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Handle some simple cases where we can see that values get annihilated.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@21771 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -113,10 +113,16 @@ unsigned Reassociate::getRank(Value *V) {
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i != e && Rank != MaxRank; ++i)
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Rank = std::max(Rank, getRank(I->getOperand(i)));
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// If this is a not or neg instruction, do not count it for rank. This
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// assures us that X and ~X will have the same rank.
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if (!I->getType()->isIntegral() ||
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(!BinaryOperator::isNot(I) && !BinaryOperator::isNeg(I)))
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++Rank;
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DEBUG(std::cerr << "Calculated Rank[" << V->getName() << "] = "
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<< Rank+1 << "\n");
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<< Rank << "\n");
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return CachedRank = Rank+1;
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return CachedRank = Rank;
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}
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/// isReassociableOp - Return true if V is an instruction of the specified
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@ -388,11 +394,40 @@ void Reassociate::ReassociateBB(BasicBlock *BB) {
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goto FoldConstants;
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}
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// FIXME: Handle destructive annihilation here. Ensure RANK(neg(x)) ==
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// RANK(x) [and not]. Handle case when Cst = 0 and op = AND f.e.
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// FIXME: Handle +0,*1,&~0,... at end of the list.
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// Check for destructive annihilation due to a constant being used.
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if (Ops.size() != 1) { // Nothing to annihilate?
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if (ConstantIntegral *CstVal = dyn_cast<ConstantIntegral>(Ops.back().Op))
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switch (I->getOpcode()) {
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default: break;
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case Instruction::And:
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if (CstVal->isNullValue()) { // ... & 0 -> 0
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Ops[0].Op = CstVal;
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Ops.erase(Ops.begin()+1, Ops.end());
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} else if (CstVal->isAllOnesValue()) { // ... & -1 -> ...
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Ops.pop_back();
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}
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break;
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case Instruction::Mul:
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if (CstVal->isNullValue()) { // ... * 0 -> 0
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Ops[0].Op = CstVal;
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Ops.erase(Ops.begin()+1, Ops.end());
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} else if (cast<ConstantInt>(CstVal)->getRawValue() == 1) {
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Ops.pop_back(); // ... * 1 -> ...
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}
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break;
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case Instruction::Or:
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if (CstVal->isAllOnesValue()) { // ... | -1 -> -1
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Ops[0].Op = CstVal;
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Ops.erase(Ops.begin()+1, Ops.end());
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}
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// FALLTHROUGH!
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case Instruction::Add:
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case Instruction::Xor:
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if (CstVal->isNullValue()) // ... [|^+] 0 -> ...
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Ops.pop_back();
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break;
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}
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}
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if (Ops.size() == 1) {
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// This expression tree simplified to something that isn't a tree,
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