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/SetVector.h"
21 #include "llvm/ADT/SmallPtrSet.h"
22 #include "llvm/ADT/Statistic.h"
23 #include "llvm/Analysis/InstructionSimplify.h"
24 #include "llvm/Analysis/LibCallSemantics.h"
25 #include "llvm/Analysis/MemoryBuiltins.h"
26 #include "llvm/Analysis/ValueTracking.h"
27 #include "llvm/IR/CFG.h"
28 #include "llvm/IR/Constants.h"
29 #include "llvm/IR/DIBuilder.h"
30 #include "llvm/IR/DataLayout.h"
31 #include "llvm/IR/DebugInfo.h"
32 #include "llvm/IR/DerivedTypes.h"
33 #include "llvm/IR/Dominators.h"
34 #include "llvm/IR/GetElementPtrTypeIterator.h"
35 #include "llvm/IR/GlobalAlias.h"
36 #include "llvm/IR/GlobalVariable.h"
37 #include "llvm/IR/IRBuilder.h"
38 #include "llvm/IR/Instructions.h"
39 #include "llvm/IR/IntrinsicInst.h"
40 #include "llvm/IR/Intrinsics.h"
41 #include "llvm/IR/MDBuilder.h"
42 #include "llvm/IR/Metadata.h"
43 #include "llvm/IR/Operator.h"
44 #include "llvm/IR/ValueHandle.h"
45 #include "llvm/Support/Debug.h"
46 #include "llvm/Support/MathExtras.h"
47 #include "llvm/Support/raw_ostream.h"
50 #define DEBUG_TYPE "local"
52 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
54 //===----------------------------------------------------------------------===//
55 // Local constant propagation.
58 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
59 /// constant value, convert it into an unconditional branch to the constant
60 /// destination. This is a nontrivial operation because the successors of this
61 /// basic block must have their PHI nodes updated.
62 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
63 /// conditions and indirectbr addresses this might make dead if
64 /// DeleteDeadConditions is true.
65 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
66 const TargetLibraryInfo *TLI) {
67 TerminatorInst *T = BB->getTerminator();
68 IRBuilder<> Builder(T);
70 // Branch - See if we are conditional jumping on constant
71 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
72 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
73 BasicBlock *Dest1 = BI->getSuccessor(0);
74 BasicBlock *Dest2 = BI->getSuccessor(1);
76 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
77 // Are we branching on constant?
78 // YES. Change to unconditional branch...
79 BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
80 BasicBlock *OldDest = Cond->getZExtValue() ? Dest2 : Dest1;
82 //cerr << "Function: " << T->getParent()->getParent()
83 // << "\nRemoving branch from " << T->getParent()
84 // << "\n\nTo: " << OldDest << endl;
86 // Let the basic block know that we are letting go of it. Based on this,
87 // it will adjust it's PHI nodes.
88 OldDest->removePredecessor(BB);
90 // Replace the conditional branch with an unconditional one.
91 Builder.CreateBr(Destination);
92 BI->eraseFromParent();
96 if (Dest2 == Dest1) { // Conditional branch to same location?
97 // This branch matches something like this:
98 // br bool %cond, label %Dest, label %Dest
99 // and changes it into: br label %Dest
101 // Let the basic block know that we are letting go of one copy of it.
102 assert(BI->getParent() && "Terminator not inserted in block!");
103 Dest1->removePredecessor(BI->getParent());
105 // Replace the conditional branch with an unconditional one.
106 Builder.CreateBr(Dest1);
107 Value *Cond = BI->getCondition();
108 BI->eraseFromParent();
109 if (DeleteDeadConditions)
110 RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
116 if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
117 // If we are switching on a constant, we can convert the switch to an
118 // unconditional branch.
119 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
120 BasicBlock *DefaultDest = SI->getDefaultDest();
121 BasicBlock *TheOnlyDest = DefaultDest;
123 // If the default is unreachable, ignore it when searching for TheOnlyDest.
124 if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
125 SI->getNumCases() > 0) {
126 TheOnlyDest = SI->case_begin().getCaseSuccessor();
129 // Figure out which case it goes to.
130 for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
132 // Found case matching a constant operand?
133 if (i.getCaseValue() == CI) {
134 TheOnlyDest = i.getCaseSuccessor();
138 // Check to see if this branch is going to the same place as the default
139 // dest. If so, eliminate it as an explicit compare.
140 if (i.getCaseSuccessor() == DefaultDest) {
141 MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
142 unsigned NCases = SI->getNumCases();
143 // Fold the case metadata into the default if there will be any branches
144 // left, unless the metadata doesn't match the switch.
145 if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
146 // Collect branch weights into a vector.
147 SmallVector<uint32_t, 8> Weights;
148 for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
151 mdconst::dyn_extract<ConstantInt>(MD->getOperand(MD_i));
153 Weights.push_back(CI->getValue().getZExtValue());
155 // Merge weight of this case to the default weight.
156 unsigned idx = i.getCaseIndex();
157 Weights[0] += Weights[idx+1];
158 // Remove weight for this case.
159 std::swap(Weights[idx+1], Weights.back());
161 SI->setMetadata(LLVMContext::MD_prof,
162 MDBuilder(BB->getContext()).
163 createBranchWeights(Weights));
165 // Remove this entry.
166 DefaultDest->removePredecessor(SI->getParent());
172 // Otherwise, check to see if the switch only branches to one destination.
173 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
175 if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
178 if (CI && !TheOnlyDest) {
179 // Branching on a constant, but not any of the cases, go to the default
181 TheOnlyDest = SI->getDefaultDest();
184 // If we found a single destination that we can fold the switch into, do so
187 // Insert the new branch.
188 Builder.CreateBr(TheOnlyDest);
189 BasicBlock *BB = SI->getParent();
191 // Remove entries from PHI nodes which we no longer branch to...
192 for (BasicBlock *Succ : SI->successors()) {
193 // Found case matching a constant operand?
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 // Update make.implicit metadata to the newly-created conditional branch.
234 MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
236 NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
238 // Delete the old switch.
239 SI->eraseFromParent();
245 if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
246 // indirectbr blockaddress(@F, @BB) -> br label @BB
247 if (BlockAddress *BA =
248 dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
249 BasicBlock *TheOnlyDest = BA->getBasicBlock();
250 // Insert the new branch.
251 Builder.CreateBr(TheOnlyDest);
253 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
254 if (IBI->getDestination(i) == TheOnlyDest)
255 TheOnlyDest = nullptr;
257 IBI->getDestination(i)->removePredecessor(IBI->getParent());
259 Value *Address = IBI->getAddress();
260 IBI->eraseFromParent();
261 if (DeleteDeadConditions)
262 RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
264 // If we didn't find our destination in the IBI successor list, then we
265 // have undefined behavior. Replace the unconditional branch with an
266 // 'unreachable' instruction.
268 BB->getTerminator()->eraseFromParent();
269 new UnreachableInst(BB->getContext(), BB);
280 //===----------------------------------------------------------------------===//
281 // Local dead code elimination.
284 /// isInstructionTriviallyDead - Return true if the result produced by the
285 /// instruction is not used, and the instruction has no side effects.
287 bool llvm::isInstructionTriviallyDead(Instruction *I,
288 const TargetLibraryInfo *TLI) {
289 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
291 // We don't want the landingpad-like instructions removed by anything this
296 // We don't want debug info removed by anything this general, unless
297 // debug info is empty.
298 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
299 if (DDI->getAddress())
303 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
309 if (!I->mayHaveSideEffects()) return true;
311 // Special case intrinsics that "may have side effects" but can be deleted
313 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
314 // Safe to delete llvm.stacksave if dead.
315 if (II->getIntrinsicID() == Intrinsic::stacksave)
318 // Lifetime intrinsics are dead when their right-hand is undef.
319 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
320 II->getIntrinsicID() == Intrinsic::lifetime_end)
321 return isa<UndefValue>(II->getArgOperand(1));
323 // Assumptions are dead if their condition is trivially true.
324 if (II->getIntrinsicID() == Intrinsic::assume) {
325 if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
326 return !Cond->isZero();
332 if (isAllocLikeFn(I, TLI)) return true;
334 if (CallInst *CI = isFreeCall(I, TLI))
335 if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
336 return C->isNullValue() || isa<UndefValue>(C);
341 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
342 /// trivially dead instruction, delete it. If that makes any of its operands
343 /// trivially dead, delete them too, recursively. Return true if any
344 /// instructions were deleted.
346 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
347 const TargetLibraryInfo *TLI) {
348 Instruction *I = dyn_cast<Instruction>(V);
349 if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
352 SmallVector<Instruction*, 16> DeadInsts;
353 DeadInsts.push_back(I);
356 I = DeadInsts.pop_back_val();
358 // Null out all of the instruction's operands to see if any operand becomes
360 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
361 Value *OpV = I->getOperand(i);
362 I->setOperand(i, nullptr);
364 if (!OpV->use_empty()) continue;
366 // If the operand is an instruction that became dead as we nulled out the
367 // operand, and if it is 'trivially' dead, delete it in a future loop
369 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
370 if (isInstructionTriviallyDead(OpI, TLI))
371 DeadInsts.push_back(OpI);
374 I->eraseFromParent();
375 } while (!DeadInsts.empty());
380 /// areAllUsesEqual - Check whether the uses of a value are all the same.
381 /// This is similar to Instruction::hasOneUse() except this will also return
382 /// true when there are no uses or multiple uses that all refer to the same
384 static bool areAllUsesEqual(Instruction *I) {
385 Value::user_iterator UI = I->user_begin();
386 Value::user_iterator UE = I->user_end();
391 for (++UI; UI != UE; ++UI) {
398 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
399 /// dead PHI node, due to being a def-use chain of single-use nodes that
400 /// either forms a cycle or is terminated by a trivially dead instruction,
401 /// delete it. If that makes any of its operands trivially dead, delete them
402 /// too, recursively. Return true if a change was made.
403 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
404 const TargetLibraryInfo *TLI) {
405 SmallPtrSet<Instruction*, 4> Visited;
406 for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
407 I = cast<Instruction>(*I->user_begin())) {
409 return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
411 // If we find an instruction more than once, we're on a cycle that
412 // won't prove fruitful.
413 if (!Visited.insert(I).second) {
414 // Break the cycle and delete the instruction and its operands.
415 I->replaceAllUsesWith(UndefValue::get(I->getType()));
416 (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
424 simplifyAndDCEInstruction(Instruction *I,
425 SmallSetVector<Instruction *, 16> &WorkList,
426 const DataLayout &DL,
427 const TargetLibraryInfo *TLI) {
428 if (isInstructionTriviallyDead(I, TLI)) {
429 // Null out all of the instruction's operands to see if any operand becomes
431 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
432 Value *OpV = I->getOperand(i);
433 I->setOperand(i, nullptr);
435 if (!OpV->use_empty() || I == OpV)
438 // If the operand is an instruction that became dead as we nulled out the
439 // operand, and if it is 'trivially' dead, delete it in a future loop
441 if (Instruction *OpI = dyn_cast<Instruction>(OpV))
442 if (isInstructionTriviallyDead(OpI, TLI))
443 WorkList.insert(OpI);
446 I->eraseFromParent();
451 if (Value *SimpleV = SimplifyInstruction(I, DL)) {
452 // Add the users to the worklist. CAREFUL: an instruction can use itself,
453 // in the case of a phi node.
454 for (User *U : I->users())
456 WorkList.insert(cast<Instruction>(U));
458 // Replace the instruction with its simplified value.
459 I->replaceAllUsesWith(SimpleV);
460 I->eraseFromParent();
466 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
467 /// simplify any instructions in it and recursively delete dead instructions.
469 /// This returns true if it changed the code, note that it can delete
470 /// instructions in other blocks as well in this block.
471 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
472 const TargetLibraryInfo *TLI) {
473 bool MadeChange = false;
474 const DataLayout &DL = BB->getModule()->getDataLayout();
477 // In debug builds, ensure that the terminator of the block is never replaced
478 // or deleted by these simplifications. The idea of simplification is that it
479 // cannot introduce new instructions, and there is no way to replace the
480 // terminator of a block without introducing a new instruction.
481 AssertingVH<Instruction> TerminatorVH(--BB->end());
484 SmallSetVector<Instruction *, 16> WorkList;
485 // Iterate over the original function, only adding insts to the worklist
486 // if they actually need to be revisited. This avoids having to pre-init
487 // the worklist with the entire function's worth of instructions.
488 for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end()); BI != E;) {
489 assert(!BI->isTerminator());
490 Instruction *I = &*BI;
493 // We're visiting this instruction now, so make sure it's not in the
494 // worklist from an earlier visit.
495 if (!WorkList.count(I))
496 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
499 while (!WorkList.empty()) {
500 Instruction *I = WorkList.pop_back_val();
501 MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
506 //===----------------------------------------------------------------------===//
507 // Control Flow Graph Restructuring.
511 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
512 /// method is called when we're about to delete Pred as a predecessor of BB. If
513 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
515 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
516 /// nodes that collapse into identity values. For example, if we have:
517 /// x = phi(1, 0, 0, 0)
520 /// .. and delete the predecessor corresponding to the '1', this will attempt to
521 /// recursively fold the and to 0.
522 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred) {
523 // This only adjusts blocks with PHI nodes.
524 if (!isa<PHINode>(BB->begin()))
527 // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
528 // them down. This will leave us with single entry phi nodes and other phis
529 // that can be removed.
530 BB->removePredecessor(Pred, true);
532 WeakVH PhiIt = &BB->front();
533 while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
534 PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
535 Value *OldPhiIt = PhiIt;
537 if (!recursivelySimplifyInstruction(PN))
540 // If recursive simplification ended up deleting the next PHI node we would
541 // iterate to, then our iterator is invalid, restart scanning from the top
543 if (PhiIt != OldPhiIt) PhiIt = &BB->front();
548 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
549 /// predecessor is known to have one successor (DestBB!). Eliminate the edge
550 /// between them, moving the instructions in the predecessor into DestBB and
551 /// deleting the predecessor block.
553 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT) {
554 // If BB has single-entry PHI nodes, fold them.
555 while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
556 Value *NewVal = PN->getIncomingValue(0);
557 // Replace self referencing PHI with undef, it must be dead.
558 if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
559 PN->replaceAllUsesWith(NewVal);
560 PN->eraseFromParent();
563 BasicBlock *PredBB = DestBB->getSinglePredecessor();
564 assert(PredBB && "Block doesn't have a single predecessor!");
566 // Zap anything that took the address of DestBB. Not doing this will give the
567 // address an invalid value.
568 if (DestBB->hasAddressTaken()) {
569 BlockAddress *BA = BlockAddress::get(DestBB);
570 Constant *Replacement =
571 ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
572 BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
574 BA->destroyConstant();
577 // Anything that branched to PredBB now branches to DestBB.
578 PredBB->replaceAllUsesWith(DestBB);
580 // Splice all the instructions from PredBB to DestBB.
581 PredBB->getTerminator()->eraseFromParent();
582 DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
584 // If the PredBB is the entry block of the function, move DestBB up to
585 // become the entry block after we erase PredBB.
586 if (PredBB == &DestBB->getParent()->getEntryBlock())
587 DestBB->moveAfter(PredBB);
590 BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
591 DT->changeImmediateDominator(DestBB, PredBBIDom);
592 DT->eraseNode(PredBB);
595 PredBB->eraseFromParent();
598 /// CanMergeValues - Return true if we can choose one of these values to use
599 /// in place of the other. Note that we will always choose the non-undef
601 static bool CanMergeValues(Value *First, Value *Second) {
602 return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
605 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
606 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
608 /// Assumption: Succ is the single successor for BB.
610 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
611 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
613 DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
614 << Succ->getName() << "\n");
615 // Shortcut, if there is only a single predecessor it must be BB and merging
617 if (Succ->getSinglePredecessor()) return true;
619 // Make a list of the predecessors of BB
620 SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
622 // Look at all the phi nodes in Succ, to see if they present a conflict when
623 // merging these blocks
624 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
625 PHINode *PN = cast<PHINode>(I);
627 // If the incoming value from BB is again a PHINode in
628 // BB which has the same incoming value for *PI as PN does, we can
629 // merge the phi nodes and then the blocks can still be merged
630 PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
631 if (BBPN && BBPN->getParent() == BB) {
632 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
633 BasicBlock *IBB = PN->getIncomingBlock(PI);
634 if (BBPreds.count(IBB) &&
635 !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
636 PN->getIncomingValue(PI))) {
637 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
638 << Succ->getName() << " is conflicting with "
639 << BBPN->getName() << " with regard to common predecessor "
640 << IBB->getName() << "\n");
645 Value* Val = PN->getIncomingValueForBlock(BB);
646 for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
647 // See if the incoming value for the common predecessor is equal to the
648 // one for BB, in which case this phi node will not prevent the merging
650 BasicBlock *IBB = PN->getIncomingBlock(PI);
651 if (BBPreds.count(IBB) &&
652 !CanMergeValues(Val, PN->getIncomingValue(PI))) {
653 DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
654 << Succ->getName() << " is conflicting with regard to common "
655 << "predecessor " << IBB->getName() << "\n");
665 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
666 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
668 /// \brief Determines the value to use as the phi node input for a block.
670 /// Select between \p OldVal any value that we know flows from \p BB
671 /// to a particular phi on the basis of which one (if either) is not
672 /// undef. Update IncomingValues based on the selected value.
674 /// \param OldVal The value we are considering selecting.
675 /// \param BB The block that the value flows in from.
676 /// \param IncomingValues A map from block-to-value for other phi inputs
677 /// that we have examined.
679 /// \returns the selected value.
680 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
681 IncomingValueMap &IncomingValues) {
682 if (!isa<UndefValue>(OldVal)) {
683 assert((!IncomingValues.count(BB) ||
684 IncomingValues.find(BB)->second == OldVal) &&
685 "Expected OldVal to match incoming value from BB!");
687 IncomingValues.insert(std::make_pair(BB, OldVal));
691 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
692 if (It != IncomingValues.end()) return It->second;
697 /// \brief Create a map from block to value for the operands of a
700 /// Create a map from block to value for each non-undef value flowing
703 /// \param PN The phi we are collecting the map for.
704 /// \param IncomingValues [out] The map from block to value for this phi.
705 static void gatherIncomingValuesToPhi(PHINode *PN,
706 IncomingValueMap &IncomingValues) {
707 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
708 BasicBlock *BB = PN->getIncomingBlock(i);
709 Value *V = PN->getIncomingValue(i);
711 if (!isa<UndefValue>(V))
712 IncomingValues.insert(std::make_pair(BB, V));
716 /// \brief Replace the incoming undef values to a phi with the values
717 /// from a block-to-value map.
719 /// \param PN The phi we are replacing the undefs in.
720 /// \param IncomingValues A map from block to value.
721 static void replaceUndefValuesInPhi(PHINode *PN,
722 const IncomingValueMap &IncomingValues) {
723 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
724 Value *V = PN->getIncomingValue(i);
726 if (!isa<UndefValue>(V)) continue;
728 BasicBlock *BB = PN->getIncomingBlock(i);
729 IncomingValueMap::const_iterator It = IncomingValues.find(BB);
730 if (It == IncomingValues.end()) continue;
732 PN->setIncomingValue(i, It->second);
736 /// \brief Replace a value flowing from a block to a phi with
737 /// potentially multiple instances of that value flowing from the
738 /// block's predecessors to the phi.
740 /// \param BB The block with the value flowing into the phi.
741 /// \param BBPreds The predecessors of BB.
742 /// \param PN The phi that we are updating.
743 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
744 const PredBlockVector &BBPreds,
746 Value *OldVal = PN->removeIncomingValue(BB, false);
747 assert(OldVal && "No entry in PHI for Pred BB!");
749 IncomingValueMap IncomingValues;
751 // We are merging two blocks - BB, and the block containing PN - and
752 // as a result we need to redirect edges from the predecessors of BB
753 // to go to the block containing PN, and update PN
754 // accordingly. Since we allow merging blocks in the case where the
755 // predecessor and successor blocks both share some predecessors,
756 // and where some of those common predecessors might have undef
757 // values flowing into PN, we want to rewrite those values to be
758 // consistent with the non-undef values.
760 gatherIncomingValuesToPhi(PN, IncomingValues);
762 // If this incoming value is one of the PHI nodes in BB, the new entries
763 // in the PHI node are the entries from the old PHI.
764 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
765 PHINode *OldValPN = cast<PHINode>(OldVal);
766 for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
767 // Note that, since we are merging phi nodes and BB and Succ might
768 // have common predecessors, we could end up with a phi node with
769 // identical incoming branches. This will be cleaned up later (and
770 // will trigger asserts if we try to clean it up now, without also
771 // simplifying the corresponding conditional branch).
772 BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
773 Value *PredVal = OldValPN->getIncomingValue(i);
774 Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
777 // And add a new incoming value for this predecessor for the
778 // newly retargeted branch.
779 PN->addIncoming(Selected, PredBB);
782 for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
783 // Update existing incoming values in PN for this
784 // predecessor of BB.
785 BasicBlock *PredBB = BBPreds[i];
786 Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
789 // And add a new incoming value for this predecessor for the
790 // newly retargeted branch.
791 PN->addIncoming(Selected, PredBB);
795 replaceUndefValuesInPhi(PN, IncomingValues);
798 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
799 /// unconditional branch, and contains no instructions other than PHI nodes,
800 /// potential side-effect free intrinsics and the branch. If possible,
801 /// eliminate BB by rewriting all the predecessors to branch to the successor
802 /// block and return true. If we can't transform, return false.
803 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
804 assert(BB != &BB->getParent()->getEntryBlock() &&
805 "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
807 // We can't eliminate infinite loops.
808 BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
809 if (BB == Succ) return false;
811 // Check to see if merging these blocks would cause conflicts for any of the
812 // phi nodes in BB or Succ. If not, we can safely merge.
813 if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
815 // Check for cases where Succ has multiple predecessors and a PHI node in BB
816 // has uses which will not disappear when the PHI nodes are merged. It is
817 // possible to handle such cases, but difficult: it requires checking whether
818 // BB dominates Succ, which is non-trivial to calculate in the case where
819 // Succ has multiple predecessors. Also, it requires checking whether
820 // constructing the necessary self-referential PHI node doesn't introduce any
821 // conflicts; this isn't too difficult, but the previous code for doing this
824 // Note that if this check finds a live use, BB dominates Succ, so BB is
825 // something like a loop pre-header (or rarely, a part of an irreducible CFG);
826 // folding the branch isn't profitable in that case anyway.
827 if (!Succ->getSinglePredecessor()) {
828 BasicBlock::iterator BBI = BB->begin();
829 while (isa<PHINode>(*BBI)) {
830 for (Use &U : BBI->uses()) {
831 if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
832 if (PN->getIncomingBlock(U) != BB)
842 DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
844 if (isa<PHINode>(Succ->begin())) {
845 // If there is more than one pred of succ, and there are PHI nodes in
846 // the successor, then we need to add incoming edges for the PHI nodes
848 const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
850 // Loop over all of the PHI nodes in the successor of BB.
851 for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
852 PHINode *PN = cast<PHINode>(I);
854 redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
858 if (Succ->getSinglePredecessor()) {
859 // BB is the only predecessor of Succ, so Succ will end up with exactly
860 // the same predecessors BB had.
862 // Copy over any phi, debug or lifetime instruction.
863 BB->getTerminator()->eraseFromParent();
864 Succ->getInstList().splice(Succ->getFirstNonPHI(), BB->getInstList());
866 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
867 // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
868 assert(PN->use_empty() && "There shouldn't be any uses here!");
869 PN->eraseFromParent();
873 // Everything that jumped to BB now goes to Succ.
874 BB->replaceAllUsesWith(Succ);
875 if (!Succ->hasName()) Succ->takeName(BB);
876 BB->eraseFromParent(); // Delete the old basic block.
880 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
881 /// nodes in this block. This doesn't try to be clever about PHI nodes
882 /// which differ only in the order of the incoming values, but instcombine
883 /// orders them so it usually won't matter.
885 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
886 // This implementation doesn't currently consider undef operands
887 // specially. Theoretically, two phis which are identical except for
888 // one having an undef where the other doesn't could be collapsed.
890 struct PHIDenseMapInfo {
891 static PHINode *getEmptyKey() {
892 return DenseMapInfo<PHINode *>::getEmptyKey();
894 static PHINode *getTombstoneKey() {
895 return DenseMapInfo<PHINode *>::getTombstoneKey();
897 static unsigned getHashValue(PHINode *PN) {
898 // Compute a hash value on the operands. Instcombine will likely have
899 // sorted them, which helps expose duplicates, but we have to check all
900 // the operands to be safe in case instcombine hasn't run.
901 return static_cast<unsigned>(hash_combine(
902 hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
903 hash_combine_range(PN->block_begin(), PN->block_end())));
905 static bool isEqual(PHINode *LHS, PHINode *RHS) {
906 if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
907 RHS == getEmptyKey() || RHS == getTombstoneKey())
909 return LHS->isIdenticalTo(RHS);
913 // Set of unique PHINodes.
914 DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
917 bool Changed = false;
918 for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
919 auto Inserted = PHISet.insert(PN);
920 if (!Inserted.second) {
921 // A duplicate. Replace this PHI with its duplicate.
922 PN->replaceAllUsesWith(*Inserted.first);
923 PN->eraseFromParent();
926 // The RAUW can change PHIs that we already visited. Start over from the
936 /// enforceKnownAlignment - If the specified pointer points to an object that
937 /// we control, modify the object's alignment to PrefAlign. This isn't
938 /// often possible though. If alignment is important, a more reliable approach
939 /// is to simply align all global variables and allocation instructions to
940 /// their preferred alignment from the beginning.
942 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
944 const DataLayout &DL) {
945 V = V->stripPointerCasts();
947 if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
948 // If the preferred alignment is greater than the natural stack alignment
949 // then don't round up. This avoids dynamic stack realignment.
950 if (DL.exceedsNaturalStackAlignment(PrefAlign))
952 // If there is a requested alignment and if this is an alloca, round up.
953 if (AI->getAlignment() >= PrefAlign)
954 return AI->getAlignment();
955 AI->setAlignment(PrefAlign);
959 if (auto *GO = dyn_cast<GlobalObject>(V)) {
960 // If there is a large requested alignment and we can, bump up the alignment
961 // of the global. If the memory we set aside for the global may not be the
962 // memory used by the final program then it is impossible for us to reliably
963 // enforce the preferred alignment.
964 if (!GO->isStrongDefinitionForLinker())
967 if (GO->getAlignment() >= PrefAlign)
968 return GO->getAlignment();
969 // We can only increase the alignment of the global if it has no alignment
970 // specified or if it is not assigned a section. If it is assigned a
971 // section, the global could be densely packed with other objects in the
972 // section, increasing the alignment could cause padding issues.
973 if (!GO->hasSection() || GO->getAlignment() == 0)
974 GO->setAlignment(PrefAlign);
975 return GO->getAlignment();
981 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
982 /// we can determine, return it, otherwise return 0. If PrefAlign is specified,
983 /// and it is more than the alignment of the ultimate object, see if we can
984 /// increase the alignment of the ultimate object, making this check succeed.
985 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
986 const DataLayout &DL,
987 const Instruction *CxtI,
989 const DominatorTree *DT) {
990 assert(V->getType()->isPointerTy() &&
991 "getOrEnforceKnownAlignment expects a pointer!");
992 unsigned BitWidth = DL.getPointerTypeSizeInBits(V->getType());
994 APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
995 computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
996 unsigned TrailZ = KnownZero.countTrailingOnes();
998 // Avoid trouble with ridiculously large TrailZ values, such as
999 // those computed from a null pointer.
1000 TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
1002 unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
1004 // LLVM doesn't support alignments larger than this currently.
1005 Align = std::min(Align, +Value::MaximumAlignment);
1007 if (PrefAlign > Align)
1008 Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
1010 // We don't need to make any adjustment.
1014 ///===---------------------------------------------------------------------===//
1015 /// Dbg Intrinsic utilities
1018 /// See if there is a dbg.value intrinsic for DIVar before I.
1019 static bool LdStHasDebugValue(const DILocalVariable *DIVar, Instruction *I) {
1020 // Since we can't guarantee that the original dbg.declare instrinsic
1021 // is removed by LowerDbgDeclare(), we need to make sure that we are
1022 // not inserting the same dbg.value intrinsic over and over.
1023 llvm::BasicBlock::InstListType::iterator PrevI(I);
1024 if (PrevI != I->getParent()->getInstList().begin()) {
1026 if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
1027 if (DVI->getValue() == I->getOperand(0) &&
1028 DVI->getOffset() == 0 &&
1029 DVI->getVariable() == DIVar)
1035 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
1036 /// that has an associated llvm.dbg.decl intrinsic.
1037 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1038 StoreInst *SI, DIBuilder &Builder) {
1039 auto *DIVar = DDI->getVariable();
1040 auto *DIExpr = DDI->getExpression();
1041 assert(DIVar && "Missing variable");
1043 if (LdStHasDebugValue(DIVar, SI))
1046 // If an argument is zero extended then use argument directly. The ZExt
1047 // may be zapped by an optimization pass in future.
1048 Argument *ExtendedArg = nullptr;
1049 if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1050 ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1051 if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1052 ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1054 Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, DIExpr,
1055 DDI->getDebugLoc(), SI);
1057 Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, DIExpr,
1058 DDI->getDebugLoc(), SI);
1062 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1063 /// that has an associated llvm.dbg.decl intrinsic.
1064 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1065 LoadInst *LI, DIBuilder &Builder) {
1066 auto *DIVar = DDI->getVariable();
1067 auto *DIExpr = DDI->getExpression();
1068 assert(DIVar && "Missing variable");
1070 if (LdStHasDebugValue(DIVar, LI))
1073 Builder.insertDbgValueIntrinsic(LI->getOperand(0), 0, DIVar, DIExpr,
1074 DDI->getDebugLoc(), LI);
1078 /// Determine whether this alloca is either a VLA or an array.
1079 static bool isArray(AllocaInst *AI) {
1080 return AI->isArrayAllocation() ||
1081 AI->getType()->getElementType()->isArrayTy();
1084 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1085 /// of llvm.dbg.value intrinsics.
1086 bool llvm::LowerDbgDeclare(Function &F) {
1087 DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1088 SmallVector<DbgDeclareInst *, 4> Dbgs;
1090 for (BasicBlock::iterator BI : FI)
1091 if (auto DDI = dyn_cast<DbgDeclareInst>(BI))
1092 Dbgs.push_back(DDI);
1097 for (auto &I : Dbgs) {
1098 DbgDeclareInst *DDI = I;
1099 AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1100 // If this is an alloca for a scalar variable, insert a dbg.value
1101 // at each load and store to the alloca and erase the dbg.declare.
1102 // The dbg.values allow tracking a variable even if it is not
1103 // stored on the stack, while the dbg.declare can only describe
1104 // the stack slot (and at a lexical-scope granularity). Later
1105 // passes will attempt to elide the stack slot.
1106 if (AI && !isArray(AI)) {
1107 for (User *U : AI->users())
1108 if (StoreInst *SI = dyn_cast<StoreInst>(U))
1109 ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1110 else if (LoadInst *LI = dyn_cast<LoadInst>(U))
1111 ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1112 else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1113 // This is a call by-value or some other instruction that
1114 // takes a pointer to the variable. Insert a *value*
1115 // intrinsic that describes the alloca.
1116 DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
1117 DDI->getExpression(), DDI->getDebugLoc(),
1120 DDI->eraseFromParent();
1126 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1127 /// alloca 'V', if any.
1128 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1129 if (auto *L = LocalAsMetadata::getIfExists(V))
1130 if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1131 for (User *U : MDV->users())
1132 if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1138 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1139 DIBuilder &Builder, bool Deref) {
1140 DbgDeclareInst *DDI = FindAllocaDbgDeclare(AI);
1143 DebugLoc Loc = DDI->getDebugLoc();
1144 auto *DIVar = DDI->getVariable();
1145 auto *DIExpr = DDI->getExpression();
1146 assert(DIVar && "Missing variable");
1149 // Create a copy of the original DIDescriptor for user variable, prepending
1150 // "deref" operation to a list of address elements, as new llvm.dbg.declare
1151 // will take a value storing address of the memory for variable, not
1153 SmallVector<uint64_t, 4> NewDIExpr;
1154 NewDIExpr.push_back(dwarf::DW_OP_deref);
1156 NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
1157 DIExpr = Builder.createExpression(NewDIExpr);
1160 // Insert llvm.dbg.declare immediately after the original alloca, and remove
1161 // old llvm.dbg.declare.
1162 Builder.insertDeclare(NewAllocaAddress, DIVar, DIExpr, Loc,
1164 DDI->eraseFromParent();
1168 /// changeToUnreachable - Insert an unreachable instruction before the specified
1169 /// instruction, making it and the rest of the code in the block dead.
1170 static void changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1171 BasicBlock *BB = I->getParent();
1172 // Loop over all of the successors, removing BB's entry from any PHI
1174 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1175 (*SI)->removePredecessor(BB);
1177 // Insert a call to llvm.trap right before this. This turns the undefined
1178 // behavior into a hard fail instead of falling through into random code.
1181 Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1182 CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1183 CallTrap->setDebugLoc(I->getDebugLoc());
1185 new UnreachableInst(I->getContext(), I);
1187 // All instructions after this are dead.
1188 BasicBlock::iterator BBI = I, BBE = BB->end();
1189 while (BBI != BBE) {
1190 if (!BBI->use_empty())
1191 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1192 BB->getInstList().erase(BBI++);
1196 /// changeToCall - Convert the specified invoke into a normal call.
1197 static void changeToCall(InvokeInst *II) {
1198 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
1199 CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, "", II);
1200 NewCall->takeName(II);
1201 NewCall->setCallingConv(II->getCallingConv());
1202 NewCall->setAttributes(II->getAttributes());
1203 NewCall->setDebugLoc(II->getDebugLoc());
1204 II->replaceAllUsesWith(NewCall);
1206 // Follow the call by a branch to the normal destination.
1207 BranchInst::Create(II->getNormalDest(), II);
1209 // Update PHI nodes in the unwind destination
1210 II->getUnwindDest()->removePredecessor(II->getParent());
1211 II->eraseFromParent();
1214 static bool markAliveBlocks(Function &F,
1215 SmallPtrSetImpl<BasicBlock*> &Reachable) {
1217 SmallVector<BasicBlock*, 128> Worklist;
1218 BasicBlock *BB = F.begin();
1219 Worklist.push_back(BB);
1220 Reachable.insert(BB);
1221 bool Changed = false;
1223 BB = Worklist.pop_back_val();
1225 // Do a quick scan of the basic block, turning any obviously unreachable
1226 // instructions into LLVM unreachable insts. The instruction combining pass
1227 // canonicalizes unreachable insts into stores to null or undef.
1228 for (BasicBlock::iterator BBI = BB->begin(), E = BB->end(); BBI != E;++BBI){
1229 // Assumptions that are known to be false are equivalent to unreachable.
1230 // Also, if the condition is undefined, then we make the choice most
1231 // beneficial to the optimizer, and choose that to also be unreachable.
1232 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(BBI))
1233 if (II->getIntrinsicID() == Intrinsic::assume) {
1234 bool MakeUnreachable = false;
1235 if (isa<UndefValue>(II->getArgOperand(0)))
1236 MakeUnreachable = true;
1237 else if (ConstantInt *Cond =
1238 dyn_cast<ConstantInt>(II->getArgOperand(0)))
1239 MakeUnreachable = Cond->isZero();
1241 if (MakeUnreachable) {
1242 // Don't insert a call to llvm.trap right before the unreachable.
1243 changeToUnreachable(BBI, false);
1249 if (CallInst *CI = dyn_cast<CallInst>(BBI)) {
1250 if (CI->doesNotReturn()) {
1251 // If we found a call to a no-return function, insert an unreachable
1252 // instruction after it. Make sure there isn't *already* one there
1255 if (!isa<UnreachableInst>(BBI)) {
1256 // Don't insert a call to llvm.trap right before the unreachable.
1257 changeToUnreachable(BBI, false);
1264 // Store to undef and store to null are undefined and used to signal that
1265 // they should be changed to unreachable by passes that can't modify the
1267 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
1268 // Don't touch volatile stores.
1269 if (SI->isVolatile()) continue;
1271 Value *Ptr = SI->getOperand(1);
1273 if (isa<UndefValue>(Ptr) ||
1274 (isa<ConstantPointerNull>(Ptr) &&
1275 SI->getPointerAddressSpace() == 0)) {
1276 changeToUnreachable(SI, true);
1283 // Turn invokes that call 'nounwind' functions into ordinary calls.
1284 if (InvokeInst *II = dyn_cast<InvokeInst>(BB->getTerminator())) {
1285 Value *Callee = II->getCalledValue();
1286 if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1287 changeToUnreachable(II, true);
1289 } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
1290 if (II->use_empty() && II->onlyReadsMemory()) {
1291 // jump to the normal destination branch.
1292 BranchInst::Create(II->getNormalDest(), II);
1293 II->getUnwindDest()->removePredecessor(II->getParent());
1294 II->eraseFromParent();
1301 Changed |= ConstantFoldTerminator(BB, true);
1302 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1303 if (Reachable.insert(*SI).second)
1304 Worklist.push_back(*SI);
1305 } while (!Worklist.empty());
1309 void llvm::removeUnwindEdge(BasicBlock *BB) {
1310 TerminatorInst *TI = BB->getTerminator();
1312 if (auto *II = dyn_cast<InvokeInst>(TI)) {
1317 TerminatorInst *NewTI;
1318 BasicBlock *UnwindDest;
1320 if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
1321 NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
1322 UnwindDest = CRI->getUnwindDest();
1323 } else if (auto *CEP = dyn_cast<CleanupEndPadInst>(TI)) {
1324 NewTI = CleanupEndPadInst::Create(CEP->getCleanupPad(), nullptr, CEP);
1325 UnwindDest = CEP->getUnwindDest();
1326 } else if (auto *CEP = dyn_cast<CatchEndPadInst>(TI)) {
1327 NewTI = CatchEndPadInst::Create(CEP->getContext(), nullptr, CEP);
1328 UnwindDest = CEP->getUnwindDest();
1329 } else if (auto *TPI = dyn_cast<TerminatePadInst>(TI)) {
1330 SmallVector<Value *, 3> TerminatePadArgs;
1331 for (Value *Operand : TPI->arg_operands())
1332 TerminatePadArgs.push_back(Operand);
1333 NewTI = TerminatePadInst::Create(TPI->getContext(), nullptr,
1334 TerminatePadArgs, TPI);
1335 UnwindDest = TPI->getUnwindDest();
1337 llvm_unreachable("Could not find unwind successor");
1340 NewTI->takeName(TI);
1341 NewTI->setDebugLoc(TI->getDebugLoc());
1342 UnwindDest->removePredecessor(BB);
1343 TI->eraseFromParent();
1346 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1347 /// if they are in a dead cycle. Return true if a change was made, false
1349 bool llvm::removeUnreachableBlocks(Function &F) {
1350 SmallPtrSet<BasicBlock*, 128> Reachable;
1351 bool Changed = markAliveBlocks(F, Reachable);
1353 // If there are unreachable blocks in the CFG...
1354 if (Reachable.size() == F.size())
1357 assert(Reachable.size() < F.size());
1358 NumRemoved += F.size()-Reachable.size();
1360 // Loop over all of the basic blocks that are not reachable, dropping all of
1361 // their internal references...
1362 for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1363 if (Reachable.count(BB))
1366 for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB); SI != SE; ++SI)
1367 if (Reachable.count(*SI))
1368 (*SI)->removePredecessor(BB);
1369 BB->dropAllReferences();
1372 for (Function::iterator I = ++F.begin(); I != F.end();)
1373 if (!Reachable.count(I))
1374 I = F.getBasicBlockList().erase(I);
1381 void llvm::combineMetadata(Instruction *K, const Instruction *J, ArrayRef<unsigned> KnownIDs) {
1382 SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
1383 K->dropUnknownNonDebugMetadata(KnownIDs);
1384 K->getAllMetadataOtherThanDebugLoc(Metadata);
1385 for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
1386 unsigned Kind = Metadata[i].first;
1387 MDNode *JMD = J->getMetadata(Kind);
1388 MDNode *KMD = Metadata[i].second;
1392 K->setMetadata(Kind, nullptr); // Remove unknown metadata
1394 case LLVMContext::MD_dbg:
1395 llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1396 case LLVMContext::MD_tbaa:
1397 K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
1399 case LLVMContext::MD_alias_scope:
1400 K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
1402 case LLVMContext::MD_noalias:
1403 K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
1405 case LLVMContext::MD_range:
1406 K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
1408 case LLVMContext::MD_fpmath:
1409 K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
1411 case LLVMContext::MD_invariant_load:
1412 // Only set the !invariant.load if it is present in both instructions.
1413 K->setMetadata(Kind, JMD);
1415 case LLVMContext::MD_nonnull:
1416 // Only set the !nonnull if it is present in both instructions.
1417 K->setMetadata(Kind, JMD);
1423 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
1425 const BasicBlockEdge &Root) {
1426 assert(From->getType() == To->getType());
1429 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1432 if (DT.dominates(Root, U)) {
1434 DEBUG(dbgs() << "Replace dominated use of '"
1435 << From->getName() << "' as "
1436 << *To << " in " << *U << "\n");
1443 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
1445 const BasicBlock *BB) {
1446 assert(From->getType() == To->getType());
1449 for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1452 auto *I = cast<Instruction>(U.getUser());
1453 if (DT.dominates(BB, I->getParent())) {
1455 DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
1456 << *To << " in " << *U << "\n");