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/Type.h"
41 #include "llvm/Analysis/AliasAnalysis.h"
42 #include "llvm/Analysis/Dominators.h"
43 #include "llvm/Analysis/LoopInfo.h"
44 #include "llvm/Support/CFG.h"
45 #include "llvm/Support/Compiler.h"
46 #include "llvm/ADT/SetOperations.h"
47 #include "llvm/ADT/SetVector.h"
48 #include "llvm/ADT/Statistic.h"
49 #include "llvm/ADT/DepthFirstIterator.h"
52 STATISTIC(NumInserted, "Number of pre-header or exit blocks inserted");
53 STATISTIC(NumNested , "Number of nested loops split out");
56 struct VISIBILITY_HIDDEN LoopSimplify : public FunctionPass {
57 static char ID; // Pass identification, replacement for typeid
58 LoopSimplify() : FunctionPass((intptr_t)&ID) {}
60 // AA - If we have an alias analysis object to update, this is it, otherwise
65 virtual bool runOnFunction(Function &F);
67 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
68 // We need loop information to identify the loops...
69 AU.addRequired<LoopInfo>();
70 AU.addRequired<DominatorTree>();
72 AU.addPreserved<LoopInfo>();
73 AU.addPreserved<DominatorTree>();
74 AU.addPreserved<DominanceFrontier>();
75 AU.addPreservedID(BreakCriticalEdgesID); // No critical edges added.
78 /// verifyAnalysis() - Verify loop nest.
79 void verifyAnalysis() const {
81 LoopInfo *NLI = &getAnalysis<LoopInfo>();
82 for (LoopInfo::iterator I = NLI->begin(), E = NLI->end(); I != E; ++I)
88 bool ProcessLoop(Loop *L);
89 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
90 const std::vector<BasicBlock*> &Preds);
91 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
92 void InsertPreheaderForLoop(Loop *L);
93 Loop *SeparateNestedLoop(Loop *L);
94 void InsertUniqueBackedgeBlock(Loop *L);
95 void PlaceSplitBlockCarefully(BasicBlock *NewBB,
96 std::vector<BasicBlock*> &SplitPreds,
100 char LoopSimplify::ID = 0;
101 RegisterPass<LoopSimplify>
102 X("loopsimplify", "Canonicalize natural loops", true);
105 // Publically exposed interface to pass...
106 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
107 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
109 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
110 /// it in any convenient order) inserting preheaders...
112 bool LoopSimplify::runOnFunction(Function &F) {
113 bool Changed = false;
114 LI = &getAnalysis<LoopInfo>();
115 AA = getAnalysisToUpdate<AliasAnalysis>();
116 DT = &getAnalysis<DominatorTree>();
118 // Check to see that no blocks (other than the header) in loops have
119 // predecessors that are not in loops. This is not valid for natural loops,
120 // but can occur if the blocks are unreachable. Since they are unreachable we
121 // can just shamelessly destroy their terminators to make them not branch into
123 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
124 // This case can only occur for unreachable blocks. Blocks that are
125 // unreachable can't be in loops, so filter those blocks out.
126 if (LI->getLoopFor(BB)) continue;
128 bool BlockUnreachable = false;
130 // Check to see if any successors of this block are non-loop-header loops
131 // that are not the header.
132 for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
133 // If this successor is not in a loop, BB is clearly ok.
134 Loop *L = LI->getLoopFor(*I);
137 // If the succ is the loop header, and if L is a top-level loop, then this
138 // is an entrance into a loop through the header, which is also ok.
139 if (L->getHeader() == *I && L->getParentLoop() == 0)
142 // Otherwise, this is an entrance into a loop from some place invalid.
143 // Either the loop structure is invalid and this is not a natural loop (in
144 // which case the compiler is buggy somewhere else) or BB is unreachable.
145 BlockUnreachable = true;
149 // If this block is ok, check the next one.
150 if (!BlockUnreachable) continue;
152 // Otherwise, this block is dead. To clean up the CFG and to allow later
153 // loop transformations to ignore this case, we delete the edges into the
154 // loop by replacing the terminator.
156 // Remove PHI entries from the successors.
157 for (succ_iterator I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
158 (*I)->removePredecessor(BB);
160 // Add a new unreachable instruction before the old terminator.
161 TerminatorInst *TI = BB->getTerminator();
162 new UnreachableInst(TI);
164 // Delete the dead terminator.
165 if (AA) AA->deleteValue(TI);
166 if (!TI->use_empty())
167 TI->replaceAllUsesWith(UndefValue::get(TI->getType()));
168 TI->eraseFromParent();
172 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
173 Changed |= ProcessLoop(*I);
178 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
179 /// all loops have preheaders.
181 bool LoopSimplify::ProcessLoop(Loop *L) {
182 bool Changed = false;
185 // Canonicalize inner loops before outer loops. Inner loop canonicalization
186 // can provide work for the outer loop to canonicalize.
187 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
188 Changed |= ProcessLoop(*I);
190 assert(L->getBlocks()[0] == L->getHeader() &&
191 "Header isn't first block in loop?");
193 // Does the loop already have a preheader? If so, don't insert one.
194 if (L->getLoopPreheader() == 0) {
195 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 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
208 for (SetVector<BasicBlock*>::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 RewriteLoopExitBlock(L, ExitBlock);
223 // If the header has more than two predecessors at this point (from the
224 // preheader and from multiple backedges), we must adjust the loop.
225 unsigned NumBackedges = L->getNumBackEdges();
226 if (NumBackedges != 1) {
227 // If this is really a nested loop, rip it out into a child loop. Don't do
228 // this for loops with a giant number of backedges, just factor them into a
229 // common backedge instead.
230 if (NumBackedges < 8) {
231 if (Loop *NL = SeparateNestedLoop(L)) {
233 // 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 InsertUniqueBackedgeBlock(L);
249 // Scan over the PHI nodes in the loop header. Since they now have only two
250 // incoming values (the loop is canonicalized), we may have simplified the PHI
251 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
253 for (BasicBlock::iterator I = L->getHeader()->begin();
254 (PN = dyn_cast<PHINode>(I++)); )
255 if (Value *V = PN->hasConstantValue()) {
256 PN->replaceAllUsesWith(V);
257 PN->eraseFromParent();
263 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
264 /// to move the predecessors specified in the Preds list to point to the new
265 /// block, leaving the remaining predecessors pointing to BB. This method
266 /// updates the SSA PHINode's, AliasAnalysis, DominatorTree and
267 /// DominanceFrontier, but no other analyses.
269 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
271 const std::vector<BasicBlock*> &Preds) {
273 // Create new basic block, insert right before the original block.
275 BasicBlock::Create(BB->getName()+Suffix, BB->getParent(), BB);
277 // The preheader first gets an unconditional branch to the loop header.
278 BranchInst *BI = BranchInst::Create(BB, NewBB);
280 // Move the edges from Preds to point to NewBB instead of BB.
281 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
282 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
284 if (Preds[i]->getUnwindDest() == BB)
285 Preds[i]->setUnwindDest(NewBB);
288 // Update dominator tree and dominator frontier if available.
289 DT->splitBlock(NewBB);
290 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
291 DF->splitBlock(NewBB);
293 // For every PHI node in the block, insert a PHI node into NewBB where the
294 // incoming values from the out of loop edges are moved to NewBB. We have two
295 // possible cases here. If the loop is dead, we just insert dummy entries
296 // into the PHI nodes for the new edge. If the loop is not dead, we move the
297 // incoming edges in BB into new PHI nodes in NewBB.
299 if (Preds.empty()) { // Is the loop obviously dead?
300 // Insert dummy values as the incoming value.
301 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
302 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
307 // Check to see if the values being merged into the new block need PHI
308 // nodes. If so, insert them.
309 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
310 PHINode *PN = cast<PHINode>(I);
313 // Check to see if all of the values coming in are the same. If so, we
314 // don't need to create a new PHI node.
315 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
316 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
317 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
322 // If the values coming into the block are not the same, we need a PHI.
324 // Create the new PHI node, insert it into NewBB at the end of the block
326 PHINode::Create(PN->getType(), PN->getName()+".ph", BI);
327 if (AA) AA->copyValue(PN, NewPHI);
329 // Move all of the edges from blocks outside the loop to the new PHI
330 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
331 Value *V = PN->removeIncomingValue(Preds[i], false);
332 NewPHI->addIncoming(V, Preds[i]);
336 // Remove all of the edges coming into the PHI nodes from outside of the
338 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
339 PN->removeIncomingValue(Preds[i], false);
342 // Add an incoming value to the PHI node in the loop for the preheader
344 PN->addIncoming(InVal, NewBB);
346 // Can we eliminate this phi node now?
347 if (Value *V = PN->hasConstantValue(true)) {
348 Instruction *I = dyn_cast<Instruction>(V);
349 if (!I || DT->dominates(I, PN)) {
350 PN->replaceAllUsesWith(V);
351 if (AA) AA->deleteValue(PN);
352 PN->eraseFromParent();
360 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
361 /// preheader, this method is called to insert one. This method has two phases:
362 /// preheader insertion and analysis updating.
364 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
365 BasicBlock *Header = L->getHeader();
367 // Compute the set of predecessors of the loop that are not in the loop.
368 std::vector<BasicBlock*> OutsideBlocks;
369 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
371 if (!L->contains(*PI)) // Coming in from outside the loop?
372 OutsideBlocks.push_back(*PI); // Keep track of it...
374 // Split out the loop pre-header.
376 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
379 //===--------------------------------------------------------------------===//
380 // Update analysis results now that we have performed the transformation
383 // We know that we have loop information to update... update it now.
384 if (Loop *Parent = L->getParentLoop())
385 Parent->addBasicBlockToLoop(NewBB, LI->getBase());
387 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
388 // code layout too horribly.
389 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
392 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
393 /// blocks. This method is used to split exit blocks that have predecessors
394 /// outside of the loop.
395 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
396 std::vector<BasicBlock*> LoopBlocks;
397 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
399 LoopBlocks.push_back(*I);
401 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
402 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
404 // Update Loop Information - we know that the new block will be in whichever
405 // loop the Exit block is in. Note that it may not be in that immediate loop,
406 // if the successor is some other loop header. In that case, we continue
407 // walking up the loop tree to find a loop that contains both the successor
408 // block and the predecessor block.
409 Loop *SuccLoop = LI->getLoopFor(Exit);
410 while (SuccLoop && !SuccLoop->contains(L->getHeader()))
411 SuccLoop = SuccLoop->getParentLoop();
413 SuccLoop->addBasicBlockToLoop(NewBB, LI->getBase());
418 /// AddBlockAndPredsToSet - Add the specified block, and all of its
419 /// predecessors, to the specified set, if it's not already in there. Stop
420 /// predecessor traversal when we reach StopBlock.
421 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
422 std::set<BasicBlock*> &Blocks) {
423 std::vector<BasicBlock *> WorkList;
424 WorkList.push_back(InputBB);
426 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
427 if (Blocks.insert(BB).second && BB != StopBlock)
428 // If BB is not already processed and it is not a stop block then
429 // insert its predecessor in the work list
430 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
431 BasicBlock *WBB = *I;
432 WorkList.push_back(WBB);
434 } while(!WorkList.empty());
437 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
438 /// PHI node that tells us how to partition the loops.
439 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
441 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
442 PHINode *PN = cast<PHINode>(I);
444 if (Value *V = PN->hasConstantValue())
445 if (!isa<Instruction>(V) || DT->dominates(cast<Instruction>(V), PN)) {
446 // This is a degenerate PHI already, don't modify it!
447 PN->replaceAllUsesWith(V);
448 if (AA) AA->deleteValue(PN);
449 PN->eraseFromParent();
453 // Scan this PHI node looking for a use of the PHI node by itself.
454 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
455 if (PN->getIncomingValue(i) == PN &&
456 L->contains(PN->getIncomingBlock(i)))
457 // We found something tasty to remove.
463 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
464 // right after some 'outside block' block. This prevents the preheader from
465 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
466 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
467 std::vector<BasicBlock*>&SplitPreds,
469 // Check to see if NewBB is already well placed.
470 Function::iterator BBI = NewBB; --BBI;
471 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
472 if (&*BBI == SplitPreds[i])
476 // If it isn't already after an outside block, move it after one. This is
477 // always good as it makes the uncond branch from the outside block into a
480 // Figure out *which* outside block to put this after. Prefer an outside
481 // block that neighbors a BB actually in the loop.
482 BasicBlock *FoundBB = 0;
483 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
484 Function::iterator BBI = SplitPreds[i];
485 if (++BBI != NewBB->getParent()->end() &&
487 FoundBB = SplitPreds[i];
492 // If our heuristic for a *good* bb to place this after doesn't find
493 // anything, just pick something. It's likely better than leaving it within
496 FoundBB = SplitPreds[0];
497 NewBB->moveAfter(FoundBB);
501 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
502 /// them out into a nested loop. This is important for code that looks like
507 /// br cond, Loop, Next
509 /// br cond2, Loop, Out
511 /// To identify this common case, we look at the PHI nodes in the header of the
512 /// loop. PHI nodes with unchanging values on one backedge correspond to values
513 /// that change in the "outer" loop, but not in the "inner" loop.
515 /// If we are able to separate out a loop, return the new outer loop that was
518 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
519 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
520 if (PN == 0) return 0; // No known way to partition.
522 // Pull out all predecessors that have varying values in the loop. This
523 // handles the case when a PHI node has multiple instances of itself as
525 std::vector<BasicBlock*> OuterLoopPreds;
526 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
527 if (PN->getIncomingValue(i) != PN ||
528 !L->contains(PN->getIncomingBlock(i)))
529 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
531 BasicBlock *Header = L->getHeader();
532 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
534 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
535 // code layout too horribly.
536 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
538 // Create the new outer loop.
539 Loop *NewOuter = new Loop();
541 // Change the parent loop to use the outer loop as its child now.
542 if (Loop *Parent = L->getParentLoop())
543 Parent->replaceChildLoopWith(L, NewOuter);
545 LI->changeTopLevelLoop(L, NewOuter);
547 // This block is going to be our new header block: add it to this loop and all
549 NewOuter->addBasicBlockToLoop(NewBB, LI->getBase());
551 // L is now a subloop of our outer loop.
552 NewOuter->addChildLoop(L);
554 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
555 NewOuter->addBlockEntry(L->getBlocks()[i]);
557 // Determine which blocks should stay in L and which should be moved out to
558 // the Outer loop now.
559 std::set<BasicBlock*> BlocksInL;
560 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
561 if (DT->dominates(Header, *PI))
562 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
565 // Scan all of the loop children of L, moving them to OuterLoop if they are
566 // not part of the inner loop.
567 const std::vector<Loop*> &SubLoops = L->getSubLoops();
568 for (size_t I = 0; I != SubLoops.size(); )
569 if (BlocksInL.count(SubLoops[I]->getHeader()))
570 ++I; // Loop remains in L
572 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
574 // Now that we know which blocks are in L and which need to be moved to
575 // OuterLoop, move any blocks that need it.
576 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
577 BasicBlock *BB = L->getBlocks()[i];
578 if (!BlocksInL.count(BB)) {
579 // Move this block to the parent, updating the exit blocks sets
580 L->removeBlockFromLoop(BB);
582 LI->changeLoopFor(BB, NewOuter);
592 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
593 /// has more than one backedge in it. If this occurs, revector all of these
594 /// backedges to target a new basic block and have that block branch to the loop
595 /// header. This ensures that loops have exactly one backedge.
597 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
598 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
600 // Get information about the loop
601 BasicBlock *Preheader = L->getLoopPreheader();
602 BasicBlock *Header = L->getHeader();
603 Function *F = Header->getParent();
605 // Figure out which basic blocks contain back-edges to the loop header.
606 std::vector<BasicBlock*> BackedgeBlocks;
607 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
608 if (*I != Preheader) BackedgeBlocks.push_back(*I);
610 // Create and insert the new backedge block...
611 BasicBlock *BEBlock = BasicBlock::Create(Header->getName()+".backedge", F);
612 BranchInst *BETerminator = BranchInst::Create(Header, BEBlock);
614 // Move the new backedge block to right after the last backedge block.
615 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
616 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
618 // Now that the block has been inserted into the function, create PHI nodes in
619 // the backedge block which correspond to any PHI nodes in the header block.
620 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
621 PHINode *PN = cast<PHINode>(I);
622 PHINode *NewPN = PHINode::Create(PN->getType(), PN->getName()+".be",
624 NewPN->reserveOperandSpace(BackedgeBlocks.size());
625 if (AA) AA->copyValue(PN, NewPN);
627 // Loop over the PHI node, moving all entries except the one for the
628 // preheader over to the new PHI node.
629 unsigned PreheaderIdx = ~0U;
630 bool HasUniqueIncomingValue = true;
631 Value *UniqueValue = 0;
632 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
633 BasicBlock *IBB = PN->getIncomingBlock(i);
634 Value *IV = PN->getIncomingValue(i);
635 if (IBB == Preheader) {
638 NewPN->addIncoming(IV, IBB);
639 if (HasUniqueIncomingValue) {
640 if (UniqueValue == 0)
642 else if (UniqueValue != IV)
643 HasUniqueIncomingValue = false;
648 // Delete all of the incoming values from the old PN except the preheader's
649 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
650 if (PreheaderIdx != 0) {
651 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
652 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
654 // Nuke all entries except the zero'th.
655 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
656 PN->removeIncomingValue(e-i, false);
658 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
659 PN->addIncoming(NewPN, BEBlock);
661 // As an optimization, if all incoming values in the new PhiNode (which is a
662 // subset of the incoming values of the old PHI node) have the same value,
663 // eliminate the PHI Node.
664 if (HasUniqueIncomingValue) {
665 NewPN->replaceAllUsesWith(UniqueValue);
666 if (AA) AA->deleteValue(NewPN);
667 BEBlock->getInstList().erase(NewPN);
671 // Now that all of the PHI nodes have been inserted and adjusted, modify the
672 // backedge blocks to branch to the BEBlock instead of the header.
673 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
674 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
675 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
676 if (TI->getSuccessor(Op) == Header)
677 TI->setSuccessor(Op, BEBlock);
679 if (BackedgeBlocks[i]->getUnwindDest() == Header)
680 BackedgeBlocks[i]->setUnwindDest(BEBlock);
683 //===--- Update all analyses which we must preserve now -----------------===//
685 // Update Loop Information - we know that this block is now in the current
686 // loop and all parent loops.
687 L->addBasicBlockToLoop(BEBlock, LI->getBase());
689 // Update dominator information
690 DT->splitBlock(BEBlock);
691 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
692 DF->splitBlock(BEBlock);