1 //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // 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 // Indirectbr instructions introduce several complications. If the loop
27 // contains or is entered by an indirectbr instruction, it may not be possible
28 // to transform the loop and make these guarantees. Client code should check
29 // that these conditions are true before relying on them.
31 // Note that the simplifycfg pass will clean up blocks which are split out but
32 // end up being unnecessary, so usage of this pass should not pessimize
35 // This pass obviously modifies the CFG, but updates loop information and
36 // dominator information.
38 //===----------------------------------------------------------------------===//
40 #define DEBUG_TYPE "loopsimplify"
41 #include "llvm/Transforms/Scalar.h"
42 #include "llvm/Constants.h"
43 #include "llvm/Instructions.h"
44 #include "llvm/Function.h"
45 #include "llvm/LLVMContext.h"
46 #include "llvm/Type.h"
47 #include "llvm/Analysis/AliasAnalysis.h"
48 #include "llvm/Analysis/Dominators.h"
49 #include "llvm/Analysis/LoopPass.h"
50 #include "llvm/Analysis/ScalarEvolution.h"
51 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
52 #include "llvm/Transforms/Utils/Local.h"
53 #include "llvm/Support/CFG.h"
54 #include "llvm/ADT/SetOperations.h"
55 #include "llvm/ADT/SetVector.h"
56 #include "llvm/ADT/Statistic.h"
57 #include "llvm/ADT/DepthFirstIterator.h"
60 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
61 STATISTIC(NumNested , "Number of nested loops split out");
64 struct LoopSimplify : public LoopPass {
65 static char ID; // Pass identification, replacement for typeid
66 LoopSimplify() : LoopPass(&ID) {}
68 // AA - If we have an alias analysis object to update, this is it, otherwise
74 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
76 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
77 // We need loop information to identify the loops...
78 AU.addRequiredTransitive<LoopInfo>();
79 AU.addRequiredTransitive<DominatorTree>();
81 AU.addPreserved<LoopInfo>();
82 AU.addPreserved<DominatorTree>();
83 AU.addPreserved<DominanceFrontier>();
84 AU.addPreserved<AliasAnalysis>();
85 AU.addPreserved<ScalarEvolution>();
86 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
89 /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
90 void verifyAnalysis() const;
93 bool ProcessLoop(Loop *L, LPPassManager &LPM);
94 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
95 BasicBlock *InsertPreheaderForLoop(Loop *L);
96 Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
97 BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
98 void PlaceSplitBlockCarefully(BasicBlock *NewBB,
99 SmallVectorImpl<BasicBlock*> &SplitPreds,
104 char LoopSimplify::ID = 0;
105 static RegisterPass<LoopSimplify>
106 X("loopsimplify", "Canonicalize natural loops", true);
108 // Publically exposed interface to pass...
109 const PassInfo *const llvm::LoopSimplifyID = &X;
110 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
112 /// runOnLoop - Run down all loops in the CFG (recursively, but we could do
113 /// it in any convenient order) inserting preheaders...
115 bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
117 bool Changed = false;
118 LI = &getAnalysis<LoopInfo>();
119 AA = getAnalysisIfAvailable<AliasAnalysis>();
120 DT = &getAnalysis<DominatorTree>();
122 Changed |= ProcessLoop(L, LPM);
127 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
128 /// all loops have preheaders.
130 bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
131 bool Changed = false;
134 // Check to see that no blocks (other than the header) in this loop that has
135 // predecessors that are not in the loop. This is not valid for natural
136 // loops, but can occur if the blocks are unreachable. Since they are
137 // unreachable we can just shamelessly delete those CFG edges!
138 for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
140 if (*BB == L->getHeader()) continue;
142 SmallPtrSet<BasicBlock *, 4> BadPreds;
143 for (pred_iterator PI = pred_begin(*BB), PE = pred_end(*BB); PI != PE; ++PI)
144 if (!L->contains(*PI))
145 BadPreds.insert(*PI);
147 // Delete each unique out-of-loop (and thus dead) predecessor.
148 for (SmallPtrSet<BasicBlock *, 4>::iterator I = BadPreds.begin(),
149 E = BadPreds.end(); I != E; ++I) {
150 // Inform each successor of each dead pred.
151 for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
152 (*SI)->removePredecessor(*I);
153 // Zap the dead pred's terminator and replace it with unreachable.
154 TerminatorInst *TI = (*I)->getTerminator();
155 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
156 (*I)->getTerminator()->eraseFromParent();
157 new UnreachableInst((*I)->getContext(), *I);
162 // Does the loop already have a preheader? If so, don't insert one.
163 BasicBlock *Preheader = L->getLoopPreheader();
165 Preheader = InsertPreheaderForLoop(L);
172 // Next, check to make sure that all exit nodes of the loop only have
173 // predecessors that are inside of the loop. This check guarantees that the
174 // loop preheader/header will dominate the exit blocks. If the exit block has
175 // predecessors from outside of the loop, split the edge now.
176 SmallVector<BasicBlock*, 8> ExitBlocks;
177 L->getExitBlocks(ExitBlocks);
179 SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
181 for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
182 E = ExitBlockSet.end(); I != E; ++I) {
183 BasicBlock *ExitBlock = *I;
184 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
186 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
188 if (!L->contains(*PI)) {
189 if (RewriteLoopExitBlock(L, ExitBlock)) {
197 // If the header has more than two predecessors at this point (from the
198 // preheader and from multiple backedges), we must adjust the loop.
199 BasicBlock *LoopLatch = L->getLoopLatch();
201 // If this is really a nested loop, rip it out into a child loop. Don't do
202 // this for loops with a giant number of backedges, just factor them into a
203 // common backedge instead.
204 if (L->getNumBackEdges() < 8) {
205 if (SeparateNestedLoop(L, LPM)) {
207 // This is a big restructuring change, reprocess the whole loop.
209 // GCC doesn't tail recursion eliminate this.
214 // If we either couldn't, or didn't want to, identify nesting of the loops,
215 // insert a new block that all backedges target, then make it jump to the
217 LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
224 // Scan over the PHI nodes in the loop header. Since they now have only two
225 // incoming values (the loop is canonicalized), we may have simplified the PHI
226 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
228 for (BasicBlock::iterator I = L->getHeader()->begin();
229 (PN = dyn_cast<PHINode>(I++)); )
230 if (Value *V = PN->hasConstantValue(DT)) {
231 if (AA) AA->deleteValue(PN);
232 PN->replaceAllUsesWith(V);
233 PN->eraseFromParent();
236 // If this loop has multiple exits and the exits all go to the same
237 // block, attempt to merge the exits. This helps several passes, such
238 // as LoopRotation, which do not support loops with multiple exits.
239 // SimplifyCFG also does this (and this code uses the same utility
240 // function), however this code is loop-aware, where SimplifyCFG is
241 // not. That gives it the advantage of being able to hoist
242 // loop-invariant instructions out of the way to open up more
243 // opportunities, and the disadvantage of having the responsibility
244 // to preserve dominator information.
245 bool UniqueExit = true;
246 if (!ExitBlocks.empty())
247 for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
248 if (ExitBlocks[i] != ExitBlocks[0]) {
253 SmallVector<BasicBlock*, 8> ExitingBlocks;
254 L->getExitingBlocks(ExitingBlocks);
255 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
256 BasicBlock *ExitingBlock = ExitingBlocks[i];
257 if (!ExitingBlock->getSinglePredecessor()) continue;
258 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
259 if (!BI || !BI->isConditional()) continue;
260 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
261 if (!CI || CI->getParent() != ExitingBlock) continue;
263 // Attempt to hoist out all instructions except for the
264 // comparison and the branch.
265 bool AllInvariant = true;
266 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
267 Instruction *Inst = I++;
270 if (!L->makeLoopInvariant(Inst, Changed,
271 Preheader ? Preheader->getTerminator() : 0)) {
272 AllInvariant = false;
276 if (!AllInvariant) continue;
278 // The block has now been cleared of all instructions except for
279 // a comparison and a conditional branch. SimplifyCFG may be able
281 if (!FoldBranchToCommonDest(BI)) continue;
283 // Success. The block is now dead, so remove it from the loop,
284 // update the dominator tree and dominance frontier, and delete it.
285 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
287 LI->removeBlock(ExitingBlock);
289 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
290 DomTreeNode *Node = DT->getNode(ExitingBlock);
291 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
293 while (!Children.empty()) {
294 DomTreeNode *Child = Children.front();
295 DT->changeImmediateDominator(Child, Node->getIDom());
296 if (DF) DF->changeImmediateDominator(Child->getBlock(),
297 Node->getIDom()->getBlock(),
300 DT->eraseNode(ExitingBlock);
301 if (DF) DF->removeBlock(ExitingBlock);
303 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
304 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
305 ExitingBlock->eraseFromParent();
312 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
313 /// preheader, this method is called to insert one. This method has two phases:
314 /// preheader insertion and analysis updating.
316 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
317 BasicBlock *Header = L->getHeader();
319 // Compute the set of predecessors of the loop that are not in the loop.
320 SmallVector<BasicBlock*, 8> OutsideBlocks;
321 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
323 if (!L->contains(*PI)) { // Coming in from outside the loop?
324 // If the loop is branched to from an indirect branch, we won't
325 // be able to fully transform the loop, because it prohibits
327 if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
330 OutsideBlocks.push_back(*PI);
333 // Split out the loop pre-header.
335 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
338 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
339 // code layout too horribly.
340 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
345 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
346 /// blocks. This method is used to split exit blocks that have predecessors
347 /// outside of the loop.
348 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
349 SmallVector<BasicBlock*, 8> LoopBlocks;
350 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
351 if (L->contains(*I)) {
352 // Don't do this if the loop is exited via an indirect branch.
353 if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
355 LoopBlocks.push_back(*I);
358 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
359 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
360 LoopBlocks.size(), ".loopexit",
366 /// AddBlockAndPredsToSet - Add the specified block, and all of its
367 /// predecessors, to the specified set, if it's not already in there. Stop
368 /// predecessor traversal when we reach StopBlock.
369 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
370 std::set<BasicBlock*> &Blocks) {
371 std::vector<BasicBlock *> WorkList;
372 WorkList.push_back(InputBB);
374 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
375 if (Blocks.insert(BB).second && BB != StopBlock)
376 // If BB is not already processed and it is not a stop block then
377 // insert its predecessor in the work list
378 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
379 BasicBlock *WBB = *I;
380 WorkList.push_back(WBB);
382 } while(!WorkList.empty());
385 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
386 /// PHI node that tells us how to partition the loops.
387 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
389 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
390 PHINode *PN = cast<PHINode>(I);
392 if (Value *V = PN->hasConstantValue(DT)) {
393 // This is a degenerate PHI already, don't modify it!
394 PN->replaceAllUsesWith(V);
395 if (AA) AA->deleteValue(PN);
396 PN->eraseFromParent();
400 // Scan this PHI node looking for a use of the PHI node by itself.
401 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
402 if (PN->getIncomingValue(i) == PN &&
403 L->contains(PN->getIncomingBlock(i)))
404 // We found something tasty to remove.
410 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
411 // right after some 'outside block' block. This prevents the preheader from
412 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
413 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
414 SmallVectorImpl<BasicBlock*> &SplitPreds,
416 // Check to see if NewBB is already well placed.
417 Function::iterator BBI = NewBB; --BBI;
418 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
419 if (&*BBI == SplitPreds[i])
423 // If it isn't already after an outside block, move it after one. This is
424 // always good as it makes the uncond branch from the outside block into a
427 // Figure out *which* outside block to put this after. Prefer an outside
428 // block that neighbors a BB actually in the loop.
429 BasicBlock *FoundBB = 0;
430 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
431 Function::iterator BBI = SplitPreds[i];
432 if (++BBI != NewBB->getParent()->end() &&
434 FoundBB = SplitPreds[i];
439 // If our heuristic for a *good* bb to place this after doesn't find
440 // anything, just pick something. It's likely better than leaving it within
443 FoundBB = SplitPreds[0];
444 NewBB->moveAfter(FoundBB);
448 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
449 /// them out into a nested loop. This is important for code that looks like
454 /// br cond, Loop, Next
456 /// br cond2, Loop, Out
458 /// To identify this common case, we look at the PHI nodes in the header of the
459 /// loop. PHI nodes with unchanging values on one backedge correspond to values
460 /// that change in the "outer" loop, but not in the "inner" loop.
462 /// If we are able to separate out a loop, return the new outer loop that was
465 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
466 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
467 if (PN == 0) return 0; // No known way to partition.
469 // Pull out all predecessors that have varying values in the loop. This
470 // handles the case when a PHI node has multiple instances of itself as
472 SmallVector<BasicBlock*, 8> OuterLoopPreds;
473 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
474 if (PN->getIncomingValue(i) != PN ||
475 !L->contains(PN->getIncomingBlock(i))) {
476 // We can't split indirectbr edges.
477 if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
480 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
483 BasicBlock *Header = L->getHeader();
484 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
485 OuterLoopPreds.size(),
488 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
489 // code layout too horribly.
490 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
492 // Create the new outer loop.
493 Loop *NewOuter = new Loop();
495 // Change the parent loop to use the outer loop as its child now.
496 if (Loop *Parent = L->getParentLoop())
497 Parent->replaceChildLoopWith(L, NewOuter);
499 LI->changeTopLevelLoop(L, NewOuter);
501 // L is now a subloop of our outer loop.
502 NewOuter->addChildLoop(L);
504 // Add the new loop to the pass manager queue.
505 LPM.insertLoopIntoQueue(NewOuter);
507 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
509 NewOuter->addBlockEntry(*I);
511 // Now reset the header in L, which had been moved by
512 // SplitBlockPredecessors for the outer loop.
513 L->moveToHeader(Header);
515 // Determine which blocks should stay in L and which should be moved out to
516 // the Outer loop now.
517 std::set<BasicBlock*> BlocksInL;
518 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
519 if (DT->dominates(Header, *PI))
520 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
523 // Scan all of the loop children of L, moving them to OuterLoop if they are
524 // not part of the inner loop.
525 const std::vector<Loop*> &SubLoops = L->getSubLoops();
526 for (size_t I = 0; I != SubLoops.size(); )
527 if (BlocksInL.count(SubLoops[I]->getHeader()))
528 ++I; // Loop remains in L
530 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
532 // Now that we know which blocks are in L and which need to be moved to
533 // OuterLoop, move any blocks that need it.
534 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
535 BasicBlock *BB = L->getBlocks()[i];
536 if (!BlocksInL.count(BB)) {
537 // Move this block to the parent, updating the exit blocks sets
538 L->removeBlockFromLoop(BB);
540 LI->changeLoopFor(BB, NewOuter);
550 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
551 /// has more than one backedge in it. If this occurs, revector all of these
552 /// backedges to target a new basic block and have that block branch to the loop
553 /// header. This ensures that loops have exactly one backedge.
556 LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
557 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
559 // Get information about the loop
560 BasicBlock *Header = L->getHeader();
561 Function *F = Header->getParent();
563 // Unique backedge insertion currently depends on having a preheader.
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 = BasicBlock::Create(Header->getContext(),
574 Header->getName()+".backedge", F);
575 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
577 // Move the new backedge block to right after the last backedge block.
578 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
579 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
581 // Now that the block has been inserted into the function, create PHI nodes in
582 // the backedge block which correspond to any PHI nodes in the header block.
583 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
584 PHINode *PN = cast<PHINode>(I);
585 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
587 NewPN->reserveOperandSpace(BackedgeBlocks.size());
588 if (AA) AA->copyValue(PN, NewPN);
590 // Loop over the PHI node, moving all entries except the one for the
591 // preheader over to the new PHI node.
592 unsigned PreheaderIdx = ~0U;
593 bool HasUniqueIncomingValue = true;
594 Value *UniqueValue = 0;
595 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
596 BasicBlock *IBB = PN->getIncomingBlock(i);
597 Value *IV = PN->getIncomingValue(i);
598 if (IBB == Preheader) {
601 NewPN->addIncoming(IV, IBB);
602 if (HasUniqueIncomingValue) {
603 if (UniqueValue == 0)
605 else if (UniqueValue != IV)
606 HasUniqueIncomingValue = false;
611 // Delete all of the incoming values from the old PN except the preheader's
612 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
613 if (PreheaderIdx != 0) {
614 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
615 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
617 // Nuke all entries except the zero'th.
618 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
619 PN->removeIncomingValue(e-i, false);
621 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
622 PN->addIncoming(NewPN, BEBlock);
624 // As an optimization, if all incoming values in the new PhiNode (which is a
625 // subset of the incoming values of the old PHI node) have the same value,
626 // eliminate the PHI Node.
627 if (HasUniqueIncomingValue) {
628 NewPN->replaceAllUsesWith(UniqueValue);
629 if (AA) AA->deleteValue(NewPN);
630 BEBlock->getInstList().erase(NewPN);
634 // Now that all of the PHI nodes have been inserted and adjusted, modify the
635 // backedge blocks to just to the BEBlock instead of the header.
636 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
637 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
638 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
639 if (TI->getSuccessor(Op) == Header)
640 TI->setSuccessor(Op, BEBlock);
643 //===--- Update all analyses which we must preserve now -----------------===//
645 // Update Loop Information - we know that this block is now in the current
646 // loop and all parent loops.
647 L->addBasicBlockToLoop(BEBlock, LI->getBase());
649 // Update dominator information
650 DT->splitBlock(BEBlock);
651 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
652 DF->splitBlock(BEBlock);
657 void LoopSimplify::verifyAnalysis() const {
658 // It used to be possible to just assert L->isLoopSimplifyForm(), however
659 // with the introduction of indirectbr, there are now cases where it's
660 // not possible to transform a loop as necessary. We can at least check
661 // that there is an indirectbr near any time there's trouble.
663 // Indirectbr can interfere with preheader and unique backedge insertion.
664 if (!L->getLoopPreheader() || !L->getLoopLatch()) {
665 bool HasIndBrPred = false;
666 for (pred_iterator PI = pred_begin(L->getHeader()),
667 PE = pred_end(L->getHeader()); PI != PE; ++PI)
668 if (isa<IndirectBrInst>((*PI)->getTerminator())) {
672 assert(HasIndBrPred &&
673 "LoopSimplify has no excuse for missing loop header info!");
676 // Indirectbr can interfere with exit block canonicalization.
677 if (!L->hasDedicatedExits()) {
678 bool HasIndBrExiting = false;
679 SmallVector<BasicBlock*, 8> ExitingBlocks;
680 L->getExitingBlocks(ExitingBlocks);
681 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
682 if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
683 HasIndBrExiting = true;
686 assert(HasIndBrExiting &&
687 "LoopSimplify has no excuse for missing exit block info!");