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Generalize the and-icmp-select instcombine further by allowing selects of the form

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(x & 2^n) ? 2^m+C : C

we can offset both arms by C to get the "(x & 2^n) ? 2^m : 0" form, optimize the
select to a shift and apply the offset afterwards.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121609 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer
2010-12-11 10:49:22 +00:00
parent 20e3b4b380
commit 2f7228b80c
3 changed files with 72 additions and 16 deletions
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lib/Transforms/InstCombine/InstCombineSelect.cpp
+22 -4
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@@ -457,10 +457,6 @@ static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
if (!IC || !IC->isEquality())
return 0;
// One of the select arms must be zero.
if (!TrueVal->isZero() && !FalseVal->isZero())
return 0;
if (ConstantInt *C = dyn_cast<ConstantInt>(IC->getOperand(1)))
if (!C->isZero())
return 0;
@@ -471,6 +467,24 @@ static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
!match(LHS, m_And(m_Value(), m_ConstantInt(AndRHS))))
return 0;
// If both select arms are non-zero see if we have a select of the form
// 'x ? 2^n + C : C'. Then we can offset both arms by C, use the logic
// for 'x ? 2^n : 0' and fix the thing up at the end.
ConstantInt *Offset = 0;
if (!TrueVal->isZero() && !FalseVal->isZero()) {
if ((TrueVal->getValue() - FalseVal->getValue()).isPowerOf2())
Offset = FalseVal;
else if ((FalseVal->getValue() - TrueVal->getValue()).isPowerOf2())
Offset = TrueVal;
else
return 0;
// Adjust TrueVal and FalseVal to the offset.
TrueVal = ConstantInt::get(Builder->getContext(),
TrueVal->getValue() - Offset->getValue());
FalseVal = ConstantInt::get(Builder->getContext(),
FalseVal->getValue() - Offset->getValue());
}
// Make sure the mask in the 'and' and one of the select arms is a power of 2.
if (!AndRHS->getValue().isPowerOf2() ||
@@ -496,6 +510,10 @@ static Value *foldSelectICmpAnd(const SelectInst &SI, ConstantInt *TrueVal,
ShouldNotVal ^= IC->getPredicate() == ICmpInst::ICMP_NE;
if (ShouldNotVal)
V = Builder->CreateXor(V, ValC);
// Apply an offset if needed.
if (Offset)
V = Builder->CreateAdd(V, Offset);
return V;
}