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InstSimplify: Compute comparison ranges for left shift instructions

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'shl nuw CI, x' produces [CI, CI << CLZ(CI)]
'shl nsw CI, x' produces [CI << CLO(CI)-1, CI] if CI is negative
'shl nsw CI, x' produces [CI, CI << CLZ(CI)-1] if CI is non-negative

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216570 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-08-27 18:03:46 +00:00
parent 0927dab0be
commit d8e448bd27
2 changed files with 43 additions and 0 deletions
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lib/Analysis/InstructionSimplify.cpp
+16
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@@ -1993,6 +1993,22 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
Upper = Upper + 1;
assert(Upper != Lower && "Upper part of range has wrapped!");
}
} else if (match(LHS, m_NUWShl(m_ConstantInt(CI2), m_Value()))) {
// 'shl nuw CI2, x' produces [CI2, CI2 << CLZ(CI2)]
Lower = CI2->getValue();
Upper = Lower.shl(Lower.countLeadingZeros()) + 1;
} else if (match(LHS, m_NSWShl(m_ConstantInt(CI2), m_Value()))) {
if (CI2->isNegative()) {
// 'shl nsw CI2, x' produces [CI2 << CLO(CI2)-1, CI2]
unsigned ShiftAmount = CI2->getValue().countLeadingOnes() - 1;
Lower = CI2->getValue().shl(ShiftAmount);
Upper = CI2->getValue() + 1;
} else {
// 'shl nsw CI2, x' produces [CI2, CI2 << CLZ(CI2)-1]
unsigned ShiftAmount = CI2->getValue().countLeadingZeros() - 1;
Lower = CI2->getValue();
Upper = CI2->getValue().shl(ShiftAmount) + 1;
}
} else if (match(LHS, m_LShr(m_Value(), m_ConstantInt(CI2)))) {
// 'lshr x, CI2' produces [0, UINT_MAX >> CI2].
APInt NegOne = APInt::getAllOnesValue(Width);