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Instcombine (X & FF00) + xx00 -> (X+xx00) & FF00, implementing and.ll:test27

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This comes up when doing adds to bitfield elements.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16836 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2004-10-08 05:07:56 +00:00
parent 8797f59758
commit b99d6b1cac
1 changed files with 25 additions and 0 deletions
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25
lib/Transforms/Scalar/InstructionCombining.cpp
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@ -623,6 +623,31 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
return BinaryOperator::createSub(C, X);
}
// (X & FF00) + xx00 -> (X+xx00) & FF00
if (LHS->hasOneUse() && match(LHS, m_And(m_Value(X), m_ConstantInt(C2)))) {
Constant *Anded = ConstantExpr::getAnd(CRHS, C2);
if (Anded == CRHS) {
// See if all bits from the first bit set in the Add RHS up are included
// in the mask. First, get the rightmost bit.
uint64_t AddRHSV = CRHS->getRawValue();
// Form a mask of all bits from the lowest bit added through the top.
uint64_t AddRHSHighBits = ~((AddRHSV & -AddRHSV)-1);
AddRHSHighBits &= (1ULL << C2->getType()->getPrimitiveSize()*8)-1;
// See if the and mask includes all of these bits.
uint64_t AddRHSHighBitsAnd = AddRHSHighBits & C2->getRawValue();
if (AddRHSHighBits == AddRHSHighBitsAnd) {
// Okay, the xform is safe. Insert the new add pronto.
Value *NewAdd = InsertNewInstBefore(BinaryOperator::createAdd(X, CRHS,
LHS->getName()), I);
return BinaryOperator::createAnd(NewAdd, C2);
}
}
}
// Try to fold constant add into select arguments.
if (SelectInst *SI = dyn_cast<SelectInst>(LHS))
if (Instruction *R = FoldBinOpIntoSelect(I, SI, this))