/// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are /// any single-entry PHI nodes in it, fold them away. This handles the case /// when all entries to the PHI nodes in a block are guaranteed equal, such as /// when the block has exactly one predecessor. void llvm::FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P) { if (!isa<PHINode>(BB->begin())) return; AliasAnalysis *AA = 0; MemoryDependenceAnalysis *MemDep = 0; if (P) { AA = P->getAnalysisIfAvailable<AliasAnalysis>(); MemDep = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>(); } while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { if (PN->getIncomingValue(0) != PN) PN->replaceAllUsesWith(PN->getIncomingValue(0)); else PN->replaceAllUsesWith(UndefValue::get(PN->getType())); if (MemDep) MemDep->removeInstruction(PN); // Memdep updates AA itself. else if (AA && isa<PointerType>(PN->getType())) AA->deleteValue(PN); PN->eraseFromParent(); } }
/// SplitBlockPredecessors - This method transforms BB by introducing a new /// basic block into the function, and moving some of the predecessors of BB to /// be predecessors of the new block. The new predecessors are indicated by the /// Preds array, which has NumPreds elements in it. The new block is given a /// suffix of 'Suffix'. /// /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree and /// DominanceFrontier, but no other analyses. BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB, BasicBlock *const *Preds, unsigned NumPreds, const char *Suffix, Pass *P) { // Create new basic block, insert right before the original block. BasicBlock *NewBB = BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB); // The new block unconditionally branches to the old block. BranchInst *BI = BranchInst::Create(BB, NewBB); // Move the edges from Preds to point to NewBB instead of BB. for (unsigned i = 0; i != NumPreds; ++i) Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); // Update dominator tree and dominator frontier if available. DominatorTree *DT = P ? P->getAnalysisIfAvailable<DominatorTree>() : 0; if (DT) DT->splitBlock(NewBB); if (DominanceFrontier *DF = P ? P->getAnalysisIfAvailable<DominanceFrontier>():0) DF->splitBlock(NewBB); AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI // node becomes an incoming value for BB's phi node. However, if the Preds // list is empty, we need to insert dummy entries into the PHI nodes in BB to // account for the newly created predecessor. if (NumPreds == 0) { // Insert dummy values as the incoming value. for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB); return NewBB; } // Otherwise, create a new PHI node in NewBB for each PHI node in BB. for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) { PHINode *PN = cast<PHINode>(I++); // Check to see if all of the values coming in are the same. If so, we // don't need to create a new PHI node. Value *InVal = PN->getIncomingValueForBlock(Preds[0]); for (unsigned i = 1; i != NumPreds; ++i) if (InVal != PN->getIncomingValueForBlock(Preds[i])) { InVal = 0; break; } if (InVal) { // If all incoming values for the new PHI would be the same, just don't // make a new PHI. Instead, just remove the incoming values from the old // PHI. for (unsigned i = 0; i != NumPreds; ++i) PN->removeIncomingValue(Preds[i], false); } else { // If the values coming into the block are not the same, we need a PHI. // Create the new PHI node, insert it into NewBB at the end of the block PHINode *NewPHI = PHINode::Create(PN->getType(), PN->getName()+".ph", BI); if (AA) AA->copyValue(PN, NewPHI); // Move all of the PHI values for 'Preds' to the new PHI. for (unsigned i = 0; i != NumPreds; ++i) { Value *V = PN->removeIncomingValue(Preds[i], false); NewPHI->addIncoming(V, Preds[i]); } InVal = NewPHI; } // Add an incoming value to the PHI node in the loop for the preheader // edge. PN->addIncoming(InVal, NewBB); // Check to see if we can eliminate this phi node. if (Value *V = PN->hasConstantValue(DT != 0)) { Instruction *I = dyn_cast<Instruction>(V); if (!I || DT == 0 || DT->dominates(I, PN)) { PN->replaceAllUsesWith(V); if (AA) AA->deleteValue(PN); PN->eraseFromParent(); } } } return NewBB; }