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/Function.h"
37 #include "llvm/iTerminators.h"
38 #include "llvm/iPHINode.h"
39 #include "llvm/Constant.h"
40 #include "llvm/Analysis/Dominators.h"
41 #include "llvm/Analysis/LoopInfo.h"
42 #include "llvm/Support/CFG.h"
43 #include "Support/SetOperations.h"
44 #include "Support/Statistic.h"
45 #include "Support/DepthFirstIterator.h"
50 NumInserted("loopsimplify", "Number of pre-header or exit blocks inserted");
52 struct LoopSimplify : public FunctionPass {
53 virtual bool runOnFunction(Function &F);
55 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
56 // We need loop information to identify the loops...
57 AU.addRequired<LoopInfo>();
58 AU.addRequired<DominatorSet>();
60 AU.addPreserved<LoopInfo>();
61 AU.addPreserved<DominatorSet>();
62 AU.addPreserved<ImmediateDominators>();
63 AU.addPreserved<DominatorTree>();
64 AU.addPreserved<DominanceFrontier>();
65 AU.addPreservedID(BreakCriticalEdgesID); // No crit edges added....
68 bool ProcessLoop(Loop *L);
69 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
70 const std::vector<BasicBlock*> &Preds);
71 void RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
72 void InsertPreheaderForLoop(Loop *L);
73 void InsertUniqueBackedgeBlock(Loop *L);
75 void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
76 std::vector<BasicBlock*> &PredBlocks);
79 RegisterOpt<LoopSimplify>
80 X("loopsimplify", "Canonicalize natural loops", true);
83 // Publically exposed interface to pass...
84 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
85 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
87 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
88 /// it in any convenient order) inserting preheaders...
90 bool LoopSimplify::runOnFunction(Function &F) {
92 LoopInfo &LI = getAnalysis<LoopInfo>();
94 for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I)
95 Changed |= ProcessLoop(*I);
101 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
102 /// all loops have preheaders.
104 bool LoopSimplify::ProcessLoop(Loop *L) {
105 bool Changed = false;
107 // Does the loop already have a preheader? If so, don't modify the loop...
108 if (L->getLoopPreheader() == 0) {
109 InsertPreheaderForLoop(L);
114 // Next, check to make sure that all exit nodes of the loop only have
115 // predecessors that are inside of the loop. This check guarantees that the
116 // loop preheader/header will dominate the exit blocks. If the exit block has
117 // predecessors from outside of the loop, split the edge now.
118 for (unsigned i = 0, e = L->getExitBlocks().size(); i != e; ++i) {
119 BasicBlock *ExitBlock = L->getExitBlocks()[i];
120 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
122 if (!L->contains(*PI)) {
123 RewriteLoopExitBlock(L, ExitBlock);
130 // The preheader may have more than two predecessors at this point (from the
131 // preheader and from the backedges). To simplify the loop more, insert an
132 // extra back-edge block in the loop so that there is exactly one backedge.
133 if (L->getNumBackEdges() != 1) {
134 InsertUniqueBackedgeBlock(L);
139 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
140 Changed |= ProcessLoop(*I);
144 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
145 /// to move the predecessors specified in the Preds list to point to the new
146 /// block, leaving the remaining predecessors pointing to BB. This method
147 /// updates the SSA PHINode's, but no other analyses.
149 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
151 const std::vector<BasicBlock*> &Preds) {
153 // Create new basic block, insert right before the original block...
154 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
156 // The preheader first gets an unconditional branch to the loop header...
157 BranchInst *BI = new BranchInst(BB, NewBB);
159 // For every PHI node in the block, insert a PHI node into NewBB where the
160 // incoming values from the out of loop edges are moved to NewBB. We have two
161 // possible cases here. If the loop is dead, we just insert dummy entries
162 // into the PHI nodes for the new edge. If the loop is not dead, we move the
163 // incoming edges in BB into new PHI nodes in NewBB.
165 if (!Preds.empty()) { // Is the loop not obviously dead?
166 // Check to see if the values being merged into the new block need PHI
167 // nodes. If so, insert them.
168 for (BasicBlock::iterator I = BB->begin();
169 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
171 // Check to see if all of the values coming in are the same. If so, we
172 // don't need to create a new PHI node.
173 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
174 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
175 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
180 // If the values coming into the block are not the same, we need a PHI.
182 // Create the new PHI node, insert it into NewBB at the end of the block
183 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
185 // Move all of the edges from blocks outside the loop to the new PHI
186 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
187 Value *V = PN->removeIncomingValue(Preds[i]);
188 NewPHI->addIncoming(V, Preds[i]);
192 // Remove all of the edges coming into the PHI nodes from outside of the
194 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
195 PN->removeIncomingValue(Preds[i], false);
198 // Add an incoming value to the PHI node in the loop for the preheader
200 PN->addIncoming(InVal, NewBB);
203 // Now that the PHI nodes are updated, actually move the edges from
204 // Preds to point to NewBB instead of BB.
206 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
207 TerminatorInst *TI = Preds[i]->getTerminator();
208 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
209 if (TI->getSuccessor(s) == BB)
210 TI->setSuccessor(s, NewBB);
213 } else { // Otherwise the loop is dead...
214 for (BasicBlock::iterator I = BB->begin();
215 PHINode *PN = dyn_cast<PHINode>(I); ++I)
216 // Insert dummy values as the incoming value...
217 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
222 // ChangeExitBlock - This recursive function is used to change any exit blocks
223 // that use OldExit to use NewExit instead. This is recursive because children
224 // may need to be processed as well.
226 static void ChangeExitBlock(Loop *L, BasicBlock *OldExit, BasicBlock *NewExit) {
227 if (L->hasExitBlock(OldExit)) {
228 L->changeExitBlock(OldExit, NewExit);
229 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
230 ChangeExitBlock(*I, OldExit, NewExit);
235 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
236 /// preheader, this method is called to insert one. This method has two phases:
237 /// preheader insertion and analysis updating.
239 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
240 BasicBlock *Header = L->getHeader();
242 // Compute the set of predecessors of the loop that are not in the loop.
243 std::vector<BasicBlock*> OutsideBlocks;
244 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
246 if (!L->contains(*PI)) // Coming in from outside the loop?
247 OutsideBlocks.push_back(*PI); // Keep track of it...
249 // Split out the loop pre-header
251 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
253 //===--------------------------------------------------------------------===//
254 // Update analysis results now that we have performed the transformation
257 // We know that we have loop information to update... update it now.
258 if (Loop *Parent = L->getParentLoop())
259 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
261 // If the header for the loop used to be an exit node for another loop, then
262 // we need to update this to know that the loop-preheader is now the exit
263 // node. Note that the only loop that could have our header as an exit node
264 // is a sibling loop, ie, one with the same parent loop, or one if it's
267 LoopInfo::iterator ParentLoops, ParentLoopsE;
268 if (Loop *Parent = L->getParentLoop()) {
269 ParentLoops = Parent->begin();
270 ParentLoopsE = Parent->end();
271 } else { // Must check top-level loops...
272 ParentLoops = getAnalysis<LoopInfo>().begin();
273 ParentLoopsE = getAnalysis<LoopInfo>().end();
276 // Loop over all sibling loops, performing the substitution (recursively to
277 // include child loops)...
278 for (; ParentLoops != ParentLoopsE; ++ParentLoops)
279 ChangeExitBlock(*ParentLoops, Header, NewBB);
281 DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info
283 // The blocks that dominate NewBB are the blocks that dominate Header,
284 // minus Header, plus NewBB.
285 DominatorSet::DomSetType DomSet = DS.getDominators(Header);
286 DomSet.insert(NewBB); // We dominate ourself
287 DomSet.erase(Header); // Header does not dominate us...
288 DS.addBasicBlock(NewBB, DomSet);
290 // The newly created basic block dominates all nodes dominated by Header.
291 for (Function::iterator I = Header->getParent()->begin(),
292 E = Header->getParent()->end(); I != E; ++I)
293 if (DS.dominates(Header, I))
294 DS.addDominator(I, NewBB);
297 // Update immediate dominator information if we have it...
298 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
299 // Whatever i-dominated the header node now immediately dominates NewBB
300 ID->addNewBlock(NewBB, ID->get(Header));
302 // The preheader now is the immediate dominator for the header node...
303 ID->setImmediateDominator(Header, NewBB);
306 // Update DominatorTree information if it is active.
307 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
308 // The immediate dominator of the preheader is the immediate dominator of
311 DominatorTree::Node *HeaderNode = DT->getNode(Header);
312 DominatorTree::Node *PHNode = DT->createNewNode(NewBB,
313 HeaderNode->getIDom());
315 // Change the header node so that PNHode is the new immediate dominator
316 DT->changeImmediateDominator(HeaderNode, PHNode);
319 // Update dominance frontier information...
320 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
321 // The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates
322 // everything that Header does, and it strictly dominates Header in
324 assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?");
325 DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second;
326 NewDFSet.erase(Header);
327 DF->addBasicBlock(NewBB, NewDFSet);
329 // Now we must loop over all of the dominance frontiers in the function,
330 // replacing occurrences of Header with NewBB in some cases. If a block
331 // dominates a (now) predecessor of NewBB, but did not strictly dominate
332 // Header, it will have Header in it's DF set, but should now have NewBB in
334 for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) {
335 // Get all of the dominators of the predecessor...
336 const DominatorSet::DomSetType &PredDoms =
337 DS.getDominators(OutsideBlocks[i]);
338 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
339 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
340 BasicBlock *PredDom = *PDI;
341 // If the loop header is in DF(PredDom), then PredDom didn't dominate
342 // the header but did dominate a predecessor outside of the loop. Now
343 // we change this entry to include the preheader in the DF instead of
345 DominanceFrontier::iterator DFI = DF->find(PredDom);
346 assert(DFI != DF->end() && "No dominance frontier for node?");
347 if (DFI->second.count(Header)) {
348 DF->removeFromFrontier(DFI, Header);
349 DF->addToFrontier(DFI, NewBB);
356 void LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
357 DominatorSet &DS = getAnalysis<DominatorSet>();
358 assert(std::find(L->getExitBlocks().begin(), L->getExitBlocks().end(), Exit)
359 != L->getExitBlocks().end() && "Not a current exit block!");
361 std::vector<BasicBlock*> LoopBlocks;
362 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
364 LoopBlocks.push_back(*I);
366 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
367 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
369 // Update Loop Information - we know that the new block will be in the parent
371 if (Loop *Parent = L->getParentLoop())
372 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
374 // Replace any instances of Exit with NewBB in this and any nested loops...
375 for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I)
376 if (I->hasExitBlock(Exit))
377 I->changeExitBlock(Exit, NewBB); // Update exit block information
379 // Update dominator information (set, immdom, domtree, and domfrontier)
380 UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
383 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
384 /// has more than one backedge in it. If this occurs, revector all of these
385 /// backedges to target a new basic block and have that block branch to the loop
386 /// header. This ensures that loops have exactly one backedge.
388 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
389 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
391 // Get information about the loop
392 BasicBlock *Preheader = L->getLoopPreheader();
393 BasicBlock *Header = L->getHeader();
394 Function *F = Header->getParent();
396 // Figure out which basic blocks contain back-edges to the loop header.
397 std::vector<BasicBlock*> BackedgeBlocks;
398 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
399 if (*I != Preheader) BackedgeBlocks.push_back(*I);
401 // Create and insert the new backedge block...
402 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
403 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
405 // Move the new backedge block to right after the last backedge block.
406 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
407 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
409 // Now that the block has been inserted into the function, create PHI nodes in
410 // the backedge block which correspond to any PHI nodes in the header block.
411 for (BasicBlock::iterator I = Header->begin();
412 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
413 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
415 NewPN->op_reserve(2*BackedgeBlocks.size());
417 // Loop over the PHI node, moving all entries except the one for the
418 // preheader over to the new PHI node.
419 unsigned PreheaderIdx = ~0U;
420 bool HasUniqueIncomingValue = true;
421 Value *UniqueValue = 0;
422 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
423 BasicBlock *IBB = PN->getIncomingBlock(i);
424 Value *IV = PN->getIncomingValue(i);
425 if (IBB == Preheader) {
428 NewPN->addIncoming(IV, IBB);
429 if (HasUniqueIncomingValue) {
430 if (UniqueValue == 0)
432 else if (UniqueValue != IV)
433 HasUniqueIncomingValue = false;
438 // Delete all of the incoming values from the old PN except the preheader's
439 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
440 if (PreheaderIdx != 0) {
441 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
442 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
444 PN->op_erase(PN->op_begin()+2, PN->op_end());
446 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
447 PN->addIncoming(NewPN, BEBlock);
449 // As an optimization, if all incoming values in the new PhiNode (which is a
450 // subset of the incoming values of the old PHI node) have the same value,
451 // eliminate the PHI Node.
452 if (HasUniqueIncomingValue) {
453 NewPN->replaceAllUsesWith(UniqueValue);
454 BEBlock->getInstList().erase(NewPN);
458 // Now that all of the PHI nodes have been inserted and adjusted, modify the
459 // backedge blocks to just to the BEBlock instead of the header.
460 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
461 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
462 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
463 if (TI->getSuccessor(Op) == Header)
464 TI->setSuccessor(Op, BEBlock);
467 //===--- Update all analyses which we must preserve now -----------------===//
469 // Update Loop Information - we know that this block is now in the current
470 // loop and all parent loops.
471 L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>());
473 // Replace any instances of Exit with NewBB in this and any nested loops...
474 for (df_iterator<Loop*> I = df_begin(L), E = df_end(L); I != E; ++I)
475 if (I->hasExitBlock(Header))
476 I->changeExitBlock(Header, BEBlock); // Update exit block information
478 // Update dominator information (set, immdom, domtree, and domfrontier)
479 UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
482 /// UpdateDomInfoForRevectoredPreds - This method is used to update the four
483 /// different kinds of dominator information (dominator sets, immediate
484 /// dominators, dominator trees, and dominance frontiers) after a new block has
485 /// been added to the CFG.
487 /// This only supports the case when an existing block (known as "NewBBSucc"),
488 /// had some of its predecessors factored into a new basic block. This
489 /// transformation inserts a new basic block ("NewBB"), with a single
490 /// unconditional branch to NewBBSucc, and moves some predecessors of
491 /// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
492 /// PredBlocks, even though they are the same as
493 /// pred_begin(NewBB)/pred_end(NewBB).
495 void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
496 std::vector<BasicBlock*> &PredBlocks) {
497 assert(!PredBlocks.empty() && "No predblocks??");
498 assert(succ_begin(NewBB) != succ_end(NewBB) &&
499 ++succ_begin(NewBB) == succ_end(NewBB) &&
500 "NewBB should have a single successor!");
501 BasicBlock *NewBBSucc = *succ_begin(NewBB);
502 DominatorSet &DS = getAnalysis<DominatorSet>();
504 // The newly inserted basic block will dominate existing basic blocks iff the
505 // PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
506 // the non-pred blocks, then they all must be the same block!
507 bool NewBBDominatesNewBBSucc = true;
509 BasicBlock *OnePred = PredBlocks[0];
510 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
511 if (PredBlocks[i] != OnePred) {
512 NewBBDominatesNewBBSucc = false;
516 if (NewBBDominatesNewBBSucc)
517 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
519 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
520 NewBBDominatesNewBBSucc = false;
525 // Update dominator information... The blocks that dominate NewBB are the
526 // intersection of the dominators of predecessors, plus the block itself.
527 // The newly created basic block does not dominate anything except itself.
529 DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
530 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
531 set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i]));
532 NewBBDomSet.insert(NewBB); // All blocks dominate themselves...
533 DS.addBasicBlock(NewBB, NewBBDomSet);
535 // If NewBB dominates some blocks, then it will dominate all blocks that
537 if (NewBBDominatesNewBBSucc) {
538 BasicBlock *PredBlock = PredBlocks[0];
539 Function *F = NewBB->getParent();
540 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
541 if (DS.dominates(NewBBSucc, I))
542 DS.addDominator(I, NewBB);
545 // Update immediate dominator information if we have it...
546 BasicBlock *NewBBIDom = 0;
547 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
548 // To find the immediate dominator of the new exit node, we trace up the
549 // immediate dominators of a predecessor until we find a basic block that
550 // dominates the exit block.
552 BasicBlock *Dom = PredBlocks[0]; // Some random predecessor...
553 while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator...
554 assert(Dom != 0 && "No shared dominator found???");
558 // Set the immediate dominator now...
559 ID->addNewBlock(NewBB, Dom);
560 NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
562 // If NewBB strictly dominates other blocks, we need to update their idom's
563 // now. The only block that need adjustment is the NewBBSucc block, whose
564 // idom should currently be set to PredBlocks[0].
565 if (NewBBDominatesNewBBSucc) {
566 assert(ID->get(NewBBSucc) == PredBlocks[0] &&
567 "Immediate dominator update code broken!");
568 ID->setImmediateDominator(NewBBSucc, NewBB);
572 // Update DominatorTree information if it is active.
573 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
574 // If we don't have ImmediateDominator info around, calculate the idom as
576 DominatorTree::Node *NewBBIDomNode;
578 NewBBIDomNode = DT->getNode(NewBBIDom);
580 NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred
581 while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
582 NewBBIDomNode = NewBBIDomNode->getIDom();
583 assert(NewBBIDomNode && "No shared dominator found??");
587 // Create the new dominator tree node... and set the idom of NewBB.
588 DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
590 // If NewBB strictly dominates other blocks, then it is now the immediate
591 // dominator of NewBBSucc. Update the dominator tree as appropriate.
592 if (NewBBDominatesNewBBSucc) {
593 DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
594 assert(NewBBSuccNode->getIDom()->getBlock() == PredBlocks[0] &&
595 "Immediate tree update code broken!");
596 DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
600 // Update dominance frontier information...
601 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
602 // If NewBB dominates NewBBSucc, then the global dominance frontiers are not
603 // changed. DF(NewBB) is now going to be the DF(PredBlocks[0]) without the
604 // stuff that the new block does not dominate a predecessor of.
605 if (NewBBDominatesNewBBSucc) {
606 DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
607 if (DFI != DF->end()) {
608 DominanceFrontier::DomSetType Set = DFI->second;
609 // Filter out stuff in Set that we do not dominate a predecessor of.
610 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
611 E = Set.end(); SetI != E;) {
612 bool DominatesPred = false;
613 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
615 if (DS.dominates(NewBB, *PI))
616 DominatesPred = true;
623 DF->addBasicBlock(NewBB, Set);
627 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
628 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
629 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
630 DominanceFrontier::DomSetType NewDFSet;
631 NewDFSet.insert(NewBBSucc);
632 DF->addBasicBlock(NewBB, NewDFSet);
634 // Now we must loop over all of the dominance frontiers in the function,
635 // replacing occurrences of NewBBSucc with NewBB in some cases. All
636 // blocks that dominate a block in PredBlocks and contained NewBBSucc in
637 // their dominance frontier must be updated to contain NewBB instead.
639 for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
640 BasicBlock *Pred = PredBlocks[i];
641 // Get all of the dominators of the predecessor...
642 const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
643 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
644 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
645 BasicBlock *PredDom = *PDI;
647 // If the NewBBSucc node is in DF(PredDom), then PredDom didn't
648 // dominate NewBBSucc but did dominate a predecessor of it. Now we
649 // change this entry to include NewBB in the DF instead of NewBBSucc.
650 DominanceFrontier::iterator DFI = DF->find(PredDom);
651 assert(DFI != DF->end() && "No dominance frontier for node?");
652 if (DFI->second.count(NewBBSucc)) {
653 DF->removeFromFrontier(DFI, NewBBSucc);
654 DF->addToFrontier(DFI, NewBB);