[Bug middle-end/98865] New: Missed transform of (a >> 63) * b

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98865

            Bug ID: 98865
           Summary: Missed transform of (a >> 63) * b
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

unsigned long foo (unsigned long a, unsigned long b)
{
  return (a >> 63) * b;
}

generates

foo:
.LFB0:
        .cfi_startproc
        shrq    $63, %rdi
        movq    %rdi, %rax
        imulq   %rsi, %rax
        ret

but we can do (like llvm):

foo:                                    # @foo
        .cfi_startproc
# %bb.0:
        movq    %rdi, %rax
        sarq    $63, %rax
        andq    %rsi, %rax
        retq