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, AliasAnalysis *AA,
69 MemoryDependenceAnalysis *MemDep) {
70 if (!isa<PHINode>(BB->begin())) return;
72 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
73 if (PN->getIncomingValue(0) != PN)
74 PN->replaceAllUsesWith(PN->getIncomingValue(0));
76 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
79 MemDep->removeInstruction(PN); // Memdep updates AA itself.
80 else if (AA && isa<PointerType>(PN->getType()))
83 PN->eraseFromParent();
88 /// DeleteDeadPHIs - Examine each PHI in the given block and delete it if it
89 /// is dead. Also recursively delete any operands that become dead as
90 /// a result. This includes tracing the def-use list from the PHI to see if
91 /// it is ultimately unused or if it reaches an unused cycle.
92 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
93 // Recursively deleting a PHI may cause multiple PHIs to be deleted
94 // or RAUW'd undef, so use an array of WeakVH for the PHIs to delete.
95 SmallVector<WeakVH, 8> PHIs;
96 for (BasicBlock::iterator I = BB->begin();
97 PHINode *PN = dyn_cast<PHINode>(I); ++I)
100 bool Changed = false;
101 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
102 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
103 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
108 /// MergeBlockIntoPredecessor - Attempts to merge a block into its predecessor,
109 /// if possible. The return value indicates success or failure.
110 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
111 LoopInfo *LI, AliasAnalysis *AA,
112 MemoryDependenceAnalysis *MemDep) {
113 // Don't merge away blocks who have their address taken.
114 if (BB->hasAddressTaken()) return false;
116 // Can't merge if there are multiple predecessors, or no predecessors.
117 BasicBlock *PredBB = BB->getUniquePredecessor();
118 if (!PredBB) return false;
120 // Don't break self-loops.
121 if (PredBB == BB) return false;
122 // Don't break invokes.
123 if (isa<InvokeInst>(PredBB->getTerminator())) return false;
125 succ_iterator SI(succ_begin(PredBB)), SE(succ_end(PredBB));
126 BasicBlock *OnlySucc = BB;
127 for (; SI != SE; ++SI)
128 if (*SI != OnlySucc) {
129 OnlySucc = nullptr; // There are multiple distinct successors!
133 // Can't merge if there are multiple successors.
134 if (!OnlySucc) return false;
136 // Can't merge if there is PHI loop.
137 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
138 if (PHINode *PN = dyn_cast<PHINode>(BI)) {
139 for (Value *IncValue : PN->incoming_values())
146 // Begin by getting rid of unneeded PHIs.
147 if (isa<PHINode>(BB->front()))
148 FoldSingleEntryPHINodes(BB, AA, MemDep);
150 // Delete the unconditional branch from the predecessor...
151 PredBB->getInstList().pop_back();
153 // Make all PHI nodes that referred to BB now refer to Pred as their
155 BB->replaceAllUsesWith(PredBB);
157 // Move all definitions in the successor to the predecessor...
158 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
160 // Inherit predecessors name if it exists.
161 if (!PredBB->hasName())
162 PredBB->takeName(BB);
164 // Finally, erase the old block and update dominator info.
166 if (DomTreeNode *DTN = DT->getNode(BB)) {
167 DomTreeNode *PredDTN = DT->getNode(PredBB);
168 SmallVector<DomTreeNode *, 8> Children(DTN->begin(), DTN->end());
169 for (SmallVectorImpl<DomTreeNode *>::iterator DI = Children.begin(),
172 DT->changeImmediateDominator(*DI, PredDTN);
181 MemDep->invalidateCachedPredecessors();
183 BB->eraseFromParent();
187 /// ReplaceInstWithValue - Replace all uses of an instruction (specified by BI)
188 /// with a value, then remove and delete the original instruction.
190 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
191 BasicBlock::iterator &BI, Value *V) {
192 Instruction &I = *BI;
193 // Replaces all of the uses of the instruction with uses of the value
194 I.replaceAllUsesWith(V);
196 // Make sure to propagate a name if there is one already.
197 if (I.hasName() && !V->hasName())
200 // Delete the unnecessary instruction now...
205 /// ReplaceInstWithInst - Replace the instruction specified by BI with the
206 /// instruction specified by I. The original instruction is deleted and BI is
207 /// updated to point to the new instruction.
209 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
210 BasicBlock::iterator &BI, Instruction *I) {
211 assert(I->getParent() == nullptr &&
212 "ReplaceInstWithInst: Instruction already inserted into basic block!");
214 // Copy debug location to newly added instruction, if it wasn't already set
216 if (!I->getDebugLoc())
217 I->setDebugLoc(BI->getDebugLoc());
219 // Insert the new instruction into the basic block...
220 BasicBlock::iterator New = BIL.insert(BI, I);
222 // Replace all uses of the old instruction, and delete it.
223 ReplaceInstWithValue(BIL, BI, I);
225 // Move BI back to point to the newly inserted instruction
229 /// ReplaceInstWithInst - Replace the instruction specified by From with the
230 /// instruction specified by To.
232 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
233 BasicBlock::iterator BI(From);
234 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
237 /// SplitEdge - Split the edge connecting specified block. Pass P must
239 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
241 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
243 // If this is a critical edge, let SplitCriticalEdge do it.
244 TerminatorInst *LatchTerm = BB->getTerminator();
245 if (SplitCriticalEdge(LatchTerm, SuccNum, CriticalEdgeSplittingOptions(DT, LI)
246 .setPreserveLCSSA()))
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 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
252 // If the successor only has a single pred, split the top of the successor
254 assert(SP == BB && "CFG broken");
256 return SplitBlock(Succ, Succ->begin(), DT, LI);
259 // Otherwise, if BB has a single successor, split it at the bottom of the
261 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
262 "Should have a single succ!");
263 return SplitBlock(BB, BB->getTerminator(), DT, LI);
267 llvm::SplitAllCriticalEdges(Function &F,
268 const CriticalEdgeSplittingOptions &Options) {
269 unsigned NumBroken = 0;
270 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
271 TerminatorInst *TI = I->getTerminator();
272 if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
273 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
274 if (SplitCriticalEdge(TI, i, Options))
280 /// SplitBlock - Split the specified block at the specified instruction - every
281 /// thing before SplitPt stays in Old and everything starting with SplitPt moves
282 /// to a new block. The two blocks are joined by an unconditional branch and
283 /// the loop info is updated.
285 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
286 DominatorTree *DT, LoopInfo *LI) {
287 BasicBlock::iterator SplitIt = SplitPt;
288 while (isa<PHINode>(SplitIt) || isa<LandingPadInst>(SplitIt))
290 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
292 // The new block lives in whichever loop the old one did. This preserves
293 // LCSSA as well, because we force the split point to be after any PHI nodes.
295 if (Loop *L = LI->getLoopFor(Old))
296 L->addBasicBlockToLoop(New, *LI);
299 // Old dominates New. New node dominates all other nodes dominated by Old.
300 if (DomTreeNode *OldNode = DT->getNode(Old)) {
301 std::vector<DomTreeNode *> Children;
302 for (DomTreeNode::iterator I = OldNode->begin(), E = OldNode->end();
304 Children.push_back(*I);
306 DomTreeNode *NewNode = DT->addNewBlock(New, Old);
307 for (std::vector<DomTreeNode *>::iterator I = Children.begin(),
308 E = Children.end(); I != E; ++I)
309 DT->changeImmediateDominator(*I, NewNode);
315 /// UpdateAnalysisInformation - Update DominatorTree, LoopInfo, and LCCSA
316 /// analysis information.
317 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
318 ArrayRef<BasicBlock *> Preds,
319 DominatorTree *DT, LoopInfo *LI,
320 bool PreserveLCSSA, bool &HasLoopExit) {
321 // Update dominator tree if available.
323 DT->splitBlock(NewBB);
325 // The rest of the logic is only relevant for updating the loop structures.
329 Loop *L = LI->getLoopFor(OldBB);
331 // If we need to preserve loop analyses, collect some information about how
332 // this split will affect loops.
333 bool IsLoopEntry = !!L;
334 bool SplitMakesNewLoopHeader = false;
335 for (ArrayRef<BasicBlock *>::iterator i = Preds.begin(), e = Preds.end();
337 BasicBlock *Pred = *i;
339 // If we need to preserve LCSSA, determine if any of the preds is a loop
342 if (Loop *PL = LI->getLoopFor(Pred))
343 if (!PL->contains(OldBB))
346 // If we need to preserve LoopInfo, note whether any of the preds crosses
347 // an interesting loop boundary.
350 if (L->contains(Pred))
353 SplitMakesNewLoopHeader = true;
356 // Unless we have a loop for OldBB, nothing else to do here.
361 // Add the new block to the nearest enclosing loop (and not an adjacent
362 // loop). To find this, examine each of the predecessors and determine which
363 // loops enclose them, and select the most-nested loop which contains the
364 // loop containing the block being split.
365 Loop *InnermostPredLoop = nullptr;
366 for (ArrayRef<BasicBlock*>::iterator
367 i = Preds.begin(), e = Preds.end(); i != e; ++i) {
368 BasicBlock *Pred = *i;
369 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
370 // Seek a loop which actually contains the block being split (to avoid
372 while (PredLoop && !PredLoop->contains(OldBB))
373 PredLoop = PredLoop->getParentLoop();
375 // Select the most-nested of these loops which contains the block.
376 if (PredLoop && PredLoop->contains(OldBB) &&
377 (!InnermostPredLoop ||
378 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
379 InnermostPredLoop = PredLoop;
383 if (InnermostPredLoop)
384 InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
386 L->addBasicBlockToLoop(NewBB, *LI);
387 if (SplitMakesNewLoopHeader)
388 L->moveToHeader(NewBB);
392 /// UpdatePHINodes - Update the PHI nodes in OrigBB to include the values coming
393 /// from NewBB. This also updates AliasAnalysis, if available.
394 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
395 ArrayRef<BasicBlock *> Preds, BranchInst *BI,
396 AliasAnalysis *AA, bool HasLoopExit) {
397 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
398 SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
399 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
400 PHINode *PN = cast<PHINode>(I++);
402 // Check to see if all of the values coming in are the same. If so, we
403 // don't need to create a new PHI node, unless it's needed for LCSSA.
404 Value *InVal = nullptr;
406 InVal = PN->getIncomingValueForBlock(Preds[0]);
407 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
408 if (!PredSet.count(PN->getIncomingBlock(i)))
411 InVal = PN->getIncomingValue(i);
412 else if (InVal != PN->getIncomingValue(i)) {
420 // If all incoming values for the new PHI would be the same, just don't
421 // make a new PHI. Instead, just remove the incoming values from the old
424 // NOTE! This loop walks backwards for a reason! First off, this minimizes
425 // the cost of removal if we end up removing a large number of values, and
426 // second off, this ensures that the indices for the incoming values
427 // aren't invalidated when we remove one.
428 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
429 if (PredSet.count(PN->getIncomingBlock(i)))
430 PN->removeIncomingValue(i, false);
432 // Add an incoming value to the PHI node in the loop for the preheader
434 PN->addIncoming(InVal, NewBB);
438 // If the values coming into the block are not the same, we need a new
440 // Create the new PHI node, insert it into NewBB at the end of the block
442 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
444 // NOTE! This loop walks backwards for a reason! First off, this minimizes
445 // the cost of removal if we end up removing a large number of values, and
446 // second off, this ensures that the indices for the incoming values aren't
447 // invalidated when we remove one.
448 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
449 BasicBlock *IncomingBB = PN->getIncomingBlock(i);
450 if (PredSet.count(IncomingBB)) {
451 Value *V = PN->removeIncomingValue(i, false);
452 NewPHI->addIncoming(V, IncomingBB);
456 PN->addIncoming(NewPHI, NewBB);
460 /// SplitBlockPredecessors - This method introduces at least one new basic block
461 /// into the function and moves some of the predecessors of BB to be
462 /// predecessors of the new block. The new predecessors are indicated by the
463 /// Preds array. The new block is given a suffix of 'Suffix'. Returns new basic
464 /// block to which predecessors from Preds are now pointing.
466 /// If BB is a landingpad block then additional basicblock might be introduced.
467 /// It will have suffix of 'Suffix'+".split_lp".
468 /// See SplitLandingPadPredecessors for more details on this case.
470 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
471 /// LoopInfo, and LCCSA but no other analyses. In particular, it does not
472 /// preserve LoopSimplify (because it's complicated to handle the case where one
473 /// of the edges being split is an exit of a loop with other exits).
475 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
476 ArrayRef<BasicBlock *> Preds,
477 const char *Suffix, AliasAnalysis *AA,
478 DominatorTree *DT, LoopInfo *LI,
479 bool PreserveLCSSA) {
480 // For the landingpads we need to act a bit differently.
481 // Delegate this work to the SplitLandingPadPredecessors.
482 if (BB->isLandingPad()) {
483 SmallVector<BasicBlock*, 2> NewBBs;
484 std::string NewName = std::string(Suffix) + ".split-lp";
486 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(),
487 NewBBs, AA, DT, LI, PreserveLCSSA);
491 // Create new basic block, insert right before the original block.
492 BasicBlock *NewBB = BasicBlock::Create(
493 BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
495 // The new block unconditionally branches to the old block.
496 BranchInst *BI = BranchInst::Create(BB, NewBB);
497 BI->setDebugLoc(BB->getFirstNonPHI()->getDebugLoc());
499 // Move the edges from Preds to point to NewBB instead of BB.
500 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
501 // This is slightly more strict than necessary; the minimum requirement
502 // is that there be no more than one indirectbr branching to BB. And
503 // all BlockAddress uses would need to be updated.
504 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
505 "Cannot split an edge from an IndirectBrInst");
506 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
509 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
510 // node becomes an incoming value for BB's phi node. However, if the Preds
511 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
512 // account for the newly created predecessor.
513 if (Preds.size() == 0) {
514 // Insert dummy values as the incoming value.
515 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
516 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
520 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
521 bool HasLoopExit = false;
522 UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, PreserveLCSSA,
525 // Update the PHI nodes in BB with the values coming from NewBB.
526 UpdatePHINodes(BB, NewBB, Preds, BI, AA, HasLoopExit);
530 /// SplitLandingPadPredecessors - This method transforms the landing pad,
531 /// OrigBB, by introducing two new basic blocks into the function. One of those
532 /// new basic blocks gets the predecessors listed in Preds. The other basic
533 /// block gets the remaining predecessors of OrigBB. The landingpad instruction
534 /// OrigBB is clone into both of the new basic blocks. The new blocks are given
535 /// the suffixes 'Suffix1' and 'Suffix2', and are returned in the NewBBs vector.
537 /// This currently updates the LLVM IR, AliasAnalysis, DominatorTree,
538 /// DominanceFrontier, LoopInfo, and LCCSA but no other analyses. In particular,
539 /// it does not preserve LoopSimplify (because it's complicated to handle the
540 /// case where one of the edges being split is an exit of a loop with other
543 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
544 ArrayRef<BasicBlock *> Preds,
545 const char *Suffix1, const char *Suffix2,
546 SmallVectorImpl<BasicBlock *> &NewBBs,
547 AliasAnalysis *AA, DominatorTree *DT,
548 LoopInfo *LI, bool PreserveLCSSA) {
549 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
551 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
552 // it right before the original block.
553 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
554 OrigBB->getName() + Suffix1,
555 OrigBB->getParent(), OrigBB);
556 NewBBs.push_back(NewBB1);
558 // The new block unconditionally branches to the old block.
559 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
560 BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
562 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
563 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
564 // This is slightly more strict than necessary; the minimum requirement
565 // is that there be no more than one indirectbr branching to BB. And
566 // all BlockAddress uses would need to be updated.
567 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
568 "Cannot split an edge from an IndirectBrInst");
569 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
572 bool HasLoopExit = false;
573 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, PreserveLCSSA,
576 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
577 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, AA, HasLoopExit);
579 // Move the remaining edges from OrigBB to point to NewBB2.
580 SmallVector<BasicBlock*, 8> NewBB2Preds;
581 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
583 BasicBlock *Pred = *i++;
584 if (Pred == NewBB1) continue;
585 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
586 "Cannot split an edge from an IndirectBrInst");
587 NewBB2Preds.push_back(Pred);
588 e = pred_end(OrigBB);
591 BasicBlock *NewBB2 = nullptr;
592 if (!NewBB2Preds.empty()) {
593 // Create another basic block for the rest of OrigBB's predecessors.
594 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
595 OrigBB->getName() + Suffix2,
596 OrigBB->getParent(), OrigBB);
597 NewBBs.push_back(NewBB2);
599 // The new block unconditionally branches to the old block.
600 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
601 BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
603 // Move the remaining edges from OrigBB to point to NewBB2.
604 for (SmallVectorImpl<BasicBlock*>::iterator
605 i = NewBB2Preds.begin(), e = NewBB2Preds.end(); i != e; ++i)
606 (*i)->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
608 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
610 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI,
611 PreserveLCSSA, HasLoopExit);
613 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
614 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, AA, HasLoopExit);
617 LandingPadInst *LPad = OrigBB->getLandingPadInst();
618 Instruction *Clone1 = LPad->clone();
619 Clone1->setName(Twine("lpad") + Suffix1);
620 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
623 Instruction *Clone2 = LPad->clone();
624 Clone2->setName(Twine("lpad") + Suffix2);
625 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
627 // Create a PHI node for the two cloned landingpad instructions.
628 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
629 PN->addIncoming(Clone1, NewBB1);
630 PN->addIncoming(Clone2, NewBB2);
631 LPad->replaceAllUsesWith(PN);
632 LPad->eraseFromParent();
634 // There is no second clone. Just replace the landing pad with the first
636 LPad->replaceAllUsesWith(Clone1);
637 LPad->eraseFromParent();
641 /// FoldReturnIntoUncondBranch - This method duplicates the specified return
642 /// instruction into a predecessor which ends in an unconditional branch. If
643 /// the return instruction returns a value defined by a PHI, propagate the
644 /// right value into the return. It returns the new return instruction in the
646 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
648 Instruction *UncondBranch = Pred->getTerminator();
649 // Clone the return and add it to the end of the predecessor.
650 Instruction *NewRet = RI->clone();
651 Pred->getInstList().push_back(NewRet);
653 // If the return instruction returns a value, and if the value was a
654 // PHI node in "BB", propagate the right value into the return.
655 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
658 Instruction *NewBC = nullptr;
659 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
660 // Return value might be bitcasted. Clone and insert it before the
661 // return instruction.
662 V = BCI->getOperand(0);
663 NewBC = BCI->clone();
664 Pred->getInstList().insert(NewRet, NewBC);
667 if (PHINode *PN = dyn_cast<PHINode>(V)) {
668 if (PN->getParent() == BB) {
670 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
672 *i = PN->getIncomingValueForBlock(Pred);
677 // Update any PHI nodes in the returning block to realize that we no
678 // longer branch to them.
679 BB->removePredecessor(Pred);
680 UncondBranch->eraseFromParent();
681 return cast<ReturnInst>(NewRet);
684 /// SplitBlockAndInsertIfThen - Split the containing block at the
685 /// specified instruction - everything before and including SplitBefore stays
686 /// in the old basic block, and everything after SplitBefore is moved to a
687 /// new block. The two blocks are connected by a conditional branch
688 /// (with value of Cmp being the condition).
700 /// If Unreachable is true, then ThenBlock ends with
701 /// UnreachableInst, otherwise it branches to Tail.
702 /// Returns the NewBasicBlock's terminator.
704 TerminatorInst *llvm::SplitBlockAndInsertIfThen(Value *Cond,
705 Instruction *SplitBefore,
707 MDNode *BranchWeights,
709 BasicBlock *Head = SplitBefore->getParent();
710 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
711 TerminatorInst *HeadOldTerm = Head->getTerminator();
712 LLVMContext &C = Head->getContext();
713 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
714 TerminatorInst *CheckTerm;
716 CheckTerm = new UnreachableInst(C, ThenBlock);
718 CheckTerm = BranchInst::Create(Tail, ThenBlock);
719 CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
720 BranchInst *HeadNewTerm =
721 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
722 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
723 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
726 if (DomTreeNode *OldNode = DT->getNode(Head)) {
727 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
729 DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
730 for (auto Child : Children)
731 DT->changeImmediateDominator(Child, NewNode);
733 // Head dominates ThenBlock.
734 DT->addNewBlock(ThenBlock, Head);
741 /// SplitBlockAndInsertIfThenElse is similar to SplitBlockAndInsertIfThen,
742 /// but also creates the ElseBlock.
755 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
756 TerminatorInst **ThenTerm,
757 TerminatorInst **ElseTerm,
758 MDNode *BranchWeights) {
759 BasicBlock *Head = SplitBefore->getParent();
760 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore);
761 TerminatorInst *HeadOldTerm = Head->getTerminator();
762 LLVMContext &C = Head->getContext();
763 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
764 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
765 *ThenTerm = BranchInst::Create(Tail, ThenBlock);
766 (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
767 *ElseTerm = BranchInst::Create(Tail, ElseBlock);
768 (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
769 BranchInst *HeadNewTerm =
770 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
771 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
772 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
776 /// GetIfCondition - Given a basic block (BB) with two predecessors,
777 /// check to see if the merge at this block is due
778 /// to an "if condition". If so, return the boolean condition that determines
779 /// which entry into BB will be taken. Also, return by references the block
780 /// that will be entered from if the condition is true, and the block that will
781 /// be entered if the condition is false.
783 /// This does no checking to see if the true/false blocks have large or unsavory
784 /// instructions in them.
785 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
786 BasicBlock *&IfFalse) {
787 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
788 BasicBlock *Pred1 = nullptr;
789 BasicBlock *Pred2 = nullptr;
792 if (SomePHI->getNumIncomingValues() != 2)
794 Pred1 = SomePHI->getIncomingBlock(0);
795 Pred2 = SomePHI->getIncomingBlock(1);
797 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
798 if (PI == PE) // No predecessor
801 if (PI == PE) // Only one predecessor
804 if (PI != PE) // More than two predecessors
808 // We can only handle branches. Other control flow will be lowered to
809 // branches if possible anyway.
810 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
811 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
812 if (!Pred1Br || !Pred2Br)
815 // Eliminate code duplication by ensuring that Pred1Br is conditional if
817 if (Pred2Br->isConditional()) {
818 // If both branches are conditional, we don't have an "if statement". In
819 // reality, we could transform this case, but since the condition will be
820 // required anyway, we stand no chance of eliminating it, so the xform is
821 // probably not profitable.
822 if (Pred1Br->isConditional())
825 std::swap(Pred1, Pred2);
826 std::swap(Pred1Br, Pred2Br);
829 if (Pred1Br->isConditional()) {
830 // The only thing we have to watch out for here is to make sure that Pred2
831 // doesn't have incoming edges from other blocks. If it does, the condition
832 // doesn't dominate BB.
833 if (!Pred2->getSinglePredecessor())
836 // If we found a conditional branch predecessor, make sure that it branches
837 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
838 if (Pred1Br->getSuccessor(0) == BB &&
839 Pred1Br->getSuccessor(1) == Pred2) {
842 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
843 Pred1Br->getSuccessor(1) == BB) {
847 // We know that one arm of the conditional goes to BB, so the other must
848 // go somewhere unrelated, and this must not be an "if statement".
852 return Pred1Br->getCondition();
855 // Ok, if we got here, both predecessors end with an unconditional branch to
856 // BB. Don't panic! If both blocks only have a single (identical)
857 // predecessor, and THAT is a conditional branch, then we're all ok!
858 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
859 if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
862 // Otherwise, if this is a conditional branch, then we can use it!
863 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
864 if (!BI) return nullptr;
866 assert(BI->isConditional() && "Two successors but not conditional?");
867 if (BI->getSuccessor(0) == Pred1) {
874 return BI->getCondition();