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 // Recursively deleting a PHI may cause multiple PHIs to be deleted
158 // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
159 SmallVector<WeakTrackingVH, 8> PHIs;
160 for (PHINode &PN : BB->phis())
163 bool Changed = false;
164 for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
165 if (PHINode *PN = dyn_cast_or_null<PHINode>(PHIs[i].operator Value*()))
166 Changed |= RecursivelyDeleteDeadPHINode(PN, TLI);
171 bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DomTreeUpdater *DTU,
172 LoopInfo *LI, MemorySSAUpdater *MSSAU,
173 MemoryDependenceResults *MemDep,
174 bool PredecessorWithTwoSuccessors) {
175 if (BB->hasAddressTaken())
178 // Can't merge if there are multiple predecessors, or no predecessors.
179 BasicBlock *PredBB = BB->getUniquePredecessor();
180 if (!PredBB) return false;
182 // Don't break self-loops.
183 if (PredBB == BB) return false;
184 // Don't break unwinding instructions.
185 if (PredBB->getTerminator()->isExceptionalTerminator())
188 // Can't merge if there are multiple distinct successors.
189 if (!PredecessorWithTwoSuccessors && PredBB->getUniqueSuccessor() != BB)
192 // Currently only allow PredBB to have two predecessors, one being BB.
193 // Update BI to branch to BB's only successor instead of BB.
194 BranchInst *PredBB_BI;
195 BasicBlock *NewSucc = nullptr;
196 unsigned FallThruPath;
197 if (PredecessorWithTwoSuccessors) {
198 if (!(PredBB_BI = dyn_cast<BranchInst>(PredBB->getTerminator())))
200 BranchInst *BB_JmpI = dyn_cast<BranchInst>(BB->getTerminator());
201 if (!BB_JmpI || !BB_JmpI->isUnconditional())
203 NewSucc = BB_JmpI->getSuccessor(0);
204 FallThruPath = PredBB_BI->getSuccessor(0) == BB ? 0 : 1;
207 // Can't merge if there is PHI loop.
208 for (PHINode &PN : BB->phis())
209 for (Value *IncValue : PN.incoming_values())
213 LLVM_DEBUG(dbgs() << "Merging: " << BB->getName() << " into "
214 << PredBB->getName() << "\n");
216 // Begin by getting rid of unneeded PHIs.
217 SmallVector<AssertingVH<Value>, 4> IncomingValues;
218 if (isa<PHINode>(BB->front())) {
219 for (PHINode &PN : BB->phis())
220 if (!isa<PHINode>(PN.getIncomingValue(0)) ||
221 cast<PHINode>(PN.getIncomingValue(0))->getParent() != BB)
222 IncomingValues.push_back(PN.getIncomingValue(0));
223 FoldSingleEntryPHINodes(BB, MemDep);
226 // DTU update: Collect all the edges that exit BB.
227 // These dominator edges will be redirected from Pred.
228 std::vector<DominatorTree::UpdateType> Updates;
230 Updates.reserve(1 + (2 * succ_size(BB)));
231 // Add insert edges first. Experimentally, for the particular case of two
232 // blocks that can be merged, with a single successor and single predecessor
233 // respectively, it is beneficial to have all insert updates first. Deleting
234 // edges first may lead to unreachable blocks, followed by inserting edges
235 // making the blocks reachable again. Such DT updates lead to high compile
236 // times. We add inserts before deletes here to reduce compile time.
237 for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
238 // This successor of BB may already have PredBB as a predecessor.
239 if (llvm::find(successors(PredBB), *I) == succ_end(PredBB))
240 Updates.push_back({DominatorTree::Insert, PredBB, *I});
241 for (auto I = succ_begin(BB), E = succ_end(BB); I != E; ++I)
242 Updates.push_back({DominatorTree::Delete, BB, *I});
243 Updates.push_back({DominatorTree::Delete, PredBB, BB});
246 Instruction *PTI = PredBB->getTerminator();
247 Instruction *STI = BB->getTerminator();
248 Instruction *Start = &*BB->begin();
249 // If there's nothing to move, mark the starting instruction as the last
250 // instruction in the block. Terminator instruction is handled separately.
254 // Move all definitions in the successor to the predecessor...
255 PredBB->getInstList().splice(PTI->getIterator(), BB->getInstList(),
256 BB->begin(), STI->getIterator());
259 MSSAU->moveAllAfterMergeBlocks(BB, PredBB, Start);
261 // Make all PHI nodes that referred to BB now refer to Pred as their
263 BB->replaceAllUsesWith(PredBB);
265 if (PredecessorWithTwoSuccessors) {
266 // Delete the unconditional branch from BB.
267 BB->getInstList().pop_back();
269 // Update branch in the predecessor.
270 PredBB_BI->setSuccessor(FallThruPath, NewSucc);
272 // Delete the unconditional branch from the predecessor.
273 PredBB->getInstList().pop_back();
275 // Move terminator instruction.
276 PredBB->getInstList().splice(PredBB->end(), BB->getInstList());
278 // Terminator may be a memory accessing instruction too.
280 if (MemoryUseOrDef *MUD = cast_or_null<MemoryUseOrDef>(
281 MSSAU->getMemorySSA()->getMemoryAccess(PredBB->getTerminator())))
282 MSSAU->moveToPlace(MUD, PredBB, MemorySSA::End);
284 // Add unreachable to now empty BB.
285 new UnreachableInst(BB->getContext(), BB);
287 // Eliminate duplicate/redundant dbg.values. This seems to be a good place to
288 // do that since we might end up with redundant dbg.values describing the
289 // entry PHI node post-splice.
290 RemoveRedundantDbgInstrs(PredBB);
292 // Inherit predecessors name if it exists.
293 if (!PredBB->hasName())
294 PredBB->takeName(BB);
300 MemDep->invalidateCachedPredecessors();
302 // Finally, erase the old block and update dominator info.
304 assert(BB->getInstList().size() == 1 &&
305 isa<UnreachableInst>(BB->getTerminator()) &&
306 "The successor list of BB isn't empty before "
307 "applying corresponding DTU updates.");
308 DTU->applyUpdatesPermissive(Updates);
311 BB->eraseFromParent(); // Nuke BB if DTU is nullptr.
317 /// Remove redundant instructions within sequences of consecutive dbg.value
318 /// instructions. This is done using a backward scan to keep the last dbg.value
319 /// describing a specific variable/fragment.
321 /// BackwardScan strategy:
322 /// ----------------------
323 /// Given a sequence of consecutive DbgValueInst like this
325 /// dbg.value ..., "x", FragmentX1 (*)
326 /// dbg.value ..., "y", FragmentY1
327 /// dbg.value ..., "x", FragmentX2
328 /// dbg.value ..., "x", FragmentX1 (**)
330 /// then the instruction marked with (*) can be removed (it is guaranteed to be
331 /// obsoleted by the instruction marked with (**) as the latter instruction is
332 /// describing the same variable using the same fragment info).
334 /// Possible improvements:
335 /// - Check fully overlapping fragments and not only identical fragments.
336 /// - Support dbg.addr, dbg.declare. dbg.label, and possibly other meta
337 /// instructions being part of the sequence of consecutive instructions.
338 static bool removeRedundantDbgInstrsUsingBackwardScan(BasicBlock *BB) {
339 SmallVector<DbgValueInst *, 8> ToBeRemoved;
340 SmallDenseSet<DebugVariable> VariableSet;
341 for (auto &I : reverse(*BB)) {
342 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
343 DebugVariable Key(DVI->getVariable(),
344 DVI->getExpression(),
345 DVI->getDebugLoc()->getInlinedAt());
346 auto R = VariableSet.insert(Key);
347 // If the same variable fragment is described more than once it is enough
348 // to keep the last one (i.e. the first found since we for reverse
351 ToBeRemoved.push_back(DVI);
354 // Sequence with consecutive dbg.value instrs ended. Clear the map to
355 // restart identifying redundant instructions if case we find another
356 // dbg.value sequence.
360 for (auto &Instr : ToBeRemoved)
361 Instr->eraseFromParent();
363 return !ToBeRemoved.empty();
366 /// Remove redundant dbg.value instructions using a forward scan. This can
367 /// remove a dbg.value instruction that is redundant due to indicating that a
368 /// variable has the same value as already being indicated by an earlier
371 /// ForwardScan strategy:
372 /// ---------------------
373 /// Given two identical dbg.value instructions, separated by a block of
374 /// instructions that isn't describing the same variable, like this
376 /// dbg.value X1, "x", FragmentX1 (**)
377 /// <block of instructions, none being "dbg.value ..., "x", ...">
378 /// dbg.value X1, "x", FragmentX1 (*)
380 /// then the instruction marked with (*) can be removed. Variable "x" is already
381 /// described as being mapped to the SSA value X1.
383 /// Possible improvements:
384 /// - Keep track of non-overlapping fragments.
385 static bool removeRedundantDbgInstrsUsingForwardScan(BasicBlock *BB) {
386 SmallVector<DbgValueInst *, 8> ToBeRemoved;
387 DenseMap<DebugVariable, std::pair<Value *, DIExpression *> > VariableMap;
388 for (auto &I : *BB) {
389 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(&I)) {
390 DebugVariable Key(DVI->getVariable(),
392 DVI->getDebugLoc()->getInlinedAt());
393 auto VMI = VariableMap.find(Key);
394 // Update the map if we found a new value/expression describing the
395 // variable, or if the variable wasn't mapped already.
396 if (VMI == VariableMap.end() ||
397 VMI->second.first != DVI->getValue() ||
398 VMI->second.second != DVI->getExpression()) {
399 VariableMap[Key] = { DVI->getValue(), DVI->getExpression() };
402 // Found an identical mapping. Remember the instruction for later removal.
403 ToBeRemoved.push_back(DVI);
407 for (auto &Instr : ToBeRemoved)
408 Instr->eraseFromParent();
410 return !ToBeRemoved.empty();
413 bool llvm::RemoveRedundantDbgInstrs(BasicBlock *BB) {
414 bool MadeChanges = false;
415 // By using the "backward scan" strategy before the "forward scan" strategy we
416 // can remove both dbg.value (2) and (3) in a situation like this:
418 // (1) dbg.value V1, "x", DIExpression()
420 // (2) dbg.value V2, "x", DIExpression()
421 // (3) dbg.value V1, "x", DIExpression()
423 // The backward scan will remove (2), it is made obsolete by (3). After
424 // getting (2) out of the way, the foward scan will remove (3) since "x"
425 // already is described as having the value V1 at (1).
426 MadeChanges |= removeRedundantDbgInstrsUsingBackwardScan(BB);
427 MadeChanges |= removeRedundantDbgInstrsUsingForwardScan(BB);
430 LLVM_DEBUG(dbgs() << "Removed redundant dbg instrs from: "
431 << BB->getName() << "\n");
435 void llvm::ReplaceInstWithValue(BasicBlock::InstListType &BIL,
436 BasicBlock::iterator &BI, Value *V) {
437 Instruction &I = *BI;
438 // Replaces all of the uses of the instruction with uses of the value
439 I.replaceAllUsesWith(V);
441 // Make sure to propagate a name if there is one already.
442 if (I.hasName() && !V->hasName())
445 // Delete the unnecessary instruction now...
449 void llvm::ReplaceInstWithInst(BasicBlock::InstListType &BIL,
450 BasicBlock::iterator &BI, Instruction *I) {
451 assert(I->getParent() == nullptr &&
452 "ReplaceInstWithInst: Instruction already inserted into basic block!");
454 // Copy debug location to newly added instruction, if it wasn't already set
456 if (!I->getDebugLoc())
457 I->setDebugLoc(BI->getDebugLoc());
459 // Insert the new instruction into the basic block...
460 BasicBlock::iterator New = BIL.insert(BI, I);
462 // Replace all uses of the old instruction, and delete it.
463 ReplaceInstWithValue(BIL, BI, I);
465 // Move BI back to point to the newly inserted instruction
469 void llvm::ReplaceInstWithInst(Instruction *From, Instruction *To) {
470 BasicBlock::iterator BI(From);
471 ReplaceInstWithInst(From->getParent()->getInstList(), BI, To);
474 BasicBlock *llvm::SplitEdge(BasicBlock *BB, BasicBlock *Succ, DominatorTree *DT,
475 LoopInfo *LI, MemorySSAUpdater *MSSAU) {
476 unsigned SuccNum = GetSuccessorNumber(BB, Succ);
478 // If this is a critical edge, let SplitCriticalEdge do it.
479 Instruction *LatchTerm = BB->getTerminator();
480 if (SplitCriticalEdge(
482 CriticalEdgeSplittingOptions(DT, LI, MSSAU).setPreserveLCSSA()))
483 return LatchTerm->getSuccessor(SuccNum);
485 // If the edge isn't critical, then BB has a single successor or Succ has a
486 // single pred. Split the block.
487 if (BasicBlock *SP = Succ->getSinglePredecessor()) {
488 // If the successor only has a single pred, split the top of the successor
490 assert(SP == BB && "CFG broken");
492 return SplitBlock(Succ, &Succ->front(), DT, LI, MSSAU);
495 // Otherwise, if BB has a single successor, split it at the bottom of the
497 assert(BB->getTerminator()->getNumSuccessors() == 1 &&
498 "Should have a single succ!");
499 return SplitBlock(BB, BB->getTerminator(), DT, LI, MSSAU);
503 llvm::SplitAllCriticalEdges(Function &F,
504 const CriticalEdgeSplittingOptions &Options) {
505 unsigned NumBroken = 0;
506 for (BasicBlock &BB : F) {
507 Instruction *TI = BB.getTerminator();
508 if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI) &&
509 !isa<CallBrInst>(TI))
510 for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
511 if (SplitCriticalEdge(TI, i, Options))
517 BasicBlock *llvm::SplitBlock(BasicBlock *Old, Instruction *SplitPt,
518 DominatorTree *DT, LoopInfo *LI,
519 MemorySSAUpdater *MSSAU, const Twine &BBName) {
520 BasicBlock::iterator SplitIt = SplitPt->getIterator();
521 while (isa<PHINode>(SplitIt) || SplitIt->isEHPad())
523 std::string Name = BBName.str();
524 BasicBlock *New = Old->splitBasicBlock(
525 SplitIt, Name.empty() ? Old->getName() + ".split" : Name);
527 // The new block lives in whichever loop the old one did. This preserves
528 // LCSSA as well, because we force the split point to be after any PHI nodes.
530 if (Loop *L = LI->getLoopFor(Old))
531 L->addBasicBlockToLoop(New, *LI);
534 // Old dominates New. New node dominates all other nodes dominated by Old.
535 if (DomTreeNode *OldNode = DT->getNode(Old)) {
536 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
538 DomTreeNode *NewNode = DT->addNewBlock(New, Old);
539 for (DomTreeNode *I : Children)
540 DT->changeImmediateDominator(I, NewNode);
543 // Move MemoryAccesses still tracked in Old, but part of New now.
544 // Update accesses in successor blocks accordingly.
546 MSSAU->moveAllAfterSpliceBlocks(Old, New, &*(New->begin()));
551 /// Update DominatorTree, LoopInfo, and LCCSA analysis information.
552 static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
553 ArrayRef<BasicBlock *> Preds,
554 DominatorTree *DT, LoopInfo *LI,
555 MemorySSAUpdater *MSSAU,
556 bool PreserveLCSSA, bool &HasLoopExit) {
557 // Update dominator tree if available.
559 if (OldBB == DT->getRootNode()->getBlock()) {
560 assert(NewBB == &NewBB->getParent()->getEntryBlock());
561 DT->setNewRoot(NewBB);
563 // Split block expects NewBB to have a non-empty set of predecessors.
564 DT->splitBlock(NewBB);
568 // Update MemoryPhis after split if MemorySSA is available
570 MSSAU->wireOldPredecessorsToNewImmediatePredecessor(OldBB, NewBB, Preds);
572 // The rest of the logic is only relevant for updating the loop structures.
576 assert(DT && "DT should be available to update LoopInfo!");
577 Loop *L = LI->getLoopFor(OldBB);
579 // If we need to preserve loop analyses, collect some information about how
580 // this split will affect loops.
581 bool IsLoopEntry = !!L;
582 bool SplitMakesNewLoopHeader = false;
583 for (BasicBlock *Pred : Preds) {
584 // Preds that are not reachable from entry should not be used to identify if
585 // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
586 // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
587 // as true and make the NewBB the header of some loop. This breaks LI.
588 if (!DT->isReachableFromEntry(Pred))
590 // If we need to preserve LCSSA, determine if any of the preds is a loop
593 if (Loop *PL = LI->getLoopFor(Pred))
594 if (!PL->contains(OldBB))
597 // If we need to preserve LoopInfo, note whether any of the preds crosses
598 // an interesting loop boundary.
601 if (L->contains(Pred))
604 SplitMakesNewLoopHeader = true;
607 // Unless we have a loop for OldBB, nothing else to do here.
612 // Add the new block to the nearest enclosing loop (and not an adjacent
613 // loop). To find this, examine each of the predecessors and determine which
614 // loops enclose them, and select the most-nested loop which contains the
615 // loop containing the block being split.
616 Loop *InnermostPredLoop = nullptr;
617 for (BasicBlock *Pred : Preds) {
618 if (Loop *PredLoop = LI->getLoopFor(Pred)) {
619 // Seek a loop which actually contains the block being split (to avoid
621 while (PredLoop && !PredLoop->contains(OldBB))
622 PredLoop = PredLoop->getParentLoop();
624 // Select the most-nested of these loops which contains the block.
625 if (PredLoop && PredLoop->contains(OldBB) &&
626 (!InnermostPredLoop ||
627 InnermostPredLoop->getLoopDepth() < PredLoop->getLoopDepth()))
628 InnermostPredLoop = PredLoop;
632 if (InnermostPredLoop)
633 InnermostPredLoop->addBasicBlockToLoop(NewBB, *LI);
635 L->addBasicBlockToLoop(NewBB, *LI);
636 if (SplitMakesNewLoopHeader)
637 L->moveToHeader(NewBB);
641 /// Update the PHI nodes in OrigBB to include the values coming from NewBB.
642 /// This also updates AliasAnalysis, if available.
643 static void UpdatePHINodes(BasicBlock *OrigBB, BasicBlock *NewBB,
644 ArrayRef<BasicBlock *> Preds, BranchInst *BI,
646 // Otherwise, create a new PHI node in NewBB for each PHI node in OrigBB.
647 SmallPtrSet<BasicBlock *, 16> PredSet(Preds.begin(), Preds.end());
648 for (BasicBlock::iterator I = OrigBB->begin(); isa<PHINode>(I); ) {
649 PHINode *PN = cast<PHINode>(I++);
651 // Check to see if all of the values coming in are the same. If so, we
652 // don't need to create a new PHI node, unless it's needed for LCSSA.
653 Value *InVal = nullptr;
655 InVal = PN->getIncomingValueForBlock(Preds[0]);
656 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
657 if (!PredSet.count(PN->getIncomingBlock(i)))
660 InVal = PN->getIncomingValue(i);
661 else if (InVal != PN->getIncomingValue(i)) {
669 // If all incoming values for the new PHI would be the same, just don't
670 // make a new PHI. Instead, just remove the incoming values from the old
673 // NOTE! This loop walks backwards for a reason! First off, this minimizes
674 // the cost of removal if we end up removing a large number of values, and
675 // second off, this ensures that the indices for the incoming values
676 // aren't invalidated when we remove one.
677 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i)
678 if (PredSet.count(PN->getIncomingBlock(i)))
679 PN->removeIncomingValue(i, false);
681 // Add an incoming value to the PHI node in the loop for the preheader
683 PN->addIncoming(InVal, NewBB);
687 // If the values coming into the block are not the same, we need a new
689 // Create the new PHI node, insert it into NewBB at the end of the block
691 PHINode::Create(PN->getType(), Preds.size(), PN->getName() + ".ph", BI);
693 // NOTE! This loop walks backwards for a reason! First off, this minimizes
694 // the cost of removal if we end up removing a large number of values, and
695 // second off, this ensures that the indices for the incoming values aren't
696 // invalidated when we remove one.
697 for (int64_t i = PN->getNumIncomingValues() - 1; i >= 0; --i) {
698 BasicBlock *IncomingBB = PN->getIncomingBlock(i);
699 if (PredSet.count(IncomingBB)) {
700 Value *V = PN->removeIncomingValue(i, false);
701 NewPHI->addIncoming(V, IncomingBB);
705 PN->addIncoming(NewPHI, NewBB);
709 BasicBlock *llvm::SplitBlockPredecessors(BasicBlock *BB,
710 ArrayRef<BasicBlock *> Preds,
711 const char *Suffix, DominatorTree *DT,
712 LoopInfo *LI, MemorySSAUpdater *MSSAU,
713 bool PreserveLCSSA) {
714 // Do not attempt to split that which cannot be split.
715 if (!BB->canSplitPredecessors())
718 // For the landingpads we need to act a bit differently.
719 // Delegate this work to the SplitLandingPadPredecessors.
720 if (BB->isLandingPad()) {
721 SmallVector<BasicBlock*, 2> NewBBs;
722 std::string NewName = std::string(Suffix) + ".split-lp";
724 SplitLandingPadPredecessors(BB, Preds, Suffix, NewName.c_str(), NewBBs, DT,
725 LI, MSSAU, PreserveLCSSA);
729 // Create new basic block, insert right before the original block.
730 BasicBlock *NewBB = BasicBlock::Create(
731 BB->getContext(), BB->getName() + Suffix, BB->getParent(), BB);
733 // The new block unconditionally branches to the old block.
734 BranchInst *BI = BranchInst::Create(BB, NewBB);
735 // Splitting the predecessors of a loop header creates a preheader block.
736 if (LI && LI->isLoopHeader(BB))
737 // Using the loop start line number prevents debuggers stepping into the
738 // loop body for this instruction.
739 BI->setDebugLoc(LI->getLoopFor(BB)->getStartLoc());
741 BI->setDebugLoc(BB->getFirstNonPHIOrDbg()->getDebugLoc());
743 // Move the edges from Preds to point to NewBB instead of BB.
744 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
745 // This is slightly more strict than necessary; the minimum requirement
746 // is that there be no more than one indirectbr branching to BB. And
747 // all BlockAddress uses would need to be updated.
748 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
749 "Cannot split an edge from an IndirectBrInst");
750 assert(!isa<CallBrInst>(Preds[i]->getTerminator()) &&
751 "Cannot split an edge from a CallBrInst");
752 Preds[i]->getTerminator()->replaceUsesOfWith(BB, NewBB);
755 // Insert a new PHI node into NewBB for every PHI node in BB and that new PHI
756 // node becomes an incoming value for BB's phi node. However, if the Preds
757 // list is empty, we need to insert dummy entries into the PHI nodes in BB to
758 // account for the newly created predecessor.
760 // Insert dummy values as the incoming value.
761 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++I)
762 cast<PHINode>(I)->addIncoming(UndefValue::get(I->getType()), NewBB);
765 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
766 bool HasLoopExit = false;
767 UpdateAnalysisInformation(BB, NewBB, Preds, DT, LI, MSSAU, PreserveLCSSA,
770 if (!Preds.empty()) {
771 // Update the PHI nodes in BB with the values coming from NewBB.
772 UpdatePHINodes(BB, NewBB, Preds, BI, HasLoopExit);
778 void llvm::SplitLandingPadPredecessors(BasicBlock *OrigBB,
779 ArrayRef<BasicBlock *> Preds,
780 const char *Suffix1, const char *Suffix2,
781 SmallVectorImpl<BasicBlock *> &NewBBs,
782 DominatorTree *DT, LoopInfo *LI,
783 MemorySSAUpdater *MSSAU,
784 bool PreserveLCSSA) {
785 assert(OrigBB->isLandingPad() && "Trying to split a non-landing pad!");
787 // Create a new basic block for OrigBB's predecessors listed in Preds. Insert
788 // it right before the original block.
789 BasicBlock *NewBB1 = BasicBlock::Create(OrigBB->getContext(),
790 OrigBB->getName() + Suffix1,
791 OrigBB->getParent(), OrigBB);
792 NewBBs.push_back(NewBB1);
794 // The new block unconditionally branches to the old block.
795 BranchInst *BI1 = BranchInst::Create(OrigBB, NewBB1);
796 BI1->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
798 // Move the edges from Preds to point to NewBB1 instead of OrigBB.
799 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
800 // This is slightly more strict than necessary; the minimum requirement
801 // is that there be no more than one indirectbr branching to BB. And
802 // all BlockAddress uses would need to be updated.
803 assert(!isa<IndirectBrInst>(Preds[i]->getTerminator()) &&
804 "Cannot split an edge from an IndirectBrInst");
805 Preds[i]->getTerminator()->replaceUsesOfWith(OrigBB, NewBB1);
808 bool HasLoopExit = false;
809 UpdateAnalysisInformation(OrigBB, NewBB1, Preds, DT, LI, MSSAU, PreserveLCSSA,
812 // Update the PHI nodes in OrigBB with the values coming from NewBB1.
813 UpdatePHINodes(OrigBB, NewBB1, Preds, BI1, HasLoopExit);
815 // Move the remaining edges from OrigBB to point to NewBB2.
816 SmallVector<BasicBlock*, 8> NewBB2Preds;
817 for (pred_iterator i = pred_begin(OrigBB), e = pred_end(OrigBB);
819 BasicBlock *Pred = *i++;
820 if (Pred == NewBB1) continue;
821 assert(!isa<IndirectBrInst>(Pred->getTerminator()) &&
822 "Cannot split an edge from an IndirectBrInst");
823 NewBB2Preds.push_back(Pred);
824 e = pred_end(OrigBB);
827 BasicBlock *NewBB2 = nullptr;
828 if (!NewBB2Preds.empty()) {
829 // Create another basic block for the rest of OrigBB's predecessors.
830 NewBB2 = BasicBlock::Create(OrigBB->getContext(),
831 OrigBB->getName() + Suffix2,
832 OrigBB->getParent(), OrigBB);
833 NewBBs.push_back(NewBB2);
835 // The new block unconditionally branches to the old block.
836 BranchInst *BI2 = BranchInst::Create(OrigBB, NewBB2);
837 BI2->setDebugLoc(OrigBB->getFirstNonPHI()->getDebugLoc());
839 // Move the remaining edges from OrigBB to point to NewBB2.
840 for (BasicBlock *NewBB2Pred : NewBB2Preds)
841 NewBB2Pred->getTerminator()->replaceUsesOfWith(OrigBB, NewBB2);
843 // Update DominatorTree, LoopInfo, and LCCSA analysis information.
845 UpdateAnalysisInformation(OrigBB, NewBB2, NewBB2Preds, DT, LI, MSSAU,
846 PreserveLCSSA, HasLoopExit);
848 // Update the PHI nodes in OrigBB with the values coming from NewBB2.
849 UpdatePHINodes(OrigBB, NewBB2, NewBB2Preds, BI2, HasLoopExit);
852 LandingPadInst *LPad = OrigBB->getLandingPadInst();
853 Instruction *Clone1 = LPad->clone();
854 Clone1->setName(Twine("lpad") + Suffix1);
855 NewBB1->getInstList().insert(NewBB1->getFirstInsertionPt(), Clone1);
858 Instruction *Clone2 = LPad->clone();
859 Clone2->setName(Twine("lpad") + Suffix2);
860 NewBB2->getInstList().insert(NewBB2->getFirstInsertionPt(), Clone2);
862 // Create a PHI node for the two cloned landingpad instructions only
863 // if the original landingpad instruction has some uses.
864 if (!LPad->use_empty()) {
865 assert(!LPad->getType()->isTokenTy() &&
866 "Split cannot be applied if LPad is token type. Otherwise an "
867 "invalid PHINode of token type would be created.");
868 PHINode *PN = PHINode::Create(LPad->getType(), 2, "lpad.phi", LPad);
869 PN->addIncoming(Clone1, NewBB1);
870 PN->addIncoming(Clone2, NewBB2);
871 LPad->replaceAllUsesWith(PN);
873 LPad->eraseFromParent();
875 // There is no second clone. Just replace the landing pad with the first
877 LPad->replaceAllUsesWith(Clone1);
878 LPad->eraseFromParent();
882 ReturnInst *llvm::FoldReturnIntoUncondBranch(ReturnInst *RI, BasicBlock *BB,
884 DomTreeUpdater *DTU) {
885 Instruction *UncondBranch = Pred->getTerminator();
886 // Clone the return and add it to the end of the predecessor.
887 Instruction *NewRet = RI->clone();
888 Pred->getInstList().push_back(NewRet);
890 // If the return instruction returns a value, and if the value was a
891 // PHI node in "BB", propagate the right value into the return.
892 for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
895 Instruction *NewBC = nullptr;
896 if (BitCastInst *BCI = dyn_cast<BitCastInst>(V)) {
897 // Return value might be bitcasted. Clone and insert it before the
898 // return instruction.
899 V = BCI->getOperand(0);
900 NewBC = BCI->clone();
901 Pred->getInstList().insert(NewRet->getIterator(), NewBC);
904 if (PHINode *PN = dyn_cast<PHINode>(V)) {
905 if (PN->getParent() == BB) {
907 NewBC->setOperand(0, PN->getIncomingValueForBlock(Pred));
909 *i = PN->getIncomingValueForBlock(Pred);
914 // Update any PHI nodes in the returning block to realize that we no
915 // longer branch to them.
916 BB->removePredecessor(Pred);
917 UncondBranch->eraseFromParent();
920 DTU->applyUpdates({{DominatorTree::Delete, Pred, BB}});
922 return cast<ReturnInst>(NewRet);
925 Instruction *llvm::SplitBlockAndInsertIfThen(Value *Cond,
926 Instruction *SplitBefore,
928 MDNode *BranchWeights,
929 DominatorTree *DT, LoopInfo *LI,
930 BasicBlock *ThenBlock) {
931 BasicBlock *Head = SplitBefore->getParent();
932 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
933 Instruction *HeadOldTerm = Head->getTerminator();
934 LLVMContext &C = Head->getContext();
935 Instruction *CheckTerm;
936 bool CreateThenBlock = (ThenBlock == nullptr);
937 if (CreateThenBlock) {
938 ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
940 CheckTerm = new UnreachableInst(C, ThenBlock);
942 CheckTerm = BranchInst::Create(Tail, ThenBlock);
943 CheckTerm->setDebugLoc(SplitBefore->getDebugLoc());
945 CheckTerm = ThenBlock->getTerminator();
946 BranchInst *HeadNewTerm =
947 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/Tail, Cond);
948 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
949 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
952 if (DomTreeNode *OldNode = DT->getNode(Head)) {
953 std::vector<DomTreeNode *> Children(OldNode->begin(), OldNode->end());
955 DomTreeNode *NewNode = DT->addNewBlock(Tail, Head);
956 for (DomTreeNode *Child : Children)
957 DT->changeImmediateDominator(Child, NewNode);
959 // Head dominates ThenBlock.
961 DT->addNewBlock(ThenBlock, Head);
963 DT->changeImmediateDominator(ThenBlock, Head);
968 if (Loop *L = LI->getLoopFor(Head)) {
969 L->addBasicBlockToLoop(ThenBlock, *LI);
970 L->addBasicBlockToLoop(Tail, *LI);
977 void llvm::SplitBlockAndInsertIfThenElse(Value *Cond, Instruction *SplitBefore,
978 Instruction **ThenTerm,
979 Instruction **ElseTerm,
980 MDNode *BranchWeights) {
981 BasicBlock *Head = SplitBefore->getParent();
982 BasicBlock *Tail = Head->splitBasicBlock(SplitBefore->getIterator());
983 Instruction *HeadOldTerm = Head->getTerminator();
984 LLVMContext &C = Head->getContext();
985 BasicBlock *ThenBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
986 BasicBlock *ElseBlock = BasicBlock::Create(C, "", Head->getParent(), Tail);
987 *ThenTerm = BranchInst::Create(Tail, ThenBlock);
988 (*ThenTerm)->setDebugLoc(SplitBefore->getDebugLoc());
989 *ElseTerm = BranchInst::Create(Tail, ElseBlock);
990 (*ElseTerm)->setDebugLoc(SplitBefore->getDebugLoc());
991 BranchInst *HeadNewTerm =
992 BranchInst::Create(/*ifTrue*/ThenBlock, /*ifFalse*/ElseBlock, Cond);
993 HeadNewTerm->setMetadata(LLVMContext::MD_prof, BranchWeights);
994 ReplaceInstWithInst(HeadOldTerm, HeadNewTerm);
997 Value *llvm::GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
998 BasicBlock *&IfFalse) {
999 PHINode *SomePHI = dyn_cast<PHINode>(BB->begin());
1000 BasicBlock *Pred1 = nullptr;
1001 BasicBlock *Pred2 = nullptr;
1004 if (SomePHI->getNumIncomingValues() != 2)
1006 Pred1 = SomePHI->getIncomingBlock(0);
1007 Pred2 = SomePHI->getIncomingBlock(1);
1009 pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
1010 if (PI == PE) // No predecessor
1013 if (PI == PE) // Only one predecessor
1016 if (PI != PE) // More than two predecessors
1020 // We can only handle branches. Other control flow will be lowered to
1021 // branches if possible anyway.
1022 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
1023 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
1024 if (!Pred1Br || !Pred2Br)
1027 // Eliminate code duplication by ensuring that Pred1Br is conditional if
1029 if (Pred2Br->isConditional()) {
1030 // If both branches are conditional, we don't have an "if statement". In
1031 // reality, we could transform this case, but since the condition will be
1032 // required anyway, we stand no chance of eliminating it, so the xform is
1033 // probably not profitable.
1034 if (Pred1Br->isConditional())
1037 std::swap(Pred1, Pred2);
1038 std::swap(Pred1Br, Pred2Br);
1041 if (Pred1Br->isConditional()) {
1042 // The only thing we have to watch out for here is to make sure that Pred2
1043 // doesn't have incoming edges from other blocks. If it does, the condition
1044 // doesn't dominate BB.
1045 if (!Pred2->getSinglePredecessor())
1048 // If we found a conditional branch predecessor, make sure that it branches
1049 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
1050 if (Pred1Br->getSuccessor(0) == BB &&
1051 Pred1Br->getSuccessor(1) == Pred2) {
1054 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
1055 Pred1Br->getSuccessor(1) == BB) {
1059 // We know that one arm of the conditional goes to BB, so the other must
1060 // go somewhere unrelated, and this must not be an "if statement".
1064 return Pred1Br->getCondition();
1067 // Ok, if we got here, both predecessors end with an unconditional branch to
1068 // BB. Don't panic! If both blocks only have a single (identical)
1069 // predecessor, and THAT is a conditional branch, then we're all ok!
1070 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
1071 if (CommonPred == nullptr || CommonPred != Pred2->getSinglePredecessor())
1074 // Otherwise, if this is a conditional branch, then we can use it!
1075 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
1076 if (!BI) return nullptr;
1078 assert(BI->isConditional() && "Two successors but not conditional?");
1079 if (BI->getSuccessor(0) == Pred1) {
1086 return BI->getCondition();