1 //===- LoopSimplify.cpp - Loop Canonicalization Pass ----------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source 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/Constant.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 bool ProcessLoop(Loop *L);
79 BasicBlock *SplitBlockPredecessors(BasicBlock *BB, const char *Suffix,
80 const std::vector<BasicBlock*> &Preds);
81 BasicBlock *RewriteLoopExitBlock(Loop *L, BasicBlock *Exit);
82 void InsertPreheaderForLoop(Loop *L);
83 Loop *SeparateNestedLoop(Loop *L);
84 void InsertUniqueBackedgeBlock(Loop *L);
85 void PlaceSplitBlockCarefully(BasicBlock *NewBB,
86 std::vector<BasicBlock*> &SplitPreds,
90 char LoopSimplify::ID = 0;
91 RegisterPass<LoopSimplify>
92 X("loopsimplify", "Canonicalize natural loops", true);
95 // Publically exposed interface to pass...
96 const PassInfo *llvm::LoopSimplifyID = X.getPassInfo();
97 FunctionPass *llvm::createLoopSimplifyPass() { return new LoopSimplify(); }
99 /// runOnFunction - Run down all loops in the CFG (recursively, but we could do
100 /// it in any convenient order) inserting preheaders...
102 bool LoopSimplify::runOnFunction(Function &F) {
103 bool Changed = false;
104 LI = &getAnalysis<LoopInfo>();
105 AA = getAnalysisToUpdate<AliasAnalysis>();
106 DT = &getAnalysis<DominatorTree>();
108 // Check to see that no blocks (other than the header) in loops have
109 // predecessors that are not in loops. This is not valid for natural loops,
110 // but can occur if the blocks are unreachable. Since they are unreachable we
111 // can just shamelessly destroy their terminators to make them not branch into
113 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB) {
114 // This case can only occur for unreachable blocks. Blocks that are
115 // unreachable can't be in loops, so filter those blocks out.
116 if (LI->getLoopFor(BB)) continue;
118 bool BlockUnreachable = false;
119 TerminatorInst *TI = BB->getTerminator();
121 // Check to see if any successors of this block are non-loop-header loops
122 // that are not the header.
123 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i) {
124 // If this successor is not in a loop, BB is clearly ok.
125 Loop *L = LI->getLoopFor(TI->getSuccessor(i));
128 // If the succ is the loop header, and if L is a top-level loop, then this
129 // is an entrance into a loop through the header, which is also ok.
130 if (L->getHeader() == TI->getSuccessor(i) && L->getParentLoop() == 0)
133 // Otherwise, this is an entrance into a loop from some place invalid.
134 // Either the loop structure is invalid and this is not a natural loop (in
135 // which case the compiler is buggy somewhere else) or BB is unreachable.
136 BlockUnreachable = true;
140 // If this block is ok, check the next one.
141 if (!BlockUnreachable) continue;
143 // Otherwise, this block is dead. To clean up the CFG and to allow later
144 // loop transformations to ignore this case, we delete the edges into the
145 // loop by replacing the terminator.
147 // Remove PHI entries from the successors.
148 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
149 TI->getSuccessor(i)->removePredecessor(BB);
151 // Add a new unreachable instruction.
152 new UnreachableInst(TI);
154 // Delete the dead terminator.
155 if (AA) AA->deleteValue(&BB->back());
156 BB->getInstList().pop_back();
160 for (LoopInfo::iterator I = LI->begin(), E = LI->end(); I != E; ++I)
161 Changed |= ProcessLoop(*I);
166 /// ProcessLoop - Walk the loop structure in depth first order, ensuring that
167 /// all loops have preheaders.
169 bool LoopSimplify::ProcessLoop(Loop *L) {
170 bool Changed = false;
173 // Canonicalize inner loops before outer loops. Inner loop canonicalization
174 // can provide work for the outer loop to canonicalize.
175 for (Loop::iterator I = L->begin(), E = L->end(); I != E; ++I)
176 Changed |= ProcessLoop(*I);
178 assert(L->getBlocks()[0] == L->getHeader() &&
179 "Header isn't first block in loop?");
181 // Does the loop already have a preheader? If so, don't insert one.
182 if (L->getLoopPreheader() == 0) {
183 InsertPreheaderForLoop(L);
188 // Next, check to make sure that all exit nodes of the loop only have
189 // predecessors that are inside of the loop. This check guarantees that the
190 // loop preheader/header will dominate the exit blocks. If the exit block has
191 // predecessors from outside of the loop, split the edge now.
192 std::vector<BasicBlock*> ExitBlocks;
193 L->getExitBlocks(ExitBlocks);
195 SetVector<BasicBlock*> ExitBlockSet(ExitBlocks.begin(), ExitBlocks.end());
196 for (SetVector<BasicBlock*>::iterator I = ExitBlockSet.begin(),
197 E = ExitBlockSet.end(); I != E; ++I) {
198 BasicBlock *ExitBlock = *I;
199 for (pred_iterator PI = pred_begin(ExitBlock), PE = pred_end(ExitBlock);
201 // Must be exactly this loop: no subloops, parent loops, or non-loop preds
203 if (!L->contains(*PI)) {
204 RewriteLoopExitBlock(L, ExitBlock);
211 // If the header has more than two predecessors at this point (from the
212 // preheader and from multiple backedges), we must adjust the loop.
213 unsigned NumBackedges = L->getNumBackEdges();
214 if (NumBackedges != 1) {
215 // If this is really a nested loop, rip it out into a child loop. Don't do
216 // this for loops with a giant number of backedges, just factor them into a
217 // common backedge instead.
218 if (NumBackedges < 8) {
219 if (Loop *NL = SeparateNestedLoop(L)) {
221 // This is a big restructuring change, reprocess the whole loop.
224 // GCC doesn't tail recursion eliminate this.
229 // If we either couldn't, or didn't want to, identify nesting of the loops,
230 // insert a new block that all backedges target, then make it jump to the
232 InsertUniqueBackedgeBlock(L);
237 // Scan over the PHI nodes in the loop header. Since they now have only two
238 // incoming values (the loop is canonicalized), we may have simplified the PHI
239 // down to 'X = phi [X, Y]', which should be replaced with 'Y'.
241 for (BasicBlock::iterator I = L->getHeader()->begin();
242 (PN = dyn_cast<PHINode>(I++)); )
243 if (Value *V = PN->hasConstantValue()) {
244 PN->replaceAllUsesWith(V);
245 PN->eraseFromParent();
251 /// SplitBlockPredecessors - Split the specified block into two blocks. We want
252 /// to move the predecessors specified in the Preds list to point to the new
253 /// block, leaving the remaining predecessors pointing to BB. This method
254 /// updates the SSA PHINode's, but no other analyses.
256 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
258 const std::vector<BasicBlock*> &Preds) {
260 // Create new basic block, insert right before the original block...
261 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
263 // The preheader first gets an unconditional branch to the loop header...
264 BranchInst *BI = new BranchInst(BB, NewBB);
266 // For every PHI node in the block, insert a PHI node into NewBB where the
267 // incoming values from the out of loop edges are moved to NewBB. We have two
268 // possible cases here. If the loop is dead, we just insert dummy entries
269 // into the PHI nodes for the new edge. If the loop is not dead, we move the
270 // incoming edges in BB into new PHI nodes in NewBB.
272 if (!Preds.empty()) { // Is the loop not obviously dead?
273 // Check to see if the values being merged into the new block need PHI
274 // nodes. If so, insert them.
275 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
276 PHINode *PN = cast<PHINode>(I);
279 // Check to see if all of the values coming in are the same. If so, we
280 // don't need to create a new PHI node.
281 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
282 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
283 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
288 // If the values coming into the block are not the same, we need a PHI.
290 // Create the new PHI node, insert it into NewBB at the end of the block
291 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
292 if (AA) AA->copyValue(PN, NewPHI);
294 // Move all of the edges from blocks outside the loop to the new PHI
295 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
296 Value *V = PN->removeIncomingValue(Preds[i], false);
297 NewPHI->addIncoming(V, Preds[i]);
301 // Remove all of the edges coming into the PHI nodes from outside of the
303 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
304 PN->removeIncomingValue(Preds[i], false);
307 // Add an incoming value to the PHI node in the loop for the preheader
309 PN->addIncoming(InVal, NewBB);
311 // Can we eliminate this phi node now?
312 if (Value *V = PN->hasConstantValue(true)) {
313 Instruction *I = dyn_cast<Instruction>(V);
314 // If I is in NewBB, the Dominator call will fail, because NewBB isn't
315 // registered in DominatorTree yet. Handle this case explicitly.
316 if (!I || (I->getParent() != NewBB &&
317 getAnalysis<DominatorTree>().dominates(I, PN))) {
318 PN->replaceAllUsesWith(V);
319 if (AA) AA->deleteValue(PN);
320 BB->getInstList().erase(PN);
325 // Now that the PHI nodes are updated, actually move the edges from
326 // Preds to point to NewBB instead of BB.
328 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
329 TerminatorInst *TI = Preds[i]->getTerminator();
330 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
331 if (TI->getSuccessor(s) == BB)
332 TI->setSuccessor(s, NewBB);
335 } else { // Otherwise the loop is dead...
336 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
337 PHINode *PN = cast<PHINode>(I);
338 // Insert dummy values as the incoming value...
339 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
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 void 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 std::vector<BasicBlock*> 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 OutsideBlocks.push_back(*PI); // Keep track of it...
360 // Split out the loop pre-header.
362 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
365 //===--------------------------------------------------------------------===//
366 // Update analysis results now that we have performed the transformation
369 // We know that we have loop information to update... update it now.
370 if (Loop *Parent = L->getParentLoop())
371 Parent->addBasicBlockToLoop(NewBB, *LI);
373 DT->splitBlock(NewBB);
374 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
375 DF->splitBlock(NewBB);
377 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
378 // code layout too horribly.
379 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
382 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
383 /// blocks. This method is used to split exit blocks that have predecessors
384 /// outside of the loop.
385 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
386 std::vector<BasicBlock*> LoopBlocks;
387 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
389 LoopBlocks.push_back(*I);
391 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
392 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
394 // Update Loop Information - we know that the new block will be in whichever
395 // loop the Exit block is in. Note that it may not be in that immediate loop,
396 // if the successor is some other loop header. In that case, we continue
397 // walking up the loop tree to find a loop that contains both the successor
398 // block and the predecessor block.
399 Loop *SuccLoop = LI->getLoopFor(Exit);
400 while (SuccLoop && !SuccLoop->contains(L->getHeader()))
401 SuccLoop = SuccLoop->getParentLoop();
403 SuccLoop->addBasicBlockToLoop(NewBB, *LI);
405 // Update Dominator Information
406 DT->splitBlock(NewBB);
407 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
408 DF->splitBlock(NewBB);
413 /// AddBlockAndPredsToSet - Add the specified block, and all of its
414 /// predecessors, to the specified set, if it's not already in there. Stop
415 /// predecessor traversal when we reach StopBlock.
416 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
417 std::set<BasicBlock*> &Blocks) {
418 std::vector<BasicBlock *> WorkList;
419 WorkList.push_back(InputBB);
421 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
422 if (Blocks.insert(BB).second && BB != StopBlock)
423 // If BB is not already processed and it is not a stop block then
424 // insert its predecessor in the work list
425 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
426 BasicBlock *WBB = *I;
427 WorkList.push_back(WBB);
429 } while(!WorkList.empty());
432 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
433 /// PHI node that tells us how to partition the loops.
434 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
436 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
437 PHINode *PN = cast<PHINode>(I);
439 if (Value *V = PN->hasConstantValue())
440 if (!isa<Instruction>(V) || DT->dominates(cast<Instruction>(V), PN)) {
441 // This is a degenerate PHI already, don't modify it!
442 PN->replaceAllUsesWith(V);
443 if (AA) AA->deleteValue(PN);
444 PN->eraseFromParent();
448 // Scan this PHI node looking for a use of the PHI node by itself.
449 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
450 if (PN->getIncomingValue(i) == PN &&
451 L->contains(PN->getIncomingBlock(i)))
452 // We found something tasty to remove.
458 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
459 // right after some 'outside block' block. This prevents the preheader from
460 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
461 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
462 std::vector<BasicBlock*>&SplitPreds,
464 // Check to see if NewBB is already well placed.
465 Function::iterator BBI = NewBB; --BBI;
466 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
467 if (&*BBI == SplitPreds[i])
471 // If it isn't already after an outside block, move it after one. This is
472 // always good as it makes the uncond branch from the outside block into a
475 // Figure out *which* outside block to put this after. Prefer an outside
476 // block that neighbors a BB actually in the loop.
477 BasicBlock *FoundBB = 0;
478 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
479 Function::iterator BBI = SplitPreds[i];
480 if (++BBI != NewBB->getParent()->end() &&
482 FoundBB = SplitPreds[i];
487 // If our heuristic for a *good* bb to place this after doesn't find
488 // anything, just pick something. It's likely better than leaving it within
491 FoundBB = SplitPreds[0];
492 NewBB->moveAfter(FoundBB);
496 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
497 /// them out into a nested loop. This is important for code that looks like
502 /// br cond, Loop, Next
504 /// br cond2, Loop, Out
506 /// To identify this common case, we look at the PHI nodes in the header of the
507 /// loop. PHI nodes with unchanging values on one backedge correspond to values
508 /// that change in the "outer" loop, but not in the "inner" loop.
510 /// If we are able to separate out a loop, return the new outer loop that was
513 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
514 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
515 if (PN == 0) return 0; // No known way to partition.
517 // Pull out all predecessors that have varying values in the loop. This
518 // handles the case when a PHI node has multiple instances of itself as
520 std::vector<BasicBlock*> OuterLoopPreds;
521 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
522 if (PN->getIncomingValue(i) != PN ||
523 !L->contains(PN->getIncomingBlock(i)))
524 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
526 BasicBlock *Header = L->getHeader();
527 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
529 // Update dominator information
530 DT->splitBlock(NewBB);
531 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
532 DF->splitBlock(NewBB);
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);
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 for (Loop::iterator I = L->begin(); I != L->end(); )
568 if (BlocksInL.count((*I)->getHeader()))
569 ++I; // Loop remains in L
571 NewOuter->addChildLoop(L->removeChildLoop(I));
573 // Now that we know which blocks are in L and which need to be moved to
574 // OuterLoop, move any blocks that need it.
575 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
576 BasicBlock *BB = L->getBlocks()[i];
577 if (!BlocksInL.count(BB)) {
578 // Move this block to the parent, updating the exit blocks sets
579 L->removeBlockFromLoop(BB);
581 LI->changeLoopFor(BB, NewOuter);
591 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
592 /// has more than one backedge in it. If this occurs, revector all of these
593 /// backedges to target a new basic block and have that block branch to the loop
594 /// header. This ensures that loops have exactly one backedge.
596 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
597 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
599 // Get information about the loop
600 BasicBlock *Preheader = L->getLoopPreheader();
601 BasicBlock *Header = L->getHeader();
602 Function *F = Header->getParent();
604 // Figure out which basic blocks contain back-edges to the loop header.
605 std::vector<BasicBlock*> BackedgeBlocks;
606 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
607 if (*I != Preheader) BackedgeBlocks.push_back(*I);
609 // Create and insert the new backedge block...
610 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
611 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
613 // Move the new backedge block to right after the last backedge block.
614 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
615 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
617 // Now that the block has been inserted into the function, create PHI nodes in
618 // the backedge block which correspond to any PHI nodes in the header block.
619 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
620 PHINode *PN = cast<PHINode>(I);
621 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
623 NewPN->reserveOperandSpace(BackedgeBlocks.size());
624 if (AA) AA->copyValue(PN, NewPN);
626 // Loop over the PHI node, moving all entries except the one for the
627 // preheader over to the new PHI node.
628 unsigned PreheaderIdx = ~0U;
629 bool HasUniqueIncomingValue = true;
630 Value *UniqueValue = 0;
631 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
632 BasicBlock *IBB = PN->getIncomingBlock(i);
633 Value *IV = PN->getIncomingValue(i);
634 if (IBB == Preheader) {
637 NewPN->addIncoming(IV, IBB);
638 if (HasUniqueIncomingValue) {
639 if (UniqueValue == 0)
641 else if (UniqueValue != IV)
642 HasUniqueIncomingValue = false;
647 // Delete all of the incoming values from the old PN except the preheader's
648 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
649 if (PreheaderIdx != 0) {
650 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
651 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
653 // Nuke all entries except the zero'th.
654 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
655 PN->removeIncomingValue(e-i, false);
657 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
658 PN->addIncoming(NewPN, BEBlock);
660 // As an optimization, if all incoming values in the new PhiNode (which is a
661 // subset of the incoming values of the old PHI node) have the same value,
662 // eliminate the PHI Node.
663 if (HasUniqueIncomingValue) {
664 NewPN->replaceAllUsesWith(UniqueValue);
665 if (AA) AA->deleteValue(NewPN);
666 BEBlock->getInstList().erase(NewPN);
670 // Now that all of the PHI nodes have been inserted and adjusted, modify the
671 // backedge blocks to just to the BEBlock instead of the header.
672 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
673 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
674 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
675 if (TI->getSuccessor(Op) == Header)
676 TI->setSuccessor(Op, BEBlock);
679 //===--- Update all analyses which we must preserve now -----------------===//
681 // Update Loop Information - we know that this block is now in the current
682 // loop and all parent loops.
683 L->addBasicBlockToLoop(BEBlock, *LI);
685 // Update dominator information
686 DT->splitBlock(BEBlock);
687 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
688 DF->splitBlock(BEBlock);