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/ADT/ArrayRef.h"
17 #include "llvm/ADT/SmallPtrSet.h"
18 #include "llvm/ADT/SmallVector.h"
19 #include "llvm/ADT/Twine.h"
20 #include "llvm/Analysis/CFG.h"
21 #include "llvm/Analysis/LoopInfo.h"
22 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
23 #include "llvm/Analysis/MemorySSAUpdater.h"
24 #include "llvm/Analysis/PostDominators.h"
25 #include "llvm/IR/BasicBlock.h"
26 #include "llvm/IR/CFG.h"
27 #include "llvm/IR/Constants.h"
28 #include "llvm/IR/DebugInfoMetadata.h"
29 #include "llvm/IR/DomTreeUpdater.h"
30 #include "llvm/IR/Dominators.h"
31 #include "llvm/IR/Function.h"
32 #include "llvm/IR/InstrTypes.h"
33 #include "llvm/IR/Instruction.h"
34 #include "llvm/IR/Instructions.h"
35 #include "llvm/IR/IntrinsicInst.h"
36 #include "llvm/IR/LLVMContext.h"
37 #include "llvm/IR/Type.h"
38 #include "llvm/IR/User.h"
39 #include "llvm/IR/Value.h"
40 #include "llvm/IR/ValueHandle.h"
41 #include "llvm/Support/Casting.h"
42 #include "llvm/Transforms/Utils/Local.h"
51 void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU) {
52 SmallVector<BasicBlock *, 1> BBs = {BB};
53 DeleteDeadBlocks(BBs, DTU);
56 void llvm::DeleteDeadBlocks(SmallVectorImpl <BasicBlock *> &BBs,
57 DomTreeUpdater *DTU) {
59 // Make sure that all predecessors of each dead block is also dead.
60 SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
61 assert(Dead.size() == BBs.size() && "Duplicating blocks?");
63 for (BasicBlock *Pred : predecessors(BB))
64 assert(Dead.count(Pred) && "All predecessors must be dead!");
67 SmallVector<DominatorTree::UpdateType, 4> Updates;
68 for (auto *BB : BBs) {
69 // Loop through all of our successors and make sure they know that one
70 // of their predecessors is going away.
71 for (BasicBlock *Succ : successors(BB)) {
72 Succ->removePredecessor(BB);
74 Updates.push_back({DominatorTree::Delete, BB, Succ});
77 // Zap all the instructions in the block.
78 while (!BB->empty()) {
79 Instruction &I = BB->back();
80 // If this instruction is used, replace uses with an arbitrary value.
81 // Because control flow can't get here, we don't care what we replace the
82 // value with. Note that since this block is unreachable, and all values
83 // contained within it must dominate their uses, that all uses will
84 // eventually be removed (they are themselves dead).
86 I.replaceAllUsesWith(UndefValue::get(I.getType()));
87 BB->getInstList().pop_back();
89 new UnreachableInst(BB->getContext(), BB);
90 assert(BB->getInstList().size() == 1 &&
91 isa<UnreachableInst>(BB->getTerminator()) &&
92 "The successor list of BB isn't empty before "
93 "applying corresponding DTU updates.");
96 DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
98 for (BasicBlock *BB : BBs)
102 BB->eraseFromParent();
105 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
106 MemoryDependenceResults *MemDep) {
107 if (!isa<PHINode>(BB->begin())) return;
109 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
110 if (PN->getIncomingValue(0) != PN)
111 PN->replaceAllUsesWith(PN->getIncomingValue(0));
113 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
116 MemDep->removeInstruction(PN); // Memdep updates AA itself.
118 PN->eraseFromParent();
122 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
123 // Recursively deleting a PHI may cause multiple PHIs to be deleted
124 // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
125 SmallVector<WeakTrackingVH, 8> PHIs;
126 for (PHINode &PN : BB->phis())
129 bool Changed = false;
130 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
131 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
132 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
137 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
138 LoopInfo *LI, MemorySSAUpdater *MSSAU,
139 MemoryDependenceResults *MemDep) {
140 if (BB->hasAddressTaken())
143 // Can't merge if there are multiple predecessors, or no predecessors.
144 BasicBlock *PredBB = BB->getUniquePredecessor();
145 if (!PredBB) return false;
147 // Don't break self-loops.
148 if (PredBB == BB) return false;
149 // Don't break unwinding instructions.
150 if (PredBB->getTerminator()->isExceptionalTerminator())
153 // Can't merge if there are multiple distinct successors.
154 if (PredBB->getUniqueSuccessor() != BB)
157 // Can't merge if there is PHI loop.
158 for (PHINode &PN : BB->phis())
159 for (Value *IncValue : PN.incoming_values())
163 // Begin by getting rid of unneeded PHIs.
164 SmallVector<AssertingVH<Value>, 4> IncomingValues;
165 if (isa<PHINode>(BB->front())) {
166 for (PHINode &PN : BB->phis())
167 if (!isa<PHINode>(PN.getIncomingValue(0)) ||
168 cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
169 IncomingValues.push_back(PN.getIncomingValue(0));
170 FoldSingleEntryPHINodes(BB, MemDep);
173 // DTU update: Collect all the edges that exit BB.
174 // These dominator edges will be redirected from Pred.
175 std::vector<DominatorTree::UpdateType> Updates;
177 Updates.reserve(1 + (2 * succ_size(BB)));
178 Updates.push_back({DominatorTree::Delete, PredBB, BB});
179 for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I) {
180 Updates.push_back({DominatorTree::Delete, BB, *I});
181 Updates.push_back({DominatorTree::Insert, PredBB, *I});
186 MSSAU->moveAllAfterMergeBlocks(BB, PredBB, &*(BB->begin()));
188 // Delete the unconditional branch from the predecessor...
189 PredBB->getInstList().pop_back();
191 // Make all PHI nodes that referred to BB now refer to Pred as their
193 BB->replaceAllUsesWith(PredBB);
195 // Move all definitions in the successor to the predecessor...
196 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
197 new UnreachableInst(BB->getContext(), BB);
199 // Eliminate duplicate dbg.values describing the entry PHI node post-splice.
200 for (auto Incoming : IncomingValues) {
201 if (isa<Instruction>(*Incoming)) {
202 SmallVector<DbgValueInst *, 2> DbgValues;
203 SmallDenseSet<std::pair<DILocalVariable *, DIExpression *>, 2>
205 llvm::findDbgValues(DbgValues, Incoming);
206 for (auto &DVI : DbgValues) {
207 auto R = DbgValueSet.insert({DVI->getVariable(), DVI->getExpression()});
209 DVI->eraseFromParent();
214 // Inherit predecessors name if it exists.
215 if (!PredBB->hasName())
216 PredBB->takeName(BB);
222 MemDep->invalidateCachedPredecessors();
224 // Finally, erase the old block and update dominator info.
226 assert(BB->getInstList().size() == 1 &&
227 isa<UnreachableInst>(BB->getTerminator()) &&
228 "The successor list of BB isn't empty before "
229 "applying corresponding DTU updates.");
230 DTU->applyUpdates(Updates, /*ForceRemoveDuplicates*/ true);
235 BB->eraseFromParent(); // Nuke BB if DTU is nullptr.
240 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
241 BasicBlock::iterator &BI, Value *V) {
242 Instruction &I = *BI;
243 // Replaces all of the uses of the instruction with uses of the value
244 I.replaceAllUsesWith(V);
246 // Make sure to propagate a name if there is one already.
247 if (I.hasName() && !V->hasName())
250 // Delete the unnecessary instruction now...
254 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
255 BasicBlock::iterator &BI, Instruction *I) {
256 assert(I->getParent() == nullptr &&
257 "ReplaceInstWithInst: Instruction already inserted into basic block!");
259 // Copy debug location to newly added instruction, if it wasn't already set
261 if (!I->getDebugLoc())
262 I->setDebugLoc(BI->getDebugLoc());
264 // Insert the new instruction into the basic block...
265 BasicBlock::iterator New = BIL.insert(BI, I);
267 // Replace all uses of the old instruction, and delete it.
268 ReplaceInstWithValue(BIL, BI, I);
270 // Move BI back to point to the newly inserted instruction
274 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
275 BasicBlock::iterator BI(From);
276 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
279 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
280 LoopInfo *LI, MemorySSAUpdater *MSSAU) {
281 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
283 // If this is a critical edge, let SplitCriticalEdge do it.
284 Instruction *LatchTerm = BB->getTerminator();
285 if (SplitCriticalEdge(
287 CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA()))
288 return LatchTerm->getSuccessor(SuccNum);
290 // If the edge isn't critical, then BB has a single successor or Succ has a
291 // single pred. Split the block.
292 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
293 // If the successor only has a single pred, split the top of the successor
295 assert(SP == BB && "CFG broken");
297 return SplitBlock(Succ, &Succ->front(), DT, LI, MSSAU);
300 // Otherwise, if BB has a single successor, split it at the bottom of the
302 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
303 "Should have a single succ!");
304 return SplitBlock(BB, BB->getTerminator(), DT, LI, MSSAU);
308 llvm::SplitAllCriticalEdges(Function &F,
309 const CriticalEdgeSplittingOptions &Options) {
310 unsigned NumBroken = 0;
311 for (BasicBlock &BB : F) {
312 Instruction *TI = BB.getTerminator();
313 if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
314 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
315 if (SplitCriticalEdge(TI, i, Options))
321 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
322 DominatorTree *DT, LoopInfo *LI,
323 MemorySSAUpdater *MSSAU) {
324 BasicBlock::iterator SplitIt = SplitPt->getIterator();
325 while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
327 BasicBlock *New = Old->splitBasicBlock(SplitIt, Old->getName()+".split");
329 // The new block lives in whichever loop the old one did. This preserves
330 // LCSSA as well, because we force the split point to be after any PHI nodes.
332 if (Loop *L = LI->getLoopFor(Old))
333 L->addBasicBlockToLoop(New, *LI);
336 // Old dominates New. New node dominates all other nodes dominated by Old.
337 if (DomTreeNode *OldNode = DT->getNode(Old)) {
338 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
340 DomTreeNode *NewNode = DT->addNewBlock(New, Old);
341 for (DomTreeNode *I : Children)
342 DT->changeImmediateDominator(I, NewNode);
345 // Move MemoryAccesses still tracked in Old, but part of New now.
346 // Update accesses in successor blocks accordingly.
348 MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
353 /// Update DominatorTree, LoopInfo, and LCCSA analysis information.
354 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
355 ArrayRef<BasicBlock *> Preds,
356 DominatorTree *DT, LoopInfo *LI,
357 MemorySSAUpdater *MSSAU,
358 bool PreserveLCSSA, bool &HasLoopExit) {
359 // Update dominator tree if available.
361 if (OldBB == DT->getRootNode()->getBlock()) {
362 assert(NewBB == &NewBB->getParent()->getEntryBlock());
363 DT->setNewRoot(NewBB);
365 // Split block expects NewBB to have a non-empty set of predecessors.
366 DT->splitBlock(NewBB);
370 // Update MemoryPhis after split if MemorySSA is available
372 MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
374 // The rest of the logic is only relevant for updating the loop structures.
378 assert(DT && "DT should be available to update LoopInfo!");
379 Loop *L = LI->getLoopFor(OldBB);
381 // If we need to preserve loop analyses, collect some information about how
382 // this split will affect loops.
383 bool IsLoopEntry = !!L;
384 bool SplitMakesNewLoopHeader = false;
385 for (BasicBlock *Pred : Preds) {
386 // Preds that are not reachable from entry should not be used to identify if
387 // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
388 // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
389 // as true and make the NewBB the header of some loop. This breaks LI.
390 if (!DT->isReachableFromEntry(Pred))
392 // If we need to preserve LCSSA, determine if any of the preds is a loop
395 if (Loop *PL = LI->getLoopFor(Pred))
396 if (!PL->contains(OldBB))
399 // If we need to preserve LoopInfo, note whether any of the preds crosses
400 // an interesting loop boundary.
403 if (L->contains(Pred))
406 SplitMakesNewLoopHeader = true;
409 // Unless we have a loop for OldBB, nothing else to do here.
414 // Add the new block to the nearest enclosing loop (and not an adjacent
415 // loop). To find this, examine each of the predecessors and determine which
416 // loops enclose them, and select the most-nested loop which contains the
417 // loop containing the block being split.
418 Loop *InnermostPredLoop = nullptr;
419 for (BasicBlock *Pred : Preds) {
420 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
421 // Seek a loop which actually contains the block being split (to avoid
423 while (PredLoop && !PredLoop->contains(OldBB))
424 PredLoop = PredLoop->getParentLoop();
426 // Select the most-nested of these loops which contains the block.
427 if (PredLoop && PredLoop->contains(OldBB) &&
428 (!InnermostPredLoop ||
429 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
430 InnermostPredLoop = PredLoop;
434 if (InnermostPredLoop)
435 InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
437 L->addBasicBlockToLoop(NewBB, *LI);
438 if (SplitMakesNewLoopHeader)
439 L->moveToHeader(NewBB);
443 /// Update the PHI nodes in OrigBB to include the values coming from NewBB.
444 /// This also updates AliasAnalysis, if available.
445 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
446 ArrayRef<BasicBlock *> Preds, BranchInst *BI,
448 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
449 SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
450 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
451 PHINode *PN = cast<PHINode>(I++);
453 // Check to see if all of the values coming in are the same. If so, we
454 // don't need to create a new PHI node, unless it's needed for LCSSA.
455 Value *InVal = nullptr;
457 InVal = PN->getIncomingValueForBlock(Preds[0]);
458 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
459 if (!PredSet.count(PN->getIncomingBlock(i)))
462 InVal = PN->getIncomingValue(i);
463 else if (InVal != PN->getIncomingValue(i)) {
471 // If all incoming values for the new PHI would be the same, just don't
472 // make a new PHI. Instead, just remove the incoming values from the old
475 // NOTE! This loop walks backwards for a reason! First off, this minimizes
476 // the cost of removal if we end up removing a large number of values, and
477 // second off, this ensures that the indices for the incoming values
478 // aren't invalidated when we remove one.
479 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
480 if (PredSet.count(PN->getIncomingBlock(i)))
481 PN->removeIncomingValue(i, false);
483 // Add an incoming value to the PHI node in the loop for the preheader
485 PN->addIncoming(InVal, NewBB);
489 // If the values coming into the block are not the same, we need a new
491 // Create the new PHI node, insert it into NewBB at the end of the block
493 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
495 // NOTE! This loop walks backwards for a reason! First off, this minimizes
496 // the cost of removal if we end up removing a large number of values, and
497 // second off, this ensures that the indices for the incoming values aren't
498 // invalidated when we remove one.
499 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
500 BasicBlock *IncomingBB = PN->getIncomingBlock(i);
501 if (PredSet.count(IncomingBB)) {
502 Value *V = PN->removeIncomingValue(i, false);
503 NewPHI->addIncoming(V, IncomingBB);
507 PN->addIncoming(NewPHI, NewBB);
511 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
512 ArrayRef<BasicBlock *> Preds,
513 const char *Suffix, DominatorTree *DT,
514 LoopInfo *LI, MemorySSAUpdater *MSSAU,
515 bool PreserveLCSSA) {
516 // Do not attempt to split that which cannot be split.
517 if (!BB->canSplitPredecessors())
520 // For the landingpads we need to act a bit differently.
521 // Delegate this work to the SplitLandingPadPredecessors.
522 if (BB->isLandingPad()) {
523 SmallVector<BasicBlock*, 2> NewBBs;
524 std::string NewName = std::string(Suffix) + ".split-lp";
526 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
527 LI, MSSAU, PreserveLCSSA);
531 // Create new basic block, insert right before the original block.
532 BasicBlock *NewBB = BasicBlock::Create(
533 BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
535 // The new block unconditionally branches to the old block.
536 BranchInst *BI = BranchInst::Create(BB, NewBB);
537 BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
539 // Move the edges from Preds to point to NewBB instead of BB.
540 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
541 // This is slightly more strict than necessary; the minimum requirement
542 // is that there be no more than one indirectbr branching to BB. And
543 // all BlockAddress uses would need to be updated.
544 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
545 "Cannot split an edge from an IndirectBrInst");
546 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
549 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
550 // node becomes an incoming value for BB's phi node. However, if the Preds
551 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
552 // account for the newly created predecessor.
554 // Insert dummy values as the incoming value.
555 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
556 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
559 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
560 bool HasLoopExit = false;
561 UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, MSSAU, PreserveLCSSA,
564 if (!Preds.empty()) {
565 // Update the PHI nodes in BB with the values coming from NewBB.
566 UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
572 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
573 ArrayRef<BasicBlock *> Preds,
574 const char *Suffix1, const char *Suffix2,
575 SmallVectorImpl<BasicBlock *> &NewBBs,
576 DominatorTree *DT, LoopInfo *LI,
577 MemorySSAUpdater *MSSAU,
578 bool PreserveLCSSA) {
579 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
581 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
582 // it right before the original block.
583 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
584 OrigBB->getName() + Suffix1,
585 OrigBB->getParent(), OrigBB);
586 NewBBs.push_back(NewBB1);
588 // The new block unconditionally branches to the old block.
589 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
590 BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
592 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
593 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
594 // This is slightly more strict than necessary; the minimum requirement
595 // is that there be no more than one indirectbr branching to BB. And
596 // all BlockAddress uses would need to be updated.
597 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
598 "Cannot split an edge from an IndirectBrInst");
599 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
602 bool HasLoopExit = false;
603 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, MSSAU, PreserveLCSSA,
606 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
607 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
609 // Move the remaining edges from OrigBB to point to NewBB2.
610 SmallVector<BasicBlock*, 8> NewBB2Preds;
611 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
613 BasicBlock *Pred = *i++;
614 if (Pred == NewBB1) continue;
615 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
616 "Cannot split an edge from an IndirectBrInst");
617 NewBB2Preds.push_back(Pred);
618 e = pred_end(OrigBB);
621 BasicBlock *NewBB2 = nullptr;
622 if (!NewBB2Preds.empty()) {
623 // Create another basic block for the rest of OrigBB's predecessors.
624 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
625 OrigBB->getName() + Suffix2,
626 OrigBB->getParent(), OrigBB);
627 NewBBs.push_back(NewBB2);
629 // The new block unconditionally branches to the old block.
630 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
631 BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
633 // Move the remaining edges from OrigBB to point to NewBB2.
634 for (BasicBlock *NewBB2Pred : NewBB2Preds)
635 NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
637 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
639 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI, MSSAU,
640 PreserveLCSSA, HasLoopExit);
642 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
643 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
646 LandingPadInst *LPad = OrigBB->getLandingPadInst();
647 Instruction *Clone1 = LPad->clone();
648 Clone1->setName(Twine("lpad") + Suffix1);
649 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
652 Instruction *Clone2 = LPad->clone();
653 Clone2->setName(Twine("lpad") + Suffix2);
654 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
656 // Create a PHI node for the two cloned landingpad instructions only
657 // if the original landingpad instruction has some uses.
658 if (!LPad->use_empty()) {
659 assert(!LPad->getType()->isTokenTy() &&
660 "Split cannot be applied if LPad is token type. Otherwise an "
661 "invalid PHINode of token type would be created.");
662 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
663 PN->addIncoming(Clone1, NewBB1);
664 PN->addIncoming(Clone2, NewBB2);
665 LPad->replaceAllUsesWith(PN);
667 LPad->eraseFromParent();
669 // There is no second clone. Just replace the landing pad with the first
671 LPad->replaceAllUsesWith(Clone1);
672 LPad->eraseFromParent();
676 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
678 DomTreeUpdater *DTU) {
679 Instruction *UncondBranch = Pred->getTerminator();
680 // Clone the return and add it to the end of the predecessor.
681 Instruction *NewRet = RI->clone();
682 Pred->getInstList().push_back(NewRet);
684 // If the return instruction returns a value, and if the value was a
685 // PHI node in "BB", propagate the right value into the return.
686 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
689 Instruction *NewBC = nullptr;
690 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
691 // Return value might be bitcasted. Clone and insert it before the
692 // return instruction.
693 V = BCI->getOperand(0);
694 NewBC = BCI->clone();
695 Pred->getInstList().insert(NewRet->getIterator(), NewBC);
698 if (PHINode *PN = dyn_cast<PHINode>(V)) {
699 if (PN->getParent() == BB) {
701 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
703 *i = PN->getIncomingValueForBlock(Pred);
708 // Update any PHI nodes in the returning block to realize that we no
709 // longer branch to them.
710 BB->removePredecessor(Pred);
711 UncondBranch->eraseFromParent();
714 DTU->deleteEdge(Pred, BB);
716 return cast<ReturnInst>(NewRet);
719 Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
720 Instruction *SplitBefore,
722 MDNode *BranchWeights,
723 DominatorTree *DT, LoopInfo *LI) {
724 BasicBlock *Head = SplitBefore->getParent();
725 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
726 Instruction *HeadOldTerm = Head->getTerminator();
727 LLVMContext &C = Head->getContext();
728 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
729 Instruction *CheckTerm;
731 CheckTerm = new UnreachableInst(C, ThenBlock);
733 CheckTerm = BranchInst::Create(Tail, ThenBlock);
734 CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
735 BranchInst *HeadNewTerm =
736 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
737 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
738 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
741 if (DomTreeNode *OldNode = DT->getNode(Head)) {
742 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
744 DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
745 for (DomTreeNode *Child : Children)
746 DT->changeImmediateDominator(Child, NewNode);
748 // Head dominates ThenBlock.
749 DT->addNewBlock(ThenBlock, Head);
754 if (Loop *L = LI->getLoopFor(Head)) {
755 L->addBasicBlockToLoop(ThenBlock, *LI);
756 L->addBasicBlockToLoop(Tail, *LI);
763 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
764 Instruction **ThenTerm,
765 Instruction **ElseTerm,
766 MDNode *BranchWeights) {
767 BasicBlock *Head = SplitBefore->getParent();
768 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
769 Instruction *HeadOldTerm = Head->getTerminator();
770 LLVMContext &C = Head->getContext();
771 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
772 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
773 *ThenTerm = BranchInst::Create(Tail, ThenBlock);
774 (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
775 *ElseTerm = BranchInst::Create(Tail, ElseBlock);
776 (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
777 BranchInst *HeadNewTerm =
778 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
779 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
780 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
783 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
784 BasicBlock *&IfFalse) {
785 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
786 BasicBlock *Pred1 = nullptr;
787 BasicBlock *Pred2 = nullptr;
790 if (SomePHI->getNumIncomingValues() != 2)
792 Pred1 = SomePHI->getIncomingBlock(0);
793 Pred2 = SomePHI->getIncomingBlock(1);
795 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
796 if (PI == PE) // No predecessor
799 if (PI == PE) // Only one predecessor
802 if (PI != PE) // More than two predecessors
806 // We can only handle branches. Other control flow will be lowered to
807 // branches if possible anyway.
808 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
809 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
810 if (!Pred1Br || !Pred2Br)
813 // Eliminate code duplication by ensuring that Pred1Br is conditional if
815 if (Pred2Br->isConditional()) {
816 // If both branches are conditional, we don't have an "if statement". In
817 // reality, we could transform this case, but since the condition will be
818 // required anyway, we stand no chance of eliminating it, so the xform is
819 // probably not profitable.
820 if (Pred1Br->isConditional())
823 std::swap(Pred1, Pred2);
824 std::swap(Pred1Br, Pred2Br);
827 if (Pred1Br->isConditional()) {
828 // The only thing we have to watch out for here is to make sure that Pred2
829 // doesn't have incoming edges from other blocks. If it does, the condition
830 // doesn't dominate BB.
831 if (!Pred2->getSinglePredecessor())
834 // If we found a conditional branch predecessor, make sure that it branches
835 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
836 if (Pred1Br->getSuccessor(0) == BB &&
837 Pred1Br->getSuccessor(1) == Pred2) {
840 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
841 Pred1Br->getSuccessor(1) == BB) {
845 // We know that one arm of the conditional goes to BB, so the other must
846 // go somewhere unrelated, and this must not be an "if statement".
850 return Pred1Br->getCondition();
853 // Ok, if we got here, both predecessors end with an unconditional branch to
854 // BB. Don't panic! If both blocks only have a single (identical)
855 // predecessor, and THAT is a conditional branch, then we're all ok!
856 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
857 if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
860 // Otherwise, if this is a conditional branch, then we can use it!
861 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
862 if (!BI) return nullptr;
864 assert(BI->isConditional() && "Two successors but not conditional?");
865 if (BI->getSuccessor(0) == Pred1) {
872 return BI->getCondition();