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 // Note that the simplifycfg pass will clean up blocks which are split out but
27 // end up being unnecessary, so usage of this pass should not pessimize
30 // This pass obviously modifies the CFG, but updates loop information and
31 // dominator information.
33 //===----------------------------------------------------------------------===//
35 #define DEBUG_TYPE "loopsimplify"
36 #include "llvm/Transforms/Scalar.h"
37 #include "llvm/Constants.h"
38 #include "llvm/Instructions.h"
39 #include "llvm/Function.h"
40 #include "llvm/LLVMContext.h"
41 #include "llvm/Type.h"
42 #include "llvm/Analysis/AliasAnalysis.h"
43 #include "llvm/Analysis/Dominators.h"
44 #include "llvm/Analysis/LoopInfo.h"
45 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
46 #include "llvm/Transforms/Utils/Local.h"
47 #include "llvm/Support/CFG.h"
48 #include "llvm/Support/Compiler.h"
49 #include "llvm/ADT/SetOperations.h"
50 #include "llvm/ADT/SetVector.h"
51 #include "llvm/ADT/Statistic.h"
52 #include "llvm/ADT/DepthFirstIterator.h"
55 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
56 STATISTIC(NumNested , "Number of nested loops split out");
59 struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass {
60 static char ID; // Pass identification, replacement for typeid
61 LoopSimplify() : FunctionPass(&ID) {}
63 // AA - If we have an alias analysis object to update, this is it, otherwise
68 virtual bool runOnFunction(Function &F);
70 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
71 // We need loop information to identify the loops...
72 AU.addRequiredTransitive<LoopInfo>();
73 AU.addRequiredTransitive<DominatorTree>();
75 AU.addPreserved<LoopInfo>();
76 AU.addPreserved<DominatorTree>();
77 AU.addPreserved<DominanceFrontier>();
78 AU.addPreserved<AliasAnalysis>();
79 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
82 /// verifyAnalysis() - Verify loop nest.
83 void verifyAnalysis() const {
85 LoopInfo *NLI = &getAnalysis<LoopInfo>();
86 for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I) {
87 // Check the special guarantees that LoopSimplify makes.
88 assert((*I)->isLoopSimplifyForm());
94 bool ProcessLoop(Loop *L);
95 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
96 BasicBlock *InsertPreheaderForLoop(Loop *L);
97 Loop *SeparateNestedLoop(Loop *L);
98 void 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 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
113 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
114 /// it in any convenient order) inserting preheaders...
116 bool LoopSimplify::runOnFunction(Function &F) {
117 bool Changed = false;
118 LI = &getAnalysis<LoopInfo>();
119 AA = getAnalysisIfAvailable<AliasAnalysis>();
120 DT = &getAnalysis<DominatorTree>();
122 // Check to see that no blocks (other than the header) in loops have
123 // predecessors that are not in loops. This is not valid for natural loops,
124 // but can occur if the blocks are unreachable. Since they are unreachable we
125 // can just shamelessly destroy their terminators to make them not branch into
127 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
128 // This case can only occur for unreachable blocks. Blocks that are
129 // unreachable can't be in loops, so filter those blocks out.
130 if (LI->getLoopFor(BB)) continue;
132 bool BlockUnreachable = false;
133 TerminatorInst *TI = BB->getTerminator();
135 // Check to see if any successors of this block are non-loop-header loops
136 // that are not the header.
137 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
138 // If this successor is not in a loop, BB is clearly ok.
139 Loop *L = LI->getLoopFor(TI->getSuccessor(i));
142 // If the succ is the loop header, and if L is a top-level loop, then this
143 // is an entrance into a loop through the header, which is also ok.
144 if (L->getHeader() == TI->getSuccessor(i) && L->getParentLoop() == 0)
147 // Otherwise, this is an entrance into a loop from some place invalid.
148 // Either the loop structure is invalid and this is not a natural loop (in
149 // which case the compiler is buggy somewhere else) or BB is unreachable.
150 BlockUnreachable = true;
154 // If this block is ok, check the next one.
155 if (!BlockUnreachable) continue;
157 // Otherwise, this block is dead. To clean up the CFG and to allow later
158 // loop transformations to ignore this case, we delete the edges into the
159 // loop by replacing the terminator.
161 // Remove PHI entries from the successors.
162 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
163 TI->getSuccessor(i)->removePredecessor(BB);
165 // Add a new unreachable instruction before the old terminator.
166 new UnreachableInst(TI->getContext(), TI);
168 // Delete the dead terminator.
169 if (AA) AA->deleteValue(TI);
170 if (!TI->use_empty())
171 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
172 TI->eraseFromParent();
176 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
177 Changed |= ProcessLoop(*I);
182 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
183 /// all loops have preheaders.
185 bool LoopSimplify::ProcessLoop(Loop *L) {
186 bool Changed = false;
189 // Canonicalize inner loops before outer loops. Inner loop canonicalization
190 // can provide work for the outer loop to canonicalize.
191 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
192 Changed |= ProcessLoop(*I);
194 assert(L->getBlocks()[0] == L->getHeader() &&
195 "Header isn't first block in loop?");
197 // Does the loop already have a preheader? If so, don't insert one.
198 BasicBlock *Preheader = L->getLoopPreheader();
200 Preheader = InsertPreheaderForLoop(L);
205 // Next, check to make sure that all exit nodes of the loop only have
206 // predecessors that are inside of the loop. This check guarantees that the
207 // loop preheader/header will dominate the exit blocks. If the exit block has
208 // predecessors from outside of the loop, split the edge now.
209 SmallVector<BasicBlock*, 8> ExitBlocks;
210 L->getExitBlocks(ExitBlocks);
212 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
213 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
214 E = ExitBlockSet.end(); I != E; ++I) {
215 BasicBlock *ExitBlock = *I;
216 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
218 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
220 if (!L->contains(*PI)) {
221 RewriteLoopExitBlock(L, ExitBlock);
228 // If the header has more than two predecessors at this point (from the
229 // preheader and from multiple backedges), we must adjust the loop.
230 unsigned NumBackedges = L->getNumBackEdges();
231 if (NumBackedges != 1) {
232 // If this is really a nested loop, rip it out into a child loop. Don't do
233 // this for loops with a giant number of backedges, just factor them into a
234 // common backedge instead.
235 if (NumBackedges < 8) {
236 if (Loop *NL = SeparateNestedLoop(L)) {
238 // This is a big restructuring change, reprocess the whole loop.
241 // GCC doesn't tail recursion eliminate this.
246 // If we either couldn't, or didn't want to, identify nesting of the loops,
247 // insert a new block that all backedges target, then make it jump to the
249 InsertUniqueBackedgeBlock(L, Preheader);
254 // Scan over the PHI nodes in the loop header. Since they now have only two
255 // incoming values (the loop is canonicalized), we may have simplified the PHI
256 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
258 for (BasicBlock::iterator I = L->getHeader()->begin();
259 (PN = dyn_cast<PHINode>(I++)); )
260 if (Value *V = PN->hasConstantValue(DT)) {
261 if (AA) AA->deleteValue(PN);
262 PN->replaceAllUsesWith(V);
263 PN->eraseFromParent();
266 // If this loop has muliple exits and the exits all go to the same
267 // block, attempt to merge the exits. This helps several passes, such
268 // as LoopRotation, which do not support loops with multiple exits.
269 // SimplifyCFG also does this (and this code uses the same utility
270 // function), however this code is loop-aware, where SimplifyCFG is
271 // not. That gives it the advantage of being able to hoist
272 // loop-invariant instructions out of the way to open up more
273 // opportunities, and the disadvantage of having the responsibility
274 // to preserve dominator information.
275 if (ExitBlocks.size() > 1 && L->getUniqueExitBlock()) {
276 SmallVector<BasicBlock*, 8> ExitingBlocks;
277 L->getExitingBlocks(ExitingBlocks);
278 for (unsigned i = 0, e = ExitingBlocks.size(); i != e; ++i) {
279 BasicBlock *ExitingBlock = ExitingBlocks[i];
280 if (!ExitingBlock->getSinglePredecessor()) continue;
281 BranchInst *BI = dyn_cast<BranchInst>(ExitingBlock->getTerminator());
282 if (!BI || !BI->isConditional()) continue;
283 CmpInst *CI = dyn_cast<CmpInst>(BI->getCondition());
284 if (!CI || CI->getParent() != ExitingBlock) continue;
286 // Attempt to hoist out all instructions except for the
287 // comparison and the branch.
288 bool AllInvariant = true;
289 for (BasicBlock::iterator I = ExitingBlock->begin(); &*I != BI; ) {
290 Instruction *Inst = I++;
293 if (!L->makeLoopInvariant(Inst, Changed, Preheader->getTerminator())) {
294 AllInvariant = false;
298 if (!AllInvariant) continue;
300 // The block has now been cleared of all instructions except for
301 // a comparison and a conditional branch. SimplifyCFG may be able
303 if (!FoldBranchToCommonDest(BI)) continue;
305 // Success. The block is now dead, so remove it from the loop,
306 // update the dominator tree and dominance frontier, and delete it.
307 assert(pred_begin(ExitingBlock) == pred_end(ExitingBlock));
309 LI->removeBlock(ExitingBlock);
311 DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>();
312 DomTreeNode *Node = DT->getNode(ExitingBlock);
313 const std::vector<DomTreeNodeBase<BasicBlock> *> &Children =
315 for (unsigned k = 0, g = Children.size(); k != g; ++k) {
316 DT->changeImmediateDominator(Children[k], Node->getIDom());
317 if (DF) DF->changeImmediateDominator(Children[k]->getBlock(),
318 Node->getIDom()->getBlock(),
321 DT->eraseNode(ExitingBlock);
322 if (DF) DF->removeBlock(ExitingBlock);
324 BI->getSuccessor(0)->removePredecessor(ExitingBlock);
325 BI->getSuccessor(1)->removePredecessor(ExitingBlock);
326 ExitingBlock->eraseFromParent();
333 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
334 /// preheader, this method is called to insert one. This method has two phases:
335 /// preheader insertion and analysis updating.
337 BasicBlock *LoopSimplify::InsertPreheaderForLoop(Loop *L) {
338 BasicBlock *Header = L->getHeader();
340 // Compute the set of predecessors of the loop that are not in the loop.
341 SmallVector<BasicBlock*, 8> OutsideBlocks;
342 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
344 if (!L->contains(*PI)) // Coming in from outside the loop?
345 OutsideBlocks.push_back(*PI); // Keep track of it...
347 // Split out the loop pre-header.
349 SplitBlockPredecessors(Header, &OutsideBlocks[0], OutsideBlocks.size(),
352 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
353 // code layout too horribly.
354 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
359 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
360 /// blocks. This method is used to split exit blocks that have predecessors
361 /// outside of the loop.
362 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
363 SmallVector<BasicBlock*, 8> LoopBlocks;
364 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
366 LoopBlocks.push_back(*I);
368 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
369 BasicBlock *NewBB = SplitBlockPredecessors(Exit, &LoopBlocks[0],
370 LoopBlocks.size(), ".loopexit",
376 /// AddBlockAndPredsToSet - Add the specified block, and all of its
377 /// predecessors, to the specified set, if it's not already in there. Stop
378 /// predecessor traversal when we reach StopBlock.
379 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
380 std::set<BasicBlock*> &Blocks) {
381 std::vector<BasicBlock *> WorkList;
382 WorkList.push_back(InputBB);
384 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
385 if (Blocks.insert(BB).second && BB != StopBlock)
386 // If BB is not already processed and it is not a stop block then
387 // insert its predecessor in the work list
388 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
389 BasicBlock *WBB = *I;
390 WorkList.push_back(WBB);
392 } while(!WorkList.empty());
395 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
396 /// PHI node that tells us how to partition the loops.
397 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
399 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
400 PHINode *PN = cast<PHINode>(I);
402 if (Value *V = PN->hasConstantValue(DT)) {
403 // This is a degenerate PHI already, don't modify it!
404 PN->replaceAllUsesWith(V);
405 if (AA) AA->deleteValue(PN);
406 PN->eraseFromParent();
410 // Scan this PHI node looking for a use of the PHI node by itself.
411 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
412 if (PN->getIncomingValue(i) == PN &&
413 L->contains(PN->getIncomingBlock(i)))
414 // We found something tasty to remove.
420 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
421 // right after some 'outside block' block. This prevents the preheader from
422 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
423 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
424 SmallVectorImpl<BasicBlock*> &SplitPreds,
426 // Check to see if NewBB is already well placed.
427 Function::iterator BBI = NewBB; --BBI;
428 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
429 if (&*BBI == SplitPreds[i])
433 // If it isn't already after an outside block, move it after one. This is
434 // always good as it makes the uncond branch from the outside block into a
437 // Figure out *which* outside block to put this after. Prefer an outside
438 // block that neighbors a BB actually in the loop.
439 BasicBlock *FoundBB = 0;
440 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
441 Function::iterator BBI = SplitPreds[i];
442 if (++BBI != NewBB->getParent()->end() &&
444 FoundBB = SplitPreds[i];
449 // If our heuristic for a *good* bb to place this after doesn't find
450 // anything, just pick something. It's likely better than leaving it within
453 FoundBB = SplitPreds[0];
454 NewBB->moveAfter(FoundBB);
458 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
459 /// them out into a nested loop. This is important for code that looks like
464 /// br cond, Loop, Next
466 /// br cond2, Loop, Out
468 /// To identify this common case, we look at the PHI nodes in the header of the
469 /// loop. PHI nodes with unchanging values on one backedge correspond to values
470 /// that change in the "outer" loop, but not in the "inner" loop.
472 /// If we are able to separate out a loop, return the new outer loop that was
475 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
476 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
477 if (PN == 0) return 0; // No known way to partition.
479 // Pull out all predecessors that have varying values in the loop. This
480 // handles the case when a PHI node has multiple instances of itself as
482 SmallVector<BasicBlock*, 8> OuterLoopPreds;
483 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
484 if (PN->getIncomingValue(i) != PN ||
485 !L->contains(PN->getIncomingBlock(i)))
486 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
488 BasicBlock *Header = L->getHeader();
489 BasicBlock *NewBB = SplitBlockPredecessors(Header, &OuterLoopPreds[0],
490 OuterLoopPreds.size(),
493 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
494 // code layout too horribly.
495 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
497 // Create the new outer loop.
498 Loop *NewOuter = new Loop();
500 // Change the parent loop to use the outer loop as its child now.
501 if (Loop *Parent = L->getParentLoop())
502 Parent->replaceChildLoopWith(L, NewOuter);
504 LI->changeTopLevelLoop(L, NewOuter);
506 // L is now a subloop of our outer loop.
507 NewOuter->addChildLoop(L);
509 for (Loop::block_iterator I = L->block_begin(), E = L->block_end();
511 NewOuter->addBlockEntry(*I);
513 // Now reset the header in L, which had been moved by
514 // SplitBlockPredecessors for the outer loop.
515 L->moveToHeader(Header);
517 // Determine which blocks should stay in L and which should be moved out to
518 // the Outer loop now.
519 std::set<BasicBlock*> BlocksInL;
520 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
521 if (DT->dominates(Header, *PI))
522 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
525 // Scan all of the loop children of L, moving them to OuterLoop if they are
526 // not part of the inner loop.
527 const std::vector<Loop*> &SubLoops = L->getSubLoops();
528 for (size_t I = 0; I != SubLoops.size(); )
529 if (BlocksInL.count(SubLoops[I]->getHeader()))
530 ++I; // Loop remains in L
532 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
534 // Now that we know which blocks are in L and which need to be moved to
535 // OuterLoop, move any blocks that need it.
536 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
537 BasicBlock *BB = L->getBlocks()[i];
538 if (!BlocksInL.count(BB)) {
539 // Move this block to the parent, updating the exit blocks sets
540 L->removeBlockFromLoop(BB);
542 LI->changeLoopFor(BB, NewOuter);
552 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
553 /// has more than one backedge in it. If this occurs, revector all of these
554 /// backedges to target a new basic block and have that block branch to the loop
555 /// header. This ensures that loops have exactly one backedge.
557 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L, BasicBlock *Preheader) {
558 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
560 // Get information about the loop
561 BasicBlock *Header = L->getHeader();
562 Function *F = Header->getParent();
564 // Figure out which basic blocks contain back-edges to the loop header.
565 std::vector<BasicBlock*> BackedgeBlocks;
566 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
567 if (*I != Preheader) BackedgeBlocks.push_back(*I);
569 // Create and insert the new backedge block...
570 BasicBlock *BEBlock = BasicBlock::Create(Header->getContext(),
571 Header->getName()+".backedge", F);
572 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
574 // Move the new backedge block to right after the last backedge block.
575 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
576 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
578 // Now that the block has been inserted into the function, create PHI nodes in
579 // the backedge block which correspond to any PHI nodes in the header block.
580 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
581 PHINode *PN = cast<PHINode>(I);
582 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
584 NewPN->reserveOperandSpace(BackedgeBlocks.size());
585 if (AA) AA->copyValue(PN, NewPN);
587 // Loop over the PHI node, moving all entries except the one for the
588 // preheader over to the new PHI node.
589 unsigned PreheaderIdx = ~0U;
590 bool HasUniqueIncomingValue = true;
591 Value *UniqueValue = 0;
592 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
593 BasicBlock *IBB = PN->getIncomingBlock(i);
594 Value *IV = PN->getIncomingValue(i);
595 if (IBB == Preheader) {
598 NewPN->addIncoming(IV, IBB);
599 if (HasUniqueIncomingValue) {
600 if (UniqueValue == 0)
602 else if (UniqueValue != IV)
603 HasUniqueIncomingValue = false;
608 // Delete all of the incoming values from the old PN except the preheader's
609 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
610 if (PreheaderIdx != 0) {
611 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
612 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
614 // Nuke all entries except the zero'th.
615 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
616 PN->removeIncomingValue(e-i, false);
618 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
619 PN->addIncoming(NewPN, BEBlock);
621 // As an optimization, if all incoming values in the new PhiNode (which is a
622 // subset of the incoming values of the old PHI node) have the same value,
623 // eliminate the PHI Node.
624 if (HasUniqueIncomingValue) {
625 NewPN->replaceAllUsesWith(UniqueValue);
626 if (AA) AA->deleteValue(NewPN);
627 BEBlock->getInstList().erase(NewPN);
631 // Now that all of the PHI nodes have been inserted and adjusted, modify the
632 // backedge blocks to just to the BEBlock instead of the header.
633 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
634 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
635 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
636 if (TI->getSuccessor(Op) == Header)
637 TI->setSuccessor(Op, BEBlock);
640 //===--- Update all analyses which we must preserve now -----------------===//
642 // Update Loop Information - we know that this block is now in the current
643 // loop and all parent loops.
644 L->addBasicBlockToLoop(BEBlock, LI->getBase());
646 // Update dominator information
647 DT->splitBlock(BEBlock);
648 if (DominanceFrontier *DF = getAnalysisIfAvailable<DominanceFrontier>())
649 DF->splitBlock(BEBlock);