llvm/test/Transforms/InstCombine/sub-xor.ll
Benjamin Kramer 49064ff770 InstCombine: Add a combine that turns (2^n)-1 ^ x back into (2^n)-1 - x iff x is smaller than 2^n and it fuses with a following add.
This was intended to undo the sub canonicalization in cases where it's not profitable, but it also
finds some cases on it's own.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147256 91177308-0d34-0410-b5e6-96231b3b80d8
2011-12-24 17:31:53 +00:00

38 lines
773 B
LLVM

; RUN: opt -instcombine -S < %s | FileCheck %s
define i32 @test1(i32 %x) nounwind {
%and = and i32 %x, 31
%sub = sub i32 63, %and
ret i32 %sub
; CHECK: @test1
; CHECK-NEXT: and i32 %x, 31
; CHECK-NEXT: xor i32 %and, 63
; CHECK-NEXT: ret
}
declare i32 @llvm.ctlz.i32(i32, i1) nounwind readnone
define i32 @test2(i32 %x) nounwind {
%count = tail call i32 @llvm.ctlz.i32(i32 %x, i1 true) nounwind readnone
%sub = sub i32 31, %count
ret i32 %sub
; CHECK: @test2
; CHECK-NEXT: ctlz
; CHECK-NEXT: xor i32 %count, 31
; CHECK-NEXT: ret
}
define i32 @test3(i32 %x) nounwind {
%and = and i32 %x, 31
%sub = xor i32 31, %and
%add = add i32 %sub, 42
ret i32 %add
; CHECK: @test3
; CHECK-NEXT: and i32 %x, 31
; CHECK-NEXT: sub i32 73, %and
; CHECK-NEXT: ret
}