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Implement ScalarRepl/select_promote.ll
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@12779 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -71,11 +71,42 @@ bool llvm::isAllocaPromotable(const AllocaInst *AI, const TargetData &TD) {
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if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
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// Scan looking for memory accesses.
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// FIXME: this should REALLY use alias analysis.
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for (--UI; !isa<PHINode>(UI); --UI)
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if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
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return false;
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// If we got this far, we can promote the PHI use.
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} else if (const SelectInst *SI = dyn_cast<SelectInst>(*UI)) {
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// We only support selects in a few simple cases. The select is only
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// allowed to have one use, which must be a load instruction, and can only
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// use alloca instructions (no random pointers). Also, there cannot be
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// any accesses to AI between the PHI node and the use of the PHI.
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if (!SI->hasOneUse()) return false;
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// Our transformation causes the unconditional loading of all pointer
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// operands of the select. Because this could cause a fault if there is a
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// critical edge in the CFG and if one of the pointers is illegal, we
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// refuse to promote the select unless it is obviously safe. For now,
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// obviously safe means that all of the operands are allocas.
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//
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if (!isa<AllocaInst>(SI->getOperand(1)) ||
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!isa<AllocaInst>(SI->getOperand(2)))
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return false;
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// Now make sure the one user instruction is in the same basic block as
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// the PHI, and that there are no loads or stores between the PHI node and
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// the access.
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BasicBlock::const_iterator UI = cast<Instruction>(SI->use_back());
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if (!isa<LoadInst>(UI) || cast<LoadInst>(UI)->isVolatile()) return false;
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// Scan looking for memory accesses.
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// FIXME: this should REALLY use alias analysis.
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for (--UI; &*UI != SI; --UI)
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if (isa<LoadInst>(UI) || isa<StoreInst>(UI) || isa<CallInst>(UI))
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return false;
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// If we got this far, we can promote the select use.
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} else {
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return false; // Not a load, store, or promotable PHI?
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}
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@ -170,6 +201,28 @@ void PromoteMem2Reg::run() {
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} else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
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// Otherwise it must be a load instruction, keep track of variable reads
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UsingBlocks.push_back(LI->getParent());
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} else if (SelectInst *SI = dyn_cast<SelectInst>(User)) {
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// Because of the restrictions we placed on Select instruction uses
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// above things are very simple. Transform the PHI of addresses into a
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// select of loaded values.
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LoadInst *Load = cast<LoadInst>(SI->use_back());
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std::string LoadName = Load->getName(); Load->setName("");
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Value *TrueVal = new LoadInst(SI->getOperand(1),
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SI->getOperand(1)->getName()+".val", SI);
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Value *FalseVal = new LoadInst(SI->getOperand(2),
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SI->getOperand(2)->getName()+".val", SI);
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Value *NewSI = new SelectInst(SI->getOperand(0), TrueVal,
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FalseVal, Load->getName(), SI);
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Load->replaceAllUsesWith(NewSI);
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Load->getParent()->getInstList().erase(Load);
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SI->getParent()->getInstList().erase(SI);
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// Restart our scan of uses...
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DefiningBlocks.clear();
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UsingBlocks.clear();
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goto RestartUseScan;
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} else {
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// Because of the restrictions we placed on PHI node uses above, the PHI
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// node reads the block in any using predecessors. Transform the PHI of
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