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Followup to 132316; accept arbitrary constants, add with a constant,

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sub with a non-constant.  Fix comments, enlarge test case.
rdar://problem/6501862


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@132348 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Stuart Hastings
2011-05-31 19:29:55 +00:00
parent f729e91353
commit df48e84b5b
2 changed files with 55 additions and 15 deletions
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25
lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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@@ -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));
}
}
}