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1 //===-- Local.cpp - Functions to perform local transformations ------------===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This family of functions perform various local transformations to the
11 // program.
12 //
13 //===----------------------------------------------------------------------===//
14 
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/EHPersonalities.h"
24 #include "llvm/Analysis/InstructionSimplify.h"
25 #include "llvm/Analysis/MemoryBuiltins.h"
26 #include "llvm/Analysis/LazyValueInfo.h"
27 #include "llvm/Analysis/ValueTracking.h"
28 #include "llvm/IR/CFG.h"
29 #include "llvm/IR/Constants.h"
30 #include "llvm/IR/DIBuilder.h"
31 #include "llvm/IR/DataLayout.h"
32 #include "llvm/IR/DebugInfo.h"
33 #include "llvm/IR/DerivedTypes.h"
34 #include "llvm/IR/Dominators.h"
35 #include "llvm/IR/GetElementPtrTypeIterator.h"
36 #include "llvm/IR/GlobalAlias.h"
37 #include "llvm/IR/GlobalVariable.h"
38 #include "llvm/IR/IRBuilder.h"
39 #include "llvm/IR/Instructions.h"
40 #include "llvm/IR/IntrinsicInst.h"
41 #include "llvm/IR/Intrinsics.h"
42 #include "llvm/IR/MDBuilder.h"
43 #include "llvm/IR/Metadata.h"
44 #include "llvm/IR/Operator.h"
45 #include "llvm/IR/PatternMatch.h"
46 #include "llvm/IR/ValueHandle.h"
47 #include "llvm/Support/Debug.h"
48 #include "llvm/Support/MathExtras.h"
49 #include "llvm/Support/raw_ostream.h"
50 using namespace llvm;
51 using namespace llvm::PatternMatch;
52 
53 #define DEBUG_TYPE "local"
54 
55 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
56 
57 //===----------------------------------------------------------------------===//
58 //  Local constant propagation.
59 //
60 
61 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
62 /// constant value, convert it into an unconditional branch to the constant
63 /// destination.  This is a nontrivial operation because the successors of this
64 /// basic block must have their PHI nodes updated.
65 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
66 /// conditions and indirectbr addresses this might make dead if
67 /// DeleteDeadConditions is true.
ConstantFoldTerminator(BasicBlock * BB,bool DeleteDeadConditions,const TargetLibraryInfo * TLI)68 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
69                                   const TargetLibraryInfo *TLI) {
70   TerminatorInst *T = BB->getTerminator();
71   IRBuilder<> Builder(T);
72 
73   // Branch - See if we are conditional jumping on constant
74   if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
75     if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
76     BasicBlock *Dest1 = BI->getSuccessor(0);
77     BasicBlock *Dest2 = BI->getSuccessor(1);
78 
79     if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
80       // Are we branching on constant?
81       // YES.  Change to unconditional branch...
82       BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
83       BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;
84 
85       //cerr << "Function: " << T->getParent()->getParent()
86       //     << "\nRemoving branch from " << T->getParent()
87       //     << "\n\nTo: " << OldDest << endl;
88 
89       // Let the basic block know that we are letting go of it.  Based on this,
90       // it will adjust it's PHI nodes.
91       OldDest->removePredecessor(BB);
92 
93       // Replace the conditional branch with an unconditional one.
94       Builder.CreateBr(Destination);
95       BI->eraseFromParent();
96       return true;
97     }
98 
99     if (Dest2 == Dest1) {       // Conditional branch to same location?
100       // This branch matches something like this:
101       //     br bool %cond, label %Dest, label %Dest
102       // and changes it into:  br label %Dest
103 
104       // Let the basic block know that we are letting go of one copy of it.
105       assert(BI->getParent() && "Terminator not inserted in block!");
106       Dest1->removePredecessor(BI->getParent());
107 
108       // Replace the conditional branch with an unconditional one.
109       Builder.CreateBr(Dest1);
110       Value *Cond = BI->getCondition();
111       BI->eraseFromParent();
112       if (DeleteDeadConditions)
113         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
114       return true;
115     }
116     return false;
117   }
118 
119   if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
120     // If we are switching on a constant, we can convert the switch to an
121     // unconditional branch.
122     ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
123     BasicBlock *DefaultDest = SI->getDefaultDest();
124     BasicBlock *TheOnlyDest = DefaultDest;
125 
126     // If the default is unreachable, ignore it when searching for TheOnlyDest.
127     if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
128         SI->getNumCases() > 0) {
129       TheOnlyDest = SI->case_begin().getCaseSuccessor();
130     }
131 
132     // Figure out which case it goes to.
133     for (SwitchInst::CaseIt i = SI->case_begin(), e = SI->case_end();
134          i != e; ++i) {
135       // Found case matching a constant operand?
136       if (i.getCaseValue() == CI) {
137         TheOnlyDest = i.getCaseSuccessor();
138         break;
139       }
140 
141       // Check to see if this branch is going to the same place as the default
142       // dest.  If so, eliminate it as an explicit compare.
143       if (i.getCaseSuccessor() == DefaultDest) {
144         MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
145         unsigned NCases = SI->getNumCases();
146         // Fold the case metadata into the default if there will be any branches
147         // left, unless the metadata doesn't match the switch.
148         if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
149           // Collect branch weights into a vector.
150           SmallVector<uint32_t, 8> Weights;
151           for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
152                ++MD_i) {
153             auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
154             Weights.push_back(CI->getValue().getZExtValue());
155           }
156           // Merge weight of this case to the default weight.
157           unsigned idx = i.getCaseIndex();
158           Weights[0] += Weights[idx+1];
159           // Remove weight for this case.
160           std::swap(Weights[idx+1], Weights.back());
161           Weights.pop_back();
162           SI->setMetadata(LLVMContext::MD_prof,
163                           MDBuilder(BB->getContext()).
164                           createBranchWeights(Weights));
165         }
166         // Remove this entry.
167         DefaultDest->removePredecessor(SI->getParent());
168         SI->removeCase(i);
169         --i; --e;
170         continue;
171       }
172 
173       // Otherwise, check to see if the switch only branches to one destination.
174       // We do this by reseting "TheOnlyDest" to null when we find two non-equal
175       // destinations.
176       if (i.getCaseSuccessor() != TheOnlyDest) TheOnlyDest = nullptr;
177     }
178 
179     if (CI && !TheOnlyDest) {
180       // Branching on a constant, but not any of the cases, go to the default
181       // successor.
182       TheOnlyDest = SI->getDefaultDest();
183     }
184 
185     // If we found a single destination that we can fold the switch into, do so
186     // now.
187     if (TheOnlyDest) {
188       // Insert the new branch.
189       Builder.CreateBr(TheOnlyDest);
190       BasicBlock *BB = SI->getParent();
191 
192       // Remove entries from PHI nodes which we no longer branch to...
193       for (BasicBlock *Succ : SI->successors()) {
194         // Found case matching a constant operand?
195         if (Succ == TheOnlyDest)
196           TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
197         else
198           Succ->removePredecessor(BB);
199       }
200 
201       // Delete the old switch.
202       Value *Cond = SI->getCondition();
203       SI->eraseFromParent();
204       if (DeleteDeadConditions)
205         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
206       return true;
207     }
208 
209     if (SI->getNumCases() == 1) {
210       // Otherwise, we can fold this switch into a conditional branch
211       // instruction if it has only one non-default destination.
212       SwitchInst::CaseIt FirstCase = SI->case_begin();
213       Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
214           FirstCase.getCaseValue(), "cond");
215 
216       // Insert the new branch.
217       BranchInst *NewBr = Builder.CreateCondBr(Cond,
218                                                FirstCase.getCaseSuccessor(),
219                                                SI->getDefaultDest());
220       MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
221       if (MD && MD->getNumOperands() == 3) {
222         ConstantInt *SICase =
223             mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
224         ConstantInt *SIDef =
225             mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
226         assert(SICase && SIDef);
227         // The TrueWeight should be the weight for the single case of SI.
228         NewBr->setMetadata(LLVMContext::MD_prof,
229                         MDBuilder(BB->getContext()).
230                         createBranchWeights(SICase->getValue().getZExtValue(),
231                                             SIDef->getValue().getZExtValue()));
232       }
233 
234       // Update make.implicit metadata to the newly-created conditional branch.
235       MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
236       if (MakeImplicitMD)
237         NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
238 
239       // Delete the old switch.
240       SI->eraseFromParent();
241       return true;
242     }
243     return false;
244   }
245 
246   if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
247     // indirectbr blockaddress(@F, @BB) -> br label @BB
248     if (BlockAddress *BA =
249           dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
250       BasicBlock *TheOnlyDest = BA->getBasicBlock();
251       // Insert the new branch.
252       Builder.CreateBr(TheOnlyDest);
253 
254       for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
255         if (IBI->getDestination(i) == TheOnlyDest)
256           TheOnlyDest = nullptr;
257         else
258           IBI->getDestination(i)->removePredecessor(IBI->getParent());
259       }
260       Value *Address = IBI->getAddress();
261       IBI->eraseFromParent();
262       if (DeleteDeadConditions)
263         RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
264 
265       // If we didn't find our destination in the IBI successor list, then we
266       // have undefined behavior.  Replace the unconditional branch with an
267       // 'unreachable' instruction.
268       if (TheOnlyDest) {
269         BB->getTerminator()->eraseFromParent();
270         new UnreachableInst(BB->getContext(), BB);
271       }
272 
273       return true;
274     }
275   }
276 
277   return false;
278 }
279 
280 
281 //===----------------------------------------------------------------------===//
282 //  Local dead code elimination.
283 //
284 
285 /// isInstructionTriviallyDead - Return true if the result produced by the
286 /// instruction is not used, and the instruction has no side effects.
287 ///
isInstructionTriviallyDead(Instruction * I,const TargetLibraryInfo * TLI)288 bool llvm::isInstructionTriviallyDead(Instruction *I,
289                                       const TargetLibraryInfo *TLI) {
290   if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
291 
292   // We don't want the landingpad-like instructions removed by anything this
293   // general.
294   if (I->isEHPad())
295     return false;
296 
297   // We don't want debug info removed by anything this general, unless
298   // debug info is empty.
299   if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
300     if (DDI->getAddress())
301       return false;
302     return true;
303   }
304   if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
305     if (DVI->getValue())
306       return false;
307     return true;
308   }
309 
310   if (!I->mayHaveSideEffects()) return true;
311 
312   // Special case intrinsics that "may have side effects" but can be deleted
313   // when dead.
314   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
315     // Safe to delete llvm.stacksave if dead.
316     if (II->getIntrinsicID() == Intrinsic::stacksave)
317       return true;
318 
319     // Lifetime intrinsics are dead when their right-hand is undef.
320     if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
321         II->getIntrinsicID() == Intrinsic::lifetime_end)
322       return isa<UndefValue>(II->getArgOperand(1));
323 
324     // Assumptions are dead if their condition is trivially true.  Guards on
325     // true are operationally no-ops.  In the future we can consider more
326     // sophisticated tradeoffs for guards considering potential for check
327     // widening, but for now we keep things simple.
328     if (II->getIntrinsicID() == Intrinsic::assume ||
329         II->getIntrinsicID() == Intrinsic::experimental_guard) {
330       if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
331         return !Cond->isZero();
332 
333       return false;
334     }
335   }
336 
337   if (isAllocLikeFn(I, TLI)) return true;
338 
339   if (CallInst *CI = isFreeCall(I, TLI))
340     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
341       return C->isNullValue() || isa<UndefValue>(C);
342 
343   return false;
344 }
345 
346 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
347 /// trivially dead instruction, delete it.  If that makes any of its operands
348 /// trivially dead, delete them too, recursively.  Return true if any
349 /// instructions were deleted.
350 bool
RecursivelyDeleteTriviallyDeadInstructions(Value * V,const TargetLibraryInfo * TLI)351 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
352                                                  const TargetLibraryInfo *TLI) {
353   Instruction *I = dyn_cast<Instruction>(V);
354   if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
355     return false;
356 
357   SmallVector<Instruction*, 16> DeadInsts;
358   DeadInsts.push_back(I);
359 
360   do {
361     I = DeadInsts.pop_back_val();
362 
363     // Null out all of the instruction's operands to see if any operand becomes
364     // dead as we go.
365     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
366       Value *OpV = I->getOperand(i);
367       I->setOperand(i, nullptr);
368 
369       if (!OpV->use_empty()) continue;
370 
371       // If the operand is an instruction that became dead as we nulled out the
372       // operand, and if it is 'trivially' dead, delete it in a future loop
373       // iteration.
374       if (Instruction *OpI = dyn_cast<Instruction>(OpV))
375         if (isInstructionTriviallyDead(OpI, TLI))
376           DeadInsts.push_back(OpI);
377     }
378 
379     I->eraseFromParent();
380   } while (!DeadInsts.empty());
381 
382   return true;
383 }
384 
385 /// areAllUsesEqual - Check whether the uses of a value are all the same.
386 /// This is similar to Instruction::hasOneUse() except this will also return
387 /// true when there are no uses or multiple uses that all refer to the same
388 /// value.
areAllUsesEqual(Instruction * I)389 static bool areAllUsesEqual(Instruction *I) {
390   Value::user_iterator UI = I->user_begin();
391   Value::user_iterator UE = I->user_end();
392   if (UI == UE)
393     return true;
394 
395   User *TheUse = *UI;
396   for (++UI; UI != UE; ++UI) {
397     if (*UI != TheUse)
398       return false;
399   }
400   return true;
401 }
402 
403 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
404 /// dead PHI node, due to being a def-use chain of single-use nodes that
405 /// either forms a cycle or is terminated by a trivially dead instruction,
406 /// delete it.  If that makes any of its operands trivially dead, delete them
407 /// too, recursively.  Return true if a change was made.
RecursivelyDeleteDeadPHINode(PHINode * PN,const TargetLibraryInfo * TLI)408 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
409                                         const TargetLibraryInfo *TLI) {
410   SmallPtrSet<Instruction*, 4> Visited;
411   for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
412        I = cast<Instruction>(*I->user_begin())) {
413     if (I->use_empty())
414       return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
415 
416     // If we find an instruction more than once, we're on a cycle that
417     // won't prove fruitful.
418     if (!Visited.insert(I).second) {
419       // Break the cycle and delete the instruction and its operands.
420       I->replaceAllUsesWith(UndefValue::get(I->getType()));
421       (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
422       return true;
423     }
424   }
425   return false;
426 }
427 
428 static bool
simplifyAndDCEInstruction(Instruction * I,SmallSetVector<Instruction *,16> & WorkList,const DataLayout & DL,const TargetLibraryInfo * TLI)429 simplifyAndDCEInstruction(Instruction *I,
430                           SmallSetVector<Instruction *, 16> &WorkList,
431                           const DataLayout &DL,
432                           const TargetLibraryInfo *TLI) {
433   if (isInstructionTriviallyDead(I, TLI)) {
434     // Null out all of the instruction's operands to see if any operand becomes
435     // dead as we go.
436     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
437       Value *OpV = I->getOperand(i);
438       I->setOperand(i, nullptr);
439 
440       if (!OpV->use_empty() || I == OpV)
441         continue;
442 
443       // If the operand is an instruction that became dead as we nulled out the
444       // operand, and if it is 'trivially' dead, delete it in a future loop
445       // iteration.
446       if (Instruction *OpI = dyn_cast<Instruction>(OpV))
447         if (isInstructionTriviallyDead(OpI, TLI))
448           WorkList.insert(OpI);
449     }
450 
451     I->eraseFromParent();
452 
453     return true;
454   }
455 
456   if (Value *SimpleV = SimplifyInstruction(I, DL)) {
457     // Add the users to the worklist. CAREFUL: an instruction can use itself,
458     // in the case of a phi node.
459     for (User *U : I->users()) {
460       if (U != I) {
461         WorkList.insert(cast<Instruction>(U));
462       }
463     }
464 
465     // Replace the instruction with its simplified value.
466     bool Changed = false;
467     if (!I->use_empty()) {
468       I->replaceAllUsesWith(SimpleV);
469       Changed = true;
470     }
471     if (isInstructionTriviallyDead(I, TLI)) {
472       I->eraseFromParent();
473       Changed = true;
474     }
475     return Changed;
476   }
477   return false;
478 }
479 
480 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
481 /// simplify any instructions in it and recursively delete dead instructions.
482 ///
483 /// This returns true if it changed the code, note that it can delete
484 /// instructions in other blocks as well in this block.
SimplifyInstructionsInBlock(BasicBlock * BB,const TargetLibraryInfo * TLI)485 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
486                                        const TargetLibraryInfo *TLI) {
487   bool MadeChange = false;
488   const DataLayout &DL = BB->getModule()->getDataLayout();
489 
490 #ifndef NDEBUG
491   // In debug builds, ensure that the terminator of the block is never replaced
492   // or deleted by these simplifications. The idea of simplification is that it
493   // cannot introduce new instructions, and there is no way to replace the
494   // terminator of a block without introducing a new instruction.
495   AssertingVH<Instruction> TerminatorVH(&BB->back());
496 #endif
497 
498   SmallSetVector<Instruction *, 16> WorkList;
499   // Iterate over the original function, only adding insts to the worklist
500   // if they actually need to be revisited. This avoids having to pre-init
501   // the worklist with the entire function's worth of instructions.
502   for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end());
503        BI != E;) {
504     assert(!BI->isTerminator());
505     Instruction *I = &*BI;
506     ++BI;
507 
508     // We're visiting this instruction now, so make sure it's not in the
509     // worklist from an earlier visit.
510     if (!WorkList.count(I))
511       MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
512   }
513 
514   while (!WorkList.empty()) {
515     Instruction *I = WorkList.pop_back_val();
516     MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
517   }
518   return MadeChange;
519 }
520 
521 //===----------------------------------------------------------------------===//
522 //  Control Flow Graph Restructuring.
523 //
524 
525 
526 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
527 /// method is called when we're about to delete Pred as a predecessor of BB.  If
528 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
529 ///
530 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
531 /// nodes that collapse into identity values.  For example, if we have:
532 ///   x = phi(1, 0, 0, 0)
533 ///   y = and x, z
534 ///
535 /// .. and delete the predecessor corresponding to the '1', this will attempt to
536 /// recursively fold the and to 0.
RemovePredecessorAndSimplify(BasicBlock * BB,BasicBlock * Pred)537 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred) {
538   // This only adjusts blocks with PHI nodes.
539   if (!isa<PHINode>(BB->begin()))
540     return;
541 
542   // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
543   // them down.  This will leave us with single entry phi nodes and other phis
544   // that can be removed.
545   BB->removePredecessor(Pred, true);
546 
547   WeakVH PhiIt = &BB->front();
548   while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
549     PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
550     Value *OldPhiIt = PhiIt;
551 
552     if (!recursivelySimplifyInstruction(PN))
553       continue;
554 
555     // If recursive simplification ended up deleting the next PHI node we would
556     // iterate to, then our iterator is invalid, restart scanning from the top
557     // of the block.
558     if (PhiIt != OldPhiIt) PhiIt = &BB->front();
559   }
560 }
561 
562 
563 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
564 /// predecessor is known to have one successor (DestBB!).  Eliminate the edge
565 /// between them, moving the instructions in the predecessor into DestBB and
566 /// deleting the predecessor block.
567 ///
MergeBasicBlockIntoOnlyPred(BasicBlock * DestBB,DominatorTree * DT)568 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT) {
569   // If BB has single-entry PHI nodes, fold them.
570   while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
571     Value *NewVal = PN->getIncomingValue(0);
572     // Replace self referencing PHI with undef, it must be dead.
573     if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
574     PN->replaceAllUsesWith(NewVal);
575     PN->eraseFromParent();
576   }
577 
578   BasicBlock *PredBB = DestBB->getSinglePredecessor();
579   assert(PredBB && "Block doesn't have a single predecessor!");
580 
581   // Zap anything that took the address of DestBB.  Not doing this will give the
582   // address an invalid value.
583   if (DestBB->hasAddressTaken()) {
584     BlockAddress *BA = BlockAddress::get(DestBB);
585     Constant *Replacement =
586       ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
587     BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
588                                                      BA->getType()));
589     BA->destroyConstant();
590   }
591 
592   // Anything that branched to PredBB now branches to DestBB.
593   PredBB->replaceAllUsesWith(DestBB);
594 
595   // Splice all the instructions from PredBB to DestBB.
596   PredBB->getTerminator()->eraseFromParent();
597   DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
598 
599   // If the PredBB is the entry block of the function, move DestBB up to
600   // become the entry block after we erase PredBB.
601   if (PredBB == &DestBB->getParent()->getEntryBlock())
602     DestBB->moveAfter(PredBB);
603 
604   if (DT) {
605     BasicBlock *PredBBIDom = DT->getNode(PredBB)->getIDom()->getBlock();
606     DT->changeImmediateDominator(DestBB, PredBBIDom);
607     DT->eraseNode(PredBB);
608   }
609   // Nuke BB.
610   PredBB->eraseFromParent();
611 }
612 
613 /// CanMergeValues - Return true if we can choose one of these values to use
614 /// in place of the other. Note that we will always choose the non-undef
615 /// value to keep.
CanMergeValues(Value * First,Value * Second)616 static bool CanMergeValues(Value *First, Value *Second) {
617   return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
618 }
619 
620 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
621 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
622 ///
623 /// Assumption: Succ is the single successor for BB.
624 ///
CanPropagatePredecessorsForPHIs(BasicBlock * BB,BasicBlock * Succ)625 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
626   assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
627 
628   DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
629         << Succ->getName() << "\n");
630   // Shortcut, if there is only a single predecessor it must be BB and merging
631   // is always safe
632   if (Succ->getSinglePredecessor()) return true;
633 
634   // Make a list of the predecessors of BB
635   SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
636 
637   // Look at all the phi nodes in Succ, to see if they present a conflict when
638   // merging these blocks
639   for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
640     PHINode *PN = cast<PHINode>(I);
641 
642     // If the incoming value from BB is again a PHINode in
643     // BB which has the same incoming value for *PI as PN does, we can
644     // merge the phi nodes and then the blocks can still be merged
645     PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
646     if (BBPN && BBPN->getParent() == BB) {
647       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
648         BasicBlock *IBB = PN->getIncomingBlock(PI);
649         if (BBPreds.count(IBB) &&
650             !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
651                             PN->getIncomingValue(PI))) {
652           DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
653                 << Succ->getName() << " is conflicting with "
654                 << BBPN->getName() << " with regard to common predecessor "
655                 << IBB->getName() << "\n");
656           return false;
657         }
658       }
659     } else {
660       Value* Val = PN->getIncomingValueForBlock(BB);
661       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
662         // See if the incoming value for the common predecessor is equal to the
663         // one for BB, in which case this phi node will not prevent the merging
664         // of the block.
665         BasicBlock *IBB = PN->getIncomingBlock(PI);
666         if (BBPreds.count(IBB) &&
667             !CanMergeValues(Val, PN->getIncomingValue(PI))) {
668           DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
669                 << Succ->getName() << " is conflicting with regard to common "
670                 << "predecessor " << IBB->getName() << "\n");
671           return false;
672         }
673       }
674     }
675   }
676 
677   return true;
678 }
679 
680 typedef SmallVector<BasicBlock *, 16> PredBlockVector;
681 typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
682 
683 /// \brief Determines the value to use as the phi node input for a block.
684 ///
685 /// Select between \p OldVal any value that we know flows from \p BB
686 /// to a particular phi on the basis of which one (if either) is not
687 /// undef. Update IncomingValues based on the selected value.
688 ///
689 /// \param OldVal The value we are considering selecting.
690 /// \param BB The block that the value flows in from.
691 /// \param IncomingValues A map from block-to-value for other phi inputs
692 /// that we have examined.
693 ///
694 /// \returns the selected value.
selectIncomingValueForBlock(Value * OldVal,BasicBlock * BB,IncomingValueMap & IncomingValues)695 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
696                                           IncomingValueMap &IncomingValues) {
697   if (!isa<UndefValue>(OldVal)) {
698     assert((!IncomingValues.count(BB) ||
699             IncomingValues.find(BB)->second == OldVal) &&
700            "Expected OldVal to match incoming value from BB!");
701 
702     IncomingValues.insert(std::make_pair(BB, OldVal));
703     return OldVal;
704   }
705 
706   IncomingValueMap::const_iterator It = IncomingValues.find(BB);
707   if (It != IncomingValues.end()) return It->second;
708 
709   return OldVal;
710 }
711 
712 /// \brief Create a map from block to value for the operands of a
713 /// given phi.
714 ///
715 /// Create a map from block to value for each non-undef value flowing
716 /// into \p PN.
717 ///
718 /// \param PN The phi we are collecting the map for.
719 /// \param IncomingValues [out] The map from block to value for this phi.
gatherIncomingValuesToPhi(PHINode * PN,IncomingValueMap & IncomingValues)720 static void gatherIncomingValuesToPhi(PHINode *PN,
721                                       IncomingValueMap &IncomingValues) {
722   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
723     BasicBlock *BB = PN->getIncomingBlock(i);
724     Value *V = PN->getIncomingValue(i);
725 
726     if (!isa<UndefValue>(V))
727       IncomingValues.insert(std::make_pair(BB, V));
728   }
729 }
730 
731 /// \brief Replace the incoming undef values to a phi with the values
732 /// from a block-to-value map.
733 ///
734 /// \param PN The phi we are replacing the undefs in.
735 /// \param IncomingValues A map from block to value.
replaceUndefValuesInPhi(PHINode * PN,const IncomingValueMap & IncomingValues)736 static void replaceUndefValuesInPhi(PHINode *PN,
737                                     const IncomingValueMap &IncomingValues) {
738   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
739     Value *V = PN->getIncomingValue(i);
740 
741     if (!isa<UndefValue>(V)) continue;
742 
743     BasicBlock *BB = PN->getIncomingBlock(i);
744     IncomingValueMap::const_iterator It = IncomingValues.find(BB);
745     if (It == IncomingValues.end()) continue;
746 
747     PN->setIncomingValue(i, It->second);
748   }
749 }
750 
751 /// \brief Replace a value flowing from a block to a phi with
752 /// potentially multiple instances of that value flowing from the
753 /// block's predecessors to the phi.
754 ///
755 /// \param BB The block with the value flowing into the phi.
756 /// \param BBPreds The predecessors of BB.
757 /// \param PN The phi that we are updating.
redirectValuesFromPredecessorsToPhi(BasicBlock * BB,const PredBlockVector & BBPreds,PHINode * PN)758 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
759                                                 const PredBlockVector &BBPreds,
760                                                 PHINode *PN) {
761   Value *OldVal = PN->removeIncomingValue(BB, false);
762   assert(OldVal && "No entry in PHI for Pred BB!");
763 
764   IncomingValueMap IncomingValues;
765 
766   // We are merging two blocks - BB, and the block containing PN - and
767   // as a result we need to redirect edges from the predecessors of BB
768   // to go to the block containing PN, and update PN
769   // accordingly. Since we allow merging blocks in the case where the
770   // predecessor and successor blocks both share some predecessors,
771   // and where some of those common predecessors might have undef
772   // values flowing into PN, we want to rewrite those values to be
773   // consistent with the non-undef values.
774 
775   gatherIncomingValuesToPhi(PN, IncomingValues);
776 
777   // If this incoming value is one of the PHI nodes in BB, the new entries
778   // in the PHI node are the entries from the old PHI.
779   if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
780     PHINode *OldValPN = cast<PHINode>(OldVal);
781     for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
782       // Note that, since we are merging phi nodes and BB and Succ might
783       // have common predecessors, we could end up with a phi node with
784       // identical incoming branches. This will be cleaned up later (and
785       // will trigger asserts if we try to clean it up now, without also
786       // simplifying the corresponding conditional branch).
787       BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
788       Value *PredVal = OldValPN->getIncomingValue(i);
789       Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
790                                                     IncomingValues);
791 
792       // And add a new incoming value for this predecessor for the
793       // newly retargeted branch.
794       PN->addIncoming(Selected, PredBB);
795     }
796   } else {
797     for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
798       // Update existing incoming values in PN for this
799       // predecessor of BB.
800       BasicBlock *PredBB = BBPreds[i];
801       Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
802                                                     IncomingValues);
803 
804       // And add a new incoming value for this predecessor for the
805       // newly retargeted branch.
806       PN->addIncoming(Selected, PredBB);
807     }
808   }
809 
810   replaceUndefValuesInPhi(PN, IncomingValues);
811 }
812 
813 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
814 /// unconditional branch, and contains no instructions other than PHI nodes,
815 /// potential side-effect free intrinsics and the branch.  If possible,
816 /// eliminate BB by rewriting all the predecessors to branch to the successor
817 /// block and return true.  If we can't transform, return false.
TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock * BB)818 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
819   assert(BB != &BB->getParent()->getEntryBlock() &&
820          "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
821 
822   // We can't eliminate infinite loops.
823   BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
824   if (BB == Succ) return false;
825 
826   // Check to see if merging these blocks would cause conflicts for any of the
827   // phi nodes in BB or Succ. If not, we can safely merge.
828   if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
829 
830   // Check for cases where Succ has multiple predecessors and a PHI node in BB
831   // has uses which will not disappear when the PHI nodes are merged.  It is
832   // possible to handle such cases, but difficult: it requires checking whether
833   // BB dominates Succ, which is non-trivial to calculate in the case where
834   // Succ has multiple predecessors.  Also, it requires checking whether
835   // constructing the necessary self-referential PHI node doesn't introduce any
836   // conflicts; this isn't too difficult, but the previous code for doing this
837   // was incorrect.
838   //
839   // Note that if this check finds a live use, BB dominates Succ, so BB is
840   // something like a loop pre-header (or rarely, a part of an irreducible CFG);
841   // folding the branch isn't profitable in that case anyway.
842   if (!Succ->getSinglePredecessor()) {
843     BasicBlock::iterator BBI = BB->begin();
844     while (isa<PHINode>(*BBI)) {
845       for (Use &U : BBI->uses()) {
846         if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
847           if (PN->getIncomingBlock(U) != BB)
848             return false;
849         } else {
850           return false;
851         }
852       }
853       ++BBI;
854     }
855   }
856 
857   DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
858 
859   if (isa<PHINode>(Succ->begin())) {
860     // If there is more than one pred of succ, and there are PHI nodes in
861     // the successor, then we need to add incoming edges for the PHI nodes
862     //
863     const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
864 
865     // Loop over all of the PHI nodes in the successor of BB.
866     for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
867       PHINode *PN = cast<PHINode>(I);
868 
869       redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
870     }
871   }
872 
873   if (Succ->getSinglePredecessor()) {
874     // BB is the only predecessor of Succ, so Succ will end up with exactly
875     // the same predecessors BB had.
876 
877     // Copy over any phi, debug or lifetime instruction.
878     BB->getTerminator()->eraseFromParent();
879     Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
880                                BB->getInstList());
881   } else {
882     while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
883       // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
884       assert(PN->use_empty() && "There shouldn't be any uses here!");
885       PN->eraseFromParent();
886     }
887   }
888 
889   // Everything that jumped to BB now goes to Succ.
890   BB->replaceAllUsesWith(Succ);
891   if (!Succ->hasName()) Succ->takeName(BB);
892   BB->eraseFromParent();              // Delete the old basic block.
893   return true;
894 }
895 
896 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
897 /// nodes in this block. This doesn't try to be clever about PHI nodes
898 /// which differ only in the order of the incoming values, but instcombine
899 /// orders them so it usually won't matter.
900 ///
EliminateDuplicatePHINodes(BasicBlock * BB)901 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
902   // This implementation doesn't currently consider undef operands
903   // specially. Theoretically, two phis which are identical except for
904   // one having an undef where the other doesn't could be collapsed.
905 
906   struct PHIDenseMapInfo {
907     static PHINode *getEmptyKey() {
908       return DenseMapInfo<PHINode *>::getEmptyKey();
909     }
910     static PHINode *getTombstoneKey() {
911       return DenseMapInfo<PHINode *>::getTombstoneKey();
912     }
913     static unsigned getHashValue(PHINode *PN) {
914       // Compute a hash value on the operands. Instcombine will likely have
915       // sorted them, which helps expose duplicates, but we have to check all
916       // the operands to be safe in case instcombine hasn't run.
917       return static_cast<unsigned>(hash_combine(
918           hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
919           hash_combine_range(PN->block_begin(), PN->block_end())));
920     }
921     static bool isEqual(PHINode *LHS, PHINode *RHS) {
922       if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
923           RHS == getEmptyKey() || RHS == getTombstoneKey())
924         return LHS == RHS;
925       return LHS->isIdenticalTo(RHS);
926     }
927   };
928 
929   // Set of unique PHINodes.
930   DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
931 
932   // Examine each PHI.
933   bool Changed = false;
934   for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
935     auto Inserted = PHISet.insert(PN);
936     if (!Inserted.second) {
937       // A duplicate. Replace this PHI with its duplicate.
938       PN->replaceAllUsesWith(*Inserted.first);
939       PN->eraseFromParent();
940       Changed = true;
941 
942       // The RAUW can change PHIs that we already visited. Start over from the
943       // beginning.
944       PHISet.clear();
945       I = BB->begin();
946     }
947   }
948 
949   return Changed;
950 }
951 
952 /// enforceKnownAlignment - If the specified pointer points to an object that
953 /// we control, modify the object's alignment to PrefAlign. This isn't
954 /// often possible though. If alignment is important, a more reliable approach
955 /// is to simply align all global variables and allocation instructions to
956 /// their preferred alignment from the beginning.
957 ///
enforceKnownAlignment(Value * V,unsigned Align,unsigned PrefAlign,const DataLayout & DL)958 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
959                                       unsigned PrefAlign,
960                                       const DataLayout &DL) {
961   assert(PrefAlign > Align);
962 
963   V = V->stripPointerCasts();
964 
965   if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
966     // TODO: ideally, computeKnownBits ought to have used
967     // AllocaInst::getAlignment() in its computation already, making
968     // the below max redundant. But, as it turns out,
969     // stripPointerCasts recurses through infinite layers of bitcasts,
970     // while computeKnownBits is not allowed to traverse more than 6
971     // levels.
972     Align = std::max(AI->getAlignment(), Align);
973     if (PrefAlign <= Align)
974       return Align;
975 
976     // If the preferred alignment is greater than the natural stack alignment
977     // then don't round up. This avoids dynamic stack realignment.
978     if (DL.exceedsNaturalStackAlignment(PrefAlign))
979       return Align;
980     AI->setAlignment(PrefAlign);
981     return PrefAlign;
982   }
983 
984   if (auto *GO = dyn_cast<GlobalObject>(V)) {
985     // TODO: as above, this shouldn't be necessary.
986     Align = std::max(GO->getAlignment(), Align);
987     if (PrefAlign <= Align)
988       return Align;
989 
990     // If there is a large requested alignment and we can, bump up the alignment
991     // of the global.  If the memory we set aside for the global may not be the
992     // memory used by the final program then it is impossible for us to reliably
993     // enforce the preferred alignment.
994     if (!GO->canIncreaseAlignment())
995       return Align;
996 
997     GO->setAlignment(PrefAlign);
998     return PrefAlign;
999   }
1000 
1001   return Align;
1002 }
1003 
1004 /// getOrEnforceKnownAlignment - If the specified pointer has an alignment that
1005 /// we can determine, return it, otherwise return 0.  If PrefAlign is specified,
1006 /// and it is more than the alignment of the ultimate object, see if we can
1007 /// increase the alignment of the ultimate object, making this check succeed.
getOrEnforceKnownAlignment(Value * V,unsigned PrefAlign,const DataLayout & DL,const Instruction * CxtI,AssumptionCache * AC,const DominatorTree * DT)1008 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
1009                                           const DataLayout &DL,
1010                                           const Instruction *CxtI,
1011                                           AssumptionCache *AC,
1012                                           const DominatorTree *DT) {
1013   assert(V->getType()->isPointerTy() &&
1014          "getOrEnforceKnownAlignment expects a pointer!");
1015   unsigned BitWidth = DL.getPointerTypeSizeInBits(V->getType());
1016 
1017   APInt KnownZero(BitWidth, 0), KnownOne(BitWidth, 0);
1018   computeKnownBits(V, KnownZero, KnownOne, DL, 0, AC, CxtI, DT);
1019   unsigned TrailZ = KnownZero.countTrailingOnes();
1020 
1021   // Avoid trouble with ridiculously large TrailZ values, such as
1022   // those computed from a null pointer.
1023   TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
1024 
1025   unsigned Align = 1u << std::min(BitWidth - 1, TrailZ);
1026 
1027   // LLVM doesn't support alignments larger than this currently.
1028   Align = std::min(Align, +Value::MaximumAlignment);
1029 
1030   if (PrefAlign > Align)
1031     Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
1032 
1033   // We don't need to make any adjustment.
1034   return Align;
1035 }
1036 
1037 ///===---------------------------------------------------------------------===//
1038 ///  Dbg Intrinsic utilities
1039 ///
1040 
1041 /// See if there is a dbg.value intrinsic for DIVar before I.
LdStHasDebugValue(DILocalVariable * DIVar,DIExpression * DIExpr,Instruction * I)1042 static bool LdStHasDebugValue(DILocalVariable *DIVar, DIExpression *DIExpr,
1043                               Instruction *I) {
1044   // Since we can't guarantee that the original dbg.declare instrinsic
1045   // is removed by LowerDbgDeclare(), we need to make sure that we are
1046   // not inserting the same dbg.value intrinsic over and over.
1047   llvm::BasicBlock::InstListType::iterator PrevI(I);
1048   if (PrevI != I->getParent()->getInstList().begin()) {
1049     --PrevI;
1050     if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
1051       if (DVI->getValue() == I->getOperand(0) &&
1052           DVI->getOffset() == 0 &&
1053           DVI->getVariable() == DIVar &&
1054           DVI->getExpression() == DIExpr)
1055         return true;
1056   }
1057   return false;
1058 }
1059 
1060 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
1061 /// that has an associated llvm.dbg.decl intrinsic.
ConvertDebugDeclareToDebugValue(DbgDeclareInst * DDI,StoreInst * SI,DIBuilder & Builder)1062 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1063                                            StoreInst *SI, DIBuilder &Builder) {
1064   auto *DIVar = DDI->getVariable();
1065   auto *DIExpr = DDI->getExpression();
1066   assert(DIVar && "Missing variable");
1067 
1068   // If an argument is zero extended then use argument directly. The ZExt
1069   // may be zapped by an optimization pass in future.
1070   Argument *ExtendedArg = nullptr;
1071   if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1072     ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1073   if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1074     ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1075   if (ExtendedArg) {
1076     // We're now only describing a subset of the variable. The piece we're
1077     // describing will always be smaller than the variable size, because
1078     // VariableSize == Size of Alloca described by DDI. Since SI stores
1079     // to the alloca described by DDI, if it's first operand is an extend,
1080     // we're guaranteed that before extension, the value was narrower than
1081     // the size of the alloca, hence the size of the described variable.
1082     SmallVector<uint64_t, 3> Ops;
1083     unsigned PieceOffset = 0;
1084     // If this already is a bit piece, we drop the bit piece from the expression
1085     // and record the offset.
1086     if (DIExpr->isBitPiece()) {
1087       Ops.append(DIExpr->elements_begin(), DIExpr->elements_end()-3);
1088       PieceOffset = DIExpr->getBitPieceOffset();
1089     } else {
1090       Ops.append(DIExpr->elements_begin(), DIExpr->elements_end());
1091     }
1092     Ops.push_back(dwarf::DW_OP_bit_piece);
1093     Ops.push_back(PieceOffset); // Offset
1094     const DataLayout &DL = DDI->getModule()->getDataLayout();
1095     Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType())); // Size
1096     auto NewDIExpr = Builder.createExpression(Ops);
1097     if (!LdStHasDebugValue(DIVar, NewDIExpr, SI))
1098       Builder.insertDbgValueIntrinsic(ExtendedArg, 0, DIVar, NewDIExpr,
1099                                       DDI->getDebugLoc(), SI);
1100   } else if (!LdStHasDebugValue(DIVar, DIExpr, SI))
1101     Builder.insertDbgValueIntrinsic(SI->getOperand(0), 0, DIVar, DIExpr,
1102                                     DDI->getDebugLoc(), SI);
1103   return true;
1104 }
1105 
1106 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1107 /// that has an associated llvm.dbg.decl intrinsic.
ConvertDebugDeclareToDebugValue(DbgDeclareInst * DDI,LoadInst * LI,DIBuilder & Builder)1108 bool llvm::ConvertDebugDeclareToDebugValue(DbgDeclareInst *DDI,
1109                                            LoadInst *LI, DIBuilder &Builder) {
1110   auto *DIVar = DDI->getVariable();
1111   auto *DIExpr = DDI->getExpression();
1112   assert(DIVar && "Missing variable");
1113 
1114   if (LdStHasDebugValue(DIVar, DIExpr, LI))
1115     return true;
1116 
1117   // We are now tracking the loaded value instead of the address. In the
1118   // future if multi-location support is added to the IR, it might be
1119   // preferable to keep tracking both the loaded value and the original
1120   // address in case the alloca can not be elided.
1121   Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
1122       LI, 0, DIVar, DIExpr, DDI->getDebugLoc(), (Instruction *)nullptr);
1123   DbgValue->insertAfter(LI);
1124   return true;
1125 }
1126 
1127 /// Determine whether this alloca is either a VLA or an array.
isArray(AllocaInst * AI)1128 static bool isArray(AllocaInst *AI) {
1129   return AI->isArrayAllocation() ||
1130     AI->getType()->getElementType()->isArrayTy();
1131 }
1132 
1133 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1134 /// of llvm.dbg.value intrinsics.
LowerDbgDeclare(Function & F)1135 bool llvm::LowerDbgDeclare(Function &F) {
1136   DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1137   SmallVector<DbgDeclareInst *, 4> Dbgs;
1138   for (auto &FI : F)
1139     for (Instruction &BI : FI)
1140       if (auto DDI = dyn_cast<DbgDeclareInst>(&BI))
1141         Dbgs.push_back(DDI);
1142 
1143   if (Dbgs.empty())
1144     return false;
1145 
1146   for (auto &I : Dbgs) {
1147     DbgDeclareInst *DDI = I;
1148     AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1149     // If this is an alloca for a scalar variable, insert a dbg.value
1150     // at each load and store to the alloca and erase the dbg.declare.
1151     // The dbg.values allow tracking a variable even if it is not
1152     // stored on the stack, while the dbg.declare can only describe
1153     // the stack slot (and at a lexical-scope granularity). Later
1154     // passes will attempt to elide the stack slot.
1155     if (AI && !isArray(AI)) {
1156       for (auto &AIUse : AI->uses()) {
1157         User *U = AIUse.getUser();
1158         if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1159           if (AIUse.getOperandNo() == 1)
1160             ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1161         } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
1162           ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1163         } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1164           // This is a call by-value or some other instruction that
1165           // takes a pointer to the variable. Insert a *value*
1166           // intrinsic that describes the alloca.
1167           SmallVector<uint64_t, 1> NewDIExpr;
1168           auto *DIExpr = DDI->getExpression();
1169           NewDIExpr.push_back(dwarf::DW_OP_deref);
1170           NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
1171           DIB.insertDbgValueIntrinsic(AI, 0, DDI->getVariable(),
1172                                       DIB.createExpression(NewDIExpr),
1173                                       DDI->getDebugLoc(), CI);
1174         }
1175       }
1176       DDI->eraseFromParent();
1177     }
1178   }
1179   return true;
1180 }
1181 
1182 /// FindAllocaDbgDeclare - Finds the llvm.dbg.declare intrinsic describing the
1183 /// alloca 'V', if any.
FindAllocaDbgDeclare(Value * V)1184 DbgDeclareInst *llvm::FindAllocaDbgDeclare(Value *V) {
1185   if (auto *L = LocalAsMetadata::getIfExists(V))
1186     if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1187       for (User *U : MDV->users())
1188         if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
1189           return DDI;
1190 
1191   return nullptr;
1192 }
1193 
DIExprAddDeref(SmallVectorImpl<uint64_t> & Expr)1194 static void DIExprAddDeref(SmallVectorImpl<uint64_t> &Expr) {
1195   Expr.push_back(dwarf::DW_OP_deref);
1196 }
1197 
DIExprAddOffset(SmallVectorImpl<uint64_t> & Expr,int Offset)1198 static void DIExprAddOffset(SmallVectorImpl<uint64_t> &Expr, int Offset) {
1199   if (Offset > 0) {
1200     Expr.push_back(dwarf::DW_OP_plus);
1201     Expr.push_back(Offset);
1202   } else if (Offset < 0) {
1203     Expr.push_back(dwarf::DW_OP_minus);
1204     Expr.push_back(-Offset);
1205   }
1206 }
1207 
BuildReplacementDIExpr(DIBuilder & Builder,DIExpression * DIExpr,bool Deref,int Offset)1208 static DIExpression *BuildReplacementDIExpr(DIBuilder &Builder,
1209                                             DIExpression *DIExpr, bool Deref,
1210                                             int Offset) {
1211   if (!Deref && !Offset)
1212     return DIExpr;
1213   // Create a copy of the original DIDescriptor for user variable, prepending
1214   // "deref" operation to a list of address elements, as new llvm.dbg.declare
1215   // will take a value storing address of the memory for variable, not
1216   // alloca itself.
1217   SmallVector<uint64_t, 4> NewDIExpr;
1218   if (Deref)
1219     DIExprAddDeref(NewDIExpr);
1220   DIExprAddOffset(NewDIExpr, Offset);
1221   if (DIExpr)
1222     NewDIExpr.append(DIExpr->elements_begin(), DIExpr->elements_end());
1223   return Builder.createExpression(NewDIExpr);
1224 }
1225 
replaceDbgDeclare(Value * Address,Value * NewAddress,Instruction * InsertBefore,DIBuilder & Builder,bool Deref,int Offset)1226 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
1227                              Instruction *InsertBefore, DIBuilder &Builder,
1228                              bool Deref, int Offset) {
1229   DbgDeclareInst *DDI = FindAllocaDbgDeclare(Address);
1230   if (!DDI)
1231     return false;
1232   DebugLoc Loc = DDI->getDebugLoc();
1233   auto *DIVar = DDI->getVariable();
1234   auto *DIExpr = DDI->getExpression();
1235   assert(DIVar && "Missing variable");
1236 
1237   DIExpr = BuildReplacementDIExpr(Builder, DIExpr, Deref, Offset);
1238 
1239   // Insert llvm.dbg.declare immediately after the original alloca, and remove
1240   // old llvm.dbg.declare.
1241   Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
1242   DDI->eraseFromParent();
1243   return true;
1244 }
1245 
replaceDbgDeclareForAlloca(AllocaInst * AI,Value * NewAllocaAddress,DIBuilder & Builder,bool Deref,int Offset)1246 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1247                                       DIBuilder &Builder, bool Deref, int Offset) {
1248   return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder,
1249                            Deref, Offset);
1250 }
1251 
replaceOneDbgValueForAlloca(DbgValueInst * DVI,Value * NewAddress,DIBuilder & Builder,int Offset)1252 static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
1253                                         DIBuilder &Builder, int Offset) {
1254   DebugLoc Loc = DVI->getDebugLoc();
1255   auto *DIVar = DVI->getVariable();
1256   auto *DIExpr = DVI->getExpression();
1257   assert(DIVar && "Missing variable");
1258 
1259   // This is an alloca-based llvm.dbg.value. The first thing it should do with
1260   // the alloca pointer is dereference it. Otherwise we don't know how to handle
1261   // it and give up.
1262   if (!DIExpr || DIExpr->getNumElements() < 1 ||
1263       DIExpr->getElement(0) != dwarf::DW_OP_deref)
1264     return;
1265 
1266   // Insert the offset immediately after the first deref.
1267   // We could just change the offset argument of dbg.value, but it's unsigned...
1268   if (Offset) {
1269     SmallVector<uint64_t, 4> NewDIExpr;
1270     DIExprAddDeref(NewDIExpr);
1271     DIExprAddOffset(NewDIExpr, Offset);
1272     NewDIExpr.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
1273     DIExpr = Builder.createExpression(NewDIExpr);
1274   }
1275 
1276   Builder.insertDbgValueIntrinsic(NewAddress, DVI->getOffset(), DIVar, DIExpr,
1277                                   Loc, DVI);
1278   DVI->eraseFromParent();
1279 }
1280 
replaceDbgValueForAlloca(AllocaInst * AI,Value * NewAllocaAddress,DIBuilder & Builder,int Offset)1281 void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1282                                     DIBuilder &Builder, int Offset) {
1283   if (auto *L = LocalAsMetadata::getIfExists(AI))
1284     if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
1285       for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) {
1286         Use &U = *UI++;
1287         if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser()))
1288           replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset);
1289       }
1290 }
1291 
removeAllNonTerminatorAndEHPadInstructions(BasicBlock * BB)1292 unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
1293   unsigned NumDeadInst = 0;
1294   // Delete the instructions backwards, as it has a reduced likelihood of
1295   // having to update as many def-use and use-def chains.
1296   Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
1297   while (EndInst != &BB->front()) {
1298     // Delete the next to last instruction.
1299     Instruction *Inst = &*--EndInst->getIterator();
1300     if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
1301       Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
1302     if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
1303       EndInst = Inst;
1304       continue;
1305     }
1306     if (!isa<DbgInfoIntrinsic>(Inst))
1307       ++NumDeadInst;
1308     Inst->eraseFromParent();
1309   }
1310   return NumDeadInst;
1311 }
1312 
changeToUnreachable(Instruction * I,bool UseLLVMTrap)1313 unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap) {
1314   BasicBlock *BB = I->getParent();
1315   // Loop over all of the successors, removing BB's entry from any PHI
1316   // nodes.
1317   for (BasicBlock *Successor : successors(BB))
1318     Successor->removePredecessor(BB);
1319 
1320   // Insert a call to llvm.trap right before this.  This turns the undefined
1321   // behavior into a hard fail instead of falling through into random code.
1322   if (UseLLVMTrap) {
1323     Function *TrapFn =
1324       Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1325     CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1326     CallTrap->setDebugLoc(I->getDebugLoc());
1327   }
1328   new UnreachableInst(I->getContext(), I);
1329 
1330   // All instructions after this are dead.
1331   unsigned NumInstrsRemoved = 0;
1332   BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end();
1333   while (BBI != BBE) {
1334     if (!BBI->use_empty())
1335       BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1336     BB->getInstList().erase(BBI++);
1337     ++NumInstrsRemoved;
1338   }
1339   return NumInstrsRemoved;
1340 }
1341 
1342 /// changeToCall - Convert the specified invoke into a normal call.
changeToCall(InvokeInst * II)1343 static void changeToCall(InvokeInst *II) {
1344   SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end());
1345   SmallVector<OperandBundleDef, 1> OpBundles;
1346   II->getOperandBundlesAsDefs(OpBundles);
1347   CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, OpBundles,
1348                                        "", II);
1349   NewCall->takeName(II);
1350   NewCall->setCallingConv(II->getCallingConv());
1351   NewCall->setAttributes(II->getAttributes());
1352   NewCall->setDebugLoc(II->getDebugLoc());
1353   II->replaceAllUsesWith(NewCall);
1354 
1355   // Follow the call by a branch to the normal destination.
1356   BranchInst::Create(II->getNormalDest(), II);
1357 
1358   // Update PHI nodes in the unwind destination
1359   II->getUnwindDest()->removePredecessor(II->getParent());
1360   II->eraseFromParent();
1361 }
1362 
markAliveBlocks(Function & F,SmallPtrSetImpl<BasicBlock * > & Reachable)1363 static bool markAliveBlocks(Function &F,
1364                             SmallPtrSetImpl<BasicBlock*> &Reachable) {
1365 
1366   SmallVector<BasicBlock*, 128> Worklist;
1367   BasicBlock *BB = &F.front();
1368   Worklist.push_back(BB);
1369   Reachable.insert(BB);
1370   bool Changed = false;
1371   do {
1372     BB = Worklist.pop_back_val();
1373 
1374     // Do a quick scan of the basic block, turning any obviously unreachable
1375     // instructions into LLVM unreachable insts.  The instruction combining pass
1376     // canonicalizes unreachable insts into stores to null or undef.
1377     for (Instruction &I : *BB) {
1378       // Assumptions that are known to be false are equivalent to unreachable.
1379       // Also, if the condition is undefined, then we make the choice most
1380       // beneficial to the optimizer, and choose that to also be unreachable.
1381       if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
1382         if (II->getIntrinsicID() == Intrinsic::assume) {
1383           if (match(II->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) {
1384             // Don't insert a call to llvm.trap right before the unreachable.
1385             changeToUnreachable(II, false);
1386             Changed = true;
1387             break;
1388           }
1389         }
1390 
1391         if (II->getIntrinsicID() == Intrinsic::experimental_guard) {
1392           // A call to the guard intrinsic bails out of the current compilation
1393           // unit if the predicate passed to it is false.  If the predicate is a
1394           // constant false, then we know the guard will bail out of the current
1395           // compile unconditionally, so all code following it is dead.
1396           //
1397           // Note: unlike in llvm.assume, it is not "obviously profitable" for
1398           // guards to treat `undef` as `false` since a guard on `undef` can
1399           // still be useful for widening.
1400           if (match(II->getArgOperand(0), m_Zero()))
1401             if (!isa<UnreachableInst>(II->getNextNode())) {
1402               changeToUnreachable(II->getNextNode(), /*UseLLVMTrap=*/ false);
1403               Changed = true;
1404               break;
1405             }
1406         }
1407       }
1408 
1409       if (auto *CI = dyn_cast<CallInst>(&I)) {
1410         Value *Callee = CI->getCalledValue();
1411         if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1412           changeToUnreachable(CI, /*UseLLVMTrap=*/false);
1413           Changed = true;
1414           break;
1415         }
1416         if (CI->doesNotReturn()) {
1417           // If we found a call to a no-return function, insert an unreachable
1418           // instruction after it.  Make sure there isn't *already* one there
1419           // though.
1420           if (!isa<UnreachableInst>(CI->getNextNode())) {
1421             // Don't insert a call to llvm.trap right before the unreachable.
1422             changeToUnreachable(CI->getNextNode(), false);
1423             Changed = true;
1424           }
1425           break;
1426         }
1427       }
1428 
1429       // Store to undef and store to null are undefined and used to signal that
1430       // they should be changed to unreachable by passes that can't modify the
1431       // CFG.
1432       if (auto *SI = dyn_cast<StoreInst>(&I)) {
1433         // Don't touch volatile stores.
1434         if (SI->isVolatile()) continue;
1435 
1436         Value *Ptr = SI->getOperand(1);
1437 
1438         if (isa<UndefValue>(Ptr) ||
1439             (isa<ConstantPointerNull>(Ptr) &&
1440              SI->getPointerAddressSpace() == 0)) {
1441           changeToUnreachable(SI, true);
1442           Changed = true;
1443           break;
1444         }
1445       }
1446     }
1447 
1448     TerminatorInst *Terminator = BB->getTerminator();
1449     if (auto *II = dyn_cast<InvokeInst>(Terminator)) {
1450       // Turn invokes that call 'nounwind' functions into ordinary calls.
1451       Value *Callee = II->getCalledValue();
1452       if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1453         changeToUnreachable(II, true);
1454         Changed = true;
1455       } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
1456         if (II->use_empty() && II->onlyReadsMemory()) {
1457           // jump to the normal destination branch.
1458           BranchInst::Create(II->getNormalDest(), II);
1459           II->getUnwindDest()->removePredecessor(II->getParent());
1460           II->eraseFromParent();
1461         } else
1462           changeToCall(II);
1463         Changed = true;
1464       }
1465     } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
1466       // Remove catchpads which cannot be reached.
1467       struct CatchPadDenseMapInfo {
1468         static CatchPadInst *getEmptyKey() {
1469           return DenseMapInfo<CatchPadInst *>::getEmptyKey();
1470         }
1471         static CatchPadInst *getTombstoneKey() {
1472           return DenseMapInfo<CatchPadInst *>::getTombstoneKey();
1473         }
1474         static unsigned getHashValue(CatchPadInst *CatchPad) {
1475           return static_cast<unsigned>(hash_combine_range(
1476               CatchPad->value_op_begin(), CatchPad->value_op_end()));
1477         }
1478         static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) {
1479           if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
1480               RHS == getEmptyKey() || RHS == getTombstoneKey())
1481             return LHS == RHS;
1482           return LHS->isIdenticalTo(RHS);
1483         }
1484       };
1485 
1486       // Set of unique CatchPads.
1487       SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
1488                     CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
1489           HandlerSet;
1490       detail::DenseSetEmpty Empty;
1491       for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(),
1492                                              E = CatchSwitch->handler_end();
1493            I != E; ++I) {
1494         BasicBlock *HandlerBB = *I;
1495         auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
1496         if (!HandlerSet.insert({CatchPad, Empty}).second) {
1497           CatchSwitch->removeHandler(I);
1498           --I;
1499           --E;
1500           Changed = true;
1501         }
1502       }
1503     }
1504 
1505     Changed |= ConstantFoldTerminator(BB, true);
1506     for (BasicBlock *Successor : successors(BB))
1507       if (Reachable.insert(Successor).second)
1508         Worklist.push_back(Successor);
1509   } while (!Worklist.empty());
1510   return Changed;
1511 }
1512 
removeUnwindEdge(BasicBlock * BB)1513 void llvm::removeUnwindEdge(BasicBlock *BB) {
1514   TerminatorInst *TI = BB->getTerminator();
1515 
1516   if (auto *II = dyn_cast<InvokeInst>(TI)) {
1517     changeToCall(II);
1518     return;
1519   }
1520 
1521   TerminatorInst *NewTI;
1522   BasicBlock *UnwindDest;
1523 
1524   if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
1525     NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
1526     UnwindDest = CRI->getUnwindDest();
1527   } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
1528     auto *NewCatchSwitch = CatchSwitchInst::Create(
1529         CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
1530         CatchSwitch->getName(), CatchSwitch);
1531     for (BasicBlock *PadBB : CatchSwitch->handlers())
1532       NewCatchSwitch->addHandler(PadBB);
1533 
1534     NewTI = NewCatchSwitch;
1535     UnwindDest = CatchSwitch->getUnwindDest();
1536   } else {
1537     llvm_unreachable("Could not find unwind successor");
1538   }
1539 
1540   NewTI->takeName(TI);
1541   NewTI->setDebugLoc(TI->getDebugLoc());
1542   UnwindDest->removePredecessor(BB);
1543   TI->replaceAllUsesWith(NewTI);
1544   TI->eraseFromParent();
1545 }
1546 
1547 /// removeUnreachableBlocksFromFn - Remove blocks that are not reachable, even
1548 /// if they are in a dead cycle.  Return true if a change was made, false
1549 /// otherwise.
removeUnreachableBlocks(Function & F,LazyValueInfo * LVI)1550 bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI) {
1551   SmallPtrSet<BasicBlock*, 16> Reachable;
1552   bool Changed = markAliveBlocks(F, Reachable);
1553 
1554   // If there are unreachable blocks in the CFG...
1555   if (Reachable.size() == F.size())
1556     return Changed;
1557 
1558   assert(Reachable.size() < F.size());
1559   NumRemoved += F.size()-Reachable.size();
1560 
1561   // Loop over all of the basic blocks that are not reachable, dropping all of
1562   // their internal references...
1563   for (Function::iterator BB = ++F.begin(), E = F.end(); BB != E; ++BB) {
1564     if (Reachable.count(&*BB))
1565       continue;
1566 
1567     for (BasicBlock *Successor : successors(&*BB))
1568       if (Reachable.count(Successor))
1569         Successor->removePredecessor(&*BB);
1570     if (LVI)
1571       LVI->eraseBlock(&*BB);
1572     BB->dropAllReferences();
1573   }
1574 
1575   for (Function::iterator I = ++F.begin(); I != F.end();)
1576     if (!Reachable.count(&*I))
1577       I = F.getBasicBlockList().erase(I);
1578     else
1579       ++I;
1580 
1581   return true;
1582 }
1583 
combineMetadata(Instruction * K,const Instruction * J,ArrayRef<unsigned> KnownIDs)1584 void llvm::combineMetadata(Instruction *K, const Instruction *J,
1585                            ArrayRef<unsigned> KnownIDs) {
1586   SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
1587   K->dropUnknownNonDebugMetadata(KnownIDs);
1588   K->getAllMetadataOtherThanDebugLoc(Metadata);
1589   for (unsigned i = 0, n = Metadata.size(); i < n; ++i) {
1590     unsigned Kind = Metadata[i].first;
1591     MDNode *JMD = J->getMetadata(Kind);
1592     MDNode *KMD = Metadata[i].second;
1593 
1594     switch (Kind) {
1595       default:
1596         K->setMetadata(Kind, nullptr); // Remove unknown metadata
1597         break;
1598       case LLVMContext::MD_dbg:
1599         llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
1600       case LLVMContext::MD_tbaa:
1601         K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
1602         break;
1603       case LLVMContext::MD_alias_scope:
1604         K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
1605         break;
1606       case LLVMContext::MD_noalias:
1607       case LLVMContext::MD_mem_parallel_loop_access:
1608         K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
1609         break;
1610       case LLVMContext::MD_range:
1611         K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
1612         break;
1613       case LLVMContext::MD_fpmath:
1614         K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
1615         break;
1616       case LLVMContext::MD_invariant_load:
1617         // Only set the !invariant.load if it is present in both instructions.
1618         K->setMetadata(Kind, JMD);
1619         break;
1620       case LLVMContext::MD_nonnull:
1621         // Only set the !nonnull if it is present in both instructions.
1622         K->setMetadata(Kind, JMD);
1623         break;
1624       case LLVMContext::MD_invariant_group:
1625         // Preserve !invariant.group in K.
1626         break;
1627       case LLVMContext::MD_align:
1628         K->setMetadata(Kind,
1629           MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
1630         break;
1631       case LLVMContext::MD_dereferenceable:
1632       case LLVMContext::MD_dereferenceable_or_null:
1633         K->setMetadata(Kind,
1634           MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
1635         break;
1636     }
1637   }
1638   // Set !invariant.group from J if J has it. If both instructions have it
1639   // then we will just pick it from J - even when they are different.
1640   // Also make sure that K is load or store - f.e. combining bitcast with load
1641   // could produce bitcast with invariant.group metadata, which is invalid.
1642   // FIXME: we should try to preserve both invariant.group md if they are
1643   // different, but right now instruction can only have one invariant.group.
1644   if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
1645     if (isa<LoadInst>(K) || isa<StoreInst>(K))
1646       K->setMetadata(LLVMContext::MD_invariant_group, JMD);
1647 }
1648 
replaceDominatedUsesWith(Value * From,Value * To,DominatorTree & DT,const BasicBlockEdge & Root)1649 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
1650                                         DominatorTree &DT,
1651                                         const BasicBlockEdge &Root) {
1652   assert(From->getType() == To->getType());
1653 
1654   unsigned Count = 0;
1655   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1656        UI != UE; ) {
1657     Use &U = *UI++;
1658     if (DT.dominates(Root, U)) {
1659       U.set(To);
1660       DEBUG(dbgs() << "Replace dominated use of '"
1661             << From->getName() << "' as "
1662             << *To << " in " << *U << "\n");
1663       ++Count;
1664     }
1665   }
1666   return Count;
1667 }
1668 
replaceDominatedUsesWith(Value * From,Value * To,DominatorTree & DT,const BasicBlock * BB)1669 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
1670                                         DominatorTree &DT,
1671                                         const BasicBlock *BB) {
1672   assert(From->getType() == To->getType());
1673 
1674   unsigned Count = 0;
1675   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
1676        UI != UE;) {
1677     Use &U = *UI++;
1678     auto *I = cast<Instruction>(U.getUser());
1679     if (DT.properlyDominates(BB, I->getParent())) {
1680       U.set(To);
1681       DEBUG(dbgs() << "Replace dominated use of '" << From->getName() << "' as "
1682                    << *To << " in " << *U << "\n");
1683       ++Count;
1684     }
1685   }
1686   return Count;
1687 }
1688 
callsGCLeafFunction(ImmutableCallSite CS)1689 bool llvm::callsGCLeafFunction(ImmutableCallSite CS) {
1690   // Check if the function is specifically marked as a gc leaf function.
1691   if (CS.hasFnAttr("gc-leaf-function"))
1692     return true;
1693   if (const Function *F = CS.getCalledFunction()) {
1694     if (F->hasFnAttribute("gc-leaf-function"))
1695       return true;
1696 
1697     if (auto IID = F->getIntrinsicID())
1698       // Most LLVM intrinsics do not take safepoints.
1699       return IID != Intrinsic::experimental_gc_statepoint &&
1700              IID != Intrinsic::experimental_deoptimize;
1701   }
1702 
1703   return false;
1704 }
1705 
1706 /// A potential constituent of a bitreverse or bswap expression. See
1707 /// collectBitParts for a fuller explanation.
1708 struct BitPart {
BitPartBitPart1709   BitPart(Value *P, unsigned BW) : Provider(P) {
1710     Provenance.resize(BW);
1711   }
1712 
1713   /// The Value that this is a bitreverse/bswap of.
1714   Value *Provider;
1715   /// The "provenance" of each bit. Provenance[A] = B means that bit A
1716   /// in Provider becomes bit B in the result of this expression.
1717   SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128.
1718 
1719   enum { Unset = -1 };
1720 };
1721 
1722 /// Analyze the specified subexpression and see if it is capable of providing
1723 /// pieces of a bswap or bitreverse. The subexpression provides a potential
1724 /// piece of a bswap or bitreverse if it can be proven that each non-zero bit in
1725 /// the output of the expression came from a corresponding bit in some other
1726 /// value. This function is recursive, and the end result is a mapping of
1727 /// bitnumber to bitnumber. It is the caller's responsibility to validate that
1728 /// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse.
1729 ///
1730 /// For example, if the current subexpression if "(shl i32 %X, 24)" then we know
1731 /// that the expression deposits the low byte of %X into the high byte of the
1732 /// result and that all other bits are zero. This expression is accepted and a
1733 /// BitPart is returned with Provider set to %X and Provenance[24-31] set to
1734 /// [0-7].
1735 ///
1736 /// To avoid revisiting values, the BitPart results are memoized into the
1737 /// provided map. To avoid unnecessary copying of BitParts, BitParts are
1738 /// constructed in-place in the \c BPS map. Because of this \c BPS needs to
1739 /// store BitParts objects, not pointers. As we need the concept of a nullptr
1740 /// BitParts (Value has been analyzed and the analysis failed), we an Optional
1741 /// type instead to provide the same functionality.
1742 ///
1743 /// Because we pass around references into \c BPS, we must use a container that
1744 /// does not invalidate internal references (std::map instead of DenseMap).
1745 ///
1746 static const Optional<BitPart> &
collectBitParts(Value * V,bool MatchBSwaps,bool MatchBitReversals,std::map<Value *,Optional<BitPart>> & BPS)1747 collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals,
1748                 std::map<Value *, Optional<BitPart>> &BPS) {
1749   auto I = BPS.find(V);
1750   if (I != BPS.end())
1751     return I->second;
1752 
1753   auto &Result = BPS[V] = None;
1754   auto BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
1755 
1756   if (Instruction *I = dyn_cast<Instruction>(V)) {
1757     // If this is an or instruction, it may be an inner node of the bswap.
1758     if (I->getOpcode() == Instruction::Or) {
1759       auto &A = collectBitParts(I->getOperand(0), MatchBSwaps,
1760                                 MatchBitReversals, BPS);
1761       auto &B = collectBitParts(I->getOperand(1), MatchBSwaps,
1762                                 MatchBitReversals, BPS);
1763       if (!A || !B)
1764         return Result;
1765 
1766       // Try and merge the two together.
1767       if (!A->Provider || A->Provider != B->Provider)
1768         return Result;
1769 
1770       Result = BitPart(A->Provider, BitWidth);
1771       for (unsigned i = 0; i < A->Provenance.size(); ++i) {
1772         if (A->Provenance[i] != BitPart::Unset &&
1773             B->Provenance[i] != BitPart::Unset &&
1774             A->Provenance[i] != B->Provenance[i])
1775           return Result = None;
1776 
1777         if (A->Provenance[i] == BitPart::Unset)
1778           Result->Provenance[i] = B->Provenance[i];
1779         else
1780           Result->Provenance[i] = A->Provenance[i];
1781       }
1782 
1783       return Result;
1784     }
1785 
1786     // If this is a logical shift by a constant, recurse then shift the result.
1787     if (I->isLogicalShift() && isa<ConstantInt>(I->getOperand(1))) {
1788       unsigned BitShift =
1789           cast<ConstantInt>(I->getOperand(1))->getLimitedValue(~0U);
1790       // Ensure the shift amount is defined.
1791       if (BitShift > BitWidth)
1792         return Result;
1793 
1794       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
1795                                   MatchBitReversals, BPS);
1796       if (!Res)
1797         return Result;
1798       Result = Res;
1799 
1800       // Perform the "shift" on BitProvenance.
1801       auto &P = Result->Provenance;
1802       if (I->getOpcode() == Instruction::Shl) {
1803         P.erase(std::prev(P.end(), BitShift), P.end());
1804         P.insert(P.begin(), BitShift, BitPart::Unset);
1805       } else {
1806         P.erase(P.begin(), std::next(P.begin(), BitShift));
1807         P.insert(P.end(), BitShift, BitPart::Unset);
1808       }
1809 
1810       return Result;
1811     }
1812 
1813     // If this is a logical 'and' with a mask that clears bits, recurse then
1814     // unset the appropriate bits.
1815     if (I->getOpcode() == Instruction::And &&
1816         isa<ConstantInt>(I->getOperand(1))) {
1817       APInt Bit(I->getType()->getPrimitiveSizeInBits(), 1);
1818       const APInt &AndMask = cast<ConstantInt>(I->getOperand(1))->getValue();
1819 
1820       // Check that the mask allows a multiple of 8 bits for a bswap, for an
1821       // early exit.
1822       unsigned NumMaskedBits = AndMask.countPopulation();
1823       if (!MatchBitReversals && NumMaskedBits % 8 != 0)
1824         return Result;
1825 
1826       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
1827                                   MatchBitReversals, BPS);
1828       if (!Res)
1829         return Result;
1830       Result = Res;
1831 
1832       for (unsigned i = 0; i < BitWidth; ++i, Bit <<= 1)
1833         // If the AndMask is zero for this bit, clear the bit.
1834         if ((AndMask & Bit) == 0)
1835           Result->Provenance[i] = BitPart::Unset;
1836       return Result;
1837     }
1838 
1839     // If this is a zext instruction zero extend the result.
1840     if (I->getOpcode() == Instruction::ZExt) {
1841       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
1842                                   MatchBitReversals, BPS);
1843       if (!Res)
1844         return Result;
1845 
1846       Result = BitPart(Res->Provider, BitWidth);
1847       auto NarrowBitWidth =
1848           cast<IntegerType>(cast<ZExtInst>(I)->getSrcTy())->getBitWidth();
1849       for (unsigned i = 0; i < NarrowBitWidth; ++i)
1850         Result->Provenance[i] = Res->Provenance[i];
1851       for (unsigned i = NarrowBitWidth; i < BitWidth; ++i)
1852         Result->Provenance[i] = BitPart::Unset;
1853       return Result;
1854     }
1855   }
1856 
1857   // Okay, we got to something that isn't a shift, 'or' or 'and'.  This must be
1858   // the input value to the bswap/bitreverse.
1859   Result = BitPart(V, BitWidth);
1860   for (unsigned i = 0; i < BitWidth; ++i)
1861     Result->Provenance[i] = i;
1862   return Result;
1863 }
1864 
bitTransformIsCorrectForBSwap(unsigned From,unsigned To,unsigned BitWidth)1865 static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To,
1866                                           unsigned BitWidth) {
1867   if (From % 8 != To % 8)
1868     return false;
1869   // Convert from bit indices to byte indices and check for a byte reversal.
1870   From >>= 3;
1871   To >>= 3;
1872   BitWidth >>= 3;
1873   return From == BitWidth - To - 1;
1874 }
1875 
bitTransformIsCorrectForBitReverse(unsigned From,unsigned To,unsigned BitWidth)1876 static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To,
1877                                                unsigned BitWidth) {
1878   return From == BitWidth - To - 1;
1879 }
1880 
1881 /// Given an OR instruction, check to see if this is a bitreverse
1882 /// idiom. If so, insert the new intrinsic and return true.
recognizeBSwapOrBitReverseIdiom(Instruction * I,bool MatchBSwaps,bool MatchBitReversals,SmallVectorImpl<Instruction * > & InsertedInsts)1883 bool llvm::recognizeBSwapOrBitReverseIdiom(
1884     Instruction *I, bool MatchBSwaps, bool MatchBitReversals,
1885     SmallVectorImpl<Instruction *> &InsertedInsts) {
1886   if (Operator::getOpcode(I) != Instruction::Or)
1887     return false;
1888   if (!MatchBSwaps && !MatchBitReversals)
1889     return false;
1890   IntegerType *ITy = dyn_cast<IntegerType>(I->getType());
1891   if (!ITy || ITy->getBitWidth() > 128)
1892     return false;   // Can't do vectors or integers > 128 bits.
1893   unsigned BW = ITy->getBitWidth();
1894 
1895   unsigned DemandedBW = BW;
1896   IntegerType *DemandedTy = ITy;
1897   if (I->hasOneUse()) {
1898     if (TruncInst *Trunc = dyn_cast<TruncInst>(I->user_back())) {
1899       DemandedTy = cast<IntegerType>(Trunc->getType());
1900       DemandedBW = DemandedTy->getBitWidth();
1901     }
1902   }
1903 
1904   // Try to find all the pieces corresponding to the bswap.
1905   std::map<Value *, Optional<BitPart>> BPS;
1906   auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS);
1907   if (!Res)
1908     return false;
1909   auto &BitProvenance = Res->Provenance;
1910 
1911   // Now, is the bit permutation correct for a bswap or a bitreverse? We can
1912   // only byteswap values with an even number of bytes.
1913   bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true;
1914   for (unsigned i = 0; i < DemandedBW; ++i) {
1915     OKForBSwap &=
1916         bitTransformIsCorrectForBSwap(BitProvenance[i], i, DemandedBW);
1917     OKForBitReverse &=
1918         bitTransformIsCorrectForBitReverse(BitProvenance[i], i, DemandedBW);
1919   }
1920 
1921   Intrinsic::ID Intrin;
1922   if (OKForBSwap && MatchBSwaps)
1923     Intrin = Intrinsic::bswap;
1924   else if (OKForBitReverse && MatchBitReversals)
1925     Intrin = Intrinsic::bitreverse;
1926   else
1927     return false;
1928 
1929   if (ITy != DemandedTy) {
1930     Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, DemandedTy);
1931     Value *Provider = Res->Provider;
1932     IntegerType *ProviderTy = cast<IntegerType>(Provider->getType());
1933     // We may need to truncate the provider.
1934     if (DemandedTy != ProviderTy) {
1935       auto *Trunc = CastInst::Create(Instruction::Trunc, Provider, DemandedTy,
1936                                      "trunc", I);
1937       InsertedInsts.push_back(Trunc);
1938       Provider = Trunc;
1939     }
1940     auto *CI = CallInst::Create(F, Provider, "rev", I);
1941     InsertedInsts.push_back(CI);
1942     auto *ExtInst = CastInst::Create(Instruction::ZExt, CI, ITy, "zext", I);
1943     InsertedInsts.push_back(ExtInst);
1944     return true;
1945   }
1946 
1947   Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, ITy);
1948   InsertedInsts.push_back(CallInst::Create(F, Res->Provider, "rev", I));
1949   return true;
1950 }
1951 
1952 // CodeGen has special handling for some string functions that may replace
1953 // them with target-specific intrinsics.  Since that'd skip our interceptors
1954 // in ASan/MSan/TSan/DFSan, and thus make us miss some memory accesses,
1955 // we mark affected calls as NoBuiltin, which will disable optimization
1956 // in CodeGen.
maybeMarkSanitizerLibraryCallNoBuiltin(CallInst * CI,const TargetLibraryInfo * TLI)1957 void llvm::maybeMarkSanitizerLibraryCallNoBuiltin(CallInst *CI,
1958                                           const TargetLibraryInfo *TLI) {
1959   Function *F = CI->getCalledFunction();
1960   LibFunc::Func Func;
1961   if (!F || F->hasLocalLinkage() || !F->hasName() ||
1962       !TLI->getLibFunc(F->getName(), Func))
1963     return;
1964   switch (Func) {
1965     default: break;
1966     case LibFunc::memcmp:
1967     case LibFunc::memchr:
1968     case LibFunc::strcpy:
1969     case LibFunc::stpcpy:
1970     case LibFunc::strcmp:
1971     case LibFunc::strlen:
1972     case LibFunc::strnlen:
1973       CI->addAttribute(AttributeSet::FunctionIndex, Attribute::NoBuiltin);
1974       break;
1975   }
1976 }
1977