1 //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
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 pass performs several transformations to transform natural loops into a
11 // simpler form, which makes subsequent analyses and transformations simpler and
14 // Loop pre-header insertion guarantees that there is a single, non-critical
15 // entry edge from outside of the loop to the loop header. This simplifies a
16 // number of analyses and transformations, such as LICM.
18 // Loop exit-block insertion guarantees that all exit blocks from the loop
19 // (blocks which are outside of the loop that have predecessors inside of the
20 // loop) only have predecessors from inside of the loop (and are thus dominated
21 // by the loop header). This simplifies transformations such as store-sinking
22 // that are built into LICM.
24 // This pass also guarantees that loops will have exactly one backedge.
26 // Note that the simplifycfg pass will clean up blocks which are split out but
27 // end up being unnecessary, so usage of this pass should not pessimize
30 // This pass obviously modifies the CFG, but updates loop information and
31 // dominator information.
33 //===----------------------------------------------------------------------===//
35 #include "llvm/Transforms/Scalar.h"
36 #include "llvm/Constant.h"
37 #include "llvm/Instructions.h"
38 #include "llvm/Function.h"
39 #include "llvm/Type.h"
40 #include "llvm/Analysis/AliasAnalysis.h"
41 #include "llvm/Analysis/Dominators.h"
42 #include "llvm/Analysis/LoopInfo.h"
43 #include "llvm/Support/CFG.h"
44 #include "llvm/ADT/SetOperations.h"
45 #include "llvm/ADT/SetVector.h"
46 #include "llvm/ADT/Statistic.h"
47 #include "llvm/ADT/DepthFirstIterator.h"
52 NumInserted("loopsimplify", "Number of pre-header or exit blocks inserted");
54 NumNested("loopsimplify", "Number of nested loops split out");
56 struct LoopSimplify : public FunctionPass {
57 // AA - If we have an alias analysis object to update, this is it, otherwise
61 virtual bool runOnFunction(Function &F);
63 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
64 // We need loop information to identify the loops...
65 AU.addRequired<LoopInfo>();
66 AU.addRequired<DominatorSet>();
67 AU.addRequired<DominatorTree>();
69 AU.addPreserved<LoopInfo>();
70 AU.addPreserved<DominatorSet>();
71 AU.addPreserved<ImmediateDominators>();
72 AU.addPreserved<ETForest>();
73 AU.addPreserved<DominatorTree>();
74 AU.addPreserved<DominanceFrontier>();
75 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
78 bool ProcessLoop(Loop *L);
79 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
80 const std::vector<BasicBlock*> &Preds);
81 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
82 void InsertPreheaderForLoop(Loop *L);
83 Loop *SeparateNestedLoop(Loop *L);
84 void InsertUniqueBackedgeBlock(Loop *L);
86 void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
87 std::vector<BasicBlock*> &PredBlocks);
90 RegisterOpt<LoopSimplify>
91 X("loopsimplify", "Canonicalize natural loops", true);
94 // Publically exposed interface to pass...
95 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
96 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
98 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
99 /// it in any convenient order) inserting preheaders...
101 bool LoopSimplify::runOnFunction(Function &F) {
102 bool Changed = false;
103 LoopInfo &LI = getAnalysis<LoopInfo>();
104 AA = getAnalysisToUpdate<AliasAnalysis>();
106 for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I)
107 Changed |= ProcessLoop(*I);
112 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
113 /// all loops have preheaders.
115 bool LoopSimplify::ProcessLoop(Loop *L) {
116 bool Changed = false;
118 // Check to see that no blocks (other than the header) in the loop have
119 // predecessors that are not in the loop. This is not valid for natural
120 // loops, but can occur if the blocks are unreachable. Since they are
121 // unreachable we can just shamelessly destroy their terminators to make them
122 // not branch into the loop!
123 assert(L->getBlocks()[0] == L->getHeader() &&
124 "Header isn't first block in loop?");
125 for (unsigned i = 1, e = L->getBlocks().size(); i != e; ++i) {
126 BasicBlock *LoopBB = L->getBlocks()[i];
128 for (pred_iterator PI = pred_begin(LoopBB), E = pred_end(LoopBB);
130 if (!L->contains(*PI)) {
131 // This predecessor is not in the loop. Kill its terminator!
132 BasicBlock *DeadBlock = *PI;
133 for (succ_iterator SI = succ_begin(DeadBlock), E = succ_end(DeadBlock);
135 (*SI)->removePredecessor(DeadBlock); // Remove PHI node entries
137 // Delete the dead terminator.
138 if (AA) AA->deleteValue(&DeadBlock->back());
139 DeadBlock->getInstList().pop_back();
142 if (LoopBB->getParent()->getReturnType() != Type::VoidTy)
143 RetVal = Constant::getNullValue(LoopBB->getParent()->getReturnType());
144 new ReturnInst(RetVal, DeadBlock);
145 goto Retry; // We just invalidated the pred_iterator. Retry.
149 // Does the loop already have a preheader? If so, don't modify the loop...
150 if (L->getLoopPreheader() == 0) {
151 InsertPreheaderForLoop(L);
156 // Next, check to make sure that all exit nodes of the loop only have
157 // predecessors that are inside of the loop. This check guarantees that the
158 // loop preheader/header will dominate the exit blocks. If the exit block has
159 // predecessors from outside of the loop, split the edge now.
160 std::vector<BasicBlock*> ExitBlocks;
161 L->getExitBlocks(ExitBlocks);
163 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
164 LoopInfo &LI = getAnalysis<LoopInfo>();
165 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
166 E = ExitBlockSet.end(); I != E; ++I) {
167 BasicBlock *ExitBlock = *I;
168 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
170 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
172 if (!L->contains(*PI)) {
173 RewriteLoopExitBlock(L, ExitBlock);
180 // If the header has more than two predecessors at this point (from the
181 // preheader and from multiple backedges), we must adjust the loop.
182 if (L->getNumBackEdges() != 1) {
184 // If this is really a nested loop, rip it out into a child loop.
185 if (Loop *NL = SeparateNestedLoop(L)) {
187 // This is a big restructuring change, reprocess the whole loop.
192 InsertUniqueBackedgeBlock(L);
197 // Scan over the PHI nodes in the loop header. Since they now have only two
198 // incoming values (the loop is canonicalized), we may have simplified the PHI
199 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
201 for (BasicBlock::iterator I = L->getHeader()->begin();
202 (PN = dyn_cast<PHINode>(I++)); )
203 if (Value *V = PN->hasConstantValue()) {
204 PN->replaceAllUsesWith(V);
205 PN->eraseFromParent();
208 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
209 Changed |= ProcessLoop(*I);
214 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
215 /// to move the predecessors specified in the Preds list to point to the new
216 /// block, leaving the remaining predecessors pointing to BB. This method
217 /// updates the SSA PHINode's, but no other analyses.
219 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
221 const std::vector<BasicBlock*> &Preds) {
223 // Create new basic block, insert right before the original block...
224 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
226 // The preheader first gets an unconditional branch to the loop header...
227 BranchInst *BI = new BranchInst(BB, NewBB);
229 // For every PHI node in the block, insert a PHI node into NewBB where the
230 // incoming values from the out of loop edges are moved to NewBB. We have two
231 // possible cases here. If the loop is dead, we just insert dummy entries
232 // into the PHI nodes for the new edge. If the loop is not dead, we move the
233 // incoming edges in BB into new PHI nodes in NewBB.
235 if (!Preds.empty()) { // Is the loop not obviously dead?
236 // Check to see if the values being merged into the new block need PHI
237 // nodes. If so, insert them.
238 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
239 PHINode *PN = cast<PHINode>(I);
242 // Check to see if all of the values coming in are the same. If so, we
243 // don't need to create a new PHI node.
244 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
245 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
246 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
251 // If the values coming into the block are not the same, we need a PHI.
253 // Create the new PHI node, insert it into NewBB at the end of the block
254 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
255 if (AA) AA->copyValue(PN, NewPHI);
257 // Move all of the edges from blocks outside the loop to the new PHI
258 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
259 Value *V = PN->removeIncomingValue(Preds[i], false);
260 NewPHI->addIncoming(V, Preds[i]);
264 // Remove all of the edges coming into the PHI nodes from outside of the
266 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
267 PN->removeIncomingValue(Preds[i], false);
270 // Add an incoming value to the PHI node in the loop for the preheader
272 PN->addIncoming(InVal, NewBB);
274 // Can we eliminate this phi node now?
275 if (Value *V = PN->hasConstantValue(true)) {
276 if (!isa<Instruction>(V) ||
277 getAnalysis<DominatorSet>().dominates(cast<Instruction>(V), PN)) {
278 PN->replaceAllUsesWith(V);
279 if (AA) AA->deleteValue(PN);
280 BB->getInstList().erase(PN);
285 // Now that the PHI nodes are updated, actually move the edges from
286 // Preds to point to NewBB instead of BB.
288 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
289 TerminatorInst *TI = Preds[i]->getTerminator();
290 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
291 if (TI->getSuccessor(s) == BB)
292 TI->setSuccessor(s, NewBB);
295 } else { // Otherwise the loop is dead...
296 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
297 PHINode *PN = cast<PHINode>(I);
298 // Insert dummy values as the incoming value...
299 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
305 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
306 /// preheader, this method is called to insert one. This method has two phases:
307 /// preheader insertion and analysis updating.
309 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
310 BasicBlock *Header = L->getHeader();
312 // Compute the set of predecessors of the loop that are not in the loop.
313 std::vector<BasicBlock*> OutsideBlocks;
314 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
316 if (!L->contains(*PI)) // Coming in from outside the loop?
317 OutsideBlocks.push_back(*PI); // Keep track of it...
319 // Split out the loop pre-header
321 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
323 //===--------------------------------------------------------------------===//
324 // Update analysis results now that we have performed the transformation
327 // We know that we have loop information to update... update it now.
328 if (Loop *Parent = L->getParentLoop())
329 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
331 DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info
332 DominatorTree &DT = getAnalysis<DominatorTree>();
335 // Update the dominator tree information.
336 // The immediate dominator of the preheader is the immediate dominator of
338 DominatorTree::Node *PHDomTreeNode =
339 DT.createNewNode(NewBB, DT.getNode(Header)->getIDom());
340 BasicBlock *oldHeaderIDom = DT.getNode(Header)->getIDom()->getBlock();
342 // Change the header node so that PNHode is the new immediate dominator
343 DT.changeImmediateDominator(DT.getNode(Header), PHDomTreeNode);
346 // The blocks that dominate NewBB are the blocks that dominate Header,
347 // minus Header, plus NewBB.
348 DominatorSet::DomSetType DomSet = DS.getDominators(Header);
349 DomSet.erase(Header); // Header does not dominate us...
350 DS.addBasicBlock(NewBB, DomSet);
352 // The newly created basic block dominates all nodes dominated by Header.
353 for (df_iterator<DominatorTree::Node*> DFI = df_begin(PHDomTreeNode),
354 E = df_end(PHDomTreeNode); DFI != E; ++DFI)
355 DS.addDominator((*DFI)->getBlock(), NewBB);
358 // Update immediate dominator information if we have it...
359 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
360 // Whatever i-dominated the header node now immediately dominates NewBB
361 ID->addNewBlock(NewBB, ID->get(Header));
363 // The preheader now is the immediate dominator for the header node...
364 ID->setImmediateDominator(Header, NewBB);
367 // Update ET Forest information if we have it...
368 if (ETForest *EF = getAnalysisToUpdate<ETForest>()) {
369 // Whatever i-dominated the header node now immediately dominates NewBB
370 EF->addNewBlock(NewBB, oldHeaderIDom);
372 // The preheader now is the immediate dominator for the header node...
373 EF->setImmediateDominator(Header, NewBB);
376 // Update dominance frontier information...
377 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
378 // The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates
379 // everything that Header does, and it strictly dominates Header in
381 assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?");
382 DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second;
383 NewDFSet.erase(Header);
384 DF->addBasicBlock(NewBB, NewDFSet);
386 // Now we must loop over all of the dominance frontiers in the function,
387 // replacing occurrences of Header with NewBB in some cases. If a block
388 // dominates a (now) predecessor of NewBB, but did not strictly dominate
389 // Header, it will have Header in it's DF set, but should now have NewBB in
391 for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) {
392 // Get all of the dominators of the predecessor...
393 const DominatorSet::DomSetType &PredDoms =
394 DS.getDominators(OutsideBlocks[i]);
395 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
396 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
397 BasicBlock *PredDom = *PDI;
398 // If the loop header is in DF(PredDom), then PredDom didn't dominate
399 // the header but did dominate a predecessor outside of the loop. Now
400 // we change this entry to include the preheader in the DF instead of
402 DominanceFrontier::iterator DFI = DF->find(PredDom);
403 assert(DFI != DF->end() && "No dominance frontier for node?");
404 if (DFI->second.count(Header)) {
405 DF->removeFromFrontier(DFI, Header);
406 DF->addToFrontier(DFI, NewBB);
413 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
414 /// blocks. This method is used to split exit blocks that have predecessors
415 /// outside of the loop.
416 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
417 DominatorSet &DS = getAnalysis<DominatorSet>();
419 std::vector<BasicBlock*> LoopBlocks;
420 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
422 LoopBlocks.push_back(*I);
424 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
425 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
427 // Update Loop Information - we know that the new block will be in the parent
429 if (Loop *Parent = L->getParentLoop())
430 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
432 // Update dominator information (set, immdom, domtree, and domfrontier)
433 UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
437 /// AddBlockAndPredsToSet - Add the specified block, and all of its
438 /// predecessors, to the specified set, if it's not already in there. Stop
439 /// predecessor traversal when we reach StopBlock.
440 static void AddBlockAndPredsToSet(BasicBlock *BB, BasicBlock *StopBlock,
441 std::set<BasicBlock*> &Blocks) {
442 if (!Blocks.insert(BB).second) return; // already processed.
443 if (BB == StopBlock) return; // Stop here!
445 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
446 AddBlockAndPredsToSet(*I, StopBlock, Blocks);
449 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
450 /// PHI node that tells us how to partition the loops.
451 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorSet &DS,
453 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
454 PHINode *PN = cast<PHINode>(I);
456 if (Value *V = PN->hasConstantValue())
457 if (!isa<Instruction>(V) || DS.dominates(cast<Instruction>(V), PN)) {
458 // This is a degenerate PHI already, don't modify it!
459 PN->replaceAllUsesWith(V);
460 if (AA) AA->deleteValue(PN);
461 PN->eraseFromParent();
465 // Scan this PHI node looking for a use of the PHI node by itself.
466 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
467 if (PN->getIncomingValue(i) == PN &&
468 L->contains(PN->getIncomingBlock(i)))
469 // We found something tasty to remove.
475 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
476 /// them out into a nested loop. This is important for code that looks like
481 /// br cond, Loop, Next
483 /// br cond2, Loop, Out
485 /// To identify this common case, we look at the PHI nodes in the header of the
486 /// loop. PHI nodes with unchanging values on one backedge correspond to values
487 /// that change in the "outer" loop, but not in the "inner" loop.
489 /// If we are able to separate out a loop, return the new outer loop that was
492 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
493 PHINode *PN = FindPHIToPartitionLoops(L, getAnalysis<DominatorSet>(), AA);
494 if (PN == 0) return 0; // No known way to partition.
496 // Pull out all predecessors that have varying values in the loop. This
497 // handles the case when a PHI node has multiple instances of itself as
499 std::vector<BasicBlock*> OuterLoopPreds;
500 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
501 if (PN->getIncomingValue(i) != PN ||
502 !L->contains(PN->getIncomingBlock(i)))
503 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
505 BasicBlock *Header = L->getHeader();
506 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
508 // Update dominator information (set, immdom, domtree, and domfrontier)
509 UpdateDomInfoForRevectoredPreds(NewBB, OuterLoopPreds);
511 // Create the new outer loop.
512 Loop *NewOuter = new Loop();
514 LoopInfo &LI = getAnalysis<LoopInfo>();
516 // Change the parent loop to use the outer loop as its child now.
517 if (Loop *Parent = L->getParentLoop())
518 Parent->replaceChildLoopWith(L, NewOuter);
520 LI.changeTopLevelLoop(L, NewOuter);
522 // This block is going to be our new header block: add it to this loop and all
524 NewOuter->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
526 // L is now a subloop of our outer loop.
527 NewOuter->addChildLoop(L);
529 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
530 NewOuter->addBlockEntry(L->getBlocks()[i]);
532 // Determine which blocks should stay in L and which should be moved out to
533 // the Outer loop now.
534 DominatorSet &DS = getAnalysis<DominatorSet>();
535 std::set<BasicBlock*> BlocksInL;
536 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
537 if (DS.dominates(Header, *PI))
538 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
541 // Scan all of the loop children of L, moving them to OuterLoop if they are
542 // not part of the inner loop.
543 for (Loop::iterator I = L->begin(); I != L->end(); )
544 if (BlocksInL.count((*I)->getHeader()))
545 ++I; // Loop remains in L
547 NewOuter->addChildLoop(L->removeChildLoop(I));
549 // Now that we know which blocks are in L and which need to be moved to
550 // OuterLoop, move any blocks that need it.
551 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
552 BasicBlock *BB = L->getBlocks()[i];
553 if (!BlocksInL.count(BB)) {
554 // Move this block to the parent, updating the exit blocks sets
555 L->removeBlockFromLoop(BB);
557 LI.changeLoopFor(BB, NewOuter);
567 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
568 /// has more than one backedge in it. If this occurs, revector all of these
569 /// backedges to target a new basic block and have that block branch to the loop
570 /// header. This ensures that loops have exactly one backedge.
572 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
573 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
575 // Get information about the loop
576 BasicBlock *Preheader = L->getLoopPreheader();
577 BasicBlock *Header = L->getHeader();
578 Function *F = Header->getParent();
580 // Figure out which basic blocks contain back-edges to the loop header.
581 std::vector<BasicBlock*> BackedgeBlocks;
582 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
583 if (*I != Preheader) BackedgeBlocks.push_back(*I);
585 // Create and insert the new backedge block...
586 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
587 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
589 // Move the new backedge block to right after the last backedge block.
590 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
591 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
593 // Now that the block has been inserted into the function, create PHI nodes in
594 // the backedge block which correspond to any PHI nodes in the header block.
595 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
596 PHINode *PN = cast<PHINode>(I);
597 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
599 NewPN->reserveOperandSpace(BackedgeBlocks.size());
600 if (AA) AA->copyValue(PN, NewPN);
602 // Loop over the PHI node, moving all entries except the one for the
603 // preheader over to the new PHI node.
604 unsigned PreheaderIdx = ~0U;
605 bool HasUniqueIncomingValue = true;
606 Value *UniqueValue = 0;
607 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
608 BasicBlock *IBB = PN->getIncomingBlock(i);
609 Value *IV = PN->getIncomingValue(i);
610 if (IBB == Preheader) {
613 NewPN->addIncoming(IV, IBB);
614 if (HasUniqueIncomingValue) {
615 if (UniqueValue == 0)
617 else if (UniqueValue != IV)
618 HasUniqueIncomingValue = false;
623 // Delete all of the incoming values from the old PN except the preheader's
624 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
625 if (PreheaderIdx != 0) {
626 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
627 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
629 // Nuke all entries except the zero'th.
630 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
631 PN->removeIncomingValue(e-i, false);
633 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
634 PN->addIncoming(NewPN, BEBlock);
636 // As an optimization, if all incoming values in the new PhiNode (which is a
637 // subset of the incoming values of the old PHI node) have the same value,
638 // eliminate the PHI Node.
639 if (HasUniqueIncomingValue) {
640 NewPN->replaceAllUsesWith(UniqueValue);
641 if (AA) AA->deleteValue(NewPN);
642 BEBlock->getInstList().erase(NewPN);
646 // Now that all of the PHI nodes have been inserted and adjusted, modify the
647 // backedge blocks to just to the BEBlock instead of the header.
648 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
649 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
650 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
651 if (TI->getSuccessor(Op) == Header)
652 TI->setSuccessor(Op, BEBlock);
655 //===--- Update all analyses which we must preserve now -----------------===//
657 // Update Loop Information - we know that this block is now in the current
658 // loop and all parent loops.
659 L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>());
661 // Update dominator information (set, immdom, domtree, and domfrontier)
662 UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
665 /// UpdateDomInfoForRevectoredPreds - This method is used to update the four
666 /// different kinds of dominator information (dominator sets, immediate
667 /// dominators, dominator trees, and dominance frontiers) after a new block has
668 /// been added to the CFG.
670 /// This only supports the case when an existing block (known as "NewBBSucc"),
671 /// had some of its predecessors factored into a new basic block. This
672 /// transformation inserts a new basic block ("NewBB"), with a single
673 /// unconditional branch to NewBBSucc, and moves some predecessors of
674 /// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
675 /// PredBlocks, even though they are the same as
676 /// pred_begin(NewBB)/pred_end(NewBB).
678 void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
679 std::vector<BasicBlock*> &PredBlocks) {
680 assert(!PredBlocks.empty() && "No predblocks??");
681 assert(succ_begin(NewBB) != succ_end(NewBB) &&
682 ++succ_begin(NewBB) == succ_end(NewBB) &&
683 "NewBB should have a single successor!");
684 BasicBlock *NewBBSucc = *succ_begin(NewBB);
685 DominatorSet &DS = getAnalysis<DominatorSet>();
687 // Update dominator information... The blocks that dominate NewBB are the
688 // intersection of the dominators of predecessors, plus the block itself.
690 DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
691 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
692 set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i]));
693 NewBBDomSet.insert(NewBB); // All blocks dominate themselves...
694 DS.addBasicBlock(NewBB, NewBBDomSet);
696 // The newly inserted basic block will dominate existing basic blocks iff the
697 // PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
698 // the non-pred blocks, then they all must be the same block!
700 bool NewBBDominatesNewBBSucc = true;
702 BasicBlock *OnePred = PredBlocks[0];
703 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
704 if (PredBlocks[i] != OnePred) {
705 NewBBDominatesNewBBSucc = false;
709 if (NewBBDominatesNewBBSucc)
710 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
712 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
713 NewBBDominatesNewBBSucc = false;
718 // The other scenario where the new block can dominate its successors are when
719 // all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
721 if (!NewBBDominatesNewBBSucc) {
722 NewBBDominatesNewBBSucc = true;
723 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
725 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
726 NewBBDominatesNewBBSucc = false;
731 // If NewBB dominates some blocks, then it will dominate all blocks that
733 if (NewBBDominatesNewBBSucc) {
734 BasicBlock *PredBlock = PredBlocks[0];
735 Function *F = NewBB->getParent();
736 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
737 if (DS.dominates(NewBBSucc, I))
738 DS.addDominator(I, NewBB);
741 // Update immediate dominator information if we have it...
742 BasicBlock *NewBBIDom = 0;
743 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
744 // To find the immediate dominator of the new exit node, we trace up the
745 // immediate dominators of a predecessor until we find a basic block that
746 // dominates the exit block.
748 BasicBlock *Dom = PredBlocks[0]; // Some random predecessor...
749 while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator...
750 assert(Dom != 0 && "No shared dominator found???");
754 // Set the immediate dominator now...
755 ID->addNewBlock(NewBB, Dom);
756 NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
758 // If NewBB strictly dominates other blocks, we need to update their idom's
759 // now. The only block that need adjustment is the NewBBSucc block, whose
760 // idom should currently be set to PredBlocks[0].
761 if (NewBBDominatesNewBBSucc)
762 ID->setImmediateDominator(NewBBSucc, NewBB);
765 // Update DominatorTree information if it is active.
766 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
767 // If we don't have ImmediateDominator info around, calculate the idom as
769 DominatorTree::Node *NewBBIDomNode;
771 NewBBIDomNode = DT->getNode(NewBBIDom);
773 NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred
774 while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
775 NewBBIDomNode = NewBBIDomNode->getIDom();
776 assert(NewBBIDomNode && "No shared dominator found??");
778 NewBBIDom = NewBBIDomNode->getBlock();
781 // Create the new dominator tree node... and set the idom of NewBB.
782 DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
784 // If NewBB strictly dominates other blocks, then it is now the immediate
785 // dominator of NewBBSucc. Update the dominator tree as appropriate.
786 if (NewBBDominatesNewBBSucc) {
787 DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
788 DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
792 // Update ET-Forest information if it is active.
793 if (ETForest *EF = getAnalysisToUpdate<ETForest>()) {
794 EF->addNewBlock(NewBB, NewBBIDom);
795 if (NewBBDominatesNewBBSucc)
796 EF->setImmediateDominator(NewBBSucc, NewBB);
799 // Update dominance frontier information...
800 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
801 // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
802 // DF(PredBlocks[0]) without the stuff that the new block does not dominate
804 if (NewBBDominatesNewBBSucc) {
805 DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
806 if (DFI != DF->end()) {
807 DominanceFrontier::DomSetType Set = DFI->second;
808 // Filter out stuff in Set that we do not dominate a predecessor of.
809 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
810 E = Set.end(); SetI != E;) {
811 bool DominatesPred = false;
812 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
814 if (DS.dominates(NewBB, *PI))
815 DominatesPred = true;
822 DF->addBasicBlock(NewBB, Set);
826 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
827 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
828 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
829 DominanceFrontier::DomSetType NewDFSet;
830 NewDFSet.insert(NewBBSucc);
831 DF->addBasicBlock(NewBB, NewDFSet);
834 // Now we must loop over all of the dominance frontiers in the function,
835 // replacing occurrences of NewBBSucc with NewBB in some cases. All
836 // blocks that dominate a block in PredBlocks and contained NewBBSucc in
837 // their dominance frontier must be updated to contain NewBB instead.
839 for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
840 BasicBlock *Pred = PredBlocks[i];
841 // Get all of the dominators of the predecessor...
842 const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
843 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
844 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
845 BasicBlock *PredDom = *PDI;
847 // If the NewBBSucc node is in DF(PredDom), then PredDom didn't
848 // dominate NewBBSucc but did dominate a predecessor of it. Now we
849 // change this entry to include NewBB in the DF instead of NewBBSucc.
850 DominanceFrontier::iterator DFI = DF->find(PredDom);
851 assert(DFI != DF->end() && "No dominance frontier for node?");
852 if (DFI->second.count(NewBBSucc)) {
853 // If NewBBSucc should not stay in our dominator frontier, remove it.
854 // We remove it unless there is a predecessor of NewBBSucc that we
855 // dominate, but we don't strictly dominate NewBBSucc.
856 bool ShouldRemove = true;
857 if (PredDom == NewBBSucc || !DS.dominates(PredDom, NewBBSucc)) {
858 // Okay, we know that PredDom does not strictly dominate NewBBSucc.
859 // Check to see if it dominates any predecessors of NewBBSucc.
860 for (pred_iterator PI = pred_begin(NewBBSucc),
861 E = pred_end(NewBBSucc); PI != E; ++PI)
862 if (DS.dominates(PredDom, *PI)) {
863 ShouldRemove = false;
869 DF->removeFromFrontier(DFI, NewBBSucc);
870 DF->addToFrontier(DFI, NewBB);