[llvm-bugs] [Bug 27356] New: [ppc] missed chance to use rlwnm

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Apr 14 13:45:10 PDT 2016


            Bug ID: 27356
           Summary: [ppc] missed chance to use rlwnm
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

This example came up in http://reviews.llvm.org/D19087 :

define i1 @and_cmp_variable_power_of_two(i32 %x, i32 %y) {
  %shl = shl i32 1, %y
  %and = and i32 %x, %shl
  %cmp = icmp eq i32 %and, %shl
  ret i1 %cmp

$ llc -o - andn.ll -mtriple=powerpc64-apple-darwin
_    li r2, 1
    slw r2, r2, r4
    and r2, r3, r2
    cntlzw     r2, r2
    nor r2, r2, r2
    rlwinm r3, r2, 27, 31, 31

Double-check to make sure because my PPC is beyond rusty, but I think this is:

        subfic r4, r4, 32
        rlwnm r3, r3, r4, 31, 31

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