From 83e8ec73e1487926d6eb6d330bb869f173c8fcf1 Mon Sep 17 00:00:00 2001 From: Nick Lewycky Date: Sat, 5 Dec 2009 05:00:00 +0000 Subject: Generalize this optimization to work on equality comparisons between any two integers that are constant except for a single bit (the same n-th bit in each). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90646 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Transforms/Scalar/InstructionCombining.cpp | 43 ++++++++++++++++---------- 1 file changed, 27 insertions(+), 16 deletions(-) (limited to 'lib') diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp index d12ad81..2b4b66b 100644 --- a/lib/Transforms/Scalar/InstructionCombining.cpp +++ b/lib/Transforms/Scalar/InstructionCombining.cpp @@ -8585,25 +8585,36 @@ Instruction *InstCombiner::transformZExtICmp(ICmpInst *ICI, Instruction &CI, if (ICI->isEquality() && CI.getType() == ICI->getOperand(0)->getType()) { if (const IntegerType *ITy = dyn_cast(CI.getType())) { uint32_t BitWidth = ITy->getBitWidth(); - if (BitWidth > 1) { - Value *LHS = ICI->getOperand(0); - Value *RHS = ICI->getOperand(1); - - APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0); - APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0); - APInt TypeMask(APInt::getHighBitsSet(BitWidth, BitWidth-1)); - ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS); - ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS); - - if (KnownZeroLHS.countLeadingOnes() == BitWidth-1 && - KnownZeroRHS.countLeadingOnes() == BitWidth-1) { + Value *LHS = ICI->getOperand(0); + Value *RHS = ICI->getOperand(1); + + APInt KnownZeroLHS(BitWidth, 0), KnownOneLHS(BitWidth, 0); + APInt KnownZeroRHS(BitWidth, 0), KnownOneRHS(BitWidth, 0); + APInt TypeMask(APInt::getAllOnesValue(BitWidth)); + ComputeMaskedBits(LHS, TypeMask, KnownZeroLHS, KnownOneLHS); + ComputeMaskedBits(RHS, TypeMask, KnownZeroRHS, KnownOneRHS); + + if (KnownZeroLHS == KnownZeroRHS && KnownOneLHS == KnownOneRHS) { + APInt KnownBits = KnownZeroLHS | KnownOneLHS; + APInt UnknownBit = ~KnownBits; + if (UnknownBit.countPopulation() == 1) { if (!DoXform) return ICI; - Value *Xor = Builder->CreateXor(LHS, RHS); + Value *Result = Builder->CreateXor(LHS, RHS); + + // Mask off any bits that are set and won't be shifted away. + if (KnownOneLHS.uge(UnknownBit)) + Result = Builder->CreateAnd(Result, + ConstantInt::get(ITy, UnknownBit)); + + // Shift the bit we're testing down to the lsb. + Result = Builder->CreateLShr( + Result, ConstantInt::get(ITy, UnknownBit.countTrailingZeros())); + if (ICI->getPredicate() == ICmpInst::ICMP_EQ) - Xor = Builder->CreateXor(Xor, ConstantInt::get(ITy, 1)); - Xor->takeName(ICI); - return ReplaceInstUsesWith(CI, Xor); + Result = Builder->CreateXor(Result, ConstantInt::get(ITy, 1)); + Result->takeName(ICI); + return ReplaceInstUsesWith(CI, Result); } } } -- cgit v1.1