//===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===// // // 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 file defines the LoopInfo class that is used to identify natural loops // and determine the loop depth of various nodes of the CFG. Note that the // loops identified may actually be several natural loops that share the same // header node... not just a single natural loop. // //===----------------------------------------------------------------------===// #include "llvm/Analysis/LoopInfo.h" #include "llvm/Analysis/Dominators.h" #include "llvm/Support/CFG.h" #include "llvm/Assembly/Writer.h" #include "Support/DepthFirstIterator.h" #include static RegisterAnalysis X("loops", "Natural Loop Construction", true); //===----------------------------------------------------------------------===// // Loop implementation // bool Loop::contains(const BasicBlock *BB) const { return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end(); } bool Loop::isLoopExit(const BasicBlock *BB) const { for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI) { if (!contains(*SI)) return true; } return false; } /// getNumBackEdges - Calculate the number of back edges to the loop header. /// unsigned Loop::getNumBackEdges() const { unsigned NumBackEdges = 0; BasicBlock *H = getHeader(); for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I) if (contains(*I)) ++NumBackEdges; return NumBackEdges; } void Loop::print(std::ostream &OS, unsigned Depth) const { OS << std::string(Depth*2, ' ') << "Loop Containing: "; for (unsigned i = 0; i < getBlocks().size(); ++i) { if (i) OS << ","; WriteAsOperand(OS, getBlocks()[i], false); } if (!ExitBlocks.empty()) { OS << "\tExitBlocks: "; for (unsigned i = 0; i < getExitBlocks().size(); ++i) { if (i) OS << ","; WriteAsOperand(OS, getExitBlocks()[i], false); } } OS << "\n"; for (unsigned i = 0, e = getSubLoops().size(); i != e; ++i) getSubLoops()[i]->print(OS, Depth+2); } void Loop::dump() const { print(std::cerr); } //===----------------------------------------------------------------------===// // LoopInfo implementation // void LoopInfo::stub() {} bool LoopInfo::runOnFunction(Function &) { releaseMemory(); Calculate(getAnalysis()); // Update return false; } void LoopInfo::releaseMemory() { for (std::vector::iterator I = TopLevelLoops.begin(), E = TopLevelLoops.end(); I != E; ++I) delete *I; // Delete all of the loops... BBMap.clear(); // Reset internal state of analysis TopLevelLoops.clear(); } void LoopInfo::Calculate(const DominatorSet &DS) { BasicBlock *RootNode = DS.getRoot(); for (df_iterator NI = df_begin(RootNode), NE = df_end(RootNode); NI != NE; ++NI) if (Loop *L = ConsiderForLoop(*NI, DS)) TopLevelLoops.push_back(L); for (unsigned i = 0; i < TopLevelLoops.size(); ++i) TopLevelLoops[i]->setLoopDepth(1); } void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const { AU.setPreservesAll(); AU.addRequired(); } void LoopInfo::print(std::ostream &OS) const { for (unsigned i = 0; i < TopLevelLoops.size(); ++i) TopLevelLoops[i]->print(OS); #if 0 for (std::map::const_iterator I = BBMap.begin(), E = BBMap.end(); I != E; ++I) OS << "BB '" << I->first->getName() << "' level = " << I->second->LoopDepth << "\n"; #endif } static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) { if (SubLoop == 0) return true; if (SubLoop == ParentLoop) return false; return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop); } Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) { if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node? std::vector TodoStack; // Scan the predecessors of BB, checking to see if BB dominates any of // them. This identifies backedges which target this node... for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) if (DS.dominates(BB, *I)) // If BB dominates it's predecessor... TodoStack.push_back(*I); if (TodoStack.empty()) return 0; // No backedges to this block... // Create a new loop to represent this basic block... Loop *L = new Loop(BB); BBMap[BB] = L; BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock(); while (!TodoStack.empty()) { // Process all the nodes in the loop BasicBlock *X = TodoStack.back(); TodoStack.pop_back(); if (!L->contains(X) && // As of yet unprocessed?? DS.dominates(EntryBlock, X)) { // X is reachable from entry block? // Check to see if this block already belongs to a loop. If this occurs // then we have a case where a loop that is supposed to be a child of the // current loop was processed before the current loop. When this occurs, // this child loop gets added to a part of the current loop, making it a // sibling to the current loop. We have to reparent this loop. if (Loop *SubLoop = const_cast(getLoopFor(X))) if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) { // Remove the subloop from it's current parent... assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L); Loop *SLP = SubLoop->ParentLoop; // SubLoopParent std::vector::iterator I = std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop); assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?"); SLP->SubLoops.erase(I); // Remove from parent... // Add the subloop to THIS loop... SubLoop->ParentLoop = L; L->SubLoops.push_back(SubLoop); } // Normal case, add the block to our loop... L->Blocks.push_back(X); // Add all of the predecessors of X to the end of the work stack... TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X)); } } // If there are any loops nested within this loop, create them now! for (std::vector::iterator I = L->Blocks.begin(), E = L->Blocks.end(); I != E; ++I) if (Loop *NewLoop = ConsiderForLoop(*I, DS)) { L->SubLoops.push_back(NewLoop); NewLoop->ParentLoop = L; } // Add the basic blocks that comprise this loop to the BBMap so that this // loop can be found for them. // for (std::vector::iterator I = L->Blocks.begin(), E = L->Blocks.end(); I != E; ++I) { std::map::iterator BBMI = BBMap.lower_bound(*I); if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet... BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level } // Now that we have a list of all of the child loops of this loop, check to // see if any of them should actually be nested inside of each other. We can // accidentally pull loops our of their parents, so we must make sure to // organize the loop nests correctly now. { std::map ContainingLoops; for (unsigned i = 0; i != L->SubLoops.size(); ++i) { Loop *Child = L->SubLoops[i]; assert(Child->getParentLoop() == L && "Not proper child loop?"); if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) { // If there is already a loop which contains this loop, move this loop // into the containing loop. MoveSiblingLoopInto(Child, ContainingLoop); --i; // The loop got removed from the SubLoops list. } else { // This is currently considered to be a top-level loop. Check to see if // any of the contained blocks are loop headers for subloops we have // already processed. for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) { Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]]; if (BlockLoop == 0) { // Child block not processed yet... BlockLoop = Child; } else if (BlockLoop != Child) { Loop *SubLoop = BlockLoop; // Reparent all of the blocks which used to belong to BlockLoops for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j) ContainingLoops[SubLoop->Blocks[j]] = Child; // There is already a loop which contains this block, that means // that we should reparent the loop which the block is currently // considered to belong to to be a child of this loop. MoveSiblingLoopInto(SubLoop, Child); --i; // We just shrunk the SubLoops list. } } } } } // Now that we know all of the blocks that make up this loop, see if there are // any branches to outside of the loop... building the ExitBlocks list. for (std::vector::iterator BI = L->Blocks.begin(), BE = L->Blocks.end(); BI != BE; ++BI) for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I) if (!L->contains(*I)) // Not in current loop? L->ExitBlocks.push_back(*I); // It must be an exit block... return L; } /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of /// the NewParent Loop, instead of being a sibling of it. void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) { Loop *OldParent = NewChild->getParentLoop(); assert(OldParent && OldParent == NewParent->getParentLoop() && NewChild != NewParent && "Not sibling loops!"); // Remove NewChild from being a child of OldParent std::vector::iterator I = std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild); assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??"); OldParent->SubLoops.erase(I); // Remove from parent's subloops list NewChild->ParentLoop = 0; InsertLoopInto(NewChild, NewParent); } /// InsertLoopInto - This inserts loop L into the specified parent loop. If the /// parent loop contains a loop which should contain L, the loop gets inserted /// into L instead. void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) { BasicBlock *LHeader = L->getHeader(); assert(Parent->contains(LHeader) && "This loop should not be inserted here!"); // Check to see if it belongs in a child loop... for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i) if (Parent->SubLoops[i]->contains(LHeader)) { InsertLoopInto(L, Parent->SubLoops[i]); return; } // If not, insert it here! Parent->SubLoops.push_back(L); L->ParentLoop = Parent; } /// getLoopPreheader - If there is a preheader for this loop, return it. A /// loop has a preheader if there is only one edge to the header of the loop /// from outside of the loop. If this is the case, the block branching to the /// header of the loop is the preheader node. The "preheaders" pass can be /// "Required" to ensure that there is always a preheader node for every loop. /// /// This method returns null if there is no preheader for the loop (either /// because the loop is dead or because multiple blocks branch to the header /// node of this loop). /// BasicBlock *Loop::getLoopPreheader() const { // Keep track of nodes outside the loop branching to the header... BasicBlock *Out = 0; // Loop over the predecessors of the header node... BasicBlock *Header = getHeader(); for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header); PI != PE; ++PI) if (!contains(*PI)) { // If the block is not in the loop... if (Out && Out != *PI) return 0; // Multiple predecessors outside the loop Out = *PI; } // Make sure there is only one exit out of the preheader... succ_iterator SI = succ_begin(Out); ++SI; if (SI != succ_end(Out)) return 0; // Multiple exits from the block, must not be a preheader. // If there is exactly one preheader, return it. If there was zero, then Out // is still null. return Out; } /// addBasicBlockToLoop - This function is used by other analyses to update loop /// information. NewBB is set to be a new member of the current loop. Because /// of this, it is added as a member of all parent loops, and is added to the /// specified LoopInfo object as being in the current basic block. It is not /// valid to replace the loop header with this method. /// void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) { assert(LI[getHeader()] == this && "Incorrect LI specified for this loop!"); assert(NewBB && "Cannot add a null basic block to the loop!"); assert(LI[NewBB] == 0 && "BasicBlock already in the loop!"); // Add the loop mapping to the LoopInfo object... LI.BBMap[NewBB] = this; // Add the basic block to this loop and all parent loops... Loop *L = this; while (L) { L->Blocks.push_back(NewBB); L = L->getParentLoop(); } } /// changeExitBlock - This method is used to update loop information. All /// instances of the specified Old basic block are removed from the exit list /// and replaced with New. /// void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) { assert(Old != New && "Cannot changeExitBlock to the same thing!"); assert(Old && New && "Cannot changeExitBlock to or from a null node!"); assert(hasExitBlock(Old) && "Old exit block not found!"); std::vector::iterator I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old); while (I != ExitBlocks.end()) { *I = New; I = std::find(I+1, ExitBlocks.end(), Old); } }