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Diffstat (limited to 'lib/Transforms/InstCombine/InstCombineMulDivRem.cpp')
-rw-r--r--lib/Transforms/InstCombine/InstCombineMulDivRem.cpp25
1 files changed, 16 insertions, 9 deletions
diff --git a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 94b619b203..b860440f60 100644
--- a/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -136,19 +136,26 @@ Instruction *InstCombiner::visitMul(BinaryOperator &I) {
}
}
- // (1 - X) * (-2) -> (x - 1) * 2, for all positive nonzero powers of 2
- // The "* 2" thus becomes a potential shifting opportunity.
+ // (Y - X) * (-(2**n)) -> (X - Y) * (2**n), for positive nonzero n
+ // (Y + const) * (-(2**n)) -> (-constY) * (2**n), for positive nonzero n
+ // The "* (2**n)" thus becomes a potential shifting opportunity.
{
const APInt & Val = CI->getValue();
const APInt &PosVal = Val.abs();
if (Val.isNegative() && PosVal.isPowerOf2()) {
- Value *X = 0;
- if (match(Op0, m_Sub(m_One(), m_Value(X)))) {
- // ConstantInt::get(Op0->getType(), 2);
- Value *Sub = Builder->CreateSub(X, ConstantInt::get(X->getType(), 1),
- "dec1");
- return BinaryOperator::CreateMul(Sub, ConstantInt::get(X->getType(),
- PosVal));
+ Value *X = 0, *Y = 0;
+ ConstantInt *C1 = 0;
+ if (Op0->hasOneUse() &&
+ (match(Op0, m_Sub(m_Value(Y), m_Value(X)))) ||
+ (match(Op0, m_Add(m_Value(Y), m_ConstantInt(C1))))) {
+ Value *Sub;
+ if (C1) // Matched ADD of constant, negate both operands:
+ Sub = Builder->CreateSub(Builder->CreateNeg(C1), Y, "subc");
+ else // Matched SUB, swap operands:
+ Sub = Builder->CreateSub(X, Y, "suba");
+ return
+ BinaryOperator::CreateMul(Sub,
+ ConstantInt::get(X->getType(), PosVal));
}
}
}