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 /// runOnFunction - 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 muliple 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 if (ExitBlocks.size() > 1 && L->getUniqueExitBlock()) {
245 SmallVector<BasicBlock*, 8> ExitingBlocks;
246 L->getExitingBlocks(ExitingBlocks);
247 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
248 BasicBlock *ExitingBlock = ExitingBlocks[i];
249 if (!ExitingBlock->getSinglePredecessor()) continue;
250 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
251 if (!BI || !BI->isConditional()) continue;
252 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
253 if (!CI || CI->getParent() != ExitingBlock) continue;
255 // Attempt to hoist out all instructions except for the
256 // comparison and the branch.
257 bool AllInvariant = true;
258 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
259 Instruction *Inst = I++;
262 if (!L->makeLoopInvariant(Inst, Changed,
263 Preheader ? Preheader->getTerminator() : 0)) {
264 AllInvariant = false;
268 if (!AllInvariant) continue;
270 // The block has now been cleared of all instructions except for
271 // a comparison and a conditional branch. SimplifyCFG may be able
273 if (!FoldBranchToCommonDest(BI)) continue;
275 // Success. The block is now dead, so remove it from the loop,
276 // update the dominator tree and dominance frontier, and delete it.
277 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
279 LI->removeBlock(ExitingBlock);
281 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
282 DomTreeNode *Node = DT->getNode(ExitingBlock);
283 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
285 while (!Children.empty()) {
286 DomTreeNode *Child = Children.front();
287 DT->changeImmediateDominator(Child, Node->getIDom());
288 if (DF) DF->changeImmediateDominator(Child->getBlock(),
289 Node->getIDom()->getBlock(),
292 DT->eraseNode(ExitingBlock);
293 if (DF) DF->removeBlock(ExitingBlock);
295 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
296 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
297 ExitingBlock->eraseFromParent();
304 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
305 /// preheader, this method is called to insert one. This method has two phases:
306 /// preheader insertion and analysis updating.
308 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
309 BasicBlock *Header = L->getHeader();
311 // Compute the set of predecessors of the loop that are not in the loop.
312 SmallVector<BasicBlock*, 8> OutsideBlocks;
313 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
315 if (!L->contains(*PI)) { // Coming in from outside the loop?
316 // If the loop is branched to from an indirect branch, we won't
317 // be able to fully transform the loop, because it prohibits
319 if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
322 OutsideBlocks.push_back(*PI);
325 // Split out the loop pre-header.
327 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
330 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
331 // code layout too horribly.
332 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
337 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
338 /// blocks. This method is used to split exit blocks that have predecessors
339 /// outside of the loop.
340 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
341 SmallVector<BasicBlock*, 8> LoopBlocks;
342 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
343 if (L->contains(*I)) {
344 // Don't do this if the loop is exited via an indirect branch.
345 if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
347 LoopBlocks.push_back(*I);
350 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
351 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
352 LoopBlocks.size(), ".loopexit",
358 /// AddBlockAndPredsToSet - Add the specified block, and all of its
359 /// predecessors, to the specified set, if it's not already in there. Stop
360 /// predecessor traversal when we reach StopBlock.
361 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
362 std::set<BasicBlock*> &Blocks) {
363 std::vector<BasicBlock *> WorkList;
364 WorkList.push_back(InputBB);
366 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
367 if (Blocks.insert(BB).second && BB != StopBlock)
368 // If BB is not already processed and it is not a stop block then
369 // insert its predecessor in the work list
370 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
371 BasicBlock *WBB = *I;
372 WorkList.push_back(WBB);
374 } while(!WorkList.empty());
377 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
378 /// PHI node that tells us how to partition the loops.
379 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
381 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
382 PHINode *PN = cast<PHINode>(I);
384 if (Value *V = PN->hasConstantValue(DT)) {
385 // This is a degenerate PHI already, don't modify it!
386 PN->replaceAllUsesWith(V);
387 if (AA) AA->deleteValue(PN);
388 PN->eraseFromParent();
392 // Scan this PHI node looking for a use of the PHI node by itself.
393 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
394 if (PN->getIncomingValue(i) == PN &&
395 L->contains(PN->getIncomingBlock(i)))
396 // We found something tasty to remove.
402 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
403 // right after some 'outside block' block. This prevents the preheader from
404 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
405 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
406 SmallVectorImpl<BasicBlock*> &SplitPreds,
408 // Check to see if NewBB is already well placed.
409 Function::iterator BBI = NewBB; --BBI;
410 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
411 if (&*BBI == SplitPreds[i])
415 // If it isn't already after an outside block, move it after one. This is
416 // always good as it makes the uncond branch from the outside block into a
419 // Figure out *which* outside block to put this after. Prefer an outside
420 // block that neighbors a BB actually in the loop.
421 BasicBlock *FoundBB = 0;
422 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
423 Function::iterator BBI = SplitPreds[i];
424 if (++BBI != NewBB->getParent()->end() &&
426 FoundBB = SplitPreds[i];
431 // If our heuristic for a *good* bb to place this after doesn't find
432 // anything, just pick something. It's likely better than leaving it within
435 FoundBB = SplitPreds[0];
436 NewBB->moveAfter(FoundBB);
440 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
441 /// them out into a nested loop. This is important for code that looks like
446 /// br cond, Loop, Next
448 /// br cond2, Loop, Out
450 /// To identify this common case, we look at the PHI nodes in the header of the
451 /// loop. PHI nodes with unchanging values on one backedge correspond to values
452 /// that change in the "outer" loop, but not in the "inner" loop.
454 /// If we are able to separate out a loop, return the new outer loop that was
457 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
458 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
459 if (PN == 0) return 0; // No known way to partition.
461 // Pull out all predecessors that have varying values in the loop. This
462 // handles the case when a PHI node has multiple instances of itself as
464 SmallVector<BasicBlock*, 8> OuterLoopPreds;
465 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
466 if (PN->getIncomingValue(i) != PN ||
467 !L->contains(PN->getIncomingBlock(i)))
468 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
470 BasicBlock *Header = L->getHeader();
471 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
472 OuterLoopPreds.size(),
475 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
476 // code layout too horribly.
477 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
479 // Create the new outer loop.
480 Loop *NewOuter = new Loop();
482 // Change the parent loop to use the outer loop as its child now.
483 if (Loop *Parent = L->getParentLoop())
484 Parent->replaceChildLoopWith(L, NewOuter);
486 LI->changeTopLevelLoop(L, NewOuter);
488 // L is now a subloop of our outer loop.
489 NewOuter->addChildLoop(L);
491 // Add the new loop to the pass manager queue.
492 LPM.insertLoopIntoQueue(NewOuter);
494 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
496 NewOuter->addBlockEntry(*I);
498 // Now reset the header in L, which had been moved by
499 // SplitBlockPredecessors for the outer loop.
500 L->moveToHeader(Header);
502 // Determine which blocks should stay in L and which should be moved out to
503 // the Outer loop now.
504 std::set<BasicBlock*> BlocksInL;
505 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
506 if (DT->dominates(Header, *PI))
507 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
510 // Scan all of the loop children of L, moving them to OuterLoop if they are
511 // not part of the inner loop.
512 const std::vector<Loop*> &SubLoops = L->getSubLoops();
513 for (size_t I = 0; I != SubLoops.size(); )
514 if (BlocksInL.count(SubLoops[I]->getHeader()))
515 ++I; // Loop remains in L
517 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
519 // Now that we know which blocks are in L and which need to be moved to
520 // OuterLoop, move any blocks that need it.
521 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
522 BasicBlock *BB = L->getBlocks()[i];
523 if (!BlocksInL.count(BB)) {
524 // Move this block to the parent, updating the exit blocks sets
525 L->removeBlockFromLoop(BB);
527 LI->changeLoopFor(BB, NewOuter);
537 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
538 /// has more than one backedge in it. If this occurs, revector all of these
539 /// backedges to target a new basic block and have that block branch to the loop
540 /// header. This ensures that loops have exactly one backedge.
543 LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
544 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
546 // Get information about the loop
547 BasicBlock *Header = L->getHeader();
548 Function *F = Header->getParent();
550 // Unique backedge insertion currently depends on having a preheader.
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 = BasicBlock::Create(Header->getContext(),
561 Header->getName()+".backedge", F);
562 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
564 // Move the new backedge block to right after the last backedge block.
565 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
566 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
568 // Now that the block has been inserted into the function, create PHI nodes in
569 // the backedge block which correspond to any PHI nodes in the header block.
570 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
571 PHINode *PN = cast<PHINode>(I);
572 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
574 NewPN->reserveOperandSpace(BackedgeBlocks.size());
575 if (AA) AA->copyValue(PN, NewPN);
577 // Loop over the PHI node, moving all entries except the one for the
578 // preheader over to the new PHI node.
579 unsigned PreheaderIdx = ~0U;
580 bool HasUniqueIncomingValue = true;
581 Value *UniqueValue = 0;
582 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
583 BasicBlock *IBB = PN->getIncomingBlock(i);
584 Value *IV = PN->getIncomingValue(i);
585 if (IBB == Preheader) {
588 NewPN->addIncoming(IV, IBB);
589 if (HasUniqueIncomingValue) {
590 if (UniqueValue == 0)
592 else if (UniqueValue != IV)
593 HasUniqueIncomingValue = false;
598 // Delete all of the incoming values from the old PN except the preheader's
599 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
600 if (PreheaderIdx != 0) {
601 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
602 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
604 // Nuke all entries except the zero'th.
605 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
606 PN->removeIncomingValue(e-i, false);
608 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
609 PN->addIncoming(NewPN, BEBlock);
611 // As an optimization, if all incoming values in the new PhiNode (which is a
612 // subset of the incoming values of the old PHI node) have the same value,
613 // eliminate the PHI Node.
614 if (HasUniqueIncomingValue) {
615 NewPN->replaceAllUsesWith(UniqueValue);
616 if (AA) AA->deleteValue(NewPN);
617 BEBlock->getInstList().erase(NewPN);
621 // Now that all of the PHI nodes have been inserted and adjusted, modify the
622 // backedge blocks to just to the BEBlock instead of the header.
623 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
624 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
625 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
626 if (TI->getSuccessor(Op) == Header)
627 TI->setSuccessor(Op, BEBlock);
630 //===--- Update all analyses which we must preserve now -----------------===//
632 // Update Loop Information - we know that this block is now in the current
633 // loop and all parent loops.
634 L->addBasicBlockToLoop(BEBlock, LI->getBase());
636 // Update dominator information
637 DT->splitBlock(BEBlock);
638 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
639 DF->splitBlock(BEBlock);
644 void LoopSimplify::verifyAnalysis() const {
645 // It used to be possible to just assert L->isLoopSimplifyForm(), however
646 // with the introduction of indirectbr, there are now cases where it's
647 // not possible to transform a loop as necessary. We can at least check
648 // that there is an indirectbr near any time there's trouble.
650 // Indirectbr can interfere with preheader and unique backedge insertion.
651 if (!L->getLoopPreheader() || !L->getLoopLatch()) {
652 bool HasIndBrPred = false;
653 for (pred_iterator PI = pred_begin(L->getHeader()),
654 PE = pred_end(L->getHeader()); PI != PE; ++PI)
655 if (isa<IndirectBrInst>((*PI)->getTerminator())) {
659 assert(HasIndBrPred &&
660 "LoopSimplify has no excuse for missing loop header info!");
663 // Indirectbr can interfere with exit block canonicalization.
664 if (!L->hasDedicatedExits()) {
665 bool HasIndBrExiting = false;
666 SmallVector<BasicBlock*, 8> ExitingBlocks;
667 L->getExitingBlocks(ExitingBlocks);
668 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
669 if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
670 HasIndBrExiting = true;
673 assert(HasIndBrExiting &&
674 "LoopSimplify has no excuse for missing exit block info!");