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/LoopInfo.h"
19 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
20 #include "llvm/IR/Constant.h"
21 #include "llvm/IR/DataLayout.h"
22 #include "llvm/IR/Dominators.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/IR/ValueHandle.h"
28 #include "llvm/Support/ErrorHandling.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 (DominatorTreeWrapperPass *DTWP =
171 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
172 DominatorTree &DT = DTWP->getDomTree();
173 if (DomTreeNode *DTN = DT.getNode(BB)) {
174 DomTreeNode *PredDTN = DT.getNode(PredBB);
175 SmallVector<DomTreeNode*, 8> Children(DTN->begin(), DTN->end());
176 for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(),
177 DE = Children.end(); DI != DE; ++DI)
178 DT.changeImmediateDominator(*DI, PredDTN);
183 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
186 if (MemoryDependenceAnalysis *MD =
187 P->getAnalysisIfAvailable<MemoryDependenceAnalysis>())
188 MD->invalidateCachedPredecessors();
192 BB->eraseFromParent();
196 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
197 /// with a value, then remove and delete the original instruction.
199 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
200 BasicBlock::iterator &BI, Value *V) {
201 Instruction &I = *BI;
202 // Replaces all of the uses of the instruction with uses of the value
203 I.replaceAllUsesWith(V);
205 // Make sure to propagate a name if there is one already.
206 if (I.hasName() && !V->hasName())
209 // Delete the unnecessary instruction now...
214 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
215 /// instruction specified by I. The original instruction is deleted and BI is
216 /// updated to point to the new instruction.
218 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
219 BasicBlock::iterator &BI, Instruction *I) {
220 assert(I->getParent() == 0 &&
221 "ReplaceInstWithInst: Instruction already inserted into basic block!");
223 // Insert the new instruction into the basic block...
224 BasicBlock::iterator New = BIL.insert(BI, I);
226 // Replace all uses of the old instruction, and delete it.
227 ReplaceInstWithValue(BIL, BI, I);
229 // Move BI back to point to the newly inserted instruction
233 /// ReplaceInstWithInst - Replace the instruction specified by From with the
234 /// instruction specified by To.
236 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
237 BasicBlock::iterator BI(From);
238 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
241 /// SplitEdge - Split the edge connecting specified block. Pass P must
243 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, Pass *P) {
244 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
246 // If this is a critical edge, let SplitCriticalEdge do it.
247 TerminatorInst *LatchTerm = BB->getTerminator();
248 if (SplitCriticalEdge(LatchTerm, SuccNum, P))
249 return LatchTerm->getSuccessor(SuccNum);
251 // If the edge isn't critical, then BB has a single successor or Succ has a
252 // single pred. Split the block.
253 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
254 // If the successor only has a single pred, split the top of the successor
256 assert(SP == BB && "CFG broken");
258 return SplitBlock(Succ, Succ->begin(), P);
261 // Otherwise, if BB has a single successor, split it at the bottom of the
263 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
264 "Should have a single succ!");
265 return SplitBlock(BB, BB->getTerminator(), P);
268 /// SplitBlock - Split the specified block at the specified instruction - every
269 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
270 /// to a new block. The two blocks are joined by an unconditional branch and
271 /// the loop info is updated.
273 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt, Pass *P) {
274 BasicBlock::iterator SplitIt = SplitPt;
275 while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))
277 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
279 // The new block lives in whichever loop the old one did. This preserves
280 // LCSSA as well, because we force the split point to be after any PHI nodes.
281 if (LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>())
282 if (Loop *L = LI->getLoopFor(Old))
283 L->addBasicBlockToLoop(New, LI->getBase());
285 if (DominatorTreeWrapperPass *DTWP =
286 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>()) {
287 DominatorTree &DT = DTWP->getDomTree();
288 // Old dominates New. New node dominates all other nodes dominated by Old.
289 if (DomTreeNode *OldNode = DT.getNode(Old)) {
290 std::vector<DomTreeNode *> Children;
291 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
293 Children.push_back(*I);
295 DomTreeNode *NewNode = DT.addNewBlock(New, Old);
296 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
297 E = Children.end(); I != E; ++I)
298 DT.changeImmediateDominator(*I, NewNode);
305 /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA
306 /// analysis information.
307 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
308 ArrayRef<BasicBlock *> Preds,
309 Pass *P, bool &HasLoopExit) {
312 LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
313 Loop *L = LI ? LI->getLoopFor(OldBB) : 0;
315 // If we need to preserve loop analyses, collect some information about how
316 // this split will affect loops.
317 bool IsLoopEntry = !!L;
318 bool SplitMakesNewLoopHeader = false;
320 bool PreserveLCSSA = P->mustPreserveAnalysisID(LCSSAID);
321 for (ArrayRef<BasicBlock*>::iterator
322 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
323 BasicBlock *Pred = *i;
325 // If we need to preserve LCSSA, determine if any of the preds is a loop
328 if (Loop *PL = LI->getLoopFor(Pred))
329 if (!PL->contains(OldBB))
332 // If we need to preserve LoopInfo, note whether any of the preds crosses
333 // an interesting loop boundary.
335 if (L->contains(Pred))
338 SplitMakesNewLoopHeader = true;
342 // Update dominator tree if available.
343 if (DominatorTreeWrapperPass *DTWP =
344 P->getAnalysisIfAvailable<DominatorTreeWrapperPass>())
345 DTWP->getDomTree().splitBlock(NewBB);
350 // Add the new block to the nearest enclosing loop (and not an adjacent
351 // loop). To find this, examine each of the predecessors and determine which
352 // loops enclose them, and select the most-nested loop which contains the
353 // loop containing the block being split.
354 Loop *InnermostPredLoop = 0;
355 for (ArrayRef<BasicBlock*>::iterator
356 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
357 BasicBlock *Pred = *i;
358 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
359 // Seek a loop which actually contains the block being split (to avoid
361 while (PredLoop && !PredLoop->contains(OldBB))
362 PredLoop = PredLoop->getParentLoop();
364 // Select the most-nested of these loops which contains the block.
365 if (PredLoop && PredLoop->contains(OldBB) &&
366 (!InnermostPredLoop ||
367 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
368 InnermostPredLoop = PredLoop;
372 if (InnermostPredLoop)
373 InnermostPredLoop->addBasicBlockToLoop(NewBB, LI->getBase());
375 L->addBasicBlockToLoop(NewBB, LI->getBase());
376 if (SplitMakesNewLoopHeader)
377 L->moveToHeader(NewBB);
381 /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
382 /// from NewBB. This also updates AliasAnalysis, if available.
383 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
384 ArrayRef<BasicBlock*> Preds, BranchInst *BI,
385 Pass *P, bool HasLoopExit) {
386 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
387 AliasAnalysis *AA = P ? P->getAnalysisIfAvailable<AliasAnalysis>() : 0;
388 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
389 PHINode *PN = cast<PHINode>(I++);
391 // Check to see if all of the values coming in are the same. If so, we
392 // don't need to create a new PHI node, unless it's needed for LCSSA.
395 InVal = PN->getIncomingValueForBlock(Preds[0]);
396 for (unsigned i = 1, e = Preds.size(); i != e; ++i)
397 if (InVal != PN->getIncomingValueForBlock(Preds[i])) {
404 // If all incoming values for the new PHI would be the same, just don't
405 // make a new PHI. Instead, just remove the incoming values from the old
407 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
408 // Explicitly check the BB index here to handle duplicates in Preds.
409 int Idx = PN->getBasicBlockIndex(Preds[i]);
411 PN->removeIncomingValue(Idx, false);
414 // If the values coming into the block are not the same, we need a PHI.
415 // Create the new PHI node, insert it into NewBB at the end of the block
417 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
418 if (AA) AA->copyValue(PN, NewPHI);
420 // Move all of the PHI values for 'Preds' to the new PHI.
421 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
422 Value *V = PN->removeIncomingValue(Preds[i], false);
423 NewPHI->addIncoming(V, Preds[i]);
429 // Add an incoming value to the PHI node in the loop for the preheader
431 PN->addIncoming(InVal, NewBB);
435 /// SplitBlockPredecessors - This method transforms BB by introducing a new
436 /// basic block into the function, and moving some of the predecessors of BB to
437 /// be predecessors of the new block. The new predecessors are indicated by the
438 /// Preds array, which has NumPreds elements in it. The new block is given a
439 /// suffix of 'Suffix'.
441 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
442 /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
443 /// preserve LoopSimplify (because it's complicated to handle the case where one
444 /// of the edges being split is an exit of a loop with other exits).
446 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
447 ArrayRef<BasicBlock*> Preds,
448 const char *Suffix, Pass *P) {
449 // Create new basic block, insert right before the original block.
450 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), BB->getName()+Suffix,
451 BB->getParent(), BB);
453 // The new block unconditionally branches to the old block.
454 BranchInst *BI = BranchInst::Create(BB, NewBB);
456 // Move the edges from Preds to point to NewBB instead of BB.
457 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
458 // This is slightly more strict than necessary; the minimum requirement
459 // is that there be no more than one indirectbr branching to BB. And
460 // all BlockAddress uses would need to be updated.
461 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
462 "Cannot split an edge from an IndirectBrInst");
463 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
466 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
467 // node becomes an incoming value for BB's phi node. However, if the Preds
468 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
469 // account for the newly created predecessor.
470 if (Preds.size() == 0) {
471 // Insert dummy values as the incoming value.
472 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
473 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
477 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
478 bool HasLoopExit = false;
479 UpdateAnalysisInformation(BB, NewBB, Preds, P, HasLoopExit);
481 // Update the PHI nodes in BB with the values coming from NewBB.
482 UpdatePHINodes(BB, NewBB, Preds, BI, P, HasLoopExit);
486 /// SplitLandingPadPredecessors - This method transforms the landing pad,
487 /// OrigBB, by introducing two new basic blocks into the function. One of those
488 /// new basic blocks gets the predecessors listed in Preds. The other basic
489 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
490 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
491 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
493 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
494 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
495 /// it does not preserve LoopSimplify (because it's complicated to handle the
496 /// case where one of the edges being split is an exit of a loop with other
499 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
500 ArrayRef<BasicBlock*> Preds,
501 const char *Suffix1, const char *Suffix2,
503 SmallVectorImpl<BasicBlock*> &NewBBs) {
504 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
506 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
507 // it right before the original block.
508 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
509 OrigBB->getName() + Suffix1,
510 OrigBB->getParent(), OrigBB);
511 NewBBs.push_back(NewBB1);
513 // The new block unconditionally branches to the old block.
514 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
516 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
517 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
518 // This is slightly more strict than necessary; the minimum requirement
519 // is that there be no more than one indirectbr branching to BB. And
520 // all BlockAddress uses would need to be updated.
521 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
522 "Cannot split an edge from an IndirectBrInst");
523 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
526 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
527 bool HasLoopExit = false;
528 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, P, HasLoopExit);
530 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
531 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, P, HasLoopExit);
533 // Move the remaining edges from OrigBB to point to NewBB2.
534 SmallVector<BasicBlock*, 8> NewBB2Preds;
535 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
537 BasicBlock *Pred = *i++;
538 if (Pred == NewBB1) continue;
539 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
540 "Cannot split an edge from an IndirectBrInst");
541 NewBB2Preds.push_back(Pred);
542 e = pred_end(OrigBB);
545 BasicBlock *NewBB2 = 0;
546 if (!NewBB2Preds.empty()) {
547 // Create another basic block for the rest of OrigBB's predecessors.
548 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
549 OrigBB->getName() + Suffix2,
550 OrigBB->getParent(), OrigBB);
551 NewBBs.push_back(NewBB2);
553 // The new block unconditionally branches to the old block.
554 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
556 // Move the remaining edges from OrigBB to point to NewBB2.
557 for (SmallVectorImpl<BasicBlock*>::iterator
558 i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
559 (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
561 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
563 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, P, HasLoopExit);
565 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
566 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, P, HasLoopExit);
569 LandingPadInst *LPad = OrigBB->getLandingPadInst();
570 Instruction *Clone1 = LPad->clone();
571 Clone1->setName(Twine("lpad") + Suffix1);
572 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
575 Instruction *Clone2 = LPad->clone();
576 Clone2->setName(Twine("lpad") + Suffix2);
577 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
579 // Create a PHI node for the two cloned landingpad instructions.
580 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
581 PN->addIncoming(Clone1, NewBB1);
582 PN->addIncoming(Clone2, NewBB2);
583 LPad->replaceAllUsesWith(PN);
584 LPad->eraseFromParent();
586 // There is no second clone. Just replace the landing pad with the first
588 LPad->replaceAllUsesWith(Clone1);
589 LPad->eraseFromParent();
593 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
594 /// instruction into a predecessor which ends in an unconditional branch. If
595 /// the return instruction returns a value defined by a PHI, propagate the
596 /// right value into the return. It returns the new return instruction in the
598 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
600 Instruction *UncondBranch = Pred->getTerminator();
601 // Clone the return and add it to the end of the predecessor.
602 Instruction *NewRet = RI->clone();
603 Pred->getInstList().push_back(NewRet);
605 // If the return instruction returns a value, and if the value was a
606 // PHI node in "BB", propagate the right value into the return.
607 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
610 Instruction *NewBC = 0;
611 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
612 // Return value might be bitcasted. Clone and insert it before the
613 // return instruction.
614 V = BCI->getOperand(0);
615 NewBC = BCI->clone();
616 Pred->getInstList().insert(NewRet, NewBC);
619 if (PHINode *PN = dyn_cast<PHINode>(V)) {
620 if (PN->getParent() == BB) {
622 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
624 *i = PN->getIncomingValueForBlock(Pred);
629 // Update any PHI nodes in the returning block to realize that we no
630 // longer branch to them.
631 BB->removePredecessor(Pred);
632 UncondBranch->eraseFromParent();
633 return cast<ReturnInst>(NewRet);
636 /// SplitBlockAndInsertIfThen - Split the containing block at the
637 /// specified instruction - everything before and including SplitBefore stays
638 /// in the old basic block, and everything after SplitBefore is moved to a
639 /// new block. The two blocks are connected by a conditional branch
640 /// (with value of Cmp being the condition).
652 /// If Unreachable is true, then ThenBlock ends with
653 /// UnreachableInst, otherwise it branches to Tail.
654 /// Returns the NewBasicBlock's terminator.
656 TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond,
657 Instruction *SplitBefore,
659 MDNode *BranchWeights) {
660 BasicBlock *Head = SplitBefore->getParent();
661 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
662 TerminatorInst *HeadOldTerm = Head->getTerminator();
663 LLVMContext &C = Head->getContext();
664 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
665 TerminatorInst *CheckTerm;
667 CheckTerm = new UnreachableInst(C, ThenBlock);
669 CheckTerm = BranchInst::Create(Tail, ThenBlock);
670 BranchInst *HeadNewTerm =
671 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
672 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
673 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
677 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
678 /// but also creates the ElseBlock.
691 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
692 TerminatorInst **ThenTerm,
693 TerminatorInst **ElseTerm,
694 MDNode *BranchWeights) {
695 BasicBlock *Head = SplitBefore->getParent();
696 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
697 TerminatorInst *HeadOldTerm = Head->getTerminator();
698 LLVMContext &C = Head->getContext();
699 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
700 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
701 *ThenTerm = BranchInst::Create(Tail, ThenBlock);
702 *ElseTerm = BranchInst::Create(Tail, ElseBlock);
703 BranchInst *HeadNewTerm =
704 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
705 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
706 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
710 /// GetIfCondition - Given a basic block (BB) with two predecessors,
711 /// check to see if the merge at this block is due
712 /// to an "if condition". If so, return the boolean condition that determines
713 /// which entry into BB will be taken. Also, return by references the block
714 /// that will be entered from if the condition is true, and the block that will
715 /// be entered if the condition is false.
717 /// This does no checking to see if the true/false blocks have large or unsavory
718 /// instructions in them.
719 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
720 BasicBlock *&IfFalse) {
721 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
722 BasicBlock *Pred1 = NULL;
723 BasicBlock *Pred2 = NULL;
726 if (SomePHI->getNumIncomingValues() != 2)
728 Pred1 = SomePHI->getIncomingBlock(0);
729 Pred2 = SomePHI->getIncomingBlock(1);
731 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
732 if (PI == PE) // No predecessor
735 if (PI == PE) // Only one predecessor
738 if (PI != PE) // More than two predecessors
742 // We can only handle branches. Other control flow will be lowered to
743 // branches if possible anyway.
744 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
745 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
746 if (Pred1Br == 0 || Pred2Br == 0)
749 // Eliminate code duplication by ensuring that Pred1Br is conditional if
751 if (Pred2Br->isConditional()) {
752 // If both branches are conditional, we don't have an "if statement". In
753 // reality, we could transform this case, but since the condition will be
754 // required anyway, we stand no chance of eliminating it, so the xform is
755 // probably not profitable.
756 if (Pred1Br->isConditional())
759 std::swap(Pred1, Pred2);
760 std::swap(Pred1Br, Pred2Br);
763 if (Pred1Br->isConditional()) {
764 // The only thing we have to watch out for here is to make sure that Pred2
765 // doesn't have incoming edges from other blocks. If it does, the condition
766 // doesn't dominate BB.
767 if (Pred2->getSinglePredecessor() == 0)
770 // If we found a conditional branch predecessor, make sure that it branches
771 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
772 if (Pred1Br->getSuccessor(0) == BB &&
773 Pred1Br->getSuccessor(1) == Pred2) {
776 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
777 Pred1Br->getSuccessor(1) == BB) {
781 // We know that one arm of the conditional goes to BB, so the other must
782 // go somewhere unrelated, and this must not be an "if statement".
786 return Pred1Br->getCondition();
789 // Ok, if we got here, both predecessors end with an unconditional branch to
790 // BB. Don't panic! If both blocks only have a single (identical)
791 // predecessor, and THAT is a conditional branch, then we're all ok!
792 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
793 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
796 // Otherwise, if this is a conditional branch, then we can use it!
797 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
798 if (BI == 0) return 0;
800 assert(BI->isConditional() && "Two successors but not conditional?");
801 if (BI->getSuccessor(0) == Pred1) {
808 return BI->getCondition();