[Bug tree-optimization/94921] New: Failure to optimize nots with sub into single add

[Bug tree-optimization/94921] New: Failure to optimize nots with sub into single add

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

            Bug ID: 94921
           Summary: Failure to optimize nots with sub into single add
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gabravier at gmail dot com
  Target Milestone: ---

int f(int x, int y)
{
    return ~(~x - y);
}

This can be optimized to `x - y`. This transformation is done by LLVM, but not
by GCC

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
x + y ?

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

Uroš Bizjak <ubizjak at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2020-05-04
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #2 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Marc Glisse from comment #1)
> x + y ?

Correct.

llvm:

        leal    (%rdi,%rsi), %eax
        retq

gcc:

        notl    %edi
        subl    %esi, %edi
        movl    %edi, %eax
        notl    %eax
        ret

Confirmed, looks like a job for a tree combiner.

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

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

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 48453
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=48453&action=edit
gcc11-pr94921.patch

Untested fix.

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

--- Comment #4 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:a7b76d574b19190da190a60c065f347f40bab59e

commit r11-132-ga7b76d574b19190da190a60c065f347f40bab59e
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed May 6 11:20:20 2020 +0200

    match.pd: Optimize ~(~X +- Y) into (X -+ Y) [PR94921]

    According to my verification proglet, this transformation for signed types
    with undefined overflow doesn't introduce nor remove any UB cases, so
should
    be valid even for signed integral types.
    Not using a for because of the :c on plus which can't be there on minus.

    2020-05-06  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/94921
            * match.pd (~(~X - Y) -> X + Y, ~(~X + Y) -> X - Y): New
            simplifications.

            * gcc.dg/tree-ssa/pr94921.c: New test.

[Bug tree-optimization/94921] Failure to optimize nots with sub into single add

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94921

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

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

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed for 11+.