[Bug c++/107295] New: [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[Bug c++/107295] New: [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

            Bug ID: 107295
           Summary: [13 Regression] Rejected code in libreoffice with -m32
                    since r13-3290-g98e341130f87984a
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: jakub at gcc dot gnu.org
  Target Milestone: ---

Since the revision, the following code is rejected:

$ g++ skia.ii -m32 -c -std=c++17
skia.ii:7:22: error: ‘(F{((float)0.0l)} + (F){0.0f})’ is not a constant
expression
    7 | constexpr F F0 = F() + 0.0f;

$ g++-12 skia.ii -m32 -c -std=c++17
$ g++ skia.ii -c -std=c++17

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-10-17
   Target Milestone|---                         |13.0
     Ever confirmed|0                           |1

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
That is likely the
"There is one exception, pr68180.C looks like a bug in the patch which is
also present in the C FE (so I'd like to get it resolved incrementally
in both).  Reduced testcase:
typedef float __attribute__((vector_size (16))) float32x4_t;
float32x4_t foo(float32x4_t x, float y) { return x + y; }
with -m32 -std=c11 -Wno-psabi or -m32 -std=c++17 -Wno-psabi
it is rejected with:
pr68180.c:2:52: error: conversion of scalar ‘long double’ to vector
‘float32x4_t’ {aka ‘__vector(4) float’} involves truncation
but without excess precision (say just -std=c11 -Wno-psabi or -std=c++17
-Wno-psabi)
it is accepted.  Perhaps we should pass down the semantic type to
scalar_to_vector and use the semantic type rather than excess precision type
in the diagnostics."
issue mentioned in the mail/commit log, though I'd have to verify that.

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Do you have a reproducer?

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #3 from Martin Liška <marxin at gcc dot gnu.org> ---
Sure, sorry, I forgot to send it:

template <typename T> struct VecHelper {
  typedef T __attribute__((vector_size(sizeof(int)))) V;
};
template <int, typename T> using Vec = typename VecHelper<T>::V;
template <typename T> using V = Vec<4, T>;
using F = V<float>;
constexpr F F0 = F() + 0.0f;

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Ah, so that is a different issue then.
And with slightly modified testcase quite old one, which regressed with:
r8-727-g6b6ae9eb9c06b6911573bb9a13cf98b5a7c98b78
template <typename T> struct VecHelper {
  typedef T __attribute__((vector_size(sizeof(int)))) V;
};
template <int, typename T> using Vec = typename VecHelper<T>::V;
template <typename T> using V = Vec<4, T>;
using F = V<float>;
constexpr F F0 = F() + (float) 0.0L;
The problem is that the NOP_EXPR around long double REAL_CST has TREE_CONSTANT
flag and so the CONSTRUCTOR around it and thus we just fold the CONSTRUCTOR in:
    case CONSTRUCTOR:
      if (TREE_CONSTANT (t) && reduced_constant_expression_p (t))
        {
          /* Don't re-process a constant CONSTRUCTOR, but do fold it to
             VECTOR_CST if applicable.  */
          verify_constructor_flags (t);
          if (TREE_CONSTANT (t))
            return fold (t);
        }
      r = cxx_eval_bare_aggregate (ctx, t, lval,
                                   non_constant_p, overflow_p);
      break;
but that handles the case where it has REAL_CST elts, but doesn't handle the
case where it has NOP_EXPRs around them.
I wonder if we just shouldn't call cxx_eval_bare_aggregate always for
VECTOR_TYPE.

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 53719
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53719&action=edit
gcc13-pr107295.patch

Untested fix.

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

--- Comment #6 from CVS 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:2cc41601d9a948e8d612a21c3b9a44ce0b977747

commit r13-3438-g2cc41601d9a948e8d612a21c3b9a44ce0b977747
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Fri Oct 21 18:04:54 2022 +0200

    c++: Don't shortcut TREE_CONSTANT vector type CONSTRUCTORs in
cxx_eval_constant_expression [PR107295]

    The excess precision support broke building skia (dependency of firefox)
    on ia32 (it has something like the a constexpr variable), but as the other
    cases show, it is actually a preexisting problem if one uses casts from
    constants with wider floating point types.
    The problem is that cxx_eval_constant_expression tries to short-cut
    processing of TREE_CONSTANT CONSTRUCTORs if they satisfy
    reduced_constant_expression_p - instead of calling cxx_eval_bare_aggregate
    on them it just verifies flags and if they are TREE_CONSTANT even after
    that, just fold.
    Now, on the testcase we have a TREE_CONSTANT CONSTRUCTOR containing
    TREE_CONSTANT NOP_EXPR of REAL_CST.  And, fold, which isn't recursive,
    doesn't optimize that into VECTOR_CST, while later on we are only able
    to optimize VECTOR_CST arithmetics, not arithmetics with vector
    CONSTRUCTORs.
    The following patch fixes that by rejecting CONSTRUCTORs with vector type
    in reduced_constant_expression_p regardless of whether they have
    CONSTRUCTOR_NO_CLEARING set or not, folding result in
cxx_eval_bare_aggregate
    even if nothing has changed but it wasn't non-constant and removing folding
    from the TREE_CONSTANT reduced_constant_expression_p short-cut.

    2022-10-21  Jakub Jelinek  <jakub@redhat.com>

            PR c++/107295
            * constexpr.cc (reduced_constant_expression_p) <case CONSTRUCTOR>:
            Return false for VECTOR_TYPE CONSTRUCTORs even without
            CONSTRUCTOR_NO_CLEARING set on them.
            (cxx_eval_bare_aggregate): If constant but !changed, fold before
            returning VECTOR_TYPE_P CONSTRUCTOR.
            (cxx_eval_constant_expression) <case CONSTRUCTOR>: Don't fold
            TREE_CONSTANT CONSTRUCTOR, just return it.

            * g++.dg/ext/vector42.C: New test.

[Bug c++/107295] [13 Regression] Rejected code in libreoffice with -m32 since r13-3290-g98e341130f87984a

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107295

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Should be fixed now.