1 //===-- Local.cpp - Functions to perform local transformations ------------===//
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 various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Transforms/Utils/Local.h"
16 #include "llvm/ADT/DenseMap.h"
17 #include "llvm/ADT/DenseSet.h"
18 #include "llvm/ADT/Hashing.h"
19 #include "llvm/ADT/STLExtras.h"
20 #include "llvm/ADT/SmallPtrSet.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/Analysis/InstructionSimplify.h"
23 #include "llvm/Analysis/LibCallSemantics.h"
24 #include "llvm/Analysis/MemoryBuiltins.h"
25 #include "llvm/Analysis/ValueTracking.h"
26 #include "llvm/IR/CFG.h"
27 #include "llvm/IR/Constants.h"
28 #include "llvm/IR/DIBuilder.h"
29 #include "llvm/IR/DataLayout.h"
30 #include "llvm/IR/DebugInfo.h"
31 #include "llvm/IR/DerivedTypes.h"
32 #include "llvm/IR/Dominators.h"
33 #include "llvm/IR/GetElementPtrTypeIterator.h"
34 #include "llvm/IR/GlobalAlias.h"
35 #include "llvm/IR/GlobalVariable.h"
36 #include "llvm/IR/IRBuilder.h"
37 #include "llvm/IR/Instructions.h"
38 #include "llvm/IR/IntrinsicInst.h"
39 #include "llvm/IR/Intrinsics.h"
40 #include "llvm/IR/MDBuilder.h"
41 #include "llvm/IR/Metadata.h"
42 #include "llvm/IR/Operator.h"
43 #include "llvm/IR/ValueHandle.h"
44 #include "llvm/Support/Debug.h"
45 #include "llvm/Support/MathExtras.h"
46 #include "llvm/Support/raw_ostream.h"
49 #define DEBUG_TYPE "local"
51 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
53 //===----------------------------------------------------------------------===//
54 // Local constant propagation.
57 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
58 /// constant value, convert it into an unconditional branch to the constant
59 /// destination. This is a nontrivial operation because the successors of this
60 /// basic block must have their PHI nodes updated.
61 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
62 /// conditions and indirectbr addresses this might make dead if
63 /// DeleteDeadConditions is true.
64 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
65 const TargetLibraryInfo *TLI) {
66 TerminatorInst *T = BB->getTerminator();
67 IRBuilder<> Builder(T);
69 // Branch - See if we are conditional jumping on constant
70 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
71 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
72 BasicBlock *Dest1 = BI->getSuccessor(0);
73 BasicBlock *Dest2 = BI->getSuccessor(1);
75 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
76 // Are we branching on constant?
77 // YES. Change to unconditional branch...
78 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
79 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
81 //cerr << "Function: " << T->getParent()->getParent()
82 // << "\nRemoving branch from " << T->getParent()
83 // << "\n\nTo: " << OldDest << endl;
85 // Let the basic block know that we are letting go of it. Based on this,
86 // it will adjust it's PHI nodes.
87 OldDest->removePredecessor(BB);
89 // Replace the conditional branch with an unconditional one.
90 Builder.CreateBr(Destination);
91 BI->eraseFromParent();
95 if (Dest2 == Dest1) { // Conditional branch to same location?
96 // This branch matches something like this:
97 // br bool %cond, label %Dest, label %Dest
98 // and changes it into: br label %Dest
100 // Let the basic block know that we are letting go of one copy of it.
101 assert(BI->getParent() && "Terminator not inserted in block!");
102 Dest1->removePredecessor(BI->getParent());
104 // Replace the conditional branch with an unconditional one.
105 Builder.CreateBr(Dest1);
106 Value *Cond = BI->getCondition();
107 BI->eraseFromParent();
108 if (DeleteDeadConditions)
109 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
115 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
116 // If we are switching on a constant, we can convert the switch to an
117 // unconditional branch.
118 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
119 BasicBlock *DefaultDest = SI->getDefaultDest();
120 BasicBlock *TheOnlyDest = DefaultDest;
122 // If the default is unreachable, ignore it when searching for TheOnlyDest.
123 if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
124 SI->getNumCases() > 0) {
125 TheOnlyDest = SI->case_begin().getCaseSuccessor();
128 // Figure out which case it goes to.
129 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
131 // Found case matching a constant operand?
132 if (i.getCaseValue() == CI) {
133 TheOnlyDest = i.getCaseSuccessor();
137 // Check to see if this branch is going to the same place as the default
138 // dest. If so, eliminate it as an explicit compare.
139 if (i.getCaseSuccessor() == DefaultDest) {
140 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
141 unsigned NCases = SI->getNumCases();
142 // Fold the case metadata into the default if there will be any branches
143 // left, unless the metadata doesn't match the switch.
144 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
145 // Collect branch weights into a vector.
146 SmallVector<uint32_t, 8> Weights;
147 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
150 mdconst::dyn_extract<ConstantInt>(MD->getOperand(MD_i));
152 Weights.push_back(CI->getValue().getZExtValue());
154 // Merge weight of this case to the default weight.
155 unsigned idx = i.getCaseIndex();
156 Weights[0] += Weights[idx+1];
157 // Remove weight for this case.
158 std::swap(Weights[idx+1], Weights.back());
160 SI->setMetadata(LLVMContext::MD_prof,
161 MDBuilder(BB->getContext()).
162 createBranchWeights(Weights));
164 // Remove this entry.
165 DefaultDest->removePredecessor(SI->getParent());
171 // Otherwise, check to see if the switch only branches to one destination.
172 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
174 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
177 if (CI && !TheOnlyDest) {
178 // Branching on a constant, but not any of the cases, go to the default
180 TheOnlyDest = SI->getDefaultDest();
183 // If we found a single destination that we can fold the switch into, do so
186 // Insert the new branch.
187 Builder.CreateBr(TheOnlyDest);
188 BasicBlock *BB = SI->getParent();
190 // Remove entries from PHI nodes which we no longer branch to...
191 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
192 // Found case matching a constant operand?
193 BasicBlock *Succ = SI->getSuccessor(i);
194 if (Succ == TheOnlyDest)
195 TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
197 Succ->removePredecessor(BB);
200 // Delete the old switch.
201 Value *Cond = SI->getCondition();
202 SI->eraseFromParent();
203 if (DeleteDeadConditions)
204 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
208 if (SI->getNumCases() == 1) {
209 // Otherwise, we can fold this switch into a conditional branch
210 // instruction if it has only one non-default destination.
211 SwitchInst::CaseIt FirstCase = SI->case_begin();
212 Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
213 FirstCase.getCaseValue(), "cond");
215 // Insert the new branch.
216 BranchInst *NewBr = Builder.CreateCondBr(Cond,
217 FirstCase.getCaseSuccessor(),
218 SI->getDefaultDest());
219 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
220 if (MD && MD->getNumOperands() == 3) {
221 ConstantInt *SICase =
222 mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
224 mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
225 assert(SICase && SIDef);
226 // The TrueWeight should be the weight for the single case of SI.
227 NewBr->setMetadata(LLVMContext::MD_prof,
228 MDBuilder(BB->getContext()).
229 createBranchWeights(SICase->getValue().getZExtValue(),
230 SIDef->getValue().getZExtValue()));
233 // Delete the old switch.
234 SI->eraseFromParent();
240 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
241 // indirectbr blockaddress(@F, @BB) -> br label @BB
242 if (BlockAddress *BA =
243 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
244 BasicBlock *TheOnlyDest = BA->getBasicBlock();
245 // Insert the new branch.
246 Builder.CreateBr(TheOnlyDest);
248 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
249 if (IBI->getDestination(i) == TheOnlyDest)
250 TheOnlyDest = nullptr;
252 IBI->getDestination(i)->removePredecessor(IBI->getParent());
254 Value *Address = IBI->getAddress();
255 IBI->eraseFromParent();
256 if (DeleteDeadConditions)
257 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
259 // If we didn't find our destination in the IBI successor list, then we
260 // have undefined behavior. Replace the unconditional branch with an
261 // 'unreachable' instruction.
263 BB->getTerminator()->eraseFromParent();
264 new UnreachableInst(BB->getContext(), BB);
275 //===----------------------------------------------------------------------===//
276 // Local dead code elimination.
279 /// isInstructionTriviallyDead - Return true if the result produced by the
280 /// instruction is not used, and the instruction has no side effects.
282 bool llvm::isInstructionTriviallyDead(Instruction *I,
283 const TargetLibraryInfo *TLI) {
284 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
286 // We don't want the landingpad instruction removed by anything this general.
287 if (isa<LandingPadInst>(I))
290 // We don't want debug info removed by anything this general, unless
291 // debug info is empty.
292 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
293 if (DDI->getAddress())
297 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
303 if (!I->mayHaveSideEffects()) return true;
305 // Special case intrinsics that "may have side effects" but can be deleted
307 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
308 // Safe to delete llvm.stacksave if dead.
309 if (II->getIntrinsicID() == Intrinsic::stacksave)
312 // Lifetime intrinsics are dead when their right-hand is undef.
313 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
314 II->getIntrinsicID() == Intrinsic::lifetime_end)
315 return isa<UndefValue>(II->getArgOperand(1));
317 // Assumptions are dead if their condition is trivially true.
318 if (II->getIntrinsicID() == Intrinsic::assume) {
319 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
320 return !Cond->isZero();
326 if (isAllocLikeFn(I, TLI)) return true;
328 if (CallInst *CI = isFreeCall(I, TLI))
329 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
330 return C->isNullValue() || isa<UndefValue>(C);
335 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
336 /// trivially dead instruction, delete it. If that makes any of its operands
337 /// trivially dead, delete them too, recursively. Return true if any
338 /// instructions were deleted.
340 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
341 const TargetLibraryInfo *TLI) {
342 Instruction *I = dyn_cast<Instruction>(V);
343 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
346 SmallVector<Instruction*, 16> DeadInsts;
347 DeadInsts.push_back(I);
350 I = DeadInsts.pop_back_val();
352 // Null out all of the instruction's operands to see if any operand becomes
354 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
355 Value *OpV = I->getOperand(i);
356 I->setOperand(i, nullptr);
358 if (!OpV->use_empty()) continue;
360 // If the operand is an instruction that became dead as we nulled out the
361 // operand, and if it is 'trivially' dead, delete it in a future loop
363 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
364 if (isInstructionTriviallyDead(OpI, TLI))
365 DeadInsts.push_back(OpI);
368 I->eraseFromParent();
369 } while (!DeadInsts.empty());
374 /// areAllUsesEqual - Check whether the uses of a value are all the same.
375 /// This is similar to Instruction::hasOneUse() except this will also return
376 /// true when there are no uses or multiple uses that all refer to the same
378 static bool areAllUsesEqual(Instruction *I) {
379 Value::user_iterator UI = I->user_begin();
380 Value::user_iterator UE = I->user_end();
385 for (++UI; UI != UE; ++UI) {
392 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
393 /// dead PHI node, due to being a def-use chain of single-use nodes that
394 /// either forms a cycle or is terminated by a trivially dead instruction,
395 /// delete it. If that makes any of its operands trivially dead, delete them
396 /// too, recursively. Return true if a change was made.
397 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
398 const TargetLibraryInfo *TLI) {
399 SmallPtrSet<Instruction*, 4> Visited;
400 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
401 I = cast<Instruction>(*I->user_begin())) {
403 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
405 // If we find an instruction more than once, we're on a cycle that
406 // won't prove fruitful.
407 if (!Visited.insert(I).second) {
408 // Break the cycle and delete the instruction and its operands.
409 I->replaceAllUsesWith(UndefValue::get(I->getType()));
410 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
417 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
418 /// simplify any instructions in it and recursively delete dead instructions.
420 /// This returns true if it changed the code, note that it can delete
421 /// instructions in other blocks as well in this block.
422 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
423 const TargetLibraryInfo *TLI) {
424 bool MadeChange = false;
427 // In debug builds, ensure that the terminator of the block is never replaced
428 // or deleted by these simplifications. The idea of simplification is that it
429 // cannot introduce new instructions, and there is no way to replace the
430 // terminator of a block without introducing a new instruction.
431 AssertingVH<Instruction> TerminatorVH(--BB->end());
434 for (BasicBlock::iterator BI = BB->begin(), E = --BB->end(); BI != E; ) {
435 assert(!BI->isTerminator());
436 Instruction *Inst = BI++;
439 if (recursivelySimplifyInstruction(Inst, TLI)) {
446 MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst, TLI);
453 //===----------------------------------------------------------------------===//
454 // Control Flow Graph Restructuring.
458 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
459 /// method is called when we're about to delete Pred as a predecessor of BB. If
460 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
462 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
463 /// nodes that collapse into identity values. For example, if we have:
464 /// x = phi(1, 0, 0, 0)
467 /// .. and delete the predecessor corresponding to the '1', this will attempt to
468 /// recursively fold the and to 0.
469 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred) {
470 // This only adjusts blocks with PHI nodes.
471 if (!isa<PHINode>(BB->begin()))
474 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
475 // them down. This will leave us with single entry phi nodes and other phis
476 // that can be removed.
477 BB->removePredecessor(Pred, true);
479 WeakVH PhiIt = &BB->front();
480 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
481 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
482 Value *OldPhiIt = PhiIt;
484 if (!recursivelySimplifyInstruction(PN))
487 // If recursive simplification ended up deleting the next PHI node we would
488 // iterate to, then our iterator is invalid, restart scanning from the top
490 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
495 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
496 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
497 /// between them, moving the instructions in the predecessor into DestBB and
498 /// deleting the predecessor block.
500 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT) {
501 // If BB has single-entry PHI nodes, fold them.
502 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
503 Value *NewVal = PN->getIncomingValue(0);
504 // Replace self referencing PHI with undef, it must be dead.
505 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
506 PN->replaceAllUsesWith(NewVal);
507 PN->eraseFromParent();
510 BasicBlock *PredBB = DestBB->getSinglePredecessor();
511 assert(PredBB && "Block doesn't have a single predecessor!");
513 // Zap anything that took the address of DestBB. Not doing this will give the
514 // address an invalid value.
515 if (DestBB->hasAddressTaken()) {
516 BlockAddress *BA = BlockAddress::get(DestBB);
517 Constant *Replacement =
518 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
519 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
521 BA->destroyConstant();
524 // Anything that branched to PredBB now branches to DestBB.
525 PredBB->replaceAllUsesWith(DestBB);
527 // Splice all the instructions from PredBB to DestBB.
528 PredBB->getTerminator()->eraseFromParent();
529 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
531 // If the PredBB is the entry block of the function, move DestBB up to
532 // become the entry block after we erase PredBB.
533 if (PredBB == &DestBB->getParent()->getEntryBlock())
534 DestBB->moveAfter(PredBB);
537 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
538 DT->changeImmediateDominator(DestBB, PredBBIDom);
539 DT->eraseNode(PredBB);
542 PredBB->eraseFromParent();
545 /// CanMergeValues - Return true if we can choose one of these values to use
546 /// in place of the other. Note that we will always choose the non-undef
548 static bool CanMergeValues(Value *First, Value *Second) {
549 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
552 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
553 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
555 /// Assumption: Succ is the single successor for BB.
557 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
558 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
560 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
561 << Succ->getName() << "\n");
562 // Shortcut, if there is only a single predecessor it must be BB and merging
564 if (Succ->getSinglePredecessor()) return true;
566 // Make a list of the predecessors of BB
567 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
569 // Look at all the phi nodes in Succ, to see if they present a conflict when
570 // merging these blocks
571 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
572 PHINode *PN = cast<PHINode>(I);
574 // If the incoming value from BB is again a PHINode in
575 // BB which has the same incoming value for *PI as PN does, we can
576 // merge the phi nodes and then the blocks can still be merged
577 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
578 if (BBPN && BBPN->getParent() == BB) {
579 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
580 BasicBlock *IBB = PN->getIncomingBlock(PI);
581 if (BBPreds.count(IBB) &&
582 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
583 PN->getIncomingValue(PI))) {
584 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
585 << Succ->getName() << " is conflicting with "
586 << BBPN->getName() << " with regard to common predecessor "
587 << IBB->getName() << "\n");
592 Value* Val = PN->getIncomingValueForBlock(BB);
593 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
594 // See if the incoming value for the common predecessor is equal to the
595 // one for BB, in which case this phi node will not prevent the merging
597 BasicBlock *IBB = PN->getIncomingBlock(PI);
598 if (BBPreds.count(IBB) &&
599 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
600 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
601 << Succ->getName() << " is conflicting with regard to common "
602 << "predecessor " << IBB->getName() << "\n");
612 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
613 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
615 /// \brief Determines the value to use as the phi node input for a block.
617 /// Select between \p OldVal any value that we know flows from \p BB
618 /// to a particular phi on the basis of which one (if either) is not
619 /// undef. Update IncomingValues based on the selected value.
621 /// \param OldVal The value we are considering selecting.
622 /// \param BB The block that the value flows in from.
623 /// \param IncomingValues A map from block-to-value for other phi inputs
624 /// that we have examined.
626 /// \returns the selected value.
627 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
628 IncomingValueMap &IncomingValues) {
629 if (!isa<UndefValue>(OldVal)) {
630 assert((!IncomingValues.count(BB) ||
631 IncomingValues.find(BB)->second == OldVal) &&
632 "Expected OldVal to match incoming value from BB!");
634 IncomingValues.insert(std::make_pair(BB, OldVal));
638 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
639 if (It != IncomingValues.end()) return It->second;
644 /// \brief Create a map from block to value for the operands of a
647 /// Create a map from block to value for each non-undef value flowing
650 /// \param PN The phi we are collecting the map for.
651 /// \param IncomingValues [out] The map from block to value for this phi.
652 static void gatherIncomingValuesToPhi(PHINode *PN,
653 IncomingValueMap &IncomingValues) {
654 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
655 BasicBlock *BB = PN->getIncomingBlock(i);
656 Value *V = PN->getIncomingValue(i);
658 if (!isa<UndefValue>(V))
659 IncomingValues.insert(std::make_pair(BB, V));
663 /// \brief Replace the incoming undef values to a phi with the values
664 /// from a block-to-value map.
666 /// \param PN The phi we are replacing the undefs in.
667 /// \param IncomingValues A map from block to value.
668 static void replaceUndefValuesInPhi(PHINode *PN,
669 const IncomingValueMap &IncomingValues) {
670 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
671 Value *V = PN->getIncomingValue(i);
673 if (!isa<UndefValue>(V)) continue;
675 BasicBlock *BB = PN->getIncomingBlock(i);
676 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
677 if (It == IncomingValues.end()) continue;
679 PN->setIncomingValue(i, It->second);
683 /// \brief Replace a value flowing from a block to a phi with
684 /// potentially multiple instances of that value flowing from the
685 /// block's predecessors to the phi.
687 /// \param BB The block with the value flowing into the phi.
688 /// \param BBPreds The predecessors of BB.
689 /// \param PN The phi that we are updating.
690 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
691 const PredBlockVector &BBPreds,
693 Value *OldVal = PN->removeIncomingValue(BB, false);
694 assert(OldVal && "No entry in PHI for Pred BB!");
696 IncomingValueMap IncomingValues;
698 // We are merging two blocks - BB, and the block containing PN - and
699 // as a result we need to redirect edges from the predecessors of BB
700 // to go to the block containing PN, and update PN
701 // accordingly. Since we allow merging blocks in the case where the
702 // predecessor and successor blocks both share some predecessors,
703 // and where some of those common predecessors might have undef
704 // values flowing into PN, we want to rewrite those values to be
705 // consistent with the non-undef values.
707 gatherIncomingValuesToPhi(PN, IncomingValues);
709 // If this incoming value is one of the PHI nodes in BB, the new entries
710 // in the PHI node are the entries from the old PHI.
711 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
712 PHINode *OldValPN = cast<PHINode>(OldVal);
713 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
714 // Note that, since we are merging phi nodes and BB and Succ might
715 // have common predecessors, we could end up with a phi node with
716 // identical incoming branches. This will be cleaned up later (and
717 // will trigger asserts if we try to clean it up now, without also
718 // simplifying the corresponding conditional branch).
719 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
720 Value *PredVal = OldValPN->getIncomingValue(i);
721 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
724 // And add a new incoming value for this predecessor for the
725 // newly retargeted branch.
726 PN->addIncoming(Selected, PredBB);
729 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
730 // Update existing incoming values in PN for this
731 // predecessor of BB.
732 BasicBlock *PredBB = BBPreds[i];
733 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
736 // And add a new incoming value for this predecessor for the
737 // newly retargeted branch.
738 PN->addIncoming(Selected, PredBB);
742 replaceUndefValuesInPhi(PN, IncomingValues);
745 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
746 /// unconditional branch, and contains no instructions other than PHI nodes,
747 /// potential side-effect free intrinsics and the branch. If possible,
748 /// eliminate BB by rewriting all the predecessors to branch to the successor
749 /// block and return true. If we can't transform, return false.
750 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
751 assert(BB != &BB->getParent()->getEntryBlock() &&
752 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
754 // We can't eliminate infinite loops.
755 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
756 if (BB == Succ) return false;
758 // Check to see if merging these blocks would cause conflicts for any of the
759 // phi nodes in BB or Succ. If not, we can safely merge.
760 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
762 // Check for cases where Succ has multiple predecessors and a PHI node in BB
763 // has uses which will not disappear when the PHI nodes are merged. It is
764 // possible to handle such cases, but difficult: it requires checking whether
765 // BB dominates Succ, which is non-trivial to calculate in the case where
766 // Succ has multiple predecessors. Also, it requires checking whether
767 // constructing the necessary self-referential PHI node doesn't introduce any
768 // conflicts; this isn't too difficult, but the previous code for doing this
771 // Note that if this check finds a live use, BB dominates Succ, so BB is
772 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
773 // folding the branch isn't profitable in that case anyway.
774 if (!Succ->getSinglePredecessor()) {
775 BasicBlock::iterator BBI = BB->begin();
776 while (isa<PHINode>(*BBI)) {
777 for (Use &U : BBI->uses()) {
778 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
779 if (PN->getIncomingBlock(U) != BB)
789 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
791 if (isa<PHINode>(Succ->begin())) {
792 // If there is more than one pred of succ, and there are PHI nodes in
793 // the successor, then we need to add incoming edges for the PHI nodes
795 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
797 // Loop over all of the PHI nodes in the successor of BB.
798 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
799 PHINode *PN = cast<PHINode>(I);
801 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
805 if (Succ->getSinglePredecessor()) {
806 // BB is the only predecessor of Succ, so Succ will end up with exactly
807 // the same predecessors BB had.
809 // Copy over any phi, debug or lifetime instruction.
810 BB->getTerminator()->eraseFromParent();
811 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
813 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
814 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
815 assert(PN->use_empty() && "There shouldn't be any uses here!");
816 PN->eraseFromParent();
820 // Everything that jumped to BB now goes to Succ.
821 BB->replaceAllUsesWith(Succ);
822 if (!Succ->hasName()) Succ->takeName(BB);
823 BB->eraseFromParent(); // Delete the old basic block.
827 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
828 /// nodes in this block. This doesn't try to be clever about PHI nodes
829 /// which differ only in the order of the incoming values, but instcombine
830 /// orders them so it usually won't matter.
832 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
833 // This implementation doesn't currently consider undef operands
834 // specially. Theoretically, two phis which are identical except for
835 // one having an undef where the other doesn't could be collapsed.
837 struct PHIDenseMapInfo {
838 static PHINode *getEmptyKey() {
839 return DenseMapInfo<PHINode *>::getEmptyKey();
841 static PHINode *getTombstoneKey() {
842 return DenseMapInfo<PHINode *>::getTombstoneKey();
844 static unsigned getHashValue(PHINode *PN) {
845 // Compute a hash value on the operands. Instcombine will likely have
846 // sorted them, which helps expose duplicates, but we have to check all
847 // the operands to be safe in case instcombine hasn't run.
848 return static_cast<unsigned>(hash_combine(
849 hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
850 hash_combine_range(PN->block_begin(), PN->block_end())));
852 static bool isEqual(PHINode *LHS, PHINode *RHS) {
853 if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
854 RHS == getEmptyKey() || RHS == getTombstoneKey())
856 return LHS->isIdenticalTo(RHS);
860 // Set of unique PHINodes.
861 DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
864 bool Changed = false;
865 for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
866 auto Inserted = PHISet.insert(PN);
867 if (!Inserted.second) {
868 // A duplicate. Replace this PHI with its duplicate.
869 PN->replaceAllUsesWith(*Inserted.first);
870 PN->eraseFromParent();
878 /// enforceKnownAlignment - If the specified pointer points to an object that
879 /// we control, modify the object's alignment to PrefAlign. This isn't
880 /// often possible though. If alignment is important, a more reliable approach
881 /// is to simply align all global variables and allocation instructions to
882 /// their preferred alignment from the beginning.
884 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
886 const DataLayout &DL) {
887 V = V->stripPointerCasts();
889 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
890 // If the preferred alignment is greater than the natural stack alignment
891 // then don't round up. This avoids dynamic stack realignment.
892 if (DL.exceedsNaturalStackAlignment(PrefAlign))
894 // If there is a requested alignment and if this is an alloca, round up.
895 if (AI->getAlignment() >= PrefAlign)
896 return AI->getAlignment();
897 AI->setAlignment(PrefAlign);
901 if (auto *GO = dyn_cast<GlobalObject>(V)) {
902 // If there is a large requested alignment and we can, bump up the alignment
903 // of the global. If the memory we set aside for the global may not be the
904 // memory used by the final program then it is impossible for us to reliably
905 // enforce the preferred alignment.
906 if (!GO->isStrongDefinitionForLinker())
909 if (GO->getAlignment() >= PrefAlign)
910 return GO->getAlignment();
911 // We can only increase the alignment of the global if it has no alignment
912 // specified or if it is not assigned a section. If it is assigned a
913 // section, the global could be densely packed with other objects in the
914 // section, increasing the alignment could cause padding issues.
915 if (!GO->hasSection() || GO->getAlignment() == 0)
916 GO->setAlignment(PrefAlign);
917 return GO->getAlignment();
923 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
924 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
925 /// and it is more than the alignment of the ultimate object, see if we can
926 /// increase the alignment of the ultimate object, making this check succeed.
927 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
928 const DataLayout &DL,
929 const Instruction *CxtI,
931 const DominatorTree *DT) {
932 assert(V->getType()->isPointerTy() &&
933 "getOrEnforceKnownAlignment expects a pointer!");
934 unsigned BitWidth = DL.getPointerTypeSizeInBits(V->getType());
936 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
937 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
938 unsigned TrailZ = KnownZero.countTrailingOnes();
940 // Avoid trouble with ridiculously large TrailZ values, such as
941 // those computed from a null pointer.
942 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
944 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
946 // LLVM doesn't support alignments larger than this currently.
947 Align = std::min(Align, +Value::MaximumAlignment);
949 if (PrefAlign > Align)
950 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
952 // We don't need to make any adjustment.
956 ///===---------------------------------------------------------------------===//
957 /// Dbg Intrinsic utilities
960 /// See if there is a dbg.value intrinsic for DIVar before I.
961 static bool LdStHasDebugValue(const DILocalVariable *DIVar, Instruction *I) {
962 // Since we can't guarantee that the original dbg.declare instrinsic
963 // is removed by LowerDbgDeclare(), we need to make sure that we are
964 // not inserting the same dbg.value intrinsic over and over.
965 llvm::BasicBlock::InstListType::iterator PrevI(I);
966 if (PrevI != I->getParent()->getInstList().begin()) {
968 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
969 if (DVI->getValue() == I->getOperand(0) &&
970 DVI->getOffset() == 0 &&
971 DVI->getVariable() == DIVar)
977 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
978 /// that has an associated llvm.dbg.decl intrinsic.
979 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
980 StoreInst *SI, DIBuilder &Builder) {
981 auto *DIVar = DDI->getVariable();
982 auto *DIExpr = DDI->getExpression();
983 assert(DIVar && "Missing variable");
985 if (LdStHasDebugValue(DIVar, SI))
988 // If an argument is zero extended then use argument directly. The ZExt
989 // may be zapped by an optimization pass in future.
990 Argument *ExtendedArg = nullptr;
991 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
992 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
993 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
994 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
996 Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, DIExpr,
997 DDI->getDebugLoc(), SI);
999 Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, DIExpr,
1000 DDI->getDebugLoc(), SI);
1004 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1005 /// that has an associated llvm.dbg.decl intrinsic.
1006 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1007 LoadInst *LI, DIBuilder &Builder) {
1008 auto *DIVar = DDI->getVariable();
1009 auto *DIExpr = DDI->getExpression();
1010 assert(DIVar && "Missing variable");
1012 if (LdStHasDebugValue(DIVar, LI))
1015 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, DIVar, DIExpr,
1016 DDI->getDebugLoc(), LI);
1020 /// Determine whether this alloca is either a VLA or an array.
1021 static bool isArray(AllocaInst *AI) {
1022 return AI->isArrayAllocation() ||
1023 AI->getType()->getElementType()->isArrayTy();
1026 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1027 /// of llvm.dbg.value intrinsics.
1028 bool llvm::LowerDbgDeclare(Function &F) {
1029 DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1030 SmallVector<DbgDeclareInst *, 4> Dbgs;
1032 for (BasicBlock::iterator BI : FI)
1033 if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
1034 Dbgs.push_back(DDI);
1039 for (auto &I : Dbgs) {
1040 DbgDeclareInst *DDI = I;
1041 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1042 // If this is an alloca for a scalar variable, insert a dbg.value
1043 // at each load and store to the alloca and erase the dbg.declare.
1044 // The dbg.values allow tracking a variable even if it is not
1045 // stored on the stack, while the dbg.declare can only describe
1046 // the stack slot (and at a lexical-scope granularity). Later
1047 // passes will attempt to elide the stack slot.
1048 if (AI && !isArray(AI)) {
1049 for (User *U : AI->users())
1050 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1051 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1052 else if (LoadInst *LI = dyn_cast<LoadInst>(U))
1053 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1054 else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1055 // This is a call by-value or some other instruction that
1056 // takes a pointer to the variable. Insert a *value*
1057 // intrinsic that describes the alloca.
1058 DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
1059 DDI->getExpression(), DDI->getDebugLoc(),
1062 DDI->eraseFromParent();
1068 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1069 /// alloca 'V', if any.
1070 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1071 if (auto *L = LocalAsMetadata::getIfExists(V))
1072 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1073 for (User *U : MDV->users())
1074 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1080 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1081 DIBuilder &Builder, bool Deref) {
1082 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1085 DebugLoc Loc = DDI->getDebugLoc();
1086 auto *DIVar = DDI->getVariable();
1087 auto *DIExpr = DDI->getExpression();
1088 assert(DIVar && "Missing variable");
1091 // Create a copy of the original DIDescriptor for user variable, prepending
1092 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1093 // will take a value storing address of the memory for variable, not
1095 SmallVector<uint64_t, 4> NewDIExpr;
1096 NewDIExpr.push_back(dwarf::DW_OP_deref);
1098 NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
1099 DIExpr = Builder.createExpression(NewDIExpr);
1102 // Insert llvm.dbg.declare in the same basic block as the original alloca,
1103 // and remove old llvm.dbg.declare.
1104 BasicBlock *BB = AI->getParent();
1105 Builder.insertDeclare(NewAllocaAddress, DIVar, DIExpr, Loc, BB);
1106 DDI->eraseFromParent();
1110 /// changeToUnreachable - Insert an unreachable instruction before the specified
1111 /// instruction, making it and the rest of the code in the block dead.
1112 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1113 BasicBlock *BB = I->getParent();
1114 // Loop over all of the successors, removing BB's entry from any PHI
1116 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1117 (*SI)->removePredecessor(BB);
1119 // Insert a call to llvm.trap right before this. This turns the undefined
1120 // behavior into a hard fail instead of falling through into random code.
1123 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1124 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1125 CallTrap->setDebugLoc(I->getDebugLoc());
1127 new UnreachableInst(I->getContext(), I);
1129 // All instructions after this are dead.
1130 BasicBlock::iterator BBI = I, BBE = BB->end();
1131 while (BBI != BBE) {
1132 if (!BBI->use_empty())
1133 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1134 BB->getInstList().erase(BBI++);
1138 /// changeToCall - Convert the specified invoke into a normal call.
1139 static void changeToCall(InvokeInst *II) {
1140 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1141 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1142 NewCall->takeName(II);
1143 NewCall->setCallingConv(II->getCallingConv());
1144 NewCall->setAttributes(II->getAttributes());
1145 NewCall->setDebugLoc(II->getDebugLoc());
1146 II->replaceAllUsesWith(NewCall);
1148 // Follow the call by a branch to the normal destination.
1149 BranchInst::Create(II->getNormalDest(), II);
1151 // Update PHI nodes in the unwind destination
1152 II->getUnwindDest()->removePredecessor(II->getParent());
1153 II->eraseFromParent();
1156 static bool markAliveBlocks(Function &F,
1157 SmallPtrSetImpl<BasicBlock*> &Reachable) {
1159 SmallVector<BasicBlock*, 128> Worklist;
1160 BasicBlock *BB = F.begin();
1161 Worklist.push_back(BB);
1162 Reachable.insert(BB);
1163 bool Changed = false;
1165 BB = Worklist.pop_back_val();
1167 // Do a quick scan of the basic block, turning any obviously unreachable
1168 // instructions into LLVM unreachable insts. The instruction combining pass
1169 // canonicalizes unreachable insts into stores to null or undef.
1170 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1171 // Assumptions that are known to be false are equivalent to unreachable.
1172 // Also, if the condition is undefined, then we make the choice most
1173 // beneficial to the optimizer, and choose that to also be unreachable.
1174 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
1175 if (II->getIntrinsicID() == Intrinsic::assume) {
1176 bool MakeUnreachable = false;
1177 if (isa<UndefValue>(II->getArgOperand(0)))
1178 MakeUnreachable = true;
1179 else if (ConstantInt *Cond =
1180 dyn_cast<ConstantInt>(II->getArgOperand(0)))
1181 MakeUnreachable = Cond->isZero();
1183 if (MakeUnreachable) {
1184 // Don't insert a call to llvm.trap right before the unreachable.
1185 changeToUnreachable(BBI, false);
1191 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1192 if (CI->doesNotReturn()) {
1193 // If we found a call to a no-return function, insert an unreachable
1194 // instruction after it. Make sure there isn't *already* one there
1197 if (!isa<UnreachableInst>(BBI)) {
1198 // Don't insert a call to llvm.trap right before the unreachable.
1199 changeToUnreachable(BBI, false);
1206 // Store to undef and store to null are undefined and used to signal that
1207 // they should be changed to unreachable by passes that can't modify the
1209 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1210 // Don't touch volatile stores.
1211 if (SI->isVolatile()) continue;
1213 Value *Ptr = SI->getOperand(1);
1215 if (isa<UndefValue>(Ptr) ||
1216 (isa<ConstantPointerNull>(Ptr) &&
1217 SI->getPointerAddressSpace() == 0)) {
1218 changeToUnreachable(SI, true);
1225 // Turn invokes that call 'nounwind' functions into ordinary calls.
1226 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1227 Value *Callee = II->getCalledValue();
1228 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1229 changeToUnreachable(II, true);
1231 } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
1232 if (II->use_empty() && II->onlyReadsMemory()) {
1233 // jump to the normal destination branch.
1234 BranchInst::Create(II->getNormalDest(), II);
1235 II->getUnwindDest()->removePredecessor(II->getParent());
1236 II->eraseFromParent();
1243 Changed |= ConstantFoldTerminator(BB, true);
1244 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1245 if (Reachable.insert(*SI).second)
1246 Worklist.push_back(*SI);
1247 } while (!Worklist.empty());
1251 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1252 /// if they are in a dead cycle. Return true if a change was made, false
1254 bool llvm::removeUnreachableBlocks(Function &F) {
1255 SmallPtrSet<BasicBlock*, 128> Reachable;
1256 bool Changed = markAliveBlocks(F, Reachable);
1258 // If there are unreachable blocks in the CFG...
1259 if (Reachable.size() == F.size())
1262 assert(Reachable.size() < F.size());
1263 NumRemoved += F.size()-Reachable.size();
1265 // Loop over all of the basic blocks that are not reachable, dropping all of
1266 // their internal references...
1267 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1268 if (Reachable.count(BB))
1271 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1272 if (Reachable.count(*SI))
1273 (*SI)->removePredecessor(BB);
1274 BB->dropAllReferences();
1277 for (Function::iterator I = ++F.begin(); I != F.end();)
1278 if (!Reachable.count(I))
1279 I = F.getBasicBlockList().erase(I);
1286 void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
1287 SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
1288 K->dropUnknownMetadata(KnownIDs);
1289 K->getAllMetadataOtherThanDebugLoc(Metadata);
1290 for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
1291 unsigned Kind = Metadata[i].first;
1292 MDNode *JMD = J->getMetadata(Kind);
1293 MDNode *KMD = Metadata[i].second;
1297 K->setMetadata(Kind, nullptr); // Remove unknown metadata
1299 case LLVMContext::MD_dbg:
1300 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1301 case LLVMContext::MD_tbaa:
1302 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
1304 case LLVMContext::MD_alias_scope:
1305 K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
1307 case LLVMContext::MD_noalias:
1308 K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
1310 case LLVMContext::MD_range:
1311 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
1313 case LLVMContext::MD_fpmath:
1314 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
1316 case LLVMContext::MD_invariant_load:
1317 // Only set the !invariant.load if it is present in both instructions.
1318 K->setMetadata(Kind, JMD);
1320 case LLVMContext::MD_nonnull:
1321 // Only set the !nonnull if it is present in both instructions.
1322 K->setMetadata(Kind, JMD);
1328 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
1330 const BasicBlockEdge &Root) {
1331 assert(From->getType() == To->getType());
1334 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1337 if (DT.dominates(Root, U)) {
1339 DEBUG(dbgs() << "Replace dominated use of '"
1340 << From->getName() << "' as "
1341 << *To << " in " << *U << "\n");