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isKnownToBeAPowerOfTwo: (X & Y) + Y is a power of 2 or zero if y is also.

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This is useful if something that looks like (x & (1 << y)) ? 64 : 32 is
the divisor in a modulo operation.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@182200 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2013-05-18 19:30:37 +00:00
parent 688b5103eb
commit cb9d4667b7
2 changed files with 25 additions and 0 deletions
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14
test/Transforms/InstCombine/rem.ll
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@@ -149,3 +149,17 @@ define i64 @test15(i32 %x, i32 %y) {
%urem = urem i64 %zext1, %zext0
ret i64 %urem
}
define i32 @test16(i32 %x, i32 %y) {
; CHECK: @test16
; CHECK-NEXT: [[SHR:%.*]] = lshr i32 %y, 11
; CHECK-NEXT: [[AND:%.*]] = and i32 [[SHR]], 4
; CHECK-NEXT: [[OR:%.*]] = or i32 [[AND]], 3
; CHECK-NEXT: [[REM:%.*]] = and i32 [[OR]], %x
; CHECK-NEXT: ret i32 [[REM]]
%shr = lshr i32 %y, 11
%and = and i32 %shr, 4
%add = add i32 %and, 4
%rem = urem i32 %x, %add
ret i32 %rem
}