[Bug tree-optimization/98304] New: Failure to optimize bitwise arithmetic pattern

[Bug tree-optimization/98304] New: Failure to optimize bitwise arithmetic pattern

[gabravier at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98304

            Bug ID: 98304
           Summary: Failure to optimize bitwise arithmetic 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 f1(int n)
{
    return n - (((n > 63) ? n : 63) & -64);
}

This can be optimized to `return (n <= 63) ? n : (n & 63);` (and presumably the
same optimization should be doable with other powers of 2).

PS: I found this optimization while looking at how this :

int f1(int n)
{
    while (n >= 64)
        n -= 64;

    return n;
}

is optimized. LLVM outputs the first example I gave here, while GCC outputs the
optimization I gave here.

[Bug tree-optimization/98304] Failure to optimize bitwise arithmetic pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98304

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-11-25
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
  _1 = MAX_EXPR <n_3(D), 63>;
  _2 = _1 & -64;
  _4 = n_3(D) - _2;

Something like:

(simplify
 (minus @0 (bit_and (max @0 INTEGER_CST@1) INTEGER_CST@2))
 (if (@1 == (@2)-1)
  (if (TYPE_SIGN (type) == UNSIGNED)
   (bit_and @0 @1)
   (cond (le @0 @1) @0 (bit_and @0 @1))
  )
 )
)

Note LLVM handles the unsigned case already.

Also note also even though GCC can handle the loop case for signed, it only
handles it on the RTL level, for gimple GCC produces:
  _3 = n_2(D) + -64;
  _8 = (unsigned int) n_2(D);
  _9 = _8 + 4294967232; // _9 = _3 - 64
  _10 = _9 >> 6; // _10 = _9/64
  _11 = (int) _10;
  _12 = _11 * -64;
  n_1 = _3 + _12;

[Bug tree-optimization/98304] Failure to optimize bitwise arithmetic pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98304

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
> @1 == (@2)-1

Should have been:
@1 == -(@2-1)

maybe check that @1 is a mask.

[Bug tree-optimization/98304] Failure to optimize bitwise arithmetic pattern

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98304

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jeff Law <law@gcc.gnu.org>:

https://gcc.gnu.org/g:d9fa599dc7584d89e758a09a3d68982f12d8751c

commit r13-1587-gd9fa599dc7584d89e758a09a3d68982f12d8751c
Author: Sam Feifer <sfeifer@redhat.com>
Date:   Sat Jul 9 12:08:01 2022 -0400

    [PATCH] match.pd: Add new bitwise arithmetic pattern [PR98304]

            PR tree-optimization/98304

    gcc:

            * match.pd (n - (((n > C1) ? n : C1) & -C2)): New simplification.

    gcc/testsuite:

            * gcc.c-torture/execute/pr98304-2.c: New test.
            * gcc.dg/pr98304-1.c: New test.

[Bug tree-optimization/98304] Failure to optimize bitwise arithmetic pattern

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98304

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |13.0
         Resolution|---                         |FIXED
             Status|NEW                         |RESOLVED

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Fixed