1 //===- BasicBlockUtils.cpp - BasicBlock Utilities --------------------------==//
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
7 //===----------------------------------------------------------------------===//
9 // This family of functions perform manipulations on basic blocks, and
10 // instructions contained within basic blocks.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
15 #include "llvm/ADT/ArrayRef.h"
16 #include "llvm/ADT/SmallPtrSet.h"
17 #include "llvm/ADT/SmallVector.h"
18 #include "llvm/ADT/Twine.h"
19 #include "llvm/Analysis/CFG.h"
20 #include "llvm/Analysis/DomTreeUpdater.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/Dominators.h"
30 #include "llvm/IR/Function.h"
31 #include "llvm/IR/InstrTypes.h"
32 #include "llvm/IR/Instruction.h"
33 #include "llvm/IR/Instructions.h"
34 #include "llvm/IR/IntrinsicInst.h"
35 #include "llvm/IR/LLVMContext.h"
36 #include "llvm/IR/Type.h"
37 #include "llvm/IR/User.h"
38 #include "llvm/IR/Value.h"
39 #include "llvm/IR/ValueHandle.h"
40 #include "llvm/Support/Casting.h"
41 #include "llvm/Support/Debug.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include "llvm/Transforms/Utils/Local.h"
52 #define DEBUG_TYPE "basicblock-utils"
54 void llvm::DetatchDeadBlocks(
55 ArrayRef<BasicBlock *> BBs,
56 SmallVectorImpl<DominatorTree::UpdateType> *Updates,
57 bool KeepOneInputPHIs) {
58 for (auto *BB : BBs) {
59 // Loop through all of our successors and make sure they know that one
60 // of their predecessors is going away.
61 SmallPtrSet<BasicBlock *, 4> UniqueSuccessors;
62 for (BasicBlock *Succ : successors(BB)) {
63 Succ->removePredecessor(BB, KeepOneInputPHIs);
64 if (Updates && UniqueSuccessors.insert(Succ).second)
65 Updates->push_back({DominatorTree::Delete, BB, Succ});
68 // Zap all the instructions in the block.
69 while (!BB->empty()) {
70 Instruction &I = BB->back();
71 // If this instruction is used, replace uses with an arbitrary value.
72 // Because control flow can't get here, we don't care what we replace the
73 // value with. Note that since this block is unreachable, and all values
74 // contained within it must dominate their uses, that all uses will
75 // eventually be removed (they are themselves dead).
77 I.replaceAllUsesWith(UndefValue::get(I.getType()));
78 BB->getInstList().pop_back();
80 new UnreachableInst(BB->getContext(), BB);
81 assert(BB->getInstList().size() == 1 &&
82 isa<UnreachableInst>(BB->getTerminator()) &&
83 "The successor list of BB isn't empty before "
84 "applying corresponding DTU updates.");
88 void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU,
89 bool KeepOneInputPHIs) {
90 DeleteDeadBlocks({BB}, DTU, KeepOneInputPHIs);
93 void llvm::DeleteDeadBlocks(ArrayRef <BasicBlock *> BBs, DomTreeUpdater *DTU,
94 bool KeepOneInputPHIs) {
96 // Make sure that all predecessors of each dead block is also dead.
97 SmallPtrSet<BasicBlock *, 4> Dead(BBs.begin(), BBs.end());
98 assert(Dead.size() == BBs.size() && "Duplicating blocks?");
100 for (BasicBlock *Pred : predecessors(BB))
101 assert(Dead.count(Pred) && "All predecessors must be dead!");
104 SmallVector<DominatorTree::UpdateType, 4> Updates;
105 DetatchDeadBlocks(BBs, DTU ? &Updates : nullptr, KeepOneInputPHIs);
108 DTU->applyUpdatesPermissive(Updates);
110 for (BasicBlock *BB : BBs)
114 BB->eraseFromParent();
117 bool llvm::EliminateUnreachableBlocks(Function &F, DomTreeUpdater *DTU,
118 bool KeepOneInputPHIs) {
119 df_iterator_default_set<BasicBlock*> Reachable;
121 // Mark all reachable blocks.
122 for (BasicBlock *BB : depth_first_ext(&F, Reachable))
123 (void)BB/* Mark all reachable blocks */;
125 // Collect all dead blocks.
126 std::vector<BasicBlock*> DeadBlocks;
127 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
128 if (!Reachable.count(&*I)) {
129 BasicBlock *BB = &*I;
130 DeadBlocks.push_back(BB);
133 // Delete the dead blocks.
134 DeleteDeadBlocks(DeadBlocks, DTU, KeepOneInputPHIs);
136 return !DeadBlocks.empty();
139 void llvm::FoldSingleEntryPHINodes(BasicBlock *BB,
140 MemoryDependenceResults *MemDep) {
141 if (!isa<PHINode>(BB->begin())) return;
143 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
144 if (PN->getIncomingValue(0) != PN)
145 PN->replaceAllUsesWith(PN->getIncomingValue(0));
147 PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
150 MemDep->removeInstruction(PN); // Memdep updates AA itself.
152 PN->eraseFromParent();
156 bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI,
157 MemorySSAUpdater *MSSAU) {
158 // Recursively deleting a PHI may cause multiple PHIs to be deleted
159 // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
160 SmallVector<WeakTrackingVH, 8> PHIs;
161 for (PHINode &PN : BB->phis())
164 bool Changed = false;
165 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
166 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
167 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI, MSSAU);
172 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
173 LoopInfo *LI, MemorySSAUpdater *MSSAU,
174 MemoryDependenceResults *MemDep,
175 bool PredecessorWithTwoSuccessors) {
176 if (BB->hasAddressTaken())
179 // Can't merge if there are multiple predecessors, or no predecessors.
180 BasicBlock *PredBB = BB->getUniquePredecessor();
181 if (!PredBB) return false;
183 // Don't break self-loops.
184 if (PredBB == BB) return false;
185 // Don't break unwinding instructions.
186 if (PredBB->getTerminator()->isExceptionalTerminator())
189 // Can't merge if there are multiple distinct successors.
190 if (!PredecessorWithTwoSuccessors && PredBB->getUniqueSuccessor() != BB)
193 // Currently only allow PredBB to have two predecessors, one being BB.
194 // Update BI to branch to BB's only successor instead of BB.
195 BranchInst *PredBB_BI;
196 BasicBlock *NewSucc = nullptr;
197 unsigned FallThruPath;
198 if (PredecessorWithTwoSuccessors) {
199 if (!(PredBB_BI = dyn_cast<BranchInst>(PredBB->getTerminator())))
201 BranchInst *BB_JmpI = dyn_cast<BranchInst>(BB->getTerminator());
202 if (!BB_JmpI || !BB_JmpI->isUnconditional())
204 NewSucc = BB_JmpI->getSuccessor(0);
205 FallThruPath = PredBB_BI->getSuccessor(0) == BB ? 0 : 1;
208 // Can't merge if there is PHI loop.
209 for (PHINode &PN : BB->phis())
210 for (Value *IncValue : PN.incoming_values())
214 LLVM_DEBUG(dbgs() << "Merging: " << BB->getName() << " into "
215 << PredBB->getName() << "\n");
217 // Begin by getting rid of unneeded PHIs.
218 SmallVector<AssertingVH<Value>, 4> IncomingValues;
219 if (isa<PHINode>(BB->front())) {
220 for (PHINode &PN : BB->phis())
221 if (!isa<PHINode>(PN.getIncomingValue(0)) ||
222 cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
223 IncomingValues.push_back(PN.getIncomingValue(0));
224 FoldSingleEntryPHINodes(BB, MemDep);
227 // DTU update: Collect all the edges that exit BB.
228 // These dominator edges will be redirected from Pred.
229 std::vector<DominatorTree::UpdateType> Updates;
231 Updates.reserve(1 + (2 * succ_size(BB)));
232 // Add insert edges first. Experimentally, for the particular case of two
233 // blocks that can be merged, with a single successor and single predecessor
234 // respectively, it is beneficial to have all insert updates first. Deleting
235 // edges first may lead to unreachable blocks, followed by inserting edges
236 // making the blocks reachable again. Such DT updates lead to high compile
237 // times. We add inserts before deletes here to reduce compile time.
238 for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
239 // This successor of BB may already have PredBB as a predecessor.
240 if (llvm::find(successors(PredBB), *I) == succ_end(PredBB))
241 Updates.push_back({DominatorTree::Insert, PredBB, *I});
242 for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
243 Updates.push_back({DominatorTree::Delete, BB, *I});
244 Updates.push_back({DominatorTree::Delete, PredBB, BB});
247 Instruction *PTI = PredBB->getTerminator();
248 Instruction *STI = BB->getTerminator();
249 Instruction *Start = &*BB->begin();
250 // If there's nothing to move, mark the starting instruction as the last
251 // instruction in the block. Terminator instruction is handled separately.
255 // Move all definitions in the successor to the predecessor...
256 PredBB->getInstList().splice(PTI->getIterator(), BB->getInstList(),
257 BB->begin(), STI->getIterator());
260 MSSAU->moveAllAfterMergeBlocks(BB, PredBB, Start);
262 // Make all PHI nodes that referred to BB now refer to Pred as their
264 BB->replaceAllUsesWith(PredBB);
266 if (PredecessorWithTwoSuccessors) {
267 // Delete the unconditional branch from BB.
268 BB->getInstList().pop_back();
270 // Update branch in the predecessor.
271 PredBB_BI->setSuccessor(FallThruPath, NewSucc);
273 // Delete the unconditional branch from the predecessor.
274 PredBB->getInstList().pop_back();
276 // Move terminator instruction.
277 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
279 // Terminator may be a memory accessing instruction too.
281 if (MemoryUseOrDef *MUD = cast_or_null<MemoryUseOrDef>(
282 MSSAU->getMemorySSA()->getMemoryAccess(PredBB->getTerminator())))
283 MSSAU->moveToPlace(MUD, PredBB, MemorySSA::End);
285 // Add unreachable to now empty BB.
286 new UnreachableInst(BB->getContext(), BB);
288 // Eliminate duplicate/redundant dbg.values. This seems to be a good place to
289 // do that since we might end up with redundant dbg.values describing the
290 // entry PHI node post-splice.
291 RemoveRedundantDbgInstrs(PredBB);
293 // Inherit predecessors name if it exists.
294 if (!PredBB->hasName())
295 PredBB->takeName(BB);
301 MemDep->invalidateCachedPredecessors();
303 // Finally, erase the old block and update dominator info.
305 assert(BB->getInstList().size() == 1 &&
306 isa<UnreachableInst>(BB->getTerminator()) &&
307 "The successor list of BB isn't empty before "
308 "applying corresponding DTU updates.");
309 DTU->applyUpdatesPermissive(Updates);
312 BB->eraseFromParent(); // Nuke BB if DTU is nullptr.
318 bool llvm::MergeBlockSuccessorsIntoGivenBlocks(
319 SmallPtrSetImpl<BasicBlock *> &MergeBlocks, Loop *L, DomTreeUpdater *DTU,
321 assert(!MergeBlocks.empty() && "MergeBlocks should not be empty");
323 bool BlocksHaveBeenMerged = false;
324 while (!MergeBlocks.empty()) {
325 BasicBlock *BB = *MergeBlocks.begin();
326 BasicBlock *Dest = BB->getSingleSuccessor();
327 if (Dest && (!L || L->contains(Dest))) {
328 BasicBlock *Fold = Dest->getUniquePredecessor();
330 if (MergeBlockIntoPredecessor(Dest, DTU, LI)) {
332 "Expecting BB to be unique predecessor of the Dest block");
333 MergeBlocks.erase(Dest);
334 BlocksHaveBeenMerged = true;
336 MergeBlocks.erase(BB);
338 MergeBlocks.erase(BB);
340 return BlocksHaveBeenMerged;
343 /// Remove redundant instructions within sequences of consecutive dbg.value
344 /// instructions. This is done using a backward scan to keep the last dbg.value
345 /// describing a specific variable/fragment.
347 /// BackwardScan strategy:
348 /// ----------------------
349 /// Given a sequence of consecutive DbgValueInst like this
351 /// dbg.value ..., "x", FragmentX1 (*)
352 /// dbg.value ..., "y", FragmentY1
353 /// dbg.value ..., "x", FragmentX2
354 /// dbg.value ..., "x", FragmentX1 (**)
356 /// then the instruction marked with (*) can be removed (it is guaranteed to be
357 /// obsoleted by the instruction marked with (**) as the latter instruction is
358 /// describing the same variable using the same fragment info).
360 /// Possible improvements:
361 /// - Check fully overlapping fragments and not only identical fragments.
362 /// - Support dbg.addr, dbg.declare. dbg.label, and possibly other meta
363 /// instructions being part of the sequence of consecutive instructions.
364 static bool removeRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
365 SmallVector<DbgValueInst *, 8> ToBeRemoved;
366 SmallDenseSet<DebugVariable> VariableSet;
367 for (auto &I : reverse(*BB)) {
368 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
369 DebugVariable Key(DVI->getVariable(),
370 DVI->getExpression(),
371 DVI->getDebugLoc()->getInlinedAt());
372 auto R = VariableSet.insert(Key);
373 // If the same variable fragment is described more than once it is enough
374 // to keep the last one (i.e. the first found since we for reverse
377 ToBeRemoved.push_back(DVI);
380 // Sequence with consecutive dbg.value instrs ended. Clear the map to
381 // restart identifying redundant instructions if case we find another
382 // dbg.value sequence.
386 for (auto &Instr : ToBeRemoved)
387 Instr->eraseFromParent();
389 return !ToBeRemoved.empty();
392 /// Remove redundant dbg.value instructions using a forward scan. This can
393 /// remove a dbg.value instruction that is redundant due to indicating that a
394 /// variable has the same value as already being indicated by an earlier
397 /// ForwardScan strategy:
398 /// ---------------------
399 /// Given two identical dbg.value instructions, separated by a block of
400 /// instructions that isn't describing the same variable, like this
402 /// dbg.value X1, "x", FragmentX1 (**)
403 /// <block of instructions, none being "dbg.value ..., "x", ...">
404 /// dbg.value X1, "x", FragmentX1 (*)
406 /// then the instruction marked with (*) can be removed. Variable "x" is already
407 /// described as being mapped to the SSA value X1.
409 /// Possible improvements:
410 /// - Keep track of non-overlapping fragments.
411 static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
412 SmallVector<DbgValueInst *, 8> ToBeRemoved;
413 DenseMap<DebugVariable, std::pair<Value *, DIExpression *> > VariableMap;
414 for (auto &I : *BB) {
415 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
416 DebugVariable Key(DVI->getVariable(),
418 DVI->getDebugLoc()->getInlinedAt());
419 auto VMI = VariableMap.find(Key);
420 // Update the map if we found a new value/expression describing the
421 // variable, or if the variable wasn't mapped already.
422 if (VMI == VariableMap.end() ||
423 VMI->second.first != DVI->getValue() ||
424 VMI->second.second != DVI->getExpression()) {
425 VariableMap[Key] = { DVI->getValue(), DVI->getExpression() };
428 // Found an identical mapping. Remember the instruction for later removal.
429 ToBeRemoved.push_back(DVI);
433 for (auto &Instr : ToBeRemoved)
434 Instr->eraseFromParent();
436 return !ToBeRemoved.empty();
439 bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB) {
440 bool MadeChanges = false;
441 // By using the "backward scan" strategy before the "forward scan" strategy we
442 // can remove both dbg.value (2) and (3) in a situation like this:
444 // (1) dbg.value V1, "x", DIExpression()
446 // (2) dbg.value V2, "x", DIExpression()
447 // (3) dbg.value V1, "x", DIExpression()
449 // The backward scan will remove (2), it is made obsolete by (3). After
450 // getting (2) out of the way, the foward scan will remove (3) since "x"
451 // already is described as having the value V1 at (1).
452 MadeChanges |= removeRedundantDbgInstrsUsingBackwardScan(BB);
453 MadeChanges |= removeRedundantDbgInstrsUsingForwardScan(BB);
456 LLVM_DEBUG(dbgs() << "Removed redundant dbg instrs from: "
457 << BB->getName() << "\n");
461 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
462 BasicBlock::iterator &BI, Value *V) {
463 Instruction &I = *BI;
464 // Replaces all of the uses of the instruction with uses of the value
465 I.replaceAllUsesWith(V);
467 // Make sure to propagate a name if there is one already.
468 if (I.hasName() && !V->hasName())
471 // Delete the unnecessary instruction now...
475 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
476 BasicBlock::iterator &BI, Instruction *I) {
477 assert(I->getParent() == nullptr &&
478 "ReplaceInstWithInst: Instruction already inserted into basic block!");
480 // Copy debug location to newly added instruction, if it wasn't already set
482 if (!I->getDebugLoc())
483 I->setDebugLoc(BI->getDebugLoc());
485 // Insert the new instruction into the basic block...
486 BasicBlock::iterator New = BIL.insert(BI, I);
488 // Replace all uses of the old instruction, and delete it.
489 ReplaceInstWithValue(BIL, BI, I);
491 // Move BI back to point to the newly inserted instruction
495 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
496 BasicBlock::iterator BI(From);
497 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
500 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
501 LoopInfo *LI, MemorySSAUpdater *MSSAU) {
502 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
504 // If this is a critical edge, let SplitCriticalEdge do it.
505 Instruction *LatchTerm = BB->getTerminator();
506 if (SplitCriticalEdge(
508 CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA()))
509 return LatchTerm->getSuccessor(SuccNum);
511 // If the edge isn't critical, then BB has a single successor or Succ has a
512 // single pred. Split the block.
513 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
514 // If the successor only has a single pred, split the top of the successor
516 assert(SP == BB && "CFG broken");
518 return SplitBlock(Succ, &Succ->front(), DT, LI, MSSAU);
521 // Otherwise, if BB has a single successor, split it at the bottom of the
523 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
524 "Should have a single succ!");
525 return SplitBlock(BB, BB->getTerminator(), DT, LI, MSSAU);
529 llvm::SplitAllCriticalEdges(Function &F,
530 const CriticalEdgeSplittingOptions &Options) {
531 unsigned NumBroken = 0;
532 for (BasicBlock &BB : F) {
533 Instruction *TI = BB.getTerminator();
534 if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI) &&
535 !isa<CallBrInst>(TI))
536 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
537 if (SplitCriticalEdge(TI, i, Options))
543 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
544 DominatorTree *DT, LoopInfo *LI,
545 MemorySSAUpdater *MSSAU, const Twine &BBName) {
546 BasicBlock::iterator SplitIt = SplitPt->getIterator();
547 while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
549 std::string Name = BBName.str();
550 BasicBlock *New = Old->splitBasicBlock(
551 SplitIt, Name.empty() ? Old->getName() + ".split" : Name);
553 // The new block lives in whichever loop the old one did. This preserves
554 // LCSSA as well, because we force the split point to be after any PHI nodes.
556 if (Loop *L = LI->getLoopFor(Old))
557 L->addBasicBlockToLoop(New, *LI);
560 // Old dominates New. New node dominates all other nodes dominated by Old.
561 if (DomTreeNode *OldNode = DT->getNode(Old)) {
562 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
564 DomTreeNode *NewNode = DT->addNewBlock(New, Old);
565 for (DomTreeNode *I : Children)
566 DT->changeImmediateDominator(I, NewNode);
569 // Move MemoryAccesses still tracked in Old, but part of New now.
570 // Update accesses in successor blocks accordingly.
572 MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
577 /// Update DominatorTree, LoopInfo, and LCCSA analysis information.
578 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
579 ArrayRef<BasicBlock *> Preds,
580 DominatorTree *DT, LoopInfo *LI,
581 MemorySSAUpdater *MSSAU,
582 bool PreserveLCSSA, bool &HasLoopExit) {
583 // Update dominator tree if available.
585 if (OldBB == DT->getRootNode()->getBlock()) {
586 assert(NewBB == &NewBB->getParent()->getEntryBlock());
587 DT->setNewRoot(NewBB);
589 // Split block expects NewBB to have a non-empty set of predecessors.
590 DT->splitBlock(NewBB);
594 // Update MemoryPhis after split if MemorySSA is available
596 MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
598 // The rest of the logic is only relevant for updating the loop structures.
602 assert(DT && "DT should be available to update LoopInfo!");
603 Loop *L = LI->getLoopFor(OldBB);
605 // If we need to preserve loop analyses, collect some information about how
606 // this split will affect loops.
607 bool IsLoopEntry = !!L;
608 bool SplitMakesNewLoopHeader = false;
609 for (BasicBlock *Pred : Preds) {
610 // Preds that are not reachable from entry should not be used to identify if
611 // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
612 // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
613 // as true and make the NewBB the header of some loop. This breaks LI.
614 if (!DT->isReachableFromEntry(Pred))
616 // If we need to preserve LCSSA, determine if any of the preds is a loop
619 if (Loop *PL = LI->getLoopFor(Pred))
620 if (!PL->contains(OldBB))
623 // If we need to preserve LoopInfo, note whether any of the preds crosses
624 // an interesting loop boundary.
627 if (L->contains(Pred))
630 SplitMakesNewLoopHeader = true;
633 // Unless we have a loop for OldBB, nothing else to do here.
638 // Add the new block to the nearest enclosing loop (and not an adjacent
639 // loop). To find this, examine each of the predecessors and determine which
640 // loops enclose them, and select the most-nested loop which contains the
641 // loop containing the block being split.
642 Loop *InnermostPredLoop = nullptr;
643 for (BasicBlock *Pred : Preds) {
644 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
645 // Seek a loop which actually contains the block being split (to avoid
647 while (PredLoop && !PredLoop->contains(OldBB))
648 PredLoop = PredLoop->getParentLoop();
650 // Select the most-nested of these loops which contains the block.
651 if (PredLoop && PredLoop->contains(OldBB) &&
652 (!InnermostPredLoop ||
653 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
654 InnermostPredLoop = PredLoop;
658 if (InnermostPredLoop)
659 InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
661 L->addBasicBlockToLoop(NewBB, *LI);
662 if (SplitMakesNewLoopHeader)
663 L->moveToHeader(NewBB);
667 /// Update the PHI nodes in OrigBB to include the values coming from NewBB.
668 /// This also updates AliasAnalysis, if available.
669 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
670 ArrayRef<BasicBlock *> Preds, BranchInst *BI,
672 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
673 SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
674 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
675 PHINode *PN = cast<PHINode>(I++);
677 // Check to see if all of the values coming in are the same. If so, we
678 // don't need to create a new PHI node, unless it's needed for LCSSA.
679 Value *InVal = nullptr;
681 InVal = PN->getIncomingValueForBlock(Preds[0]);
682 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
683 if (!PredSet.count(PN->getIncomingBlock(i)))
686 InVal = PN->getIncomingValue(i);
687 else if (InVal != PN->getIncomingValue(i)) {
695 // If all incoming values for the new PHI would be the same, just don't
696 // make a new PHI. Instead, just remove the incoming values from the old
699 // NOTE! This loop walks backwards for a reason! First off, this minimizes
700 // the cost of removal if we end up removing a large number of values, and
701 // second off, this ensures that the indices for the incoming values
702 // aren't invalidated when we remove one.
703 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
704 if (PredSet.count(PN->getIncomingBlock(i)))
705 PN->removeIncomingValue(i, false);
707 // Add an incoming value to the PHI node in the loop for the preheader
709 PN->addIncoming(InVal, NewBB);
713 // If the values coming into the block are not the same, we need a new
715 // Create the new PHI node, insert it into NewBB at the end of the block
717 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
719 // NOTE! This loop walks backwards for a reason! First off, this minimizes
720 // the cost of removal if we end up removing a large number of values, and
721 // second off, this ensures that the indices for the incoming values aren't
722 // invalidated when we remove one.
723 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
724 BasicBlock *IncomingBB = PN->getIncomingBlock(i);
725 if (PredSet.count(IncomingBB)) {
726 Value *V = PN->removeIncomingValue(i, false);
727 NewPHI->addIncoming(V, IncomingBB);
731 PN->addIncoming(NewPHI, NewBB);
735 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
736 ArrayRef<BasicBlock *> Preds,
737 const char *Suffix, DominatorTree *DT,
738 LoopInfo *LI, MemorySSAUpdater *MSSAU,
739 bool PreserveLCSSA) {
740 // Do not attempt to split that which cannot be split.
741 if (!BB->canSplitPredecessors())
744 // For the landingpads we need to act a bit differently.
745 // Delegate this work to the SplitLandingPadPredecessors.
746 if (BB->isLandingPad()) {
747 SmallVector<BasicBlock*, 2> NewBBs;
748 std::string NewName = std::string(Suffix) + ".split-lp";
750 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
751 LI, MSSAU, PreserveLCSSA);
755 // Create new basic block, insert right before the original block.
756 BasicBlock *NewBB = BasicBlock::Create(
757 BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
759 // The new block unconditionally branches to the old block.
760 BranchInst *BI = BranchInst::Create(BB, NewBB);
761 // Splitting the predecessors of a loop header creates a preheader block.
762 if (LI && LI->isLoopHeader(BB))
763 // Using the loop start line number prevents debuggers stepping into the
764 // loop body for this instruction.
765 BI->setDebugLoc(LI->getLoopFor(BB)->getStartLoc());
767 BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
769 // Move the edges from Preds to point to NewBB instead of BB.
770 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
771 // This is slightly more strict than necessary; the minimum requirement
772 // is that there be no more than one indirectbr branching to BB. And
773 // all BlockAddress uses would need to be updated.
774 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
775 "Cannot split an edge from an IndirectBrInst");
776 assert(!isa<CallBrInst>(Preds[i]->getTerminator()) &&
777 "Cannot split an edge from a CallBrInst");
778 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
781 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
782 // node becomes an incoming value for BB's phi node. However, if the Preds
783 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
784 // account for the newly created predecessor.
786 // Insert dummy values as the incoming value.
787 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
788 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
791 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
792 bool HasLoopExit = false;
793 UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, MSSAU, PreserveLCSSA,
796 if (!Preds.empty()) {
797 // Update the PHI nodes in BB with the values coming from NewBB.
798 UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
804 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
805 ArrayRef<BasicBlock *> Preds,
806 const char *Suffix1, const char *Suffix2,
807 SmallVectorImpl<BasicBlock *> &NewBBs,
808 DominatorTree *DT, LoopInfo *LI,
809 MemorySSAUpdater *MSSAU,
810 bool PreserveLCSSA) {
811 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
813 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
814 // it right before the original block.
815 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
816 OrigBB->getName() + Suffix1,
817 OrigBB->getParent(), OrigBB);
818 NewBBs.push_back(NewBB1);
820 // The new block unconditionally branches to the old block.
821 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
822 BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
824 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
825 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
826 // This is slightly more strict than necessary; the minimum requirement
827 // is that there be no more than one indirectbr branching to BB. And
828 // all BlockAddress uses would need to be updated.
829 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
830 "Cannot split an edge from an IndirectBrInst");
831 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
834 bool HasLoopExit = false;
835 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, MSSAU, PreserveLCSSA,
838 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
839 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
841 // Move the remaining edges from OrigBB to point to NewBB2.
842 SmallVector<BasicBlock*, 8> NewBB2Preds;
843 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
845 BasicBlock *Pred = *i++;
846 if (Pred == NewBB1) continue;
847 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
848 "Cannot split an edge from an IndirectBrInst");
849 NewBB2Preds.push_back(Pred);
850 e = pred_end(OrigBB);
853 BasicBlock *NewBB2 = nullptr;
854 if (!NewBB2Preds.empty()) {
855 // Create another basic block for the rest of OrigBB's predecessors.
856 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
857 OrigBB->getName() + Suffix2,
858 OrigBB->getParent(), OrigBB);
859 NewBBs.push_back(NewBB2);
861 // The new block unconditionally branches to the old block.
862 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
863 BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
865 // Move the remaining edges from OrigBB to point to NewBB2.
866 for (BasicBlock *NewBB2Pred : NewBB2Preds)
867 NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
869 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
871 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI, MSSAU,
872 PreserveLCSSA, HasLoopExit);
874 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
875 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
878 LandingPadInst *LPad = OrigBB->getLandingPadInst();
879 Instruction *Clone1 = LPad->clone();
880 Clone1->setName(Twine("lpad") + Suffix1);
881 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
884 Instruction *Clone2 = LPad->clone();
885 Clone2->setName(Twine("lpad") + Suffix2);
886 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
888 // Create a PHI node for the two cloned landingpad instructions only
889 // if the original landingpad instruction has some uses.
890 if (!LPad->use_empty()) {
891 assert(!LPad->getType()->isTokenTy() &&
892 "Split cannot be applied if LPad is token type. Otherwise an "
893 "invalid PHINode of token type would be created.");
894 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
895 PN->addIncoming(Clone1, NewBB1);
896 PN->addIncoming(Clone2, NewBB2);
897 LPad->replaceAllUsesWith(PN);
899 LPad->eraseFromParent();
901 // There is no second clone. Just replace the landing pad with the first
903 LPad->replaceAllUsesWith(Clone1);
904 LPad->eraseFromParent();
908 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
910 DomTreeUpdater *DTU) {
911 Instruction *UncondBranch = Pred->getTerminator();
912 // Clone the return and add it to the end of the predecessor.
913 Instruction *NewRet = RI->clone();
914 Pred->getInstList().push_back(NewRet);
916 // If the return instruction returns a value, and if the value was a
917 // PHI node in "BB", propagate the right value into the return.
918 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
921 Instruction *NewBC = nullptr;
922 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
923 // Return value might be bitcasted. Clone and insert it before the
924 // return instruction.
925 V = BCI->getOperand(0);
926 NewBC = BCI->clone();
927 Pred->getInstList().insert(NewRet->getIterator(), NewBC);
931 Instruction *NewEV = nullptr;
932 if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(V)) {
933 V = EVI->getOperand(0);
934 NewEV = EVI->clone();
936 NewBC->setOperand(0, NewEV);
937 Pred->getInstList().insert(NewBC->getIterator(), NewEV);
939 Pred->getInstList().insert(NewRet->getIterator(), NewEV);
944 if (PHINode *PN = dyn_cast<PHINode>(V)) {
945 if (PN->getParent() == BB) {
947 NewEV->setOperand(0, PN->getIncomingValueForBlock(Pred));
949 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
951 *i = PN->getIncomingValueForBlock(Pred);
956 // Update any PHI nodes in the returning block to realize that we no
957 // longer branch to them.
958 BB->removePredecessor(Pred);
959 UncondBranch->eraseFromParent();
962 DTU->applyUpdates({{DominatorTree::Delete, Pred, BB}});
964 return cast<ReturnInst>(NewRet);
967 Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
968 Instruction *SplitBefore,
970 MDNode *BranchWeights,
971 DominatorTree *DT, LoopInfo *LI,
972 BasicBlock *ThenBlock) {
973 BasicBlock *Head = SplitBefore->getParent();
974 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
975 Instruction *HeadOldTerm = Head->getTerminator();
976 LLVMContext &C = Head->getContext();
977 Instruction *CheckTerm;
978 bool CreateThenBlock = (ThenBlock == nullptr);
979 if (CreateThenBlock) {
980 ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
982 CheckTerm = new UnreachableInst(C, ThenBlock);
984 CheckTerm = BranchInst::Create(Tail, ThenBlock);
985 CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
987 CheckTerm = ThenBlock->getTerminator();
988 BranchInst *HeadNewTerm =
989 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
990 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
991 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
994 if (DomTreeNode *OldNode = DT->getNode(Head)) {
995 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
997 DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
998 for (DomTreeNode *Child : Children)
999 DT->changeImmediateDominator(Child, NewNode);
1001 // Head dominates ThenBlock.
1002 if (CreateThenBlock)
1003 DT->addNewBlock(ThenBlock, Head);
1005 DT->changeImmediateDominator(ThenBlock, Head);
1010 if (Loop *L = LI->getLoopFor(Head)) {
1011 L->addBasicBlockToLoop(ThenBlock, *LI);
1012 L->addBasicBlockToLoop(Tail, *LI);
1019 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
1020 Instruction **ThenTerm,
1021 Instruction **ElseTerm,
1022 MDNode *BranchWeights) {
1023 BasicBlock *Head = SplitBefore->getParent();
1024 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
1025 Instruction *HeadOldTerm = Head->getTerminator();
1026 LLVMContext &C = Head->getContext();
1027 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
1028 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
1029 *ThenTerm = BranchInst::Create(Tail, ThenBlock);
1030 (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
1031 *ElseTerm = BranchInst::Create(Tail, ElseBlock);
1032 (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
1033 BranchInst *HeadNewTerm =
1034 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
1035 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
1036 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
1039 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
1040 BasicBlock *&IfFalse) {
1041 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
1042 BasicBlock *Pred1 = nullptr;
1043 BasicBlock *Pred2 = nullptr;
1046 if (SomePHI->getNumIncomingValues() != 2)
1048 Pred1 = SomePHI->getIncomingBlock(0);
1049 Pred2 = SomePHI->getIncomingBlock(1);
1051 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
1052 if (PI == PE) // No predecessor
1055 if (PI == PE) // Only one predecessor
1058 if (PI != PE) // More than two predecessors
1062 // We can only handle branches. Other control flow will be lowered to
1063 // branches if possible anyway.
1064 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
1065 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
1066 if (!Pred1Br || !Pred2Br)
1069 // Eliminate code duplication by ensuring that Pred1Br is conditional if
1071 if (Pred2Br->isConditional()) {
1072 // If both branches are conditional, we don't have an "if statement". In
1073 // reality, we could transform this case, but since the condition will be
1074 // required anyway, we stand no chance of eliminating it, so the xform is
1075 // probably not profitable.
1076 if (Pred1Br->isConditional())
1079 std::swap(Pred1, Pred2);
1080 std::swap(Pred1Br, Pred2Br);
1083 if (Pred1Br->isConditional()) {
1084 // The only thing we have to watch out for here is to make sure that Pred2
1085 // doesn't have incoming edges from other blocks. If it does, the condition
1086 // doesn't dominate BB.
1087 if (!Pred2->getSinglePredecessor())
1090 // If we found a conditional branch predecessor, make sure that it branches
1091 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
1092 if (Pred1Br->getSuccessor(0) == BB &&
1093 Pred1Br->getSuccessor(1) == Pred2) {
1096 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
1097 Pred1Br->getSuccessor(1) == BB) {
1101 // We know that one arm of the conditional goes to BB, so the other must
1102 // go somewhere unrelated, and this must not be an "if statement".
1106 return Pred1Br->getCondition();
1109 // Ok, if we got here, both predecessors end with an unconditional branch to
1110 // BB. Don't panic! If both blocks only have a single (identical)
1111 // predecessor, and THAT is a conditional branch, then we're all ok!
1112 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
1113 if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
1116 // Otherwise, if this is a conditional branch, then we can use it!
1117 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
1118 if (!BI) return nullptr;
1120 assert(BI->isConditional() && "Two successors but not conditional?");
1121 if (BI->getSuccessor(0) == Pred1) {
1128 return BI->getCondition();
1131 // After creating a control flow hub, the operands of PHINodes in an outgoing
1132 // block Out no longer match the predecessors of that block. Predecessors of Out
1133 // that are incoming blocks to the hub are now replaced by just one edge from
1134 // the hub. To match this new control flow, the corresponding values from each
1135 // PHINode must now be moved a new PHINode in the first guard block of the hub.
1137 // This operation cannot be performed with SSAUpdater, because it involves one
1138 // new use: If the block Out is in the list of Incoming blocks, then the newly
1139 // created PHI in the Hub will use itself along that edge from Out to Hub.
1140 static void reconnectPhis(BasicBlock *Out, BasicBlock *GuardBlock,
1141 const SetVector<BasicBlock *> &Incoming,
1142 BasicBlock *FirstGuardBlock) {
1143 auto I = Out->begin();
1144 while (I != Out->end() && isa<PHINode>(I)) {
1145 auto Phi = cast<PHINode>(I);
1147 PHINode::Create(Phi->getType(), Incoming.size(),
1148 Phi->getName() + ".moved", &FirstGuardBlock->back());
1149 for (auto In : Incoming) {
1150 Value *V = UndefValue::get(Phi->getType());
1153 } else if (Phi->getBasicBlockIndex(In) != -1) {
1154 V = Phi->removeIncomingValue(In, false);
1156 NewPhi->addIncoming(V, In);
1158 assert(NewPhi->getNumIncomingValues() == Incoming.size());
1159 if (Phi->getNumOperands() == 0) {
1160 Phi->replaceAllUsesWith(NewPhi);
1161 I = Phi->eraseFromParent();
1164 Phi->addIncoming(NewPhi, GuardBlock);
1169 using BBPredicates = DenseMap<BasicBlock *, PHINode *>;
1170 using BBSetVector = SetVector<BasicBlock *>;
1172 // Redirects the terminator of the incoming block to the first guard
1173 // block in the hub. The condition of the original terminator (if it
1174 // was conditional) and its original successors are returned as a
1175 // tuple <condition, succ0, succ1>. The function additionally filters
1176 // out successors that are not in the set of outgoing blocks.
1178 // - condition is non-null iff the branch is conditional.
1179 // - Succ1 is non-null iff the sole/taken target is an outgoing block.
1180 // - Succ2 is non-null iff condition is non-null and the fallthrough
1181 // target is an outgoing block.
1182 static std::tuple<Value *, BasicBlock *, BasicBlock *>
1183 redirectToHub(BasicBlock *BB, BasicBlock *FirstGuardBlock,
1184 const BBSetVector &Outgoing) {
1185 auto Branch = cast<BranchInst>(BB->getTerminator());
1186 auto Condition = Branch->isConditional() ? Branch->getCondition() : nullptr;
1188 BasicBlock *Succ0 = Branch->getSuccessor(0);
1189 BasicBlock *Succ1 = nullptr;
1190 Succ0 = Outgoing.count(Succ0) ? Succ0 : nullptr;
1192 if (Branch->isUnconditional()) {
1193 Branch->setSuccessor(0, FirstGuardBlock);
1196 Succ1 = Branch->getSuccessor(1);
1197 Succ1 = Outgoing.count(Succ1) ? Succ1 : nullptr;
1198 assert(Succ0 || Succ1);
1199 if (Succ0 && !Succ1) {
1200 Branch->setSuccessor(0, FirstGuardBlock);
1201 } else if (Succ1 && !Succ0) {
1202 Branch->setSuccessor(1, FirstGuardBlock);
1204 Branch->eraseFromParent();
1205 BranchInst::Create(FirstGuardBlock, BB);
1209 assert(Succ0 || Succ1);
1210 return std::make_tuple(Condition, Succ0, Succ1);
1213 // Capture the existing control flow as guard predicates, and redirect
1214 // control flow from every incoming block to the first guard block in
1217 // There is one guard predicate for each outgoing block OutBB. The
1218 // predicate is a PHINode with one input for each InBB which
1219 // represents whether the hub should transfer control flow to OutBB if
1220 // it arrived from InBB. These predicates are NOT ORTHOGONAL. The Hub
1221 // evaluates them in the same order as the Outgoing set-vector, and
1222 // control branches to the first outgoing block whose predicate
1223 // evaluates to true.
1224 static void convertToGuardPredicates(
1225 BasicBlock *FirstGuardBlock, BBPredicates &GuardPredicates,
1226 SmallVectorImpl<WeakVH> &DeletionCandidates, const BBSetVector &Incoming,
1227 const BBSetVector &Outgoing) {
1228 auto &Context = Incoming.front()->getContext();
1229 auto BoolTrue = ConstantInt::getTrue(Context);
1230 auto BoolFalse = ConstantInt::getFalse(Context);
1232 // The predicate for the last outgoing is trivially true, and so we
1233 // process only the first N-1 successors.
1234 for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
1235 auto Out = Outgoing[i];
1236 LLVM_DEBUG(dbgs() << "Creating guard for " << Out->getName() << "\n");
1238 PHINode::Create(Type::getInt1Ty(Context), Incoming.size(),
1239 StringRef("Guard.") + Out->getName(), FirstGuardBlock);
1240 GuardPredicates[Out] = Phi;
1243 for (auto In : Incoming) {
1247 std::tie(Condition, Succ0, Succ1) =
1248 redirectToHub(In, FirstGuardBlock, Outgoing);
1250 // Optimization: Consider an incoming block A with both successors
1251 // Succ0 and Succ1 in the set of outgoing blocks. The predicates
1252 // for Succ0 and Succ1 complement each other. If Succ0 is visited
1253 // first in the loop below, control will branch to Succ0 using the
1254 // corresponding predicate. But if that branch is not taken, then
1255 // control must reach Succ1, which means that the predicate for
1256 // Succ1 is always true.
1257 bool OneSuccessorDone = false;
1258 for (int i = 0, e = Outgoing.size() - 1; i != e; ++i) {
1259 auto Out = Outgoing[i];
1260 auto Phi = GuardPredicates[Out];
1261 if (Out != Succ0 && Out != Succ1) {
1262 Phi->addIncoming(BoolFalse, In);
1265 // Optimization: When only one successor is an outgoing block,
1266 // the predicate is always true.
1267 if (!Succ0 || !Succ1 || OneSuccessorDone) {
1268 Phi->addIncoming(BoolTrue, In);
1271 assert(Succ0 && Succ1);
1272 OneSuccessorDone = true;
1274 Phi->addIncoming(Condition, In);
1277 auto Inverted = invertCondition(Condition);
1278 DeletionCandidates.push_back(Condition);
1279 Phi->addIncoming(Inverted, In);
1284 // For each outgoing block OutBB, create a guard block in the Hub. The
1285 // first guard block was already created outside, and available as the
1286 // first element in the vector of guard blocks.
1288 // Each guard block terminates in a conditional branch that transfers
1289 // control to the corresponding outgoing block or the next guard
1290 // block. The last guard block has two outgoing blocks as successors
1291 // since the condition for the final outgoing block is trivially
1292 // true. So we create one less block (including the first guard block)
1293 // than the number of outgoing blocks.
1294 static void createGuardBlocks(SmallVectorImpl<BasicBlock *> &GuardBlocks,
1295 Function *F, const BBSetVector &Outgoing,
1296 BBPredicates &GuardPredicates, StringRef Prefix) {
1297 for (int i = 0, e = Outgoing.size() - 2; i != e; ++i) {
1298 GuardBlocks.push_back(
1299 BasicBlock::Create(F->getContext(), Prefix + ".guard", F));
1301 assert(GuardBlocks.size() == GuardPredicates.size());
1303 // To help keep the loop simple, temporarily append the last
1304 // outgoing block to the list of guard blocks.
1305 GuardBlocks.push_back(Outgoing.back());
1307 for (int i = 0, e = GuardBlocks.size() - 1; i != e; ++i) {
1308 auto Out = Outgoing[i];
1309 assert(GuardPredicates.count(Out));
1310 BranchInst::Create(Out, GuardBlocks[i + 1], GuardPredicates[Out],
1314 // Remove the last block from the guard list.
1315 GuardBlocks.pop_back();
1318 BasicBlock *llvm::CreateControlFlowHub(
1319 DomTreeUpdater *DTU, SmallVectorImpl<BasicBlock *> &GuardBlocks,
1320 const BBSetVector &Incoming, const BBSetVector &Outgoing,
1321 const StringRef Prefix) {
1322 auto F = Incoming.front()->getParent();
1323 auto FirstGuardBlock =
1324 BasicBlock::Create(F->getContext(), Prefix + ".guard", F);
1326 SmallVector<DominatorTree::UpdateType, 16> Updates;
1328 for (auto In : Incoming) {
1329 for (auto Succ : successors(In)) {
1330 if (Outgoing.count(Succ))
1331 Updates.push_back({DominatorTree::Delete, In, Succ});
1333 Updates.push_back({DominatorTree::Insert, In, FirstGuardBlock});
1337 BBPredicates GuardPredicates;
1338 SmallVector<WeakVH, 8> DeletionCandidates;
1339 convertToGuardPredicates(FirstGuardBlock, GuardPredicates, DeletionCandidates,
1340 Incoming, Outgoing);
1342 GuardBlocks.push_back(FirstGuardBlock);
1343 createGuardBlocks(GuardBlocks, F, Outgoing, GuardPredicates, Prefix);
1345 // Update the PHINodes in each outgoing block to match the new control flow.
1346 for (int i = 0, e = GuardBlocks.size(); i != e; ++i) {
1347 reconnectPhis(Outgoing[i], GuardBlocks[i], Incoming, FirstGuardBlock);
1349 reconnectPhis(Outgoing.back(), GuardBlocks.back(), Incoming, FirstGuardBlock);
1352 int NumGuards = GuardBlocks.size();
1353 assert((int)Outgoing.size() == NumGuards + 1);
1354 for (int i = 0; i != NumGuards - 1; ++i) {
1355 Updates.push_back({DominatorTree::Insert, GuardBlocks[i], Outgoing[i]});
1357 {DominatorTree::Insert, GuardBlocks[i], GuardBlocks[i + 1]});
1359 Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
1360 Outgoing[NumGuards - 1]});
1361 Updates.push_back({DominatorTree::Insert, GuardBlocks[NumGuards - 1],
1362 Outgoing[NumGuards]});
1363 DTU->applyUpdates(Updates);
1366 for (auto I : DeletionCandidates) {
1368 if (auto Inst = dyn_cast_or_null<Instruction>(I))
1369 Inst->eraseFromParent();
1372 return FirstGuardBlock;