1 //===- LoopInfo.cpp - Natural Loop Calculator -----------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the LoopInfo class that is used to identify natural loops
11 // and determine the loop depth of various nodes of the CFG. Note that the
12 // loops identified may actually be several natural loops that share the same
13 // header node... not just a single natural loop.
15 //===----------------------------------------------------------------------===//
17 #include "llvm/Analysis/Dominators.h"
18 #include "llvm/Analysis/LoopInfo.h"
19 #include "llvm/Assembly/Writer.h"
20 #include "llvm/Support/CFG.h"
21 #include "Support/DepthFirstIterator.h"
25 static RegisterAnalysis<LoopInfo>
26 X("loops", "Natural Loop Construction", true);
28 //===----------------------------------------------------------------------===//
29 // Loop implementation
31 bool Loop::contains(const BasicBlock *BB) const {
32 return find(Blocks.begin(), Blocks.end(), BB) != Blocks.end();
35 bool Loop::isLoopExit(const BasicBlock *BB) const {
36 for (succ_const_iterator SI = succ_begin(BB), SE = succ_end(BB);
44 /// getNumBackEdges - Calculate the number of back edges to the loop header.
46 unsigned Loop::getNumBackEdges() const {
47 unsigned NumBackEdges = 0;
48 BasicBlock *H = getHeader();
50 for (pred_iterator I = pred_begin(H), E = pred_end(H); I != E; ++I)
57 void Loop::print(std::ostream &OS, unsigned Depth) const {
58 OS << std::string(Depth*2, ' ') << "Loop Containing: ";
60 for (unsigned i = 0; i < getBlocks().size(); ++i) {
62 WriteAsOperand(OS, getBlocks()[i], false);
64 if (!ExitBlocks.empty()) {
65 OS << "\tExitBlocks: ";
66 for (unsigned i = 0; i < getExitBlocks().size(); ++i) {
68 WriteAsOperand(OS, getExitBlocks()[i], false);
74 for (iterator I = begin(), E = end(); I != E; ++I)
75 (*I)->print(OS, Depth+2);
78 void Loop::dump() const {
83 //===----------------------------------------------------------------------===//
84 // LoopInfo implementation
86 void LoopInfo::stub() {}
88 bool LoopInfo::runOnFunction(Function &) {
90 Calculate(getAnalysis<DominatorSet>()); // Update
94 void LoopInfo::releaseMemory() {
95 for (std::vector<Loop*>::iterator I = TopLevelLoops.begin(),
96 E = TopLevelLoops.end(); I != E; ++I)
97 delete *I; // Delete all of the loops...
99 BBMap.clear(); // Reset internal state of analysis
100 TopLevelLoops.clear();
104 void LoopInfo::Calculate(const DominatorSet &DS) {
105 BasicBlock *RootNode = DS.getRoot();
107 for (df_iterator<BasicBlock*> NI = df_begin(RootNode),
108 NE = df_end(RootNode); NI != NE; ++NI)
109 if (Loop *L = ConsiderForLoop(*NI, DS))
110 TopLevelLoops.push_back(L);
112 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
113 TopLevelLoops[i]->setLoopDepth(1);
116 void LoopInfo::getAnalysisUsage(AnalysisUsage &AU) const {
117 AU.setPreservesAll();
118 AU.addRequired<DominatorSet>();
121 void LoopInfo::print(std::ostream &OS) const {
122 for (unsigned i = 0; i < TopLevelLoops.size(); ++i)
123 TopLevelLoops[i]->print(OS);
125 for (std::map<BasicBlock*, Loop*>::const_iterator I = BBMap.begin(),
126 E = BBMap.end(); I != E; ++I)
127 OS << "BB '" << I->first->getName() << "' level = "
128 << I->second->LoopDepth << "\n";
132 static bool isNotAlreadyContainedIn(Loop *SubLoop, Loop *ParentLoop) {
133 if (SubLoop == 0) return true;
134 if (SubLoop == ParentLoop) return false;
135 return isNotAlreadyContainedIn(SubLoop->getParentLoop(), ParentLoop);
138 Loop *LoopInfo::ConsiderForLoop(BasicBlock *BB, const DominatorSet &DS) {
139 if (BBMap.find(BB) != BBMap.end()) return 0; // Haven't processed this node?
141 std::vector<BasicBlock *> TodoStack;
143 // Scan the predecessors of BB, checking to see if BB dominates any of
144 // them. This identifies backedges which target this node...
145 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
146 if (DS.dominates(BB, *I)) // If BB dominates it's predecessor...
147 TodoStack.push_back(*I);
149 if (TodoStack.empty()) return 0; // No backedges to this block...
151 // Create a new loop to represent this basic block...
152 Loop *L = new Loop(BB);
155 BasicBlock *EntryBlock = &BB->getParent()->getEntryBlock();
157 while (!TodoStack.empty()) { // Process all the nodes in the loop
158 BasicBlock *X = TodoStack.back();
159 TodoStack.pop_back();
161 if (!L->contains(X) && // As of yet unprocessed??
162 DS.dominates(EntryBlock, X)) { // X is reachable from entry block?
163 // Check to see if this block already belongs to a loop. If this occurs
164 // then we have a case where a loop that is supposed to be a child of the
165 // current loop was processed before the current loop. When this occurs,
166 // this child loop gets added to a part of the current loop, making it a
167 // sibling to the current loop. We have to reparent this loop.
168 if (Loop *SubLoop = const_cast<Loop*>(getLoopFor(X)))
169 if (SubLoop->getHeader() == X && isNotAlreadyContainedIn(SubLoop, L)) {
170 // Remove the subloop from it's current parent...
171 assert(SubLoop->ParentLoop && SubLoop->ParentLoop != L);
172 Loop *SLP = SubLoop->ParentLoop; // SubLoopParent
173 std::vector<Loop*>::iterator I =
174 std::find(SLP->SubLoops.begin(), SLP->SubLoops.end(), SubLoop);
175 assert(I != SLP->SubLoops.end() && "SubLoop not a child of parent?");
176 SLP->SubLoops.erase(I); // Remove from parent...
178 // Add the subloop to THIS loop...
179 SubLoop->ParentLoop = L;
180 L->SubLoops.push_back(SubLoop);
183 // Normal case, add the block to our loop...
184 L->Blocks.push_back(X);
186 // Add all of the predecessors of X to the end of the work stack...
187 TodoStack.insert(TodoStack.end(), pred_begin(X), pred_end(X));
191 // If there are any loops nested within this loop, create them now!
192 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
193 E = L->Blocks.end(); I != E; ++I)
194 if (Loop *NewLoop = ConsiderForLoop(*I, DS)) {
195 L->SubLoops.push_back(NewLoop);
196 NewLoop->ParentLoop = L;
199 // Add the basic blocks that comprise this loop to the BBMap so that this
200 // loop can be found for them.
202 for (std::vector<BasicBlock*>::iterator I = L->Blocks.begin(),
203 E = L->Blocks.end(); I != E; ++I) {
204 std::map<BasicBlock*, Loop*>::iterator BBMI = BBMap.lower_bound(*I);
205 if (BBMI == BBMap.end() || BBMI->first != *I) // Not in map yet...
206 BBMap.insert(BBMI, std::make_pair(*I, L)); // Must be at this level
209 // Now that we have a list of all of the child loops of this loop, check to
210 // see if any of them should actually be nested inside of each other. We can
211 // accidentally pull loops our of their parents, so we must make sure to
212 // organize the loop nests correctly now.
214 std::map<BasicBlock*, Loop*> ContainingLoops;
215 for (unsigned i = 0; i != L->SubLoops.size(); ++i) {
216 Loop *Child = L->SubLoops[i];
217 assert(Child->getParentLoop() == L && "Not proper child loop?");
219 if (Loop *ContainingLoop = ContainingLoops[Child->getHeader()]) {
220 // If there is already a loop which contains this loop, move this loop
221 // into the containing loop.
222 MoveSiblingLoopInto(Child, ContainingLoop);
223 --i; // The loop got removed from the SubLoops list.
225 // This is currently considered to be a top-level loop. Check to see if
226 // any of the contained blocks are loop headers for subloops we have
227 // already processed.
228 for (unsigned b = 0, e = Child->Blocks.size(); b != e; ++b) {
229 Loop *&BlockLoop = ContainingLoops[Child->Blocks[b]];
230 if (BlockLoop == 0) { // Child block not processed yet...
232 } else if (BlockLoop != Child) {
233 Loop *SubLoop = BlockLoop;
234 // Reparent all of the blocks which used to belong to BlockLoops
235 for (unsigned j = 0, e = SubLoop->Blocks.size(); j != e; ++j)
236 ContainingLoops[SubLoop->Blocks[j]] = Child;
238 // There is already a loop which contains this block, that means
239 // that we should reparent the loop which the block is currently
240 // considered to belong to to be a child of this loop.
241 MoveSiblingLoopInto(SubLoop, Child);
242 --i; // We just shrunk the SubLoops list.
249 // Now that we know all of the blocks that make up this loop, see if there are
250 // any branches to outside of the loop... building the ExitBlocks list.
251 for (std::vector<BasicBlock*>::iterator BI = L->Blocks.begin(),
252 BE = L->Blocks.end(); BI != BE; ++BI)
253 for (succ_iterator I = succ_begin(*BI), E = succ_end(*BI); I != E; ++I)
254 if (!L->contains(*I)) // Not in current loop?
255 L->ExitBlocks.push_back(*I); // It must be an exit block...
260 /// MoveSiblingLoopInto - This method moves the NewChild loop to live inside of
261 /// the NewParent Loop, instead of being a sibling of it.
262 void LoopInfo::MoveSiblingLoopInto(Loop *NewChild, Loop *NewParent) {
263 Loop *OldParent = NewChild->getParentLoop();
264 assert(OldParent && OldParent == NewParent->getParentLoop() &&
265 NewChild != NewParent && "Not sibling loops!");
267 // Remove NewChild from being a child of OldParent
268 std::vector<Loop*>::iterator I =
269 std::find(OldParent->SubLoops.begin(), OldParent->SubLoops.end(), NewChild);
270 assert(I != OldParent->SubLoops.end() && "Parent fields incorrect??");
271 OldParent->SubLoops.erase(I); // Remove from parent's subloops list
272 NewChild->ParentLoop = 0;
274 InsertLoopInto(NewChild, NewParent);
277 /// InsertLoopInto - This inserts loop L into the specified parent loop. If the
278 /// parent loop contains a loop which should contain L, the loop gets inserted
280 void LoopInfo::InsertLoopInto(Loop *L, Loop *Parent) {
281 BasicBlock *LHeader = L->getHeader();
282 assert(Parent->contains(LHeader) && "This loop should not be inserted here!");
284 // Check to see if it belongs in a child loop...
285 for (unsigned i = 0, e = Parent->SubLoops.size(); i != e; ++i)
286 if (Parent->SubLoops[i]->contains(LHeader)) {
287 InsertLoopInto(L, Parent->SubLoops[i]);
291 // If not, insert it here!
292 Parent->SubLoops.push_back(L);
293 L->ParentLoop = Parent;
296 /// changeLoopFor - Change the top-level loop that contains BB to the
297 /// specified loop. This should be used by transformations that restructure
298 /// the loop hierarchy tree.
299 void LoopInfo::changeLoopFor(BasicBlock *BB, Loop *L) {
300 Loop *&OldLoop = BBMap[BB];
301 assert(OldLoop && "Block not in a loop yet!");
305 /// changeTopLevelLoop - Replace the specified loop in the top-level loops
306 /// list with the indicated loop.
307 void LoopInfo::changeTopLevelLoop(Loop *OldLoop, Loop *NewLoop) {
308 std::vector<Loop*>::iterator I = std::find(TopLevelLoops.begin(),
309 TopLevelLoops.end(), OldLoop);
310 assert(I != TopLevelLoops.end() && "Old loop not at top level!");
312 assert(NewLoop->ParentLoop == 0 && OldLoop->ParentLoop == 0 &&
313 "Loops already embedded into a subloop!");
316 /// getLoopPreheader - If there is a preheader for this loop, return it. A
317 /// loop has a preheader if there is only one edge to the header of the loop
318 /// from outside of the loop. If this is the case, the block branching to the
319 /// header of the loop is the preheader node. The "preheaders" pass can be
320 /// "Required" to ensure that there is always a preheader node for every loop.
322 /// This method returns null if there is no preheader for the loop (either
323 /// because the loop is dead or because multiple blocks branch to the header
324 /// node of this loop).
326 BasicBlock *Loop::getLoopPreheader() const {
327 // Keep track of nodes outside the loop branching to the header...
330 // Loop over the predecessors of the header node...
331 BasicBlock *Header = getHeader();
332 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
334 if (!contains(*PI)) { // If the block is not in the loop...
335 if (Out && Out != *PI)
336 return 0; // Multiple predecessors outside the loop
340 // Make sure there is only one exit out of the preheader...
341 succ_iterator SI = succ_begin(Out);
343 if (SI != succ_end(Out))
344 return 0; // Multiple exits from the block, must not be a preheader.
347 // If there is exactly one preheader, return it. If there was zero, then Out
352 /// addBasicBlockToLoop - This function is used by other analyses to update loop
353 /// information. NewBB is set to be a new member of the current loop. Because
354 /// of this, it is added as a member of all parent loops, and is added to the
355 /// specified LoopInfo object as being in the current basic block. It is not
356 /// valid to replace the loop header with this method.
358 void Loop::addBasicBlockToLoop(BasicBlock *NewBB, LoopInfo &LI) {
359 assert((Blocks.empty() || LI[getHeader()] == this) &&
360 "Incorrect LI specified for this loop!");
361 assert(NewBB && "Cannot add a null basic block to the loop!");
362 assert(LI[NewBB] == 0 && "BasicBlock already in the loop!");
364 // Add the loop mapping to the LoopInfo object...
365 LI.BBMap[NewBB] = this;
367 // Add the basic block to this loop and all parent loops...
370 L->Blocks.push_back(NewBB);
371 L = L->getParentLoop();
375 /// changeExitBlock - This method is used to update loop information. All
376 /// instances of the specified Old basic block are removed from the exit list
377 /// and replaced with New.
379 void Loop::changeExitBlock(BasicBlock *Old, BasicBlock *New) {
380 assert(Old != New && "Cannot changeExitBlock to the same thing!");
381 assert(Old && New && "Cannot changeExitBlock to or from a null node!");
382 assert(hasExitBlock(Old) && "Old exit block not found!");
383 std::vector<BasicBlock*>::iterator
384 I = std::find(ExitBlocks.begin(), ExitBlocks.end(), Old);
385 while (I != ExitBlocks.end()) {
387 I = std::find(I+1, ExitBlocks.end(), Old);
391 /// replaceChildLoopWith - This is used when splitting loops up. It replaces
392 /// the OldChild entry in our children list with NewChild, and updates the
393 /// parent pointers of the two loops as appropriate.
394 void Loop::replaceChildLoopWith(Loop *OldChild, Loop *NewChild) {
395 assert(OldChild->ParentLoop == this && "This loop is already broken!");
396 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
397 std::vector<Loop*>::iterator I = std::find(SubLoops.begin(), SubLoops.end(),
399 assert(I != SubLoops.end() && "OldChild not in loop!");
401 OldChild->ParentLoop = 0;
402 NewChild->ParentLoop = this;
404 // Update the loop depth of the new child.
405 NewChild->setLoopDepth(LoopDepth+1);
408 /// addChildLoop - Add the specified loop to be a child of this loop.
410 void Loop::addChildLoop(Loop *NewChild) {
411 assert(NewChild->ParentLoop == 0 && "NewChild already has a parent!");
412 NewChild->ParentLoop = this;
413 SubLoops.push_back(NewChild);
415 // Update the loop depth of the new child.
416 NewChild->setLoopDepth(LoopDepth+1);
420 static void RemoveFromVector(std::vector<T*> &V, T *N) {
421 typename std::vector<T*>::iterator I = std::find(V.begin(), V.end(), N);
422 assert(I != V.end() && "N is not in this list!");
426 /// removeChildLoop - This removes the specified child from being a subloop of
427 /// this loop. The loop is not deleted, as it will presumably be inserted
428 /// into another loop.
429 Loop *Loop::removeChildLoop(iterator I) {
430 assert(I != SubLoops.end() && "Cannot remove end iterator!");
432 assert(Child->ParentLoop == this && "Child is not a child of this loop!");
433 SubLoops.erase(SubLoops.begin()+(I-begin()));
434 Child->ParentLoop = 0;
439 /// removeBlockFromLoop - This removes the specified basic block from the
440 /// current loop, updating the Blocks and ExitBlocks lists as appropriate. This
441 /// does not update the mapping in the LoopInfo class.
442 void Loop::removeBlockFromLoop(BasicBlock *BB) {
443 RemoveFromVector(Blocks, BB);
445 // If this block branched out of this loop, remove any exit blocks entries due
447 for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
448 if (!contains(*SI) && *SI != BB)
449 RemoveFromVector(ExitBlocks, *SI);
451 // If any blocks in this loop branch to BB, add it to the exit blocks set.
452 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
454 ExitBlocks.push_back(BB);