From 650b6ea893c118bf0c6e40cd3002954cc34df2bb Mon Sep 17 00:00:00 2001 From: Nick Lewycky Date: Thu, 19 Jun 2014 03:35:49 +0000 Subject: Make instsimplify's analysis of icmp eq/ne use computeKnownBits to determine whether the icmp is always true or false. Patch by Suyog Sarda! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211251 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/InstructionSimplify.cpp | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) (limited to 'lib/Analysis') diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp index 3684fda854..b06d9948ac 100644 --- a/lib/Analysis/InstructionSimplify.cpp +++ b/lib/Analysis/InstructionSimplify.cpp @@ -2241,6 +2241,25 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS, } } + // If a bit is known to be zero for A and known to be one for B, + // then A and B cannot be equal. + if (ICmpInst::isEquality(Pred)) { + if (ConstantInt *CI = dyn_cast(RHS)) { + uint32_t BitWidth = CI->getBitWidth(); + APInt LHSKnownZero(BitWidth, 0); + APInt LHSKnownOne(BitWidth, 0); + computeKnownBits(LHS, LHSKnownZero, LHSKnownOne); + APInt RHSKnownZero(BitWidth, 0); + APInt RHSKnownOne(BitWidth, 0); + computeKnownBits(RHS, RHSKnownZero, RHSKnownOne); + if (((LHSKnownOne & RHSKnownZero) != 0) || + ((LHSKnownZero & RHSKnownOne) != 0)) + return (Pred == ICmpInst::ICMP_EQ) + ? ConstantInt::getFalse(CI->getContext()) + : ConstantInt::getTrue(CI->getContext()); + } + } + // Special logic for binary operators. BinaryOperator *LBO = dyn_cast(LHS); BinaryOperator *RBO = dyn_cast(RHS); -- cgit v1.2.3