[Bug target/114665] New: [14] RISC-V rv64gcv: miscompile at -O3

[Bug target/114665] New: [14] RISC-V rv64gcv: miscompile at -O3

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

            Bug ID: 114665
           Summary: [14] RISC-V rv64gcv: miscompile at -O3
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

Testcase:
signed char b;
_Bool c[15][15];
int main()
{
  for (long f = 0; f < 5; ++f)
    for (long g = 0; g < 5; ++g)
      c[f][g] = 1;
  _Bool(*h)[15] = c;
  for (int f = 0; f < 15; f += 1)
    for (int g = 0; g < 15; g += 1)
      b -= c[g][g] ? c[g][g] : h[f][g];
  __builtin_printf("%X\n", b);
}

Commands:
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -O3 red.c -o red.out
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/qemu-riscv64 red.out
35
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -O2 red.c -o red.out
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/qemu-riscv64 red.out
FFFFFFB5

Discovered/tested using r14-9877-g1f719aa7c0d (not bisected)

Found via fuzzer.

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #1 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Hmm, my local version is a bit older and seems to give the same result for both
-O2 and -O3.  At least a good starting point for bisection then.

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #2 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Checked with the latest commit on a different machine but still cannot
reproduce the error.  PR114668 I can reproduce.  Maybe a copy and paste
problem?

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #3 from Patrick O'Neill <patrick at rivosinc dot com> ---
Created attachment 57922
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=57922&action=edit
Generated assembly files

Hmm doesn't look like it from my side - maybe there's some stack related
weirdness going on here.

Using r14-9877-g1f719aa7c0d

> cat red.c
signed char b;
_Bool c[15][15];
int main()
{
  for (long f = 0; f < 5; ++f)
    for (long g = 0; g < 5; ++g)
      c[f][g] = 1;
  _Bool(*h)[15] = c;
  for (int f = 0; f < 15; f += 1)
    for (int g = 0; g < 15; g += 1)
      b -= c[g][g] ? c[g][g] : h[f][g];
  __builtin_printf("%X\n", b);
}
>  /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -O3 red.c -o red.out
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/qemu-riscv64 red.out
35
>  /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -O2 red.c -o red.out
> /scratch/tc-testing/tc-apr-9/build-rv64gcv/bin/qemu-riscv64 red.out
FFFFFFB5

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #4 from Patrick O'Neill <patrick at rivosinc dot com> ---
Reran as requested in pr114668. Still present with that fix.

I'll triage some other testcases and file those as well. Hopefully one of them
is a duplicate to this one that is easily reproducible.

GCC: r14-9976-gf8409c3109d
QEMU: v8.2.1 (f48c205fb42be48e2e47b7e1cd9a2802e5ca17b0)

Commands:
> /scratch/tc-testing/tc-apr-15/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc -march=rv64gcv -O3 red.c -o red.out
> /scratch/tc-testing/tc-apr-15/build-rv64gcv/bin/qemu-riscv64 red.out
35
> /scratch/tc-testing/tc-apr-15/build-rv64gcv/bin/riscv64-unknown-linux-gnu-gcc red.c -o red.out
> /scratch/tc-testing/tc-apr-15/build-rv64gcv/bin/qemu-riscv64 red.out
FFFFFFB5

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #5 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Weird,  I tried your exact qemu version and still can't reproduce the problem.  
My results are always FFFFFFB5.

Binutils difference?  Very unlikely.  Could you post your QEMU_CPU settings
just to be sure?

[Bug target/114665] [14] RISC-V rv64gcv: miscompile at -O3

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114665

--- Comment #6 from Patrick O'Neill <patrick at rivosinc dot com> ---
Binutils: #binutils-2_42 (c7f28aad0c99d1d2fec4e52ebfa3735d90ceb8e9)

QEMU_CPU=rv64,vlen=128,v=true,vext_spec=v1.0,zve32f=true,zve64f=true