| //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file 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/Constants.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Function.h" |
| #include "llvm/LLVMContext.h" |
| #include "llvm/Type.h" |
| #include "llvm/Analysis/AliasAnalysis.h" |
| #include "llvm/Analysis/Dominators.h" |
| #include "llvm/Analysis/LoopInfo.h" |
| #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| #include "llvm/Transforms/Utils/Local.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 char ID; // Pass identification, replacement for typeid |
| LoopSimplify() : FunctionPass(&ID) {} |
| |
| // AA - If we have an alias analysis object to update, this is it, otherwise |
| // this is null. |
| AliasAnalysis *AA; |
| LoopInfo *LI; |
| DominatorTree *DT; |
| 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.addPreserved<LoopInfo>(); |
| AU.addPreserved<DominatorTree>(); |
| AU.addPreserved<DominanceFrontier>(); |
| AU.addPreserved<AliasAnalysis>(); |
| AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added. |
| } |
| |
| /// verifyAnalysis() - Verify loop nest. |
| void verifyAnalysis() const { |
| #ifndef NDEBUG |
| LoopInfo *NLI = &getAnalysis<LoopInfo>(); |
| for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I) |
| (*I)->verifyLoop(); |
| #endif |
| } |
| |
| private: |
| bool ProcessLoop(Loop *L); |
| BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit); |
| BasicBlock *InsertPreheaderForLoop(Loop *L); |
| Loop *SeparateNestedLoop(Loop *L); |
| void InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader); |
| void PlaceSplitBlockCarefully(BasicBlock *NewBB, |
| SmallVectorImpl<BasicBlock*> &SplitPreds, |
| Loop *L); |
| }; |
| } |
| |
| char LoopSimplify::ID = 0; |
| static RegisterPass<LoopSimplify> |
| X("loopsimplify", "Canonicalize natural loops", true); |
| |
| // Publically exposed interface to pass... |
| const PassInfo *const llvm::LoopSimplifyID = &X; |
| 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 = getAnalysisIfAvailable<AliasAnalysis>(); |
| DT = &getAnalysis<DominatorTree>(); |
| |
| // 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 before the old terminator. |
| new UnreachableInst(TI->getContext(), TI); |
| |
| // Delete the dead terminator. |
| if (AA) AA->deleteValue(TI); |
| if (!TI->use_empty()) |
| TI->replaceAllUsesWith(UndefValue::get(TI->getType())); |
| TI->eraseFromParent(); |
| 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. |
| BasicBlock *Preheader = L->getLoopPreheader(); |
| if (!Preheader) { |
| Preheader = 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. |
| SmallVector<BasicBlock*, 8> 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, Preheader); |
| 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()) { |
| if (AA) AA->deleteValue(PN); |
| PN->replaceAllUsesWith(V); |
| PN->eraseFromParent(); |
| } |
| |
| // If this loop has muliple exits and the exits all go to the same |
| // block, attempt to merge the exits. This helps several passes, such |
| // as LoopRotation, which do not support loops with multiple exits. |
| // SimplifyCFG also does this (and this code uses the same utility |
| // function), however this code is loop-aware, where SimplifyCFG is |
| // not. That gives it the advantage of being able to hoist |
| // loop-invariant instructions out of the way to open up more |
| // opportunities, and the disadvantage of having the responsibility |
| // to preserve dominator information. |
| if (ExitBlocks.size() > 1 && L->getUniqueExitBlock()) { |
| SmallVector<BasicBlock*, 8> ExitingBlocks; |
| L->getExitingBlocks(ExitingBlocks); |
| for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) { |
| BasicBlock *ExitingBlock = ExitingBlocks[i]; |
| if (!ExitingBlock->getSinglePredecessor()) continue; |
| BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator()); |
| if (!BI || !BI->isConditional()) continue; |
| CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition()); |
| if (!CI || CI->getParent() != ExitingBlock) continue; |
| |
| // Attempt to hoist out all instructions except for the |
| // comparison and the branch. |
| bool AllInvariant = true; |
| for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) { |
| Instruction *Inst = I++; |
| if (Inst == CI) |
| continue; |
| if (!L->makeLoopInvariant(Inst, Changed, Preheader->getTerminator())) { |
| AllInvariant = false; |
| break; |
| } |
| } |
| if (!AllInvariant) continue; |
| |
| // The block has now been cleared of all instructions except for |
| // a comparison and a conditional branch. SimplifyCFG may be able |
| // to fold it now. |
| if (!FoldBranchToCommonDest(BI)) continue; |
| |
| // Success. The block is now dead, so remove it from the loop, |
| // update the dominator tree and dominance frontier, and delete it. |
| assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock)); |
| Changed = true; |
| LI->removeBlock(ExitingBlock); |
| |
| DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>(); |
| DomTreeNode *Node = DT->getNode(ExitingBlock); |
| const std::vector<DomTreeNodeBase<BasicBlock> *> &Children = |
| Node->getChildren(); |
| for (unsigned k = 0, g = Children.size(); k != g; ++k) { |
| DT->changeImmediateDominator(Children[k], Node->getIDom()); |
| if (DF) DF->changeImmediateDominator(Children[k]->getBlock(), |
| Node->getIDom()->getBlock(), |
| DT); |
| } |
| DT->eraseNode(ExitingBlock); |
| if (DF) DF->removeBlock(ExitingBlock); |
| |
| BI->getSuccessor(0)->removePredecessor(ExitingBlock); |
| BI->getSuccessor(1)->removePredecessor(ExitingBlock); |
| ExitingBlock->eraseFromParent(); |
| } |
| } |
| |
| return Changed; |
| } |
| |
| /// 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. |
| /// |
| BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) { |
| BasicBlock *Header = L->getHeader(); |
| |
| // Compute the set of predecessors of the loop that are not in the loop. |
| SmallVector<BasicBlock*, 8> 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, &OutsideBlocks[0], OutsideBlocks.size(), |
| ".preheader", this); |
| |
| |
| //===--------------------------------------------------------------------===// |
| // 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->getBase()); |
| |
| // Make sure that NewBB is put someplace intelligent, which doesn't mess up |
| // code layout too horribly. |
| PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L); |
| |
| return 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) { |
| SmallVector<BasicBlock*, 8> 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, &LoopBlocks[0], |
| LoopBlocks.size(), ".loopexit", |
| this); |
| |
| // 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->getBase()); |
| |
| 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, DominatorTree *DT, |
| 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) || DT->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, |
| SmallVectorImpl<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) { |
| PHINode *PN = FindPHIToPartitionLoops(L, DT, 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. |
| SmallVector<BasicBlock*, 8> 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, &OuterLoopPreds[0], |
| OuterLoopPreds.size(), |
| ".outer", this); |
| |
| // 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->getBase()); |
| |
| // L is now a subloop of our outer loop. |
| NewOuter->addChildLoop(L); |
| |
| for (Loop::block_iterator I = L->block_begin(), E = L->block_end(); |
| I != E; ++I) |
| NewOuter->addBlockEntry(*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 (DT->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. |
| const std::vector<Loop*> &SubLoops = L->getSubLoops(); |
| for (size_t I = 0; I != SubLoops.size(); ) |
| if (BlocksInL.count(SubLoops[I]->getHeader())) |
| ++I; // Loop remains in L |
| else |
| NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + 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, BasicBlock *Preheader) { |
| assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!"); |
| |
| // Get information about the loop |
| 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 = BasicBlock::Create(Header->getContext(), |
| Header->getName()+".backedge", F); |
| BranchInst *BETerminator = BranchInst::Create(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 = PHINode::Create(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->getBase()); |
| |
| // Update dominator information |
| DT->splitBlock(BEBlock); |
| if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>()) |
| DF->splitBlock(BEBlock); |
| } |