| //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass performs several transformations to transform natural loops into a |
| // simpler form, which makes subsequent analyses and transformations simpler and |
| // more effective. |
| // |
| // Loop pre-header insertion guarantees that there is a single, non-critical |
| // entry edge from outside of the loop to the loop header. This simplifies a |
| // number of analyses and transformations, such as LICM. |
| // |
| // Loop exit-block insertion guarantees that all exit blocks from the loop |
| // (blocks which are outside of the loop that have predecessors inside of the |
| // loop) only have predecessors from inside of the loop (and are thus dominated |
| // by the loop header). This simplifies transformations such as store-sinking |
| // that are built into LICM. |
| // |
| // This pass also guarantees that loops will have exactly one backedge. |
| // |
| // Note that the simplifycfg pass will clean up blocks which are split out but |
| // end up being unnecessary, so usage of this pass should not pessimize |
| // generated code. |
| // |
| // This pass obviously modifies the CFG, but updates loop information and |
| // dominator information. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Function.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Support/CFG.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/ADT/SetOperations.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| using namespace llvm; |
| |
| namespace { |
| Statistic<> |
| NumInserted("loopsimplify", "Number of pre-header or exit blocks inserted"); |
| Statistic<> |
| NumNested("loopsimplify", "Number of nested loops split out"); |
| |
| struct LoopSimplify : public FunctionPass { |
| virtual bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| // We need loop information to identify the loops... |
| AU.addRequired<LoopInfo>(); |
| AU.addRequired<DominatorSet>(); |
| AU.addRequired<DominatorTree>(); |
| |
| AU.addPreserved<LoopInfo>(); |
| AU.addPreserved<DominatorSet>(); |
| AU.addPreserved<ImmediateDominators>(); |
| AU.addPreserved<DominatorTree>(); |
| AU.addPreserved<DominanceFrontier>(); |
| AU.addPreservedID(BreakCriticalEdgesID); // No crit edges added.... |
| } |
| private: |
| bool ProcessLoop(Loop *L); |
| BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix, |
| const std::vector<BasicBlock*> &Preds); |
| BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit); |
| void InsertPreheaderForLoop(Loop *L); |
| Loop *SeparateNestedLoop(Loop *L); |
| void InsertUniqueBackedgeBlock(Loop *L); |
| |
| void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB, |
| std::vector<BasicBlock*> &PredBlocks); |
| }; |
| |
| RegisterOpt<LoopSimplify> |
| X("loopsimplify", "Canonicalize natural loops", true); |
| } |
| |
| // Publically exposed interface to pass... |
| const PassInfo *llvm::LoopSimplifyID = X.getPassInfo(); |
| Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); } |
| |
| /// runOnFunction - Run down all loops in the CFG (recursively, but we could do |
| /// it in any convenient order) inserting preheaders... |
| /// |
| bool LoopSimplify::runOnFunction(Function &F) { |
| bool Changed = false; |
| LoopInfo &LI = getAnalysis<LoopInfo>(); |
| |
| for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I) |
| Changed |= ProcessLoop(*I); |
| |
| return Changed; |
| } |
| |
| |
| /// ProcessLoop - Walk the loop structure in depth first order, ensuring that |
| /// all loops have preheaders. |
| /// |
| bool LoopSimplify::ProcessLoop(Loop *L) { |
| bool Changed = false; |
| |
| // Check to see that no blocks (other than the header) in the loop have |
| // predecessors that are not in the loop. This is not valid for natural |
| // loops, but can occur if the blocks are unreachable. Since they are |
| // unreachable we can just shamelessly destroy their terminators to make them |
| // not branch into the loop! |
| assert(L->getBlocks()[0] == L->getHeader() && |
| "Header isn't first block in loop?"); |
| for (unsigned i = 1, e = L->getBlocks().size(); i != e; ++i) { |
| BasicBlock *LoopBB = L->getBlocks()[i]; |
| Retry: |
| for (pred_iterator PI = pred_begin(LoopBB), E = pred_end(LoopBB); |
| PI != E; ++PI) |
| if (!L->contains(*PI)) { |
| // This predecessor is not in the loop. Kill its terminator! |
| BasicBlock *DeadBlock = *PI; |
| for (succ_iterator SI = succ_begin(DeadBlock), E = succ_end(DeadBlock); |
| SI != E; ++SI) |
| (*SI)->removePredecessor(DeadBlock); // Remove PHI node entries |
| |
| // Delete the dead terminator. |
| DeadBlock->getInstList().pop_back(); |
| |
| Value *RetVal = 0; |
| if (LoopBB->getParent()->getReturnType() != Type::VoidTy) |
| RetVal = Constant::getNullValue(LoopBB->getParent()->getReturnType()); |
| new ReturnInst(RetVal, DeadBlock); |
| goto Retry; // We just invalidated the pred_iterator. Retry. |
| } |
| } |
| |
| // Does the loop already have a preheader? If so, don't modify the loop... |
| if (L->getLoopPreheader() == 0) { |
| InsertPreheaderForLoop(L); |
| NumInserted++; |
| Changed = true; |
| } |
| |
| // Next, check to make sure that all exit nodes of the loop only have |
| // predecessors that are inside of the loop. This check guarantees that the |
| // loop preheader/header will dominate the exit blocks. If the exit block has |
| // predecessors from outside of the loop, split the edge now. |
| std::vector<BasicBlock*> ExitBlocks; |
| L->getExitBlocks(ExitBlocks); |
| |
| SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end()); |
| for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(), |
| E = ExitBlockSet.end(); I != E; ++I) { |
| BasicBlock *ExitBlock = *I; |
| for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock); |
| PI != PE; ++PI) |
| if (!L->contains(*PI)) { |
| RewriteLoopExitBlock(L, ExitBlock); |
| NumInserted++; |
| Changed = true; |
| break; |
| } |
| } |
| |
| // If the header has more than two predecessors at this point (from the |
| // preheader and from multiple backedges), we must adjust the loop. |
| if (L->getNumBackEdges() != 1) { |
| // If this is really a nested loop, rip it out into a child loop. |
| if (Loop *NL = SeparateNestedLoop(L)) { |
| ++NumNested; |
| // This is a big restructuring change, reprocess the whole loop. |
| ProcessLoop(NL); |
| return true; |
| } |
| |
| InsertUniqueBackedgeBlock(L); |
| NumInserted++; |
| Changed = true; |
| } |
| |
| for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) |
| Changed |= ProcessLoop(*I); |
| return Changed; |
| } |
| |
| /// SplitBlockPredecessors - Split the specified block into two blocks. We want |
| /// to move the predecessors specified in the Preds list to point to the new |
| /// block, leaving the remaining predecessors pointing to BB. This method |
| /// updates the SSA PHINode's, but no other analyses. |
| /// |
| BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB, |
| const char *Suffix, |
| const std::vector<BasicBlock*> &Preds) { |
| |
| // Create new basic block, insert right before the original block... |
| BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB); |
| |
| // The preheader first gets an unconditional branch to the loop header... |
| BranchInst *BI = new BranchInst(BB, NewBB); |
| |
| // For every PHI node in the block, insert a PHI node into NewBB where the |
| // incoming values from the out of loop edges are moved to NewBB. We have two |
| // possible cases here. If the loop is dead, we just insert dummy entries |
| // into the PHI nodes for the new edge. If the loop is not dead, we move the |
| // incoming edges in BB into new PHI nodes in NewBB. |
| // |
| if (!Preds.empty()) { // Is the loop not obviously dead? |
| // Check to see if the values being merged into the new block need PHI |
| // nodes. If so, insert them. |
| for (BasicBlock::iterator I = BB->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ) { |
| ++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, e = Preds.size(); i != e; ++i) |
| if (InVal != PN->getIncomingValueForBlock(Preds[i])) { |
| InVal = 0; |
| break; |
| } |
| |
| // If the values coming into the block are not the same, we need a PHI. |
| if (InVal == 0) { |
| // Create the new PHI node, insert it into NewBB at the end of the block |
| PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI); |
| |
| // Move all of the edges from blocks outside the loop to the new PHI |
| for (unsigned i = 0, e = Preds.size(); i != e; ++i) { |
| Value *V = PN->removeIncomingValue(Preds[i], false); |
| NewPHI->addIncoming(V, Preds[i]); |
| } |
| InVal = NewPHI; |
| } else { |
| // Remove all of the edges coming into the PHI nodes from outside of the |
| // block. |
| for (unsigned i = 0, e = Preds.size(); i != e; ++i) |
| PN->removeIncomingValue(Preds[i], false); |
| } |
| |
| // Add an incoming value to the PHI node in the loop for the preheader |
| // edge. |
| PN->addIncoming(InVal, NewBB); |
| |
| // Can we eliminate this phi node now? |
| if (Value *V = hasConstantValue(PN)) { |
| PN->replaceAllUsesWith(V); |
| BB->getInstList().erase(PN); |
| } |
| } |
| |
| // Now that the PHI nodes are updated, actually move the edges from |
| // Preds to point to NewBB instead of BB. |
| // |
| for (unsigned i = 0, e = Preds.size(); i != e; ++i) { |
| TerminatorInst *TI = Preds[i]->getTerminator(); |
| for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s) |
| if (TI->getSuccessor(s) == BB) |
| TI->setSuccessor(s, NewBB); |
| } |
| |
| } else { // Otherwise the loop is dead... |
| for (BasicBlock::iterator I = BB->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) |
| // Insert dummy values as the incoming value... |
| PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB); |
| } |
| return NewBB; |
| } |
| |
| /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a |
| /// preheader, this method is called to insert one. This method has two phases: |
| /// preheader insertion and analysis updating. |
| /// |
| void LoopSimplify::InsertPreheaderForLoop(Loop *L) { |
| BasicBlock *Header = L->getHeader(); |
| |
| // Compute the set of predecessors of the loop that are not in the loop. |
| std::vector<BasicBlock*> OutsideBlocks; |
| for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header); |
| PI != PE; ++PI) |
| if (!L->contains(*PI)) // Coming in from outside the loop? |
| OutsideBlocks.push_back(*PI); // Keep track of it... |
| |
| // Split out the loop pre-header |
| BasicBlock *NewBB = |
| SplitBlockPredecessors(Header, ".preheader", OutsideBlocks); |
| |
| //===--------------------------------------------------------------------===// |
| // Update analysis results now that we have performed the transformation |
| // |
| |
| // We know that we have loop information to update... update it now. |
| if (Loop *Parent = L->getParentLoop()) |
| Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>()); |
| |
| // If the header for the loop used to be an exit node for another loop, then |
| // we need to update this to know that the loop-preheader is now the exit |
| // node. Note that the only loop that could have our header as an exit node |
| // is a sibling loop, ie, one with the same parent loop, or one if it's |
| // children. |
| // |
| LoopInfo::iterator ParentLoops, ParentLoopsE; |
| if (Loop *Parent = L->getParentLoop()) { |
| ParentLoops = Parent->begin(); |
| ParentLoopsE = Parent->end(); |
| } else { // Must check top-level loops... |
| ParentLoops = getAnalysis<LoopInfo>().begin(); |
| ParentLoopsE = getAnalysis<LoopInfo>().end(); |
| } |
| |
| DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info |
| DominatorTree &DT = getAnalysis<DominatorTree>(); |
| |
| |
| // Update the dominator tree information. |
| // The immediate dominator of the preheader is the immediate dominator of |
| // the old header. |
| DominatorTree::Node *PHDomTreeNode = |
| DT.createNewNode(NewBB, DT.getNode(Header)->getIDom()); |
| |
| // Change the header node so that PNHode is the new immediate dominator |
| DT.changeImmediateDominator(DT.getNode(Header), PHDomTreeNode); |
| |
| { |
| // The blocks that dominate NewBB are the blocks that dominate Header, |
| // minus Header, plus NewBB. |
| DominatorSet::DomSetType DomSet = DS.getDominators(Header); |
| DomSet.erase(Header); // Header does not dominate us... |
| DS.addBasicBlock(NewBB, DomSet); |
| |
| // The newly created basic block dominates all nodes dominated by Header. |
| for (df_iterator<DominatorTree::Node*> DFI = df_begin(PHDomTreeNode), |
| E = df_end(PHDomTreeNode); DFI != E; ++DFI) |
| DS.addDominator((*DFI)->getBlock(), NewBB); |
| } |
| |
| // Update immediate dominator information if we have it... |
| if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) { |
| // Whatever i-dominated the header node now immediately dominates NewBB |
| ID->addNewBlock(NewBB, ID->get(Header)); |
| |
| // The preheader now is the immediate dominator for the header node... |
| ID->setImmediateDominator(Header, NewBB); |
| } |
| |
| // Update dominance frontier information... |
| if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) { |
| // The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates |
| // everything that Header does, and it strictly dominates Header in |
| // addition. |
| assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?"); |
| DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second; |
| NewDFSet.erase(Header); |
| DF->addBasicBlock(NewBB, NewDFSet); |
| |
| // Now we must loop over all of the dominance frontiers in the function, |
| // replacing occurrences of Header with NewBB in some cases. If a block |
| // dominates a (now) predecessor of NewBB, but did not strictly dominate |
| // Header, it will have Header in it's DF set, but should now have NewBB in |
| // its set. |
| for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) { |
| // Get all of the dominators of the predecessor... |
| const DominatorSet::DomSetType &PredDoms = |
| DS.getDominators(OutsideBlocks[i]); |
| for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(), |
| PDE = PredDoms.end(); PDI != PDE; ++PDI) { |
| BasicBlock *PredDom = *PDI; |
| // If the loop header is in DF(PredDom), then PredDom didn't dominate |
| // the header but did dominate a predecessor outside of the loop. Now |
| // we change this entry to include the preheader in the DF instead of |
| // the header. |
| DominanceFrontier::iterator DFI = DF->find(PredDom); |
| assert(DFI != DF->end() && "No dominance frontier for node?"); |
| if (DFI->second.count(Header)) { |
| DF->removeFromFrontier(DFI, Header); |
| DF->addToFrontier(DFI, NewBB); |
| } |
| } |
| } |
| } |
| } |
| |
| /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit |
| /// blocks. This method is used to split exit blocks that have predecessors |
| /// outside of the loop. |
| BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) { |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| |
| std::vector<BasicBlock*> LoopBlocks; |
| for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I) |
| if (L->contains(*I)) |
| LoopBlocks.push_back(*I); |
| |
| assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?"); |
| BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks); |
| |
| // Update Loop Information - we know that the new block will be in the parent |
| // loop of L. |
| if (Loop *Parent = L->getParentLoop()) |
| Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>()); |
| |
| // Update dominator information (set, immdom, domtree, and domfrontier) |
| UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks); |
| return NewBB; |
| } |
| |
| /// AddBlockAndPredsToSet - Add the specified block, and all of its |
| /// predecessors, to the specified set, if it's not already in there. Stop |
| /// predecessor traversal when we reach StopBlock. |
| static void AddBlockAndPredsToSet(BasicBlock *BB, BasicBlock *StopBlock, |
| std::set<BasicBlock*> &Blocks) { |
| if (!Blocks.insert(BB).second) return; // already processed. |
| if (BB == StopBlock) return; // Stop here! |
| |
| for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) |
| AddBlockAndPredsToSet(*I, StopBlock, Blocks); |
| } |
| |
| /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a |
| /// PHI node that tells us how to partition the loops. |
| static PHINode *FindPHIToPartitionLoops(Loop *L) { |
| for (BasicBlock::iterator I = L->getHeader()->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ) { |
| ++I; |
| if (Value *V = hasConstantValue(PN)) { |
| // This is a degenerate PHI already, don't modify it! |
| PN->replaceAllUsesWith(V); |
| PN->getParent()->getInstList().erase(PN); |
| } else { |
| // Scan this PHI node looking for a use of the PHI node by itself. |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) == PN && |
| L->contains(PN->getIncomingBlock(i))) |
| // We found something tasty to remove. |
| return PN; |
| } |
| } |
| return 0; |
| } |
| |
| /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of |
| /// them out into a nested loop. This is important for code that looks like |
| /// this: |
| /// |
| /// Loop: |
| /// ... |
| /// br cond, Loop, Next |
| /// ... |
| /// br cond2, Loop, Out |
| /// |
| /// To identify this common case, we look at the PHI nodes in the header of the |
| /// loop. PHI nodes with unchanging values on one backedge correspond to values |
| /// that change in the "outer" loop, but not in the "inner" loop. |
| /// |
| /// If we are able to separate out a loop, return the new outer loop that was |
| /// created. |
| /// |
| Loop *LoopSimplify::SeparateNestedLoop(Loop *L) { |
| PHINode *PN = FindPHIToPartitionLoops(L); |
| if (PN == 0) return 0; // No known way to partition. |
| |
| // Pull out all predecessors that have varying values in the loop. This |
| // handles the case when a PHI node has multiple instances of itself as |
| // arguments. |
| std::vector<BasicBlock*> OuterLoopPreds; |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| if (PN->getIncomingValue(i) != PN || |
| !L->contains(PN->getIncomingBlock(i))) |
| OuterLoopPreds.push_back(PN->getIncomingBlock(i)); |
| |
| BasicBlock *Header = L->getHeader(); |
| BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds); |
| |
| // Update dominator information (set, immdom, domtree, and domfrontier) |
| UpdateDomInfoForRevectoredPreds(NewBB, OuterLoopPreds); |
| |
| // Create the new outer loop. |
| Loop *NewOuter = new Loop(); |
| |
| LoopInfo &LI = getAnalysis<LoopInfo>(); |
| |
| // Change the parent loop to use the outer loop as its child now. |
| if (Loop *Parent = L->getParentLoop()) |
| Parent->replaceChildLoopWith(L, NewOuter); |
| else |
| LI.changeTopLevelLoop(L, NewOuter); |
| |
| // This block is going to be our new header block: add it to this loop and all |
| // parent loops. |
| NewOuter->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>()); |
| |
| // L is now a subloop of our outer loop. |
| NewOuter->addChildLoop(L); |
| |
| for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i) |
| NewOuter->addBlockEntry(L->getBlocks()[i]); |
| |
| // Determine which blocks should stay in L and which should be moved out to |
| // the Outer loop now. |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| std::set<BasicBlock*> BlocksInL; |
| for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) |
| if (DS.dominates(Header, *PI)) |
| AddBlockAndPredsToSet(*PI, Header, BlocksInL); |
| |
| |
| // Scan all of the loop children of L, moving them to OuterLoop if they are |
| // not part of the inner loop. |
| for (Loop::iterator I = L->begin(); I != L->end(); ) |
| if (BlocksInL.count((*I)->getHeader())) |
| ++I; // Loop remains in L |
| else |
| NewOuter->addChildLoop(L->removeChildLoop(I)); |
| |
| // Now that we know which blocks are in L and which need to be moved to |
| // OuterLoop, move any blocks that need it. |
| for (unsigned i = 0; i != L->getBlocks().size(); ++i) { |
| BasicBlock *BB = L->getBlocks()[i]; |
| if (!BlocksInL.count(BB)) { |
| // Move this block to the parent, updating the exit blocks sets |
| L->removeBlockFromLoop(BB); |
| if (LI[BB] == L) |
| LI.changeLoopFor(BB, NewOuter); |
| --i; |
| } |
| } |
| |
| return NewOuter; |
| } |
| |
| |
| |
| /// InsertUniqueBackedgeBlock - This method is called when the specified loop |
| /// has more than one backedge in it. If this occurs, revector all of these |
| /// backedges to target a new basic block and have that block branch to the loop |
| /// header. This ensures that loops have exactly one backedge. |
| /// |
| void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) { |
| assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!"); |
| |
| // Get information about the loop |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| BasicBlock *Header = L->getHeader(); |
| Function *F = Header->getParent(); |
| |
| // Figure out which basic blocks contain back-edges to the loop header. |
| std::vector<BasicBlock*> BackedgeBlocks; |
| for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I) |
| if (*I != Preheader) BackedgeBlocks.push_back(*I); |
| |
| // Create and insert the new backedge block... |
| BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F); |
| BranchInst *BETerminator = new BranchInst(Header, BEBlock); |
| |
| // Move the new backedge block to right after the last backedge block. |
| Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos; |
| F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock); |
| |
| // Now that the block has been inserted into the function, create PHI nodes in |
| // the backedge block which correspond to any PHI nodes in the header block. |
| for (BasicBlock::iterator I = Header->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
| PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be", |
| BETerminator); |
| NewPN->op_reserve(2*BackedgeBlocks.size()); |
| |
| // Loop over the PHI node, moving all entries except the one for the |
| // preheader over to the new PHI node. |
| unsigned PreheaderIdx = ~0U; |
| bool HasUniqueIncomingValue = true; |
| Value *UniqueValue = 0; |
| for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) { |
| BasicBlock *IBB = PN->getIncomingBlock(i); |
| Value *IV = PN->getIncomingValue(i); |
| if (IBB == Preheader) { |
| PreheaderIdx = i; |
| } else { |
| NewPN->addIncoming(IV, IBB); |
| if (HasUniqueIncomingValue) { |
| if (UniqueValue == 0) |
| UniqueValue = IV; |
| else if (UniqueValue != IV) |
| HasUniqueIncomingValue = false; |
| } |
| } |
| } |
| |
| // Delete all of the incoming values from the old PN except the preheader's |
| assert(PreheaderIdx != ~0U && "PHI has no preheader entry??"); |
| if (PreheaderIdx != 0) { |
| PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx)); |
| PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx)); |
| } |
| PN->op_erase(PN->op_begin()+2, PN->op_end()); |
| |
| // Finally, add the newly constructed PHI node as the entry for the BEBlock. |
| PN->addIncoming(NewPN, BEBlock); |
| |
| // As an optimization, if all incoming values in the new PhiNode (which is a |
| // subset of the incoming values of the old PHI node) have the same value, |
| // eliminate the PHI Node. |
| if (HasUniqueIncomingValue) { |
| NewPN->replaceAllUsesWith(UniqueValue); |
| BEBlock->getInstList().erase(NewPN); |
| } |
| } |
| |
| // Now that all of the PHI nodes have been inserted and adjusted, modify the |
| // backedge blocks to just to the BEBlock instead of the header. |
| for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) { |
| TerminatorInst *TI = BackedgeBlocks[i]->getTerminator(); |
| for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op) |
| if (TI->getSuccessor(Op) == Header) |
| TI->setSuccessor(Op, BEBlock); |
| } |
| |
| //===--- Update all analyses which we must preserve now -----------------===// |
| |
| // Update Loop Information - we know that this block is now in the current |
| // loop and all parent loops. |
| L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>()); |
| |
| // Update dominator information (set, immdom, domtree, and domfrontier) |
| UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks); |
| } |
| |
| /// UpdateDomInfoForRevectoredPreds - This method is used to update the four |
| /// different kinds of dominator information (dominator sets, immediate |
| /// dominators, dominator trees, and dominance frontiers) after a new block has |
| /// been added to the CFG. |
| /// |
| /// This only supports the case when an existing block (known as "NewBBSucc"), |
| /// had some of its predecessors factored into a new basic block. This |
| /// transformation inserts a new basic block ("NewBB"), with a single |
| /// unconditional branch to NewBBSucc, and moves some predecessors of |
| /// "NewBBSucc" to now branch to NewBB. These predecessors are listed in |
| /// PredBlocks, even though they are the same as |
| /// pred_begin(NewBB)/pred_end(NewBB). |
| /// |
| void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB, |
| std::vector<BasicBlock*> &PredBlocks) { |
| assert(!PredBlocks.empty() && "No predblocks??"); |
| assert(succ_begin(NewBB) != succ_end(NewBB) && |
| ++succ_begin(NewBB) == succ_end(NewBB) && |
| "NewBB should have a single successor!"); |
| BasicBlock *NewBBSucc = *succ_begin(NewBB); |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| |
| // Update dominator information... The blocks that dominate NewBB are the |
| // intersection of the dominators of predecessors, plus the block itself. |
| // |
| DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]); |
| for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i) |
| set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i])); |
| NewBBDomSet.insert(NewBB); // All blocks dominate themselves... |
| DS.addBasicBlock(NewBB, NewBBDomSet); |
| |
| // The newly inserted basic block will dominate existing basic blocks iff the |
| // PredBlocks dominate all of the non-pred blocks. If all predblocks dominate |
| // the non-pred blocks, then they all must be the same block! |
| // |
| bool NewBBDominatesNewBBSucc = true; |
| { |
| BasicBlock *OnePred = PredBlocks[0]; |
| for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i) |
| if (PredBlocks[i] != OnePred) { |
| NewBBDominatesNewBBSucc = false; |
| break; |
| } |
| |
| if (NewBBDominatesNewBBSucc) |
| for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc); |
| PI != E; ++PI) |
| if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) { |
| NewBBDominatesNewBBSucc = false; |
| break; |
| } |
| } |
| |
| // The other scenario where the new block can dominate its successors are when |
| // all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc |
| // already. |
| if (!NewBBDominatesNewBBSucc) { |
| NewBBDominatesNewBBSucc = true; |
| for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc); |
| PI != E; ++PI) |
| if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) { |
| NewBBDominatesNewBBSucc = false; |
| break; |
| } |
| } |
| |
| // If NewBB dominates some blocks, then it will dominate all blocks that |
| // NewBBSucc does. |
| if (NewBBDominatesNewBBSucc) { |
| BasicBlock *PredBlock = PredBlocks[0]; |
| Function *F = NewBB->getParent(); |
| for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) |
| if (DS.dominates(NewBBSucc, I)) |
| DS.addDominator(I, NewBB); |
| } |
| |
| // Update immediate dominator information if we have it... |
| BasicBlock *NewBBIDom = 0; |
| if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) { |
| // To find the immediate dominator of the new exit node, we trace up the |
| // immediate dominators of a predecessor until we find a basic block that |
| // dominates the exit block. |
| // |
| BasicBlock *Dom = PredBlocks[0]; // Some random predecessor... |
| while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator... |
| assert(Dom != 0 && "No shared dominator found???"); |
| Dom = ID->get(Dom); |
| } |
| |
| // Set the immediate dominator now... |
| ID->addNewBlock(NewBB, Dom); |
| NewBBIDom = Dom; // Reuse this if calculating DominatorTree info... |
| |
| // If NewBB strictly dominates other blocks, we need to update their idom's |
| // now. The only block that need adjustment is the NewBBSucc block, whose |
| // idom should currently be set to PredBlocks[0]. |
| if (NewBBDominatesNewBBSucc) |
| ID->setImmediateDominator(NewBBSucc, NewBB); |
| } |
| |
| // Update DominatorTree information if it is active. |
| if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) { |
| // If we don't have ImmediateDominator info around, calculate the idom as |
| // above. |
| DominatorTree::Node *NewBBIDomNode; |
| if (NewBBIDom) { |
| NewBBIDomNode = DT->getNode(NewBBIDom); |
| } else { |
| NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred |
| while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) { |
| NewBBIDomNode = NewBBIDomNode->getIDom(); |
| assert(NewBBIDomNode && "No shared dominator found??"); |
| } |
| } |
| |
| // Create the new dominator tree node... and set the idom of NewBB. |
| DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode); |
| |
| // If NewBB strictly dominates other blocks, then it is now the immediate |
| // dominator of NewBBSucc. Update the dominator tree as appropriate. |
| if (NewBBDominatesNewBBSucc) { |
| DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc); |
| DT->changeImmediateDominator(NewBBSuccNode, NewBBNode); |
| } |
| } |
| |
| // Update dominance frontier information... |
| if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) { |
| // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the |
| // DF(PredBlocks[0]) without the stuff that the new block does not dominate |
| // a predecessor of. |
| if (NewBBDominatesNewBBSucc) { |
| DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]); |
| if (DFI != DF->end()) { |
| DominanceFrontier::DomSetType Set = DFI->second; |
| // Filter out stuff in Set that we do not dominate a predecessor of. |
| for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(), |
| E = Set.end(); SetI != E;) { |
| bool DominatesPred = false; |
| for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI); |
| PI != E; ++PI) |
| if (DS.dominates(NewBB, *PI)) |
| DominatesPred = true; |
| if (!DominatesPred) |
| Set.erase(SetI++); |
| else |
| ++SetI; |
| } |
| |
| DF->addBasicBlock(NewBB, Set); |
| } |
| |
| } else { |
| // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate |
| // NewBBSucc, but it does dominate itself (and there is an edge (NewBB -> |
| // NewBBSucc)). NewBBSucc is the single successor of NewBB. |
| DominanceFrontier::DomSetType NewDFSet; |
| NewDFSet.insert(NewBBSucc); |
| DF->addBasicBlock(NewBB, NewDFSet); |
| } |
| |
| // Now we must loop over all of the dominance frontiers in the function, |
| // replacing occurrences of NewBBSucc with NewBB in some cases. All |
| // blocks that dominate a block in PredBlocks and contained NewBBSucc in |
| // their dominance frontier must be updated to contain NewBB instead. |
| // |
| for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) { |
| BasicBlock *Pred = PredBlocks[i]; |
| // Get all of the dominators of the predecessor... |
| const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred); |
| for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(), |
| PDE = PredDoms.end(); PDI != PDE; ++PDI) { |
| BasicBlock *PredDom = *PDI; |
| |
| // If the NewBBSucc node is in DF(PredDom), then PredDom didn't |
| // dominate NewBBSucc but did dominate a predecessor of it. Now we |
| // change this entry to include NewBB in the DF instead of NewBBSucc. |
| DominanceFrontier::iterator DFI = DF->find(PredDom); |
| assert(DFI != DF->end() && "No dominance frontier for node?"); |
| if (DFI->second.count(NewBBSucc)) { |
| // If NewBBSucc should not stay in our dominator frontier, remove it. |
| // We remove it unless there is a predecessor of NewBBSucc that we |
| // dominate, but we don't strictly dominate NewBBSucc. |
| bool ShouldRemove = true; |
| if (PredDom == NewBBSucc || !DS.dominates(PredDom, NewBBSucc)) { |
| // Okay, we know that PredDom does not strictly dominate NewBBSucc. |
| // Check to see if it dominates any predecessors of NewBBSucc. |
| for (pred_iterator PI = pred_begin(NewBBSucc), |
| E = pred_end(NewBBSucc); PI != E; ++PI) |
| if (DS.dominates(PredDom, *PI)) { |
| ShouldRemove = false; |
| break; |
| } |
| } |
| |
| if (ShouldRemove) |
| DF->removeFromFrontier(DFI, NewBBSucc); |
| DF->addToFrontier(DFI, NewBB); |
| } |
| } |
| } |
| } |
| } |
| |