//===-- 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/Analysis/AliasAnalysis.h" #include "llvm/Analysis/CFG.h" #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/MemoryDependenceAnalysis.h" #include "llvm/IR/Constant.h" #include "llvm/IR/DataLayout.h" #include "llvm/IR/Dominators.h" #include "llvm/IR/Function.h" #include "llvm/IR/Instructions.h" #include "llvm/IR/IntrinsicInst.h" #include "llvm/IR/Type.h" #include "llvm/IR/ValueHandle.h" #include "llvm/Support/ErrorHandling.h" #include "llvm/Transforms/Scalar.h" #include "llvm/Transforms/Utils/Local.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, Pass *P) { if (!isa<PHINode>(BB->begin())) return; AliasAnalysis *AA = nullptr; MemoryDependenceAnalysis *MemDep = nullptr; 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(); } } /// 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, const TargetLibraryInfo *TLI) { // 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, TLI); 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 = nullptr; // 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. if (isa<PHINode>(BB->front())) FoldSingleEntryPHINodes(BB, P); // Delete the unconditional branch from the predecessor... PredBB->getInstList().pop_back(); // Make all PHI nodes that referred to BB now refer to Pred as their // source... BB->replaceAllUsesWith(PredBB); // Move all definitions in the successor to the predecessor... PredBB->getInstList().splice(PredBB->end(), BB->getInstList()); // Inherit predecessors name if it exists. if (!PredBB->hasName()) PredBB->takeName(BB); // Finally, erase the old block and update dominator info. if (P) { if (DominatorTreeWrapperPass *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { DominatorTree &DT = DTWP->getDomTree(); if (DomTreeNode *DTN = DT.getNode(BB)) { DomTreeNode *PredDTN = DT.getNode(PredBB); SmallVector<DomTreeNode*, 8> Children(DTN->begin(), DTN->end()); for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(), DE = Children.end(); DI != DE; ++DI) DT.changeImmediateDominator(*DI, PredDTN); DT.eraseNode(BB); } if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>()) LI->removeBlock(BB); if (MemoryDependenceAnalysis *MD = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>()) MD->invalidateCachedPredecessors(); } } 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() == nullptr && "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); } /// 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. 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 = nullptr; return SplitBlock(Succ, Succ->begin(), P); } // 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) || isa<LandingPadInst>(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 (DominatorTreeWrapperPass *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) { DominatorTree &DT = DTWP->getDomTree(); // Old dominates New. New node dominates all other nodes dominated by Old. if (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); } } return New; } /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA /// analysis information. static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB, ArrayRef<BasicBlock *> Preds, Pass *P, bool &HasLoopExit) { if (!P) return; LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>(); Loop *L = LI ? LI->getLoopFor(OldBB) : nullptr; // If we need to preserve loop analyses, collect some information about how // this split will affect loops. bool IsLoopEntry = !!L; bool SplitMakesNewLoopHeader = false; if (LI) { bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID); for (ArrayRef<BasicBlock*>::iterator i = Preds.begin(), e = Preds.end(); i != e; ++i) { BasicBlock *Pred = *i; // If we need to preserve LCSSA, determine if any of the preds is a loop // exit. if (PreserveLCSSA) if (Loop *PL = LI->getLoopFor(Pred)) if (!PL->contains(OldBB)) HasLoopExit = true; // If we need to preserve LoopInfo, note whether any of the preds crosses // an interesting loop boundary. if (!L) continue; if (L->contains(Pred)) IsLoopEntry = false; else SplitMakesNewLoopHeader = true; } } // Update dominator tree if available. if (DominatorTreeWrapperPass *DTWP = P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) DTWP->getDomTree().splitBlock(NewBB); if (!L) return; 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 = nullptr; for (ArrayRef<BasicBlock*>::iterator i = Preds.begin(), e = Preds.end(); i != e; ++i) { BasicBlock *Pred = *i; if (Loop *PredLoop = LI->getLoopFor(Pred)) { // Seek a loop which actually contains the block being split (to avoid // adjacent loops). while (PredLoop && !PredLoop->contains(OldBB)) PredLoop = PredLoop->getParentLoop(); // Select the most-nested of these loops which contains the block. if (PredLoop && PredLoop->contains(OldBB) && (!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); } } /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming /// from NewBB. This also updates AliasAnalysis, if available. static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB, ArrayRef<BasicBlock*> Preds, BranchInst *BI, Pass *P, bool HasLoopExit) { // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB. AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : nullptr; SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end()); for (BasicBlock::iterator I = OrigBB->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 = nullptr; if (!HasLoopExit) { InVal = PN->getIncomingValueForBlock(Preds[0]); for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { if (!PredSet.count(PN->getIncomingBlock(i))) continue; if (!InVal) InVal = PN->getIncomingValue(i); else if (InVal != PN->getIncomingValue(i)) { InVal = nullptr; 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. // NOTE! This loop walks backwards for a reason! First off, this minimizes // the cost of removal if we end up removing a large number of values, and // second off, this ensures that the indices for the incoming values // aren't invalidated when we remove one. for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) if (PredSet.count(PN->getIncomingBlock(i))) PN->removeIncomingValue(i, false); // Add an incoming value to the PHI node in the loop for the preheader // edge. PN->addIncoming(InVal, NewBB); continue; } // If the values coming into the block are not the same, we need a new // PHI. // Create the new PHI node, insert it into NewBB at the end of the block PHINode *NewPHI = PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI); if (AA) AA->copyValue(PN, NewPHI); // NOTE! This loop walks backwards for a reason! First off, this minimizes // the cost of removal if we end up removing a large number of values, and // second off, this ensures that the indices for the incoming values aren't // invalidated when we remove one. for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) { BasicBlock *IncomingBB = PN->getIncomingBlock(i); if (PredSet.count(IncomingBB)) { Value *V = PN->removeIncomingValue(i, false); NewPHI->addIncoming(V, IncomingBB); } } PN->addIncoming(NewPHI, NewBB); } } /// 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, /// 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, ArrayRef<BasicBlock*> Preds, 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); // Move the edges from Preds to point to NewBB instead of BB. for (unsigned i = 0, e = Preds.size(); i != e; ++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); } // 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 (Preds.size() == 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; } // Update DominatorTree, LoopInfo, and LCCSA analysis information. bool HasLoopExit = false; UpdateAnalysisInformation(BB, NewBB, Preds, P, HasLoopExit); // Update the PHI nodes in BB with the values coming from NewBB. UpdatePHINodes(BB, NewBB, Preds, BI, P, HasLoopExit); return NewBB; } /// SplitLandingPadPredecessors - This method transforms the landing pad, /// OrigBB, by introducing two new basic blocks into the function. One of those /// new basic blocks gets the predecessors listed in Preds. The other basic /// block gets the remaining predecessors of OrigBB. The landingpad instruction /// OrigBB is clone into both of the new basic blocks. The new blocks are given /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector. /// /// 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). /// void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB, ArrayRef<BasicBlock*> Preds, const char *Suffix1, const char *Suffix2, Pass *P, SmallVectorImpl<BasicBlock*> &NewBBs) { assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!"); // Create a new basic block for OrigBB's predecessors listed in Preds. Insert // it right before the original block. BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(), OrigBB->getName() + Suffix1, OrigBB->getParent(), OrigBB); NewBBs.push_back(NewBB1); // The new block unconditionally branches to the old block. BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1); // Move the edges from Preds to point to NewBB1 instead of OrigBB. for (unsigned i = 0, e = Preds.size(); i != e; ++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(OrigBB, NewBB1); } // Update DominatorTree, LoopInfo, and LCCSA analysis information. bool HasLoopExit = false; UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit); // Update the PHI nodes in OrigBB with the values coming from NewBB1. UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit); // Move the remaining edges from OrigBB to point to NewBB2. SmallVector<BasicBlock*, 8> NewBB2Preds; for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB); i != e; ) { BasicBlock *Pred = *i++; if (Pred == NewBB1) continue; assert(!isa<IndirectBrInst>(Pred->getTerminator()) && "Cannot split an edge from an IndirectBrInst"); NewBB2Preds.push_back(Pred); e = pred_end(OrigBB); } BasicBlock *NewBB2 = nullptr; if (!NewBB2Preds.empty()) { // Create another basic block for the rest of OrigBB's predecessors. NewBB2 = BasicBlock::Create(OrigBB->getContext(), OrigBB->getName() + Suffix2, OrigBB->getParent(), OrigBB); NewBBs.push_back(NewBB2); // The new block unconditionally branches to the old block. BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2); // Move the remaining edges from OrigBB to point to NewBB2. for (SmallVectorImpl<BasicBlock*>::iterator i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i) (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2); // Update DominatorTree, LoopInfo, and LCCSA analysis information. HasLoopExit = false; UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit); // Update the PHI nodes in OrigBB with the values coming from NewBB2. UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit); } LandingPadInst *LPad = OrigBB->getLandingPadInst(); Instruction *Clone1 = LPad->clone(); Clone1->setName(Twine("lpad") + Suffix1); NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1); if (NewBB2) { Instruction *Clone2 = LPad->clone(); Clone2->setName(Twine("lpad") + Suffix2); NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2); // Create a PHI node for the two cloned landingpad instructions. PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad); PN->addIncoming(Clone1, NewBB1); PN->addIncoming(Clone2, NewBB2); LPad->replaceAllUsesWith(PN); LPad->eraseFromParent(); } else { // There is no second clone. Just replace the landing pad with the first // clone. LPad->replaceAllUsesWith(Clone1); LPad->eraseFromParent(); } } /// FoldReturnIntoUncondBranch - This method duplicates the specified return /// instruction into a predecessor which ends in an unconditional branch. If /// the return instruction returns a value defined by a PHI, propagate the /// right value into the return. It returns the new return instruction in the /// predecessor. ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB, BasicBlock *Pred) { Instruction *UncondBranch = Pred->getTerminator(); // Clone the return and add it to the end of the predecessor. Instruction *NewRet = RI->clone(); Pred->getInstList().push_back(NewRet); // If the return instruction returns a value, and if the value was a // PHI node in "BB", propagate the right value into the return. for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end(); i != e; ++i) { Value *V = *i; Instruction *NewBC = nullptr; if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) { // Return value might be bitcasted. Clone and insert it before the // return instruction. V = BCI->getOperand(0); NewBC = BCI->clone(); Pred->getInstList().insert(NewRet, NewBC); *i = NewBC; } if (PHINode *PN = dyn_cast<PHINode>(V)) { if (PN->getParent() == BB) { if (NewBC) NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred)); else *i = PN->getIncomingValueForBlock(Pred); } } } // Update any PHI nodes in the returning block to realize that we no // longer branch to them. BB->removePredecessor(Pred); UncondBranch->eraseFromParent(); return cast<ReturnInst>(NewRet); } /// SplitBlockAndInsertIfThen - Split the containing block at the /// specified instruction - everything before and including SplitBefore stays /// in the old basic block, and everything after SplitBefore is moved to a /// new block. The two blocks are connected by a conditional branch /// (with value of Cmp being the condition). /// Before: /// Head /// SplitBefore /// Tail /// After: /// Head /// if (Cond) /// ThenBlock /// SplitBefore /// Tail /// /// If Unreachable is true, then ThenBlock ends with /// UnreachableInst, otherwise it branches to Tail. /// Returns the NewBasicBlock's terminator. TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond, Instruction *SplitBefore, bool Unreachable, MDNode *BranchWeights) { BasicBlock *Head = SplitBefore->getParent(); BasicBlock *Tail = Head->splitBasicBlock(SplitBefore); TerminatorInst *HeadOldTerm = Head->getTerminator(); LLVMContext &C = Head->getContext(); BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); TerminatorInst *CheckTerm; if (Unreachable) CheckTerm = new UnreachableInst(C, ThenBlock); else CheckTerm = BranchInst::Create(Tail, ThenBlock); CheckTerm->setDebugLoc(SplitBefore->getDebugLoc()); BranchInst *HeadNewTerm = BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond); HeadNewTerm->setDebugLoc(SplitBefore->getDebugLoc()); HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights); ReplaceInstWithInst(HeadOldTerm, HeadNewTerm); return CheckTerm; } /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen, /// but also creates the ElseBlock. /// Before: /// Head /// SplitBefore /// Tail /// After: /// Head /// if (Cond) /// ThenBlock /// else /// ElseBlock /// SplitBefore /// Tail void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore, TerminatorInst **ThenTerm, TerminatorInst **ElseTerm, MDNode *BranchWeights) { BasicBlock *Head = SplitBefore->getParent(); BasicBlock *Tail = Head->splitBasicBlock(SplitBefore); TerminatorInst *HeadOldTerm = Head->getTerminator(); LLVMContext &C = Head->getContext(); BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail); *ThenTerm = BranchInst::Create(Tail, ThenBlock); (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc()); *ElseTerm = BranchInst::Create(Tail, ElseBlock); (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc()); BranchInst *HeadNewTerm = BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond); HeadNewTerm->setDebugLoc(SplitBefore->getDebugLoc()); HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights); ReplaceInstWithInst(HeadOldTerm, HeadNewTerm); } /// GetIfCondition - Given a basic block (BB) with two predecessors, /// check to see if the merge at this block is due /// to an "if condition". If so, return the boolean condition that determines /// which entry into BB will be taken. Also, return by references the block /// that will be entered from if the condition is true, and the block that will /// be entered if the condition is false. /// /// This does no checking to see if the true/false blocks have large or unsavory /// instructions in them. Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue, BasicBlock *&IfFalse) { PHINode *SomePHI = dyn_cast<PHINode>(BB->begin()); BasicBlock *Pred1 = nullptr; BasicBlock *Pred2 = nullptr; if (SomePHI) { if (SomePHI->getNumIncomingValues() != 2) return nullptr; Pred1 = SomePHI->getIncomingBlock(0); Pred2 = SomePHI->getIncomingBlock(1); } else { pred_iterator PI = pred_begin(BB), PE = pred_end(BB); if (PI == PE) // No predecessor return nullptr; Pred1 = *PI++; if (PI == PE) // Only one predecessor return nullptr; Pred2 = *PI++; if (PI != PE) // More than two predecessors return nullptr; } // We can only handle branches. Other control flow will be lowered to // branches if possible anyway. BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator()); BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator()); if (!Pred1Br || !Pred2Br) return nullptr; // Eliminate code duplication by ensuring that Pred1Br is conditional if // either are. if (Pred2Br->isConditional()) { // If both branches are conditional, we don't have an "if statement". In // reality, we could transform this case, but since the condition will be // required anyway, we stand no chance of eliminating it, so the xform is // probably not profitable. if (Pred1Br->isConditional()) return nullptr; std::swap(Pred1, Pred2); std::swap(Pred1Br, Pred2Br); } if (Pred1Br->isConditional()) { // The only thing we have to watch out for here is to make sure that Pred2 // doesn't have incoming edges from other blocks. If it does, the condition // doesn't dominate BB. if (!Pred2->getSinglePredecessor()) return nullptr; // If we found a conditional branch predecessor, make sure that it branches // to BB and Pred2Br. If it doesn't, this isn't an "if statement". if (Pred1Br->getSuccessor(0) == BB && Pred1Br->getSuccessor(1) == Pred2) { IfTrue = Pred1; IfFalse = Pred2; } else if (Pred1Br->getSuccessor(0) == Pred2 && Pred1Br->getSuccessor(1) == BB) { IfTrue = Pred2; IfFalse = Pred1; } else { // We know that one arm of the conditional goes to BB, so the other must // go somewhere unrelated, and this must not be an "if statement". return nullptr; } return Pred1Br->getCondition(); } // Ok, if we got here, both predecessors end with an unconditional branch to // BB. Don't panic! If both blocks only have a single (identical) // predecessor, and THAT is a conditional branch, then we're all ok! BasicBlock *CommonPred = Pred1->getSinglePredecessor(); if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor()) return nullptr; // Otherwise, if this is a conditional branch, then we can use it! BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator()); if (!BI) return nullptr; assert(BI->isConditional() && "Two successors but not conditional?"); if (BI->getSuccessor(0) == Pred1) { IfTrue = Pred1; IfFalse = Pred2; } else { IfTrue = Pred2; IfFalse = Pred1; } return BI->getCondition(); }