[Bug target/120242] New: [15/16 regression] RISC-V: Miscompile at -O[23]

[ewlu at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120242

            Bug ID: 120242
           Summary: [15/16 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:
char f1(char a, char b) {
  return b == 0 ? a : b;
}
int f2(int a, int b) {
  return b ? a : 0;
}
struct l {
  unsigned m;
  int n;
};
struct l ae;
char af = -2;
unsigned ah = 4;
int aj = 8;
int *test = &aj;
int main() {
ao:
  if (f2(f1(4, af++), *test) <= 0) {
    for (; ae.n; ae.n++)
      ;
    if (ah)
      goto ao;
  }
  __builtin_printf("%d\n", af);
}


Commands:
-O3
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -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 
> 12
2

-O2
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -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 
> 12
2

-O1
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -O1 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 
> 12
1

Bisected to r15-9239-g4d7a634f6d4 as the first bad commit

Found via fuzzer