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Diffstat (limited to 'lib/Transforms/Utils/LoopSimplify.cpp')
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1 files changed, 855 insertions, 0 deletions
diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp new file mode 100644 index 0000000000..2df10ce92f --- /dev/null +++ b/lib/Transforms/Utils/LoopSimplify.cpp @@ -0,0 +1,855 @@ +//===- 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/AliasAnalysis.h" +#include "llvm/Analysis/Dominators.h" +#include "llvm/Analysis/LoopInfo.h" +#include "llvm/Support/CFG.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 { + // AA - If we have an alias analysis object to update, this is it, otherwise + // this is null. + AliasAnalysis *AA; + + 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 critical 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(); +FunctionPass *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>(); + AA = getAnalysisToUpdate<AliasAnalysis>(); + + 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. + if (AA) AA->deleteValue(&DeadBlock->back()); + 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; + } + + // Scan over the PHI nodes in the loop header. Since they now have only two + // incoming values (the loop is canonicalized), we may have simplified the PHI + // down to 'X = phi [X, Y]', which should be replaced with 'Y'. + PHINode *PN; + DominatorSet &DS = getAnalysis<DominatorSet>(); + for (BasicBlock::iterator I = L->getHeader()->begin(); + (PN = dyn_cast<PHINode>(I++)); ) + if (Value *V = PN->hasConstantValue()) { + PN->replaceAllUsesWith(V); + PN->eraseFromParent(); + } + + 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(); isa<PHINode>(I); ) { + PHINode *PN = 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); + if (AA) AA->copyValue(PN, NewPHI); + + // 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 = PN->hasConstantValue(true)) { + if (!isa<Instruction>(V) || + getAnalysis<DominatorSet>().dominates(cast<Instruction>(V), PN)) { + PN->replaceAllUsesWith(V); + if (AA) AA->deleteValue(PN); + 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(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(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>()); + + 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, DominatorSet &DS, + AliasAnalysis *AA) { + for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) { + PHINode *PN = cast<PHINode>(I); + ++I; + if (Value *V = PN->hasConstantValue()) + if (!isa<Instruction>(V) || DS.dominates(cast<Instruction>(V), PN)) { + // This is a degenerate PHI already, don't modify it! + PN->replaceAllUsesWith(V); + if (AA) AA->deleteValue(PN); + PN->eraseFromParent(); + continue; + } + + // 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, getAnalysis<DominatorSet>(), AA); + 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(); isa<PHINode>(I); ++I) { + PHINode *PN = cast<PHINode>(I); + PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be", + BETerminator); + NewPN->reserveOperandSpace(BackedgeBlocks.size()); + if (AA) AA->copyValue(PN, NewPN); + + // 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)); + } + // Nuke all entries except the zero'th. + for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i) + PN->removeIncomingValue(e-i, false); + + // 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); + if (AA) AA->deleteValue(NewPN); + 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); + } + } + } + } +} + |