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InstSimplify: Handle some simple tautological comparisons

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This handles cases where we are comparing a masked value against itself.
The analysis could be further improved by making it recursive but such
expense is not currently justified.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222716 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-11-25 02:55:48 +00:00
parent 25efc8dbce
commit 044b644f54
2 changed files with 98 additions and 0 deletions
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34
lib/Analysis/InstructionSimplify.cpp
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@ -2477,6 +2477,40 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
// icmp pred (or X, Y), X
if (LBO && match(LBO, m_CombineOr(m_Or(m_Value(), m_Specific(RHS)),
m_Or(m_Specific(RHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_ULT)
return getFalse(ITy);
if (Pred == ICmpInst::ICMP_UGE)
return getTrue(ITy);
}
// icmp pred X, (or X, Y)
if (RBO && match(RBO, m_CombineOr(m_Or(m_Value(), m_Specific(LHS)),
m_Or(m_Specific(LHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_ULE)
return getTrue(ITy);
if (Pred == ICmpInst::ICMP_UGT)
return getFalse(ITy);
}
// icmp pred (and X, Y), X
if (LBO && match(LBO, m_CombineOr(m_And(m_Value(), m_Specific(RHS)),
m_And(m_Specific(RHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_UGT)
return getFalse(ITy);
if (Pred == ICmpInst::ICMP_ULE)
return getTrue(ITy);
}
// icmp pred X, (and X, Y)
if (RBO && match(RBO, m_CombineOr(m_And(m_Value(), m_Specific(LHS)),
m_And(m_Specific(LHS), m_Value())))) {
if (Pred == ICmpInst::ICMP_UGE)
return getTrue(ITy);
if (Pred == ICmpInst::ICMP_ULT)
return getFalse(ITy);
}
// 0 - (zext X) pred C
if (!CmpInst::isUnsigned(Pred) && match(LHS, m_Neg(m_ZExt(m_Value())))) {
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(RHS)) {