| //===- 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. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "loopsimplify" |
| #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/Support/Compiler.h" |
| #include "llvm/ADT/SetOperations.h" |
| #include "llvm/ADT/SetVector.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/ADT/DepthFirstIterator.h" |
| using namespace llvm; |
| |
| STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted"); |
| STATISTIC(NumNested , "Number of nested loops split out"); |
| |
| namespace { |
| struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass { |
| static const char ID; // Pass identifcation, replacement for typeid |
| LoopSimplify() : FunctionPass((intptr_t)&ID) {} |
| |
| // AA - If we have an alias analysis object to update, this is it, otherwise |
| // this is null. |
| AliasAnalysis *AA; |
| LoopInfo *LI; |
| |
| virtual bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| // We need loop information to identify the loops... |
| AU.addRequired<LoopInfo>(); |
| AU.addRequired<DominatorTree>(); |
| AU.addRequired<ETForest>(); |
| |
| AU.addPreserved<LoopInfo>(); |
| AU.addPreserved<ETForest>(); |
| 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 PlaceSplitBlockCarefully(BasicBlock *NewBB, |
| std::vector<BasicBlock*> &SplitPreds, |
| Loop *L); |
| |
| void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB, |
| std::vector<BasicBlock*> &PredBlocks); |
| }; |
| |
| const char LoopSimplify::ID = 0; |
| RegisterPass<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; |
| LI = &getAnalysis<LoopInfo>(); |
| AA = getAnalysisToUpdate<AliasAnalysis>(); |
| |
| // Check to see that no blocks (other than the header) in loops have |
| // predecessors that are not in loops. 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! |
| for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) { |
| // This case can only occur for unreachable blocks. Blocks that are |
| // unreachable can't be in loops, so filter those blocks out. |
| if (LI->getLoopFor(BB)) continue; |
| |
| bool BlockUnreachable = false; |
| TerminatorInst *TI = BB->getTerminator(); |
| |
| // Check to see if any successors of this block are non-loop-header loops |
| // that are not the header. |
| for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) { |
| // If this successor is not in a loop, BB is clearly ok. |
| Loop *L = LI->getLoopFor(TI->getSuccessor(i)); |
| if (!L) continue; |
| |
| // If the succ is the loop header, and if L is a top-level loop, then this |
| // is an entrance into a loop through the header, which is also ok. |
| if (L->getHeader() == TI->getSuccessor(i) && L->getParentLoop() == 0) |
| continue; |
| |
| // Otherwise, this is an entrance into a loop from some place invalid. |
| // Either the loop structure is invalid and this is not a natural loop (in |
| // which case the compiler is buggy somewhere else) or BB is unreachable. |
| BlockUnreachable = true; |
| break; |
| } |
| |
| // If this block is ok, check the next one. |
| if (!BlockUnreachable) continue; |
| |
| // Otherwise, this block is dead. To clean up the CFG and to allow later |
| // loop transformations to ignore this case, we delete the edges into the |
| // loop by replacing the terminator. |
| |
| // Remove PHI entries from the successors. |
| for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) |
| TI->getSuccessor(i)->removePredecessor(BB); |
| |
| // Add a new unreachable instruction. |
| new UnreachableInst(TI); |
| |
| // Delete the dead terminator. |
| if (AA) AA->deleteValue(&BB->back()); |
| BB->getInstList().pop_back(); |
| Changed |= true; |
| } |
| |
| 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; |
| ReprocessLoop: |
| |
| // Canonicalize inner loops before outer loops. Inner loop canonicalization |
| // can provide work for the outer loop to canonicalize. |
| for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I) |
| Changed |= ProcessLoop(*I); |
| |
| assert(L->getBlocks()[0] == L->getHeader() && |
| "Header isn't first block in loop?"); |
| |
| // Does the loop already have a preheader? If so, don't insert one. |
| 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) |
| // Must be exactly this loop: no subloops, parent loops, or non-loop preds |
| // allowed. |
| 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. |
| unsigned NumBackedges = L->getNumBackEdges(); |
| if (NumBackedges != 1) { |
| // If this is really a nested loop, rip it out into a child loop. Don't do |
| // this for loops with a giant number of backedges, just factor them into a |
| // common backedge instead. |
| if (NumBackedges < 8) { |
| if (Loop *NL = SeparateNestedLoop(L)) { |
| ++NumNested; |
| // This is a big restructuring change, reprocess the whole loop. |
| ProcessLoop(NL); |
| Changed = true; |
| // GCC doesn't tail recursion eliminate this. |
| goto ReprocessLoop; |
| } |
| } |
| |
| // If we either couldn't, or didn't want to, identify nesting of the loops, |
| // insert a new block that all backedges target, then make it jump to the |
| // loop header. |
| 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; |
| for (BasicBlock::iterator I = L->getHeader()->begin(); |
| (PN = dyn_cast<PHINode>(I++)); ) |
| if (Value *V = PN->hasConstantValue()) { |
| PN->replaceAllUsesWith(V); |
| PN->eraseFromParent(); |
| } |
| |
| 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)) { |
| Instruction *I = dyn_cast<Instruction>(V); |
| // If I is in NewBB, the ETForest call will fail, because NewBB isn't |
| // registered in ETForest yet. Handle this case explicitly. |
| if (!I || (I->getParent() != NewBB && |
| getAnalysis<ETForest>().dominates(I, 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, *LI); |
| |
| UpdateDomInfoForRevectoredPreds(NewBB, OutsideBlocks); |
| |
| // Make sure that NewBB is put someplace intelligent, which doesn't mess up |
| // code layout too horribly. |
| PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L); |
| } |
| |
| /// 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) { |
| 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 whichever |
| // loop the Exit block is in. Note that it may not be in that immediate loop, |
| // if the successor is some other loop header. In that case, we continue |
| // walking up the loop tree to find a loop that contains both the successor |
| // block and the predecessor block. |
| Loop *SuccLoop = LI->getLoopFor(Exit); |
| while (SuccLoop && !SuccLoop->contains(L->getHeader())) |
| SuccLoop = SuccLoop->getParentLoop(); |
| if (SuccLoop) |
| SuccLoop->addBasicBlockToLoop(NewBB, *LI); |
| |
| // 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 *InputBB, BasicBlock *StopBlock, |
| std::set<BasicBlock*> &Blocks) { |
| std::vector<BasicBlock *> WorkList; |
| WorkList.push_back(InputBB); |
| do { |
| BasicBlock *BB = WorkList.back(); WorkList.pop_back(); |
| if (Blocks.insert(BB).second && BB != StopBlock) |
| // If BB is not already processed and it is not a stop block then |
| // insert its predecessor in the work list |
| for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) { |
| BasicBlock *WBB = *I; |
| WorkList.push_back(WBB); |
| } |
| } while(!WorkList.empty()); |
| } |
| |
| /// 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, ETForest *EF, |
| 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) || EF->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; |
| } |
| |
| // PlaceSplitBlockCarefully - If the block isn't already, move the new block to |
| // right after some 'outside block' block. This prevents the preheader from |
| // being placed inside the loop body, e.g. when the loop hasn't been rotated. |
| void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB, |
| std::vector<BasicBlock*>&SplitPreds, |
| Loop *L) { |
| // Check to see if NewBB is already well placed. |
| Function::iterator BBI = NewBB; --BBI; |
| for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { |
| if (&*BBI == SplitPreds[i]) |
| return; |
| } |
| |
| // If it isn't already after an outside block, move it after one. This is |
| // always good as it makes the uncond branch from the outside block into a |
| // fall-through. |
| |
| // Figure out *which* outside block to put this after. Prefer an outside |
| // block that neighbors a BB actually in the loop. |
| BasicBlock *FoundBB = 0; |
| for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) { |
| Function::iterator BBI = SplitPreds[i]; |
| if (++BBI != NewBB->getParent()->end() && |
| L->contains(BBI)) { |
| FoundBB = SplitPreds[i]; |
| break; |
| } |
| } |
| |
| // If our heuristic for a *good* bb to place this after doesn't find |
| // anything, just pick something. It's likely better than leaving it within |
| // the loop. |
| if (!FoundBB) |
| FoundBB = SplitPreds[0]; |
| NewBB->moveAfter(FoundBB); |
| } |
| |
| |
| /// 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) { |
| ETForest *EF = getAnalysisToUpdate<ETForest>(); |
| PHINode *PN = FindPHIToPartitionLoops(L, EF, 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); |
| |
| // Make sure that NewBB is put someplace intelligent, which doesn't mess up |
| // code layout too horribly. |
| PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L); |
| |
| // Create the new outer loop. |
| Loop *NewOuter = new Loop(); |
| |
| // 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, *LI); |
| |
| // 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. |
| std::set<BasicBlock*> BlocksInL; |
| for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI) |
| if (EF->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, *LI); |
| |
| // Update dominator information (set, immdom, domtree, and domfrontier) |
| UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks); |
| } |
| |
| // Returns true if BasicBlock A dominates at least one block in vector B |
| // Helper function for UpdateDomInfoForRevectoredPreds |
| static bool BlockDominatesAny(BasicBlock* A, const std::vector<BasicBlock*>& B, |
| ETForest& ETF) { |
| for (std::vector<BasicBlock*>::const_iterator BI = B.begin(), BE = B.end(); |
| BI != BE; ++BI) { |
| if (ETF.dominates(A, *BI)) |
| return true; |
| } |
| return false; |
| } |
| |
| /// UpdateDomInfoForRevectoredPreds - This method is used to update the four |
| /// different kinds of dominator information (immediate dominators, |
| /// dominator trees, et-forest 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); |
| ETForest& ETF = getAnalysis<ETForest>(); |
| |
| // 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]; |
| unsigned i = 1, e = PredBlocks.size(); |
| for (i = 1; !ETF.isReachableFromEntry(OnePred); ++i) { |
| assert(i != e && "Didn't find reachable pred?"); |
| OnePred = PredBlocks[i]; |
| } |
| |
| for (; i != e; ++i) |
| if (PredBlocks[i] != OnePred && ETF.isReachableFromEntry(OnePred)){ |
| NewBBDominatesNewBBSucc = false; |
| break; |
| } |
| |
| if (NewBBDominatesNewBBSucc) |
| for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc); |
| PI != E; ++PI) |
| if (*PI != NewBB && !ETF.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 && !ETF.dominates(NewBBSucc, *PI)) { |
| NewBBDominatesNewBBSucc = false; |
| break; |
| } |
| } |
| |
| BasicBlock *NewBBIDom = 0; |
| |
| // 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. |
| if (!NewBBIDom) { |
| unsigned i = 0; |
| for (i = 0; i < PredBlocks.size(); ++i) |
| if (ETF.dominates(&PredBlocks[i]->getParent()->getEntryBlock(), PredBlocks[i])) { |
| NewBBIDom = PredBlocks[i]; |
| break; |
| } |
| assert(i != PredBlocks.size() && "No reachable preds?"); |
| for (i = i + 1; i < PredBlocks.size(); ++i) { |
| if (ETF.dominates(&PredBlocks[i]->getParent()->getEntryBlock(), PredBlocks[i])) |
| NewBBIDom = ETF.nearestCommonDominator(NewBBIDom, PredBlocks[i]); |
| } |
| assert(NewBBIDom && "No immediate dominator found??"); |
| } |
| DominatorTree::Node *NewBBIDomNode = DT->getNode(NewBBIDom); |
| |
| // 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 ET-Forest information if it is active. |
| if (ETForest *EF = getAnalysisToUpdate<ETForest>()) { |
| EF->addNewBlock(NewBB, NewBBIDom); |
| if (NewBBDominatesNewBBSucc) |
| EF->setImmediateDominator(NewBBSucc, NewBB); |
| } |
| |
| // 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 (ETF.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 (Function::iterator FI = NewBB->getParent()->begin(), |
| FE = NewBB->getParent()->end(); FI != FE; ++FI) { |
| DominanceFrontier::iterator DFI = DF->find(FI); |
| if (DFI == DF->end()) continue; // unreachable block. |
| |
| // Only consider dominators of NewBBSucc |
| if (!DFI->second.count(NewBBSucc)) continue; |
| |
| if (BlockDominatesAny(FI, PredBlocks, ETF)) { |
| // 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 ((BasicBlock*)FI == NewBBSucc || !ETF.dominates(FI, 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 (ETF.dominates(FI, *PI)) { |
| ShouldRemove = false; |
| break; |
| } |
| |
| if (ShouldRemove) |
| DF->removeFromFrontier(DFI, NewBBSucc); |
| DF->addToFrontier(DFI, NewBB); |
| |
| break; |
| } |
| } |
| } |
| } |
| } |
| |
| |