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Re-reapply r221924: "[GVN] Perform Scalar PRE on gep indices that feed loads before
doing Load PRE" It's not really expected to stick around, last time it provoked a weird LTO build failure that I can't reproduce now, and the bot logs are long gone. I'll re-revert it if the failures recur. Original description: Perform Scalar PRE on gep indices that feed loads before doing Load PRE. llvm-svn: 225536
This commit is contained in:
Tim Northover
parent
7363918430
commit
ef7d18507b
@ -20,6 +20,7 @@
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/Hashing.h"
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#include "llvm/ADT/MapVector.h"
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#include "llvm/ADT/PostOrderIterator.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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@ -709,6 +710,7 @@ namespace {
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void dump(DenseMap<uint32_t, Value*> &d);
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bool iterateOnFunction(Function &F);
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bool performPRE(Function &F);
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bool performScalarPRE(Instruction *I);
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Value *findLeader(const BasicBlock *BB, uint32_t num);
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void cleanupGlobalSets();
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void verifyRemoved(const Instruction *I) const;
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@ -1728,6 +1730,15 @@ bool GVN::processNonLocalLoad(LoadInst *LI) {
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return false;
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}
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// If this load follows a GEP, see if we can PRE the indices before analyzing.
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if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(LI->getOperand(0))) {
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for (GetElementPtrInst::op_iterator OI = GEP->idx_begin(),
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OE = GEP->idx_end();
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OI != OE; ++OI)
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if (Instruction *I = dyn_cast<Instruction>(OI->get()))
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performScalarPRE(I);
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}
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// Step 2: Analyze the availability of the load
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AvailValInBlkVect ValuesPerBlock;
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UnavailBlkVect UnavailableBlocks;
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@ -2430,175 +2441,182 @@ bool GVN::processBlock(BasicBlock *BB) {
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return ChangedFunction;
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}
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bool GVN::performScalarPRE(Instruction *CurInst) {
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SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap;
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if (isa<AllocaInst>(CurInst) || isa<TerminatorInst>(CurInst) ||
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isa<PHINode>(CurInst) || CurInst->getType()->isVoidTy() ||
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CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
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isa<DbgInfoIntrinsic>(CurInst))
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return false;
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// Don't do PRE on compares. The PHI would prevent CodeGenPrepare from
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// sinking the compare again, and it would force the code generator to
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// move the i1 from processor flags or predicate registers into a general
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// purpose register.
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if (isa<CmpInst>(CurInst))
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return false;
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// We don't currently value number ANY inline asm calls.
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if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
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if (CallI->isInlineAsm())
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return false;
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uint32_t ValNo = VN.lookup(CurInst);
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// Look for the predecessors for PRE opportunities. We're
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// only trying to solve the basic diamond case, where
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// a value is computed in the successor and one predecessor,
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// but not the other. We also explicitly disallow cases
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// where the successor is its own predecessor, because they're
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// more complicated to get right.
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unsigned NumWith = 0;
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unsigned NumWithout = 0;
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BasicBlock *PREPred = nullptr;
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BasicBlock *CurrentBlock = CurInst->getParent();
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predMap.clear();
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for (pred_iterator PI = pred_begin(CurrentBlock), PE = pred_end(CurrentBlock);
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PI != PE; ++PI) {
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BasicBlock *P = *PI;
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// We're not interested in PRE where the block is its
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// own predecessor, or in blocks with predecessors
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// that are not reachable.
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if (P == CurrentBlock) {
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NumWithout = 2;
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break;
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} else if (!DT->isReachableFromEntry(P)) {
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NumWithout = 2;
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break;
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}
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Value *predV = findLeader(P, ValNo);
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if (!predV) {
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predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P));
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PREPred = P;
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++NumWithout;
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} else if (predV == CurInst) {
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/* CurInst dominates this predecessor. */
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NumWithout = 2;
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break;
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} else {
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predMap.push_back(std::make_pair(predV, P));
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++NumWith;
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}
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}
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// Don't do PRE when it might increase code size, i.e. when
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// we would need to insert instructions in more than one pred.
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if (NumWithout != 1 || NumWith == 0)
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return false;
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// Don't do PRE across indirect branch.
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if (isa<IndirectBrInst>(PREPred->getTerminator()))
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return false;
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// We can't do PRE safely on a critical edge, so instead we schedule
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// the edge to be split and perform the PRE the next time we iterate
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// on the function.
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unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
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if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
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toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
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return false;
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}
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// Instantiate the expression in the predecessor that lacked it.
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// Because we are going top-down through the block, all value numbers
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// will be available in the predecessor by the time we need them. Any
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// that weren't originally present will have been instantiated earlier
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// in this loop.
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Instruction *PREInstr = CurInst->clone();
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bool success = true;
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for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
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Value *Op = PREInstr->getOperand(i);
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if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
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continue;
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if (Value *V = findLeader(PREPred, VN.lookup(Op))) {
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PREInstr->setOperand(i, V);
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} else {
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success = false;
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break;
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}
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}
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// Fail out if we encounter an operand that is not available in
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// the PRE predecessor. This is typically because of loads which
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// are not value numbered precisely.
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if (!success) {
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DEBUG(verifyRemoved(PREInstr));
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delete PREInstr;
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return false;
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}
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PREInstr->insertBefore(PREPred->getTerminator());
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PREInstr->setName(CurInst->getName() + ".pre");
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PREInstr->setDebugLoc(CurInst->getDebugLoc());
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VN.add(PREInstr, ValNo);
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++NumGVNPRE;
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// Update the availability map to include the new instruction.
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addToLeaderTable(ValNo, PREInstr, PREPred);
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// Create a PHI to make the value available in this block.
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PHINode *Phi =
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PHINode::Create(CurInst->getType(), predMap.size(),
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CurInst->getName() + ".pre-phi", CurrentBlock->begin());
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for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
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if (Value *V = predMap[i].first)
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Phi->addIncoming(V, predMap[i].second);
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else
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Phi->addIncoming(PREInstr, PREPred);
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}
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VN.add(Phi, ValNo);
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addToLeaderTable(ValNo, Phi, CurrentBlock);
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Phi->setDebugLoc(CurInst->getDebugLoc());
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CurInst->replaceAllUsesWith(Phi);
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if (Phi->getType()->getScalarType()->isPointerTy()) {
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// Because we have added a PHI-use of the pointer value, it has now
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// "escaped" from alias analysis' perspective. We need to inform
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// AA of this.
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for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee; ++ii) {
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unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
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VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj));
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}
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if (MD)
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MD->invalidateCachedPointerInfo(Phi);
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}
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VN.erase(CurInst);
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removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
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DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
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if (MD)
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MD->removeInstruction(CurInst);
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DEBUG(verifyRemoved(CurInst));
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CurInst->eraseFromParent();
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return true;
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}
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/// performPRE - Perform a purely local form of PRE that looks for diamond
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/// control flow patterns and attempts to perform simple PRE at the join point.
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bool GVN::performPRE(Function &F) {
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bool Changed = false;
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SmallVector<std::pair<Value*, BasicBlock*>, 8> predMap;
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for (BasicBlock *CurrentBlock : depth_first(&F.getEntryBlock())) {
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// Nothing to PRE in the entry block.
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if (CurrentBlock == &F.getEntryBlock()) continue;
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if (CurrentBlock == &F.getEntryBlock())
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continue;
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// Don't perform PRE on a landing pad.
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if (CurrentBlock->isLandingPad()) continue;
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if (CurrentBlock->isLandingPad())
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continue;
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for (BasicBlock::iterator BI = CurrentBlock->begin(),
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BE = CurrentBlock->end(); BI != BE; ) {
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BE = CurrentBlock->end();
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BI != BE;) {
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Instruction *CurInst = BI++;
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if (isa<AllocaInst>(CurInst) ||
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isa<TerminatorInst>(CurInst) || isa<PHINode>(CurInst) ||
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CurInst->getType()->isVoidTy() ||
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CurInst->mayReadFromMemory() || CurInst->mayHaveSideEffects() ||
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isa<DbgInfoIntrinsic>(CurInst))
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continue;
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// Don't do PRE on compares. The PHI would prevent CodeGenPrepare from
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// sinking the compare again, and it would force the code generator to
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// move the i1 from processor flags or predicate registers into a general
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// purpose register.
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if (isa<CmpInst>(CurInst))
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continue;
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// We don't currently value number ANY inline asm calls.
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if (CallInst *CallI = dyn_cast<CallInst>(CurInst))
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if (CallI->isInlineAsm())
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continue;
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uint32_t ValNo = VN.lookup(CurInst);
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// Look for the predecessors for PRE opportunities. We're
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// only trying to solve the basic diamond case, where
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// a value is computed in the successor and one predecessor,
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// but not the other. We also explicitly disallow cases
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// where the successor is its own predecessor, because they're
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// more complicated to get right.
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unsigned NumWith = 0;
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unsigned NumWithout = 0;
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BasicBlock *PREPred = nullptr;
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predMap.clear();
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for (pred_iterator PI = pred_begin(CurrentBlock),
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PE = pred_end(CurrentBlock); PI != PE; ++PI) {
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BasicBlock *P = *PI;
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// We're not interested in PRE where the block is its
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// own predecessor, or in blocks with predecessors
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// that are not reachable.
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if (P == CurrentBlock) {
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NumWithout = 2;
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break;
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} else if (!DT->isReachableFromEntry(P)) {
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NumWithout = 2;
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break;
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}
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Value* predV = findLeader(P, ValNo);
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if (!predV) {
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predMap.push_back(std::make_pair(static_cast<Value *>(nullptr), P));
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PREPred = P;
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++NumWithout;
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} else if (predV == CurInst) {
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/* CurInst dominates this predecessor. */
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NumWithout = 2;
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break;
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} else {
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predMap.push_back(std::make_pair(predV, P));
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++NumWith;
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}
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}
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// Don't do PRE when it might increase code size, i.e. when
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// we would need to insert instructions in more than one pred.
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if (NumWithout != 1 || NumWith == 0)
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continue;
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// Don't do PRE across indirect branch.
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if (isa<IndirectBrInst>(PREPred->getTerminator()))
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continue;
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// We can't do PRE safely on a critical edge, so instead we schedule
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// the edge to be split and perform the PRE the next time we iterate
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// on the function.
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unsigned SuccNum = GetSuccessorNumber(PREPred, CurrentBlock);
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if (isCriticalEdge(PREPred->getTerminator(), SuccNum)) {
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toSplit.push_back(std::make_pair(PREPred->getTerminator(), SuccNum));
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continue;
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}
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// Instantiate the expression in the predecessor that lacked it.
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// Because we are going top-down through the block, all value numbers
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// will be available in the predecessor by the time we need them. Any
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// that weren't originally present will have been instantiated earlier
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// in this loop.
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Instruction *PREInstr = CurInst->clone();
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bool success = true;
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for (unsigned i = 0, e = CurInst->getNumOperands(); i != e; ++i) {
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Value *Op = PREInstr->getOperand(i);
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if (isa<Argument>(Op) || isa<Constant>(Op) || isa<GlobalValue>(Op))
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continue;
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if (Value *V = findLeader(PREPred, VN.lookup(Op))) {
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PREInstr->setOperand(i, V);
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} else {
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success = false;
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break;
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}
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}
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// Fail out if we encounter an operand that is not available in
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// the PRE predecessor. This is typically because of loads which
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// are not value numbered precisely.
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if (!success) {
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DEBUG(verifyRemoved(PREInstr));
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delete PREInstr;
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continue;
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}
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PREInstr->insertBefore(PREPred->getTerminator());
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PREInstr->setName(CurInst->getName() + ".pre");
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PREInstr->setDebugLoc(CurInst->getDebugLoc());
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VN.add(PREInstr, ValNo);
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++NumGVNPRE;
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// Update the availability map to include the new instruction.
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addToLeaderTable(ValNo, PREInstr, PREPred);
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// Create a PHI to make the value available in this block.
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PHINode* Phi = PHINode::Create(CurInst->getType(), predMap.size(),
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CurInst->getName() + ".pre-phi",
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CurrentBlock->begin());
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for (unsigned i = 0, e = predMap.size(); i != e; ++i) {
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if (Value *V = predMap[i].first)
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Phi->addIncoming(V, predMap[i].second);
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else
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Phi->addIncoming(PREInstr, PREPred);
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}
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VN.add(Phi, ValNo);
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addToLeaderTable(ValNo, Phi, CurrentBlock);
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Phi->setDebugLoc(CurInst->getDebugLoc());
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CurInst->replaceAllUsesWith(Phi);
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if (Phi->getType()->getScalarType()->isPointerTy()) {
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// Because we have added a PHI-use of the pointer value, it has now
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// "escaped" from alias analysis' perspective. We need to inform
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// AA of this.
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for (unsigned ii = 0, ee = Phi->getNumIncomingValues(); ii != ee;
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++ii) {
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unsigned jj = PHINode::getOperandNumForIncomingValue(ii);
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VN.getAliasAnalysis()->addEscapingUse(Phi->getOperandUse(jj));
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}
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if (MD)
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MD->invalidateCachedPointerInfo(Phi);
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}
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VN.erase(CurInst);
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removeFromLeaderTable(ValNo, CurInst, CurrentBlock);
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DEBUG(dbgs() << "GVN PRE removed: " << *CurInst << '\n');
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if (MD) MD->removeInstruction(CurInst);
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DEBUG(verifyRemoved(CurInst));
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CurInst->eraseFromParent();
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Changed = true;
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Changed = performScalarPRE(CurInst);
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}
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}
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@ -2636,25 +2654,21 @@ bool GVN::iterateOnFunction(Function &F) {
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// Top-down walk of the dominator tree
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bool Changed = false;
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#if 0
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// Needed for value numbering with phi construction to work.
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ReversePostOrderTraversal<Function*> RPOT(&F);
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for (ReversePostOrderTraversal<Function*>::rpo_iterator RI = RPOT.begin(),
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RE = RPOT.end(); RI != RE; ++RI)
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Changed |= processBlock(*RI);
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#else
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// Save the blocks this function have before transformation begins. GVN may
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// split critical edge, and hence may invalidate the RPO/DT iterator.
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//
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std::vector<BasicBlock *> BBVect;
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BBVect.reserve(256);
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for (DomTreeNode *X : depth_first(DT->getRootNode()))
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BBVect.push_back(X->getBlock());
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// Needed for value numbering with phi construction to work.
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ReversePostOrderTraversal<Function *> RPOT(&F);
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for (ReversePostOrderTraversal<Function *>::rpo_iterator RI = RPOT.begin(),
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RE = RPOT.end();
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RI != RE; ++RI)
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BBVect.push_back(*RI);
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for (std::vector<BasicBlock *>::iterator I = BBVect.begin(), E = BBVect.end();
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I != E; I++)
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Changed |= processBlock(*I);
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#endif
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return Changed;
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}
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@ -46,12 +46,12 @@ entry:
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br i1 %c, label %if.else, label %if.then
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if.then:
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%t = load i32* %p, !tbaa !4
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%t = load i32* %p, !tbaa !3
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store i32 %t, i32* %q
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ret void
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if.else:
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%u = load i32* %p, !tbaa !3
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%u = load i32* %p, !tbaa !4
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store i32 %u, i32* %q
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ret void
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}
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@ -61,11 +61,11 @@ if.else:
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; CHECK: @watch_out_for_another_type_change
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; CHECK: if.then:
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; CHECK: %t = load i32* %p
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; CHECK: store i32 %t, i32* %q
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; CHECK: store i32 0, i32* %q
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; CHECK: ret void
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; CHECK: if.else:
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; CHECK: store i32 0, i32* %q
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; CHECK: %u = load i32* %p
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; CHECK: store i32 %u, i32* %q
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define void @watch_out_for_another_type_change(i1 %c, i32* %p, i32* %p1, i32* %q) nounwind {
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entry:
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@ -74,12 +74,12 @@ entry:
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br i1 %c, label %if.else, label %if.then
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if.then:
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%t = load i32* %p, !tbaa !3
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%t = load i32* %p, !tbaa !4
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store i32 %t, i32* %q
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ret void
|
||||
|
||||
if.else:
|
||||
%u = load i32* %p, !tbaa !4
|
||||
%u = load i32* %p, !tbaa !3
|
||||
store i32 %u, i32* %q
|
||||
ret void
|
||||
}
|
||||
|
||||
49
test/Transforms/GVN/pre-gep-load.ll
Normal file
49
test/Transforms/GVN/pre-gep-load.ll
Normal file
@ -0,0 +1,49 @@
|
||||
; RUN: opt < %s -basicaa -gvn -enable-load-pre -S | FileCheck %s
|
||||
target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
|
||||
target triple = "aarch64--linux-gnu"
|
||||
|
||||
define double @foo(i32 %stat, i32 %i, double** %p) {
|
||||
; CHECK-LABEL: @foo(
|
||||
entry:
|
||||
switch i32 %stat, label %sw.default [
|
||||
i32 0, label %sw.bb
|
||||
i32 1, label %sw.bb
|
||||
i32 2, label %sw.bb2
|
||||
]
|
||||
|
||||
sw.bb: ; preds = %entry, %entry
|
||||
%idxprom = sext i32 %i to i64
|
||||
%arrayidx = getelementptr inbounds double** %p, i64 0
|
||||
%0 = load double** %arrayidx, align 8
|
||||
%arrayidx1 = getelementptr inbounds double* %0, i64 %idxprom
|
||||
%1 = load double* %arrayidx1, align 8
|
||||
%sub = fsub double %1, 1.000000e+00
|
||||
%cmp = fcmp olt double %sub, 0.000000e+00
|
||||
br i1 %cmp, label %if.then, label %if.end
|
||||
|
||||
if.then: ; preds = %sw.bb
|
||||
br label %return
|
||||
|
||||
if.end: ; preds = %sw.bb
|
||||
br label %sw.bb2
|
||||
|
||||
sw.bb2: ; preds = %if.end, %entry
|
||||
%idxprom3 = sext i32 %i to i64
|
||||
%arrayidx4 = getelementptr inbounds double** %p, i64 0
|
||||
%2 = load double** %arrayidx4, align 8
|
||||
%arrayidx5 = getelementptr inbounds double* %2, i64 %idxprom3
|
||||
%3 = load double* %arrayidx5, align 8
|
||||
; CHECK: sw.bb2:
|
||||
; CHECK-NEXT-NOT: sext
|
||||
; CHECK-NEXT: phi double [
|
||||
; CHECK-NOT: load
|
||||
%sub6 = fsub double 3.000000e+00, %3
|
||||
br label %return
|
||||
|
||||
sw.default: ; preds = %entry
|
||||
br label %return
|
||||
|
||||
return: ; preds = %sw.default, %sw.bb2, %if.then
|
||||
%retval.0 = phi double [ 0.000000e+00, %sw.default ], [ %sub6, %sw.bb2 ], [ %sub, %if.then ]
|
||||
ret double %retval.0
|
||||
}
|
||||
Loading…
Reference in New Issue
Block a user