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Fix a miscompilation from Dan's recent apintification.

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llvm-svn: 47128
This commit is contained in:
Chris Lattner 2008-02-14 18:48:56 +00:00
parent 9deedb0114
commit 9c24f3ec37
2 changed files with 9 additions and 3 deletions
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4
lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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@ -1437,12 +1437,10 @@ void SelectionDAG::ComputeMaskedBits(SDOperand Op, const APInt &Mask,
// We know that the top bits of C-X are clear if X contains less bits
// than C (i.e. no wrap-around can happen). For example, 20-X is
// positive if we can prove that X is >= 0 and < 16.
// sign bit clear
if (CLHS->getAPIntValue().isNonNegative()) {
unsigned NLZ = (CLHS->getAPIntValue()+1).countLeadingZeros();
// NLZ can't be BitWidth with no sign bit
APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ);
APInt MaskV = APInt::getHighBitsSet(BitWidth, NLZ+1);
ComputeMaskedBits(Op.getOperand(1), MaskV, KnownZero, KnownOne, Depth+1);
// If all of the MaskV bits are known to be zero, then we know the output

8
test/CodeGen/X86/2008-02-14-BitMiscompile.ll Normal file
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@ -0,0 +1,8 @@
; RUN: llvm-as < %s | llc -march=x86 | grep and
define i32 @test(i1 %A) {
%B = zext i1 %A to i32 ; <i32> [#uses=1]
%C = sub i32 0, %B ; <i32> [#uses=1]
%D = and i32 %C, 255 ; <i32> [#uses=1]
ret i32 %D
}