[Bug target/118931] New: [15] RISC-V: rv64gcv miscompile at -O[23] since r15-3228-g771256bcb9d

[ewlu at rivosinc dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118931

            Bug ID: 118931
           Summary: [15] RISC-V: rv64gcv miscompile at -O[23] since
                    r15-3228-g771256bcb9d
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ewlu at rivosinc dot com
  Target Milestone: ---

Testcase:

long long m;
char f = 151;
char h = 103;
unsigned char a = 109;
int main() {
  for (char l = 0; l < 255 - 241; l += h - 102)
    a *= f;
  m = a;
  __builtin_printf("%llu\n", m);
}

Commands:
> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -flto -O3 -mrvv-vector-bits=zvl red.c -o red.out
> 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
>  /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 red.out 1
247

> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -flto -O2 -mrvv-vector-bits=zvl red.c -o red.out
> 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
>  /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 red.out 1
247

> /scratch/ewlu/daily-upstream-build/build-gcv/bin/riscv64-unknown-linux-gnu-gcc
>  -march=rv64gcv -flto -O1 -mrvv-vector-bits=zvl red.c -o red.out
> 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
>  /scratch/ewlu/daily-upstream-build/build-gcv/bin/qemu-riscv64 red.out 1
29

Looks like another latent bug exposed by costing more patterns.
x86 also outputs 29

Found via fuzzer