[Bug middle-end/114733] New: [14] Miscompile with -march=rv64gcv -O3 on riscv

[Bug middle-end/114733] New: [14] Miscompile with -march=rv64gcv -O3 on riscv

[patrick at rivosinc dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

            Bug ID: 114733
           Summary: [14] Miscompile with -march=rv64gcv -O3 on riscv
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: patrick at rivosinc dot com
  Target Milestone: ---

Testcase:
long b = 1;
signed char c;
int d[25];
int main() {
  for (signed char g = 0; g < 8; g += 1)
    for (short h = 0; h < 25; h += 2) {
      b *= -1;
      c ^= d[h];
    }
  __builtin_printf("%ld\n", b);
}

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
-1
> /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
1

This testcase looks extremely similar to pr114485 so they are likely related -
from my testing pr114485 has NOT regressed.

Tested using r14-9976-gf8409c3109d (not bisected)

Found via fuzzer.

[Bug middle-end/114733] [14] Miscompile with -march=rv64gcv -O3 on riscv

[rdapp at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

--- Comment #1 from Robin Dapp <rdapp at gcc dot gnu.org> ---
Confirmed, also shows up here.

[Bug middle-end/114733] [14] Miscompile with -march=rv64gcv -O3 on riscv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
  <bb 2> [local count: 9582068]:
  b_lsm.9_16 = b;
  _20 = -b_lsm.9_16;
  b = _20;
  __builtin_printf ("%ld\n", _20);
  return 0;

we unroll the inner loop and then vectorize with 8 byte vectors which
means exposing V1DImode vectors which I think runs into the very same
issue (VF is "even").

[Bug middle-end/114733] [14] Miscompile with -march=rv64gcv -O3 on riscv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
So the issue is that we do

  switch (induction_type)
    {
    case vect_step_op_neg:
      if (TREE_CODE (init_expr) != INTEGER_CST
          && TREE_CODE (init_expr) != REAL_CST)
        {
          /* Check for backend support of NEGATE_EXPR and vec_perm.  */
          if (!directly_supported_p (NEGATE_EXPR, vectype))
            return false;

          /* The encoding has 2 interleaved stepped patterns.  */
          vec_perm_builder sel (nunits, 2, 3);
          machine_mode mode = TYPE_MODE (vectype);
          sel.quick_grow (6);
          for (i = 0; i < 3; i++)
            {
              sel[i * 2] = i;
              sel[i * 2 + 1] = i + nunits;
            }

but this scheme doesn't work for a V1DImode vector type.

[Bug middle-end/114733] [14] Miscompile with -march=rv64gcv -O3 on riscv

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

--- Comment #4 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Richard Biener <rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:45a41ace55d0ffb1097e374868242329788ec82a

commit r14-9992-g45a41ace55d0ffb1097e374868242329788ec82a
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Apr 16 10:46:03 2024 +0200

    tree-optimization/114733 - neg induction fails for 1 element vectors

    The neg induction vectorization code isn't prepared to deal with
    single element vectors.

            PR tree-optimization/114733
            * tree-vect-loop.cc (vectorizable_nonlinear_induction): Reject
            neg induction vectorization of single element vectors.

            * gcc.dg/vect/pr114733.c: New testcase.

[Bug middle-end/114733] [13 Regression] Miscompile with -march=rv64gcv -O3 on riscv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
   Target Milestone|---                         |13.3
            Summary|[14] Miscompile with        |[13 Regression] Miscompile
                   |-march=rv64gcv -O3 on riscv |with -march=rv64gcv -O3 on
                   |                            |riscv
      Known to work|                            |14.0

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Should be also at least latent on the 13 branch.

[Bug middle-end/114733] [13 Regression] Miscompile with -march=rv64gcv -O3 on riscv

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Richard Biener
<rguenth@gcc.gnu.org>:

https://gcc.gnu.org/g:b3f9f10e03c570074a517dcfe9df8d3eeddd6aca

commit r13-8680-gb3f9f10e03c570074a517dcfe9df8d3eeddd6aca
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Apr 16 10:46:03 2024 +0200

    tree-optimization/114733 - neg induction fails for 1 element vectors

    The neg induction vectorization code isn't prepared to deal with
    single element vectors.

            PR tree-optimization/114733
            * tree-vect-loop.cc (vectorizable_nonlinear_induction): Reject
            neg induction vectorization of single element vectors.

            * gcc.dg/vect/pr114733.c: New testcase.

    (cherry picked from commit 45a41ace55d0ffb1097e374868242329788ec82a)

[Bug middle-end/114733] [13 Regression] Miscompile with -march=rv64gcv -O3 on riscv

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114733

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
      Known to work|                            |13.2.1
      Known to fail|                            |13.2.0
             Status|ASSIGNED                    |RESOLVED

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Fixed.