[Bug tree-optimization/96928] New: Failure to optimize one's complement abs pattern

[Bug tree-optimization/96928] New: Failure to optimize one's complement abs pattern

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96928

            Bug ID: 96928
           Summary: Failure to optimize one's complement abs pattern
           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 a)
{
    return (a < 0) ? ~a : a;
}

This can be optimized to `return (a >> 31) ^ a;`. This transformation is done
by LLVM, but not by GCC.

[Bug tree-optimization/96928] Failure to optimize one's complement abs pattern

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96928

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-01-04
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |jakub at gcc dot gnu.org

--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Created attachment 49874
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=49874&action=edit
gcc11-pr96928.patch

Untested fix.

[Bug tree-optimization/96928] Failure to optimize one's complement abs pattern

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96928

--- Comment #2 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:576714b309b330df0e80e34114bcdf0bba35e146

commit r11-6472-g576714b309b330df0e80e34114bcdf0bba35e146
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Tue Jan 5 16:35:22 2021 +0100

    phiopt: Optimize x < 0 ? ~y : y to (x >> 31) ^ y [PR96928]

    As requested in the PR, the one's complement abs can be done more
    efficiently without cmov or branching.

    Had to change the ifcvt-onecmpl-abs-1.c testcase, we no longer optimize
    it in ifcvt, on x86_64 with -m32 we generate in the end the exact same
    code, but with -m64:
            movl    %edi, %eax
    -       notl    %eax
    -       cmpl    %edi, %eax
    -       cmovl   %edi, %eax
    +       sarl    $31, %eax
    +       xorl    %edi, %eax
            ret

    2021-01-05  Jakub Jelinek  <jakub@redhat.com>

            PR tree-optimization/96928
            * tree-ssa-phiopt.c (xor_replacement): New function.
            (tree_ssa_phiopt_worker): Call it.

            * gcc.dg/tree-ssa/pr96928.c: New test.
            * gcc.target/i386/ifcvt-onecmpl-abs-1.c: Remove -fdump-rtl-ce1,
            instead of scanning rtl dump for ifcvt message check assembly
            for xor instruction.

[Bug tree-optimization/96928] Failure to optimize one's complement abs pattern

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96928

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

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

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed.

[Bug tree-optimization/96928] Failure to optimize one's complement abs pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96928

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note while moving this optimization to match-and-simplify I noticed that the
gimple produced is:
(~a) ^ b

But this get changed around to:
~(a ^ b)
By PRE latter on.

I only noticed this because the testcase is failing as it depends being that.