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/Support/Debug.h"
55 #include "llvm/ADT/SetOperations.h"
56 #include "llvm/ADT/SetVector.h"
57 #include "llvm/ADT/Statistic.h"
58 #include "llvm/ADT/DepthFirstIterator.h"
61 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
62 STATISTIC(NumNested , "Number of nested loops split out");
65 struct LoopSimplify : public LoopPass {
66 static char ID; // Pass identification, replacement for typeid
67 LoopSimplify() : LoopPass(&ID) {}
69 // AA - If we have an alias analysis object to update, this is it, otherwise
75 virtual bool runOnLoop(Loop *L, LPPassManager &LPM);
77 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
78 // We need loop information to identify the loops...
79 AU.addRequiredTransitive<LoopInfo>();
80 AU.addRequiredTransitive<DominatorTree>();
82 AU.addPreserved<LoopInfo>();
83 AU.addPreserved<DominatorTree>();
84 AU.addPreserved<DominanceFrontier>();
85 AU.addPreserved<AliasAnalysis>();
86 AU.addPreserved<ScalarEvolution>();
87 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
90 /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
91 void verifyAnalysis() const;
94 bool ProcessLoop(Loop *L, LPPassManager &LPM);
95 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
96 BasicBlock *InsertPreheaderForLoop(Loop *L);
97 Loop *SeparateNestedLoop(Loop *L, LPPassManager &LPM);
98 BasicBlock *InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader);
99 void PlaceSplitBlockCarefully(BasicBlock *NewBB,
100 SmallVectorImpl<BasicBlock*> &SplitPreds,
105 char LoopSimplify::ID = 0;
106 static RegisterPass<LoopSimplify>
107 X("loopsimplify", "Canonicalize natural loops", true);
109 // Publically exposed interface to pass...
110 const PassInfo *const llvm::LoopSimplifyID = &X;
111 Pass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
113 /// runOnLoop - Run down all loops in the CFG (recursively, but we could do
114 /// it in any convenient order) inserting preheaders...
116 bool LoopSimplify::runOnLoop(Loop *l, LPPassManager &LPM) {
118 bool Changed = false;
119 LI = &getAnalysis<LoopInfo>();
120 AA = getAnalysisIfAvailable<AliasAnalysis>();
121 DT = &getAnalysis<DominatorTree>();
123 Changed |= ProcessLoop(L, LPM);
128 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
129 /// all loops have preheaders.
131 bool LoopSimplify::ProcessLoop(Loop *L, LPPassManager &LPM) {
132 bool Changed = false;
135 // Check to see that no blocks (other than the header) in this loop that has
136 // predecessors that are not in the loop. This is not valid for natural
137 // loops, but can occur if the blocks are unreachable. Since they are
138 // unreachable we can just shamelessly delete those CFG edges!
139 for (Loop::block_iterator BB = L->block_begin(), E = L->block_end();
141 if (*BB == L->getHeader()) continue;
143 SmallPtrSet<BasicBlock *, 4> BadPreds;
144 for (pred_iterator PI = pred_begin(*BB), PE = pred_end(*BB); PI != PE; ++PI)
145 if (!L->contains(*PI))
146 BadPreds.insert(*PI);
148 // Delete each unique out-of-loop (and thus dead) predecessor.
149 for (SmallPtrSet<BasicBlock *, 4>::iterator I = BadPreds.begin(),
150 E = BadPreds.end(); I != E; ++I) {
152 DEBUG(dbgs() << "LoopSimplify: Deleting edge from dead predecessor ";
153 WriteAsOperand(dbgs(), *I, false);
156 // Inform each successor of each dead pred.
157 for (succ_iterator SI = succ_begin(*I), SE = succ_end(*I); SI != SE; ++SI)
158 (*SI)->removePredecessor(*I);
159 // Zap the dead pred's terminator and replace it with unreachable.
160 TerminatorInst *TI = (*I)->getTerminator();
161 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
162 (*I)->getTerminator()->eraseFromParent();
163 new UnreachableInst((*I)->getContext(), *I);
168 // If there are exiting blocks with branches on undef, resolve the undef in
169 // the direction which will exit the loop. This will help simplify loop
170 // trip count computations.
171 SmallVector<BasicBlock*, 8> ExitingBlocks;
172 L->getExitingBlocks(ExitingBlocks);
173 for (SmallVectorImpl<BasicBlock *>::iterator I = ExitingBlocks.begin(),
174 E = ExitingBlocks.end(); I != E; ++I)
175 if (BranchInst *BI = dyn_cast<BranchInst>((*I)->getTerminator()))
176 if (BI->isConditional()) {
177 if (UndefValue *Cond = dyn_cast<UndefValue>(BI->getCondition())) {
179 DEBUG(dbgs() << "LoopSimplify: Resolving \"br i1 undef\" to exit in ";
180 WriteAsOperand(dbgs(), *I, false);
183 BI->setCondition(ConstantInt::get(Cond->getType(),
184 !L->contains(BI->getSuccessor(0))));
189 // Does the loop already have a preheader? If so, don't insert one.
190 BasicBlock *Preheader = L->getLoopPreheader();
192 Preheader = InsertPreheaderForLoop(L);
199 // Next, check to make sure that all exit nodes of the loop only have
200 // predecessors that are inside of the loop. This check guarantees that the
201 // loop preheader/header will dominate the exit blocks. If the exit block has
202 // predecessors from outside of the loop, split the edge now.
203 SmallVector<BasicBlock*, 8> ExitBlocks;
204 L->getExitBlocks(ExitBlocks);
206 SmallSetVector<BasicBlock *, 8> ExitBlockSet(ExitBlocks.begin(),
208 for (SmallSetVector<BasicBlock *, 8>::iterator I = ExitBlockSet.begin(),
209 E = ExitBlockSet.end(); I != E; ++I) {
210 BasicBlock *ExitBlock = *I;
211 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
213 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
215 if (!L->contains(*PI)) {
216 if (RewriteLoopExitBlock(L, ExitBlock)) {
224 // If the header has more than two predecessors at this point (from the
225 // preheader and from multiple backedges), we must adjust the loop.
226 BasicBlock *LoopLatch = L->getLoopLatch();
228 // If this is really a nested loop, rip it out into a child loop. Don't do
229 // this for loops with a giant number of backedges, just factor them into a
230 // common backedge instead.
231 if (L->getNumBackEdges() < 8) {
232 if (SeparateNestedLoop(L, LPM)) {
234 // This is a big restructuring change, reprocess the whole loop.
236 // GCC doesn't tail recursion eliminate this.
241 // If we either couldn't, or didn't want to, identify nesting of the loops,
242 // insert a new block that all backedges target, then make it jump to the
244 LoopLatch = InsertUniqueBackedgeBlock(L, Preheader);
251 // Scan over the PHI nodes in the loop header. Since they now have only two
252 // incoming values (the loop is canonicalized), we may have simplified the PHI
253 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
255 for (BasicBlock::iterator I = L->getHeader()->begin();
256 (PN = dyn_cast<PHINode>(I++)); )
257 if (Value *V = PN->hasConstantValue(DT)) {
258 if (AA) AA->deleteValue(PN);
259 PN->replaceAllUsesWith(V);
260 PN->eraseFromParent();
263 // If this loop has multiple exits and the exits all go to the same
264 // block, attempt to merge the exits. This helps several passes, such
265 // as LoopRotation, which do not support loops with multiple exits.
266 // SimplifyCFG also does this (and this code uses the same utility
267 // function), however this code is loop-aware, where SimplifyCFG is
268 // not. That gives it the advantage of being able to hoist
269 // loop-invariant instructions out of the way to open up more
270 // opportunities, and the disadvantage of having the responsibility
271 // to preserve dominator information.
272 bool UniqueExit = true;
273 if (!ExitBlocks.empty())
274 for (unsigned i = 1, e = ExitBlocks.size(); i != e; ++i)
275 if (ExitBlocks[i] != ExitBlocks[0]) {
280 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
281 BasicBlock *ExitingBlock = ExitingBlocks[i];
282 if (!ExitingBlock->getSinglePredecessor()) continue;
283 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
284 if (!BI || !BI->isConditional()) continue;
285 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
286 if (!CI || CI->getParent() != ExitingBlock) continue;
288 // Attempt to hoist out all instructions except for the
289 // comparison and the branch.
290 bool AllInvariant = true;
291 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
292 Instruction *Inst = I++;
295 if (!L->makeLoopInvariant(Inst, Changed,
296 Preheader ? Preheader->getTerminator() : 0)) {
297 AllInvariant = false;
301 if (!AllInvariant) continue;
303 // The block has now been cleared of all instructions except for
304 // a comparison and a conditional branch. SimplifyCFG may be able
306 if (!FoldBranchToCommonDest(BI)) continue;
308 // Success. The block is now dead, so remove it from the loop,
309 // update the dominator tree and dominance frontier, and delete it.
311 DEBUG(dbgs() << "LoopSimplify: Eliminating exiting block ";
312 WriteAsOperand(dbgs(), ExitingBlock, false);
315 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
317 LI->removeBlock(ExitingBlock);
319 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
320 DomTreeNode *Node = DT->getNode(ExitingBlock);
321 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
323 while (!Children.empty()) {
324 DomTreeNode *Child = Children.front();
325 DT->changeImmediateDominator(Child, Node->getIDom());
326 if (DF) DF->changeImmediateDominator(Child->getBlock(),
327 Node->getIDom()->getBlock(),
330 DT->eraseNode(ExitingBlock);
331 if (DF) DF->removeBlock(ExitingBlock);
333 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
334 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
335 ExitingBlock->eraseFromParent();
342 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
343 /// preheader, this method is called to insert one. This method has two phases:
344 /// preheader insertion and analysis updating.
346 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
347 BasicBlock *Header = L->getHeader();
349 // Compute the set of predecessors of the loop that are not in the loop.
350 SmallVector<BasicBlock*, 8> OutsideBlocks;
351 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
353 if (!L->contains(*PI)) { // Coming in from outside the loop?
354 // If the loop is branched to from an indirect branch, we won't
355 // be able to fully transform the loop, because it prohibits
357 if (isa<IndirectBrInst>((*PI)->getTerminator())) return 0;
360 OutsideBlocks.push_back(*PI);
363 // Split out the loop pre-header.
365 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
368 DEBUG(dbgs() << "LoopSimplify: Creating pre-header ";
369 WriteAsOperand(dbgs(), NewBB, false);
372 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
373 // code layout too horribly.
374 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
379 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
380 /// blocks. This method is used to split exit blocks that have predecessors
381 /// outside of the loop.
382 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
383 SmallVector<BasicBlock*, 8> LoopBlocks;
384 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
385 if (L->contains(*I)) {
386 // Don't do this if the loop is exited via an indirect branch.
387 if (isa<IndirectBrInst>((*I)->getTerminator())) return 0;
389 LoopBlocks.push_back(*I);
392 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
393 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
394 LoopBlocks.size(), ".loopexit",
397 DEBUG(dbgs() << "LoopSimplify: Creating dedicated exit block ";
398 WriteAsOperand(dbgs(), NewBB, false);
404 /// AddBlockAndPredsToSet - Add the specified block, and all of its
405 /// predecessors, to the specified set, if it's not already in there. Stop
406 /// predecessor traversal when we reach StopBlock.
407 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
408 std::set<BasicBlock*> &Blocks) {
409 std::vector<BasicBlock *> WorkList;
410 WorkList.push_back(InputBB);
412 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
413 if (Blocks.insert(BB).second && BB != StopBlock)
414 // If BB is not already processed and it is not a stop block then
415 // insert its predecessor in the work list
416 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
417 BasicBlock *WBB = *I;
418 WorkList.push_back(WBB);
420 } while(!WorkList.empty());
423 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
424 /// PHI node that tells us how to partition the loops.
425 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
427 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
428 PHINode *PN = cast<PHINode>(I);
430 if (Value *V = PN->hasConstantValue(DT)) {
431 // This is a degenerate PHI already, don't modify it!
432 PN->replaceAllUsesWith(V);
433 if (AA) AA->deleteValue(PN);
434 PN->eraseFromParent();
438 // Scan this PHI node looking for a use of the PHI node by itself.
439 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
440 if (PN->getIncomingValue(i) == PN &&
441 L->contains(PN->getIncomingBlock(i)))
442 // We found something tasty to remove.
448 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
449 // right after some 'outside block' block. This prevents the preheader from
450 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
451 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
452 SmallVectorImpl<BasicBlock*> &SplitPreds,
454 // Check to see if NewBB is already well placed.
455 Function::iterator BBI = NewBB; --BBI;
456 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
457 if (&*BBI == SplitPreds[i])
461 // If it isn't already after an outside block, move it after one. This is
462 // always good as it makes the uncond branch from the outside block into a
465 // Figure out *which* outside block to put this after. Prefer an outside
466 // block that neighbors a BB actually in the loop.
467 BasicBlock *FoundBB = 0;
468 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
469 Function::iterator BBI = SplitPreds[i];
470 if (++BBI != NewBB->getParent()->end() &&
472 FoundBB = SplitPreds[i];
477 // If our heuristic for a *good* bb to place this after doesn't find
478 // anything, just pick something. It's likely better than leaving it within
481 FoundBB = SplitPreds[0];
482 NewBB->moveAfter(FoundBB);
486 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
487 /// them out into a nested loop. This is important for code that looks like
492 /// br cond, Loop, Next
494 /// br cond2, Loop, Out
496 /// To identify this common case, we look at the PHI nodes in the header of the
497 /// loop. PHI nodes with unchanging values on one backedge correspond to values
498 /// that change in the "outer" loop, but not in the "inner" loop.
500 /// If we are able to separate out a loop, return the new outer loop that was
503 Loop *LoopSimplify::SeparateNestedLoop(Loop *L, LPPassManager &LPM) {
504 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
505 if (PN == 0) return 0; // No known way to partition.
507 // Pull out all predecessors that have varying values in the loop. This
508 // handles the case when a PHI node has multiple instances of itself as
510 SmallVector<BasicBlock*, 8> OuterLoopPreds;
511 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
512 if (PN->getIncomingValue(i) != PN ||
513 !L->contains(PN->getIncomingBlock(i))) {
514 // We can't split indirectbr edges.
515 if (isa<IndirectBrInst>(PN->getIncomingBlock(i)->getTerminator()))
518 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
521 DEBUG(dbgs() << "LoopSimplify: Splitting out a new outer loop\n");
523 BasicBlock *Header = L->getHeader();
524 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
525 OuterLoopPreds.size(),
528 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
529 // code layout too horribly.
530 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
532 // Create the new outer loop.
533 Loop *NewOuter = new Loop();
535 // Change the parent loop to use the outer loop as its child now.
536 if (Loop *Parent = L->getParentLoop())
537 Parent->replaceChildLoopWith(L, NewOuter);
539 LI->changeTopLevelLoop(L, NewOuter);
541 // L is now a subloop of our outer loop.
542 NewOuter->addChildLoop(L);
544 // Add the new loop to the pass manager queue.
545 LPM.insertLoopIntoQueue(NewOuter);
547 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
549 NewOuter->addBlockEntry(*I);
551 // Now reset the header in L, which had been moved by
552 // SplitBlockPredecessors for the outer loop.
553 L->moveToHeader(Header);
555 // Determine which blocks should stay in L and which should be moved out to
556 // the Outer loop now.
557 std::set<BasicBlock*> BlocksInL;
558 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
559 if (DT->dominates(Header, *PI))
560 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
563 // Scan all of the loop children of L, moving them to OuterLoop if they are
564 // not part of the inner loop.
565 const std::vector<Loop*> &SubLoops = L->getSubLoops();
566 for (size_t I = 0; I != SubLoops.size(); )
567 if (BlocksInL.count(SubLoops[I]->getHeader()))
568 ++I; // Loop remains in L
570 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
572 // Now that we know which blocks are in L and which need to be moved to
573 // OuterLoop, move any blocks that need it.
574 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
575 BasicBlock *BB = L->getBlocks()[i];
576 if (!BlocksInL.count(BB)) {
577 // Move this block to the parent, updating the exit blocks sets
578 L->removeBlockFromLoop(BB);
580 LI->changeLoopFor(BB, NewOuter);
590 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
591 /// has more than one backedge in it. If this occurs, revector all of these
592 /// backedges to target a new basic block and have that block branch to the loop
593 /// header. This ensures that loops have exactly one backedge.
596 LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
597 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
599 // Get information about the loop
600 BasicBlock *Header = L->getHeader();
601 Function *F = Header->getParent();
603 // Unique backedge insertion currently depends on having a preheader.
607 // Figure out which basic blocks contain back-edges to the loop header.
608 std::vector<BasicBlock*> BackedgeBlocks;
609 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
610 if (*I != Preheader) BackedgeBlocks.push_back(*I);
612 // Create and insert the new backedge block...
613 BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
614 Header->getName()+".backedge", F);
615 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
617 DEBUG(dbgs() << "LoopSimplify: Inserting unique backedge block ";
618 WriteAsOperand(dbgs(), BEBlock, false);
621 // Move the new backedge block to right after the last backedge block.
622 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
623 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
625 // Now that the block has been inserted into the function, create PHI nodes in
626 // the backedge block which correspond to any PHI nodes in the header block.
627 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
628 PHINode *PN = cast<PHINode>(I);
629 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
631 NewPN->reserveOperandSpace(BackedgeBlocks.size());
632 if (AA) AA->copyValue(PN, NewPN);
634 // Loop over the PHI node, moving all entries except the one for the
635 // preheader over to the new PHI node.
636 unsigned PreheaderIdx = ~0U;
637 bool HasUniqueIncomingValue = true;
638 Value *UniqueValue = 0;
639 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
640 BasicBlock *IBB = PN->getIncomingBlock(i);
641 Value *IV = PN->getIncomingValue(i);
642 if (IBB == Preheader) {
645 NewPN->addIncoming(IV, IBB);
646 if (HasUniqueIncomingValue) {
647 if (UniqueValue == 0)
649 else if (UniqueValue != IV)
650 HasUniqueIncomingValue = false;
655 // Delete all of the incoming values from the old PN except the preheader's
656 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
657 if (PreheaderIdx != 0) {
658 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
659 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
661 // Nuke all entries except the zero'th.
662 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
663 PN->removeIncomingValue(e-i, false);
665 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
666 PN->addIncoming(NewPN, BEBlock);
668 // As an optimization, if all incoming values in the new PhiNode (which is a
669 // subset of the incoming values of the old PHI node) have the same value,
670 // eliminate the PHI Node.
671 if (HasUniqueIncomingValue) {
672 NewPN->replaceAllUsesWith(UniqueValue);
673 if (AA) AA->deleteValue(NewPN);
674 BEBlock->getInstList().erase(NewPN);
678 // Now that all of the PHI nodes have been inserted and adjusted, modify the
679 // backedge blocks to just to the BEBlock instead of the header.
680 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
681 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
682 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
683 if (TI->getSuccessor(Op) == Header)
684 TI->setSuccessor(Op, BEBlock);
687 //===--- Update all analyses which we must preserve now -----------------===//
689 // Update Loop Information - we know that this block is now in the current
690 // loop and all parent loops.
691 L->addBasicBlockToLoop(BEBlock, LI->getBase());
693 // Update dominator information
694 DT->splitBlock(BEBlock);
695 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
696 DF->splitBlock(BEBlock);
701 void LoopSimplify::verifyAnalysis() const {
702 // It used to be possible to just assert L->isLoopSimplifyForm(), however
703 // with the introduction of indirectbr, there are now cases where it's
704 // not possible to transform a loop as necessary. We can at least check
705 // that there is an indirectbr near any time there's trouble.
707 // Indirectbr can interfere with preheader and unique backedge insertion.
708 if (!L->getLoopPreheader() || !L->getLoopLatch()) {
709 bool HasIndBrPred = false;
710 for (pred_iterator PI = pred_begin(L->getHeader()),
711 PE = pred_end(L->getHeader()); PI != PE; ++PI)
712 if (isa<IndirectBrInst>((*PI)->getTerminator())) {
716 assert(HasIndBrPred &&
717 "LoopSimplify has no excuse for missing loop header info!");
720 // Indirectbr can interfere with exit block canonicalization.
721 if (!L->hasDedicatedExits()) {
722 bool HasIndBrExiting = false;
723 SmallVector<BasicBlock*, 8> ExitingBlocks;
724 L->getExitingBlocks(ExitingBlocks);
725 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i)
726 if (isa<IndirectBrInst>((ExitingBlocks[i])->getTerminator())) {
727 HasIndBrExiting = true;
730 assert(HasIndBrExiting &&
731 "LoopSimplify has no excuse for missing exit block info!");