| //===- 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) are 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/Analysis/Dominators.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Function.h" |
| #include "llvm/iTerminators.h" |
| #include "llvm/iPHINode.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Support/CFG.h" |
| #include "Support/SetOperations.h" |
| #include "Support/Statistic.h" |
| #include "Support/DepthFirstIterator.h" |
| |
| namespace llvm { |
| |
| namespace { |
| Statistic<> |
| NumInserted("loopsimplify", "Number of pre-header blocks inserted"); |
| |
| 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.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); |
| void RewriteLoopExitBlock(Loop *L, BasicBlock *Exit); |
| void InsertPreheaderForLoop(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 *LoopSimplifyID = X.getPassInfo(); |
| Pass *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 (unsigned i = 0, e = LI.getTopLevelLoops().size(); i != e; ++i) |
| Changed |= ProcessLoop(LI.getTopLevelLoops()[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; |
| |
| // Does the loop already have a preheader? If so, don't modify the loop... |
| if (L->getLoopPreheader() == 0) { |
| InsertPreheaderForLoop(L); |
| NumInserted++; |
| Changed = true; |
| } |
| |
| // Regardless of whether or not we added a preheader to the loop we must |
| // guarantee that the preheader dominates all exit nodes. If there are any |
| // exit nodes not dominated, split them now. |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| BasicBlock *Header = L->getHeader(); |
| for (unsigned i = 0, e = L->getExitBlocks().size(); i != e; ++i) |
| if (!DS.dominates(Header, L->getExitBlocks()[i])) { |
| RewriteLoopExitBlock(L, L->getExitBlocks()[i]); |
| assert(DS.dominates(Header, L->getExitBlocks()[i]) && |
| "RewriteLoopExitBlock failed?"); |
| NumInserted++; |
| Changed = true; |
| } |
| |
| // The preheader may have more than two predecessors at this point (from the |
| // preheader and from the backedges). To simplify the loop more, insert an |
| // extra back-edge block in the loop so that there is exactly one backedge. |
| if (L->getNumBackEdges() != 1) { |
| InsertUniqueBackedgeBlock(L); |
| NumInserted++; |
| Changed = true; |
| } |
| |
| const std::vector<Loop*> &SubLoops = L->getSubLoops(); |
| for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) |
| Changed |= ProcessLoop(SubLoops[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); |
| |
| // The preheader first gets an unconditional branch to the loop header... |
| BranchInst *BI = new BranchInst(BB); |
| NewBB->getInstList().push_back(BI); |
| |
| // 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? |
| for (BasicBlock::iterator I = BB->begin(); |
| PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
| |
| // 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]); |
| NewPHI->addIncoming(V, Preds[i]); |
| } |
| |
| // Add an incoming value to the PHI node in the loop for the preheader |
| // edge |
| PN->addIncoming(NewPHI, NewBB); |
| } |
| |
| // 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; |
| } |
| |
| // ChangeExitBlock - This recursive function is used to change any exit blocks |
| // that use OldExit to use NewExit instead. This is recursive because children |
| // may need to be processed as well. |
| // |
| static void ChangeExitBlock(Loop *L, BasicBlock *OldExit, BasicBlock *NewExit) { |
| if (L->hasExitBlock(OldExit)) { |
| L->changeExitBlock(OldExit, NewExit); |
| const std::vector<Loop*> &SubLoops = L->getSubLoops(); |
| for (unsigned i = 0, e = SubLoops.size(); i != e; ++i) |
| ChangeExitBlock(SubLoops[i], OldExit, NewExit); |
| } |
| } |
| |
| |
| /// 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. |
| // |
| const std::vector<Loop*> *ParentSubLoops; |
| if (Loop *Parent = L->getParentLoop()) |
| ParentSubLoops = &Parent->getSubLoops(); |
| else // Must check top-level loops... |
| ParentSubLoops = &getAnalysis<LoopInfo>().getTopLevelLoops(); |
| |
| // Loop over all sibling loops, performing the substitution (recursively to |
| // include child loops)... |
| for (unsigned i = 0, e = ParentSubLoops->size(); i != e; ++i) |
| ChangeExitBlock((*ParentSubLoops)[i], Header, NewBB); |
| |
| DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info |
| { |
| // The blocks that dominate NewBB are the blocks that dominate Header, |
| // minus Header, plus NewBB. |
| DominatorSet::DomSetType DomSet = DS.getDominators(Header); |
| DomSet.insert(NewBB); // We dominate ourself |
| DomSet.erase(Header); // Header does not dominate us... |
| DS.addBasicBlock(NewBB, DomSet); |
| |
| // The newly created basic block dominates all nodes dominated by Header. |
| for (Function::iterator I = Header->getParent()->begin(), |
| E = Header->getParent()->end(); I != E; ++I) |
| if (DS.dominates(Header, I)) |
| DS.addDominator(I, 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 DominatorTree information if it is active. |
| if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) { |
| // The immediate dominator of the preheader is the immediate dominator of |
| // the old header. |
| // |
| DominatorTree::Node *HeaderNode = DT->getNode(Header); |
| DominatorTree::Node *PHNode = DT->createNewNode(NewBB, |
| HeaderNode->getIDom()); |
| |
| // Change the header node so that PNHode is the new immediate dominator |
| DT->changeImmediateDominator(HeaderNode, PHNode); |
| } |
| |
| // 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); |
| } |
| } |
| } |
| } |
| } |
| |
| void LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) { |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| assert(!DS.dominates(L->getHeader(), Exit) && |
| "Loop already dominates exit block??"); |
| assert(std::find(L->getExitBlocks().begin(), L->getExitBlocks().end(), Exit) |
| != L->getExitBlocks().end() && "Not a current exit block!"); |
| |
| 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>()); |
| |
| // Replace any instances of Exit with NewBB in this and any nested loops... |
| for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I) |
| if (I->hasExitBlock(Exit)) |
| I->changeExitBlock(Exit, NewBB); // Update exit block information |
| |
| // Update dominator information (set, immdom, domtree, and domfrontier) |
| UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks); |
| } |
| |
| /// 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); |
| Instruction *BETerminator = new BranchInst(Header); |
| BEBlock->getInstList().push_back(BETerminator); |
| |
| // 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>()); |
| |
| // Replace any instances of Exit with NewBB in this and any nested loops... |
| for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I) |
| if (I->hasExitBlock(Header)) |
| I->changeExitBlock(Header, BEBlock); // Update exit block information |
| |
| // 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 "Exit"), 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 Exit, and moves some predecessors of "Exit" 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(succ_begin(NewBB) != succ_end(NewBB) && |
| ++succ_begin(NewBB) == succ_end(NewBB) && |
| "NewBB should have a single successor!"); |
| DominatorSet &DS = getAnalysis<DominatorSet>(); |
| |
| // Update dominator information... The blocks that dominate NewBB are the |
| // intersection of the dominators of predecessors, plus the block itself. |
| // The newly created basic block does not dominate anything except 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); |
| |
| // Update immediate dominator information if we have it... |
| BasicBlock *NewBBIDom = 0; |
| if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) { |
| // This block does not strictly dominate anything, so it is not an immediate |
| // dominator. 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... |
| } |
| |
| // Update DominatorTree information if it is active. |
| if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) { |
| // NewBB doesn't dominate anything, so just create a node and link it into |
| // its immediate dominator. 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... |
| DT->createNewNode(NewBB, NewBBIDomNode); |
| } |
| |
| // Update dominance frontier information... |
| if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) { |
| // DF(NewBB) is {Exit} because NewBB does not strictly dominate Exit, but it |
| // does dominate itself (and there is an edge (NewBB -> Exit)). Exit is the |
| // single successor of NewBB. |
| DominanceFrontier::DomSetType NewDFSet; |
| BasicBlock *Exit = *succ_begin(NewBB); |
| NewDFSet.insert(Exit); |
| DF->addBasicBlock(NewBB, NewDFSet); |
| |
| // Now we must loop over all of the dominance frontiers in the function, |
| // replacing occurrences of Exit with NewBB in some cases. All blocks that |
| // dominate a block in PredBlocks and contained Exit in their dominance |
| // frontier must be updated to contain NewBB instead. This only occurs if |
| // there is more than one block in PredBlocks. |
| // |
| if (PredBlocks.size() > 1) { |
| 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 Exit node is in DF(PredDom), then PredDom didn't dominate |
| // Exit but did dominate a predecessor of it. Now we change this |
| // entry to include NewBB in the DF instead of Exit. |
| DominanceFrontier::iterator DFI = DF->find(PredDom); |
| assert(DFI != DF->end() && "No dominance frontier for node?"); |
| if (DFI->second.count(Exit)) { |
| DF->removeFromFrontier(DFI, Exit); |
| DF->addToFrontier(DFI, NewBB); |
| } |
| } |
| } |
| } |
| } |
| } |
| |
| } // End llvm namespace |