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/CFG.h"
18 #include "llvm/Analysis/Dominators.h"
19 #include "llvm/Analysis/LoopInfo.h"
20 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
21 #include "llvm/IR/Constant.h"
22 #include "llvm/IR/DataLayout.h"
23 #include "llvm/IR/Function.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/IntrinsicInst.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/Support/ErrorHandling.h"
28 #include "llvm/Support/ValueHandle.h"
29 #include "llvm/Transforms/Scalar.h"
30 #include "llvm/Transforms/Utils/Local.h"
34 /// DeleteDeadBlock - Delete the specified block, which must have no
36 void llvm::DeleteDeadBlock(BasicBlock *BB) {
37 assert((pred_begin(BB) == pred_end(BB) ||
38 // Can delete self loop.
39 BB->getSinglePredecessor() == BB) && "Block is not dead!");
40 TerminatorInst *BBTerm = BB->getTerminator();
42 // Loop through all of our successors and make sure they know that one
43 // of their predecessors is going away.
44 for (unsigned i = 0, e = BBTerm->getNumSuccessors(); i != e; ++i)
45 BBTerm->getSuccessor(i)->removePredecessor(BB);
47 // Zap all the instructions in the block.
48 while (!BB->empty()) {
49 Instruction &I = BB->back();
50 // If this instruction is used, replace uses with an arbitrary value.
51 // Because control flow can't get here, we don't care what we replace the
52 // value with. Note that since this block is unreachable, and all values
53 // contained within it must dominate their uses, that all uses will
54 // eventually be removed (they are themselves dead).
56 I.replaceAllUsesWith(UndefValue::get(I.getType()));
57 BB->getInstList().pop_back();
61 BB->eraseFromParent();
64 /// FoldSingleEntryPHINodes - We know that BB has one predecessor. If there are
65 /// any single-entry PHI nodes in it, fold them away. This handles the case
66 /// when all entries to the PHI nodes in a block are guaranteed equal, such as
67 /// when the block has exactly one predecessor.
68 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB, Pass *P) {
69 if (!isa<PHINode>(BB->begin())) return;
71 AliasAnalysis *AA = 0;
72 MemoryDependenceAnalysis *MemDep = 0;
74 AA = P->getAnalysisIfAvailable<AliasAnalysis>();
75 MemDep = P->getAnalysisIfAvailable<MemoryDependenceAnalysis>();
78 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
79 if (PN->getIncomingValue(0) != PN)
80 PN->replaceAllUsesWith(PN->getIncomingValue(0));
82 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
85 MemDep->removeInstruction(PN); // Memdep updates AA itself.
86 else if (AA && isa<PointerType>(PN->getType()))
89 PN->eraseFromParent();
94 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
95 /// is dead. Also recursively delete any operands that become dead as
96 /// a result. This includes tracing the def-use list from the PHI to see if
97 /// it is ultimately unused or if it reaches an unused cycle.
98 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
99 // Recursively deleting a PHI may cause multiple PHIs to be deleted
100 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
101 SmallVector<WeakVH, 8> PHIs;
102 for (BasicBlock::iterator I = BB->begin();
103 PHINode *PN = dyn_cast<PHINode>(I); ++I)
106 bool Changed = false;
107 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
108 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
109 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
114 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
115 /// if possible. The return value indicates success or failure.
116 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, Pass *P) {
117 // Don't merge away blocks who have their address taken.
118 if (BB->hasAddressTaken()) return false;
120 // Can't merge if there are multiple predecessors, or no predecessors.
121 BasicBlock *PredBB = BB->getUniquePredecessor();
122 if (!PredBB) return false;
124 // Don't break self-loops.
125 if (PredBB == BB) return false;
126 // Don't break invokes.
127 if (isa<InvokeInst>(PredBB->getTerminator())) return false;
129 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
130 BasicBlock *OnlySucc = BB;
131 for (; SI != SE; ++SI)
132 if (*SI != OnlySucc) {
133 OnlySucc = 0; // There are multiple distinct successors!
137 // Can't merge if there are multiple successors.
138 if (!OnlySucc) return false;
140 // Can't merge if there is PHI loop.
141 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
142 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
143 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
144 if (PN->getIncomingValue(i) == PN)
150 // Begin by getting rid of unneeded PHIs.
151 if (isa<PHINode>(BB->front()))
152 FoldSingleEntryPHINodes(BB, P);
154 // Delete the unconditional branch from the predecessor...
155 PredBB->getInstList().pop_back();
157 // Make all PHI nodes that referred to BB now refer to Pred as their
159 BB->replaceAllUsesWith(PredBB);
161 // Move all definitions in the successor to the predecessor...
162 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
164 // Inherit predecessors name if it exists.
165 if (!PredBB->hasName())
166 PredBB->takeName(BB);
168 // Finally, erase the old block and update dominator info.
170 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) {
171 if (DomTreeNode *DTN = DT->getNode(BB)) {
172 DomTreeNode *PredDTN = DT->getNode(PredBB);
173 SmallVector<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
174 for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(),
175 DE = Children.end(); DI != DE; ++DI)
176 DT->changeImmediateDominator(*DI, PredDTN);
181 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
184 if (MemoryDependenceAnalysis *MD =
185 P->getAnalysisIfAvailable<MemoryDependenceAnalysis>())
186 MD->invalidateCachedPredecessors();
190 BB->eraseFromParent();
194 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
195 /// with a value, then remove and delete the original instruction.
197 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
198 BasicBlock::iterator &BI, Value *V) {
199 Instruction &I = *BI;
200 // Replaces all of the uses of the instruction with uses of the value
201 I.replaceAllUsesWith(V);
203 // Make sure to propagate a name if there is one already.
204 if (I.hasName() && !V->hasName())
207 // Delete the unnecessary instruction now...
212 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
213 /// instruction specified by I. The original instruction is deleted and BI is
214 /// updated to point to the new instruction.
216 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
217 BasicBlock::iterator &BI, Instruction *I) {
218 assert(I->getParent() == 0 &&
219 "ReplaceInstWithInst: Instruction already inserted into basic block!");
221 // Insert the new instruction into the basic block...
222 BasicBlock::iterator New = BIL.insert(BI, I);
224 // Replace all uses of the old instruction, and delete it.
225 ReplaceInstWithValue(BIL, BI, I);
227 // Move BI back to point to the newly inserted instruction
231 /// ReplaceInstWithInst - Replace the instruction specified by From with the
232 /// instruction specified by To.
234 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
235 BasicBlock::iterator BI(From);
236 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
239 /// SplitEdge - Split the edge connecting specified block. Pass P must
241 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
242 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
244 // If this is a critical edge, let SplitCriticalEdge do it.
245 TerminatorInst *LatchTerm = BB->getTerminator();
246 if (SplitCriticalEdge(LatchTerm, SuccNum, P))
247 return LatchTerm->getSuccessor(SuccNum);
249 // If the edge isn't critical, then BB has a single successor or Succ has a
250 // single pred. Split the block.
251 BasicBlock::iterator SplitPoint;
252 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
253 // If the successor only has a single pred, split the top of the successor
255 assert(SP == BB && "CFG broken");
257 return SplitBlock(Succ, Succ->begin(), P);
260 // Otherwise, if BB has a single successor, split it at the bottom of the
262 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
263 "Should have a single succ!");
264 return SplitBlock(BB, BB->getTerminator(), P);
267 /// SplitBlock - Split the specified block at the specified instruction - every
268 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
269 /// to a new block. The two blocks are joined by an unconditional branch and
270 /// the loop info is updated.
272 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
273 BasicBlock::iterator SplitIt = SplitPt;
274 while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))
276 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
278 // The new block lives in whichever loop the old one did. This preserves
279 // LCSSA as well, because we force the split point to be after any PHI nodes.
280 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
281 if (Loop *L = LI->getLoopFor(Old))
282 L->addBasicBlockToLoop(New, LI->getBase());
284 if (DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>()) {
285 // Old dominates New. New node dominates all other nodes dominated by Old.
286 if (DomTreeNode *OldNode = DT->getNode(Old)) {
287 std::vector<DomTreeNode *> Children;
288 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
290 Children.push_back(*I);
292 DomTreeNode *NewNode = DT->addNewBlock(New,Old);
293 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
294 E = Children.end(); I != E; ++I)
295 DT->changeImmediateDominator(*I, NewNode);
302 /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA
303 /// analysis information.
304 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
305 ArrayRef<BasicBlock *> Preds,
306 Pass *P, bool &HasLoopExit) {
309 LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
310 Loop *L = LI ? LI->getLoopFor(OldBB) : 0;
312 // If we need to preserve loop analyses, collect some information about how
313 // this split will affect loops.
314 bool IsLoopEntry = !!L;
315 bool SplitMakesNewLoopHeader = false;
317 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
318 for (ArrayRef<BasicBlock*>::iterator
319 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
320 BasicBlock *Pred = *i;
322 // If we need to preserve LCSSA, determine if any of the preds is a loop
325 if (Loop *PL = LI->getLoopFor(Pred))
326 if (!PL->contains(OldBB))
329 // If we need to preserve LoopInfo, note whether any of the preds crosses
330 // an interesting loop boundary.
332 if (L->contains(Pred))
335 SplitMakesNewLoopHeader = true;
339 // Update dominator tree if available.
340 DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
342 DT->splitBlock(NewBB);
347 // Add the new block to the nearest enclosing loop (and not an adjacent
348 // loop). To find this, examine each of the predecessors and determine which
349 // loops enclose them, and select the most-nested loop which contains the
350 // loop containing the block being split.
351 Loop *InnermostPredLoop = 0;
352 for (ArrayRef<BasicBlock*>::iterator
353 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
354 BasicBlock *Pred = *i;
355 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
356 // Seek a loop which actually contains the block being split (to avoid
358 while (PredLoop && !PredLoop->contains(OldBB))
359 PredLoop = PredLoop->getParentLoop();
361 // Select the most-nested of these loops which contains the block.
362 if (PredLoop && PredLoop->contains(OldBB) &&
363 (!InnermostPredLoop ||
364 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
365 InnermostPredLoop = PredLoop;
369 if (InnermostPredLoop)
370 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
372 L->addBasicBlockToLoop(NewBB, LI->getBase());
373 if (SplitMakesNewLoopHeader)
374 L->moveToHeader(NewBB);
378 /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
379 /// from NewBB. This also updates AliasAnalysis, if available.
380 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
381 ArrayRef<BasicBlock*> Preds, BranchInst *BI,
382 Pass *P, bool HasLoopExit) {
383 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
384 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
385 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
386 PHINode *PN = cast<PHINode>(I++);
388 // Check to see if all of the values coming in are the same. If so, we
389 // don't need to create a new PHI node, unless it's needed for LCSSA.
392 InVal = PN->getIncomingValueForBlock(Preds[0]);
393 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
394 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
401 // If all incoming values for the new PHI would be the same, just don't
402 // make a new PHI. Instead, just remove the incoming values from the old
404 for (unsigned i = 0, e = Preds.size(); i != e; ++i)
405 PN->removeIncomingValue(Preds[i], false);
407 // If the values coming into the block are not the same, we need a PHI.
408 // Create the new PHI node, insert it into NewBB at the end of the block
410 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
411 if (AA) AA->copyValue(PN, NewPHI);
413 // Move all of the PHI values for 'Preds' to the new PHI.
414 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
415 Value *V = PN->removeIncomingValue(Preds[i], false);
416 NewPHI->addIncoming(V, Preds[i]);
422 // Add an incoming value to the PHI node in the loop for the preheader
424 PN->addIncoming(InVal, NewBB);
428 /// SplitBlockPredecessors - This method transforms BB by introducing a new
429 /// basic block into the function, and moving some of the predecessors of BB to
430 /// be predecessors of the new block. The new predecessors are indicated by the
431 /// Preds array, which has NumPreds elements in it. The new block is given a
432 /// suffix of 'Suffix'.
434 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
435 /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
436 /// preserve LoopSimplify (because it's complicated to handle the case where one
437 /// of the edges being split is an exit of a loop with other exits).
439 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
440 ArrayRef<BasicBlock*> Preds,
441 const char *Suffix, Pass *P) {
442 // Create new basic block, insert right before the original block.
443 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
444 BB->getParent(), BB);
446 // The new block unconditionally branches to the old block.
447 BranchInst *BI = BranchInst::Create(BB, NewBB);
449 // Move the edges from Preds to point to NewBB instead of BB.
450 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
451 // This is slightly more strict than necessary; the minimum requirement
452 // is that there be no more than one indirectbr branching to BB. And
453 // all BlockAddress uses would need to be updated.
454 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
455 "Cannot split an edge from an IndirectBrInst");
456 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
459 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
460 // node becomes an incoming value for BB's phi node. However, if the Preds
461 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
462 // account for the newly created predecessor.
463 if (Preds.size() == 0) {
464 // Insert dummy values as the incoming value.
465 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
466 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
470 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
471 bool HasLoopExit = false;
472 UpdateAnalysisInformation(BB, NewBB, Preds, P, HasLoopExit);
474 // Update the PHI nodes in BB with the values coming from NewBB.
475 UpdatePHINodes(BB, NewBB, Preds, BI, P, HasLoopExit);
479 /// SplitLandingPadPredecessors - This method transforms the landing pad,
480 /// OrigBB, by introducing two new basic blocks into the function. One of those
481 /// new basic blocks gets the predecessors listed in Preds. The other basic
482 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
483 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
484 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
486 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
487 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
488 /// it does not preserve LoopSimplify (because it's complicated to handle the
489 /// case where one of the edges being split is an exit of a loop with other
492 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
493 ArrayRef<BasicBlock*> Preds,
494 const char *Suffix1, const char *Suffix2,
496 SmallVectorImpl<BasicBlock*> &NewBBs) {
497 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
499 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
500 // it right before the original block.
501 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
502 OrigBB->getName() + Suffix1,
503 OrigBB->getParent(), OrigBB);
504 NewBBs.push_back(NewBB1);
506 // The new block unconditionally branches to the old block.
507 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
509 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
510 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
511 // This is slightly more strict than necessary; the minimum requirement
512 // is that there be no more than one indirectbr branching to BB. And
513 // all BlockAddress uses would need to be updated.
514 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
515 "Cannot split an edge from an IndirectBrInst");
516 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
519 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
520 bool HasLoopExit = false;
521 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit);
523 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
524 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit);
526 // Move the remaining edges from OrigBB to point to NewBB2.
527 SmallVector<BasicBlock*, 8> NewBB2Preds;
528 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
530 BasicBlock *Pred = *i++;
531 if (Pred == NewBB1) continue;
532 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
533 "Cannot split an edge from an IndirectBrInst");
534 NewBB2Preds.push_back(Pred);
535 e = pred_end(OrigBB);
538 BasicBlock *NewBB2 = 0;
539 if (!NewBB2Preds.empty()) {
540 // Create another basic block for the rest of OrigBB's predecessors.
541 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
542 OrigBB->getName() + Suffix2,
543 OrigBB->getParent(), OrigBB);
544 NewBBs.push_back(NewBB2);
546 // The new block unconditionally branches to the old block.
547 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
549 // Move the remaining edges from OrigBB to point to NewBB2.
550 for (SmallVectorImpl<BasicBlock*>::iterator
551 i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
552 (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
554 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
556 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit);
558 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
559 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit);
562 LandingPadInst *LPad = OrigBB->getLandingPadInst();
563 Instruction *Clone1 = LPad->clone();
564 Clone1->setName(Twine("lpad") + Suffix1);
565 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
568 Instruction *Clone2 = LPad->clone();
569 Clone2->setName(Twine("lpad") + Suffix2);
570 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
572 // Create a PHI node for the two cloned landingpad instructions.
573 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
574 PN->addIncoming(Clone1, NewBB1);
575 PN->addIncoming(Clone2, NewBB2);
576 LPad->replaceAllUsesWith(PN);
577 LPad->eraseFromParent();
579 // There is no second clone. Just replace the landing pad with the first
581 LPad->replaceAllUsesWith(Clone1);
582 LPad->eraseFromParent();
586 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
587 /// instruction into a predecessor which ends in an unconditional branch. If
588 /// the return instruction returns a value defined by a PHI, propagate the
589 /// right value into the return. It returns the new return instruction in the
591 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
593 Instruction *UncondBranch = Pred->getTerminator();
594 // Clone the return and add it to the end of the predecessor.
595 Instruction *NewRet = RI->clone();
596 Pred->getInstList().push_back(NewRet);
598 // If the return instruction returns a value, and if the value was a
599 // PHI node in "BB", propagate the right value into the return.
600 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
603 Instruction *NewBC = 0;
604 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
605 // Return value might be bitcasted. Clone and insert it before the
606 // return instruction.
607 V = BCI->getOperand(0);
608 NewBC = BCI->clone();
609 Pred->getInstList().insert(NewRet, NewBC);
612 if (PHINode *PN = dyn_cast<PHINode>(V)) {
613 if (PN->getParent() == BB) {
615 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
617 *i = PN->getIncomingValueForBlock(Pred);
622 // Update any PHI nodes in the returning block to realize that we no
623 // longer branch to them.
624 BB->removePredecessor(Pred);
625 UncondBranch->eraseFromParent();
626 return cast<ReturnInst>(NewRet);
629 /// SplitBlockAndInsertIfThen - Split the containing block at the
630 /// specified instruction - everything before and including Cmp stays
631 /// in the old basic block, and everything after Cmp is moved to a
632 /// new block. The two blocks are connected by a conditional branch
633 /// (with value of Cmp being the condition).
645 /// If Unreachable is true, then ThenBlock ends with
646 /// UnreachableInst, otherwise it branches to Tail.
647 /// Returns the NewBasicBlock's terminator.
649 TerminatorInst *llvm::SplitBlockAndInsertIfThen(Instruction *Cmp,
650 bool Unreachable, MDNode *BranchWeights) {
651 Instruction *SplitBefore = Cmp->getNextNode();
652 BasicBlock *Head = SplitBefore->getParent();
653 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
654 TerminatorInst *HeadOldTerm = Head->getTerminator();
655 LLVMContext &C = Head->getContext();
656 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
657 TerminatorInst *CheckTerm;
659 CheckTerm = new UnreachableInst(C, ThenBlock);
661 CheckTerm = BranchInst::Create(Tail, ThenBlock);
662 BranchInst *HeadNewTerm =
663 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cmp);
664 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
665 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
669 /// GetIfCondition - Given a basic block (BB) with two predecessors,
670 /// check to see if the merge at this block is due
671 /// to an "if condition". If so, return the boolean condition that determines
672 /// which entry into BB will be taken. Also, return by references the block
673 /// that will be entered from if the condition is true, and the block that will
674 /// be entered if the condition is false.
676 /// This does no checking to see if the true/false blocks have large or unsavory
677 /// instructions in them.
678 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
679 BasicBlock *&IfFalse) {
680 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
681 BasicBlock *Pred1 = NULL;
682 BasicBlock *Pred2 = NULL;
685 if (SomePHI->getNumIncomingValues() != 2)
687 Pred1 = SomePHI->getIncomingBlock(0);
688 Pred2 = SomePHI->getIncomingBlock(1);
690 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
691 if (PI == PE) // No predecessor
694 if (PI == PE) // Only one predecessor
697 if (PI != PE) // More than two predecessors
701 // We can only handle branches. Other control flow will be lowered to
702 // branches if possible anyway.
703 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
704 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
705 if (Pred1Br == 0 || Pred2Br == 0)
708 // Eliminate code duplication by ensuring that Pred1Br is conditional if
710 if (Pred2Br->isConditional()) {
711 // If both branches are conditional, we don't have an "if statement". In
712 // reality, we could transform this case, but since the condition will be
713 // required anyway, we stand no chance of eliminating it, so the xform is
714 // probably not profitable.
715 if (Pred1Br->isConditional())
718 std::swap(Pred1, Pred2);
719 std::swap(Pred1Br, Pred2Br);
722 if (Pred1Br->isConditional()) {
723 // The only thing we have to watch out for here is to make sure that Pred2
724 // doesn't have incoming edges from other blocks. If it does, the condition
725 // doesn't dominate BB.
726 if (Pred2->getSinglePredecessor() == 0)
729 // If we found a conditional branch predecessor, make sure that it branches
730 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
731 if (Pred1Br->getSuccessor(0) == BB &&
732 Pred1Br->getSuccessor(1) == Pred2) {
735 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
736 Pred1Br->getSuccessor(1) == BB) {
740 // We know that one arm of the conditional goes to BB, so the other must
741 // go somewhere unrelated, and this must not be an "if statement".
745 return Pred1Br->getCondition();
748 // Ok, if we got here, both predecessors end with an unconditional branch to
749 // BB. Don't panic! If both blocks only have a single (identical)
750 // predecessor, and THAT is a conditional branch, then we're all ok!
751 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
752 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
755 // Otherwise, if this is a conditional branch, then we can use it!
756 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
757 if (BI == 0) return 0;
759 assert(BI->isConditional() && "Two successors but not conditional?");
760 if (BI->getSuccessor(0) == Pred1) {
767 return BI->getCondition();