1 //===-- BasicBlockUtils.cpp - BasicBlock Utilities -------------------------==//
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 family of functions perform manipulations on basic blocks, and
11 // instructions contained within basic blocks.
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
16 #include "llvm/Analysis/AliasAnalysis.h"
17 #include "llvm/Analysis/Dominators.h"
18 #include "llvm/Analysis/LoopInfo.h"
19 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
20 #include "llvm/IR/Constant.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Function.h"
23 #include "llvm/IR/Instructions.h"
24 #include "llvm/IR/IntrinsicInst.h"
25 #include "llvm/IR/Type.h"
26 #include "llvm/Support/ErrorHandling.h"
27 #include "llvm/Support/ValueHandle.h"
28 #include "llvm/Transforms/Scalar.h"
29 #include "llvm/Transforms/Utils/Local.h"
33 /// DeleteDeadBlock - Delete the specified block, which must have no
35 void llvm::DeleteDeadBlock(BasicBlock *BB) {
36 assert((pred_begin(BB) == pred_end(BB) ||
37 // Can delete self loop.
38 BB->getSinglePredecessor() == BB) && "Block is not dead!");
39 TerminatorInst *BBTerm = BB->getTerminator();
41 // Loop through all of our successors and make sure they know that one
42 // of their predecessors is going away.
43 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
44 BBTerm->getSuccessor(i)->removePredecessor(BB);
46 // Zap all the instructions in the block.
47 while (!BB->empty()) {
48 Instruction &I = BB->back();
49 // If this instruction is used, replace uses with an arbitrary value.
50 // Because control flow can't get here, we don't care what we replace the
51 // value with. Note that since this block is unreachable, and all values
52 // contained within it must dominate their uses, that all uses will
53 // eventually be removed (they are themselves dead).
55 I.replaceAllUsesWith(UndefValue::get(I.getType()));
56 BB->getInstList().pop_back();
60 BB->eraseFromParent();
63 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
64 /// any single-entry PHI nodes in it, fold them away. This handles the case
65 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
66 /// when the block has exactly one predecessor.
67 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P) {
68 if (!isa<PHINode>(BB->begin())) return;
70 AliasAnalysis *AA = 0;
71 MemoryDependenceAnalysis *MemDep = 0;
73 AA = P->getAnalysisIfAvailable<AliasAnalysis>();
74 MemDep = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>();
77 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
78 if (PN->getIncomingValue(0) != PN)
79 PN->replaceAllUsesWith(PN->getIncomingValue(0));
81 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
84 MemDep->removeInstruction(PN); // Memdep updates AA itself.
85 else if (AA && isa<PointerType>(PN->getType()))
88 PN->eraseFromParent();
93 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
94 /// is dead. Also recursively delete any operands that become dead as
95 /// a result. This includes tracing the def-use list from the PHI to see if
96 /// it is ultimately unused or if it reaches an unused cycle.
97 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
98 // Recursively deleting a PHI may cause multiple PHIs to be deleted
99 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
100 SmallVector<WeakVH, 8> PHIs;
101 for (BasicBlock::iterator I = BB->begin();
102 PHINode *PN = dyn_cast<PHINode>(I); ++I)
105 bool Changed = false;
106 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
107 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
108 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
113 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
114 /// if possible. The return value indicates success or failure.
115 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
116 // Don't merge away blocks who have their address taken.
117 if (BB->hasAddressTaken()) return false;
119 // Can't merge if there are multiple predecessors, or no predecessors.
120 BasicBlock *PredBB = BB->getUniquePredecessor();
121 if (!PredBB) return false;
123 // Don't break self-loops.
124 if (PredBB == BB) return false;
125 // Don't break invokes.
126 if (isa<InvokeInst>(PredBB->getTerminator())) return false;
128 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
129 BasicBlock *OnlySucc = BB;
130 for (; SI != SE; ++SI)
131 if (*SI != OnlySucc) {
132 OnlySucc = 0; // There are multiple distinct successors!
136 // Can't merge if there are multiple successors.
137 if (!OnlySucc) return false;
139 // Can't merge if there is PHI loop.
140 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
141 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
142 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
143 if (PN->getIncomingValue(i) == PN)
149 // Begin by getting rid of unneeded PHIs.
150 if (isa<PHINode>(BB->front()))
151 FoldSingleEntryPHINodes(BB, P);
153 // Delete the unconditional branch from the predecessor...
154 PredBB->getInstList().pop_back();
156 // Make all PHI nodes that referred to BB now refer to Pred as their
158 BB->replaceAllUsesWith(PredBB);
160 // Move all definitions in the successor to the predecessor...
161 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
163 // Inherit predecessors name if it exists.
164 if (!PredBB->hasName())
165 PredBB->takeName(BB);
167 // Finally, erase the old block and update dominator info.
169 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) {
170 if (DomTreeNode *DTN = DT->getNode(BB)) {
171 DomTreeNode *PredDTN = DT->getNode(PredBB);
172 SmallVector<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
173 for (SmallVector<DomTreeNode*, 8>::iterator DI = Children.begin(),
174 DE = Children.end(); DI != DE; ++DI)
175 DT->changeImmediateDominator(*DI, PredDTN);
180 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
183 if (MemoryDependenceAnalysis *MD =
184 P->getAnalysisIfAvailable<MemoryDependenceAnalysis>())
185 MD->invalidateCachedPredecessors();
189 BB->eraseFromParent();
193 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
194 /// with a value, then remove and delete the original instruction.
196 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
197 BasicBlock::iterator &BI, Value *V) {
198 Instruction &I = *BI;
199 // Replaces all of the uses of the instruction with uses of the value
200 I.replaceAllUsesWith(V);
202 // Make sure to propagate a name if there is one already.
203 if (I.hasName() && !V->hasName())
206 // Delete the unnecessary instruction now...
211 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
212 /// instruction specified by I. The original instruction is deleted and BI is
213 /// updated to point to the new instruction.
215 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
216 BasicBlock::iterator &BI, Instruction *I) {
217 assert(I->getParent() == 0 &&
218 "ReplaceInstWithInst: Instruction already inserted into basic block!");
220 // Insert the new instruction into the basic block...
221 BasicBlock::iterator New = BIL.insert(BI, I);
223 // Replace all uses of the old instruction, and delete it.
224 ReplaceInstWithValue(BIL, BI, I);
226 // Move BI back to point to the newly inserted instruction
230 /// ReplaceInstWithInst - Replace the instruction specified by From with the
231 /// instruction specified by To.
233 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
234 BasicBlock::iterator BI(From);
235 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
238 /// GetSuccessorNumber - Search for the specified successor of basic block BB
239 /// and return its position in the terminator instruction's list of
240 /// successors. It is an error to call this with a block that is not a
242 unsigned llvm::GetSuccessorNumber(BasicBlock *BB, BasicBlock *Succ) {
243 TerminatorInst *Term = BB->getTerminator();
245 unsigned e = Term->getNumSuccessors();
247 for (unsigned i = 0; ; ++i) {
248 assert(i != e && "Didn't find edge?");
249 if (Term->getSuccessor(i) == Succ)
254 /// SplitEdge - Split the edge connecting specified block. Pass P must
256 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
257 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
259 // If this is a critical edge, let SplitCriticalEdge do it.
260 TerminatorInst *LatchTerm = BB->getTerminator();
261 if (SplitCriticalEdge(LatchTerm, SuccNum, P))
262 return LatchTerm->getSuccessor(SuccNum);
264 // If the edge isn't critical, then BB has a single successor or Succ has a
265 // single pred. Split the block.
266 BasicBlock::iterator SplitPoint;
267 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
268 // If the successor only has a single pred, split the top of the successor
270 assert(SP == BB && "CFG broken");
272 return SplitBlock(Succ, Succ->begin(), P);
275 // Otherwise, if BB has a single successor, split it at the bottom of the
277 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
278 "Should have a single succ!");
279 return SplitBlock(BB, BB->getTerminator(), P);
282 /// SplitBlock - Split the specified block at the specified instruction - every
283 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
284 /// to a new block. The two blocks are joined by an unconditional branch and
285 /// the loop info is updated.
287 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
288 BasicBlock::iterator SplitIt = SplitPt;
289 while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))
291 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
293 // The new block lives in whichever loop the old one did. This preserves
294 // LCSSA as well, because we force the split point to be after any PHI nodes.
295 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
296 if (Loop *L = LI->getLoopFor(Old))
297 L->addBasicBlockToLoop(New, LI->getBase());
299 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) {
300 // Old dominates New. New node dominates all other nodes dominated by Old.
301 if (DomTreeNode *OldNode = DT->getNode(Old)) {
302 std::vector<DomTreeNode *> Children;
303 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
305 Children.push_back(*I);
307 DomTreeNode *NewNode = DT->addNewBlock(New,Old);
308 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
309 E = Children.end(); I != E; ++I)
310 DT->changeImmediateDominator(*I, NewNode);
317 /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA
318 /// analysis information.
319 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
320 ArrayRef<BasicBlock *> Preds,
321 Pass *P, bool &HasLoopExit) {
324 LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
325 Loop *L = LI ? LI->getLoopFor(OldBB) : 0;
327 // If we need to preserve loop analyses, collect some information about how
328 // this split will affect loops.
329 bool IsLoopEntry = !!L;
330 bool SplitMakesNewLoopHeader = false;
332 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
333 for (ArrayRef<BasicBlock*>::iterator
334 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
335 BasicBlock *Pred = *i;
337 // If we need to preserve LCSSA, determine if any of the preds is a loop
340 if (Loop *PL = LI->getLoopFor(Pred))
341 if (!PL->contains(OldBB))
344 // If we need to preserve LoopInfo, note whether any of the preds crosses
345 // an interesting loop boundary.
347 if (L->contains(Pred))
350 SplitMakesNewLoopHeader = true;
354 // Update dominator tree if available.
355 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
357 DT->splitBlock(NewBB);
362 // Add the new block to the nearest enclosing loop (and not an adjacent
363 // loop). To find this, examine each of the predecessors and determine which
364 // loops enclose them, and select the most-nested loop which contains the
365 // loop containing the block being split.
366 Loop *InnermostPredLoop = 0;
367 for (ArrayRef<BasicBlock*>::iterator
368 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
369 BasicBlock *Pred = *i;
370 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
371 // Seek a loop which actually contains the block being split (to avoid
373 while (PredLoop && !PredLoop->contains(OldBB))
374 PredLoop = PredLoop->getParentLoop();
376 // Select the most-nested of these loops which contains the block.
377 if (PredLoop && PredLoop->contains(OldBB) &&
378 (!InnermostPredLoop ||
379 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
380 InnermostPredLoop = PredLoop;
384 if (InnermostPredLoop)
385 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
387 L->addBasicBlockToLoop(NewBB, LI->getBase());
388 if (SplitMakesNewLoopHeader)
389 L->moveToHeader(NewBB);
393 /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
394 /// from NewBB. This also updates AliasAnalysis, if available.
395 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
396 ArrayRef<BasicBlock*> Preds, BranchInst *BI,
397 Pass *P, bool HasLoopExit) {
398 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
399 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
400 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
401 PHINode *PN = cast<PHINode>(I++);
403 // Check to see if all of the values coming in are the same. If so, we
404 // don't need to create a new PHI node, unless it's needed for LCSSA.
407 InVal = PN->getIncomingValueForBlock(Preds[0]);
408 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
409 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
416 // If all incoming values for the new PHI would be the same, just don't
417 // make a new PHI. Instead, just remove the incoming values from the old
419 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
420 PN->removeIncomingValue(Preds[i], false);
422 // If the values coming into the block are not the same, we need a PHI.
423 // Create the new PHI node, insert it into NewBB at the end of the block
425 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
426 if (AA) AA->copyValue(PN, NewPHI);
428 // Move all of the PHI values for 'Preds' to the new PHI.
429 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
430 Value *V = PN->removeIncomingValue(Preds[i], false);
431 NewPHI->addIncoming(V, Preds[i]);
437 // Add an incoming value to the PHI node in the loop for the preheader
439 PN->addIncoming(InVal, NewBB);
443 /// SplitBlockPredecessors - This method transforms BB by introducing a new
444 /// basic block into the function, and moving some of the predecessors of BB to
445 /// be predecessors of the new block. The new predecessors are indicated by the
446 /// Preds array, which has NumPreds elements in it. The new block is given a
447 /// suffix of 'Suffix'.
449 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
450 /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
451 /// preserve LoopSimplify (because it's complicated to handle the case where one
452 /// of the edges being split is an exit of a loop with other exits).
454 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
455 ArrayRef<BasicBlock*> Preds,
456 const char *Suffix, Pass *P) {
457 // Create new basic block, insert right before the original block.
458 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
459 BB->getParent(), BB);
461 // The new block unconditionally branches to the old block.
462 BranchInst *BI = BranchInst::Create(BB, NewBB);
464 // Move the edges from Preds to point to NewBB instead of BB.
465 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
466 // This is slightly more strict than necessary; the minimum requirement
467 // is that there be no more than one indirectbr branching to BB. And
468 // all BlockAddress uses would need to be updated.
469 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
470 "Cannot split an edge from an IndirectBrInst");
471 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
474 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
475 // node becomes an incoming value for BB's phi node. However, if the Preds
476 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
477 // account for the newly created predecessor.
478 if (Preds.size() == 0) {
479 // Insert dummy values as the incoming value.
480 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
481 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
485 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
486 bool HasLoopExit = false;
487 UpdateAnalysisInformation(BB, NewBB, Preds, P, HasLoopExit);
489 // Update the PHI nodes in BB with the values coming from NewBB.
490 UpdatePHINodes(BB, NewBB, Preds, BI, P, HasLoopExit);
494 /// SplitLandingPadPredecessors - This method transforms the landing pad,
495 /// OrigBB, by introducing two new basic blocks into the function. One of those
496 /// new basic blocks gets the predecessors listed in Preds. The other basic
497 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
498 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
499 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
501 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
502 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
503 /// it does not preserve LoopSimplify (because it's complicated to handle the
504 /// case where one of the edges being split is an exit of a loop with other
507 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
508 ArrayRef<BasicBlock*> Preds,
509 const char *Suffix1, const char *Suffix2,
511 SmallVectorImpl<BasicBlock*> &NewBBs) {
512 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
514 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
515 // it right before the original block.
516 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
517 OrigBB->getName() + Suffix1,
518 OrigBB->getParent(), OrigBB);
519 NewBBs.push_back(NewBB1);
521 // The new block unconditionally branches to the old block.
522 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
524 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
525 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
526 // This is slightly more strict than necessary; the minimum requirement
527 // is that there be no more than one indirectbr branching to BB. And
528 // all BlockAddress uses would need to be updated.
529 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
530 "Cannot split an edge from an IndirectBrInst");
531 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
534 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
535 bool HasLoopExit = false;
536 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit);
538 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
539 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit);
541 // Move the remaining edges from OrigBB to point to NewBB2.
542 SmallVector<BasicBlock*, 8> NewBB2Preds;
543 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
545 BasicBlock *Pred = *i++;
546 if (Pred == NewBB1) continue;
547 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
548 "Cannot split an edge from an IndirectBrInst");
549 NewBB2Preds.push_back(Pred);
550 e = pred_end(OrigBB);
553 BasicBlock *NewBB2 = 0;
554 if (!NewBB2Preds.empty()) {
555 // Create another basic block for the rest of OrigBB's predecessors.
556 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
557 OrigBB->getName() + Suffix2,
558 OrigBB->getParent(), OrigBB);
559 NewBBs.push_back(NewBB2);
561 // The new block unconditionally branches to the old block.
562 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
564 // Move the remaining edges from OrigBB to point to NewBB2.
565 for (SmallVectorImpl<BasicBlock*>::iterator
566 i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
567 (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
569 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
571 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit);
573 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
574 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit);
577 LandingPadInst *LPad = OrigBB->getLandingPadInst();
578 Instruction *Clone1 = LPad->clone();
579 Clone1->setName(Twine("lpad") + Suffix1);
580 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
583 Instruction *Clone2 = LPad->clone();
584 Clone2->setName(Twine("lpad") + Suffix2);
585 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
587 // Create a PHI node for the two cloned landingpad instructions.
588 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
589 PN->addIncoming(Clone1, NewBB1);
590 PN->addIncoming(Clone2, NewBB2);
591 LPad->replaceAllUsesWith(PN);
592 LPad->eraseFromParent();
594 // There is no second clone. Just replace the landing pad with the first
596 LPad->replaceAllUsesWith(Clone1);
597 LPad->eraseFromParent();
601 /// FindFunctionBackedges - Analyze the specified function to find all of the
602 /// loop backedges in the function and return them. This is a relatively cheap
603 /// (compared to computing dominators and loop info) analysis.
605 /// The output is added to Result, as pairs of <from,to> edge info.
606 void llvm::FindFunctionBackedges(const Function &F,
607 SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
608 const BasicBlock *BB = &F.getEntryBlock();
609 if (succ_begin(BB) == succ_end(BB))
612 SmallPtrSet<const BasicBlock*, 8> Visited;
613 SmallVector<std::pair<const BasicBlock*, succ_const_iterator>, 8> VisitStack;
614 SmallPtrSet<const BasicBlock*, 8> InStack;
617 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
620 std::pair<const BasicBlock*, succ_const_iterator> &Top = VisitStack.back();
621 const BasicBlock *ParentBB = Top.first;
622 succ_const_iterator &I = Top.second;
624 bool FoundNew = false;
625 while (I != succ_end(ParentBB)) {
627 if (Visited.insert(BB)) {
631 // Successor is in VisitStack, it's a back edge.
632 if (InStack.count(BB))
633 Result.push_back(std::make_pair(ParentBB, BB));
637 // Go down one level if there is a unvisited successor.
639 VisitStack.push_back(std::make_pair(BB, succ_begin(BB)));
642 InStack.erase(VisitStack.pop_back_val().first);
644 } while (!VisitStack.empty());
647 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
648 /// instruction into a predecessor which ends in an unconditional branch. If
649 /// the return instruction returns a value defined by a PHI, propagate the
650 /// right value into the return. It returns the new return instruction in the
652 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
654 Instruction *UncondBranch = Pred->getTerminator();
655 // Clone the return and add it to the end of the predecessor.
656 Instruction *NewRet = RI->clone();
657 Pred->getInstList().push_back(NewRet);
659 // If the return instruction returns a value, and if the value was a
660 // PHI node in "BB", propagate the right value into the return.
661 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
664 Instruction *NewBC = 0;
665 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
666 // Return value might be bitcasted. Clone and insert it before the
667 // return instruction.
668 V = BCI->getOperand(0);
669 NewBC = BCI->clone();
670 Pred->getInstList().insert(NewRet, NewBC);
673 if (PHINode *PN = dyn_cast<PHINode>(V)) {
674 if (PN->getParent() == BB) {
676 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
678 *i = PN->getIncomingValueForBlock(Pred);
683 // Update any PHI nodes in the returning block to realize that we no
684 // longer branch to them.
685 BB->removePredecessor(Pred);
686 UncondBranch->eraseFromParent();
687 return cast<ReturnInst>(NewRet);
690 /// SplitBlockAndInsertIfThen - Split the containing block at the
691 /// specified instruction - everything before and including Cmp stays
692 /// in the old basic block, and everything after Cmp is moved to a
693 /// new block. The two blocks are connected by a conditional branch
694 /// (with value of Cmp being the condition).
706 /// If Unreachable is true, then ThenBlock ends with
707 /// UnreachableInst, otherwise it branches to Tail.
708 /// Returns the NewBasicBlock's terminator.
710 TerminatorInst *llvm::SplitBlockAndInsertIfThen(Instruction *Cmp,
711 bool Unreachable, MDNode *BranchWeights) {
712 Instruction *SplitBefore = Cmp->getNextNode();
713 BasicBlock *Head = SplitBefore->getParent();
714 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
715 TerminatorInst *HeadOldTerm = Head->getTerminator();
716 LLVMContext &C = Head->getContext();
717 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
718 TerminatorInst *CheckTerm;
720 CheckTerm = new UnreachableInst(C, ThenBlock);
722 CheckTerm = BranchInst::Create(Tail, ThenBlock);
723 BranchInst *HeadNewTerm =
724 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cmp);
725 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
726 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);