[Bug target/120688] New: [16 Regression] RISC-V: Miscompile at -O3 since r15-579-ga9251ab3c91

[ewlu at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120688

            Bug ID: 120688
           Summary: [16 Regression] RISC-V: Miscompile at -O3 since
                    r15-579-ga9251ab3c91
           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:
char p;
int *volatile ad;
int ag = 6;
const int at() {
  int ci;
  int cj;
  char *ck = &p;
  ad = &cj;
  *ck = ad != &ci;
  return 0;
}
int main() {
  at();
  for (int i = 0;;) {
    if (ag)
      break;
  }
  ++p;
  __builtin_printf("%d\n", p);
}

Commands:
# -O3
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -O3 ./runtime-bisect/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
1

# -O2
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -O2 ./runtime-bisect/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
2

Found via fuzzer