -fno-strict-aliasing -fwrapv
> QEMU_CPU=rv64,vlen=128,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
234635117

# -O2
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -flto -O2 red.c -o user-config.out -fsigned-char 
> -fno-strict-aliasing -fwrapv
> QEMU_CPU=rv64,vlen=128,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
234635118

Bisected to r15-6657-g405c99c1721 as first bad commit

Tried manually reducing testcase more but failed to reproduce the error when
doing so. 

Found via fuzzer