[Bug middle-end/109038] New: Miss optimization to simplify bit_and + rotate to shift

[Bug middle-end/109038] New: Miss optimization to simplify bit_and + rotate to shift

[crazylht at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109038

            Bug ID: 109038
           Summary: Miss optimization to simplify bit_and + rotate to
                    shift
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---
            Target: x86_64-*-* i?86-*-*

unsigned
foo (unsigned int a)
{
  unsigned int b = a & 0x00FFFFFF;
  unsigned int c = ((b & 0x000000FF) << 8
                    | (b & 0x0000FF00) << 8
                    | (b & 0x00FF0000) << 8
                    | (b & 0xFF000000) >> 24);
  return c;
}

gcc generates

foo:
        mov     eax, edi
        and     eax, 16777215
        rol     eax, 8
        ret

But it can be optimized as below

foo:                                    # @foo
        mov     eax, edi
        shl     eax, 8
        ret

[Bug middle-end/109038] Miss optimization to simplify bit_and + rotate to shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109038

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 109037 has been marked as a duplicate of this bug. ***

[Bug tree-optimization/109038] Miss optimization to simplify bit_and + rotate to shift

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109038

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-05-19
     Ever confirmed|0                           |1
          Component|middle-end                  |tree-optimization

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

(simplify
 (rrotate (bit_and @0 INTEGER_CST@1) INTEGER_CST@2)
 (if (@1 == (type)(~0) >> (typebits-@2))
  (lshift @0 { typebits - @2; }))

(simplify
 (lrotate (bit_and @0 INTEGER_CST@1) INTEGER_CST@2)
 (if (@1 == (type)(~0) >> (@2))
  (lshift @0 { @2; }))

There could be more dealing with the result being logical shift right.