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ValueTracking: Teach isKnownToBeAPowerOfTwo about (ADD X, (XOR X, Y)) where X is a power of two

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This allows us to simplify urem instructions involving the add+xor to
turn into simpler math.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185272 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2013-06-29 23:44:53 +00:00
parent bebf6222f6
commit 58b6dc032a
2 changed files with 33 additions and 10 deletions
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15
test/Transforms/InstCombine/rem.ll
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@@ -163,3 +163,18 @@ define i32 @test16(i32 %x, i32 %y) {
%rem = urem i32 %x, %add
ret i32 %rem
}
define i32 @test17(i16 %x, i32 %y) {
; CHECK: @test17
; CHECK-NEXT: [[AND:%.*]] = and i16 %x, 4
; CHECK-NEXT: [[EXT:%.*]] = zext i16 [[AND]] to i32
; CHECK-NEXT: [[SHL:%.*]] = shl nuw nsw i32 [[EXT]], 3
; CHECK-NEXT: [[XOR:%.*]] = xor i32 [[SHL]], 63
; CHECK-NEXT: [[REM:%.*]] = and i32 [[XOR]], %y
; CHECK-NEXT: ret i32 [[REM]]
%1 = and i16 %x, 4
%2 = icmp ne i16 %1, 0
%3 = select i1 %2, i32 32, i32 64
%4 = urem i32 %y, %3
ret i32 %4
}