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Reapply r88830 with a bugfix: this transform only applies to icmp eq/ne. This
fixes part of PR5438. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@89639 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -8539,6 +8539,36 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI,
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}
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}
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// icmp ne A, B is equal to xor A, B when A and B only really have one bit.
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// It is also profitable to transform icmp eq into not(xor(A, B)) because that
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// may lead to additional simplifications.
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if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) {
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if (const IntegerType *ITy = dyn_cast<IntegerType>(CI.getType())) {
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uint32_t BitWidth = ITy->getBitWidth();
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if (BitWidth > 1) {
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Value *LHS = ICI->getOperand(0);
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Value *RHS = ICI->getOperand(1);
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APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0);
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APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0);
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APInt TypeMask(APInt::getHighBitsSet(BitWidth, BitWidth-1));
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ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS);
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ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS);
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if (KnownZeroLHS.countLeadingOnes() == BitWidth-1 &&
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KnownZeroRHS.countLeadingOnes() == BitWidth-1) {
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if (!DoXform) return ICI;
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Value *Xor = Builder->CreateXor(LHS, RHS);
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if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
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Xor = Builder->CreateXor(Xor, ConstantInt::get(ITy, 1));
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Xor->takeName(ICI);
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return ReplaceInstUsesWith(CI, Xor);
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}
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}
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}
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}
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return 0;
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}
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@ -1,5 +1,4 @@
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; RUN: opt %s -instcombine -S | FileCheck %s
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; XFAIL: *
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; PR5438
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; TODO: This should also optimize down.
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