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 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
180 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
181 E = ExitBlockSet.end(); I != E; ++I) {
182 BasicBlock *ExitBlock = *I;
183 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
185 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
187 if (!L->contains(*PI)) {
188 if (RewriteLoopExitBlock(L, ExitBlock)) {
196 // If the header has more than two predecessors at this point (from the
197 // preheader and from multiple backedges), we must adjust the loop.
198 BasicBlock *LoopLatch = L->getLoopLatch();
200 // If this is really a nested loop, rip it out into a child loop. Don't do
201 // this for loops with a giant number of backedges, just factor them into a
202 // common backedge instead.
203 if (L->getNumBackEdges() < 8) {
204 if (SeparateNestedLoop(L, LPM)) {
206 // This is a big restructuring change, reprocess the whole loop.
208 // GCC doesn't tail recursion eliminate this.
213 // If we either couldn't, or didn't want to, identify nesting of the loops,
214 // insert a new block that all backedges target, then make it jump to the
216 LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
223 // Scan over the PHI nodes in the loop header. Since they now have only two
224 // incoming values (the loop is canonicalized), we may have simplified the PHI
225 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
227 for (BasicBlock::iterator I = L->getHeader()->begin();
228 (PN = dyn_cast<PHINode>(I++)); )
229 if (Value *V = PN->hasConstantValue(DT)) {
230 if (AA) AA->deleteValue(PN);
231 PN->replaceAllUsesWith(V);
232 PN->eraseFromParent();
235 // If this loop has multiple exits and the exits all go to the same
236 // block, attempt to merge the exits. This helps several passes, such
237 // as LoopRotation, which do not support loops with multiple exits.
238 // SimplifyCFG also does this (and this code uses the same utility
239 // function), however this code is loop-aware, where SimplifyCFG is
240 // not. That gives it the advantage of being able to hoist
241 // loop-invariant instructions out of the way to open up more
242 // opportunities, and the disadvantage of having the responsibility
243 // to preserve dominator information.
244 bool UniqueExit = true;
245 if (!ExitBlocks.empty())
246 for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
247 if (ExitBlocks[i] != ExitBlocks[0]) {
252 SmallVector<BasicBlock*, 8> ExitingBlocks;
253 L->getExitingBlocks(ExitingBlocks);
254 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
255 BasicBlock *ExitingBlock = ExitingBlocks[i];
256 if (!ExitingBlock->getSinglePredecessor()) continue;
257 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
258 if (!BI || !BI->isConditional()) continue;
259 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
260 if (!CI || CI->getParent() != ExitingBlock) continue;
262 // Attempt to hoist out all instructions except for the
263 // comparison and the branch.
264 bool AllInvariant = true;
265 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
266 Instruction *Inst = I++;
269 if (!L->makeLoopInvariant(Inst, Changed,
270 Preheader ? Preheader->getTerminator() : 0)) {
271 AllInvariant = false;
275 if (!AllInvariant) continue;
277 // The block has now been cleared of all instructions except for
278 // a comparison and a conditional branch. SimplifyCFG may be able
280 if (!FoldBranchToCommonDest(BI)) continue;
282 // Success. The block is now dead, so remove it from the loop,
283 // update the dominator tree and dominance frontier, and delete it.
284 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
286 LI->removeBlock(ExitingBlock);
288 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
289 DomTreeNode *Node = DT->getNode(ExitingBlock);
290 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
292 while (!Children.empty()) {
293 DomTreeNode *Child = Children.front();
294 DT->changeImmediateDominator(Child, Node->getIDom());
295 if (DF) DF->changeImmediateDominator(Child->getBlock(),
296 Node->getIDom()->getBlock(),
299 DT->eraseNode(ExitingBlock);
300 if (DF) DF->removeBlock(ExitingBlock);
302 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
303 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
304 ExitingBlock->eraseFromParent();
311 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
312 /// preheader, this method is called to insert one. This method has two phases:
313 /// preheader insertion and analysis updating.
315 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
316 BasicBlock *Header = L->getHeader();
318 // Compute the set of predecessors of the loop that are not in the loop.
319 SmallVector<BasicBlock*, 8> OutsideBlocks;
320 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
322 if (!L->contains(*PI)) { // Coming in from outside the loop?
323 // If the loop is branched to from an indirect branch, we won't
324 // be able to fully transform the loop, because it prohibits
326 if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
329 OutsideBlocks.push_back(*PI);
332 // Split out the loop pre-header.
334 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
337 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
338 // code layout too horribly.
339 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
344 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
345 /// blocks. This method is used to split exit blocks that have predecessors
346 /// outside of the loop.
347 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
348 SmallVector<BasicBlock*, 8> LoopBlocks;
349 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
350 if (L->contains(*I)) {
351 // Don't do this if the loop is exited via an indirect branch.
352 if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
354 LoopBlocks.push_back(*I);
357 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
358 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
359 LoopBlocks.size(), ".loopexit",
365 /// AddBlockAndPredsToSet - Add the specified block, and all of its
366 /// predecessors, to the specified set, if it's not already in there. Stop
367 /// predecessor traversal when we reach StopBlock.
368 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
369 std::set<BasicBlock*> &Blocks) {
370 std::vector<BasicBlock *> WorkList;
371 WorkList.push_back(InputBB);
373 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
374 if (Blocks.insert(BB).second && BB != StopBlock)
375 // If BB is not already processed and it is not a stop block then
376 // insert its predecessor in the work list
377 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
378 BasicBlock *WBB = *I;
379 WorkList.push_back(WBB);
381 } while(!WorkList.empty());
384 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
385 /// PHI node that tells us how to partition the loops.
386 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
388 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
389 PHINode *PN = cast<PHINode>(I);
391 if (Value *V = PN->hasConstantValue(DT)) {
392 // This is a degenerate PHI already, don't modify it!
393 PN->replaceAllUsesWith(V);
394 if (AA) AA->deleteValue(PN);
395 PN->eraseFromParent();
399 // Scan this PHI node looking for a use of the PHI node by itself.
400 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
401 if (PN->getIncomingValue(i) == PN &&
402 L->contains(PN->getIncomingBlock(i)))
403 // We found something tasty to remove.
409 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
410 // right after some 'outside block' block. This prevents the preheader from
411 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
412 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
413 SmallVectorImpl<BasicBlock*> &SplitPreds,
415 // Check to see if NewBB is already well placed.
416 Function::iterator BBI = NewBB; --BBI;
417 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
418 if (&*BBI == SplitPreds[i])
422 // If it isn't already after an outside block, move it after one. This is
423 // always good as it makes the uncond branch from the outside block into a
426 // Figure out *which* outside block to put this after. Prefer an outside
427 // block that neighbors a BB actually in the loop.
428 BasicBlock *FoundBB = 0;
429 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
430 Function::iterator BBI = SplitPreds[i];
431 if (++BBI != NewBB->getParent()->end() &&
433 FoundBB = SplitPreds[i];
438 // If our heuristic for a *good* bb to place this after doesn't find
439 // anything, just pick something. It's likely better than leaving it within
442 FoundBB = SplitPreds[0];
443 NewBB->moveAfter(FoundBB);
447 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
448 /// them out into a nested loop. This is important for code that looks like
453 /// br cond, Loop, Next
455 /// br cond2, Loop, Out
457 /// To identify this common case, we look at the PHI nodes in the header of the
458 /// loop. PHI nodes with unchanging values on one backedge correspond to values
459 /// that change in the "outer" loop, but not in the "inner" loop.
461 /// If we are able to separate out a loop, return the new outer loop that was
464 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
465 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
466 if (PN == 0) return 0; // No known way to partition.
468 // Pull out all predecessors that have varying values in the loop. This
469 // handles the case when a PHI node has multiple instances of itself as
471 SmallVector<BasicBlock*, 8> OuterLoopPreds;
472 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
473 if (PN->getIncomingValue(i) != PN ||
474 !L->contains(PN->getIncomingBlock(i))) {
475 // We can't split indirectbr edges.
476 if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
479 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
482 BasicBlock *Header = L->getHeader();
483 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
484 OuterLoopPreds.size(),
487 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
488 // code layout too horribly.
489 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
491 // Create the new outer loop.
492 Loop *NewOuter = new Loop();
494 // Change the parent loop to use the outer loop as its child now.
495 if (Loop *Parent = L->getParentLoop())
496 Parent->replaceChildLoopWith(L, NewOuter);
498 LI->changeTopLevelLoop(L, NewOuter);
500 // L is now a subloop of our outer loop.
501 NewOuter->addChildLoop(L);
503 // Add the new loop to the pass manager queue.
504 LPM.insertLoopIntoQueue(NewOuter);
506 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
508 NewOuter->addBlockEntry(*I);
510 // Now reset the header in L, which had been moved by
511 // SplitBlockPredecessors for the outer loop.
512 L->moveToHeader(Header);
514 // Determine which blocks should stay in L and which should be moved out to
515 // the Outer loop now.
516 std::set<BasicBlock*> BlocksInL;
517 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
518 if (DT->dominates(Header, *PI))
519 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
522 // Scan all of the loop children of L, moving them to OuterLoop if they are
523 // not part of the inner loop.
524 const std::vector<Loop*> &SubLoops = L->getSubLoops();
525 for (size_t I = 0; I != SubLoops.size(); )
526 if (BlocksInL.count(SubLoops[I]->getHeader()))
527 ++I; // Loop remains in L
529 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
531 // Now that we know which blocks are in L and which need to be moved to
532 // OuterLoop, move any blocks that need it.
533 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
534 BasicBlock *BB = L->getBlocks()[i];
535 if (!BlocksInL.count(BB)) {
536 // Move this block to the parent, updating the exit blocks sets
537 L->removeBlockFromLoop(BB);
539 LI->changeLoopFor(BB, NewOuter);
549 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
550 /// has more than one backedge in it. If this occurs, revector all of these
551 /// backedges to target a new basic block and have that block branch to the loop
552 /// header. This ensures that loops have exactly one backedge.
555 LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
556 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
558 // Get information about the loop
559 BasicBlock *Header = L->getHeader();
560 Function *F = Header->getParent();
562 // Unique backedge insertion currently depends on having a preheader.
566 // Figure out which basic blocks contain back-edges to the loop header.
567 std::vector<BasicBlock*> BackedgeBlocks;
568 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
569 if (*I != Preheader) BackedgeBlocks.push_back(*I);
571 // Create and insert the new backedge block...
572 BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
573 Header->getName()+".backedge", F);
574 BranchInst *BETerminator = BranchInst::Create(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 = PHINode::Create(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, LI->getBase());
648 // Update dominator information
649 DT->splitBlock(BEBlock);
650 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
651 DF->splitBlock(BEBlock);
656 void LoopSimplify::verifyAnalysis() const {
657 // It used to be possible to just assert L->isLoopSimplifyForm(), however
658 // with the introduction of indirectbr, there are now cases where it's
659 // not possible to transform a loop as necessary. We can at least check
660 // that there is an indirectbr near any time there's trouble.
662 // Indirectbr can interfere with preheader and unique backedge insertion.
663 if (!L->getLoopPreheader() || !L->getLoopLatch()) {
664 bool HasIndBrPred = false;
665 for (pred_iterator PI = pred_begin(L->getHeader()),
666 PE = pred_end(L->getHeader()); PI != PE; ++PI)
667 if (isa<IndirectBrInst>((*PI)->getTerminator())) {
671 assert(HasIndBrPred &&
672 "LoopSimplify has no excuse for missing loop header info!");
675 // Indirectbr can interfere with exit block canonicalization.
676 if (!L->hasDedicatedExits()) {
677 bool HasIndBrExiting = false;
678 SmallVector<BasicBlock*, 8> ExitingBlocks;
679 L->getExitingBlocks(ExitingBlocks);
680 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
681 if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
682 HasIndBrExiting = true;
685 assert(HasIndBrExiting &&
686 "LoopSimplify has no excuse for missing exit block info!");