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Make use of the exact bit when optimizing '(X >>exact 3) << 1' to eliminate the

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'and' that would zero out the trailing bits, and to produce an exact shift
ourselves.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147391 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2011-12-31 21:30:22 +00:00
parent ccc9a59614
commit 57ed0948b8
2 changed files with 29 additions and 5 deletions
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18
test/Transforms/InstCombine/shift.ll
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@ -542,3 +542,21 @@ define i32 @test45(i32 %a) nounwind {
; CHECK-NEXT: %y = lshr i32 %a, 5
; CHECK-NEXT: ret i32 %y
}
define i32 @test46(i32 %a) {
%y = ashr exact i32 %a, 3
%z = shl i32 %y, 1
ret i32 %z
; CHECK: @test46
; CHECK-NEXT: %z = ashr exact i32 %a, 2
; CHECK-NEXT: ret i32 %z
}
define i32 @test47(i32 %a) {
%y = lshr exact i32 %a, 3
%z = shl i32 %y, 1
ret i32 %z
; CHECK: @test47
; CHECK-NEXT: %z = lshr exact i32 %a, 2
; CHECK-NEXT: ret i32 %z
}