[Bug tree-optimization/114075] New: [14 Regression] s390x miscompilation since r14-322

[Bug tree-optimization/114075] New: [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

            Bug ID: 114075
           Summary: [14 Regression] s390x miscompilation since r14-322
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

Since r14-322-g821ef93976e750c118d42a2ad33b96dbd1b9f3a5 the following testcase
is miscompiled at -O2 -fopenmp-simd -march=z13 on s390x-linux:
typedef float V __attribute__((__vector_size__ (16)));

__attribute__((__always_inline__)) inline static float
foo (V a)
{
  float r = 0;
#pragma omp simd reduction(+:r)
  for (unsigned long i = 0; i < (sizeof (a) / sizeof (float)); i++)
    r += a[i];
  return r;
}

int
main ()
{
  static const struct { V a; float r; } t[] = {
    { (V) { -654.47f, -946.98f, -606.16f, 426.64f }, -1780.97f },
    { (V) { 663.94f, 660.23f, 682.64f, -644.47f }, 1362.34f },
    { (V) { -909.10f, 23.60f, -382.13f, -563.57f }, -1831.20f }
  };
  for (unsigned long i = 0; i < (sizeof (t) / sizeof (t[0])); i++)
    {
      float r = foo (t[i].a);
      if (r < t[i].r - 1.0f || r > t[i].r + 1.0f)
        __builtin_abort ();
    }
}

Before that change, all the 3 results were correct, now all of them are +-0.0f.

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2024-02-23
   Target Milestone|---                         |14.0

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
In r14-321 this wasn't vectorized, in r14-322 it is with vf 2, but the floating
point addition is performed in some weird unsigned long operation instead:
  _14 = VIEW_CONVERT_EXPR<unsigned long>(vect__17.11_42);
  _32 = VIEW_CONVERT_EXPR<unsigned long>(vect__18.12_29);
  _35 = _14 ^ _32;
  _34 = _32 & 9223372034707292159;
  _33 = _14 & 9223372034707292159;
  _51 = _35 & 9223372039002259456;
  _52 = _33 + _34;
  _53 = _52 ^ _51;
  _54 = VIEW_CONVERT_EXPR<vector(2) float>(_53);
  _19 = _17 + _18;
  MEM <vector(2) float> [(float *)&D.2632] = _54;
The involved constants are 0x7fffffff7fffffff and 0x8000000080000000.
Perhaps using the emulated vectors should be restricted only to integer types?

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jchrist at linux dot ibm.com,
                   |                            |rguenth at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, there is
https://gcc.gnu.org/pipermail/gcc-patches/2024-February/645928.html
but that didn't come up with a testcase.
Not sure if checking FLOAT_MODE_P is the right thing, whether it wouldn't be
better to check !ANY_INTEGRAL_TYPE_P (vectype) or !INTEGRAL_TYPE_P (TREE_TYPE
(vectype)).

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #1)
> In r14-321 this wasn't vectorized, in r14-322 it is with vf 2, but the
> floating point addition is performed in some weird unsigned long operation
> instead:
>   _14 = VIEW_CONVERT_EXPR<unsigned long>(vect__17.11_42);
>   _32 = VIEW_CONVERT_EXPR<unsigned long>(vect__18.12_29);
>   _35 = _14 ^ _32;
>   _34 = _32 & 9223372034707292159;
>   _33 = _14 & 9223372034707292159;
>   _51 = _35 & 9223372039002259456;
>   _52 = _33 + _34;
>   _53 = _52 ^ _51;
>   _54 = VIEW_CONVERT_EXPR<vector(2) float>(_53);
>   _19 = _17 + _18;
>   MEM <vector(2) float> [(float *)&D.2632] = _54;
> The involved constants are 0x7fffffff7fffffff and 0x8000000080000000.

OT, wouldn't it be cheaper to use 0xffffffff7fffffff and 0x80000000 constants
instead,
i.e. for the MSB just use normal addition/subtraction behavior, there we don't
need to be afraid of overflow into another emulated element?
Though, maybe 0x7f7f7f7f7f7f7f7f and 0x8080808080808080 are cheaper than
0xff7f7f7f7f7f7f7f and 0x0080808080808080.

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jchrist at linux dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #4 from jchrist at linux dot ibm.com ---
(In reply to Jakub Jelinek from comment #2)
> Ah, there is
> https://gcc.gnu.org/pipermail/gcc-patches/2024-February/645928.html
> but that didn't come up with a testcase.
> Not sure if checking FLOAT_MODE_P is the right thing, whether it wouldn't be
> better to check !ANY_INTEGRAL_TYPE_P (vectype) or !INTEGRAL_TYPE_P
> (TREE_TYPE (vectype)).

Hi,

yes, that patch was designed to fix this problem.  But thinking about it, I
guess your second suggestion would be better.

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jchrist at linux dot ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #5 from jchrist at linux dot ibm.com ---
Just sent a v2 of the patch including your suggested test and updated the
commit message.

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Juergen Christ <jchrist@gcc.gnu.org>:

https://gcc.gnu.org/g:82ebfd35da49e5df87da132a7b8c41baeebc57b4

commit r14-9205-g82ebfd35da49e5df87da132a7b8c41baeebc57b4
Author: Juergen Christ <jchrist@linux.ibm.com>
Date:   Mon Feb 19 10:10:35 2024 +0100

    Only emulate integral vectors.

    The emulation via word mode tries to perform integer arithmetic on floating
    point values instead of floating point arithmetic.  This leads to
    mis-compilations.

    Failure occured on s390x on these existing test cases:
    gcc.dg/vect/tsvc/vect-tsvc-s112.c
    gcc.dg/vect/tsvc/vect-tsvc-s113.c
    gcc.dg/vect/tsvc/vect-tsvc-s119.c
    gcc.dg/vect/tsvc/vect-tsvc-s121.c
    gcc.dg/vect/tsvc/vect-tsvc-s131.c
    gcc.dg/vect/tsvc/vect-tsvc-s132.c
    gcc.dg/vect/tsvc/vect-tsvc-s2233.c
    gcc.dg/vect/tsvc/vect-tsvc-s421.c
    gcc.dg/vect/vect-alias-check-14.c
    gcc.target/s390/vector/partial/s390-vec-length-epil-run-1.c
    gcc.target/s390/vector/partial/s390-vec-length-epil-run-3.c
    gcc.target/s390/vector/partial/s390-vec-length-full-run-3.c

    gcc/ChangeLog:

            PR tree-optimization/114075

            * tree-vect-stmts.cc (vectorizable_operation): Don't emulate
floating
            point vectors

    Signed-off-by: Juergen Christ <jchrist@linux.ibm.com>

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

--- Comment #7 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>:

https://gcc.gnu.org/g:db465230cccf0844e803dd6701756054fe97244a

commit r14-9206-gdb465230cccf0844e803dd6701756054fe97244a
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Feb 28 11:49:29 2024 +0100

    testsuite: Add testcase for recently fixed PR [PR114075]

    This adds testcase from PR114075 which has been fixed by the r14-9205
    change on s390x-linux with -march=z13.

    2024-02-28  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/114075
            * gcc.dg/gomp/pr114075.c: New test.

[Bug tree-optimization/114075] [14 Regression] s390x miscompilation since r14-322

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114075

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jchrist at linux dot ibm.com
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed, thanks.