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/Dominators.h"
41 #include "llvm/Analysis/LoopInfo.h"
42 #include "llvm/Support/CFG.h"
43 #include "llvm/Transforms/Utils/Local.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 virtual bool runOnFunction(Function &F);
59 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
60 // We need loop information to identify the loops...
61 AU.addRequired<LoopInfo>();
62 AU.addRequired<DominatorSet>();
63 AU.addRequired<DominatorTree>();
65 AU.addPreserved<LoopInfo>();
66 AU.addPreserved<DominatorSet>();
67 AU.addPreserved<ImmediateDominators>();
68 AU.addPreserved<DominatorTree>();
69 AU.addPreserved<DominanceFrontier>();
70 AU.addPreservedID(BreakCriticalEdgesID); // No crit edges added....
73 bool ProcessLoop(Loop *L);
74 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
75 const std::vector<BasicBlock*> &Preds);
76 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
77 void InsertPreheaderForLoop(Loop *L);
78 Loop *SeparateNestedLoop(Loop *L);
79 void InsertUniqueBackedgeBlock(Loop *L);
81 void UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
82 std::vector<BasicBlock*> &PredBlocks);
85 RegisterOpt<LoopSimplify>
86 X("loopsimplify", "Canonicalize natural loops", true);
89 // Publically exposed interface to pass...
90 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
91 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
93 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
94 /// it in any convenient order) inserting preheaders...
96 bool LoopSimplify::runOnFunction(Function &F) {
98 LoopInfo &LI = getAnalysis<LoopInfo>();
100 for (LoopInfo::iterator I = LI.begin(), E = LI.end(); I != E; ++I)
101 Changed |= ProcessLoop(*I);
107 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
108 /// all loops have preheaders.
110 bool LoopSimplify::ProcessLoop(Loop *L) {
111 bool Changed = false;
113 // Check to see that no blocks (other than the header) in the loop have
114 // predecessors that are not in the loop. This is not valid for natural
115 // loops, but can occur if the blocks are unreachable. Since they are
116 // unreachable we can just shamelessly destroy their terminators to make them
117 // not branch into the loop!
118 assert(L->getBlocks()[0] == L->getHeader() &&
119 "Header isn't first block in loop?");
120 for (unsigned i = 1, e = L->getBlocks().size(); i != e; ++i) {
121 BasicBlock *LoopBB = L->getBlocks()[i];
123 for (pred_iterator PI = pred_begin(LoopBB), E = pred_end(LoopBB);
125 if (!L->contains(*PI)) {
126 // This predecessor is not in the loop. Kill its terminator!
127 BasicBlock *DeadBlock = *PI;
128 for (succ_iterator SI = succ_begin(DeadBlock), E = succ_end(DeadBlock);
130 (*SI)->removePredecessor(DeadBlock); // Remove PHI node entries
132 // Delete the dead terminator.
133 DeadBlock->getInstList().pop_back();
136 if (LoopBB->getParent()->getReturnType() != Type::VoidTy)
137 RetVal = Constant::getNullValue(LoopBB->getParent()->getReturnType());
138 new ReturnInst(RetVal, DeadBlock);
139 goto Retry; // We just invalidated the pred_iterator. Retry.
143 // Does the loop already have a preheader? If so, don't modify the loop...
144 if (L->getLoopPreheader() == 0) {
145 InsertPreheaderForLoop(L);
150 // Next, check to make sure that all exit nodes of the loop only have
151 // predecessors that are inside of the loop. This check guarantees that the
152 // loop preheader/header will dominate the exit blocks. If the exit block has
153 // predecessors from outside of the loop, split the edge now.
154 std::vector<BasicBlock*> ExitBlocks;
155 L->getExitBlocks(ExitBlocks);
157 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
158 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
159 E = ExitBlockSet.end(); I != E; ++I) {
160 BasicBlock *ExitBlock = *I;
161 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
163 if (!L->contains(*PI)) {
164 RewriteLoopExitBlock(L, ExitBlock);
171 // If the header has more than two predecessors at this point (from the
172 // preheader and from multiple backedges), we must adjust the loop.
173 if (L->getNumBackEdges() != 1) {
174 // If this is really a nested loop, rip it out into a child loop.
175 if (Loop *NL = SeparateNestedLoop(L)) {
177 // This is a big restructuring change, reprocess the whole loop.
182 InsertUniqueBackedgeBlock(L);
187 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
188 Changed |= ProcessLoop(*I);
192 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
193 /// to move the predecessors specified in the Preds list to point to the new
194 /// block, leaving the remaining predecessors pointing to BB. This method
195 /// updates the SSA PHINode's, but no other analyses.
197 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
199 const std::vector<BasicBlock*> &Preds) {
201 // Create new basic block, insert right before the original block...
202 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
204 // The preheader first gets an unconditional branch to the loop header...
205 BranchInst *BI = new BranchInst(BB, NewBB);
207 // For every PHI node in the block, insert a PHI node into NewBB where the
208 // incoming values from the out of loop edges are moved to NewBB. We have two
209 // possible cases here. If the loop is dead, we just insert dummy entries
210 // into the PHI nodes for the new edge. If the loop is not dead, we move the
211 // incoming edges in BB into new PHI nodes in NewBB.
213 if (!Preds.empty()) { // Is the loop not obviously dead?
214 // Check to see if the values being merged into the new block need PHI
215 // nodes. If so, insert them.
216 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
217 PHINode *PN = cast<PHINode>(I);
220 // Check to see if all of the values coming in are the same. If so, we
221 // don't need to create a new PHI node.
222 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
223 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
224 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
229 // If the values coming into the block are not the same, we need a PHI.
231 // Create the new PHI node, insert it into NewBB at the end of the block
232 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
234 // Move all of the edges from blocks outside the loop to the new PHI
235 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
236 Value *V = PN->removeIncomingValue(Preds[i], false);
237 NewPHI->addIncoming(V, Preds[i]);
241 // Remove all of the edges coming into the PHI nodes from outside of the
243 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
244 PN->removeIncomingValue(Preds[i], false);
247 // Add an incoming value to the PHI node in the loop for the preheader
249 PN->addIncoming(InVal, NewBB);
251 // Can we eliminate this phi node now?
252 if (Value *V = hasConstantValue(PN)) {
253 PN->replaceAllUsesWith(V);
254 BB->getInstList().erase(PN);
258 // Now that the PHI nodes are updated, actually move the edges from
259 // Preds to point to NewBB instead of BB.
261 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
262 TerminatorInst *TI = Preds[i]->getTerminator();
263 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
264 if (TI->getSuccessor(s) == BB)
265 TI->setSuccessor(s, NewBB);
268 } else { // Otherwise the loop is dead...
269 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
270 PHINode *PN = cast<PHINode>(I);
271 // Insert dummy values as the incoming value...
272 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
278 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
279 /// preheader, this method is called to insert one. This method has two phases:
280 /// preheader insertion and analysis updating.
282 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
283 BasicBlock *Header = L->getHeader();
285 // Compute the set of predecessors of the loop that are not in the loop.
286 std::vector<BasicBlock*> OutsideBlocks;
287 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
289 if (!L->contains(*PI)) // Coming in from outside the loop?
290 OutsideBlocks.push_back(*PI); // Keep track of it...
292 // Split out the loop pre-header
294 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
296 //===--------------------------------------------------------------------===//
297 // Update analysis results now that we have performed the transformation
300 // We know that we have loop information to update... update it now.
301 if (Loop *Parent = L->getParentLoop())
302 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
304 // If the header for the loop used to be an exit node for another loop, then
305 // we need to update this to know that the loop-preheader is now the exit
306 // node. Note that the only loop that could have our header as an exit node
307 // is a sibling loop, ie, one with the same parent loop, or one if it's
310 LoopInfo::iterator ParentLoops, ParentLoopsE;
311 if (Loop *Parent = L->getParentLoop()) {
312 ParentLoops = Parent->begin();
313 ParentLoopsE = Parent->end();
314 } else { // Must check top-level loops...
315 ParentLoops = getAnalysis<LoopInfo>().begin();
316 ParentLoopsE = getAnalysis<LoopInfo>().end();
319 DominatorSet &DS = getAnalysis<DominatorSet>(); // Update dominator info
320 DominatorTree &DT = getAnalysis<DominatorTree>();
323 // Update the dominator tree information.
324 // The immediate dominator of the preheader is the immediate dominator of
326 DominatorTree::Node *PHDomTreeNode =
327 DT.createNewNode(NewBB, DT.getNode(Header)->getIDom());
329 // Change the header node so that PNHode is the new immediate dominator
330 DT.changeImmediateDominator(DT.getNode(Header), PHDomTreeNode);
333 // The blocks that dominate NewBB are the blocks that dominate Header,
334 // minus Header, plus NewBB.
335 DominatorSet::DomSetType DomSet = DS.getDominators(Header);
336 DomSet.erase(Header); // Header does not dominate us...
337 DS.addBasicBlock(NewBB, DomSet);
339 // The newly created basic block dominates all nodes dominated by Header.
340 for (df_iterator<DominatorTree::Node*> DFI = df_begin(PHDomTreeNode),
341 E = df_end(PHDomTreeNode); DFI != E; ++DFI)
342 DS.addDominator((*DFI)->getBlock(), NewBB);
345 // Update immediate dominator information if we have it...
346 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
347 // Whatever i-dominated the header node now immediately dominates NewBB
348 ID->addNewBlock(NewBB, ID->get(Header));
350 // The preheader now is the immediate dominator for the header node...
351 ID->setImmediateDominator(Header, NewBB);
354 // Update dominance frontier information...
355 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
356 // The DF(NewBB) is just (DF(Header)-Header), because NewBB dominates
357 // everything that Header does, and it strictly dominates Header in
359 assert(DF->find(Header) != DF->end() && "Header node doesn't have DF set?");
360 DominanceFrontier::DomSetType NewDFSet = DF->find(Header)->second;
361 NewDFSet.erase(Header);
362 DF->addBasicBlock(NewBB, NewDFSet);
364 // Now we must loop over all of the dominance frontiers in the function,
365 // replacing occurrences of Header with NewBB in some cases. If a block
366 // dominates a (now) predecessor of NewBB, but did not strictly dominate
367 // Header, it will have Header in it's DF set, but should now have NewBB in
369 for (unsigned i = 0, e = OutsideBlocks.size(); i != e; ++i) {
370 // Get all of the dominators of the predecessor...
371 const DominatorSet::DomSetType &PredDoms =
372 DS.getDominators(OutsideBlocks[i]);
373 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
374 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
375 BasicBlock *PredDom = *PDI;
376 // If the loop header is in DF(PredDom), then PredDom didn't dominate
377 // the header but did dominate a predecessor outside of the loop. Now
378 // we change this entry to include the preheader in the DF instead of
380 DominanceFrontier::iterator DFI = DF->find(PredDom);
381 assert(DFI != DF->end() && "No dominance frontier for node?");
382 if (DFI->second.count(Header)) {
383 DF->removeFromFrontier(DFI, Header);
384 DF->addToFrontier(DFI, NewBB);
391 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
392 /// blocks. This method is used to split exit blocks that have predecessors
393 /// outside of the loop.
394 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
395 DominatorSet &DS = getAnalysis<DominatorSet>();
397 std::vector<BasicBlock*> LoopBlocks;
398 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
400 LoopBlocks.push_back(*I);
402 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
403 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
405 // Update Loop Information - we know that the new block will be in the parent
407 if (Loop *Parent = L->getParentLoop())
408 Parent->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
410 // Update dominator information (set, immdom, domtree, and domfrontier)
411 UpdateDomInfoForRevectoredPreds(NewBB, LoopBlocks);
415 /// AddBlockAndPredsToSet - Add the specified block, and all of its
416 /// predecessors, to the specified set, if it's not already in there. Stop
417 /// predecessor traversal when we reach StopBlock.
418 static void AddBlockAndPredsToSet(BasicBlock *BB, BasicBlock *StopBlock,
419 std::set<BasicBlock*> &Blocks) {
420 if (!Blocks.insert(BB).second) return; // already processed.
421 if (BB == StopBlock) return; // Stop here!
423 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I)
424 AddBlockAndPredsToSet(*I, StopBlock, Blocks);
427 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
428 /// PHI node that tells us how to partition the loops.
429 static PHINode *FindPHIToPartitionLoops(Loop *L) {
430 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
431 PHINode *PN = cast<PHINode>(I);
433 if (Value *V = hasConstantValue(PN)) {
434 // This is a degenerate PHI already, don't modify it!
435 PN->replaceAllUsesWith(V);
436 PN->getParent()->getInstList().erase(PN);
438 // Scan this PHI node looking for a use of the PHI node by itself.
439 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
440 if (PN->getIncomingValue(i) == PN &&
441 L->contains(PN->getIncomingBlock(i)))
442 // We found something tasty to remove.
449 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
450 /// them out into a nested loop. This is important for code that looks like
455 /// br cond, Loop, Next
457 /// br cond2, Loop, Out
459 /// To identify this common case, we look at the PHI nodes in the header of the
460 /// loop. PHI nodes with unchanging values on one backedge correspond to values
461 /// that change in the "outer" loop, but not in the "inner" loop.
463 /// If we are able to separate out a loop, return the new outer loop that was
466 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
467 PHINode *PN = FindPHIToPartitionLoops(L);
468 if (PN == 0) return 0; // No known way to partition.
470 // Pull out all predecessors that have varying values in the loop. This
471 // handles the case when a PHI node has multiple instances of itself as
473 std::vector<BasicBlock*> OuterLoopPreds;
474 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
475 if (PN->getIncomingValue(i) != PN ||
476 !L->contains(PN->getIncomingBlock(i)))
477 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
479 BasicBlock *Header = L->getHeader();
480 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
482 // Update dominator information (set, immdom, domtree, and domfrontier)
483 UpdateDomInfoForRevectoredPreds(NewBB, OuterLoopPreds);
485 // Create the new outer loop.
486 Loop *NewOuter = new Loop();
488 LoopInfo &LI = getAnalysis<LoopInfo>();
490 // Change the parent loop to use the outer loop as its child now.
491 if (Loop *Parent = L->getParentLoop())
492 Parent->replaceChildLoopWith(L, NewOuter);
494 LI.changeTopLevelLoop(L, NewOuter);
496 // This block is going to be our new header block: add it to this loop and all
498 NewOuter->addBasicBlockToLoop(NewBB, getAnalysis<LoopInfo>());
500 // L is now a subloop of our outer loop.
501 NewOuter->addChildLoop(L);
503 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
504 NewOuter->addBlockEntry(L->getBlocks()[i]);
506 // Determine which blocks should stay in L and which should be moved out to
507 // the Outer loop now.
508 DominatorSet &DS = getAnalysis<DominatorSet>();
509 std::set<BasicBlock*> BlocksInL;
510 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
511 if (DS.dominates(Header, *PI))
512 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
515 // Scan all of the loop children of L, moving them to OuterLoop if they are
516 // not part of the inner loop.
517 for (Loop::iterator I = L->begin(); I != L->end(); )
518 if (BlocksInL.count((*I)->getHeader()))
519 ++I; // Loop remains in L
521 NewOuter->addChildLoop(L->removeChildLoop(I));
523 // Now that we know which blocks are in L and which need to be moved to
524 // OuterLoop, move any blocks that need it.
525 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
526 BasicBlock *BB = L->getBlocks()[i];
527 if (!BlocksInL.count(BB)) {
528 // Move this block to the parent, updating the exit blocks sets
529 L->removeBlockFromLoop(BB);
531 LI.changeLoopFor(BB, NewOuter);
541 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
542 /// has more than one backedge in it. If this occurs, revector all of these
543 /// backedges to target a new basic block and have that block branch to the loop
544 /// header. This ensures that loops have exactly one backedge.
546 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
547 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
549 // Get information about the loop
550 BasicBlock *Preheader = L->getLoopPreheader();
551 BasicBlock *Header = L->getHeader();
552 Function *F = Header->getParent();
554 // Figure out which basic blocks contain back-edges to the loop header.
555 std::vector<BasicBlock*> BackedgeBlocks;
556 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
557 if (*I != Preheader) BackedgeBlocks.push_back(*I);
559 // Create and insert the new backedge block...
560 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
561 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
563 // Move the new backedge block to right after the last backedge block.
564 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
565 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
567 // Now that the block has been inserted into the function, create PHI nodes in
568 // the backedge block which correspond to any PHI nodes in the header block.
569 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
570 PHINode *PN = cast<PHINode>(I);
571 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
573 NewPN->op_reserve(2*BackedgeBlocks.size());
575 // Loop over the PHI node, moving all entries except the one for the
576 // preheader over to the new PHI node.
577 unsigned PreheaderIdx = ~0U;
578 bool HasUniqueIncomingValue = true;
579 Value *UniqueValue = 0;
580 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
581 BasicBlock *IBB = PN->getIncomingBlock(i);
582 Value *IV = PN->getIncomingValue(i);
583 if (IBB == Preheader) {
586 NewPN->addIncoming(IV, IBB);
587 if (HasUniqueIncomingValue) {
588 if (UniqueValue == 0)
590 else if (UniqueValue != IV)
591 HasUniqueIncomingValue = false;
596 // Delete all of the incoming values from the old PN except the preheader's
597 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
598 if (PreheaderIdx != 0) {
599 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
600 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
602 PN->op_erase(PN->op_begin()+2, PN->op_end());
604 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
605 PN->addIncoming(NewPN, BEBlock);
607 // As an optimization, if all incoming values in the new PhiNode (which is a
608 // subset of the incoming values of the old PHI node) have the same value,
609 // eliminate the PHI Node.
610 if (HasUniqueIncomingValue) {
611 NewPN->replaceAllUsesWith(UniqueValue);
612 BEBlock->getInstList().erase(NewPN);
616 // Now that all of the PHI nodes have been inserted and adjusted, modify the
617 // backedge blocks to just to the BEBlock instead of the header.
618 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
619 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
620 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
621 if (TI->getSuccessor(Op) == Header)
622 TI->setSuccessor(Op, BEBlock);
625 //===--- Update all analyses which we must preserve now -----------------===//
627 // Update Loop Information - we know that this block is now in the current
628 // loop and all parent loops.
629 L->addBasicBlockToLoop(BEBlock, getAnalysis<LoopInfo>());
631 // Update dominator information (set, immdom, domtree, and domfrontier)
632 UpdateDomInfoForRevectoredPreds(BEBlock, BackedgeBlocks);
635 /// UpdateDomInfoForRevectoredPreds - This method is used to update the four
636 /// different kinds of dominator information (dominator sets, immediate
637 /// dominators, dominator trees, and dominance frontiers) after a new block has
638 /// been added to the CFG.
640 /// This only supports the case when an existing block (known as "NewBBSucc"),
641 /// had some of its predecessors factored into a new basic block. This
642 /// transformation inserts a new basic block ("NewBB"), with a single
643 /// unconditional branch to NewBBSucc, and moves some predecessors of
644 /// "NewBBSucc" to now branch to NewBB. These predecessors are listed in
645 /// PredBlocks, even though they are the same as
646 /// pred_begin(NewBB)/pred_end(NewBB).
648 void LoopSimplify::UpdateDomInfoForRevectoredPreds(BasicBlock *NewBB,
649 std::vector<BasicBlock*> &PredBlocks) {
650 assert(!PredBlocks.empty() && "No predblocks??");
651 assert(succ_begin(NewBB) != succ_end(NewBB) &&
652 ++succ_begin(NewBB) == succ_end(NewBB) &&
653 "NewBB should have a single successor!");
654 BasicBlock *NewBBSucc = *succ_begin(NewBB);
655 DominatorSet &DS = getAnalysis<DominatorSet>();
657 // Update dominator information... The blocks that dominate NewBB are the
658 // intersection of the dominators of predecessors, plus the block itself.
660 DominatorSet::DomSetType NewBBDomSet = DS.getDominators(PredBlocks[0]);
661 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
662 set_intersect(NewBBDomSet, DS.getDominators(PredBlocks[i]));
663 NewBBDomSet.insert(NewBB); // All blocks dominate themselves...
664 DS.addBasicBlock(NewBB, NewBBDomSet);
666 // The newly inserted basic block will dominate existing basic blocks iff the
667 // PredBlocks dominate all of the non-pred blocks. If all predblocks dominate
668 // the non-pred blocks, then they all must be the same block!
670 bool NewBBDominatesNewBBSucc = true;
672 BasicBlock *OnePred = PredBlocks[0];
673 for (unsigned i = 1, e = PredBlocks.size(); i != e; ++i)
674 if (PredBlocks[i] != OnePred) {
675 NewBBDominatesNewBBSucc = false;
679 if (NewBBDominatesNewBBSucc)
680 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
682 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
683 NewBBDominatesNewBBSucc = false;
688 // The other scenario where the new block can dominate its successors are when
689 // all predecessors of NewBBSucc that are not NewBB are dominated by NewBBSucc
691 if (!NewBBDominatesNewBBSucc) {
692 NewBBDominatesNewBBSucc = true;
693 for (pred_iterator PI = pred_begin(NewBBSucc), E = pred_end(NewBBSucc);
695 if (*PI != NewBB && !DS.dominates(NewBBSucc, *PI)) {
696 NewBBDominatesNewBBSucc = false;
701 // If NewBB dominates some blocks, then it will dominate all blocks that
703 if (NewBBDominatesNewBBSucc) {
704 BasicBlock *PredBlock = PredBlocks[0];
705 Function *F = NewBB->getParent();
706 for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I)
707 if (DS.dominates(NewBBSucc, I))
708 DS.addDominator(I, NewBB);
711 // Update immediate dominator information if we have it...
712 BasicBlock *NewBBIDom = 0;
713 if (ImmediateDominators *ID = getAnalysisToUpdate<ImmediateDominators>()) {
714 // To find the immediate dominator of the new exit node, we trace up the
715 // immediate dominators of a predecessor until we find a basic block that
716 // dominates the exit block.
718 BasicBlock *Dom = PredBlocks[0]; // Some random predecessor...
719 while (!NewBBDomSet.count(Dom)) { // Loop until we find a dominator...
720 assert(Dom != 0 && "No shared dominator found???");
724 // Set the immediate dominator now...
725 ID->addNewBlock(NewBB, Dom);
726 NewBBIDom = Dom; // Reuse this if calculating DominatorTree info...
728 // If NewBB strictly dominates other blocks, we need to update their idom's
729 // now. The only block that need adjustment is the NewBBSucc block, whose
730 // idom should currently be set to PredBlocks[0].
731 if (NewBBDominatesNewBBSucc)
732 ID->setImmediateDominator(NewBBSucc, NewBB);
735 // Update DominatorTree information if it is active.
736 if (DominatorTree *DT = getAnalysisToUpdate<DominatorTree>()) {
737 // If we don't have ImmediateDominator info around, calculate the idom as
739 DominatorTree::Node *NewBBIDomNode;
741 NewBBIDomNode = DT->getNode(NewBBIDom);
743 NewBBIDomNode = DT->getNode(PredBlocks[0]); // Random pred
744 while (!NewBBDomSet.count(NewBBIDomNode->getBlock())) {
745 NewBBIDomNode = NewBBIDomNode->getIDom();
746 assert(NewBBIDomNode && "No shared dominator found??");
750 // Create the new dominator tree node... and set the idom of NewBB.
751 DominatorTree::Node *NewBBNode = DT->createNewNode(NewBB, NewBBIDomNode);
753 // If NewBB strictly dominates other blocks, then it is now the immediate
754 // dominator of NewBBSucc. Update the dominator tree as appropriate.
755 if (NewBBDominatesNewBBSucc) {
756 DominatorTree::Node *NewBBSuccNode = DT->getNode(NewBBSucc);
757 DT->changeImmediateDominator(NewBBSuccNode, NewBBNode);
761 // Update dominance frontier information...
762 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>()) {
763 // If NewBB dominates NewBBSucc, then DF(NewBB) is now going to be the
764 // DF(PredBlocks[0]) without the stuff that the new block does not dominate
766 if (NewBBDominatesNewBBSucc) {
767 DominanceFrontier::iterator DFI = DF->find(PredBlocks[0]);
768 if (DFI != DF->end()) {
769 DominanceFrontier::DomSetType Set = DFI->second;
770 // Filter out stuff in Set that we do not dominate a predecessor of.
771 for (DominanceFrontier::DomSetType::iterator SetI = Set.begin(),
772 E = Set.end(); SetI != E;) {
773 bool DominatesPred = false;
774 for (pred_iterator PI = pred_begin(*SetI), E = pred_end(*SetI);
776 if (DS.dominates(NewBB, *PI))
777 DominatesPred = true;
784 DF->addBasicBlock(NewBB, Set);
788 // DF(NewBB) is {NewBBSucc} because NewBB does not strictly dominate
789 // NewBBSucc, but it does dominate itself (and there is an edge (NewBB ->
790 // NewBBSucc)). NewBBSucc is the single successor of NewBB.
791 DominanceFrontier::DomSetType NewDFSet;
792 NewDFSet.insert(NewBBSucc);
793 DF->addBasicBlock(NewBB, NewDFSet);
796 // Now we must loop over all of the dominance frontiers in the function,
797 // replacing occurrences of NewBBSucc with NewBB in some cases. All
798 // blocks that dominate a block in PredBlocks and contained NewBBSucc in
799 // their dominance frontier must be updated to contain NewBB instead.
801 for (unsigned i = 0, e = PredBlocks.size(); i != e; ++i) {
802 BasicBlock *Pred = PredBlocks[i];
803 // Get all of the dominators of the predecessor...
804 const DominatorSet::DomSetType &PredDoms = DS.getDominators(Pred);
805 for (DominatorSet::DomSetType::const_iterator PDI = PredDoms.begin(),
806 PDE = PredDoms.end(); PDI != PDE; ++PDI) {
807 BasicBlock *PredDom = *PDI;
809 // If the NewBBSucc node is in DF(PredDom), then PredDom didn't
810 // dominate NewBBSucc but did dominate a predecessor of it. Now we
811 // change this entry to include NewBB in the DF instead of NewBBSucc.
812 DominanceFrontier::iterator DFI = DF->find(PredDom);
813 assert(DFI != DF->end() && "No dominance frontier for node?");
814 if (DFI->second.count(NewBBSucc)) {
815 // If NewBBSucc should not stay in our dominator frontier, remove it.
816 // We remove it unless there is a predecessor of NewBBSucc that we
817 // dominate, but we don't strictly dominate NewBBSucc.
818 bool ShouldRemove = true;
819 if (PredDom == NewBBSucc || !DS.dominates(PredDom, NewBBSucc)) {
820 // Okay, we know that PredDom does not strictly dominate NewBBSucc.
821 // Check to see if it dominates any predecessors of NewBBSucc.
822 for (pred_iterator PI = pred_begin(NewBBSucc),
823 E = pred_end(NewBBSucc); PI != E; ++PI)
824 if (DS.dominates(PredDom, *PI)) {
825 ShouldRemove = false;
831 DF->removeFromFrontier(DFI, NewBBSucc);
832 DF->addToFrontier(DFI, NewBB);