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<DominatorTree>();
73 AU.addPreserved<DominanceFrontier>();
74 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
77 bool ProcessLoop(Loop *L);
78 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
79 const std::vector<BasicBlock*> &Preds);
80 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
81 void InsertPreheaderForLoop(Loop *L);
82 Loop *SeparateNestedLoop(Loop *L);
83 void InsertUniqueBackedgeBlock(Loop *L);
85 void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
86 std::vector<BasicBlock*> &PredBlocks);
89 RegisterOpt<LoopSimplify>
90 X("loopsimplify", "Canonicalize natural loops", true);
93 // Publically exposed interface to pass...
94 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
95 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
97 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
98 /// it in any convenient order) inserting preheaders...
100 bool LoopSimplify::runOnFunction(Function &F) {
101 bool Changed = false;
102 LoopInfo &LI = getAnalysis<LoopInfo>();
103 AA = getAnalysisToUpdate<AliasAnalysis>();
105 for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I)
106 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 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
165 E = ExitBlockSet.end(); I != E; ++I) {
166 BasicBlock *ExitBlock = *I;
167 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
169 if (!L->contains(*PI)) {
170 RewriteLoopExitBlock(L, ExitBlock);
177 // If the header has more than two predecessors at this point (from the
178 // preheader and from multiple backedges), we must adjust the loop.
179 if (L->getNumBackEdges() != 1) {
180 // If this is really a nested loop, rip it out into a child loop.
181 if (Loop *NL = SeparateNestedLoop(L)) {
183 // This is a big restructuring change, reprocess the whole loop.
188 InsertUniqueBackedgeBlock(L);
193 // Scan over the PHI nodes in the loop header. Since they now have only two
194 // incoming values (the loop is canonicalized), we may have simplified the PHI
195 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
197 DominatorSet &DS = getAnalysis<DominatorSet>();
198 for (BasicBlock::iterator I = L->getHeader()->begin();
199 (PN = dyn_cast<PHINode>(I++)); )
200 if (Value *V = PN->hasConstantValue()) {
201 PN->replaceAllUsesWith(V);
202 PN->eraseFromParent();
205 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
206 Changed |= ProcessLoop(*I);
211 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
212 /// to move the predecessors specified in the Preds list to point to the new
213 /// block, leaving the remaining predecessors pointing to BB. This method
214 /// updates the SSA PHINode's, but no other analyses.
216 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
218 const std::vector<BasicBlock*> &Preds) {
220 // Create new basic block, insert right before the original block...
221 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
223 // The preheader first gets an unconditional branch to the loop header...
224 BranchInst *BI = new BranchInst(BB, NewBB);
226 // For every PHI node in the block, insert a PHI node into NewBB where the
227 // incoming values from the out of loop edges are moved to NewBB. We have two
228 // possible cases here. If the loop is dead, we just insert dummy entries
229 // into the PHI nodes for the new edge. If the loop is not dead, we move the
230 // incoming edges in BB into new PHI nodes in NewBB.
232 if (!Preds.empty()) { // Is the loop not obviously dead?
233 // Check to see if the values being merged into the new block need PHI
234 // nodes. If so, insert them.
235 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
236 PHINode *PN = cast<PHINode>(I);
239 // Check to see if all of the values coming in are the same. If so, we
240 // don't need to create a new PHI node.
241 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
242 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
243 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
248 // If the values coming into the block are not the same, we need a PHI.
250 // Create the new PHI node, insert it into NewBB at the end of the block
251 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
252 if (AA) AA->copyValue(PN, NewPHI);
254 // Move all of the edges from blocks outside the loop to the new PHI
255 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
256 Value *V = PN->removeIncomingValue(Preds[i], false);
257 NewPHI->addIncoming(V, Preds[i]);
261 // Remove all of the edges coming into the PHI nodes from outside of the
263 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
264 PN->removeIncomingValue(Preds[i], false);
267 // Add an incoming value to the PHI node in the loop for the preheader
269 PN->addIncoming(InVal, NewBB);
271 // Can we eliminate this phi node now?
272 if (Value *V = PN->hasConstantValue(true)) {
273 if (!isa<Instruction>(V) ||
274 getAnalysis<DominatorSet>().dominates(cast<Instruction>(V), PN)) {
275 PN->replaceAllUsesWith(V);
276 if (AA) AA->deleteValue(PN);
277 BB->getInstList().erase(PN);
282 // Now that the PHI nodes are updated, actually move the edges from
283 // Preds to point to NewBB instead of BB.
285 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
286 TerminatorInst *TI = Preds[i]->getTerminator();
287 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
288 if (TI->getSuccessor(s) == BB)
289 TI->setSuccessor(s, NewBB);
292 } else { // Otherwise the loop is dead...
293 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
294 PHINode *PN = cast<PHINode>(I);
295 // Insert dummy values as the incoming value...
296 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
302 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
303 /// preheader, this method is called to insert one. This method has two phases:
304 /// preheader insertion and analysis updating.
306 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
307 BasicBlock *Header = L->getHeader();
309 // Compute the set of predecessors of the loop that are not in the loop.
310 std::vector<BasicBlock*> OutsideBlocks;
311 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
313 if (!L->contains(*PI)) // Coming in from outside the loop?
314 OutsideBlocks.push_back(*PI); // Keep track of it...
316 // Split out the loop pre-header
318 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
320 //===--------------------------------------------------------------------===//
321 // Update analysis results now that we have performed the transformation
324 // We know that we have loop information to update... update it now.
325 if (Loop *Parent = L->getParentLoop())
326 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
328 DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info
329 DominatorTree &DT = getAnalysis<DominatorTree>();
332 // Update the dominator tree information.
333 // The immediate dominator of the preheader is the immediate dominator of
335 DominatorTree::Node *PHDomTreeNode =
336 DT.createNewNode(NewBB, DT.getNode(Header)->getIDom());
338 // Change the header node so that PNHode is the new immediate dominator
339 DT.changeImmediateDominator(DT.getNode(Header), PHDomTreeNode);
342 // The blocks that dominate NewBB are the blocks that dominate Header,
343 // minus Header, plus NewBB.
344 DominatorSet::DomSetType DomSet = DS.getDominators(Header);
345 DomSet.erase(Header); // Header does not dominate us...
346 DS.addBasicBlock(NewBB, DomSet);
348 // The newly created basic block dominates all nodes dominated by Header.
349 for (df_iterator<DominatorTree::Node*> DFI = df_begin(PHDomTreeNode),
350 E = df_end(PHDomTreeNode); DFI != E; ++DFI)
351 DS.addDominator((*DFI)->getBlock(), NewBB);
354 // Update immediate dominator information if we have it...
355 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
356 // Whatever i-dominated the header node now immediately dominates NewBB
357 ID->addNewBlock(NewBB, ID->get(Header));
359 // The preheader now is the immediate dominator for the header node...
360 ID->setImmediateDominator(Header, NewBB);
363 // Update dominance frontier information...
364 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
365 // The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates
366 // everything that Header does, and it strictly dominates Header in
368 assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?");
369 DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second;
370 NewDFSet.erase(Header);
371 DF->addBasicBlock(NewBB, NewDFSet);
373 // Now we must loop over all of the dominance frontiers in the function,
374 // replacing occurrences of Header with NewBB in some cases. If a block
375 // dominates a (now) predecessor of NewBB, but did not strictly dominate
376 // Header, it will have Header in it's DF set, but should now have NewBB in
378 for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) {
379 // Get all of the dominators of the predecessor...
380 const DominatorSet::DomSetType &PredDoms =
381 DS.getDominators(OutsideBlocks[i]);
382 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
383 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
384 BasicBlock *PredDom = *PDI;
385 // If the loop header is in DF(PredDom), then PredDom didn't dominate
386 // the header but did dominate a predecessor outside of the loop. Now
387 // we change this entry to include the preheader in the DF instead of
389 DominanceFrontier::iterator DFI = DF->find(PredDom);
390 assert(DFI != DF->end() && "No dominance frontier for node?");
391 if (DFI->second.count(Header)) {
392 DF->removeFromFrontier(DFI, Header);
393 DF->addToFrontier(DFI, NewBB);
400 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
401 /// blocks. This method is used to split exit blocks that have predecessors
402 /// outside of the loop.
403 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
404 DominatorSet &DS = getAnalysis<DominatorSet>();
406 std::vector<BasicBlock*> LoopBlocks;
407 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
409 LoopBlocks.push_back(*I);
411 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
412 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
414 // Update Loop Information - we know that the new block will be in the parent
416 if (Loop *Parent = L->getParentLoop())
417 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
419 // Update dominator information (set, immdom, domtree, and domfrontier)
420 UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
424 /// AddBlockAndPredsToSet - Add the specified block, and all of its
425 /// predecessors, to the specified set, if it's not already in there. Stop
426 /// predecessor traversal when we reach StopBlock.
427 static void AddBlockAndPredsToSet(BasicBlock *BB, BasicBlock *StopBlock,
428 std::set<BasicBlock*> &Blocks) {
429 if (!Blocks.insert(BB).second) return; // already processed.
430 if (BB == StopBlock) return; // Stop here!
432 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
433 AddBlockAndPredsToSet(*I, StopBlock, Blocks);
436 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
437 /// PHI node that tells us how to partition the loops.
438 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorSet &DS,
440 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
441 PHINode *PN = cast<PHINode>(I);
443 if (Value *V = PN->hasConstantValue())
444 if (!isa<Instruction>(V) || DS.dominates(cast<Instruction>(V), PN)) {
445 // This is a degenerate PHI already, don't modify it!
446 PN->replaceAllUsesWith(V);
447 if (AA) AA->deleteValue(PN);
448 PN->eraseFromParent();
452 // Scan this PHI node looking for a use of the PHI node by itself.
453 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
454 if (PN->getIncomingValue(i) == PN &&
455 L->contains(PN->getIncomingBlock(i)))
456 // We found something tasty to remove.
462 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
463 /// them out into a nested loop. This is important for code that looks like
468 /// br cond, Loop, Next
470 /// br cond2, Loop, Out
472 /// To identify this common case, we look at the PHI nodes in the header of the
473 /// loop. PHI nodes with unchanging values on one backedge correspond to values
474 /// that change in the "outer" loop, but not in the "inner" loop.
476 /// If we are able to separate out a loop, return the new outer loop that was
479 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
480 PHINode *PN = FindPHIToPartitionLoops(L, getAnalysis<DominatorSet>(), AA);
481 if (PN == 0) return 0; // No known way to partition.
483 // Pull out all predecessors that have varying values in the loop. This
484 // handles the case when a PHI node has multiple instances of itself as
486 std::vector<BasicBlock*> OuterLoopPreds;
487 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
488 if (PN->getIncomingValue(i) != PN ||
489 !L->contains(PN->getIncomingBlock(i)))
490 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
492 BasicBlock *Header = L->getHeader();
493 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
495 // Update dominator information (set, immdom, domtree, and domfrontier)
496 UpdateDomInfoForRevectoredPreds(NewBB, OuterLoopPreds);
498 // Create the new outer loop.
499 Loop *NewOuter = new Loop();
501 LoopInfo &LI = getAnalysis<LoopInfo>();
503 // Change the parent loop to use the outer loop as its child now.
504 if (Loop *Parent = L->getParentLoop())
505 Parent->replaceChildLoopWith(L, NewOuter);
507 LI.changeTopLevelLoop(L, NewOuter);
509 // This block is going to be our new header block: add it to this loop and all
511 NewOuter->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
513 // L is now a subloop of our outer loop.
514 NewOuter->addChildLoop(L);
516 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
517 NewOuter->addBlockEntry(L->getBlocks()[i]);
519 // Determine which blocks should stay in L and which should be moved out to
520 // the Outer loop now.
521 DominatorSet &DS = getAnalysis<DominatorSet>();
522 std::set<BasicBlock*> BlocksInL;
523 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
524 if (DS.dominates(Header, *PI))
525 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
528 // Scan all of the loop children of L, moving them to OuterLoop if they are
529 // not part of the inner loop.
530 for (Loop::iterator I = L->begin(); I != L->end(); )
531 if (BlocksInL.count((*I)->getHeader()))
532 ++I; // Loop remains in L
534 NewOuter->addChildLoop(L->removeChildLoop(I));
536 // Now that we know which blocks are in L and which need to be moved to
537 // OuterLoop, move any blocks that need it.
538 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
539 BasicBlock *BB = L->getBlocks()[i];
540 if (!BlocksInL.count(BB)) {
541 // Move this block to the parent, updating the exit blocks sets
542 L->removeBlockFromLoop(BB);
544 LI.changeLoopFor(BB, NewOuter);
554 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
555 /// has more than one backedge in it. If this occurs, revector all of these
556 /// backedges to target a new basic block and have that block branch to the loop
557 /// header. This ensures that loops have exactly one backedge.
559 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
560 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
562 // Get information about the loop
563 BasicBlock *Preheader = L->getLoopPreheader();
564 BasicBlock *Header = L->getHeader();
565 Function *F = Header->getParent();
567 // Figure out which basic blocks contain back-edges to the loop header.
568 std::vector<BasicBlock*> BackedgeBlocks;
569 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
570 if (*I != Preheader) BackedgeBlocks.push_back(*I);
572 // Create and insert the new backedge block...
573 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
574 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
576 // Move the new backedge block to right after the last backedge block.
577 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
578 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
580 // Now that the block has been inserted into the function, create PHI nodes in
581 // the backedge block which correspond to any PHI nodes in the header block.
582 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
583 PHINode *PN = cast<PHINode>(I);
584 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
586 NewPN->reserveOperandSpace(BackedgeBlocks.size());
587 if (AA) AA->copyValue(PN, NewPN);
589 // Loop over the PHI node, moving all entries except the one for the
590 // preheader over to the new PHI node.
591 unsigned PreheaderIdx = ~0U;
592 bool HasUniqueIncomingValue = true;
593 Value *UniqueValue = 0;
594 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
595 BasicBlock *IBB = PN->getIncomingBlock(i);
596 Value *IV = PN->getIncomingValue(i);
597 if (IBB == Preheader) {
600 NewPN->addIncoming(IV, IBB);
601 if (HasUniqueIncomingValue) {
602 if (UniqueValue == 0)
604 else if (UniqueValue != IV)
605 HasUniqueIncomingValue = false;
610 // Delete all of the incoming values from the old PN except the preheader's
611 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
612 if (PreheaderIdx != 0) {
613 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
614 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
616 // Nuke all entries except the zero'th.
617 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
618 PN->removeIncomingValue(e-i, false);
620 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
621 PN->addIncoming(NewPN, BEBlock);
623 // As an optimization, if all incoming values in the new PhiNode (which is a
624 // subset of the incoming values of the old PHI node) have the same value,
625 // eliminate the PHI Node.
626 if (HasUniqueIncomingValue) {
627 NewPN->replaceAllUsesWith(UniqueValue);
628 if (AA) AA->deleteValue(NewPN);
629 BEBlock->getInstList().erase(NewPN);
633 // Now that all of the PHI nodes have been inserted and adjusted, modify the
634 // backedge blocks to just to the BEBlock instead of the header.
635 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
636 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
637 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
638 if (TI->getSuccessor(Op) == Header)
639 TI->setSuccessor(Op, BEBlock);
642 //===--- Update all analyses which we must preserve now -----------------===//
644 // Update Loop Information - we know that this block is now in the current
645 // loop and all parent loops.
646 L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>());
648 // Update dominator information (set, immdom, domtree, and domfrontier)
649 UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
652 /// UpdateDomInfoForRevectoredPreds - This method is used to update the four
653 /// different kinds of dominator information (dominator sets, immediate
654 /// dominators, dominator trees, and dominance frontiers) after a new block has
655 /// been added to the CFG.
657 /// This only supports the case when an existing block (known as "NewBBSucc"),
658 /// had some of its predecessors factored into a new basic block. This
659 /// transformation inserts a new basic block ("NewBB"), with a single
660 /// unconditional branch to NewBBSucc, and moves some predecessors of
661 /// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
662 /// PredBlocks, even though they are the same as
663 /// pred_begin(NewBB)/pred_end(NewBB).
665 void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
666 std::vector<BasicBlock*> &PredBlocks) {
667 assert(!PredBlocks.empty() && "No predblocks??");
668 assert(succ_begin(NewBB) != succ_end(NewBB) &&
669 ++succ_begin(NewBB) == succ_end(NewBB) &&
670 "NewBB should have a single successor!");
671 BasicBlock *NewBBSucc = *succ_begin(NewBB);
672 DominatorSet &DS = getAnalysis<DominatorSet>();
674 // Update dominator information... The blocks that dominate NewBB are the
675 // intersection of the dominators of predecessors, plus the block itself.
677 DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
678 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
679 set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i]));
680 NewBBDomSet.insert(NewBB); // All blocks dominate themselves...
681 DS.addBasicBlock(NewBB, NewBBDomSet);
683 // The newly inserted basic block will dominate existing basic blocks iff the
684 // PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
685 // the non-pred blocks, then they all must be the same block!
687 bool NewBBDominatesNewBBSucc = true;
689 BasicBlock *OnePred = PredBlocks[0];
690 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
691 if (PredBlocks[i] != OnePred) {
692 NewBBDominatesNewBBSucc = false;
696 if (NewBBDominatesNewBBSucc)
697 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
699 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
700 NewBBDominatesNewBBSucc = false;
705 // The other scenario where the new block can dominate its successors are when
706 // all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
708 if (!NewBBDominatesNewBBSucc) {
709 NewBBDominatesNewBBSucc = true;
710 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
712 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
713 NewBBDominatesNewBBSucc = false;
718 // If NewBB dominates some blocks, then it will dominate all blocks that
720 if (NewBBDominatesNewBBSucc) {
721 BasicBlock *PredBlock = PredBlocks[0];
722 Function *F = NewBB->getParent();
723 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
724 if (DS.dominates(NewBBSucc, I))
725 DS.addDominator(I, NewBB);
728 // Update immediate dominator information if we have it...
729 BasicBlock *NewBBIDom = 0;
730 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
731 // To find the immediate dominator of the new exit node, we trace up the
732 // immediate dominators of a predecessor until we find a basic block that
733 // dominates the exit block.
735 BasicBlock *Dom = PredBlocks[0]; // Some random predecessor...
736 while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator...
737 assert(Dom != 0 && "No shared dominator found???");
741 // Set the immediate dominator now...
742 ID->addNewBlock(NewBB, Dom);
743 NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
745 // If NewBB strictly dominates other blocks, we need to update their idom's
746 // now. The only block that need adjustment is the NewBBSucc block, whose
747 // idom should currently be set to PredBlocks[0].
748 if (NewBBDominatesNewBBSucc)
749 ID->setImmediateDominator(NewBBSucc, NewBB);
752 // Update DominatorTree information if it is active.
753 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
754 // If we don't have ImmediateDominator info around, calculate the idom as
756 DominatorTree::Node *NewBBIDomNode;
758 NewBBIDomNode = DT->getNode(NewBBIDom);
760 NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred
761 while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
762 NewBBIDomNode = NewBBIDomNode->getIDom();
763 assert(NewBBIDomNode && "No shared dominator found??");
767 // Create the new dominator tree node... and set the idom of NewBB.
768 DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
770 // If NewBB strictly dominates other blocks, then it is now the immediate
771 // dominator of NewBBSucc. Update the dominator tree as appropriate.
772 if (NewBBDominatesNewBBSucc) {
773 DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
774 DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
778 // Update dominance frontier information...
779 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
780 // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
781 // DF(PredBlocks[0]) without the stuff that the new block does not dominate
783 if (NewBBDominatesNewBBSucc) {
784 DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
785 if (DFI != DF->end()) {
786 DominanceFrontier::DomSetType Set = DFI->second;
787 // Filter out stuff in Set that we do not dominate a predecessor of.
788 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
789 E = Set.end(); SetI != E;) {
790 bool DominatesPred = false;
791 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
793 if (DS.dominates(NewBB, *PI))
794 DominatesPred = true;
801 DF->addBasicBlock(NewBB, Set);
805 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
806 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
807 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
808 DominanceFrontier::DomSetType NewDFSet;
809 NewDFSet.insert(NewBBSucc);
810 DF->addBasicBlock(NewBB, NewDFSet);
813 // Now we must loop over all of the dominance frontiers in the function,
814 // replacing occurrences of NewBBSucc with NewBB in some cases. All
815 // blocks that dominate a block in PredBlocks and contained NewBBSucc in
816 // their dominance frontier must be updated to contain NewBB instead.
818 for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
819 BasicBlock *Pred = PredBlocks[i];
820 // Get all of the dominators of the predecessor...
821 const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
822 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
823 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
824 BasicBlock *PredDom = *PDI;
826 // If the NewBBSucc node is in DF(PredDom), then PredDom didn't
827 // dominate NewBBSucc but did dominate a predecessor of it. Now we
828 // change this entry to include NewBB in the DF instead of NewBBSucc.
829 DominanceFrontier::iterator DFI = DF->find(PredDom);
830 assert(DFI != DF->end() && "No dominance frontier for node?");
831 if (DFI->second.count(NewBBSucc)) {
832 // If NewBBSucc should not stay in our dominator frontier, remove it.
833 // We remove it unless there is a predecessor of NewBBSucc that we
834 // dominate, but we don't strictly dominate NewBBSucc.
835 bool ShouldRemove = true;
836 if (PredDom == NewBBSucc || !DS.dominates(PredDom, NewBBSucc)) {
837 // Okay, we know that PredDom does not strictly dominate NewBBSucc.
838 // Check to see if it dominates any predecessors of NewBBSucc.
839 for (pred_iterator PI = pred_begin(NewBBSucc),
840 E = pred_end(NewBBSucc); PI != E; ++PI)
841 if (DS.dominates(PredDom, *PI)) {
842 ShouldRemove = false;
848 DF->removeFromFrontier(DFI, NewBBSucc);
849 DF->addToFrontier(DFI, NewBB);