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Make instsimplify's analysis of icmp eq/ne use computeKnownBits to determine whether the icmp is always true or false. Patch by Suyog Sarda!

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211251 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky
2014-06-19 03:35:49 +00:00
parent bdb4aca202
commit 650b6ea893
3 changed files with 39 additions and 1 deletions
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lib/Analysis/InstructionSimplify.cpp
+19
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@@ -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<ConstantInt>(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<BinaryOperator>(LHS);
BinaryOperator *RBO = dyn_cast<BinaryOperator>(RHS);