| //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This family of functions perform manipulations on basic blocks, and |
| // instructions contained within basic blocks. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Function.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/IntrinsicInst.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Target/TargetData.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Support/ErrorHandling.h" |
| #include "llvm/Support/ValueHandle.h" |
| #include <algorithm> |
| using namespace llvm; |
| |
| /// DeleteDeadBlock - Delete the specified block, which must have no |
| /// predecessors. |
| void llvm::DeleteDeadBlock(BasicBlock *BB) { |
| assert((pred_begin(BB) == pred_end(BB) || |
| // Can delete self loop. |
| BB->getSinglePredecessor() == BB) && "Block is not dead!"); |
| TerminatorInst *BBTerm = BB->getTerminator(); |
| |
| // Loop through all of our successors and make sure they know that one |
| // of their predecessors is going away. |
| for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i) |
| BBTerm->getSuccessor(i)->removePredecessor(BB); |
| |
| // Zap all the instructions in the block. |
| while (!BB->empty()) { |
| Instruction &I = BB->back(); |
| // If this instruction is used, replace uses with an arbitrary value. |
| // Because control flow can't get here, we don't care what we replace the |
| // value with. Note that since this block is unreachable, and all values |
| // contained within it must dominate their uses, that all uses will |
| // eventually be removed (they are themselves dead). |
| if (!I.use_empty()) |
| I.replaceAllUsesWith(UndefValue::get(I.getType())); |
| BB->getInstList().pop_back(); |
| } |
| |
| // Zap the block! |
| BB->eraseFromParent(); |
| } |
| |
| /// 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) { |
| 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())); |
| PN->eraseFromParent(); |
| } |
| } |
| |
| |
| /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it |
| /// is dead. Also recursively delete any operands that become dead as |
| /// a result. This includes tracing the def-use list from the PHI to see if |
| /// it is ultimately unused or if it reaches an unused cycle. |
| bool llvm::DeleteDeadPHIs(BasicBlock *BB) { |
| // Recursively deleting a PHI may cause multiple PHIs to be deleted |
| // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete. |
| SmallVector<WeakVH, 8> PHIs; |
| for (BasicBlock::iterator I = BB->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) |
| PHIs.push_back(PN); |
| |
| bool Changed = false; |
| for (unsigned i = 0, e = PHIs.size(); i != e; ++i) |
| if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*())) |
| Changed |= RecursivelyDeleteDeadPHINode(PN); |
| |
| return Changed; |
| } |
| |
| /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor, |
| /// if possible. The return value indicates success or failure. |
| bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) { |
| // Don't merge away blocks who have their address taken. |
| if (BB->hasAddressTaken()) return false; |
| |
| // Can't merge if there are multiple predecessors, or no predecessors. |
| BasicBlock *PredBB = BB->getUniquePredecessor(); |
| if (!PredBB) return false; |
| |
| // Don't break self-loops. |
| if (PredBB == BB) return false; |
| // Don't break invokes. |
| if (isa<InvokeInst>(PredBB->getTerminator())) return false; |
| |
| succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB)); |
| BasicBlock* OnlySucc = BB; |
| for (; SI != SE; ++SI) |
| if (*SI != OnlySucc) { |
| OnlySucc = 0; // There are multiple distinct successors! |
| break; |
| } |
| |
| // Can't merge if there are multiple successors. |
| if (!OnlySucc) return false; |
| |
| // Can't merge if there is PHI loop. |
| for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) { |
| if (PHINode *PN = dyn_cast<PHINode>(BI)) { |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) == PN) |
| return false; |
| } else |
| break; |
| } |
| |
| // Begin by getting rid of unneeded PHIs. |
| while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { |
| PN->replaceAllUsesWith(PN->getIncomingValue(0)); |
| BB->getInstList().pop_front(); // Delete the phi node... |
| } |
| |
| // Delete the unconditional branch from the predecessor... |
| PredBB->getInstList().pop_back(); |
| |
| // Move all definitions in the successor to the predecessor... |
| PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); |
| |
| // Make all PHI nodes that referred to BB now refer to Pred as their |
| // source... |
| BB->replaceAllUsesWith(PredBB); |
| |
| // Inherit predecessors name if it exists. |
| if (!PredBB->hasName()) |
| PredBB->takeName(BB); |
| |
| // Finally, erase the old block and update dominator info. |
| if (P) { |
| if (DominatorTree* DT = P->getAnalysisIfAvailable<DominatorTree>()) { |
| DomTreeNode* DTN = DT->getNode(BB); |
| DomTreeNode* PredDTN = DT->getNode(PredBB); |
| |
| if (DTN) { |
| SmallPtrSet<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); |
| for (SmallPtrSet<DomTreeNode*, 8>::iterator DI = Children.begin(), |
| DE = Children.end(); DI != DE; ++DI) |
| DT->changeImmediateDominator(*DI, PredDTN); |
| |
| DT->eraseNode(BB); |
| } |
| } |
| } |
| |
| BB->eraseFromParent(); |
| |
| |
| return true; |
| } |
| |
| /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI) |
| /// with a value, then remove and delete the original instruction. |
| /// |
| void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL, |
| BasicBlock::iterator &BI, Value *V) { |
| Instruction &I = *BI; |
| // Replaces all of the uses of the instruction with uses of the value |
| I.replaceAllUsesWith(V); |
| |
| // Make sure to propagate a name if there is one already. |
| if (I.hasName() && !V->hasName()) |
| V->takeName(&I); |
| |
| // Delete the unnecessary instruction now... |
| BI = BIL.erase(BI); |
| } |
| |
| |
| /// ReplaceInstWithInst - Replace the instruction specified by BI with the |
| /// instruction specified by I. The original instruction is deleted and BI is |
| /// updated to point to the new instruction. |
| /// |
| void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL, |
| BasicBlock::iterator &BI, Instruction *I) { |
| assert(I->getParent() == 0 && |
| "ReplaceInstWithInst: Instruction already inserted into basic block!"); |
| |
| // Insert the new instruction into the basic block... |
| BasicBlock::iterator New = BIL.insert(BI, I); |
| |
| // Replace all uses of the old instruction, and delete it. |
| ReplaceInstWithValue(BIL, BI, I); |
| |
| // Move BI back to point to the newly inserted instruction |
| BI = New; |
| } |
| |
| /// ReplaceInstWithInst - Replace the instruction specified by From with the |
| /// instruction specified by To. |
| /// |
| void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) { |
| BasicBlock::iterator BI(From); |
| ReplaceInstWithInst(From->getParent()->getInstList(), BI, To); |
| } |
| |
| /// RemoveSuccessor - Change the specified terminator instruction such that its |
| /// successor SuccNum no longer exists. Because this reduces the outgoing |
| /// degree of the current basic block, the actual terminator instruction itself |
| /// may have to be changed. In the case where the last successor of the block |
| /// is deleted, a return instruction is inserted in its place which can cause a |
| /// surprising change in program behavior if it is not expected. |
| /// |
| void llvm::RemoveSuccessor(TerminatorInst *TI, unsigned SuccNum) { |
| assert(SuccNum < TI->getNumSuccessors() && |
| "Trying to remove a nonexistant successor!"); |
| |
| // If our old successor block contains any PHI nodes, remove the entry in the |
| // PHI nodes that comes from this branch... |
| // |
| BasicBlock *BB = TI->getParent(); |
| TI->getSuccessor(SuccNum)->removePredecessor(BB); |
| |
| TerminatorInst *NewTI = 0; |
| switch (TI->getOpcode()) { |
| case Instruction::Br: |
| // If this is a conditional branch... convert to unconditional branch. |
| if (TI->getNumSuccessors() == 2) { |
| cast<BranchInst>(TI)->setUnconditionalDest(TI->getSuccessor(1-SuccNum)); |
| } else { // Otherwise convert to a return instruction... |
| Value *RetVal = 0; |
| |
| // Create a value to return... if the function doesn't return null... |
| if (!BB->getParent()->getReturnType()->isVoidTy()) |
| RetVal = Constant::getNullValue(BB->getParent()->getReturnType()); |
| |
| // Create the return... |
| NewTI = ReturnInst::Create(TI->getContext(), RetVal); |
| } |
| break; |
| |
| case Instruction::Invoke: // Should convert to call |
| case Instruction::Switch: // Should remove entry |
| default: |
| case Instruction::Ret: // Cannot happen, has no successors! |
| llvm_unreachable("Unhandled terminator inst type in RemoveSuccessor!"); |
| } |
| |
| if (NewTI) // If it's a different instruction, replace. |
| ReplaceInstWithInst(TI, NewTI); |
| } |
| |
| /// GetSuccessorNumber - Search for the specified successor of basic block BB |
| /// and return its position in the terminator instruction's list of |
| /// successors. It is an error to call this with a block that is not a |
| /// successor. |
| unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) { |
| TerminatorInst *Term = BB->getTerminator(); |
| #ifndef NDEBUG |
| unsigned e = Term->getNumSuccessors(); |
| #endif |
| for (unsigned i = 0; ; ++i) { |
| assert(i != e && "Didn't find edge?"); |
| if (Term->getSuccessor(i) == Succ) |
| return i; |
| } |
| return 0; |
| } |
| |
| /// SplitEdge - Split the edge connecting specified block. Pass P must |
| /// not be NULL. |
| BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) { |
| unsigned SuccNum = GetSuccessorNumber(BB, Succ); |
| |
| // If this is a critical edge, let SplitCriticalEdge do it. |
| TerminatorInst *LatchTerm = BB->getTerminator(); |
| if (SplitCriticalEdge(LatchTerm, SuccNum, P)) |
| return LatchTerm->getSuccessor(SuccNum); |
| |
| // If the edge isn't critical, then BB has a single successor or Succ has a |
| // single pred. Split the block. |
| BasicBlock::iterator SplitPoint; |
| if (BasicBlock *SP = Succ->getSinglePredecessor()) { |
| // If the successor only has a single pred, split the top of the successor |
| // block. |
| assert(SP == BB && "CFG broken"); |
| SP = NULL; |
| return SplitBlock(Succ, Succ->begin(), P); |
| } else { |
| // Otherwise, if BB has a single successor, split it at the bottom of the |
| // block. |
| assert(BB->getTerminator()->getNumSuccessors() == 1 && |
| "Should have a single succ!"); |
| return SplitBlock(BB, BB->getTerminator(), P); |
| } |
| } |
| |
| /// SplitBlock - Split the specified block at the specified instruction - every |
| /// thing before SplitPt stays in Old and everything starting with SplitPt moves |
| /// to a new block. The two blocks are joined by an unconditional branch and |
| /// the loop info is updated. |
| /// |
| BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) { |
| BasicBlock::iterator SplitIt = SplitPt; |
| while (isa<PHINode>(SplitIt)) |
| ++SplitIt; |
| BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split"); |
| |
| // The new block lives in whichever loop the old one did. This preserves |
| // LCSSA as well, because we force the split point to be after any PHI nodes. |
| if (LoopInfo* LI = P->getAnalysisIfAvailable<LoopInfo>()) |
| if (Loop *L = LI->getLoopFor(Old)) |
| L->addBasicBlockToLoop(New, LI->getBase()); |
| |
| if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) { |
| // Old dominates New. New node domiantes all other nodes dominated by Old. |
| DomTreeNode *OldNode = DT->getNode(Old); |
| std::vector<DomTreeNode *> Children; |
| for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end(); |
| I != E; ++I) |
| Children.push_back(*I); |
| |
| DomTreeNode *NewNode = DT->addNewBlock(New,Old); |
| for (std::vector<DomTreeNode *>::iterator I = Children.begin(), |
| E = Children.end(); I != E; ++I) |
| DT->changeImmediateDominator(*I, NewNode); |
| } |
| |
| if (DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>()) |
| DF->splitBlock(Old); |
| |
| return New; |
| } |
| |
| |
| /// 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, |
| /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. |
| /// In particular, it does not preserve LoopSimplify (because it's |
| /// complicated to handle the case where one of the edges being split |
| /// is an exit of a loop with other exits). |
| /// |
| 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->getContext(), BB->getName()+Suffix, |
| BB->getParent(), BB); |
| |
| // The new block unconditionally branches to the old block. |
| BranchInst *BI = BranchInst::Create(BB, NewBB); |
| |
| LoopInfo *LI = P ? P->getAnalysisIfAvailable<LoopInfo>() : 0; |
| Loop *L = LI ? LI->getLoopFor(BB) : 0; |
| bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); |
| |
| // Move the edges from Preds to point to NewBB instead of BB. |
| // While here, if we need to preserve loop analyses, collect |
| // some information about how this split will affect loops. |
| bool HasLoopExit = false; |
| bool IsLoopEntry = !!L; |
| bool SplitMakesNewLoopHeader = false; |
| for (unsigned i = 0; i != NumPreds; ++i) { |
| // This is slightly more strict than necessary; the minimum requirement |
| // is that there be no more than one indirectbr branching to BB. And |
| // all BlockAddress uses would need to be updated. |
| assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) && |
| "Cannot split an edge from an IndirectBrInst"); |
| |
| Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB); |
| |
| if (LI) { |
| // If we need to preserve LCSSA, determine if any of |
| // the preds is a loop exit. |
| if (PreserveLCSSA) |
| if (Loop *PL = LI->getLoopFor(Preds[i])) |
| if (!PL->contains(BB)) |
| HasLoopExit = true; |
| // If we need to preserve LoopInfo, note whether any of the |
| // preds crosses an interesting loop boundary. |
| if (L) { |
| if (L->contains(Preds[i])) |
| IsLoopEntry = false; |
| else |
| SplitMakesNewLoopHeader = true; |
| } |
| } |
| } |
| |
| // 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); |
| |
| // 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; |
| } |
| |
| AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0; |
| |
| if (L) { |
| if (IsLoopEntry) { |
| // Add the new block to the nearest enclosing loop (and not an |
| // adjacent loop). To find this, examine each of the predecessors and |
| // determine which loops enclose them, and select the most-nested loop |
| // which contains the loop containing the block being split. |
| Loop *InnermostPredLoop = 0; |
| for (unsigned i = 0; i != NumPreds; ++i) |
| if (Loop *PredLoop = LI->getLoopFor(Preds[i])) { |
| // Seek a loop which actually contains the block being split (to |
| // avoid adjacent loops). |
| while (PredLoop && !PredLoop->contains(BB)) |
| PredLoop = PredLoop->getParentLoop(); |
| // Select the most-nested of these loops which contains the block. |
| if (PredLoop && |
| PredLoop->contains(BB) && |
| (!InnermostPredLoop || |
| InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth())) |
| InnermostPredLoop = PredLoop; |
| } |
| if (InnermostPredLoop) |
| InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase()); |
| } else { |
| L->addBasicBlockToLoop(NewBB, LI->getBase()); |
| if (SplitMakesNewLoopHeader) |
| L->moveToHeader(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, unless it's needed for LCSSA. |
| Value *InVal = 0; |
| if (!HasLoopExit) { |
| 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); |
| } |
| |
| return NewBB; |
| } |
| |
| /// FindFunctionBackedges - Analyze the specified function to find all of the |
| /// loop backedges in the function and return them. This is a relatively cheap |
| /// (compared to computing dominators and loop info) analysis. |
| /// |
| /// The output is added to Result, as pairs of <from,to> edge info. |
| void llvm::FindFunctionBackedges(const Function &F, |
| SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) { |
| const BasicBlock *BB = &F.getEntryBlock(); |
| if (succ_begin(BB) == succ_end(BB)) |
| return; |
| |
| SmallPtrSet<const BasicBlock*, 8> Visited; |
| SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack; |
| SmallPtrSet<const BasicBlock*, 8> InStack; |
| |
| Visited.insert(BB); |
| VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); |
| InStack.insert(BB); |
| do { |
| std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back(); |
| const BasicBlock *ParentBB = Top.first; |
| succ_const_iterator &I = Top.second; |
| |
| bool FoundNew = false; |
| while (I != succ_end(ParentBB)) { |
| BB = *I++; |
| if (Visited.insert(BB)) { |
| FoundNew = true; |
| break; |
| } |
| // Successor is in VisitStack, it's a back edge. |
| if (InStack.count(BB)) |
| Result.push_back(std::make_pair(ParentBB, BB)); |
| } |
| |
| if (FoundNew) { |
| // Go down one level if there is a unvisited successor. |
| InStack.insert(BB); |
| VisitStack.push_back(std::make_pair(BB, succ_begin(BB))); |
| } else { |
| // Go up one level. |
| InStack.erase(VisitStack.pop_back_val().first); |
| } |
| } while (!VisitStack.empty()); |
| |
| |
| } |