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/IntrinsicInst.h"
45 #include "llvm/Function.h"
46 #include "llvm/LLVMContext.h"
47 #include "llvm/Type.h"
48 #include "llvm/Analysis/AliasAnalysis.h"
49 #include "llvm/Analysis/Dominators.h"
50 #include "llvm/Analysis/LoopPass.h"
51 #include "llvm/Analysis/ScalarEvolution.h"
52 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
53 #include "llvm/Transforms/Utils/Local.h"
54 #include "llvm/Support/CFG.h"
55 #include "llvm/Support/Debug.h"
56 #include "llvm/ADT/SetOperations.h"
57 #include "llvm/ADT/SetVector.h"
58 #include "llvm/ADT/Statistic.h"
59 #include "llvm/ADT/DepthFirstIterator.h"
62 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
63 STATISTIC(NumNested , "Number of nested loops split out");
66 struct LoopSimplify : public LoopPass {
67 static char ID; // Pass identification, replacement for typeid
68 LoopSimplify() : LoopPass(&ID) {}
70 // AA - If we have an alias analysis object to update, this is it, otherwise
76 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
78 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
79 // We need loop information to identify the loops...
80 AU.addRequiredTransitive<LoopInfo>();
81 AU.addRequiredTransitive<DominatorTree>();
83 AU.addPreserved<LoopInfo>();
84 AU.addPreserved<DominatorTree>();
85 AU.addPreserved<DominanceFrontier>();
86 AU.addPreserved<AliasAnalysis>();
87 AU.addPreserved<ScalarEvolution>();
88 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
91 /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
92 void verifyAnalysis() const;
95 bool ProcessLoop(Loop *L, LPPassManager &LPM);
96 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
97 BasicBlock *InsertPreheaderForLoop(Loop *L);
98 Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
99 BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
100 void PlaceSplitBlockCarefully(BasicBlock *NewBB,
101 SmallVectorImpl<BasicBlock*> &SplitPreds,
106 char LoopSimplify::ID = 0;
107 static RegisterPass<LoopSimplify>
108 X("loopsimplify", "Canonicalize natural loops", true);
110 // Publically exposed interface to pass...
111 const PassInfo *const llvm::LoopSimplifyID = &X;
112 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
114 /// runOnLoop - Run down all loops in the CFG (recursively, but we could do
115 /// it in any convenient order) inserting preheaders...
117 bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
119 bool Changed = false;
120 LI = &getAnalysis<LoopInfo>();
121 AA = getAnalysisIfAvailable<AliasAnalysis>();
122 DT = &getAnalysis<DominatorTree>();
124 Changed |= ProcessLoop(L, LPM);
129 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
130 /// all loops have preheaders.
132 bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
133 bool Changed = false;
136 // Check to see that no blocks (other than the header) in this loop have
137 // predecessors that are not in the loop. This is not valid for natural
138 // loops, but can occur if the blocks are unreachable. Since they are
139 // unreachable we can just shamelessly delete those CFG edges!
140 for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
142 if (*BB == L->getHeader()) continue;
144 SmallPtrSet<BasicBlock *, 4> BadPreds;
145 for (pred_iterator PI = pred_begin(*BB), PE = pred_end(*BB); PI != PE; ++PI)
146 if (!L->contains(*PI))
147 BadPreds.insert(*PI);
149 // Delete each unique out-of-loop (and thus dead) predecessor.
150 for (SmallPtrSet<BasicBlock *, 4>::iterator I = BadPreds.begin(),
151 E = BadPreds.end(); I != E; ++I) {
153 DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor ";
154 WriteAsOperand(dbgs(), *I, false);
157 // Inform each successor of each dead pred.
158 for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
159 (*SI)->removePredecessor(*I);
160 // Zap the dead pred's terminator and replace it with unreachable.
161 TerminatorInst *TI = (*I)->getTerminator();
162 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
163 (*I)->getTerminator()->eraseFromParent();
164 new UnreachableInst((*I)->getContext(), *I);
169 // If there are exiting blocks with branches on undef, resolve the undef in
170 // the direction which will exit the loop. This will help simplify loop
171 // trip count computations.
172 SmallVector<BasicBlock*, 8> ExitingBlocks;
173 L->getExitingBlocks(ExitingBlocks);
174 for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
175 E = ExitingBlocks.end(); I != E; ++I)
176 if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator()))
177 if (BI->isConditional()) {
178 if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {
180 DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in ";
181 WriteAsOperand(dbgs(), *I, false);
184 BI->setCondition(ConstantInt::get(Cond->getType(),
185 !L->contains(BI->getSuccessor(0))));
190 // Does the loop already have a preheader? If so, don't insert one.
191 BasicBlock *Preheader = L->getLoopPreheader();
193 Preheader = InsertPreheaderForLoop(L);
200 // Next, check to make sure that all exit nodes of the loop only have
201 // predecessors that are inside of the loop. This check guarantees that the
202 // loop preheader/header will dominate the exit blocks. If the exit block has
203 // predecessors from outside of the loop, split the edge now.
204 SmallVector<BasicBlock*, 8> ExitBlocks;
205 L->getExitBlocks(ExitBlocks);
207 SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
209 for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
210 E = ExitBlockSet.end(); I != E; ++I) {
211 BasicBlock *ExitBlock = *I;
212 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
214 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
216 if (!L->contains(*PI)) {
217 if (RewriteLoopExitBlock(L, ExitBlock)) {
225 // If the header has more than two predecessors at this point (from the
226 // preheader and from multiple backedges), we must adjust the loop.
227 BasicBlock *LoopLatch = L->getLoopLatch();
229 // If this is really a nested loop, rip it out into a child loop. Don't do
230 // this for loops with a giant number of backedges, just factor them into a
231 // common backedge instead.
232 if (L->getNumBackEdges() < 8) {
233 if (SeparateNestedLoop(L, LPM)) {
235 // This is a big restructuring change, reprocess the whole loop.
237 // GCC doesn't tail recursion eliminate this.
242 // If we either couldn't, or didn't want to, identify nesting of the loops,
243 // insert a new block that all backedges target, then make it jump to the
245 LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
252 // Scan over the PHI nodes in the loop header. Since they now have only two
253 // incoming values (the loop is canonicalized), we may have simplified the PHI
254 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
256 for (BasicBlock::iterator I = L->getHeader()->begin();
257 (PN = dyn_cast<PHINode>(I++)); )
258 if (Value *V = PN->hasConstantValue(DT)) {
259 if (AA) AA->deleteValue(PN);
260 PN->replaceAllUsesWith(V);
261 PN->eraseFromParent();
264 // If this loop has multiple exits and the exits all go to the same
265 // block, attempt to merge the exits. This helps several passes, such
266 // as LoopRotation, which do not support loops with multiple exits.
267 // SimplifyCFG also does this (and this code uses the same utility
268 // function), however this code is loop-aware, where SimplifyCFG is
269 // not. That gives it the advantage of being able to hoist
270 // loop-invariant instructions out of the way to open up more
271 // opportunities, and the disadvantage of having the responsibility
272 // to preserve dominator information.
273 bool UniqueExit = true;
274 if (!ExitBlocks.empty())
275 for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
276 if (ExitBlocks[i] != ExitBlocks[0]) {
281 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
282 BasicBlock *ExitingBlock = ExitingBlocks[i];
283 if (!ExitingBlock->getSinglePredecessor()) continue;
284 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
285 if (!BI || !BI->isConditional()) continue;
286 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
287 if (!CI || CI->getParent() != ExitingBlock) continue;
289 // Attempt to hoist out all instructions except for the
290 // comparison and the branch.
291 bool AllInvariant = true;
292 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
293 Instruction *Inst = I++;
294 // Skip debug info intrinsics.
295 if (isa<DbgInfoIntrinsic>(Inst))
299 if (!L->makeLoopInvariant(Inst, Changed,
300 Preheader ? Preheader->getTerminator() : 0)) {
301 AllInvariant = false;
305 if (!AllInvariant) continue;
307 // The block has now been cleared of all instructions except for
308 // a comparison and a conditional branch. SimplifyCFG may be able
310 if (!FoldBranchToCommonDest(BI)) continue;
312 // Success. The block is now dead, so remove it from the loop,
313 // update the dominator tree and dominance frontier, and delete it.
315 DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block ";
316 WriteAsOperand(dbgs(), ExitingBlock, false);
319 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
321 LI->removeBlock(ExitingBlock);
323 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
324 DomTreeNode *Node = DT->getNode(ExitingBlock);
325 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
327 while (!Children.empty()) {
328 DomTreeNode *Child = Children.front();
329 DT->changeImmediateDominator(Child, Node->getIDom());
330 if (DF) DF->changeImmediateDominator(Child->getBlock(),
331 Node->getIDom()->getBlock(),
334 DT->eraseNode(ExitingBlock);
335 if (DF) DF->removeBlock(ExitingBlock);
337 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
338 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
339 ExitingBlock->eraseFromParent();
346 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
347 /// preheader, this method is called to insert one. This method has two phases:
348 /// preheader insertion and analysis updating.
350 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
351 BasicBlock *Header = L->getHeader();
353 // Compute the set of predecessors of the loop that are not in the loop.
354 SmallVector<BasicBlock*, 8> OutsideBlocks;
355 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
357 if (!L->contains(*PI)) { // Coming in from outside the loop?
358 // If the loop is branched to from an indirect branch, we won't
359 // be able to fully transform the loop, because it prohibits
361 if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
364 OutsideBlocks.push_back(*PI);
367 // Split out the loop pre-header.
369 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
372 DEBUG(dbgs() << "LoopSimplify: Creating pre-header ";
373 WriteAsOperand(dbgs(), NewBB, false);
376 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
377 // code layout too horribly.
378 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
383 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
384 /// blocks. This method is used to split exit blocks that have predecessors
385 /// outside of the loop.
386 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
387 SmallVector<BasicBlock*, 8> LoopBlocks;
388 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
389 if (L->contains(*I)) {
390 // Don't do this if the loop is exited via an indirect branch.
391 if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
393 LoopBlocks.push_back(*I);
396 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
397 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
398 LoopBlocks.size(), ".loopexit",
401 DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block ";
402 WriteAsOperand(dbgs(), NewBB, false);
408 /// AddBlockAndPredsToSet - Add the specified block, and all of its
409 /// predecessors, to the specified set, if it's not already in there. Stop
410 /// predecessor traversal when we reach StopBlock.
411 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
412 std::set<BasicBlock*> &Blocks) {
413 std::vector<BasicBlock *> WorkList;
414 WorkList.push_back(InputBB);
416 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
417 if (Blocks.insert(BB).second && BB != StopBlock)
418 // If BB is not already processed and it is not a stop block then
419 // insert its predecessor in the work list
420 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
421 BasicBlock *WBB = *I;
422 WorkList.push_back(WBB);
424 } while(!WorkList.empty());
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, DominatorTree *DT,
431 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
432 PHINode *PN = cast<PHINode>(I);
434 if (Value *V = PN->hasConstantValue(DT)) {
435 // This is a degenerate PHI already, don't modify it!
436 PN->replaceAllUsesWith(V);
437 if (AA) AA->deleteValue(PN);
438 PN->eraseFromParent();
442 // Scan this PHI node looking for a use of the PHI node by itself.
443 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
444 if (PN->getIncomingValue(i) == PN &&
445 L->contains(PN->getIncomingBlock(i)))
446 // We found something tasty to remove.
452 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
453 // right after some 'outside block' block. This prevents the preheader from
454 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
455 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
456 SmallVectorImpl<BasicBlock*> &SplitPreds,
458 // Check to see if NewBB is already well placed.
459 Function::iterator BBI = NewBB; --BBI;
460 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
461 if (&*BBI == SplitPreds[i])
465 // If it isn't already after an outside block, move it after one. This is
466 // always good as it makes the uncond branch from the outside block into a
469 // Figure out *which* outside block to put this after. Prefer an outside
470 // block that neighbors a BB actually in the loop.
471 BasicBlock *FoundBB = 0;
472 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
473 Function::iterator BBI = SplitPreds[i];
474 if (++BBI != NewBB->getParent()->end() &&
476 FoundBB = SplitPreds[i];
481 // If our heuristic for a *good* bb to place this after doesn't find
482 // anything, just pick something. It's likely better than leaving it within
485 FoundBB = SplitPreds[0];
486 NewBB->moveAfter(FoundBB);
490 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
491 /// them out into a nested loop. This is important for code that looks like
496 /// br cond, Loop, Next
498 /// br cond2, Loop, Out
500 /// To identify this common case, we look at the PHI nodes in the header of the
501 /// loop. PHI nodes with unchanging values on one backedge correspond to values
502 /// that change in the "outer" loop, but not in the "inner" loop.
504 /// If we are able to separate out a loop, return the new outer loop that was
507 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
508 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
509 if (PN == 0) return 0; // No known way to partition.
511 // Pull out all predecessors that have varying values in the loop. This
512 // handles the case when a PHI node has multiple instances of itself as
514 SmallVector<BasicBlock*, 8> OuterLoopPreds;
515 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
516 if (PN->getIncomingValue(i) != PN ||
517 !L->contains(PN->getIncomingBlock(i))) {
518 // We can't split indirectbr edges.
519 if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
522 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
525 DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
527 BasicBlock *Header = L->getHeader();
528 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
529 OuterLoopPreds.size(),
532 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
533 // code layout too horribly.
534 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
536 // Create the new outer loop.
537 Loop *NewOuter = new Loop();
539 // Change the parent loop to use the outer loop as its child now.
540 if (Loop *Parent = L->getParentLoop())
541 Parent->replaceChildLoopWith(L, NewOuter);
543 LI->changeTopLevelLoop(L, NewOuter);
545 // L is now a subloop of our outer loop.
546 NewOuter->addChildLoop(L);
548 // Add the new loop to the pass manager queue.
549 LPM.insertLoopIntoQueue(NewOuter);
551 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
553 NewOuter->addBlockEntry(*I);
555 // Now reset the header in L, which had been moved by
556 // SplitBlockPredecessors for the outer loop.
557 L->moveToHeader(Header);
559 // Determine which blocks should stay in L and which should be moved out to
560 // the Outer loop now.
561 std::set<BasicBlock*> BlocksInL;
562 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
563 if (DT->dominates(Header, *PI))
564 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
567 // Scan all of the loop children of L, moving them to OuterLoop if they are
568 // not part of the inner loop.
569 const std::vector<Loop*> &SubLoops = L->getSubLoops();
570 for (size_t I = 0; I != SubLoops.size(); )
571 if (BlocksInL.count(SubLoops[I]->getHeader()))
572 ++I; // Loop remains in L
574 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
576 // Now that we know which blocks are in L and which need to be moved to
577 // OuterLoop, move any blocks that need it.
578 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
579 BasicBlock *BB = L->getBlocks()[i];
580 if (!BlocksInL.count(BB)) {
581 // Move this block to the parent, updating the exit blocks sets
582 L->removeBlockFromLoop(BB);
584 LI->changeLoopFor(BB, NewOuter);
594 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
595 /// has more than one backedge in it. If this occurs, revector all of these
596 /// backedges to target a new basic block and have that block branch to the loop
597 /// header. This ensures that loops have exactly one backedge.
600 LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
601 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
603 // Get information about the loop
604 BasicBlock *Header = L->getHeader();
605 Function *F = Header->getParent();
607 // Unique backedge insertion currently depends on having a preheader.
611 // Figure out which basic blocks contain back-edges to the loop header.
612 std::vector<BasicBlock*> BackedgeBlocks;
613 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
614 if (*I != Preheader) BackedgeBlocks.push_back(*I);
616 // Create and insert the new backedge block...
617 BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
618 Header->getName()+".backedge", F);
619 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
621 DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block ";
622 WriteAsOperand(dbgs(), BEBlock, false);
625 // Move the new backedge block to right after the last backedge block.
626 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
627 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
629 // Now that the block has been inserted into the function, create PHI nodes in
630 // the backedge block which correspond to any PHI nodes in the header block.
631 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
632 PHINode *PN = cast<PHINode>(I);
633 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
635 NewPN->reserveOperandSpace(BackedgeBlocks.size());
636 if (AA) AA->copyValue(PN, NewPN);
638 // Loop over the PHI node, moving all entries except the one for the
639 // preheader over to the new PHI node.
640 unsigned PreheaderIdx = ~0U;
641 bool HasUniqueIncomingValue = true;
642 Value *UniqueValue = 0;
643 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
644 BasicBlock *IBB = PN->getIncomingBlock(i);
645 Value *IV = PN->getIncomingValue(i);
646 if (IBB == Preheader) {
649 NewPN->addIncoming(IV, IBB);
650 if (HasUniqueIncomingValue) {
651 if (UniqueValue == 0)
653 else if (UniqueValue != IV)
654 HasUniqueIncomingValue = false;
659 // Delete all of the incoming values from the old PN except the preheader's
660 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
661 if (PreheaderIdx != 0) {
662 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
663 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
665 // Nuke all entries except the zero'th.
666 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
667 PN->removeIncomingValue(e-i, false);
669 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
670 PN->addIncoming(NewPN, BEBlock);
672 // As an optimization, if all incoming values in the new PhiNode (which is a
673 // subset of the incoming values of the old PHI node) have the same value,
674 // eliminate the PHI Node.
675 if (HasUniqueIncomingValue) {
676 NewPN->replaceAllUsesWith(UniqueValue);
677 if (AA) AA->deleteValue(NewPN);
678 BEBlock->getInstList().erase(NewPN);
682 // Now that all of the PHI nodes have been inserted and adjusted, modify the
683 // backedge blocks to just to the BEBlock instead of the header.
684 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
685 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
686 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
687 if (TI->getSuccessor(Op) == Header)
688 TI->setSuccessor(Op, BEBlock);
691 //===--- Update all analyses which we must preserve now -----------------===//
693 // Update Loop Information - we know that this block is now in the current
694 // loop and all parent loops.
695 L->addBasicBlockToLoop(BEBlock, LI->getBase());
697 // Update dominator information
698 DT->splitBlock(BEBlock);
699 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
700 DF->splitBlock(BEBlock);
705 void LoopSimplify::verifyAnalysis() const {
706 // It used to be possible to just assert L->isLoopSimplifyForm(), however
707 // with the introduction of indirectbr, there are now cases where it's
708 // not possible to transform a loop as necessary. We can at least check
709 // that there is an indirectbr near any time there's trouble.
711 // Indirectbr can interfere with preheader and unique backedge insertion.
712 if (!L->getLoopPreheader() || !L->getLoopLatch()) {
713 bool HasIndBrPred = false;
714 for (pred_iterator PI = pred_begin(L->getHeader()),
715 PE = pred_end(L->getHeader()); PI != PE; ++PI)
716 if (isa<IndirectBrInst>((*PI)->getTerminator())) {
720 assert(HasIndBrPred &&
721 "LoopSimplify has no excuse for missing loop header info!");
724 // Indirectbr can interfere with exit block canonicalization.
725 if (!L->hasDedicatedExits()) {
726 bool HasIndBrExiting = false;
727 SmallVector<BasicBlock*, 8> ExitingBlocks;
728 L->getExitingBlocks(ExitingBlocks);
729 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
730 if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
731 HasIndBrExiting = true;
734 assert(HasIndBrExiting &&
735 "LoopSimplify has no excuse for missing exit block info!");