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, but no other analyses.
268 BasicBlock *LoopSimplify::SplitBlockPredecessors(BasicBlock *BB,
270 const std::vector<BasicBlock*> &Preds) {
272 // Create new basic block, insert right before the original block...
273 BasicBlock *NewBB = new BasicBlock(BB->getName()+Suffix, BB->getParent(), BB);
275 // The preheader first gets an unconditional branch to the loop header...
276 BranchInst *BI = new BranchInst(BB, NewBB);
278 // For every PHI node in the block, insert a PHI node into NewBB where the
279 // incoming values from the out of loop edges are moved to NewBB. We have two
280 // possible cases here. If the loop is dead, we just insert dummy entries
281 // into the PHI nodes for the new edge. If the loop is not dead, we move the
282 // incoming edges in BB into new PHI nodes in NewBB.
284 if (!Preds.empty()) { // Is the loop not obviously dead?
285 // Check to see if the values being merged into the new block need PHI
286 // nodes. If so, insert them.
287 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ) {
288 PHINode *PN = cast<PHINode>(I);
291 // Check to see if all of the values coming in are the same. If so, we
292 // don't need to create a new PHI node.
293 Value *InVal = PN->getIncomingValueForBlock(Preds[0]);
294 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
295 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
300 // If the values coming into the block are not the same, we need a PHI.
302 // Create the new PHI node, insert it into NewBB at the end of the block
303 PHINode *NewPHI = new PHINode(PN->getType(), PN->getName()+".ph", BI);
304 if (AA) AA->copyValue(PN, NewPHI);
306 // Move all of the edges from blocks outside the loop to the new PHI
307 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
308 Value *V = PN->removeIncomingValue(Preds[i], false);
309 NewPHI->addIncoming(V, Preds[i]);
313 // Remove all of the edges coming into the PHI nodes from outside of the
315 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
316 PN->removeIncomingValue(Preds[i], false);
319 // Add an incoming value to the PHI node in the loop for the preheader
321 PN->addIncoming(InVal, NewBB);
323 // Can we eliminate this phi node now?
324 if (Value *V = PN->hasConstantValue(true)) {
325 Instruction *I = dyn_cast<Instruction>(V);
326 // If I is in NewBB, the Dominator call will fail, because NewBB isn't
327 // registered in DominatorTree yet. Handle this case explicitly.
328 if (!I || (I->getParent() != NewBB &&
329 getAnalysis<DominatorTree>().dominates(I, PN))) {
330 PN->replaceAllUsesWith(V);
331 if (AA) AA->deleteValue(PN);
332 BB->getInstList().erase(PN);
337 // Now that the PHI nodes are updated, actually move the edges from
338 // Preds to point to NewBB instead of BB.
340 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
341 TerminatorInst *TI = Preds[i]->getTerminator();
342 for (unsigned s = 0, e = TI->getNumSuccessors(); s != e; ++s)
343 if (TI->getSuccessor(s) == BB)
344 TI->setSuccessor(s, NewBB);
346 if (Preds[i]->getUnwindDest() == BB)
347 Preds[i]->setUnwindDest(NewBB);
350 } else { // Otherwise the loop is dead...
351 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I) {
352 PHINode *PN = cast<PHINode>(I);
353 // Insert dummy values as the incoming value...
354 PN->addIncoming(Constant::getNullValue(PN->getType()), NewBB);
361 /// InsertPreheaderForLoop - Once we discover that a loop doesn't have a
362 /// preheader, this method is called to insert one. This method has two phases:
363 /// preheader insertion and analysis updating.
365 void LoopSimplify::InsertPreheaderForLoop(Loop *L) {
366 BasicBlock *Header = L->getHeader();
368 // Compute the set of predecessors of the loop that are not in the loop.
369 std::vector<BasicBlock*> OutsideBlocks;
370 for (pred_iterator PI = pred_begin(Header), PE = pred_end(Header);
372 if (!L->contains(*PI)) // Coming in from outside the loop?
373 OutsideBlocks.push_back(*PI); // Keep track of it...
375 // Split out the loop pre-header.
377 SplitBlockPredecessors(Header, ".preheader", OutsideBlocks);
380 //===--------------------------------------------------------------------===//
381 // Update analysis results now that we have performed the transformation
384 // We know that we have loop information to update... update it now.
385 if (Loop *Parent = L->getParentLoop())
386 Parent->addBasicBlockToLoop(NewBB, LI->getBase());
388 DT->splitBlock(NewBB);
389 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
390 DF->splitBlock(NewBB);
392 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
393 // code layout too horribly.
394 PlaceSplitBlockCarefully(NewBB, OutsideBlocks, L);
397 /// RewriteLoopExitBlock - Ensure that the loop preheader dominates all exit
398 /// blocks. This method is used to split exit blocks that have predecessors
399 /// outside of the loop.
400 BasicBlock *LoopSimplify::RewriteLoopExitBlock(Loop *L, BasicBlock *Exit) {
401 std::vector<BasicBlock*> LoopBlocks;
402 for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit); I != E; ++I)
404 LoopBlocks.push_back(*I);
406 assert(!LoopBlocks.empty() && "No edges coming in from outside the loop?");
407 BasicBlock *NewBB = SplitBlockPredecessors(Exit, ".loopexit", LoopBlocks);
409 // Update Loop Information - we know that the new block will be in whichever
410 // loop the Exit block is in. Note that it may not be in that immediate loop,
411 // if the successor is some other loop header. In that case, we continue
412 // walking up the loop tree to find a loop that contains both the successor
413 // block and the predecessor block.
414 Loop *SuccLoop = LI->getLoopFor(Exit);
415 while (SuccLoop && !SuccLoop->contains(L->getHeader()))
416 SuccLoop = SuccLoop->getParentLoop();
418 SuccLoop->addBasicBlockToLoop(NewBB, LI->getBase());
420 // Update Dominator Information
421 DT->splitBlock(NewBB);
422 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
423 DF->splitBlock(NewBB);
428 /// AddBlockAndPredsToSet - Add the specified block, and all of its
429 /// predecessors, to the specified set, if it's not already in there. Stop
430 /// predecessor traversal when we reach StopBlock.
431 static void AddBlockAndPredsToSet(BasicBlock *InputBB, BasicBlock *StopBlock,
432 std::set<BasicBlock*> &Blocks) {
433 std::vector<BasicBlock *> WorkList;
434 WorkList.push_back(InputBB);
436 BasicBlock *BB = WorkList.back(); WorkList.pop_back();
437 if (Blocks.insert(BB).second && BB != StopBlock)
438 // If BB is not already processed and it is not a stop block then
439 // insert its predecessor in the work list
440 for (pred_iterator I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
441 BasicBlock *WBB = *I;
442 WorkList.push_back(WBB);
444 } while(!WorkList.empty());
447 /// FindPHIToPartitionLoops - The first part of loop-nestification is to find a
448 /// PHI node that tells us how to partition the loops.
449 static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
451 for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
452 PHINode *PN = cast<PHINode>(I);
454 if (Value *V = PN->hasConstantValue())
455 if (!isa<Instruction>(V) || DT->dominates(cast<Instruction>(V), PN)) {
456 // This is a degenerate PHI already, don't modify it!
457 PN->replaceAllUsesWith(V);
458 if (AA) AA->deleteValue(PN);
459 PN->eraseFromParent();
463 // Scan this PHI node looking for a use of the PHI node by itself.
464 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
465 if (PN->getIncomingValue(i) == PN &&
466 L->contains(PN->getIncomingBlock(i)))
467 // We found something tasty to remove.
473 // PlaceSplitBlockCarefully - If the block isn't already, move the new block to
474 // right after some 'outside block' block. This prevents the preheader from
475 // being placed inside the loop body, e.g. when the loop hasn't been rotated.
476 void LoopSimplify::PlaceSplitBlockCarefully(BasicBlock *NewBB,
477 std::vector<BasicBlock*>&SplitPreds,
479 // Check to see if NewBB is already well placed.
480 Function::iterator BBI = NewBB; --BBI;
481 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
482 if (&*BBI == SplitPreds[i])
486 // If it isn't already after an outside block, move it after one. This is
487 // always good as it makes the uncond branch from the outside block into a
490 // Figure out *which* outside block to put this after. Prefer an outside
491 // block that neighbors a BB actually in the loop.
492 BasicBlock *FoundBB = 0;
493 for (unsigned i = 0, e = SplitPreds.size(); i != e; ++i) {
494 Function::iterator BBI = SplitPreds[i];
495 if (++BBI != NewBB->getParent()->end() &&
497 FoundBB = SplitPreds[i];
502 // If our heuristic for a *good* bb to place this after doesn't find
503 // anything, just pick something. It's likely better than leaving it within
506 FoundBB = SplitPreds[0];
507 NewBB->moveAfter(FoundBB);
511 /// SeparateNestedLoop - If this loop has multiple backedges, try to pull one of
512 /// them out into a nested loop. This is important for code that looks like
517 /// br cond, Loop, Next
519 /// br cond2, Loop, Out
521 /// To identify this common case, we look at the PHI nodes in the header of the
522 /// loop. PHI nodes with unchanging values on one backedge correspond to values
523 /// that change in the "outer" loop, but not in the "inner" loop.
525 /// If we are able to separate out a loop, return the new outer loop that was
528 Loop *LoopSimplify::SeparateNestedLoop(Loop *L) {
529 PHINode *PN = FindPHIToPartitionLoops(L, DT, AA);
530 if (PN == 0) return 0; // No known way to partition.
532 // Pull out all predecessors that have varying values in the loop. This
533 // handles the case when a PHI node has multiple instances of itself as
535 std::vector<BasicBlock*> OuterLoopPreds;
536 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
537 if (PN->getIncomingValue(i) != PN ||
538 !L->contains(PN->getIncomingBlock(i)))
539 OuterLoopPreds.push_back(PN->getIncomingBlock(i));
541 BasicBlock *Header = L->getHeader();
542 BasicBlock *NewBB = SplitBlockPredecessors(Header, ".outer", OuterLoopPreds);
544 // Update dominator information
545 DT->splitBlock(NewBB);
546 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
547 DF->splitBlock(NewBB);
549 // Make sure that NewBB is put someplace intelligent, which doesn't mess up
550 // code layout too horribly.
551 PlaceSplitBlockCarefully(NewBB, OuterLoopPreds, L);
553 // Create the new outer loop.
554 Loop *NewOuter = new Loop();
556 // Change the parent loop to use the outer loop as its child now.
557 if (Loop *Parent = L->getParentLoop())
558 Parent->replaceChildLoopWith(L, NewOuter);
560 LI->changeTopLevelLoop(L, NewOuter);
562 // This block is going to be our new header block: add it to this loop and all
564 NewOuter->addBasicBlockToLoop(NewBB, LI->getBase());
566 // L is now a subloop of our outer loop.
567 NewOuter->addChildLoop(L);
569 for (unsigned i = 0, e = L->getBlocks().size(); i != e; ++i)
570 NewOuter->addBlockEntry(L->getBlocks()[i]);
572 // Determine which blocks should stay in L and which should be moved out to
573 // the Outer loop now.
574 std::set<BasicBlock*> BlocksInL;
575 for (pred_iterator PI = pred_begin(Header), E = pred_end(Header); PI!=E; ++PI)
576 if (DT->dominates(Header, *PI))
577 AddBlockAndPredsToSet(*PI, Header, BlocksInL);
580 // Scan all of the loop children of L, moving them to OuterLoop if they are
581 // not part of the inner loop.
582 const std::vector<Loop*> &SubLoops = L->getSubLoops();
583 for (size_t I = 0; I != SubLoops.size(); )
584 if (BlocksInL.count(SubLoops[I]->getHeader()))
585 ++I; // Loop remains in L
587 NewOuter->addChildLoop(L->removeChildLoop(SubLoops.begin() + I));
589 // Now that we know which blocks are in L and which need to be moved to
590 // OuterLoop, move any blocks that need it.
591 for (unsigned i = 0; i != L->getBlocks().size(); ++i) {
592 BasicBlock *BB = L->getBlocks()[i];
593 if (!BlocksInL.count(BB)) {
594 // Move this block to the parent, updating the exit blocks sets
595 L->removeBlockFromLoop(BB);
597 LI->changeLoopFor(BB, NewOuter);
607 /// InsertUniqueBackedgeBlock - This method is called when the specified loop
608 /// has more than one backedge in it. If this occurs, revector all of these
609 /// backedges to target a new basic block and have that block branch to the loop
610 /// header. This ensures that loops have exactly one backedge.
612 void LoopSimplify::InsertUniqueBackedgeBlock(Loop *L) {
613 assert(L->getNumBackEdges() > 1 && "Must have > 1 backedge!");
615 // Get information about the loop
616 BasicBlock *Preheader = L->getLoopPreheader();
617 BasicBlock *Header = L->getHeader();
618 Function *F = Header->getParent();
620 // Figure out which basic blocks contain back-edges to the loop header.
621 std::vector<BasicBlock*> BackedgeBlocks;
622 for (pred_iterator I = pred_begin(Header), E = pred_end(Header); I != E; ++I)
623 if (*I != Preheader) BackedgeBlocks.push_back(*I);
625 // Create and insert the new backedge block...
626 BasicBlock *BEBlock = new BasicBlock(Header->getName()+".backedge", F);
627 BranchInst *BETerminator = new BranchInst(Header, BEBlock);
629 // Move the new backedge block to right after the last backedge block.
630 Function::iterator InsertPos = BackedgeBlocks.back(); ++InsertPos;
631 F->getBasicBlockList().splice(InsertPos, F->getBasicBlockList(), BEBlock);
633 // Now that the block has been inserted into the function, create PHI nodes in
634 // the backedge block which correspond to any PHI nodes in the header block.
635 for (BasicBlock::iterator I = Header->begin(); isa<PHINode>(I); ++I) {
636 PHINode *PN = cast<PHINode>(I);
637 PHINode *NewPN = new PHINode(PN->getType(), PN->getName()+".be",
639 NewPN->reserveOperandSpace(BackedgeBlocks.size());
640 if (AA) AA->copyValue(PN, NewPN);
642 // Loop over the PHI node, moving all entries except the one for the
643 // preheader over to the new PHI node.
644 unsigned PreheaderIdx = ~0U;
645 bool HasUniqueIncomingValue = true;
646 Value *UniqueValue = 0;
647 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
648 BasicBlock *IBB = PN->getIncomingBlock(i);
649 Value *IV = PN->getIncomingValue(i);
650 if (IBB == Preheader) {
653 NewPN->addIncoming(IV, IBB);
654 if (HasUniqueIncomingValue) {
655 if (UniqueValue == 0)
657 else if (UniqueValue != IV)
658 HasUniqueIncomingValue = false;
663 // Delete all of the incoming values from the old PN except the preheader's
664 assert(PreheaderIdx != ~0U && "PHI has no preheader entry??");
665 if (PreheaderIdx != 0) {
666 PN->setIncomingValue(0, PN->getIncomingValue(PreheaderIdx));
667 PN->setIncomingBlock(0, PN->getIncomingBlock(PreheaderIdx));
669 // Nuke all entries except the zero'th.
670 for (unsigned i = 0, e = PN->getNumIncomingValues()-1; i != e; ++i)
671 PN->removeIncomingValue(e-i, false);
673 // Finally, add the newly constructed PHI node as the entry for the BEBlock.
674 PN->addIncoming(NewPN, BEBlock);
676 // As an optimization, if all incoming values in the new PhiNode (which is a
677 // subset of the incoming values of the old PHI node) have the same value,
678 // eliminate the PHI Node.
679 if (HasUniqueIncomingValue) {
680 NewPN->replaceAllUsesWith(UniqueValue);
681 if (AA) AA->deleteValue(NewPN);
682 BEBlock->getInstList().erase(NewPN);
686 // Now that all of the PHI nodes have been inserted and adjusted, modify the
687 // backedge blocks to branch to the BEBlock instead of the header.
688 for (unsigned i = 0, e = BackedgeBlocks.size(); i != e; ++i) {
689 TerminatorInst *TI = BackedgeBlocks[i]->getTerminator();
690 for (unsigned Op = 0, e = TI->getNumSuccessors(); Op != e; ++Op)
691 if (TI->getSuccessor(Op) == Header)
692 TI->setSuccessor(Op, BEBlock);
694 if (BackedgeBlocks[i]->getUnwindDest() == Header)
695 BackedgeBlocks[i]->setUnwindDest(BEBlock);
698 //===--- Update all analyses which we must preserve now -----------------===//
700 // Update Loop Information - we know that this block is now in the current
701 // loop and all parent loops.
702 L->addBasicBlockToLoop(BEBlock, LI->getBase());
704 // Update dominator information
705 DT->splitBlock(BEBlock);
706 if (DominanceFrontier *DF = getAnalysisToUpdate<DominanceFrontier>())
707 DF->splitBlock(BEBlock);