xref: /llvm-project/llvm/lib/Transforms/Utils/Local.cpp (revision 8dd6cf711f75f296cdeae2be7c6760b29cc68f57)
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/APInt.h"
17 #include "llvm/ADT/DenseMap.h"
18 #include "llvm/ADT/DenseMapInfo.h"
19 #include "llvm/ADT/DenseSet.h"
20 #include "llvm/ADT/Hashing.h"
21 #include "llvm/ADT/None.h"
22 #include "llvm/ADT/Optional.h"
23 #include "llvm/ADT/STLExtras.h"
24 #include "llvm/ADT/SetVector.h"
25 #include "llvm/ADT/SmallPtrSet.h"
26 #include "llvm/ADT/SmallVector.h"
27 #include "llvm/ADT/Statistic.h"
28 #include "llvm/ADT/TinyPtrVector.h"
29 #include "llvm/Analysis/ConstantFolding.h"
30 #include "llvm/Analysis/EHPersonalities.h"
31 #include "llvm/Analysis/InstructionSimplify.h"
32 #include "llvm/Analysis/LazyValueInfo.h"
33 #include "llvm/Analysis/MemoryBuiltins.h"
34 #include "llvm/Analysis/TargetLibraryInfo.h"
35 #include "llvm/Analysis/ValueTracking.h"
36 #include "llvm/BinaryFormat/Dwarf.h"
37 #include "llvm/IR/Argument.h"
38 #include "llvm/IR/Attributes.h"
39 #include "llvm/IR/BasicBlock.h"
40 #include "llvm/IR/CFG.h"
41 #include "llvm/IR/CallSite.h"
42 #include "llvm/IR/Constant.h"
43 #include "llvm/IR/ConstantRange.h"
44 #include "llvm/IR/Constants.h"
45 #include "llvm/IR/DIBuilder.h"
46 #include "llvm/IR/DataLayout.h"
47 #include "llvm/IR/DebugInfoMetadata.h"
48 #include "llvm/IR/DebugLoc.h"
49 #include "llvm/IR/DerivedTypes.h"
50 #include "llvm/IR/Dominators.h"
51 #include "llvm/IR/Function.h"
52 #include "llvm/IR/GetElementPtrTypeIterator.h"
53 #include "llvm/IR/GlobalObject.h"
54 #include "llvm/IR/IRBuilder.h"
55 #include "llvm/IR/InstrTypes.h"
56 #include "llvm/IR/Instruction.h"
57 #include "llvm/IR/Instructions.h"
58 #include "llvm/IR/IntrinsicInst.h"
59 #include "llvm/IR/Intrinsics.h"
60 #include "llvm/IR/LLVMContext.h"
61 #include "llvm/IR/MDBuilder.h"
62 #include "llvm/IR/Metadata.h"
63 #include "llvm/IR/Module.h"
64 #include "llvm/IR/Operator.h"
65 #include "llvm/IR/PatternMatch.h"
66 #include "llvm/IR/Type.h"
67 #include "llvm/IR/Use.h"
68 #include "llvm/IR/User.h"
69 #include "llvm/IR/Value.h"
70 #include "llvm/IR/ValueHandle.h"
71 #include "llvm/Support/Casting.h"
72 #include "llvm/Support/Debug.h"
73 #include "llvm/Support/ErrorHandling.h"
74 #include "llvm/Support/KnownBits.h"
75 #include "llvm/Support/raw_ostream.h"
76 #include "llvm/Transforms/Utils/ValueMapper.h"
77 #include <algorithm>
78 #include <cassert>
79 #include <climits>
80 #include <cstdint>
81 #include <iterator>
82 #include <map>
83 #include <utility>
84 
85 using namespace llvm;
86 using namespace llvm::PatternMatch;
87 
88 #define DEBUG_TYPE "local"
89 
90 STATISTIC(NumRemoved, "Number of unreachable basic blocks removed");
91 
92 //===----------------------------------------------------------------------===//
93 //  Local constant propagation.
94 //
95 
96 /// ConstantFoldTerminator - If a terminator instruction is predicated on a
97 /// constant value, convert it into an unconditional branch to the constant
98 /// destination.  This is a nontrivial operation because the successors of this
99 /// basic block must have their PHI nodes updated.
100 /// Also calls RecursivelyDeleteTriviallyDeadInstructions() on any branch/switch
101 /// conditions and indirectbr addresses this might make dead if
102 /// DeleteDeadConditions is true.
103 bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
104                                   const TargetLibraryInfo *TLI,
105                                   DeferredDominance *DDT) {
106   TerminatorInst *T = BB->getTerminator();
107   IRBuilder<> Builder(T);
108 
109   // Branch - See if we are conditional jumping on constant
110   if (auto *BI = dyn_cast<BranchInst>(T)) {
111     if (BI->isUnconditional()) return false;  // Can't optimize uncond branch
112     BasicBlock *Dest1 = BI->getSuccessor(0);
113     BasicBlock *Dest2 = BI->getSuccessor(1);
114 
115     if (auto *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
116       // Are we branching on constant?
117       // YES.  Change to unconditional branch...
118       BasicBlock *Destination = Cond->getZExtValue() ? Dest1 : Dest2;
119       BasicBlock *OldDest     = Cond->getZExtValue() ? Dest2 : Dest1;
120 
121       // Let the basic block know that we are letting go of it.  Based on this,
122       // it will adjust it's PHI nodes.
123       OldDest->removePredecessor(BB);
124 
125       // Replace the conditional branch with an unconditional one.
126       Builder.CreateBr(Destination);
127       BI->eraseFromParent();
128       if (DDT)
129         DDT->deleteEdge(BB, OldDest);
130       return true;
131     }
132 
133     if (Dest2 == Dest1) {       // Conditional branch to same location?
134       // This branch matches something like this:
135       //     br bool %cond, label %Dest, label %Dest
136       // and changes it into:  br label %Dest
137 
138       // Let the basic block know that we are letting go of one copy of it.
139       assert(BI->getParent() && "Terminator not inserted in block!");
140       Dest1->removePredecessor(BI->getParent());
141 
142       // Replace the conditional branch with an unconditional one.
143       Builder.CreateBr(Dest1);
144       Value *Cond = BI->getCondition();
145       BI->eraseFromParent();
146       if (DeleteDeadConditions)
147         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
148       return true;
149     }
150     return false;
151   }
152 
153   if (auto *SI = dyn_cast<SwitchInst>(T)) {
154     // If we are switching on a constant, we can convert the switch to an
155     // unconditional branch.
156     auto *CI = dyn_cast<ConstantInt>(SI->getCondition());
157     BasicBlock *DefaultDest = SI->getDefaultDest();
158     BasicBlock *TheOnlyDest = DefaultDest;
159 
160     // If the default is unreachable, ignore it when searching for TheOnlyDest.
161     if (isa<UnreachableInst>(DefaultDest->getFirstNonPHIOrDbg()) &&
162         SI->getNumCases() > 0) {
163       TheOnlyDest = SI->case_begin()->getCaseSuccessor();
164     }
165 
166     // Figure out which case it goes to.
167     for (auto i = SI->case_begin(), e = SI->case_end(); i != e;) {
168       // Found case matching a constant operand?
169       if (i->getCaseValue() == CI) {
170         TheOnlyDest = i->getCaseSuccessor();
171         break;
172       }
173 
174       // Check to see if this branch is going to the same place as the default
175       // dest.  If so, eliminate it as an explicit compare.
176       if (i->getCaseSuccessor() == DefaultDest) {
177         MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
178         unsigned NCases = SI->getNumCases();
179         // Fold the case metadata into the default if there will be any branches
180         // left, unless the metadata doesn't match the switch.
181         if (NCases > 1 && MD && MD->getNumOperands() == 2 + NCases) {
182           // Collect branch weights into a vector.
183           SmallVector<uint32_t, 8> Weights;
184           for (unsigned MD_i = 1, MD_e = MD->getNumOperands(); MD_i < MD_e;
185                ++MD_i) {
186             auto *CI = mdconst::extract<ConstantInt>(MD->getOperand(MD_i));
187             Weights.push_back(CI->getValue().getZExtValue());
188           }
189           // Merge weight of this case to the default weight.
190           unsigned idx = i->getCaseIndex();
191           Weights[0] += Weights[idx+1];
192           // Remove weight for this case.
193           std::swap(Weights[idx+1], Weights.back());
194           Weights.pop_back();
195           SI->setMetadata(LLVMContext::MD_prof,
196                           MDBuilder(BB->getContext()).
197                           createBranchWeights(Weights));
198         }
199         // Remove this entry.
200         BasicBlock *ParentBB = SI->getParent();
201         DefaultDest->removePredecessor(ParentBB);
202         i = SI->removeCase(i);
203         e = SI->case_end();
204         if (DDT)
205           DDT->deleteEdge(ParentBB, DefaultDest);
206         continue;
207       }
208 
209       // Otherwise, check to see if the switch only branches to one destination.
210       // We do this by reseting "TheOnlyDest" to null when we find two non-equal
211       // destinations.
212       if (i->getCaseSuccessor() != TheOnlyDest)
213         TheOnlyDest = nullptr;
214 
215       // Increment this iterator as we haven't removed the case.
216       ++i;
217     }
218 
219     if (CI && !TheOnlyDest) {
220       // Branching on a constant, but not any of the cases, go to the default
221       // successor.
222       TheOnlyDest = SI->getDefaultDest();
223     }
224 
225     // If we found a single destination that we can fold the switch into, do so
226     // now.
227     if (TheOnlyDest) {
228       // Insert the new branch.
229       Builder.CreateBr(TheOnlyDest);
230       BasicBlock *BB = SI->getParent();
231       std::vector <DominatorTree::UpdateType> Updates;
232       if (DDT)
233         Updates.reserve(SI->getNumSuccessors() - 1);
234 
235       // Remove entries from PHI nodes which we no longer branch to...
236       for (BasicBlock *Succ : SI->successors()) {
237         // Found case matching a constant operand?
238         if (Succ == TheOnlyDest) {
239           TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
240         } else {
241           Succ->removePredecessor(BB);
242           if (DDT)
243             Updates.push_back({DominatorTree::Delete, BB, Succ});
244         }
245       }
246 
247       // Delete the old switch.
248       Value *Cond = SI->getCondition();
249       SI->eraseFromParent();
250       if (DeleteDeadConditions)
251         RecursivelyDeleteTriviallyDeadInstructions(Cond, TLI);
252       if (DDT)
253         DDT->applyUpdates(Updates);
254       return true;
255     }
256 
257     if (SI->getNumCases() == 1) {
258       // Otherwise, we can fold this switch into a conditional branch
259       // instruction if it has only one non-default destination.
260       auto FirstCase = *SI->case_begin();
261       Value *Cond = Builder.CreateICmpEQ(SI->getCondition(),
262           FirstCase.getCaseValue(), "cond");
263 
264       // Insert the new branch.
265       BranchInst *NewBr = Builder.CreateCondBr(Cond,
266                                                FirstCase.getCaseSuccessor(),
267                                                SI->getDefaultDest());
268       MDNode *MD = SI->getMetadata(LLVMContext::MD_prof);
269       if (MD && MD->getNumOperands() == 3) {
270         ConstantInt *SICase =
271             mdconst::dyn_extract<ConstantInt>(MD->getOperand(2));
272         ConstantInt *SIDef =
273             mdconst::dyn_extract<ConstantInt>(MD->getOperand(1));
274         assert(SICase && SIDef);
275         // The TrueWeight should be the weight for the single case of SI.
276         NewBr->setMetadata(LLVMContext::MD_prof,
277                         MDBuilder(BB->getContext()).
278                         createBranchWeights(SICase->getValue().getZExtValue(),
279                                             SIDef->getValue().getZExtValue()));
280       }
281 
282       // Update make.implicit metadata to the newly-created conditional branch.
283       MDNode *MakeImplicitMD = SI->getMetadata(LLVMContext::MD_make_implicit);
284       if (MakeImplicitMD)
285         NewBr->setMetadata(LLVMContext::MD_make_implicit, MakeImplicitMD);
286 
287       // Delete the old switch.
288       SI->eraseFromParent();
289       return true;
290     }
291     return false;
292   }
293 
294   if (auto *IBI = dyn_cast<IndirectBrInst>(T)) {
295     // indirectbr blockaddress(@F, @BB) -> br label @BB
296     if (auto *BA =
297           dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
298       BasicBlock *TheOnlyDest = BA->getBasicBlock();
299       std::vector <DominatorTree::UpdateType> Updates;
300       if (DDT)
301         Updates.reserve(IBI->getNumDestinations() - 1);
302 
303       // Insert the new branch.
304       Builder.CreateBr(TheOnlyDest);
305 
306       for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
307         if (IBI->getDestination(i) == TheOnlyDest) {
308           TheOnlyDest = nullptr;
309         } else {
310           BasicBlock *ParentBB = IBI->getParent();
311           BasicBlock *DestBB = IBI->getDestination(i);
312           DestBB->removePredecessor(ParentBB);
313           if (DDT)
314             Updates.push_back({DominatorTree::Delete, ParentBB, DestBB});
315         }
316       }
317       Value *Address = IBI->getAddress();
318       IBI->eraseFromParent();
319       if (DeleteDeadConditions)
320         RecursivelyDeleteTriviallyDeadInstructions(Address, TLI);
321 
322       // If we didn't find our destination in the IBI successor list, then we
323       // have undefined behavior.  Replace the unconditional branch with an
324       // 'unreachable' instruction.
325       if (TheOnlyDest) {
326         BB->getTerminator()->eraseFromParent();
327         new UnreachableInst(BB->getContext(), BB);
328       }
329 
330       if (DDT)
331         DDT->applyUpdates(Updates);
332       return true;
333     }
334   }
335 
336   return false;
337 }
338 
339 //===----------------------------------------------------------------------===//
340 //  Local dead code elimination.
341 //
342 
343 /// isInstructionTriviallyDead - Return true if the result produced by the
344 /// instruction is not used, and the instruction has no side effects.
345 ///
346 bool llvm::isInstructionTriviallyDead(Instruction *I,
347                                       const TargetLibraryInfo *TLI) {
348   if (!I->use_empty())
349     return false;
350   return wouldInstructionBeTriviallyDead(I, TLI);
351 }
352 
353 bool llvm::wouldInstructionBeTriviallyDead(Instruction *I,
354                                            const TargetLibraryInfo *TLI) {
355   if (isa<TerminatorInst>(I))
356     return false;
357 
358   // We don't want the landingpad-like instructions removed by anything this
359   // general.
360   if (I->isEHPad())
361     return false;
362 
363   // We don't want debug info removed by anything this general, unless
364   // debug info is empty.
365   if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(I)) {
366     if (DDI->getAddress())
367       return false;
368     return true;
369   }
370   if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(I)) {
371     if (DVI->getValue())
372       return false;
373     return true;
374   }
375   if (DbgLabelInst *DLI = dyn_cast<DbgLabelInst>(I)) {
376     if (DLI->getLabel())
377       return false;
378     return true;
379   }
380 
381   if (!I->mayHaveSideEffects())
382     return true;
383 
384   // Special case intrinsics that "may have side effects" but can be deleted
385   // when dead.
386   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
387     // Safe to delete llvm.stacksave and launder.invariant.group if dead.
388     if (II->getIntrinsicID() == Intrinsic::stacksave ||
389         II->getIntrinsicID() == Intrinsic::launder_invariant_group)
390       return true;
391 
392     // Lifetime intrinsics are dead when their right-hand is undef.
393     if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
394         II->getIntrinsicID() == Intrinsic::lifetime_end)
395       return isa<UndefValue>(II->getArgOperand(1));
396 
397     // Assumptions are dead if their condition is trivially true.  Guards on
398     // true are operationally no-ops.  In the future we can consider more
399     // sophisticated tradeoffs for guards considering potential for check
400     // widening, but for now we keep things simple.
401     if (II->getIntrinsicID() == Intrinsic::assume ||
402         II->getIntrinsicID() == Intrinsic::experimental_guard) {
403       if (ConstantInt *Cond = dyn_cast<ConstantInt>(II->getArgOperand(0)))
404         return !Cond->isZero();
405 
406       return false;
407     }
408   }
409 
410   if (isAllocLikeFn(I, TLI))
411     return true;
412 
413   if (CallInst *CI = isFreeCall(I, TLI))
414     if (Constant *C = dyn_cast<Constant>(CI->getArgOperand(0)))
415       return C->isNullValue() || isa<UndefValue>(C);
416 
417   if (CallSite CS = CallSite(I))
418     if (isMathLibCallNoop(CS, TLI))
419       return true;
420 
421   return false;
422 }
423 
424 /// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
425 /// trivially dead instruction, delete it.  If that makes any of its operands
426 /// trivially dead, delete them too, recursively.  Return true if any
427 /// instructions were deleted.
428 bool
429 llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V,
430                                                  const TargetLibraryInfo *TLI) {
431   Instruction *I = dyn_cast<Instruction>(V);
432   if (!I || !I->use_empty() || !isInstructionTriviallyDead(I, TLI))
433     return false;
434 
435   SmallVector<Instruction*, 16> DeadInsts;
436   DeadInsts.push_back(I);
437   RecursivelyDeleteTriviallyDeadInstructions(DeadInsts, TLI);
438 
439   return true;
440 }
441 
442 void llvm::RecursivelyDeleteTriviallyDeadInstructions(
443     SmallVectorImpl<Instruction *> &DeadInsts, const TargetLibraryInfo *TLI) {
444   // Process the dead instruction list until empty.
445   while (!DeadInsts.empty()) {
446     Instruction &I = *DeadInsts.pop_back_val();
447     assert(I.use_empty() && "Instructions with uses are not dead.");
448     assert(isInstructionTriviallyDead(&I, TLI) &&
449            "Live instruction found in dead worklist!");
450 
451     // Don't lose the debug info while deleting the instructions.
452     salvageDebugInfo(I);
453 
454     // Null out all of the instruction's operands to see if any operand becomes
455     // dead as we go.
456     for (Use &OpU : I.operands()) {
457       Value *OpV = OpU.get();
458       OpU.set(nullptr);
459 
460       if (!OpV->use_empty())
461         continue;
462 
463       // If the operand is an instruction that became dead as we nulled out the
464       // operand, and if it is 'trivially' dead, delete it in a future loop
465       // iteration.
466       if (Instruction *OpI = dyn_cast<Instruction>(OpV))
467         if (isInstructionTriviallyDead(OpI, TLI))
468           DeadInsts.push_back(OpI);
469     }
470 
471     I.eraseFromParent();
472   }
473 }
474 
475 /// areAllUsesEqual - Check whether the uses of a value are all the same.
476 /// This is similar to Instruction::hasOneUse() except this will also return
477 /// true when there are no uses or multiple uses that all refer to the same
478 /// value.
479 static bool areAllUsesEqual(Instruction *I) {
480   Value::user_iterator UI = I->user_begin();
481   Value::user_iterator UE = I->user_end();
482   if (UI == UE)
483     return true;
484 
485   User *TheUse = *UI;
486   for (++UI; UI != UE; ++UI) {
487     if (*UI != TheUse)
488       return false;
489   }
490   return true;
491 }
492 
493 /// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
494 /// dead PHI node, due to being a def-use chain of single-use nodes that
495 /// either forms a cycle or is terminated by a trivially dead instruction,
496 /// delete it.  If that makes any of its operands trivially dead, delete them
497 /// too, recursively.  Return true if a change was made.
498 bool llvm::RecursivelyDeleteDeadPHINode(PHINode *PN,
499                                         const TargetLibraryInfo *TLI) {
500   SmallPtrSet<Instruction*, 4> Visited;
501   for (Instruction *I = PN; areAllUsesEqual(I) && !I->mayHaveSideEffects();
502        I = cast<Instruction>(*I->user_begin())) {
503     if (I->use_empty())
504       return RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
505 
506     // If we find an instruction more than once, we're on a cycle that
507     // won't prove fruitful.
508     if (!Visited.insert(I).second) {
509       // Break the cycle and delete the instruction and its operands.
510       I->replaceAllUsesWith(UndefValue::get(I->getType()));
511       (void)RecursivelyDeleteTriviallyDeadInstructions(I, TLI);
512       return true;
513     }
514   }
515   return false;
516 }
517 
518 static bool
519 simplifyAndDCEInstruction(Instruction *I,
520                           SmallSetVector<Instruction *, 16> &WorkList,
521                           const DataLayout &DL,
522                           const TargetLibraryInfo *TLI) {
523   if (isInstructionTriviallyDead(I, TLI)) {
524     salvageDebugInfo(*I);
525 
526     // Null out all of the instruction's operands to see if any operand becomes
527     // dead as we go.
528     for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
529       Value *OpV = I->getOperand(i);
530       I->setOperand(i, nullptr);
531 
532       if (!OpV->use_empty() || I == OpV)
533         continue;
534 
535       // If the operand is an instruction that became dead as we nulled out the
536       // operand, and if it is 'trivially' dead, delete it in a future loop
537       // iteration.
538       if (Instruction *OpI = dyn_cast<Instruction>(OpV))
539         if (isInstructionTriviallyDead(OpI, TLI))
540           WorkList.insert(OpI);
541     }
542 
543     I->eraseFromParent();
544 
545     return true;
546   }
547 
548   if (Value *SimpleV = SimplifyInstruction(I, DL)) {
549     // Add the users to the worklist. CAREFUL: an instruction can use itself,
550     // in the case of a phi node.
551     for (User *U : I->users()) {
552       if (U != I) {
553         WorkList.insert(cast<Instruction>(U));
554       }
555     }
556 
557     // Replace the instruction with its simplified value.
558     bool Changed = false;
559     if (!I->use_empty()) {
560       I->replaceAllUsesWith(SimpleV);
561       Changed = true;
562     }
563     if (isInstructionTriviallyDead(I, TLI)) {
564       I->eraseFromParent();
565       Changed = true;
566     }
567     return Changed;
568   }
569   return false;
570 }
571 
572 /// SimplifyInstructionsInBlock - Scan the specified basic block and try to
573 /// simplify any instructions in it and recursively delete dead instructions.
574 ///
575 /// This returns true if it changed the code, note that it can delete
576 /// instructions in other blocks as well in this block.
577 bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB,
578                                        const TargetLibraryInfo *TLI) {
579   bool MadeChange = false;
580   const DataLayout &DL = BB->getModule()->getDataLayout();
581 
582 #ifndef NDEBUG
583   // In debug builds, ensure that the terminator of the block is never replaced
584   // or deleted by these simplifications. The idea of simplification is that it
585   // cannot introduce new instructions, and there is no way to replace the
586   // terminator of a block without introducing a new instruction.
587   AssertingVH<Instruction> TerminatorVH(&BB->back());
588 #endif
589 
590   SmallSetVector<Instruction *, 16> WorkList;
591   // Iterate over the original function, only adding insts to the worklist
592   // if they actually need to be revisited. This avoids having to pre-init
593   // the worklist with the entire function's worth of instructions.
594   for (BasicBlock::iterator BI = BB->begin(), E = std::prev(BB->end());
595        BI != E;) {
596     assert(!BI->isTerminator());
597     Instruction *I = &*BI;
598     ++BI;
599 
600     // We're visiting this instruction now, so make sure it's not in the
601     // worklist from an earlier visit.
602     if (!WorkList.count(I))
603       MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
604   }
605 
606   while (!WorkList.empty()) {
607     Instruction *I = WorkList.pop_back_val();
608     MadeChange |= simplifyAndDCEInstruction(I, WorkList, DL, TLI);
609   }
610   return MadeChange;
611 }
612 
613 //===----------------------------------------------------------------------===//
614 //  Control Flow Graph Restructuring.
615 //
616 
617 /// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
618 /// method is called when we're about to delete Pred as a predecessor of BB.  If
619 /// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
620 ///
621 /// Unlike the removePredecessor method, this attempts to simplify uses of PHI
622 /// nodes that collapse into identity values.  For example, if we have:
623 ///   x = phi(1, 0, 0, 0)
624 ///   y = and x, z
625 ///
626 /// .. and delete the predecessor corresponding to the '1', this will attempt to
627 /// recursively fold the and to 0.
628 void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
629                                         DeferredDominance *DDT) {
630   // This only adjusts blocks with PHI nodes.
631   if (!isa<PHINode>(BB->begin()))
632     return;
633 
634   // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
635   // them down.  This will leave us with single entry phi nodes and other phis
636   // that can be removed.
637   BB->removePredecessor(Pred, true);
638 
639   WeakTrackingVH PhiIt = &BB->front();
640   while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
641     PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
642     Value *OldPhiIt = PhiIt;
643 
644     if (!recursivelySimplifyInstruction(PN))
645       continue;
646 
647     // If recursive simplification ended up deleting the next PHI node we would
648     // iterate to, then our iterator is invalid, restart scanning from the top
649     // of the block.
650     if (PhiIt != OldPhiIt) PhiIt = &BB->front();
651   }
652   if (DDT)
653     DDT->deleteEdge(Pred, BB);
654 }
655 
656 /// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
657 /// predecessor is known to have one successor (DestBB!).  Eliminate the edge
658 /// between them, moving the instructions in the predecessor into DestBB and
659 /// deleting the predecessor block.
660 void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, DominatorTree *DT,
661                                        DeferredDominance *DDT) {
662   assert(!(DT && DDT) && "Cannot call with both DT and DDT.");
663 
664   // If BB has single-entry PHI nodes, fold them.
665   while (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
666     Value *NewVal = PN->getIncomingValue(0);
667     // Replace self referencing PHI with undef, it must be dead.
668     if (NewVal == PN) NewVal = UndefValue::get(PN->getType());
669     PN->replaceAllUsesWith(NewVal);
670     PN->eraseFromParent();
671   }
672 
673   BasicBlock *PredBB = DestBB->getSinglePredecessor();
674   assert(PredBB && "Block doesn't have a single predecessor!");
675 
676   bool ReplaceEntryBB = false;
677   if (PredBB == &DestBB->getParent()->getEntryBlock())
678     ReplaceEntryBB = true;
679 
680   // Deferred DT update: Collect all the edges that enter PredBB. These
681   // dominator edges will be redirected to DestBB.
682   std::vector <DominatorTree::UpdateType> Updates;
683   if (DDT && !ReplaceEntryBB) {
684     Updates.reserve(1 + (2 * pred_size(PredBB)));
685     Updates.push_back({DominatorTree::Delete, PredBB, DestBB});
686     for (auto I = pred_begin(PredBB), E = pred_end(PredBB); I != E; ++I) {
687       Updates.push_back({DominatorTree::Delete, *I, PredBB});
688       // This predecessor of PredBB may already have DestBB as a successor.
689       if (llvm::find(successors(*I), DestBB) == succ_end(*I))
690         Updates.push_back({DominatorTree::Insert, *I, DestBB});
691     }
692   }
693 
694   // Zap anything that took the address of DestBB.  Not doing this will give the
695   // address an invalid value.
696   if (DestBB->hasAddressTaken()) {
697     BlockAddress *BA = BlockAddress::get(DestBB);
698     Constant *Replacement =
699       ConstantInt::get(Type::getInt32Ty(BA->getContext()), 1);
700     BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
701                                                      BA->getType()));
702     BA->destroyConstant();
703   }
704 
705   // Anything that branched to PredBB now branches to DestBB.
706   PredBB->replaceAllUsesWith(DestBB);
707 
708   // Splice all the instructions from PredBB to DestBB.
709   PredBB->getTerminator()->eraseFromParent();
710   DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
711 
712   // If the PredBB is the entry block of the function, move DestBB up to
713   // become the entry block after we erase PredBB.
714   if (ReplaceEntryBB)
715     DestBB->moveAfter(PredBB);
716 
717   if (DT) {
718     // For some irreducible CFG we end up having forward-unreachable blocks
719     // so check if getNode returns a valid node before updating the domtree.
720     if (DomTreeNode *DTN = DT->getNode(PredBB)) {
721       BasicBlock *PredBBIDom = DTN->getIDom()->getBlock();
722       DT->changeImmediateDominator(DestBB, PredBBIDom);
723       DT->eraseNode(PredBB);
724     }
725   }
726 
727   if (DDT) {
728     DDT->deleteBB(PredBB); // Deferred deletion of BB.
729     if (ReplaceEntryBB)
730       // The entry block was removed and there is no external interface for the
731       // dominator tree to be notified of this change. In this corner-case we
732       // recalculate the entire tree.
733       DDT->recalculate(*(DestBB->getParent()));
734     else
735       DDT->applyUpdates(Updates);
736   } else {
737     PredBB->eraseFromParent(); // Nuke BB.
738   }
739 }
740 
741 /// CanMergeValues - Return true if we can choose one of these values to use
742 /// in place of the other. Note that we will always choose the non-undef
743 /// value to keep.
744 static bool CanMergeValues(Value *First, Value *Second) {
745   return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
746 }
747 
748 /// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
749 /// almost-empty BB ending in an unconditional branch to Succ, into Succ.
750 ///
751 /// Assumption: Succ is the single successor for BB.
752 static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
753   assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
754 
755   LLVM_DEBUG(dbgs() << "Looking to fold " << BB->getName() << " into "
756                     << Succ->getName() << "\n");
757   // Shortcut, if there is only a single predecessor it must be BB and merging
758   // is always safe
759   if (Succ->getSinglePredecessor()) return true;
760 
761   // Make a list of the predecessors of BB
762   SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
763 
764   // Look at all the phi nodes in Succ, to see if they present a conflict when
765   // merging these blocks
766   for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
767     PHINode *PN = cast<PHINode>(I);
768 
769     // If the incoming value from BB is again a PHINode in
770     // BB which has the same incoming value for *PI as PN does, we can
771     // merge the phi nodes and then the blocks can still be merged
772     PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
773     if (BBPN && BBPN->getParent() == BB) {
774       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
775         BasicBlock *IBB = PN->getIncomingBlock(PI);
776         if (BBPreds.count(IBB) &&
777             !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
778                             PN->getIncomingValue(PI))) {
779           LLVM_DEBUG(dbgs()
780                      << "Can't fold, phi node " << PN->getName() << " in "
781                      << Succ->getName() << " is conflicting with "
782                      << BBPN->getName() << " with regard to common predecessor "
783                      << IBB->getName() << "\n");
784           return false;
785         }
786       }
787     } else {
788       Value* Val = PN->getIncomingValueForBlock(BB);
789       for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
790         // See if the incoming value for the common predecessor is equal to the
791         // one for BB, in which case this phi node will not prevent the merging
792         // of the block.
793         BasicBlock *IBB = PN->getIncomingBlock(PI);
794         if (BBPreds.count(IBB) &&
795             !CanMergeValues(Val, PN->getIncomingValue(PI))) {
796           LLVM_DEBUG(dbgs() << "Can't fold, phi node " << PN->getName()
797                             << " in " << Succ->getName()
798                             << " is conflicting with regard to common "
799                             << "predecessor " << IBB->getName() << "\n");
800           return false;
801         }
802       }
803     }
804   }
805 
806   return true;
807 }
808 
809 using PredBlockVector = SmallVector<BasicBlock *, 16>;
810 using IncomingValueMap = DenseMap<BasicBlock *, Value *>;
811 
812 /// Determines the value to use as the phi node input for a block.
813 ///
814 /// Select between \p OldVal any value that we know flows from \p BB
815 /// to a particular phi on the basis of which one (if either) is not
816 /// undef. Update IncomingValues based on the selected value.
817 ///
818 /// \param OldVal The value we are considering selecting.
819 /// \param BB The block that the value flows in from.
820 /// \param IncomingValues A map from block-to-value for other phi inputs
821 /// that we have examined.
822 ///
823 /// \returns the selected value.
824 static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
825                                           IncomingValueMap &IncomingValues) {
826   if (!isa<UndefValue>(OldVal)) {
827     assert((!IncomingValues.count(BB) ||
828             IncomingValues.find(BB)->second == OldVal) &&
829            "Expected OldVal to match incoming value from BB!");
830 
831     IncomingValues.insert(std::make_pair(BB, OldVal));
832     return OldVal;
833   }
834 
835   IncomingValueMap::const_iterator It = IncomingValues.find(BB);
836   if (It != IncomingValues.end()) return It->second;
837 
838   return OldVal;
839 }
840 
841 /// Create a map from block to value for the operands of a
842 /// given phi.
843 ///
844 /// Create a map from block to value for each non-undef value flowing
845 /// into \p PN.
846 ///
847 /// \param PN The phi we are collecting the map for.
848 /// \param IncomingValues [out] The map from block to value for this phi.
849 static void gatherIncomingValuesToPhi(PHINode *PN,
850                                       IncomingValueMap &IncomingValues) {
851   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
852     BasicBlock *BB = PN->getIncomingBlock(i);
853     Value *V = PN->getIncomingValue(i);
854 
855     if (!isa<UndefValue>(V))
856       IncomingValues.insert(std::make_pair(BB, V));
857   }
858 }
859 
860 /// Replace the incoming undef values to a phi with the values
861 /// from a block-to-value map.
862 ///
863 /// \param PN The phi we are replacing the undefs in.
864 /// \param IncomingValues A map from block to value.
865 static void replaceUndefValuesInPhi(PHINode *PN,
866                                     const IncomingValueMap &IncomingValues) {
867   for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
868     Value *V = PN->getIncomingValue(i);
869 
870     if (!isa<UndefValue>(V)) continue;
871 
872     BasicBlock *BB = PN->getIncomingBlock(i);
873     IncomingValueMap::const_iterator It = IncomingValues.find(BB);
874     if (It == IncomingValues.end()) continue;
875 
876     PN->setIncomingValue(i, It->second);
877   }
878 }
879 
880 /// Replace a value flowing from a block to a phi with
881 /// potentially multiple instances of that value flowing from the
882 /// block's predecessors to the phi.
883 ///
884 /// \param BB The block with the value flowing into the phi.
885 /// \param BBPreds The predecessors of BB.
886 /// \param PN The phi that we are updating.
887 static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
888                                                 const PredBlockVector &BBPreds,
889                                                 PHINode *PN) {
890   Value *OldVal = PN->removeIncomingValue(BB, false);
891   assert(OldVal && "No entry in PHI for Pred BB!");
892 
893   IncomingValueMap IncomingValues;
894 
895   // We are merging two blocks - BB, and the block containing PN - and
896   // as a result we need to redirect edges from the predecessors of BB
897   // to go to the block containing PN, and update PN
898   // accordingly. Since we allow merging blocks in the case where the
899   // predecessor and successor blocks both share some predecessors,
900   // and where some of those common predecessors might have undef
901   // values flowing into PN, we want to rewrite those values to be
902   // consistent with the non-undef values.
903 
904   gatherIncomingValuesToPhi(PN, IncomingValues);
905 
906   // If this incoming value is one of the PHI nodes in BB, the new entries
907   // in the PHI node are the entries from the old PHI.
908   if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
909     PHINode *OldValPN = cast<PHINode>(OldVal);
910     for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
911       // Note that, since we are merging phi nodes and BB and Succ might
912       // have common predecessors, we could end up with a phi node with
913       // identical incoming branches. This will be cleaned up later (and
914       // will trigger asserts if we try to clean it up now, without also
915       // simplifying the corresponding conditional branch).
916       BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
917       Value *PredVal = OldValPN->getIncomingValue(i);
918       Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
919                                                     IncomingValues);
920 
921       // And add a new incoming value for this predecessor for the
922       // newly retargeted branch.
923       PN->addIncoming(Selected, PredBB);
924     }
925   } else {
926     for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
927       // Update existing incoming values in PN for this
928       // predecessor of BB.
929       BasicBlock *PredBB = BBPreds[i];
930       Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
931                                                     IncomingValues);
932 
933       // And add a new incoming value for this predecessor for the
934       // newly retargeted branch.
935       PN->addIncoming(Selected, PredBB);
936     }
937   }
938 
939   replaceUndefValuesInPhi(PN, IncomingValues);
940 }
941 
942 /// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
943 /// unconditional branch, and contains no instructions other than PHI nodes,
944 /// potential side-effect free intrinsics and the branch.  If possible,
945 /// eliminate BB by rewriting all the predecessors to branch to the successor
946 /// block and return true.  If we can't transform, return false.
947 bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
948                                                    DeferredDominance *DDT) {
949   assert(BB != &BB->getParent()->getEntryBlock() &&
950          "TryToSimplifyUncondBranchFromEmptyBlock called on entry block!");
951 
952   // We can't eliminate infinite loops.
953   BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
954   if (BB == Succ) return false;
955 
956   // Check to see if merging these blocks would cause conflicts for any of the
957   // phi nodes in BB or Succ. If not, we can safely merge.
958   if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
959 
960   // Check for cases where Succ has multiple predecessors and a PHI node in BB
961   // has uses which will not disappear when the PHI nodes are merged.  It is
962   // possible to handle such cases, but difficult: it requires checking whether
963   // BB dominates Succ, which is non-trivial to calculate in the case where
964   // Succ has multiple predecessors.  Also, it requires checking whether
965   // constructing the necessary self-referential PHI node doesn't introduce any
966   // conflicts; this isn't too difficult, but the previous code for doing this
967   // was incorrect.
968   //
969   // Note that if this check finds a live use, BB dominates Succ, so BB is
970   // something like a loop pre-header (or rarely, a part of an irreducible CFG);
971   // folding the branch isn't profitable in that case anyway.
972   if (!Succ->getSinglePredecessor()) {
973     BasicBlock::iterator BBI = BB->begin();
974     while (isa<PHINode>(*BBI)) {
975       for (Use &U : BBI->uses()) {
976         if (PHINode* PN = dyn_cast<PHINode>(U.getUser())) {
977           if (PN->getIncomingBlock(U) != BB)
978             return false;
979         } else {
980           return false;
981         }
982       }
983       ++BBI;
984     }
985   }
986 
987   LLVM_DEBUG(dbgs() << "Killing Trivial BB: \n" << *BB);
988 
989   std::vector<DominatorTree::UpdateType> Updates;
990   if (DDT) {
991     Updates.reserve(1 + (2 * pred_size(BB)));
992     Updates.push_back({DominatorTree::Delete, BB, Succ});
993     // All predecessors of BB will be moved to Succ.
994     for (auto I = pred_begin(BB), E = pred_end(BB); I != E; ++I) {
995       Updates.push_back({DominatorTree::Delete, *I, BB});
996       // This predecessor of BB may already have Succ as a successor.
997       if (llvm::find(successors(*I), Succ) == succ_end(*I))
998         Updates.push_back({DominatorTree::Insert, *I, Succ});
999     }
1000   }
1001 
1002   if (isa<PHINode>(Succ->begin())) {
1003     // If there is more than one pred of succ, and there are PHI nodes in
1004     // the successor, then we need to add incoming edges for the PHI nodes
1005     //
1006     const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
1007 
1008     // Loop over all of the PHI nodes in the successor of BB.
1009     for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
1010       PHINode *PN = cast<PHINode>(I);
1011 
1012       redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
1013     }
1014   }
1015 
1016   if (Succ->getSinglePredecessor()) {
1017     // BB is the only predecessor of Succ, so Succ will end up with exactly
1018     // the same predecessors BB had.
1019 
1020     // Copy over any phi, debug or lifetime instruction.
1021     BB->getTerminator()->eraseFromParent();
1022     Succ->getInstList().splice(Succ->getFirstNonPHI()->getIterator(),
1023                                BB->getInstList());
1024   } else {
1025     while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
1026       // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
1027       assert(PN->use_empty() && "There shouldn't be any uses here!");
1028       PN->eraseFromParent();
1029     }
1030   }
1031 
1032   // If the unconditional branch we replaced contains llvm.loop metadata, we
1033   // add the metadata to the branch instructions in the predecessors.
1034   unsigned LoopMDKind = BB->getContext().getMDKindID("llvm.loop");
1035   Instruction *TI = BB->getTerminator();
1036   if (TI)
1037     if (MDNode *LoopMD = TI->getMetadata(LoopMDKind))
1038       for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1039         BasicBlock *Pred = *PI;
1040         Pred->getTerminator()->setMetadata(LoopMDKind, LoopMD);
1041       }
1042 
1043   // Everything that jumped to BB now goes to Succ.
1044   BB->replaceAllUsesWith(Succ);
1045   if (!Succ->hasName()) Succ->takeName(BB);
1046 
1047   if (DDT) {
1048     DDT->deleteBB(BB); // Deferred deletion of the old basic block.
1049     DDT->applyUpdates(Updates);
1050   } else {
1051     BB->eraseFromParent(); // Delete the old basic block.
1052   }
1053   return true;
1054 }
1055 
1056 /// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
1057 /// nodes in this block. This doesn't try to be clever about PHI nodes
1058 /// which differ only in the order of the incoming values, but instcombine
1059 /// orders them so it usually won't matter.
1060 bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
1061   // This implementation doesn't currently consider undef operands
1062   // specially. Theoretically, two phis which are identical except for
1063   // one having an undef where the other doesn't could be collapsed.
1064 
1065   struct PHIDenseMapInfo {
1066     static PHINode *getEmptyKey() {
1067       return DenseMapInfo<PHINode *>::getEmptyKey();
1068     }
1069 
1070     static PHINode *getTombstoneKey() {
1071       return DenseMapInfo<PHINode *>::getTombstoneKey();
1072     }
1073 
1074     static unsigned getHashValue(PHINode *PN) {
1075       // Compute a hash value on the operands. Instcombine will likely have
1076       // sorted them, which helps expose duplicates, but we have to check all
1077       // the operands to be safe in case instcombine hasn't run.
1078       return static_cast<unsigned>(hash_combine(
1079           hash_combine_range(PN->value_op_begin(), PN->value_op_end()),
1080           hash_combine_range(PN->block_begin(), PN->block_end())));
1081     }
1082 
1083     static bool isEqual(PHINode *LHS, PHINode *RHS) {
1084       if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
1085           RHS == getEmptyKey() || RHS == getTombstoneKey())
1086         return LHS == RHS;
1087       return LHS->isIdenticalTo(RHS);
1088     }
1089   };
1090 
1091   // Set of unique PHINodes.
1092   DenseSet<PHINode *, PHIDenseMapInfo> PHISet;
1093 
1094   // Examine each PHI.
1095   bool Changed = false;
1096   for (auto I = BB->begin(); PHINode *PN = dyn_cast<PHINode>(I++);) {
1097     auto Inserted = PHISet.insert(PN);
1098     if (!Inserted.second) {
1099       // A duplicate. Replace this PHI with its duplicate.
1100       PN->replaceAllUsesWith(*Inserted.first);
1101       PN->eraseFromParent();
1102       Changed = true;
1103 
1104       // The RAUW can change PHIs that we already visited. Start over from the
1105       // beginning.
1106       PHISet.clear();
1107       I = BB->begin();
1108     }
1109   }
1110 
1111   return Changed;
1112 }
1113 
1114 /// enforceKnownAlignment - If the specified pointer points to an object that
1115 /// we control, modify the object's alignment to PrefAlign. This isn't
1116 /// often possible though. If alignment is important, a more reliable approach
1117 /// is to simply align all global variables and allocation instructions to
1118 /// their preferred alignment from the beginning.
1119 static unsigned enforceKnownAlignment(Value *V, unsigned Align,
1120                                       unsigned PrefAlign,
1121                                       const DataLayout &DL) {
1122   assert(PrefAlign > Align);
1123 
1124   V = V->stripPointerCasts();
1125 
1126   if (AllocaInst *AI = dyn_cast<AllocaInst>(V)) {
1127     // TODO: ideally, computeKnownBits ought to have used
1128     // AllocaInst::getAlignment() in its computation already, making
1129     // the below max redundant. But, as it turns out,
1130     // stripPointerCasts recurses through infinite layers of bitcasts,
1131     // while computeKnownBits is not allowed to traverse more than 6
1132     // levels.
1133     Align = std::max(AI->getAlignment(), Align);
1134     if (PrefAlign <= Align)
1135       return Align;
1136 
1137     // If the preferred alignment is greater than the natural stack alignment
1138     // then don't round up. This avoids dynamic stack realignment.
1139     if (DL.exceedsNaturalStackAlignment(PrefAlign))
1140       return Align;
1141     AI->setAlignment(PrefAlign);
1142     return PrefAlign;
1143   }
1144 
1145   if (auto *GO = dyn_cast<GlobalObject>(V)) {
1146     // TODO: as above, this shouldn't be necessary.
1147     Align = std::max(GO->getAlignment(), Align);
1148     if (PrefAlign <= Align)
1149       return Align;
1150 
1151     // If there is a large requested alignment and we can, bump up the alignment
1152     // of the global.  If the memory we set aside for the global may not be the
1153     // memory used by the final program then it is impossible for us to reliably
1154     // enforce the preferred alignment.
1155     if (!GO->canIncreaseAlignment())
1156       return Align;
1157 
1158     GO->setAlignment(PrefAlign);
1159     return PrefAlign;
1160   }
1161 
1162   return Align;
1163 }
1164 
1165 unsigned llvm::getOrEnforceKnownAlignment(Value *V, unsigned PrefAlign,
1166                                           const DataLayout &DL,
1167                                           const Instruction *CxtI,
1168                                           AssumptionCache *AC,
1169                                           const DominatorTree *DT) {
1170   assert(V->getType()->isPointerTy() &&
1171          "getOrEnforceKnownAlignment expects a pointer!");
1172 
1173   KnownBits Known = computeKnownBits(V, DL, 0, AC, CxtI, DT);
1174   unsigned TrailZ = Known.countMinTrailingZeros();
1175 
1176   // Avoid trouble with ridiculously large TrailZ values, such as
1177   // those computed from a null pointer.
1178   TrailZ = std::min(TrailZ, unsigned(sizeof(unsigned) * CHAR_BIT - 1));
1179 
1180   unsigned Align = 1u << std::min(Known.getBitWidth() - 1, TrailZ);
1181 
1182   // LLVM doesn't support alignments larger than this currently.
1183   Align = std::min(Align, +Value::MaximumAlignment);
1184 
1185   if (PrefAlign > Align)
1186     Align = enforceKnownAlignment(V, Align, PrefAlign, DL);
1187 
1188   // We don't need to make any adjustment.
1189   return Align;
1190 }
1191 
1192 ///===---------------------------------------------------------------------===//
1193 ///  Dbg Intrinsic utilities
1194 ///
1195 
1196 /// See if there is a dbg.value intrinsic for DIVar before I.
1197 static bool LdStHasDebugValue(DILocalVariable *DIVar, DIExpression *DIExpr,
1198                               Instruction *I) {
1199   // Since we can't guarantee that the original dbg.declare instrinsic
1200   // is removed by LowerDbgDeclare(), we need to make sure that we are
1201   // not inserting the same dbg.value intrinsic over and over.
1202   BasicBlock::InstListType::iterator PrevI(I);
1203   if (PrevI != I->getParent()->getInstList().begin()) {
1204     --PrevI;
1205     if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(PrevI))
1206       if (DVI->getValue() == I->getOperand(0) &&
1207           DVI->getVariable() == DIVar &&
1208           DVI->getExpression() == DIExpr)
1209         return true;
1210   }
1211   return false;
1212 }
1213 
1214 /// See if there is a dbg.value intrinsic for DIVar for the PHI node.
1215 static bool PhiHasDebugValue(DILocalVariable *DIVar,
1216                              DIExpression *DIExpr,
1217                              PHINode *APN) {
1218   // Since we can't guarantee that the original dbg.declare instrinsic
1219   // is removed by LowerDbgDeclare(), we need to make sure that we are
1220   // not inserting the same dbg.value intrinsic over and over.
1221   SmallVector<DbgValueInst *, 1> DbgValues;
1222   findDbgValues(DbgValues, APN);
1223   for (auto *DVI : DbgValues) {
1224     assert(DVI->getValue() == APN);
1225     if ((DVI->getVariable() == DIVar) && (DVI->getExpression() == DIExpr))
1226       return true;
1227   }
1228   return false;
1229 }
1230 
1231 /// Check if the alloc size of \p ValTy is large enough to cover the variable
1232 /// (or fragment of the variable) described by \p DII.
1233 ///
1234 /// This is primarily intended as a helper for the different
1235 /// ConvertDebugDeclareToDebugValue functions. The dbg.declare/dbg.addr that is
1236 /// converted describes an alloca'd variable, so we need to use the
1237 /// alloc size of the value when doing the comparison. E.g. an i1 value will be
1238 /// identified as covering an n-bit fragment, if the store size of i1 is at
1239 /// least n bits.
1240 static bool valueCoversEntireFragment(Type *ValTy, DbgInfoIntrinsic *DII) {
1241   const DataLayout &DL = DII->getModule()->getDataLayout();
1242   uint64_t ValueSize = DL.getTypeAllocSizeInBits(ValTy);
1243   if (auto FragmentSize = DII->getFragmentSizeInBits())
1244     return ValueSize >= *FragmentSize;
1245   // We can't always calculate the size of the DI variable (e.g. if it is a
1246   // VLA). Try to use the size of the alloca that the dbg intrinsic describes
1247   // intead.
1248   if (DII->isAddressOfVariable())
1249     if (auto *AI = dyn_cast_or_null<AllocaInst>(DII->getVariableLocation()))
1250       if (auto FragmentSize = AI->getAllocationSizeInBits(DL))
1251         return ValueSize >= *FragmentSize;
1252   // Could not determine size of variable. Conservatively return false.
1253   return false;
1254 }
1255 
1256 /// Inserts a llvm.dbg.value intrinsic before a store to an alloca'd value
1257 /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
1258 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1259                                            StoreInst *SI, DIBuilder &Builder) {
1260   assert(DII->isAddressOfVariable());
1261   auto *DIVar = DII->getVariable();
1262   assert(DIVar && "Missing variable");
1263   auto *DIExpr = DII->getExpression();
1264   Value *DV = SI->getOperand(0);
1265 
1266   if (!valueCoversEntireFragment(SI->getValueOperand()->getType(), DII)) {
1267     // FIXME: If storing to a part of the variable described by the dbg.declare,
1268     // then we want to insert a dbg.value for the corresponding fragment.
1269     LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
1270                       << *DII << '\n');
1271     // For now, when there is a store to parts of the variable (but we do not
1272     // know which part) we insert an dbg.value instrinsic to indicate that we
1273     // know nothing about the variable's content.
1274     DV = UndefValue::get(DV->getType());
1275     if (!LdStHasDebugValue(DIVar, DIExpr, SI))
1276       Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
1277                                       SI);
1278     return;
1279   }
1280 
1281   // If an argument is zero extended then use argument directly. The ZExt
1282   // may be zapped by an optimization pass in future.
1283   Argument *ExtendedArg = nullptr;
1284   if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
1285     ExtendedArg = dyn_cast<Argument>(ZExt->getOperand(0));
1286   if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
1287     ExtendedArg = dyn_cast<Argument>(SExt->getOperand(0));
1288   if (ExtendedArg) {
1289     // If this DII was already describing only a fragment of a variable, ensure
1290     // that fragment is appropriately narrowed here.
1291     // But if a fragment wasn't used, describe the value as the original
1292     // argument (rather than the zext or sext) so that it remains described even
1293     // if the sext/zext is optimized away. This widens the variable description,
1294     // leaving it up to the consumer to know how the smaller value may be
1295     // represented in a larger register.
1296     if (auto Fragment = DIExpr->getFragmentInfo()) {
1297       unsigned FragmentOffset = Fragment->OffsetInBits;
1298       SmallVector<uint64_t, 3> Ops(DIExpr->elements_begin(),
1299                                    DIExpr->elements_end() - 3);
1300       Ops.push_back(dwarf::DW_OP_LLVM_fragment);
1301       Ops.push_back(FragmentOffset);
1302       const DataLayout &DL = DII->getModule()->getDataLayout();
1303       Ops.push_back(DL.getTypeSizeInBits(ExtendedArg->getType()));
1304       DIExpr = Builder.createExpression(Ops);
1305     }
1306     DV = ExtendedArg;
1307   }
1308   if (!LdStHasDebugValue(DIVar, DIExpr, SI))
1309     Builder.insertDbgValueIntrinsic(DV, DIVar, DIExpr, DII->getDebugLoc(),
1310                                     SI);
1311 }
1312 
1313 /// Inserts a llvm.dbg.value intrinsic before a load of an alloca'd value
1314 /// that has an associated llvm.dbg.declare or llvm.dbg.addr intrinsic.
1315 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1316                                            LoadInst *LI, DIBuilder &Builder) {
1317   auto *DIVar = DII->getVariable();
1318   auto *DIExpr = DII->getExpression();
1319   assert(DIVar && "Missing variable");
1320 
1321   if (LdStHasDebugValue(DIVar, DIExpr, LI))
1322     return;
1323 
1324   if (!valueCoversEntireFragment(LI->getType(), DII)) {
1325     // FIXME: If only referring to a part of the variable described by the
1326     // dbg.declare, then we want to insert a dbg.value for the corresponding
1327     // fragment.
1328     LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
1329                       << *DII << '\n');
1330     return;
1331   }
1332 
1333   // We are now tracking the loaded value instead of the address. In the
1334   // future if multi-location support is added to the IR, it might be
1335   // preferable to keep tracking both the loaded value and the original
1336   // address in case the alloca can not be elided.
1337   Instruction *DbgValue = Builder.insertDbgValueIntrinsic(
1338       LI, DIVar, DIExpr, DII->getDebugLoc(), (Instruction *)nullptr);
1339   DbgValue->insertAfter(LI);
1340 }
1341 
1342 /// Inserts a llvm.dbg.value intrinsic after a phi that has an associated
1343 /// llvm.dbg.declare or llvm.dbg.addr intrinsic.
1344 void llvm::ConvertDebugDeclareToDebugValue(DbgInfoIntrinsic *DII,
1345                                            PHINode *APN, DIBuilder &Builder) {
1346   auto *DIVar = DII->getVariable();
1347   auto *DIExpr = DII->getExpression();
1348   assert(DIVar && "Missing variable");
1349 
1350   if (PhiHasDebugValue(DIVar, DIExpr, APN))
1351     return;
1352 
1353   if (!valueCoversEntireFragment(APN->getType(), DII)) {
1354     // FIXME: If only referring to a part of the variable described by the
1355     // dbg.declare, then we want to insert a dbg.value for the corresponding
1356     // fragment.
1357     LLVM_DEBUG(dbgs() << "Failed to convert dbg.declare to dbg.value: "
1358                       << *DII << '\n');
1359     return;
1360   }
1361 
1362   BasicBlock *BB = APN->getParent();
1363   auto InsertionPt = BB->getFirstInsertionPt();
1364 
1365   // The block may be a catchswitch block, which does not have a valid
1366   // insertion point.
1367   // FIXME: Insert dbg.value markers in the successors when appropriate.
1368   if (InsertionPt != BB->end())
1369     Builder.insertDbgValueIntrinsic(APN, DIVar, DIExpr, DII->getDebugLoc(),
1370                                     &*InsertionPt);
1371 }
1372 
1373 /// Determine whether this alloca is either a VLA or an array.
1374 static bool isArray(AllocaInst *AI) {
1375   return AI->isArrayAllocation() ||
1376     AI->getType()->getElementType()->isArrayTy();
1377 }
1378 
1379 /// LowerDbgDeclare - Lowers llvm.dbg.declare intrinsics into appropriate set
1380 /// of llvm.dbg.value intrinsics.
1381 bool llvm::LowerDbgDeclare(Function &F) {
1382   DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
1383   SmallVector<DbgDeclareInst *, 4> Dbgs;
1384   for (auto &FI : F)
1385     for (Instruction &BI : FI)
1386       if (auto DDI = dyn_cast<DbgDeclareInst>(&BI))
1387         Dbgs.push_back(DDI);
1388 
1389   if (Dbgs.empty())
1390     return false;
1391 
1392   for (auto &I : Dbgs) {
1393     DbgDeclareInst *DDI = I;
1394     AllocaInst *AI = dyn_cast_or_null<AllocaInst>(DDI->getAddress());
1395     // If this is an alloca for a scalar variable, insert a dbg.value
1396     // at each load and store to the alloca and erase the dbg.declare.
1397     // The dbg.values allow tracking a variable even if it is not
1398     // stored on the stack, while the dbg.declare can only describe
1399     // the stack slot (and at a lexical-scope granularity). Later
1400     // passes will attempt to elide the stack slot.
1401     if (!AI || isArray(AI))
1402       continue;
1403 
1404     // A volatile load/store means that the alloca can't be elided anyway.
1405     if (llvm::any_of(AI->users(), [](User *U) -> bool {
1406           if (LoadInst *LI = dyn_cast<LoadInst>(U))
1407             return LI->isVolatile();
1408           if (StoreInst *SI = dyn_cast<StoreInst>(U))
1409             return SI->isVolatile();
1410           return false;
1411         }))
1412       continue;
1413 
1414     for (auto &AIUse : AI->uses()) {
1415       User *U = AIUse.getUser();
1416       if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
1417         if (AIUse.getOperandNo() == 1)
1418           ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
1419       } else if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
1420         ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
1421       } else if (CallInst *CI = dyn_cast<CallInst>(U)) {
1422         // This is a call by-value or some other instruction that
1423         // takes a pointer to the variable. Insert a *value*
1424         // intrinsic that describes the alloca.
1425         DIB.insertDbgValueIntrinsic(AI, DDI->getVariable(),
1426                                     DDI->getExpression(), DDI->getDebugLoc(),
1427                                     CI);
1428       }
1429     }
1430     DDI->eraseFromParent();
1431   }
1432   return true;
1433 }
1434 
1435 /// Propagate dbg.value intrinsics through the newly inserted PHIs.
1436 void llvm::insertDebugValuesForPHIs(BasicBlock *BB,
1437                                     SmallVectorImpl<PHINode *> &InsertedPHIs) {
1438   assert(BB && "No BasicBlock to clone dbg.value(s) from.");
1439   if (InsertedPHIs.size() == 0)
1440     return;
1441 
1442   // Map existing PHI nodes to their dbg.values.
1443   ValueToValueMapTy DbgValueMap;
1444   for (auto &I : *BB) {
1445     if (auto DbgII = dyn_cast<DbgInfoIntrinsic>(&I)) {
1446       if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
1447         DbgValueMap.insert({Loc, DbgII});
1448     }
1449   }
1450   if (DbgValueMap.size() == 0)
1451     return;
1452 
1453   // Then iterate through the new PHIs and look to see if they use one of the
1454   // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
1455   // propagate the info through the new PHI.
1456   LLVMContext &C = BB->getContext();
1457   for (auto PHI : InsertedPHIs) {
1458     BasicBlock *Parent = PHI->getParent();
1459     // Avoid inserting an intrinsic into an EH block.
1460     if (Parent->getFirstNonPHI()->isEHPad())
1461       continue;
1462     auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
1463     for (auto VI : PHI->operand_values()) {
1464       auto V = DbgValueMap.find(VI);
1465       if (V != DbgValueMap.end()) {
1466         auto *DbgII = cast<DbgInfoIntrinsic>(V->second);
1467         Instruction *NewDbgII = DbgII->clone();
1468         NewDbgII->setOperand(0, PhiMAV);
1469         auto InsertionPt = Parent->getFirstInsertionPt();
1470         assert(InsertionPt != Parent->end() && "Ill-formed basic block");
1471         NewDbgII->insertBefore(&*InsertionPt);
1472       }
1473     }
1474   }
1475 }
1476 
1477 /// Finds all intrinsics declaring local variables as living in the memory that
1478 /// 'V' points to. This may include a mix of dbg.declare and
1479 /// dbg.addr intrinsics.
1480 TinyPtrVector<DbgInfoIntrinsic *> llvm::FindDbgAddrUses(Value *V) {
1481   // This function is hot. Check whether the value has any metadata to avoid a
1482   // DenseMap lookup.
1483   if (!V->isUsedByMetadata())
1484     return {};
1485   auto *L = LocalAsMetadata::getIfExists(V);
1486   if (!L)
1487     return {};
1488   auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L);
1489   if (!MDV)
1490     return {};
1491 
1492   TinyPtrVector<DbgInfoIntrinsic *> Declares;
1493   for (User *U : MDV->users()) {
1494     if (auto *DII = dyn_cast<DbgInfoIntrinsic>(U))
1495       if (DII->isAddressOfVariable())
1496         Declares.push_back(DII);
1497   }
1498 
1499   return Declares;
1500 }
1501 
1502 void llvm::findDbgValues(SmallVectorImpl<DbgValueInst *> &DbgValues, Value *V) {
1503   // This function is hot. Check whether the value has any metadata to avoid a
1504   // DenseMap lookup.
1505   if (!V->isUsedByMetadata())
1506     return;
1507   if (auto *L = LocalAsMetadata::getIfExists(V))
1508     if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1509       for (User *U : MDV->users())
1510         if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
1511           DbgValues.push_back(DVI);
1512 }
1513 
1514 void llvm::findDbgUsers(SmallVectorImpl<DbgInfoIntrinsic *> &DbgUsers,
1515                         Value *V) {
1516   // This function is hot. Check whether the value has any metadata to avoid a
1517   // DenseMap lookup.
1518   if (!V->isUsedByMetadata())
1519     return;
1520   if (auto *L = LocalAsMetadata::getIfExists(V))
1521     if (auto *MDV = MetadataAsValue::getIfExists(V->getContext(), L))
1522       for (User *U : MDV->users())
1523         if (DbgInfoIntrinsic *DII = dyn_cast<DbgInfoIntrinsic>(U))
1524           DbgUsers.push_back(DII);
1525 }
1526 
1527 bool llvm::replaceDbgDeclare(Value *Address, Value *NewAddress,
1528                              Instruction *InsertBefore, DIBuilder &Builder,
1529                              bool DerefBefore, int Offset, bool DerefAfter) {
1530   auto DbgAddrs = FindDbgAddrUses(Address);
1531   for (DbgInfoIntrinsic *DII : DbgAddrs) {
1532     DebugLoc Loc = DII->getDebugLoc();
1533     auto *DIVar = DII->getVariable();
1534     auto *DIExpr = DII->getExpression();
1535     assert(DIVar && "Missing variable");
1536     DIExpr = DIExpression::prepend(DIExpr, DerefBefore, Offset, DerefAfter);
1537     // Insert llvm.dbg.declare immediately after InsertBefore, and remove old
1538     // llvm.dbg.declare.
1539     Builder.insertDeclare(NewAddress, DIVar, DIExpr, Loc, InsertBefore);
1540     if (DII == InsertBefore)
1541       InsertBefore = &*std::next(InsertBefore->getIterator());
1542     DII->eraseFromParent();
1543   }
1544   return !DbgAddrs.empty();
1545 }
1546 
1547 bool llvm::replaceDbgDeclareForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1548                                       DIBuilder &Builder, bool DerefBefore,
1549                                       int Offset, bool DerefAfter) {
1550   return replaceDbgDeclare(AI, NewAllocaAddress, AI->getNextNode(), Builder,
1551                            DerefBefore, Offset, DerefAfter);
1552 }
1553 
1554 static void replaceOneDbgValueForAlloca(DbgValueInst *DVI, Value *NewAddress,
1555                                         DIBuilder &Builder, int Offset) {
1556   DebugLoc Loc = DVI->getDebugLoc();
1557   auto *DIVar = DVI->getVariable();
1558   auto *DIExpr = DVI->getExpression();
1559   assert(DIVar && "Missing variable");
1560 
1561   // This is an alloca-based llvm.dbg.value. The first thing it should do with
1562   // the alloca pointer is dereference it. Otherwise we don't know how to handle
1563   // it and give up.
1564   if (!DIExpr || DIExpr->getNumElements() < 1 ||
1565       DIExpr->getElement(0) != dwarf::DW_OP_deref)
1566     return;
1567 
1568   // Insert the offset immediately after the first deref.
1569   // We could just change the offset argument of dbg.value, but it's unsigned...
1570   if (Offset) {
1571     SmallVector<uint64_t, 4> Ops;
1572     Ops.push_back(dwarf::DW_OP_deref);
1573     DIExpression::appendOffset(Ops, Offset);
1574     Ops.append(DIExpr->elements_begin() + 1, DIExpr->elements_end());
1575     DIExpr = Builder.createExpression(Ops);
1576   }
1577 
1578   Builder.insertDbgValueIntrinsic(NewAddress, DIVar, DIExpr, Loc, DVI);
1579   DVI->eraseFromParent();
1580 }
1581 
1582 void llvm::replaceDbgValueForAlloca(AllocaInst *AI, Value *NewAllocaAddress,
1583                                     DIBuilder &Builder, int Offset) {
1584   if (auto *L = LocalAsMetadata::getIfExists(AI))
1585     if (auto *MDV = MetadataAsValue::getIfExists(AI->getContext(), L))
1586       for (auto UI = MDV->use_begin(), UE = MDV->use_end(); UI != UE;) {
1587         Use &U = *UI++;
1588         if (auto *DVI = dyn_cast<DbgValueInst>(U.getUser()))
1589           replaceOneDbgValueForAlloca(DVI, NewAllocaAddress, Builder, Offset);
1590       }
1591 }
1592 
1593 void llvm::salvageDebugInfo(Instruction &I) {
1594   SmallVector<DbgInfoIntrinsic *, 1> DbgUsers;
1595   findDbgUsers(DbgUsers, &I);
1596   if (DbgUsers.empty())
1597     return;
1598 
1599   auto &M = *I.getModule();
1600   auto &DL = M.getDataLayout();
1601 
1602   auto wrapMD = [&](Value *V) {
1603     return MetadataAsValue::get(I.getContext(), ValueAsMetadata::get(V));
1604   };
1605 
1606   auto doSalvage = [&](DbgInfoIntrinsic *DII, SmallVectorImpl<uint64_t> &Ops) {
1607     auto *DIExpr = DII->getExpression();
1608     if (!Ops.empty()) {
1609       // Do not add DW_OP_stack_value for DbgDeclare and DbgAddr, because they
1610       // are implicitly pointing out the value as a DWARF memory location
1611       // description.
1612       bool WithStackValue = isa<DbgValueInst>(DII);
1613       DIExpr = DIExpression::prependOpcodes(DIExpr, Ops, WithStackValue);
1614     }
1615     DII->setOperand(0, wrapMD(I.getOperand(0)));
1616     DII->setOperand(2, MetadataAsValue::get(I.getContext(), DIExpr));
1617     LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
1618   };
1619 
1620   auto applyOffset = [&](DbgInfoIntrinsic *DII, uint64_t Offset) {
1621     SmallVector<uint64_t, 8> Ops;
1622     DIExpression::appendOffset(Ops, Offset);
1623     doSalvage(DII, Ops);
1624   };
1625 
1626   auto applyOps = [&](DbgInfoIntrinsic *DII,
1627                       std::initializer_list<uint64_t> Opcodes) {
1628     SmallVector<uint64_t, 8> Ops(Opcodes);
1629     doSalvage(DII, Ops);
1630   };
1631 
1632   if (auto *CI = dyn_cast<CastInst>(&I)) {
1633     if (!CI->isNoopCast(DL))
1634       return;
1635 
1636     // No-op casts are irrelevant for debug info.
1637     MetadataAsValue *CastSrc = wrapMD(I.getOperand(0));
1638     for (auto *DII : DbgUsers) {
1639       DII->setOperand(0, CastSrc);
1640       LLVM_DEBUG(dbgs() << "SALVAGE: " << *DII << '\n');
1641     }
1642   } else if (auto *GEP = dyn_cast<GetElementPtrInst>(&I)) {
1643     unsigned BitWidth =
1644         M.getDataLayout().getIndexSizeInBits(GEP->getPointerAddressSpace());
1645     // Rewrite a constant GEP into a DIExpression.  Since we are performing
1646     // arithmetic to compute the variable's *value* in the DIExpression, we
1647     // need to mark the expression with a DW_OP_stack_value.
1648     APInt Offset(BitWidth, 0);
1649     if (GEP->accumulateConstantOffset(M.getDataLayout(), Offset))
1650       for (auto *DII : DbgUsers)
1651         applyOffset(DII, Offset.getSExtValue());
1652   } else if (auto *BI = dyn_cast<BinaryOperator>(&I)) {
1653     // Rewrite binary operations with constant integer operands.
1654     auto *ConstInt = dyn_cast<ConstantInt>(I.getOperand(1));
1655     if (!ConstInt || ConstInt->getBitWidth() > 64)
1656       return;
1657 
1658     uint64_t Val = ConstInt->getSExtValue();
1659     for (auto *DII : DbgUsers) {
1660       switch (BI->getOpcode()) {
1661       case Instruction::Add:
1662         applyOffset(DII, Val);
1663         break;
1664       case Instruction::Sub:
1665         applyOffset(DII, -int64_t(Val));
1666         break;
1667       case Instruction::Mul:
1668         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_mul});
1669         break;
1670       case Instruction::SDiv:
1671         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_div});
1672         break;
1673       case Instruction::SRem:
1674         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_mod});
1675         break;
1676       case Instruction::Or:
1677         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_or});
1678         break;
1679       case Instruction::And:
1680         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_and});
1681         break;
1682       case Instruction::Xor:
1683         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_xor});
1684         break;
1685       case Instruction::Shl:
1686         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shl});
1687         break;
1688       case Instruction::LShr:
1689         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shr});
1690         break;
1691       case Instruction::AShr:
1692         applyOps(DII, {dwarf::DW_OP_constu, Val, dwarf::DW_OP_shra});
1693         break;
1694       default:
1695         // TODO: Salvage constants from each kind of binop we know about.
1696         continue;
1697       }
1698     }
1699   } else if (isa<LoadInst>(&I)) {
1700     MetadataAsValue *AddrMD = wrapMD(I.getOperand(0));
1701     for (auto *DII : DbgUsers) {
1702       // Rewrite the load into DW_OP_deref.
1703       auto *DIExpr = DII->getExpression();
1704       DIExpr = DIExpression::prepend(DIExpr, DIExpression::WithDeref);
1705       DII->setOperand(0, AddrMD);
1706       DII->setOperand(2, MetadataAsValue::get(I.getContext(), DIExpr));
1707       LLVM_DEBUG(dbgs() << "SALVAGE:  " << *DII << '\n');
1708     }
1709   }
1710 }
1711 
1712 void llvm::insertReplacementDbgValues(
1713     Value &From, Value &To, Instruction &InsertBefore,
1714     function_ref<DIExpression *(DbgInfoIntrinsic &OldDII)> RewriteExpr) {
1715   // Collect all debug users of From.
1716   SmallVector<DbgInfoIntrinsic *, 1> Users;
1717   findDbgUsers(Users, &From);
1718   if (Users.empty())
1719     return;
1720 
1721   // Insert a replacement debug value for each old debug user. It's assumed
1722   // that the old debug users will be erased later.
1723   DIBuilder DIB(*InsertBefore.getModule());
1724   for (auto *OldDII : Users)
1725     if (DIExpression *Expr = RewriteExpr(*OldDII)) {
1726       auto *I = DIB.insertDbgValueIntrinsic(&To, OldDII->getVariable(), Expr,
1727                                             OldDII->getDebugLoc().get(),
1728                                             &InsertBefore);
1729       (void)I;
1730       LLVM_DEBUG(dbgs() << "REPLACE:  " << *I << '\n');
1731     }
1732 }
1733 
1734 void llvm::insertReplacementDbgValues(Value &From, Value &To,
1735                                       Instruction &InsertBefore) {
1736   return llvm::insertReplacementDbgValues(
1737       From, To, InsertBefore,
1738       [](DbgInfoIntrinsic &OldDII) { return OldDII.getExpression(); });
1739 }
1740 
1741 unsigned llvm::removeAllNonTerminatorAndEHPadInstructions(BasicBlock *BB) {
1742   unsigned NumDeadInst = 0;
1743   // Delete the instructions backwards, as it has a reduced likelihood of
1744   // having to update as many def-use and use-def chains.
1745   Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
1746   while (EndInst != &BB->front()) {
1747     // Delete the next to last instruction.
1748     Instruction *Inst = &*--EndInst->getIterator();
1749     if (!Inst->use_empty() && !Inst->getType()->isTokenTy())
1750       Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
1751     if (Inst->isEHPad() || Inst->getType()->isTokenTy()) {
1752       EndInst = Inst;
1753       continue;
1754     }
1755     if (!isa<DbgInfoIntrinsic>(Inst))
1756       ++NumDeadInst;
1757     Inst->eraseFromParent();
1758   }
1759   return NumDeadInst;
1760 }
1761 
1762 unsigned llvm::changeToUnreachable(Instruction *I, bool UseLLVMTrap,
1763                                    bool PreserveLCSSA, DeferredDominance *DDT) {
1764   BasicBlock *BB = I->getParent();
1765   std::vector <DominatorTree::UpdateType> Updates;
1766 
1767   // Loop over all of the successors, removing BB's entry from any PHI
1768   // nodes.
1769   if (DDT)
1770     Updates.reserve(BB->getTerminator()->getNumSuccessors());
1771   for (BasicBlock *Successor : successors(BB)) {
1772     Successor->removePredecessor(BB, PreserveLCSSA);
1773     if (DDT)
1774       Updates.push_back({DominatorTree::Delete, BB, Successor});
1775   }
1776   // Insert a call to llvm.trap right before this.  This turns the undefined
1777   // behavior into a hard fail instead of falling through into random code.
1778   if (UseLLVMTrap) {
1779     Function *TrapFn =
1780       Intrinsic::getDeclaration(BB->getParent()->getParent(), Intrinsic::trap);
1781     CallInst *CallTrap = CallInst::Create(TrapFn, "", I);
1782     CallTrap->setDebugLoc(I->getDebugLoc());
1783   }
1784   new UnreachableInst(I->getContext(), I);
1785 
1786   // All instructions after this are dead.
1787   unsigned NumInstrsRemoved = 0;
1788   BasicBlock::iterator BBI = I->getIterator(), BBE = BB->end();
1789   while (BBI != BBE) {
1790     if (!BBI->use_empty())
1791       BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
1792     BB->getInstList().erase(BBI++);
1793     ++NumInstrsRemoved;
1794   }
1795   if (DDT)
1796     DDT->applyUpdates(Updates);
1797   return NumInstrsRemoved;
1798 }
1799 
1800 /// changeToCall - Convert the specified invoke into a normal call.
1801 static void changeToCall(InvokeInst *II, DeferredDominance *DDT = nullptr) {
1802   SmallVector<Value*, 8> Args(II->arg_begin(), II->arg_end());
1803   SmallVector<OperandBundleDef, 1> OpBundles;
1804   II->getOperandBundlesAsDefs(OpBundles);
1805   CallInst *NewCall = CallInst::Create(II->getCalledValue(), Args, OpBundles,
1806                                        "", II);
1807   NewCall->takeName(II);
1808   NewCall->setCallingConv(II->getCallingConv());
1809   NewCall->setAttributes(II->getAttributes());
1810   NewCall->setDebugLoc(II->getDebugLoc());
1811   II->replaceAllUsesWith(NewCall);
1812 
1813   // Follow the call by a branch to the normal destination.
1814   BasicBlock *NormalDestBB = II->getNormalDest();
1815   BranchInst::Create(NormalDestBB, II);
1816 
1817   // Update PHI nodes in the unwind destination
1818   BasicBlock *BB = II->getParent();
1819   BasicBlock *UnwindDestBB = II->getUnwindDest();
1820   UnwindDestBB->removePredecessor(BB);
1821   II->eraseFromParent();
1822   if (DDT)
1823     DDT->deleteEdge(BB, UnwindDestBB);
1824 }
1825 
1826 BasicBlock *llvm::changeToInvokeAndSplitBasicBlock(CallInst *CI,
1827                                                    BasicBlock *UnwindEdge) {
1828   BasicBlock *BB = CI->getParent();
1829 
1830   // Convert this function call into an invoke instruction.  First, split the
1831   // basic block.
1832   BasicBlock *Split =
1833       BB->splitBasicBlock(CI->getIterator(), CI->getName() + ".noexc");
1834 
1835   // Delete the unconditional branch inserted by splitBasicBlock
1836   BB->getInstList().pop_back();
1837 
1838   // Create the new invoke instruction.
1839   SmallVector<Value *, 8> InvokeArgs(CI->arg_begin(), CI->arg_end());
1840   SmallVector<OperandBundleDef, 1> OpBundles;
1841 
1842   CI->getOperandBundlesAsDefs(OpBundles);
1843 
1844   // Note: we're round tripping operand bundles through memory here, and that
1845   // can potentially be avoided with a cleverer API design that we do not have
1846   // as of this time.
1847 
1848   InvokeInst *II = InvokeInst::Create(CI->getCalledValue(), Split, UnwindEdge,
1849                                       InvokeArgs, OpBundles, CI->getName(), BB);
1850   II->setDebugLoc(CI->getDebugLoc());
1851   II->setCallingConv(CI->getCallingConv());
1852   II->setAttributes(CI->getAttributes());
1853 
1854   // Make sure that anything using the call now uses the invoke!  This also
1855   // updates the CallGraph if present, because it uses a WeakTrackingVH.
1856   CI->replaceAllUsesWith(II);
1857 
1858   // Delete the original call
1859   Split->getInstList().pop_front();
1860   return Split;
1861 }
1862 
1863 static bool markAliveBlocks(Function &F,
1864                             SmallPtrSetImpl<BasicBlock*> &Reachable,
1865                             DeferredDominance *DDT = nullptr) {
1866   SmallVector<BasicBlock*, 128> Worklist;
1867   BasicBlock *BB = &F.front();
1868   Worklist.push_back(BB);
1869   Reachable.insert(BB);
1870   bool Changed = false;
1871   do {
1872     BB = Worklist.pop_back_val();
1873 
1874     // Do a quick scan of the basic block, turning any obviously unreachable
1875     // instructions into LLVM unreachable insts.  The instruction combining pass
1876     // canonicalizes unreachable insts into stores to null or undef.
1877     for (Instruction &I : *BB) {
1878       // Assumptions that are known to be false are equivalent to unreachable.
1879       // Also, if the condition is undefined, then we make the choice most
1880       // beneficial to the optimizer, and choose that to also be unreachable.
1881       if (auto *II = dyn_cast<IntrinsicInst>(&I)) {
1882         if (II->getIntrinsicID() == Intrinsic::assume) {
1883           if (match(II->getArgOperand(0), m_CombineOr(m_Zero(), m_Undef()))) {
1884             // Don't insert a call to llvm.trap right before the unreachable.
1885             changeToUnreachable(II, false, false, DDT);
1886             Changed = true;
1887             break;
1888           }
1889         }
1890 
1891         if (II->getIntrinsicID() == Intrinsic::experimental_guard) {
1892           // A call to the guard intrinsic bails out of the current compilation
1893           // unit if the predicate passed to it is false.  If the predicate is a
1894           // constant false, then we know the guard will bail out of the current
1895           // compile unconditionally, so all code following it is dead.
1896           //
1897           // Note: unlike in llvm.assume, it is not "obviously profitable" for
1898           // guards to treat `undef` as `false` since a guard on `undef` can
1899           // still be useful for widening.
1900           if (match(II->getArgOperand(0), m_Zero()))
1901             if (!isa<UnreachableInst>(II->getNextNode())) {
1902               changeToUnreachable(II->getNextNode(), /*UseLLVMTrap=*/false,
1903                                   false, DDT);
1904               Changed = true;
1905               break;
1906             }
1907         }
1908       }
1909 
1910       if (auto *CI = dyn_cast<CallInst>(&I)) {
1911         Value *Callee = CI->getCalledValue();
1912         if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1913           changeToUnreachable(CI, /*UseLLVMTrap=*/false, false, DDT);
1914           Changed = true;
1915           break;
1916         }
1917         if (CI->doesNotReturn()) {
1918           // If we found a call to a no-return function, insert an unreachable
1919           // instruction after it.  Make sure there isn't *already* one there
1920           // though.
1921           if (!isa<UnreachableInst>(CI->getNextNode())) {
1922             // Don't insert a call to llvm.trap right before the unreachable.
1923             changeToUnreachable(CI->getNextNode(), false, false, DDT);
1924             Changed = true;
1925           }
1926           break;
1927         }
1928       }
1929 
1930       // Store to undef and store to null are undefined and used to signal that
1931       // they should be changed to unreachable by passes that can't modify the
1932       // CFG.
1933       if (auto *SI = dyn_cast<StoreInst>(&I)) {
1934         // Don't touch volatile stores.
1935         if (SI->isVolatile()) continue;
1936 
1937         Value *Ptr = SI->getOperand(1);
1938 
1939         if (isa<UndefValue>(Ptr) ||
1940             (isa<ConstantPointerNull>(Ptr) &&
1941              SI->getPointerAddressSpace() == 0)) {
1942           changeToUnreachable(SI, true, false, DDT);
1943           Changed = true;
1944           break;
1945         }
1946       }
1947     }
1948 
1949     TerminatorInst *Terminator = BB->getTerminator();
1950     if (auto *II = dyn_cast<InvokeInst>(Terminator)) {
1951       // Turn invokes that call 'nounwind' functions into ordinary calls.
1952       Value *Callee = II->getCalledValue();
1953       if (isa<ConstantPointerNull>(Callee) || isa<UndefValue>(Callee)) {
1954         changeToUnreachable(II, true, false, DDT);
1955         Changed = true;
1956       } else if (II->doesNotThrow() && canSimplifyInvokeNoUnwind(&F)) {
1957         if (II->use_empty() && II->onlyReadsMemory()) {
1958           // jump to the normal destination branch.
1959           BasicBlock *NormalDestBB = II->getNormalDest();
1960           BasicBlock *UnwindDestBB = II->getUnwindDest();
1961           BranchInst::Create(NormalDestBB, II);
1962           UnwindDestBB->removePredecessor(II->getParent());
1963           II->eraseFromParent();
1964           if (DDT)
1965             DDT->deleteEdge(BB, UnwindDestBB);
1966         } else
1967           changeToCall(II, DDT);
1968         Changed = true;
1969       }
1970     } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(Terminator)) {
1971       // Remove catchpads which cannot be reached.
1972       struct CatchPadDenseMapInfo {
1973         static CatchPadInst *getEmptyKey() {
1974           return DenseMapInfo<CatchPadInst *>::getEmptyKey();
1975         }
1976 
1977         static CatchPadInst *getTombstoneKey() {
1978           return DenseMapInfo<CatchPadInst *>::getTombstoneKey();
1979         }
1980 
1981         static unsigned getHashValue(CatchPadInst *CatchPad) {
1982           return static_cast<unsigned>(hash_combine_range(
1983               CatchPad->value_op_begin(), CatchPad->value_op_end()));
1984         }
1985 
1986         static bool isEqual(CatchPadInst *LHS, CatchPadInst *RHS) {
1987           if (LHS == getEmptyKey() || LHS == getTombstoneKey() ||
1988               RHS == getEmptyKey() || RHS == getTombstoneKey())
1989             return LHS == RHS;
1990           return LHS->isIdenticalTo(RHS);
1991         }
1992       };
1993 
1994       // Set of unique CatchPads.
1995       SmallDenseMap<CatchPadInst *, detail::DenseSetEmpty, 4,
1996                     CatchPadDenseMapInfo, detail::DenseSetPair<CatchPadInst *>>
1997           HandlerSet;
1998       detail::DenseSetEmpty Empty;
1999       for (CatchSwitchInst::handler_iterator I = CatchSwitch->handler_begin(),
2000                                              E = CatchSwitch->handler_end();
2001            I != E; ++I) {
2002         BasicBlock *HandlerBB = *I;
2003         auto *CatchPad = cast<CatchPadInst>(HandlerBB->getFirstNonPHI());
2004         if (!HandlerSet.insert({CatchPad, Empty}).second) {
2005           CatchSwitch->removeHandler(I);
2006           --I;
2007           --E;
2008           Changed = true;
2009         }
2010       }
2011     }
2012 
2013     Changed |= ConstantFoldTerminator(BB, true, nullptr, DDT);
2014     for (BasicBlock *Successor : successors(BB))
2015       if (Reachable.insert(Successor).second)
2016         Worklist.push_back(Successor);
2017   } while (!Worklist.empty());
2018   return Changed;
2019 }
2020 
2021 void llvm::removeUnwindEdge(BasicBlock *BB, DeferredDominance *DDT) {
2022   TerminatorInst *TI = BB->getTerminator();
2023 
2024   if (auto *II = dyn_cast<InvokeInst>(TI)) {
2025     changeToCall(II, DDT);
2026     return;
2027   }
2028 
2029   TerminatorInst *NewTI;
2030   BasicBlock *UnwindDest;
2031 
2032   if (auto *CRI = dyn_cast<CleanupReturnInst>(TI)) {
2033     NewTI = CleanupReturnInst::Create(CRI->getCleanupPad(), nullptr, CRI);
2034     UnwindDest = CRI->getUnwindDest();
2035   } else if (auto *CatchSwitch = dyn_cast<CatchSwitchInst>(TI)) {
2036     auto *NewCatchSwitch = CatchSwitchInst::Create(
2037         CatchSwitch->getParentPad(), nullptr, CatchSwitch->getNumHandlers(),
2038         CatchSwitch->getName(), CatchSwitch);
2039     for (BasicBlock *PadBB : CatchSwitch->handlers())
2040       NewCatchSwitch->addHandler(PadBB);
2041 
2042     NewTI = NewCatchSwitch;
2043     UnwindDest = CatchSwitch->getUnwindDest();
2044   } else {
2045     llvm_unreachable("Could not find unwind successor");
2046   }
2047 
2048   NewTI->takeName(TI);
2049   NewTI->setDebugLoc(TI->getDebugLoc());
2050   UnwindDest->removePredecessor(BB);
2051   TI->replaceAllUsesWith(NewTI);
2052   TI->eraseFromParent();
2053   if (DDT)
2054     DDT->deleteEdge(BB, UnwindDest);
2055 }
2056 
2057 /// removeUnreachableBlocks - Remove blocks that are not reachable, even
2058 /// if they are in a dead cycle.  Return true if a change was made, false
2059 /// otherwise. If `LVI` is passed, this function preserves LazyValueInfo
2060 /// after modifying the CFG.
2061 bool llvm::removeUnreachableBlocks(Function &F, LazyValueInfo *LVI,
2062                                    DeferredDominance *DDT) {
2063   SmallPtrSet<BasicBlock*, 16> Reachable;
2064   bool Changed = markAliveBlocks(F, Reachable, DDT);
2065 
2066   // If there are unreachable blocks in the CFG...
2067   if (Reachable.size() == F.size())
2068     return Changed;
2069 
2070   assert(Reachable.size() < F.size());
2071   NumRemoved += F.size()-Reachable.size();
2072 
2073   // Loop over all of the basic blocks that are not reachable, dropping all of
2074   // their internal references. Update DDT and LVI if available.
2075   std::vector <DominatorTree::UpdateType> Updates;
2076   for (Function::iterator I = ++F.begin(), E = F.end(); I != E; ++I) {
2077     auto *BB = &*I;
2078     if (Reachable.count(BB))
2079       continue;
2080     for (BasicBlock *Successor : successors(BB)) {
2081       if (Reachable.count(Successor))
2082         Successor->removePredecessor(BB);
2083       if (DDT)
2084         Updates.push_back({DominatorTree::Delete, BB, Successor});
2085     }
2086     if (LVI)
2087       LVI->eraseBlock(BB);
2088     BB->dropAllReferences();
2089   }
2090 
2091   for (Function::iterator I = ++F.begin(); I != F.end();) {
2092     auto *BB = &*I;
2093     if (Reachable.count(BB)) {
2094       ++I;
2095       continue;
2096     }
2097     if (DDT) {
2098       DDT->deleteBB(BB); // deferred deletion of BB.
2099       ++I;
2100     } else {
2101       I = F.getBasicBlockList().erase(I);
2102     }
2103   }
2104 
2105   if (DDT)
2106     DDT->applyUpdates(Updates);
2107   return true;
2108 }
2109 
2110 void llvm::combineMetadata(Instruction *K, const Instruction *J,
2111                            ArrayRef<unsigned> KnownIDs) {
2112   SmallVector<std::pair<unsigned, MDNode *>, 4> Metadata;
2113   K->dropUnknownNonDebugMetadata(KnownIDs);
2114   K->getAllMetadataOtherThanDebugLoc(Metadata);
2115   for (const auto &MD : Metadata) {
2116     unsigned Kind = MD.first;
2117     MDNode *JMD = J->getMetadata(Kind);
2118     MDNode *KMD = MD.second;
2119 
2120     switch (Kind) {
2121       default:
2122         K->setMetadata(Kind, nullptr); // Remove unknown metadata
2123         break;
2124       case LLVMContext::MD_dbg:
2125         llvm_unreachable("getAllMetadataOtherThanDebugLoc returned a MD_dbg");
2126       case LLVMContext::MD_tbaa:
2127         K->setMetadata(Kind, MDNode::getMostGenericTBAA(JMD, KMD));
2128         break;
2129       case LLVMContext::MD_alias_scope:
2130         K->setMetadata(Kind, MDNode::getMostGenericAliasScope(JMD, KMD));
2131         break;
2132       case LLVMContext::MD_noalias:
2133       case LLVMContext::MD_mem_parallel_loop_access:
2134         K->setMetadata(Kind, MDNode::intersect(JMD, KMD));
2135         break;
2136       case LLVMContext::MD_range:
2137         K->setMetadata(Kind, MDNode::getMostGenericRange(JMD, KMD));
2138         break;
2139       case LLVMContext::MD_fpmath:
2140         K->setMetadata(Kind, MDNode::getMostGenericFPMath(JMD, KMD));
2141         break;
2142       case LLVMContext::MD_invariant_load:
2143         // Only set the !invariant.load if it is present in both instructions.
2144         K->setMetadata(Kind, JMD);
2145         break;
2146       case LLVMContext::MD_nonnull:
2147         // Only set the !nonnull if it is present in both instructions.
2148         K->setMetadata(Kind, JMD);
2149         break;
2150       case LLVMContext::MD_invariant_group:
2151         // Preserve !invariant.group in K.
2152         break;
2153       case LLVMContext::MD_align:
2154         K->setMetadata(Kind,
2155           MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
2156         break;
2157       case LLVMContext::MD_dereferenceable:
2158       case LLVMContext::MD_dereferenceable_or_null:
2159         K->setMetadata(Kind,
2160           MDNode::getMostGenericAlignmentOrDereferenceable(JMD, KMD));
2161         break;
2162     }
2163   }
2164   // Set !invariant.group from J if J has it. If both instructions have it
2165   // then we will just pick it from J - even when they are different.
2166   // Also make sure that K is load or store - f.e. combining bitcast with load
2167   // could produce bitcast with invariant.group metadata, which is invalid.
2168   // FIXME: we should try to preserve both invariant.group md if they are
2169   // different, but right now instruction can only have one invariant.group.
2170   if (auto *JMD = J->getMetadata(LLVMContext::MD_invariant_group))
2171     if (isa<LoadInst>(K) || isa<StoreInst>(K))
2172       K->setMetadata(LLVMContext::MD_invariant_group, JMD);
2173 }
2174 
2175 void llvm::combineMetadataForCSE(Instruction *K, const Instruction *J) {
2176   unsigned KnownIDs[] = {
2177       LLVMContext::MD_tbaa,            LLVMContext::MD_alias_scope,
2178       LLVMContext::MD_noalias,         LLVMContext::MD_range,
2179       LLVMContext::MD_invariant_load,  LLVMContext::MD_nonnull,
2180       LLVMContext::MD_invariant_group, LLVMContext::MD_align,
2181       LLVMContext::MD_dereferenceable,
2182       LLVMContext::MD_dereferenceable_or_null};
2183   combineMetadata(K, J, KnownIDs);
2184 }
2185 
2186 template <typename RootType, typename DominatesFn>
2187 static unsigned replaceDominatedUsesWith(Value *From, Value *To,
2188                                          const RootType &Root,
2189                                          const DominatesFn &Dominates) {
2190   assert(From->getType() == To->getType());
2191 
2192   unsigned Count = 0;
2193   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
2194        UI != UE;) {
2195     Use &U = *UI++;
2196     if (!Dominates(Root, U))
2197       continue;
2198     U.set(To);
2199     LLVM_DEBUG(dbgs() << "Replace dominated use of '" << From->getName()
2200                       << "' as " << *To << " in " << *U << "\n");
2201     ++Count;
2202   }
2203   return Count;
2204 }
2205 
2206 unsigned llvm::replaceNonLocalUsesWith(Instruction *From, Value *To) {
2207    assert(From->getType() == To->getType());
2208    auto *BB = From->getParent();
2209    unsigned Count = 0;
2210 
2211   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
2212        UI != UE;) {
2213     Use &U = *UI++;
2214     auto *I = cast<Instruction>(U.getUser());
2215     if (I->getParent() == BB)
2216       continue;
2217     U.set(To);
2218     ++Count;
2219   }
2220   return Count;
2221 }
2222 
2223 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
2224                                         DominatorTree &DT,
2225                                         const BasicBlockEdge &Root) {
2226   auto Dominates = [&DT](const BasicBlockEdge &Root, const Use &U) {
2227     return DT.dominates(Root, U);
2228   };
2229   return ::replaceDominatedUsesWith(From, To, Root, Dominates);
2230 }
2231 
2232 unsigned llvm::replaceDominatedUsesWith(Value *From, Value *To,
2233                                         DominatorTree &DT,
2234                                         const BasicBlock *BB) {
2235   auto ProperlyDominates = [&DT](const BasicBlock *BB, const Use &U) {
2236     auto *I = cast<Instruction>(U.getUser())->getParent();
2237     return DT.properlyDominates(BB, I);
2238   };
2239   return ::replaceDominatedUsesWith(From, To, BB, ProperlyDominates);
2240 }
2241 
2242 bool llvm::callsGCLeafFunction(ImmutableCallSite CS,
2243                                const TargetLibraryInfo &TLI) {
2244   // Check if the function is specifically marked as a gc leaf function.
2245   if (CS.hasFnAttr("gc-leaf-function"))
2246     return true;
2247   if (const Function *F = CS.getCalledFunction()) {
2248     if (F->hasFnAttribute("gc-leaf-function"))
2249       return true;
2250 
2251     if (auto IID = F->getIntrinsicID())
2252       // Most LLVM intrinsics do not take safepoints.
2253       return IID != Intrinsic::experimental_gc_statepoint &&
2254              IID != Intrinsic::experimental_deoptimize;
2255   }
2256 
2257   // Lib calls can be materialized by some passes, and won't be
2258   // marked as 'gc-leaf-function.' All available Libcalls are
2259   // GC-leaf.
2260   LibFunc LF;
2261   if (TLI.getLibFunc(CS, LF)) {
2262     return TLI.has(LF);
2263   }
2264 
2265   return false;
2266 }
2267 
2268 void llvm::copyNonnullMetadata(const LoadInst &OldLI, MDNode *N,
2269                                LoadInst &NewLI) {
2270   auto *NewTy = NewLI.getType();
2271 
2272   // This only directly applies if the new type is also a pointer.
2273   if (NewTy->isPointerTy()) {
2274     NewLI.setMetadata(LLVMContext::MD_nonnull, N);
2275     return;
2276   }
2277 
2278   // The only other translation we can do is to integral loads with !range
2279   // metadata.
2280   if (!NewTy->isIntegerTy())
2281     return;
2282 
2283   MDBuilder MDB(NewLI.getContext());
2284   const Value *Ptr = OldLI.getPointerOperand();
2285   auto *ITy = cast<IntegerType>(NewTy);
2286   auto *NullInt = ConstantExpr::getPtrToInt(
2287       ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
2288   auto *NonNullInt = ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
2289   NewLI.setMetadata(LLVMContext::MD_range,
2290                     MDB.createRange(NonNullInt, NullInt));
2291 }
2292 
2293 void llvm::copyRangeMetadata(const DataLayout &DL, const LoadInst &OldLI,
2294                              MDNode *N, LoadInst &NewLI) {
2295   auto *NewTy = NewLI.getType();
2296 
2297   // Give up unless it is converted to a pointer where there is a single very
2298   // valuable mapping we can do reliably.
2299   // FIXME: It would be nice to propagate this in more ways, but the type
2300   // conversions make it hard.
2301   if (!NewTy->isPointerTy())
2302     return;
2303 
2304   unsigned BitWidth = DL.getIndexTypeSizeInBits(NewTy);
2305   if (!getConstantRangeFromMetadata(*N).contains(APInt(BitWidth, 0))) {
2306     MDNode *NN = MDNode::get(OldLI.getContext(), None);
2307     NewLI.setMetadata(LLVMContext::MD_nonnull, NN);
2308   }
2309 }
2310 
2311 namespace {
2312 
2313 /// A potential constituent of a bitreverse or bswap expression. See
2314 /// collectBitParts for a fuller explanation.
2315 struct BitPart {
2316   BitPart(Value *P, unsigned BW) : Provider(P) {
2317     Provenance.resize(BW);
2318   }
2319 
2320   /// The Value that this is a bitreverse/bswap of.
2321   Value *Provider;
2322 
2323   /// The "provenance" of each bit. Provenance[A] = B means that bit A
2324   /// in Provider becomes bit B in the result of this expression.
2325   SmallVector<int8_t, 32> Provenance; // int8_t means max size is i128.
2326 
2327   enum { Unset = -1 };
2328 };
2329 
2330 } // end anonymous namespace
2331 
2332 /// Analyze the specified subexpression and see if it is capable of providing
2333 /// pieces of a bswap or bitreverse. The subexpression provides a potential
2334 /// piece of a bswap or bitreverse if it can be proven that each non-zero bit in
2335 /// the output of the expression came from a corresponding bit in some other
2336 /// value. This function is recursive, and the end result is a mapping of
2337 /// bitnumber to bitnumber. It is the caller's responsibility to validate that
2338 /// the bitnumber to bitnumber mapping is correct for a bswap or bitreverse.
2339 ///
2340 /// For example, if the current subexpression if "(shl i32 %X, 24)" then we know
2341 /// that the expression deposits the low byte of %X into the high byte of the
2342 /// result and that all other bits are zero. This expression is accepted and a
2343 /// BitPart is returned with Provider set to %X and Provenance[24-31] set to
2344 /// [0-7].
2345 ///
2346 /// To avoid revisiting values, the BitPart results are memoized into the
2347 /// provided map. To avoid unnecessary copying of BitParts, BitParts are
2348 /// constructed in-place in the \c BPS map. Because of this \c BPS needs to
2349 /// store BitParts objects, not pointers. As we need the concept of a nullptr
2350 /// BitParts (Value has been analyzed and the analysis failed), we an Optional
2351 /// type instead to provide the same functionality.
2352 ///
2353 /// Because we pass around references into \c BPS, we must use a container that
2354 /// does not invalidate internal references (std::map instead of DenseMap).
2355 static const Optional<BitPart> &
2356 collectBitParts(Value *V, bool MatchBSwaps, bool MatchBitReversals,
2357                 std::map<Value *, Optional<BitPart>> &BPS) {
2358   auto I = BPS.find(V);
2359   if (I != BPS.end())
2360     return I->second;
2361 
2362   auto &Result = BPS[V] = None;
2363   auto BitWidth = cast<IntegerType>(V->getType())->getBitWidth();
2364 
2365   if (Instruction *I = dyn_cast<Instruction>(V)) {
2366     // If this is an or instruction, it may be an inner node of the bswap.
2367     if (I->getOpcode() == Instruction::Or) {
2368       auto &A = collectBitParts(I->getOperand(0), MatchBSwaps,
2369                                 MatchBitReversals, BPS);
2370       auto &B = collectBitParts(I->getOperand(1), MatchBSwaps,
2371                                 MatchBitReversals, BPS);
2372       if (!A || !B)
2373         return Result;
2374 
2375       // Try and merge the two together.
2376       if (!A->Provider || A->Provider != B->Provider)
2377         return Result;
2378 
2379       Result = BitPart(A->Provider, BitWidth);
2380       for (unsigned i = 0; i < A->Provenance.size(); ++i) {
2381         if (A->Provenance[i] != BitPart::Unset &&
2382             B->Provenance[i] != BitPart::Unset &&
2383             A->Provenance[i] != B->Provenance[i])
2384           return Result = None;
2385 
2386         if (A->Provenance[i] == BitPart::Unset)
2387           Result->Provenance[i] = B->Provenance[i];
2388         else
2389           Result->Provenance[i] = A->Provenance[i];
2390       }
2391 
2392       return Result;
2393     }
2394 
2395     // If this is a logical shift by a constant, recurse then shift the result.
2396     if (I->isLogicalShift() && isa<ConstantInt>(I->getOperand(1))) {
2397       unsigned BitShift =
2398           cast<ConstantInt>(I->getOperand(1))->getLimitedValue(~0U);
2399       // Ensure the shift amount is defined.
2400       if (BitShift > BitWidth)
2401         return Result;
2402 
2403       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2404                                   MatchBitReversals, BPS);
2405       if (!Res)
2406         return Result;
2407       Result = Res;
2408 
2409       // Perform the "shift" on BitProvenance.
2410       auto &P = Result->Provenance;
2411       if (I->getOpcode() == Instruction::Shl) {
2412         P.erase(std::prev(P.end(), BitShift), P.end());
2413         P.insert(P.begin(), BitShift, BitPart::Unset);
2414       } else {
2415         P.erase(P.begin(), std::next(P.begin(), BitShift));
2416         P.insert(P.end(), BitShift, BitPart::Unset);
2417       }
2418 
2419       return Result;
2420     }
2421 
2422     // If this is a logical 'and' with a mask that clears bits, recurse then
2423     // unset the appropriate bits.
2424     if (I->getOpcode() == Instruction::And &&
2425         isa<ConstantInt>(I->getOperand(1))) {
2426       APInt Bit(I->getType()->getPrimitiveSizeInBits(), 1);
2427       const APInt &AndMask = cast<ConstantInt>(I->getOperand(1))->getValue();
2428 
2429       // Check that the mask allows a multiple of 8 bits for a bswap, for an
2430       // early exit.
2431       unsigned NumMaskedBits = AndMask.countPopulation();
2432       if (!MatchBitReversals && NumMaskedBits % 8 != 0)
2433         return Result;
2434 
2435       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2436                                   MatchBitReversals, BPS);
2437       if (!Res)
2438         return Result;
2439       Result = Res;
2440 
2441       for (unsigned i = 0; i < BitWidth; ++i, Bit <<= 1)
2442         // If the AndMask is zero for this bit, clear the bit.
2443         if ((AndMask & Bit) == 0)
2444           Result->Provenance[i] = BitPart::Unset;
2445       return Result;
2446     }
2447 
2448     // If this is a zext instruction zero extend the result.
2449     if (I->getOpcode() == Instruction::ZExt) {
2450       auto &Res = collectBitParts(I->getOperand(0), MatchBSwaps,
2451                                   MatchBitReversals, BPS);
2452       if (!Res)
2453         return Result;
2454 
2455       Result = BitPart(Res->Provider, BitWidth);
2456       auto NarrowBitWidth =
2457           cast<IntegerType>(cast<ZExtInst>(I)->getSrcTy())->getBitWidth();
2458       for (unsigned i = 0; i < NarrowBitWidth; ++i)
2459         Result->Provenance[i] = Res->Provenance[i];
2460       for (unsigned i = NarrowBitWidth; i < BitWidth; ++i)
2461         Result->Provenance[i] = BitPart::Unset;
2462       return Result;
2463     }
2464   }
2465 
2466   // Okay, we got to something that isn't a shift, 'or' or 'and'.  This must be
2467   // the input value to the bswap/bitreverse.
2468   Result = BitPart(V, BitWidth);
2469   for (unsigned i = 0; i < BitWidth; ++i)
2470     Result->Provenance[i] = i;
2471   return Result;
2472 }
2473 
2474 static bool bitTransformIsCorrectForBSwap(unsigned From, unsigned To,
2475                                           unsigned BitWidth) {
2476   if (From % 8 != To % 8)
2477     return false;
2478   // Convert from bit indices to byte indices and check for a byte reversal.
2479   From >>= 3;
2480   To >>= 3;
2481   BitWidth >>= 3;
2482   return From == BitWidth - To - 1;
2483 }
2484 
2485 static bool bitTransformIsCorrectForBitReverse(unsigned From, unsigned To,
2486                                                unsigned BitWidth) {
2487   return From == BitWidth - To - 1;
2488 }
2489 
2490 bool llvm::recognizeBSwapOrBitReverseIdiom(
2491     Instruction *I, bool MatchBSwaps, bool MatchBitReversals,
2492     SmallVectorImpl<Instruction *> &InsertedInsts) {
2493   if (Operator::getOpcode(I) != Instruction::Or)
2494     return false;
2495   if (!MatchBSwaps && !MatchBitReversals)
2496     return false;
2497   IntegerType *ITy = dyn_cast<IntegerType>(I->getType());
2498   if (!ITy || ITy->getBitWidth() > 128)
2499     return false;   // Can't do vectors or integers > 128 bits.
2500   unsigned BW = ITy->getBitWidth();
2501 
2502   unsigned DemandedBW = BW;
2503   IntegerType *DemandedTy = ITy;
2504   if (I->hasOneUse()) {
2505     if (TruncInst *Trunc = dyn_cast<TruncInst>(I->user_back())) {
2506       DemandedTy = cast<IntegerType>(Trunc->getType());
2507       DemandedBW = DemandedTy->getBitWidth();
2508     }
2509   }
2510 
2511   // Try to find all the pieces corresponding to the bswap.
2512   std::map<Value *, Optional<BitPart>> BPS;
2513   auto Res = collectBitParts(I, MatchBSwaps, MatchBitReversals, BPS);
2514   if (!Res)
2515     return false;
2516   auto &BitProvenance = Res->Provenance;
2517 
2518   // Now, is the bit permutation correct for a bswap or a bitreverse? We can
2519   // only byteswap values with an even number of bytes.
2520   bool OKForBSwap = DemandedBW % 16 == 0, OKForBitReverse = true;
2521   for (unsigned i = 0; i < DemandedBW; ++i) {
2522     OKForBSwap &=
2523         bitTransformIsCorrectForBSwap(BitProvenance[i], i, DemandedBW);
2524     OKForBitReverse &=
2525         bitTransformIsCorrectForBitReverse(BitProvenance[i], i, DemandedBW);
2526   }
2527 
2528   Intrinsic::ID Intrin;
2529   if (OKForBSwap && MatchBSwaps)
2530     Intrin = Intrinsic::bswap;
2531   else if (OKForBitReverse && MatchBitReversals)
2532     Intrin = Intrinsic::bitreverse;
2533   else
2534     return false;
2535 
2536   if (ITy != DemandedTy) {
2537     Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, DemandedTy);
2538     Value *Provider = Res->Provider;
2539     IntegerType *ProviderTy = cast<IntegerType>(Provider->getType());
2540     // We may need to truncate the provider.
2541     if (DemandedTy != ProviderTy) {
2542       auto *Trunc = CastInst::Create(Instruction::Trunc, Provider, DemandedTy,
2543                                      "trunc", I);
2544       InsertedInsts.push_back(Trunc);
2545       Provider = Trunc;
2546     }
2547     auto *CI = CallInst::Create(F, Provider, "rev", I);
2548     InsertedInsts.push_back(CI);
2549     auto *ExtInst = CastInst::Create(Instruction::ZExt, CI, ITy, "zext", I);
2550     InsertedInsts.push_back(ExtInst);
2551     return true;
2552   }
2553 
2554   Function *F = Intrinsic::getDeclaration(I->getModule(), Intrin, ITy);
2555   InsertedInsts.push_back(CallInst::Create(F, Res->Provider, "rev", I));
2556   return true;
2557 }
2558 
2559 // CodeGen has special handling for some string functions that may replace
2560 // them with target-specific intrinsics.  Since that'd skip our interceptors
2561 // in ASan/MSan/TSan/DFSan, and thus make us miss some memory accesses,
2562 // we mark affected calls as NoBuiltin, which will disable optimization
2563 // in CodeGen.
2564 void llvm::maybeMarkSanitizerLibraryCallNoBuiltin(
2565     CallInst *CI, const TargetLibraryInfo *TLI) {
2566   Function *F = CI->getCalledFunction();
2567   LibFunc Func;
2568   if (F && !F->hasLocalLinkage() && F->hasName() &&
2569       TLI->getLibFunc(F->getName(), Func) && TLI->hasOptimizedCodeGen(Func) &&
2570       !F->doesNotAccessMemory())
2571     CI->addAttribute(AttributeList::FunctionIndex, Attribute::NoBuiltin);
2572 }
2573 
2574 bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
2575   // We can't have a PHI with a metadata type.
2576   if (I->getOperand(OpIdx)->getType()->isMetadataTy())
2577     return false;
2578 
2579   // Early exit.
2580   if (!isa<Constant>(I->getOperand(OpIdx)))
2581     return true;
2582 
2583   switch (I->getOpcode()) {
2584   default:
2585     return true;
2586   case Instruction::Call:
2587   case Instruction::Invoke:
2588     // Can't handle inline asm. Skip it.
2589     if (isa<InlineAsm>(ImmutableCallSite(I).getCalledValue()))
2590       return false;
2591     // Many arithmetic intrinsics have no issue taking a
2592     // variable, however it's hard to distingish these from
2593     // specials such as @llvm.frameaddress that require a constant.
2594     if (isa<IntrinsicInst>(I))
2595       return false;
2596 
2597     // Constant bundle operands may need to retain their constant-ness for
2598     // correctness.
2599     if (ImmutableCallSite(I).isBundleOperand(OpIdx))
2600       return false;
2601     return true;
2602   case Instruction::ShuffleVector:
2603     // Shufflevector masks are constant.
2604     return OpIdx != 2;
2605   case Instruction::Switch:
2606   case Instruction::ExtractValue:
2607     // All operands apart from the first are constant.
2608     return OpIdx == 0;
2609   case Instruction::InsertValue:
2610     // All operands apart from the first and the second are constant.
2611     return OpIdx < 2;
2612   case Instruction::Alloca:
2613     // Static allocas (constant size in the entry block) are handled by
2614     // prologue/epilogue insertion so they're free anyway. We definitely don't
2615     // want to make them non-constant.
2616     return !cast<AllocaInst>(I)->isStaticAlloca();
2617   case Instruction::GetElementPtr:
2618     if (OpIdx == 0)
2619       return true;
2620     gep_type_iterator It = gep_type_begin(I);
2621     for (auto E = std::next(It, OpIdx); It != E; ++It)
2622       if (It.isStruct())
2623         return false;
2624     return true;
2625   }
2626 }
2627