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InstCombine: Move Sub->Xor rule from SimplifyDemanded to InstCombine

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The rule that turns a sub to xor if the LHS is 2^n-1 and the remaining bits
are known zero, does not use the demanded bits at all: Move it to the
normal InstCombine code path.

Differential Revision: http://reviews.llvm.org/D9417

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236268 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
2015-04-30 22:04:26 +00:00
parent a55dd52dc8
commit e233e19ac6
2 changed files with 13 additions and 10 deletions
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13
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@@ -1586,6 +1586,19 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
CI->getValue() == I.getType()->getPrimitiveSizeInBits() - 1)
return BinaryOperator::CreateLShr(X, CI);
}
// Turn this into a xor if LHS is 2^n-1 and the remaining bits are known
// zero.
APInt IntVal = C->getValue();
if ((IntVal + 1).isPowerOf2()) {
unsigned BitWidth = I.getType()->getScalarSizeInBits();
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
computeKnownBits(&I, KnownZero, KnownOne, 0, &I);
if ((IntVal | KnownZero).isAllOnesValue()) {
return BinaryOperator::CreateXor(Op1, C);
}
}
}