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InstSimplify: Optimize signed icmp of -(zext V)

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Summary:
We know that -(zext V) will always be <= zero, simplify signed icmps
that have these.

Uncovered using http://www.cs.utah.edu/~regehr/souper/

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3754

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208809 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-05-14 20:16:28 +00:00
parent e0776de2df
commit cd237ed585
2 changed files with 82 additions and 0 deletions
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22
lib/Analysis/InstructionSimplify.cpp
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@@ -2280,6 +2280,28 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
// 0 - (zext X) pred C
if (!CmpInst::isUnsigned(Pred) && match(LHS, m_Neg(m_ZExt(m_Value())))) {
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {
if (RHSC->getValue().isStrictlyPositive()) {
if (Pred == ICmpInst::ICMP_SLT)
return ConstantInt::getTrue(RHSC->getContext());
if (Pred == ICmpInst::ICMP_SGE)
return ConstantInt::getFalse(RHSC->getContext());
if (Pred == ICmpInst::ICMP_EQ)
return ConstantInt::getFalse(RHSC->getContext());
if (Pred == ICmpInst::ICMP_NE)
return ConstantInt::getTrue(RHSC->getContext());
}
if (RHSC->getValue().isNonNegative()) {
if (Pred == ICmpInst::ICMP_SLE)
return ConstantInt::getTrue(RHSC->getContext());
if (Pred == ICmpInst::ICMP_SGT)
return ConstantInt::getFalse(RHSC->getContext());
}
}
}
// icmp pred (urem X, Y), Y
if (LBO && match(LBO, m_URem(m_Value(), m_Specific(RHS)))) {
bool KnownNonNegative, KnownNegative;