1 //===- InstCombineLoadStoreAlloca.cpp -------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the visit functions for load, store and alloca.
10 //
11 //===----------------------------------------------------------------------===//
12
13 #include "InstCombineInternal.h"
14 #include "llvm/ADT/MapVector.h"
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/Analysis/Loads.h"
18 #include "llvm/Transforms/Utils/Local.h"
19 #include "llvm/IR/ConstantRange.h"
20 #include "llvm/IR/DataLayout.h"
21 #include "llvm/IR/DebugInfoMetadata.h"
22 #include "llvm/IR/IntrinsicInst.h"
23 #include "llvm/IR/LLVMContext.h"
24 #include "llvm/IR/MDBuilder.h"
25 #include "llvm/IR/PatternMatch.h"
26 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
27 using namespace llvm;
28 using namespace PatternMatch;
29
30 #define DEBUG_TYPE "instcombine"
31
32 STATISTIC(NumDeadStore, "Number of dead stores eliminated");
33 STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global");
34
35 /// pointsToConstantGlobal - Return true if V (possibly indirectly) points to
36 /// some part of a constant global variable. This intentionally only accepts
37 /// constant expressions because we can't rewrite arbitrary instructions.
pointsToConstantGlobal(Value * V)38 static bool pointsToConstantGlobal(Value *V) {
39 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
40 return GV->isConstant();
41
42 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
43 if (CE->getOpcode() == Instruction::BitCast ||
44 CE->getOpcode() == Instruction::AddrSpaceCast ||
45 CE->getOpcode() == Instruction::GetElementPtr)
46 return pointsToConstantGlobal(CE->getOperand(0));
47 }
48 return false;
49 }
50
51 /// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
52 /// pointer to an alloca. Ignore any reads of the pointer, return false if we
53 /// see any stores or other unknown uses. If we see pointer arithmetic, keep
54 /// track of whether it moves the pointer (with IsOffset) but otherwise traverse
55 /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
56 /// the alloca, and if the source pointer is a pointer to a constant global, we
57 /// can optimize this.
58 static bool
isOnlyCopiedFromConstantGlobal(Value * V,MemTransferInst * & TheCopy,SmallVectorImpl<Instruction * > & ToDelete)59 isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
60 SmallVectorImpl<Instruction *> &ToDelete) {
61 // We track lifetime intrinsics as we encounter them. If we decide to go
62 // ahead and replace the value with the global, this lets the caller quickly
63 // eliminate the markers.
64
65 SmallVector<std::pair<Value *, bool>, 35> ValuesToInspect;
66 ValuesToInspect.emplace_back(V, false);
67 while (!ValuesToInspect.empty()) {
68 auto ValuePair = ValuesToInspect.pop_back_val();
69 const bool IsOffset = ValuePair.second;
70 for (auto &U : ValuePair.first->uses()) {
71 auto *I = cast<Instruction>(U.getUser());
72
73 if (auto *LI = dyn_cast<LoadInst>(I)) {
74 // Ignore non-volatile loads, they are always ok.
75 if (!LI->isSimple()) return false;
76 continue;
77 }
78
79 if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
80 // If uses of the bitcast are ok, we are ok.
81 ValuesToInspect.emplace_back(I, IsOffset);
82 continue;
83 }
84 if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
85 // If the GEP has all zero indices, it doesn't offset the pointer. If it
86 // doesn't, it does.
87 ValuesToInspect.emplace_back(I, IsOffset || !GEP->hasAllZeroIndices());
88 continue;
89 }
90
91 if (auto *Call = dyn_cast<CallBase>(I)) {
92 // If this is the function being called then we treat it like a load and
93 // ignore it.
94 if (Call->isCallee(&U))
95 continue;
96
97 unsigned DataOpNo = Call->getDataOperandNo(&U);
98 bool IsArgOperand = Call->isArgOperand(&U);
99
100 // Inalloca arguments are clobbered by the call.
101 if (IsArgOperand && Call->isInAllocaArgument(DataOpNo))
102 return false;
103
104 // If this is a readonly/readnone call site, then we know it is just a
105 // load (but one that potentially returns the value itself), so we can
106 // ignore it if we know that the value isn't captured.
107 if (Call->onlyReadsMemory() &&
108 (Call->use_empty() || Call->doesNotCapture(DataOpNo)))
109 continue;
110
111 // If this is being passed as a byval argument, the caller is making a
112 // copy, so it is only a read of the alloca.
113 if (IsArgOperand && Call->isByValArgument(DataOpNo))
114 continue;
115 }
116
117 // Lifetime intrinsics can be handled by the caller.
118 if (I->isLifetimeStartOrEnd()) {
119 assert(I->use_empty() && "Lifetime markers have no result to use!");
120 ToDelete.push_back(I);
121 continue;
122 }
123
124 // If this is isn't our memcpy/memmove, reject it as something we can't
125 // handle.
126 MemTransferInst *MI = dyn_cast<MemTransferInst>(I);
127 if (!MI)
128 return false;
129
130 // If the transfer is using the alloca as a source of the transfer, then
131 // ignore it since it is a load (unless the transfer is volatile).
132 if (U.getOperandNo() == 1) {
133 if (MI->isVolatile()) return false;
134 continue;
135 }
136
137 // If we already have seen a copy, reject the second one.
138 if (TheCopy) return false;
139
140 // If the pointer has been offset from the start of the alloca, we can't
141 // safely handle this.
142 if (IsOffset) return false;
143
144 // If the memintrinsic isn't using the alloca as the dest, reject it.
145 if (U.getOperandNo() != 0) return false;
146
147 // If the source of the memcpy/move is not a constant global, reject it.
148 if (!pointsToConstantGlobal(MI->getSource()))
149 return false;
150
151 // Otherwise, the transform is safe. Remember the copy instruction.
152 TheCopy = MI;
153 }
154 }
155 return true;
156 }
157
158 /// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
159 /// modified by a copy from a constant global. If we can prove this, we can
160 /// replace any uses of the alloca with uses of the global directly.
161 static MemTransferInst *
isOnlyCopiedFromConstantGlobal(AllocaInst * AI,SmallVectorImpl<Instruction * > & ToDelete)162 isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
163 SmallVectorImpl<Instruction *> &ToDelete) {
164 MemTransferInst *TheCopy = nullptr;
165 if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete))
166 return TheCopy;
167 return nullptr;
168 }
169
170 /// Returns true if V is dereferenceable for size of alloca.
isDereferenceableForAllocaSize(const Value * V,const AllocaInst * AI,const DataLayout & DL)171 static bool isDereferenceableForAllocaSize(const Value *V, const AllocaInst *AI,
172 const DataLayout &DL) {
173 if (AI->isArrayAllocation())
174 return false;
175 uint64_t AllocaSize = DL.getTypeStoreSize(AI->getAllocatedType());
176 if (!AllocaSize)
177 return false;
178 return isDereferenceableAndAlignedPointer(V, AI->getAlignment(),
179 APInt(64, AllocaSize), DL);
180 }
181
simplifyAllocaArraySize(InstCombiner & IC,AllocaInst & AI)182 static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
183 // Check for array size of 1 (scalar allocation).
184 if (!AI.isArrayAllocation()) {
185 // i32 1 is the canonical array size for scalar allocations.
186 if (AI.getArraySize()->getType()->isIntegerTy(32))
187 return nullptr;
188
189 // Canonicalize it.
190 Value *V = IC.Builder.getInt32(1);
191 AI.setOperand(0, V);
192 return &AI;
193 }
194
195 // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
196 if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
197 if (C->getValue().getActiveBits() <= 64) {
198 Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
199 AllocaInst *New = IC.Builder.CreateAlloca(NewTy, nullptr, AI.getName());
200 New->setAlignment(AI.getAlignment());
201
202 // Scan to the end of the allocation instructions, to skip over a block of
203 // allocas if possible...also skip interleaved debug info
204 //
205 BasicBlock::iterator It(New);
206 while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It))
207 ++It;
208
209 // Now that I is pointing to the first non-allocation-inst in the block,
210 // insert our getelementptr instruction...
211 //
212 Type *IdxTy = IC.getDataLayout().getIntPtrType(AI.getType());
213 Value *NullIdx = Constant::getNullValue(IdxTy);
214 Value *Idx[2] = {NullIdx, NullIdx};
215 Instruction *GEP = GetElementPtrInst::CreateInBounds(
216 NewTy, New, Idx, New->getName() + ".sub");
217 IC.InsertNewInstBefore(GEP, *It);
218
219 // Now make everything use the getelementptr instead of the original
220 // allocation.
221 return IC.replaceInstUsesWith(AI, GEP);
222 }
223 }
224
225 if (isa<UndefValue>(AI.getArraySize()))
226 return IC.replaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
227
228 // Ensure that the alloca array size argument has type intptr_t, so that
229 // any casting is exposed early.
230 Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
231 if (AI.getArraySize()->getType() != IntPtrTy) {
232 Value *V = IC.Builder.CreateIntCast(AI.getArraySize(), IntPtrTy, false);
233 AI.setOperand(0, V);
234 return &AI;
235 }
236
237 return nullptr;
238 }
239
240 namespace {
241 // If I and V are pointers in different address space, it is not allowed to
242 // use replaceAllUsesWith since I and V have different types. A
243 // non-target-specific transformation should not use addrspacecast on V since
244 // the two address space may be disjoint depending on target.
245 //
246 // This class chases down uses of the old pointer until reaching the load
247 // instructions, then replaces the old pointer in the load instructions with
248 // the new pointer. If during the chasing it sees bitcast or GEP, it will
249 // create new bitcast or GEP with the new pointer and use them in the load
250 // instruction.
251 class PointerReplacer {
252 public:
PointerReplacer(InstCombiner & IC)253 PointerReplacer(InstCombiner &IC) : IC(IC) {}
254 void replacePointer(Instruction &I, Value *V);
255
256 private:
257 void findLoadAndReplace(Instruction &I);
258 void replace(Instruction *I);
259 Value *getReplacement(Value *I);
260
261 SmallVector<Instruction *, 4> Path;
262 MapVector<Value *, Value *> WorkMap;
263 InstCombiner &IC;
264 };
265 } // end anonymous namespace
266
findLoadAndReplace(Instruction & I)267 void PointerReplacer::findLoadAndReplace(Instruction &I) {
268 for (auto U : I.users()) {
269 auto *Inst = dyn_cast<Instruction>(&*U);
270 if (!Inst)
271 return;
272 LLVM_DEBUG(dbgs() << "Found pointer user: " << *U << '\n');
273 if (isa<LoadInst>(Inst)) {
274 for (auto P : Path)
275 replace(P);
276 replace(Inst);
277 } else if (isa<GetElementPtrInst>(Inst) || isa<BitCastInst>(Inst)) {
278 Path.push_back(Inst);
279 findLoadAndReplace(*Inst);
280 Path.pop_back();
281 } else {
282 return;
283 }
284 }
285 }
286
getReplacement(Value * V)287 Value *PointerReplacer::getReplacement(Value *V) {
288 auto Loc = WorkMap.find(V);
289 if (Loc != WorkMap.end())
290 return Loc->second;
291 return nullptr;
292 }
293
replace(Instruction * I)294 void PointerReplacer::replace(Instruction *I) {
295 if (getReplacement(I))
296 return;
297
298 if (auto *LT = dyn_cast<LoadInst>(I)) {
299 auto *V = getReplacement(LT->getPointerOperand());
300 assert(V && "Operand not replaced");
301 auto *NewI = new LoadInst(I->getType(), V);
302 NewI->takeName(LT);
303 IC.InsertNewInstWith(NewI, *LT);
304 IC.replaceInstUsesWith(*LT, NewI);
305 WorkMap[LT] = NewI;
306 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
307 auto *V = getReplacement(GEP->getPointerOperand());
308 assert(V && "Operand not replaced");
309 SmallVector<Value *, 8> Indices;
310 Indices.append(GEP->idx_begin(), GEP->idx_end());
311 auto *NewI = GetElementPtrInst::Create(
312 V->getType()->getPointerElementType(), V, Indices);
313 IC.InsertNewInstWith(NewI, *GEP);
314 NewI->takeName(GEP);
315 WorkMap[GEP] = NewI;
316 } else if (auto *BC = dyn_cast<BitCastInst>(I)) {
317 auto *V = getReplacement(BC->getOperand(0));
318 assert(V && "Operand not replaced");
319 auto *NewT = PointerType::get(BC->getType()->getPointerElementType(),
320 V->getType()->getPointerAddressSpace());
321 auto *NewI = new BitCastInst(V, NewT);
322 IC.InsertNewInstWith(NewI, *BC);
323 NewI->takeName(BC);
324 WorkMap[BC] = NewI;
325 } else {
326 llvm_unreachable("should never reach here");
327 }
328 }
329
replacePointer(Instruction & I,Value * V)330 void PointerReplacer::replacePointer(Instruction &I, Value *V) {
331 #ifndef NDEBUG
332 auto *PT = cast<PointerType>(I.getType());
333 auto *NT = cast<PointerType>(V->getType());
334 assert(PT != NT && PT->getElementType() == NT->getElementType() &&
335 "Invalid usage");
336 #endif
337 WorkMap[&I] = V;
338 findLoadAndReplace(I);
339 }
340
visitAllocaInst(AllocaInst & AI)341 Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
342 if (auto *I = simplifyAllocaArraySize(*this, AI))
343 return I;
344
345 if (AI.getAllocatedType()->isSized()) {
346 // If the alignment is 0 (unspecified), assign it the preferred alignment.
347 if (AI.getAlignment() == 0)
348 AI.setAlignment(DL.getPrefTypeAlignment(AI.getAllocatedType()));
349
350 // Move all alloca's of zero byte objects to the entry block and merge them
351 // together. Note that we only do this for alloca's, because malloc should
352 // allocate and return a unique pointer, even for a zero byte allocation.
353 if (DL.getTypeAllocSize(AI.getAllocatedType()) == 0) {
354 // For a zero sized alloca there is no point in doing an array allocation.
355 // This is helpful if the array size is a complicated expression not used
356 // elsewhere.
357 if (AI.isArrayAllocation()) {
358 AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1));
359 return &AI;
360 }
361
362 // Get the first instruction in the entry block.
363 BasicBlock &EntryBlock = AI.getParent()->getParent()->getEntryBlock();
364 Instruction *FirstInst = EntryBlock.getFirstNonPHIOrDbg();
365 if (FirstInst != &AI) {
366 // If the entry block doesn't start with a zero-size alloca then move
367 // this one to the start of the entry block. There is no problem with
368 // dominance as the array size was forced to a constant earlier already.
369 AllocaInst *EntryAI = dyn_cast<AllocaInst>(FirstInst);
370 if (!EntryAI || !EntryAI->getAllocatedType()->isSized() ||
371 DL.getTypeAllocSize(EntryAI->getAllocatedType()) != 0) {
372 AI.moveBefore(FirstInst);
373 return &AI;
374 }
375
376 // If the alignment of the entry block alloca is 0 (unspecified),
377 // assign it the preferred alignment.
378 if (EntryAI->getAlignment() == 0)
379 EntryAI->setAlignment(
380 DL.getPrefTypeAlignment(EntryAI->getAllocatedType()));
381 // Replace this zero-sized alloca with the one at the start of the entry
382 // block after ensuring that the address will be aligned enough for both
383 // types.
384 unsigned MaxAlign = std::max(EntryAI->getAlignment(),
385 AI.getAlignment());
386 EntryAI->setAlignment(MaxAlign);
387 if (AI.getType() != EntryAI->getType())
388 return new BitCastInst(EntryAI, AI.getType());
389 return replaceInstUsesWith(AI, EntryAI);
390 }
391 }
392 }
393
394 if (AI.getAlignment()) {
395 // Check to see if this allocation is only modified by a memcpy/memmove from
396 // a constant global whose alignment is equal to or exceeds that of the
397 // allocation. If this is the case, we can change all users to use
398 // the constant global instead. This is commonly produced by the CFE by
399 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
400 // is only subsequently read.
401 SmallVector<Instruction *, 4> ToDelete;
402 if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
403 unsigned SourceAlign = getOrEnforceKnownAlignment(
404 Copy->getSource(), AI.getAlignment(), DL, &AI, &AC, &DT);
405 if (AI.getAlignment() <= SourceAlign &&
406 isDereferenceableForAllocaSize(Copy->getSource(), &AI, DL)) {
407 LLVM_DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
408 LLVM_DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
409 for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
410 eraseInstFromFunction(*ToDelete[i]);
411 Constant *TheSrc = cast<Constant>(Copy->getSource());
412 auto *SrcTy = TheSrc->getType();
413 auto *DestTy = PointerType::get(AI.getType()->getPointerElementType(),
414 SrcTy->getPointerAddressSpace());
415 Constant *Cast =
416 ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, DestTy);
417 if (AI.getType()->getPointerAddressSpace() ==
418 SrcTy->getPointerAddressSpace()) {
419 Instruction *NewI = replaceInstUsesWith(AI, Cast);
420 eraseInstFromFunction(*Copy);
421 ++NumGlobalCopies;
422 return NewI;
423 } else {
424 PointerReplacer PtrReplacer(*this);
425 PtrReplacer.replacePointer(AI, Cast);
426 ++NumGlobalCopies;
427 }
428 }
429 }
430 }
431
432 // At last, use the generic allocation site handler to aggressively remove
433 // unused allocas.
434 return visitAllocSite(AI);
435 }
436
437 // Are we allowed to form a atomic load or store of this type?
isSupportedAtomicType(Type * Ty)438 static bool isSupportedAtomicType(Type *Ty) {
439 return Ty->isIntOrPtrTy() || Ty->isFloatingPointTy();
440 }
441
442 /// Helper to combine a load to a new type.
443 ///
444 /// This just does the work of combining a load to a new type. It handles
445 /// metadata, etc., and returns the new instruction. The \c NewTy should be the
446 /// loaded *value* type. This will convert it to a pointer, cast the operand to
447 /// that pointer type, load it, etc.
448 ///
449 /// Note that this will create all of the instructions with whatever insert
450 /// point the \c InstCombiner currently is using.
combineLoadToNewType(InstCombiner & IC,LoadInst & LI,Type * NewTy,const Twine & Suffix="")451 static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewTy,
452 const Twine &Suffix = "") {
453 assert((!LI.isAtomic() || isSupportedAtomicType(NewTy)) &&
454 "can't fold an atomic load to requested type");
455
456 Value *Ptr = LI.getPointerOperand();
457 unsigned AS = LI.getPointerAddressSpace();
458 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
459 LI.getAllMetadata(MD);
460
461 Value *NewPtr = nullptr;
462 if (!(match(Ptr, m_BitCast(m_Value(NewPtr))) &&
463 NewPtr->getType()->getPointerElementType() == NewTy &&
464 NewPtr->getType()->getPointerAddressSpace() == AS))
465 NewPtr = IC.Builder.CreateBitCast(Ptr, NewTy->getPointerTo(AS));
466
467 LoadInst *NewLoad = IC.Builder.CreateAlignedLoad(
468 NewTy, NewPtr, LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
469 NewLoad->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
470 MDBuilder MDB(NewLoad->getContext());
471 for (const auto &MDPair : MD) {
472 unsigned ID = MDPair.first;
473 MDNode *N = MDPair.second;
474 // Note, essentially every kind of metadata should be preserved here! This
475 // routine is supposed to clone a load instruction changing *only its type*.
476 // The only metadata it makes sense to drop is metadata which is invalidated
477 // when the pointer type changes. This should essentially never be the case
478 // in LLVM, but we explicitly switch over only known metadata to be
479 // conservatively correct. If you are adding metadata to LLVM which pertains
480 // to loads, you almost certainly want to add it here.
481 switch (ID) {
482 case LLVMContext::MD_dbg:
483 case LLVMContext::MD_tbaa:
484 case LLVMContext::MD_prof:
485 case LLVMContext::MD_fpmath:
486 case LLVMContext::MD_tbaa_struct:
487 case LLVMContext::MD_invariant_load:
488 case LLVMContext::MD_alias_scope:
489 case LLVMContext::MD_noalias:
490 case LLVMContext::MD_nontemporal:
491 case LLVMContext::MD_mem_parallel_loop_access:
492 case LLVMContext::MD_access_group:
493 // All of these directly apply.
494 NewLoad->setMetadata(ID, N);
495 break;
496
497 case LLVMContext::MD_nonnull:
498 copyNonnullMetadata(LI, N, *NewLoad);
499 break;
500 case LLVMContext::MD_align:
501 case LLVMContext::MD_dereferenceable:
502 case LLVMContext::MD_dereferenceable_or_null:
503 // These only directly apply if the new type is also a pointer.
504 if (NewTy->isPointerTy())
505 NewLoad->setMetadata(ID, N);
506 break;
507 case LLVMContext::MD_range:
508 copyRangeMetadata(IC.getDataLayout(), LI, N, *NewLoad);
509 break;
510 }
511 }
512 return NewLoad;
513 }
514
515 /// Combine a store to a new type.
516 ///
517 /// Returns the newly created store instruction.
combineStoreToNewValue(InstCombiner & IC,StoreInst & SI,Value * V)518 static StoreInst *combineStoreToNewValue(InstCombiner &IC, StoreInst &SI, Value *V) {
519 assert((!SI.isAtomic() || isSupportedAtomicType(V->getType())) &&
520 "can't fold an atomic store of requested type");
521
522 Value *Ptr = SI.getPointerOperand();
523 unsigned AS = SI.getPointerAddressSpace();
524 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
525 SI.getAllMetadata(MD);
526
527 StoreInst *NewStore = IC.Builder.CreateAlignedStore(
528 V, IC.Builder.CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
529 SI.getAlignment(), SI.isVolatile());
530 NewStore->setAtomic(SI.getOrdering(), SI.getSyncScopeID());
531 for (const auto &MDPair : MD) {
532 unsigned ID = MDPair.first;
533 MDNode *N = MDPair.second;
534 // Note, essentially every kind of metadata should be preserved here! This
535 // routine is supposed to clone a store instruction changing *only its
536 // type*. The only metadata it makes sense to drop is metadata which is
537 // invalidated when the pointer type changes. This should essentially
538 // never be the case in LLVM, but we explicitly switch over only known
539 // metadata to be conservatively correct. If you are adding metadata to
540 // LLVM which pertains to stores, you almost certainly want to add it
541 // here.
542 switch (ID) {
543 case LLVMContext::MD_dbg:
544 case LLVMContext::MD_tbaa:
545 case LLVMContext::MD_prof:
546 case LLVMContext::MD_fpmath:
547 case LLVMContext::MD_tbaa_struct:
548 case LLVMContext::MD_alias_scope:
549 case LLVMContext::MD_noalias:
550 case LLVMContext::MD_nontemporal:
551 case LLVMContext::MD_mem_parallel_loop_access:
552 case LLVMContext::MD_access_group:
553 // All of these directly apply.
554 NewStore->setMetadata(ID, N);
555 break;
556 case LLVMContext::MD_invariant_load:
557 case LLVMContext::MD_nonnull:
558 case LLVMContext::MD_range:
559 case LLVMContext::MD_align:
560 case LLVMContext::MD_dereferenceable:
561 case LLVMContext::MD_dereferenceable_or_null:
562 // These don't apply for stores.
563 break;
564 }
565 }
566
567 return NewStore;
568 }
569
570 /// Returns true if instruction represent minmax pattern like:
571 /// select ((cmp load V1, load V2), V1, V2).
isMinMaxWithLoads(Value * V)572 static bool isMinMaxWithLoads(Value *V) {
573 assert(V->getType()->isPointerTy() && "Expected pointer type.");
574 // Ignore possible ty* to ixx* bitcast.
575 V = peekThroughBitcast(V);
576 // Check that select is select ((cmp load V1, load V2), V1, V2) - minmax
577 // pattern.
578 CmpInst::Predicate Pred;
579 Instruction *L1;
580 Instruction *L2;
581 Value *LHS;
582 Value *RHS;
583 if (!match(V, m_Select(m_Cmp(Pred, m_Instruction(L1), m_Instruction(L2)),
584 m_Value(LHS), m_Value(RHS))))
585 return false;
586 return (match(L1, m_Load(m_Specific(LHS))) &&
587 match(L2, m_Load(m_Specific(RHS)))) ||
588 (match(L1, m_Load(m_Specific(RHS))) &&
589 match(L2, m_Load(m_Specific(LHS))));
590 }
591
592 /// Combine loads to match the type of their uses' value after looking
593 /// through intervening bitcasts.
594 ///
595 /// The core idea here is that if the result of a load is used in an operation,
596 /// we should load the type most conducive to that operation. For example, when
597 /// loading an integer and converting that immediately to a pointer, we should
598 /// instead directly load a pointer.
599 ///
600 /// However, this routine must never change the width of a load or the number of
601 /// loads as that would introduce a semantic change. This combine is expected to
602 /// be a semantic no-op which just allows loads to more closely model the types
603 /// of their consuming operations.
604 ///
605 /// Currently, we also refuse to change the precise type used for an atomic load
606 /// or a volatile load. This is debatable, and might be reasonable to change
607 /// later. However, it is risky in case some backend or other part of LLVM is
608 /// relying on the exact type loaded to select appropriate atomic operations.
combineLoadToOperationType(InstCombiner & IC,LoadInst & LI)609 static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
610 // FIXME: We could probably with some care handle both volatile and ordered
611 // atomic loads here but it isn't clear that this is important.
612 if (!LI.isUnordered())
613 return nullptr;
614
615 if (LI.use_empty())
616 return nullptr;
617
618 // swifterror values can't be bitcasted.
619 if (LI.getPointerOperand()->isSwiftError())
620 return nullptr;
621
622 Type *Ty = LI.getType();
623 const DataLayout &DL = IC.getDataLayout();
624
625 // Try to canonicalize loads which are only ever stored to operate over
626 // integers instead of any other type. We only do this when the loaded type
627 // is sized and has a size exactly the same as its store size and the store
628 // size is a legal integer type.
629 // Do not perform canonicalization if minmax pattern is found (to avoid
630 // infinite loop).
631 if (!Ty->isIntegerTy() && Ty->isSized() &&
632 DL.isLegalInteger(DL.getTypeStoreSizeInBits(Ty)) &&
633 DL.typeSizeEqualsStoreSize(Ty) &&
634 !DL.isNonIntegralPointerType(Ty) &&
635 !isMinMaxWithLoads(
636 peekThroughBitcast(LI.getPointerOperand(), /*OneUseOnly=*/true))) {
637 if (all_of(LI.users(), [&LI](User *U) {
638 auto *SI = dyn_cast<StoreInst>(U);
639 return SI && SI->getPointerOperand() != &LI &&
640 !SI->getPointerOperand()->isSwiftError();
641 })) {
642 LoadInst *NewLoad = combineLoadToNewType(
643 IC, LI,
644 Type::getIntNTy(LI.getContext(), DL.getTypeStoreSizeInBits(Ty)));
645 // Replace all the stores with stores of the newly loaded value.
646 for (auto UI = LI.user_begin(), UE = LI.user_end(); UI != UE;) {
647 auto *SI = cast<StoreInst>(*UI++);
648 IC.Builder.SetInsertPoint(SI);
649 combineStoreToNewValue(IC, *SI, NewLoad);
650 IC.eraseInstFromFunction(*SI);
651 }
652 assert(LI.use_empty() && "Failed to remove all users of the load!");
653 // Return the old load so the combiner can delete it safely.
654 return &LI;
655 }
656 }
657
658 // Fold away bit casts of the loaded value by loading the desired type.
659 // We can do this for BitCastInsts as well as casts from and to pointer types,
660 // as long as those are noops (i.e., the source or dest type have the same
661 // bitwidth as the target's pointers).
662 if (LI.hasOneUse())
663 if (auto* CI = dyn_cast<CastInst>(LI.user_back()))
664 if (CI->isNoopCast(DL))
665 if (!LI.isAtomic() || isSupportedAtomicType(CI->getDestTy())) {
666 LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
667 CI->replaceAllUsesWith(NewLoad);
668 IC.eraseInstFromFunction(*CI);
669 return &LI;
670 }
671
672 // FIXME: We should also canonicalize loads of vectors when their elements are
673 // cast to other types.
674 return nullptr;
675 }
676
unpackLoadToAggregate(InstCombiner & IC,LoadInst & LI)677 static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
678 // FIXME: We could probably with some care handle both volatile and atomic
679 // stores here but it isn't clear that this is important.
680 if (!LI.isSimple())
681 return nullptr;
682
683 Type *T = LI.getType();
684 if (!T->isAggregateType())
685 return nullptr;
686
687 StringRef Name = LI.getName();
688 assert(LI.getAlignment() && "Alignment must be set at this point");
689
690 if (auto *ST = dyn_cast<StructType>(T)) {
691 // If the struct only have one element, we unpack.
692 auto NumElements = ST->getNumElements();
693 if (NumElements == 1) {
694 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
695 ".unpack");
696 AAMDNodes AAMD;
697 LI.getAAMetadata(AAMD);
698 NewLoad->setAAMetadata(AAMD);
699 return IC.replaceInstUsesWith(LI, IC.Builder.CreateInsertValue(
700 UndefValue::get(T), NewLoad, 0, Name));
701 }
702
703 // We don't want to break loads with padding here as we'd loose
704 // the knowledge that padding exists for the rest of the pipeline.
705 const DataLayout &DL = IC.getDataLayout();
706 auto *SL = DL.getStructLayout(ST);
707 if (SL->hasPadding())
708 return nullptr;
709
710 auto Align = LI.getAlignment();
711 if (!Align)
712 Align = DL.getABITypeAlignment(ST);
713
714 auto *Addr = LI.getPointerOperand();
715 auto *IdxType = Type::getInt32Ty(T->getContext());
716 auto *Zero = ConstantInt::get(IdxType, 0);
717
718 Value *V = UndefValue::get(T);
719 for (unsigned i = 0; i < NumElements; i++) {
720 Value *Indices[2] = {
721 Zero,
722 ConstantInt::get(IdxType, i),
723 };
724 auto *Ptr = IC.Builder.CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
725 Name + ".elt");
726 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
727 auto *L = IC.Builder.CreateAlignedLoad(ST->getElementType(i), Ptr,
728 EltAlign, Name + ".unpack");
729 // Propagate AA metadata. It'll still be valid on the narrowed load.
730 AAMDNodes AAMD;
731 LI.getAAMetadata(AAMD);
732 L->setAAMetadata(AAMD);
733 V = IC.Builder.CreateInsertValue(V, L, i);
734 }
735
736 V->setName(Name);
737 return IC.replaceInstUsesWith(LI, V);
738 }
739
740 if (auto *AT = dyn_cast<ArrayType>(T)) {
741 auto *ET = AT->getElementType();
742 auto NumElements = AT->getNumElements();
743 if (NumElements == 1) {
744 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
745 AAMDNodes AAMD;
746 LI.getAAMetadata(AAMD);
747 NewLoad->setAAMetadata(AAMD);
748 return IC.replaceInstUsesWith(LI, IC.Builder.CreateInsertValue(
749 UndefValue::get(T), NewLoad, 0, Name));
750 }
751
752 // Bail out if the array is too large. Ideally we would like to optimize
753 // arrays of arbitrary size but this has a terrible impact on compile time.
754 // The threshold here is chosen arbitrarily, maybe needs a little bit of
755 // tuning.
756 if (NumElements > IC.MaxArraySizeForCombine)
757 return nullptr;
758
759 const DataLayout &DL = IC.getDataLayout();
760 auto EltSize = DL.getTypeAllocSize(ET);
761 auto Align = LI.getAlignment();
762 if (!Align)
763 Align = DL.getABITypeAlignment(T);
764
765 auto *Addr = LI.getPointerOperand();
766 auto *IdxType = Type::getInt64Ty(T->getContext());
767 auto *Zero = ConstantInt::get(IdxType, 0);
768
769 Value *V = UndefValue::get(T);
770 uint64_t Offset = 0;
771 for (uint64_t i = 0; i < NumElements; i++) {
772 Value *Indices[2] = {
773 Zero,
774 ConstantInt::get(IdxType, i),
775 };
776 auto *Ptr = IC.Builder.CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
777 Name + ".elt");
778 auto *L = IC.Builder.CreateAlignedLoad(
779 AT->getElementType(), Ptr, MinAlign(Align, Offset), Name + ".unpack");
780 AAMDNodes AAMD;
781 LI.getAAMetadata(AAMD);
782 L->setAAMetadata(AAMD);
783 V = IC.Builder.CreateInsertValue(V, L, i);
784 Offset += EltSize;
785 }
786
787 V->setName(Name);
788 return IC.replaceInstUsesWith(LI, V);
789 }
790
791 return nullptr;
792 }
793
794 // If we can determine that all possible objects pointed to by the provided
795 // pointer value are, not only dereferenceable, but also definitively less than
796 // or equal to the provided maximum size, then return true. Otherwise, return
797 // false (constant global values and allocas fall into this category).
798 //
799 // FIXME: This should probably live in ValueTracking (or similar).
isObjectSizeLessThanOrEq(Value * V,uint64_t MaxSize,const DataLayout & DL)800 static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize,
801 const DataLayout &DL) {
802 SmallPtrSet<Value *, 4> Visited;
803 SmallVector<Value *, 4> Worklist(1, V);
804
805 do {
806 Value *P = Worklist.pop_back_val();
807 P = P->stripPointerCasts();
808
809 if (!Visited.insert(P).second)
810 continue;
811
812 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
813 Worklist.push_back(SI->getTrueValue());
814 Worklist.push_back(SI->getFalseValue());
815 continue;
816 }
817
818 if (PHINode *PN = dyn_cast<PHINode>(P)) {
819 for (Value *IncValue : PN->incoming_values())
820 Worklist.push_back(IncValue);
821 continue;
822 }
823
824 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(P)) {
825 if (GA->isInterposable())
826 return false;
827 Worklist.push_back(GA->getAliasee());
828 continue;
829 }
830
831 // If we know how big this object is, and it is less than MaxSize, continue
832 // searching. Otherwise, return false.
833 if (AllocaInst *AI = dyn_cast<AllocaInst>(P)) {
834 if (!AI->getAllocatedType()->isSized())
835 return false;
836
837 ConstantInt *CS = dyn_cast<ConstantInt>(AI->getArraySize());
838 if (!CS)
839 return false;
840
841 uint64_t TypeSize = DL.getTypeAllocSize(AI->getAllocatedType());
842 // Make sure that, even if the multiplication below would wrap as an
843 // uint64_t, we still do the right thing.
844 if ((CS->getValue().zextOrSelf(128)*APInt(128, TypeSize)).ugt(MaxSize))
845 return false;
846 continue;
847 }
848
849 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
850 if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
851 return false;
852
853 uint64_t InitSize = DL.getTypeAllocSize(GV->getValueType());
854 if (InitSize > MaxSize)
855 return false;
856 continue;
857 }
858
859 return false;
860 } while (!Worklist.empty());
861
862 return true;
863 }
864
865 // If we're indexing into an object of a known size, and the outer index is
866 // not a constant, but having any value but zero would lead to undefined
867 // behavior, replace it with zero.
868 //
869 // For example, if we have:
870 // @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
871 // ...
872 // %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x
873 // ... = load i32* %arrayidx, align 4
874 // Then we know that we can replace %x in the GEP with i64 0.
875 //
876 // FIXME: We could fold any GEP index to zero that would cause UB if it were
877 // not zero. Currently, we only handle the first such index. Also, we could
878 // also search through non-zero constant indices if we kept track of the
879 // offsets those indices implied.
canReplaceGEPIdxWithZero(InstCombiner & IC,GetElementPtrInst * GEPI,Instruction * MemI,unsigned & Idx)880 static bool canReplaceGEPIdxWithZero(InstCombiner &IC, GetElementPtrInst *GEPI,
881 Instruction *MemI, unsigned &Idx) {
882 if (GEPI->getNumOperands() < 2)
883 return false;
884
885 // Find the first non-zero index of a GEP. If all indices are zero, return
886 // one past the last index.
887 auto FirstNZIdx = [](const GetElementPtrInst *GEPI) {
888 unsigned I = 1;
889 for (unsigned IE = GEPI->getNumOperands(); I != IE; ++I) {
890 Value *V = GEPI->getOperand(I);
891 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V))
892 if (CI->isZero())
893 continue;
894
895 break;
896 }
897
898 return I;
899 };
900
901 // Skip through initial 'zero' indices, and find the corresponding pointer
902 // type. See if the next index is not a constant.
903 Idx = FirstNZIdx(GEPI);
904 if (Idx == GEPI->getNumOperands())
905 return false;
906 if (isa<Constant>(GEPI->getOperand(Idx)))
907 return false;
908
909 SmallVector<Value *, 4> Ops(GEPI->idx_begin(), GEPI->idx_begin() + Idx);
910 Type *AllocTy =
911 GetElementPtrInst::getIndexedType(GEPI->getSourceElementType(), Ops);
912 if (!AllocTy || !AllocTy->isSized())
913 return false;
914 const DataLayout &DL = IC.getDataLayout();
915 uint64_t TyAllocSize = DL.getTypeAllocSize(AllocTy);
916
917 // If there are more indices after the one we might replace with a zero, make
918 // sure they're all non-negative. If any of them are negative, the overall
919 // address being computed might be before the base address determined by the
920 // first non-zero index.
921 auto IsAllNonNegative = [&]() {
922 for (unsigned i = Idx+1, e = GEPI->getNumOperands(); i != e; ++i) {
923 KnownBits Known = IC.computeKnownBits(GEPI->getOperand(i), 0, MemI);
924 if (Known.isNonNegative())
925 continue;
926 return false;
927 }
928
929 return true;
930 };
931
932 // FIXME: If the GEP is not inbounds, and there are extra indices after the
933 // one we'll replace, those could cause the address computation to wrap
934 // (rendering the IsAllNonNegative() check below insufficient). We can do
935 // better, ignoring zero indices (and other indices we can prove small
936 // enough not to wrap).
937 if (Idx+1 != GEPI->getNumOperands() && !GEPI->isInBounds())
938 return false;
939
940 // Note that isObjectSizeLessThanOrEq will return true only if the pointer is
941 // also known to be dereferenceable.
942 return isObjectSizeLessThanOrEq(GEPI->getOperand(0), TyAllocSize, DL) &&
943 IsAllNonNegative();
944 }
945
946 // If we're indexing into an object with a variable index for the memory
947 // access, but the object has only one element, we can assume that the index
948 // will always be zero. If we replace the GEP, return it.
949 template <typename T>
replaceGEPIdxWithZero(InstCombiner & IC,Value * Ptr,T & MemI)950 static Instruction *replaceGEPIdxWithZero(InstCombiner &IC, Value *Ptr,
951 T &MemI) {
952 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) {
953 unsigned Idx;
954 if (canReplaceGEPIdxWithZero(IC, GEPI, &MemI, Idx)) {
955 Instruction *NewGEPI = GEPI->clone();
956 NewGEPI->setOperand(Idx,
957 ConstantInt::get(GEPI->getOperand(Idx)->getType(), 0));
958 NewGEPI->insertBefore(GEPI);
959 MemI.setOperand(MemI.getPointerOperandIndex(), NewGEPI);
960 return NewGEPI;
961 }
962 }
963
964 return nullptr;
965 }
966
canSimplifyNullStoreOrGEP(StoreInst & SI)967 static bool canSimplifyNullStoreOrGEP(StoreInst &SI) {
968 if (NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace()))
969 return false;
970
971 auto *Ptr = SI.getPointerOperand();
972 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr))
973 Ptr = GEPI->getOperand(0);
974 return (isa<ConstantPointerNull>(Ptr) &&
975 !NullPointerIsDefined(SI.getFunction(), SI.getPointerAddressSpace()));
976 }
977
canSimplifyNullLoadOrGEP(LoadInst & LI,Value * Op)978 static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) {
979 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
980 const Value *GEPI0 = GEPI->getOperand(0);
981 if (isa<ConstantPointerNull>(GEPI0) &&
982 !NullPointerIsDefined(LI.getFunction(), GEPI->getPointerAddressSpace()))
983 return true;
984 }
985 if (isa<UndefValue>(Op) ||
986 (isa<ConstantPointerNull>(Op) &&
987 !NullPointerIsDefined(LI.getFunction(), LI.getPointerAddressSpace())))
988 return true;
989 return false;
990 }
991
visitLoadInst(LoadInst & LI)992 Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
993 Value *Op = LI.getOperand(0);
994
995 // Try to canonicalize the loaded type.
996 if (Instruction *Res = combineLoadToOperationType(*this, LI))
997 return Res;
998
999 // Attempt to improve the alignment.
1000 unsigned KnownAlign = getOrEnforceKnownAlignment(
1001 Op, DL.getPrefTypeAlignment(LI.getType()), DL, &LI, &AC, &DT);
1002 unsigned LoadAlign = LI.getAlignment();
1003 unsigned EffectiveLoadAlign =
1004 LoadAlign != 0 ? LoadAlign : DL.getABITypeAlignment(LI.getType());
1005
1006 if (KnownAlign > EffectiveLoadAlign)
1007 LI.setAlignment(KnownAlign);
1008 else if (LoadAlign == 0)
1009 LI.setAlignment(EffectiveLoadAlign);
1010
1011 // Replace GEP indices if possible.
1012 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Op, LI)) {
1013 Worklist.Add(NewGEPI);
1014 return &LI;
1015 }
1016
1017 if (Instruction *Res = unpackLoadToAggregate(*this, LI))
1018 return Res;
1019
1020 // Do really simple store-to-load forwarding and load CSE, to catch cases
1021 // where there are several consecutive memory accesses to the same location,
1022 // separated by a few arithmetic operations.
1023 BasicBlock::iterator BBI(LI);
1024 bool IsLoadCSE = false;
1025 if (Value *AvailableVal = FindAvailableLoadedValue(
1026 &LI, LI.getParent(), BBI, DefMaxInstsToScan, AA, &IsLoadCSE)) {
1027 if (IsLoadCSE)
1028 combineMetadataForCSE(cast<LoadInst>(AvailableVal), &LI, false);
1029
1030 return replaceInstUsesWith(
1031 LI, Builder.CreateBitOrPointerCast(AvailableVal, LI.getType(),
1032 LI.getName() + ".cast"));
1033 }
1034
1035 // None of the following transforms are legal for volatile/ordered atomic
1036 // loads. Most of them do apply for unordered atomics.
1037 if (!LI.isUnordered()) return nullptr;
1038
1039 // load(gep null, ...) -> unreachable
1040 // load null/undef -> unreachable
1041 // TODO: Consider a target hook for valid address spaces for this xforms.
1042 if (canSimplifyNullLoadOrGEP(LI, Op)) {
1043 // Insert a new store to null instruction before the load to indicate
1044 // that this code is not reachable. We do this instead of inserting
1045 // an unreachable instruction directly because we cannot modify the
1046 // CFG.
1047 StoreInst *SI = new StoreInst(UndefValue::get(LI.getType()),
1048 Constant::getNullValue(Op->getType()), &LI);
1049 SI->setDebugLoc(LI.getDebugLoc());
1050 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
1051 }
1052
1053 if (Op->hasOneUse()) {
1054 // Change select and PHI nodes to select values instead of addresses: this
1055 // helps alias analysis out a lot, allows many others simplifications, and
1056 // exposes redundancy in the code.
1057 //
1058 // Note that we cannot do the transformation unless we know that the
1059 // introduced loads cannot trap! Something like this is valid as long as
1060 // the condition is always false: load (select bool %C, int* null, int* %G),
1061 // but it would not be valid if we transformed it to load from null
1062 // unconditionally.
1063 //
1064 if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
1065 // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
1066 unsigned Align = LI.getAlignment();
1067 if (isSafeToLoadUnconditionally(SI->getOperand(1), LI.getType(), Align,
1068 DL, SI) &&
1069 isSafeToLoadUnconditionally(SI->getOperand(2), LI.getType(), Align,
1070 DL, SI)) {
1071 LoadInst *V1 =
1072 Builder.CreateLoad(LI.getType(), SI->getOperand(1),
1073 SI->getOperand(1)->getName() + ".val");
1074 LoadInst *V2 =
1075 Builder.CreateLoad(LI.getType(), SI->getOperand(2),
1076 SI->getOperand(2)->getName() + ".val");
1077 assert(LI.isUnordered() && "implied by above");
1078 V1->setAlignment(Align);
1079 V1->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
1080 V2->setAlignment(Align);
1081 V2->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
1082 return SelectInst::Create(SI->getCondition(), V1, V2);
1083 }
1084
1085 // load (select (cond, null, P)) -> load P
1086 if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
1087 !NullPointerIsDefined(SI->getFunction(),
1088 LI.getPointerAddressSpace())) {
1089 LI.setOperand(0, SI->getOperand(2));
1090 return &LI;
1091 }
1092
1093 // load (select (cond, P, null)) -> load P
1094 if (isa<ConstantPointerNull>(SI->getOperand(2)) &&
1095 !NullPointerIsDefined(SI->getFunction(),
1096 LI.getPointerAddressSpace())) {
1097 LI.setOperand(0, SI->getOperand(1));
1098 return &LI;
1099 }
1100 }
1101 }
1102 return nullptr;
1103 }
1104
1105 /// Look for extractelement/insertvalue sequence that acts like a bitcast.
1106 ///
1107 /// \returns underlying value that was "cast", or nullptr otherwise.
1108 ///
1109 /// For example, if we have:
1110 ///
1111 /// %E0 = extractelement <2 x double> %U, i32 0
1112 /// %V0 = insertvalue [2 x double] undef, double %E0, 0
1113 /// %E1 = extractelement <2 x double> %U, i32 1
1114 /// %V1 = insertvalue [2 x double] %V0, double %E1, 1
1115 ///
1116 /// and the layout of a <2 x double> is isomorphic to a [2 x double],
1117 /// then %V1 can be safely approximated by a conceptual "bitcast" of %U.
1118 /// Note that %U may contain non-undef values where %V1 has undef.
likeBitCastFromVector(InstCombiner & IC,Value * V)1119 static Value *likeBitCastFromVector(InstCombiner &IC, Value *V) {
1120 Value *U = nullptr;
1121 while (auto *IV = dyn_cast<InsertValueInst>(V)) {
1122 auto *E = dyn_cast<ExtractElementInst>(IV->getInsertedValueOperand());
1123 if (!E)
1124 return nullptr;
1125 auto *W = E->getVectorOperand();
1126 if (!U)
1127 U = W;
1128 else if (U != W)
1129 return nullptr;
1130 auto *CI = dyn_cast<ConstantInt>(E->getIndexOperand());
1131 if (!CI || IV->getNumIndices() != 1 || CI->getZExtValue() != *IV->idx_begin())
1132 return nullptr;
1133 V = IV->getAggregateOperand();
1134 }
1135 if (!isa<UndefValue>(V) ||!U)
1136 return nullptr;
1137
1138 auto *UT = cast<VectorType>(U->getType());
1139 auto *VT = V->getType();
1140 // Check that types UT and VT are bitwise isomorphic.
1141 const auto &DL = IC.getDataLayout();
1142 if (DL.getTypeStoreSizeInBits(UT) != DL.getTypeStoreSizeInBits(VT)) {
1143 return nullptr;
1144 }
1145 if (auto *AT = dyn_cast<ArrayType>(VT)) {
1146 if (AT->getNumElements() != UT->getNumElements())
1147 return nullptr;
1148 } else {
1149 auto *ST = cast<StructType>(VT);
1150 if (ST->getNumElements() != UT->getNumElements())
1151 return nullptr;
1152 for (const auto *EltT : ST->elements()) {
1153 if (EltT != UT->getElementType())
1154 return nullptr;
1155 }
1156 }
1157 return U;
1158 }
1159
1160 /// Combine stores to match the type of value being stored.
1161 ///
1162 /// The core idea here is that the memory does not have any intrinsic type and
1163 /// where we can we should match the type of a store to the type of value being
1164 /// stored.
1165 ///
1166 /// However, this routine must never change the width of a store or the number of
1167 /// stores as that would introduce a semantic change. This combine is expected to
1168 /// be a semantic no-op which just allows stores to more closely model the types
1169 /// of their incoming values.
1170 ///
1171 /// Currently, we also refuse to change the precise type used for an atomic or
1172 /// volatile store. This is debatable, and might be reasonable to change later.
1173 /// However, it is risky in case some backend or other part of LLVM is relying
1174 /// on the exact type stored to select appropriate atomic operations.
1175 ///
1176 /// \returns true if the store was successfully combined away. This indicates
1177 /// the caller must erase the store instruction. We have to let the caller erase
1178 /// the store instruction as otherwise there is no way to signal whether it was
1179 /// combined or not: IC.EraseInstFromFunction returns a null pointer.
combineStoreToValueType(InstCombiner & IC,StoreInst & SI)1180 static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
1181 // FIXME: We could probably with some care handle both volatile and ordered
1182 // atomic stores here but it isn't clear that this is important.
1183 if (!SI.isUnordered())
1184 return false;
1185
1186 // swifterror values can't be bitcasted.
1187 if (SI.getPointerOperand()->isSwiftError())
1188 return false;
1189
1190 Value *V = SI.getValueOperand();
1191
1192 // Fold away bit casts of the stored value by storing the original type.
1193 if (auto *BC = dyn_cast<BitCastInst>(V)) {
1194 V = BC->getOperand(0);
1195 if (!SI.isAtomic() || isSupportedAtomicType(V->getType())) {
1196 combineStoreToNewValue(IC, SI, V);
1197 return true;
1198 }
1199 }
1200
1201 if (Value *U = likeBitCastFromVector(IC, V))
1202 if (!SI.isAtomic() || isSupportedAtomicType(U->getType())) {
1203 combineStoreToNewValue(IC, SI, U);
1204 return true;
1205 }
1206
1207 // FIXME: We should also canonicalize stores of vectors when their elements
1208 // are cast to other types.
1209 return false;
1210 }
1211
unpackStoreToAggregate(InstCombiner & IC,StoreInst & SI)1212 static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
1213 // FIXME: We could probably with some care handle both volatile and atomic
1214 // stores here but it isn't clear that this is important.
1215 if (!SI.isSimple())
1216 return false;
1217
1218 Value *V = SI.getValueOperand();
1219 Type *T = V->getType();
1220
1221 if (!T->isAggregateType())
1222 return false;
1223
1224 if (auto *ST = dyn_cast<StructType>(T)) {
1225 // If the struct only have one element, we unpack.
1226 unsigned Count = ST->getNumElements();
1227 if (Count == 1) {
1228 V = IC.Builder.CreateExtractValue(V, 0);
1229 combineStoreToNewValue(IC, SI, V);
1230 return true;
1231 }
1232
1233 // We don't want to break loads with padding here as we'd loose
1234 // the knowledge that padding exists for the rest of the pipeline.
1235 const DataLayout &DL = IC.getDataLayout();
1236 auto *SL = DL.getStructLayout(ST);
1237 if (SL->hasPadding())
1238 return false;
1239
1240 auto Align = SI.getAlignment();
1241 if (!Align)
1242 Align = DL.getABITypeAlignment(ST);
1243
1244 SmallString<16> EltName = V->getName();
1245 EltName += ".elt";
1246 auto *Addr = SI.getPointerOperand();
1247 SmallString<16> AddrName = Addr->getName();
1248 AddrName += ".repack";
1249
1250 auto *IdxType = Type::getInt32Ty(ST->getContext());
1251 auto *Zero = ConstantInt::get(IdxType, 0);
1252 for (unsigned i = 0; i < Count; i++) {
1253 Value *Indices[2] = {
1254 Zero,
1255 ConstantInt::get(IdxType, i),
1256 };
1257 auto *Ptr = IC.Builder.CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
1258 AddrName);
1259 auto *Val = IC.Builder.CreateExtractValue(V, i, EltName);
1260 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
1261 llvm::Instruction *NS = IC.Builder.CreateAlignedStore(Val, Ptr, EltAlign);
1262 AAMDNodes AAMD;
1263 SI.getAAMetadata(AAMD);
1264 NS->setAAMetadata(AAMD);
1265 }
1266
1267 return true;
1268 }
1269
1270 if (auto *AT = dyn_cast<ArrayType>(T)) {
1271 // If the array only have one element, we unpack.
1272 auto NumElements = AT->getNumElements();
1273 if (NumElements == 1) {
1274 V = IC.Builder.CreateExtractValue(V, 0);
1275 combineStoreToNewValue(IC, SI, V);
1276 return true;
1277 }
1278
1279 // Bail out if the array is too large. Ideally we would like to optimize
1280 // arrays of arbitrary size but this has a terrible impact on compile time.
1281 // The threshold here is chosen arbitrarily, maybe needs a little bit of
1282 // tuning.
1283 if (NumElements > IC.MaxArraySizeForCombine)
1284 return false;
1285
1286 const DataLayout &DL = IC.getDataLayout();
1287 auto EltSize = DL.getTypeAllocSize(AT->getElementType());
1288 auto Align = SI.getAlignment();
1289 if (!Align)
1290 Align = DL.getABITypeAlignment(T);
1291
1292 SmallString<16> EltName = V->getName();
1293 EltName += ".elt";
1294 auto *Addr = SI.getPointerOperand();
1295 SmallString<16> AddrName = Addr->getName();
1296 AddrName += ".repack";
1297
1298 auto *IdxType = Type::getInt64Ty(T->getContext());
1299 auto *Zero = ConstantInt::get(IdxType, 0);
1300
1301 uint64_t Offset = 0;
1302 for (uint64_t i = 0; i < NumElements; i++) {
1303 Value *Indices[2] = {
1304 Zero,
1305 ConstantInt::get(IdxType, i),
1306 };
1307 auto *Ptr = IC.Builder.CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
1308 AddrName);
1309 auto *Val = IC.Builder.CreateExtractValue(V, i, EltName);
1310 auto EltAlign = MinAlign(Align, Offset);
1311 Instruction *NS = IC.Builder.CreateAlignedStore(Val, Ptr, EltAlign);
1312 AAMDNodes AAMD;
1313 SI.getAAMetadata(AAMD);
1314 NS->setAAMetadata(AAMD);
1315 Offset += EltSize;
1316 }
1317
1318 return true;
1319 }
1320
1321 return false;
1322 }
1323
1324 /// equivalentAddressValues - Test if A and B will obviously have the same
1325 /// value. This includes recognizing that %t0 and %t1 will have the same
1326 /// value in code like this:
1327 /// %t0 = getelementptr \@a, 0, 3
1328 /// store i32 0, i32* %t0
1329 /// %t1 = getelementptr \@a, 0, 3
1330 /// %t2 = load i32* %t1
1331 ///
equivalentAddressValues(Value * A,Value * B)1332 static bool equivalentAddressValues(Value *A, Value *B) {
1333 // Test if the values are trivially equivalent.
1334 if (A == B) return true;
1335
1336 // Test if the values come form identical arithmetic instructions.
1337 // This uses isIdenticalToWhenDefined instead of isIdenticalTo because
1338 // its only used to compare two uses within the same basic block, which
1339 // means that they'll always either have the same value or one of them
1340 // will have an undefined value.
1341 if (isa<BinaryOperator>(A) ||
1342 isa<CastInst>(A) ||
1343 isa<PHINode>(A) ||
1344 isa<GetElementPtrInst>(A))
1345 if (Instruction *BI = dyn_cast<Instruction>(B))
1346 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
1347 return true;
1348
1349 // Otherwise they may not be equivalent.
1350 return false;
1351 }
1352
1353 /// Converts store (bitcast (load (bitcast (select ...)))) to
1354 /// store (load (select ...)), where select is minmax:
1355 /// select ((cmp load V1, load V2), V1, V2).
removeBitcastsFromLoadStoreOnMinMax(InstCombiner & IC,StoreInst & SI)1356 static bool removeBitcastsFromLoadStoreOnMinMax(InstCombiner &IC,
1357 StoreInst &SI) {
1358 // bitcast?
1359 if (!match(SI.getPointerOperand(), m_BitCast(m_Value())))
1360 return false;
1361 // load? integer?
1362 Value *LoadAddr;
1363 if (!match(SI.getValueOperand(), m_Load(m_BitCast(m_Value(LoadAddr)))))
1364 return false;
1365 auto *LI = cast<LoadInst>(SI.getValueOperand());
1366 if (!LI->getType()->isIntegerTy())
1367 return false;
1368 if (!isMinMaxWithLoads(LoadAddr))
1369 return false;
1370
1371 if (!all_of(LI->users(), [LI, LoadAddr](User *U) {
1372 auto *SI = dyn_cast<StoreInst>(U);
1373 return SI && SI->getPointerOperand() != LI &&
1374 peekThroughBitcast(SI->getPointerOperand()) != LoadAddr &&
1375 !SI->getPointerOperand()->isSwiftError();
1376 }))
1377 return false;
1378
1379 IC.Builder.SetInsertPoint(LI);
1380 LoadInst *NewLI = combineLoadToNewType(
1381 IC, *LI, LoadAddr->getType()->getPointerElementType());
1382 // Replace all the stores with stores of the newly loaded value.
1383 for (auto *UI : LI->users()) {
1384 auto *USI = cast<StoreInst>(UI);
1385 IC.Builder.SetInsertPoint(USI);
1386 combineStoreToNewValue(IC, *USI, NewLI);
1387 }
1388 IC.replaceInstUsesWith(*LI, UndefValue::get(LI->getType()));
1389 IC.eraseInstFromFunction(*LI);
1390 return true;
1391 }
1392
visitStoreInst(StoreInst & SI)1393 Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
1394 Value *Val = SI.getOperand(0);
1395 Value *Ptr = SI.getOperand(1);
1396
1397 // Try to canonicalize the stored type.
1398 if (combineStoreToValueType(*this, SI))
1399 return eraseInstFromFunction(SI);
1400
1401 // Attempt to improve the alignment.
1402 unsigned KnownAlign = getOrEnforceKnownAlignment(
1403 Ptr, DL.getPrefTypeAlignment(Val->getType()), DL, &SI, &AC, &DT);
1404 unsigned StoreAlign = SI.getAlignment();
1405 unsigned EffectiveStoreAlign =
1406 StoreAlign != 0 ? StoreAlign : DL.getABITypeAlignment(Val->getType());
1407
1408 if (KnownAlign > EffectiveStoreAlign)
1409 SI.setAlignment(KnownAlign);
1410 else if (StoreAlign == 0)
1411 SI.setAlignment(EffectiveStoreAlign);
1412
1413 // Try to canonicalize the stored type.
1414 if (unpackStoreToAggregate(*this, SI))
1415 return eraseInstFromFunction(SI);
1416
1417 if (removeBitcastsFromLoadStoreOnMinMax(*this, SI))
1418 return eraseInstFromFunction(SI);
1419
1420 // Replace GEP indices if possible.
1421 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {
1422 Worklist.Add(NewGEPI);
1423 return &SI;
1424 }
1425
1426 // Don't hack volatile/ordered stores.
1427 // FIXME: Some bits are legal for ordered atomic stores; needs refactoring.
1428 if (!SI.isUnordered()) return nullptr;
1429
1430 // If the RHS is an alloca with a single use, zapify the store, making the
1431 // alloca dead.
1432 if (Ptr->hasOneUse()) {
1433 if (isa<AllocaInst>(Ptr))
1434 return eraseInstFromFunction(SI);
1435 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
1436 if (isa<AllocaInst>(GEP->getOperand(0))) {
1437 if (GEP->getOperand(0)->hasOneUse())
1438 return eraseInstFromFunction(SI);
1439 }
1440 }
1441 }
1442
1443 // If we have a store to a location which is known constant, we can conclude
1444 // that the store must be storing the constant value (else the memory
1445 // wouldn't be constant), and this must be a noop.
1446 if (AA->pointsToConstantMemory(Ptr))
1447 return eraseInstFromFunction(SI);
1448
1449 // Do really simple DSE, to catch cases where there are several consecutive
1450 // stores to the same location, separated by a few arithmetic operations. This
1451 // situation often occurs with bitfield accesses.
1452 BasicBlock::iterator BBI(SI);
1453 for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
1454 --ScanInsts) {
1455 --BBI;
1456 // Don't count debug info directives, lest they affect codegen,
1457 // and we skip pointer-to-pointer bitcasts, which are NOPs.
1458 if (isa<DbgInfoIntrinsic>(BBI) ||
1459 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1460 ScanInsts++;
1461 continue;
1462 }
1463
1464 if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
1465 // Prev store isn't volatile, and stores to the same location?
1466 if (PrevSI->isUnordered() && equivalentAddressValues(PrevSI->getOperand(1),
1467 SI.getOperand(1))) {
1468 ++NumDeadStore;
1469 ++BBI;
1470 eraseInstFromFunction(*PrevSI);
1471 continue;
1472 }
1473 break;
1474 }
1475
1476 // If this is a load, we have to stop. However, if the loaded value is from
1477 // the pointer we're loading and is producing the pointer we're storing,
1478 // then *this* store is dead (X = load P; store X -> P).
1479 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
1480 if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr)) {
1481 assert(SI.isUnordered() && "can't eliminate ordering operation");
1482 return eraseInstFromFunction(SI);
1483 }
1484
1485 // Otherwise, this is a load from some other location. Stores before it
1486 // may not be dead.
1487 break;
1488 }
1489
1490 // Don't skip over loads, throws or things that can modify memory.
1491 if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory() || BBI->mayThrow())
1492 break;
1493 }
1494
1495 // store X, null -> turns into 'unreachable' in SimplifyCFG
1496 // store X, GEP(null, Y) -> turns into 'unreachable' in SimplifyCFG
1497 if (canSimplifyNullStoreOrGEP(SI)) {
1498 if (!isa<UndefValue>(Val)) {
1499 SI.setOperand(0, UndefValue::get(Val->getType()));
1500 if (Instruction *U = dyn_cast<Instruction>(Val))
1501 Worklist.Add(U); // Dropped a use.
1502 }
1503 return nullptr; // Do not modify these!
1504 }
1505
1506 // store undef, Ptr -> noop
1507 if (isa<UndefValue>(Val))
1508 return eraseInstFromFunction(SI);
1509
1510 // If this store is the second-to-last instruction in the basic block
1511 // (excluding debug info and bitcasts of pointers) and if the block ends with
1512 // an unconditional branch, try to move the store to the successor block.
1513 BBI = SI.getIterator();
1514 do {
1515 ++BBI;
1516 } while (isa<DbgInfoIntrinsic>(BBI) ||
1517 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
1518
1519 if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
1520 if (BI->isUnconditional())
1521 mergeStoreIntoSuccessor(SI);
1522
1523 return nullptr;
1524 }
1525
1526 /// Try to transform:
1527 /// if () { *P = v1; } else { *P = v2 }
1528 /// or:
1529 /// *P = v1; if () { *P = v2; }
1530 /// into a phi node with a store in the successor.
mergeStoreIntoSuccessor(StoreInst & SI)1531 bool InstCombiner::mergeStoreIntoSuccessor(StoreInst &SI) {
1532 assert(SI.isUnordered() &&
1533 "This code has not been audited for volatile or ordered store case.");
1534
1535 // Check if the successor block has exactly 2 incoming edges.
1536 BasicBlock *StoreBB = SI.getParent();
1537 BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
1538 if (!DestBB->hasNPredecessors(2))
1539 return false;
1540
1541 // Capture the other block (the block that doesn't contain our store).
1542 pred_iterator PredIter = pred_begin(DestBB);
1543 if (*PredIter == StoreBB)
1544 ++PredIter;
1545 BasicBlock *OtherBB = *PredIter;
1546
1547 // Bail out if all of the relevant blocks aren't distinct. This can happen,
1548 // for example, if SI is in an infinite loop.
1549 if (StoreBB == DestBB || OtherBB == DestBB)
1550 return false;
1551
1552 // Verify that the other block ends in a branch and is not otherwise empty.
1553 BasicBlock::iterator BBI(OtherBB->getTerminator());
1554 BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
1555 if (!OtherBr || BBI == OtherBB->begin())
1556 return false;
1557
1558 // If the other block ends in an unconditional branch, check for the 'if then
1559 // else' case. There is an instruction before the branch.
1560 StoreInst *OtherStore = nullptr;
1561 if (OtherBr->isUnconditional()) {
1562 --BBI;
1563 // Skip over debugging info.
1564 while (isa<DbgInfoIntrinsic>(BBI) ||
1565 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1566 if (BBI==OtherBB->begin())
1567 return false;
1568 --BBI;
1569 }
1570 // If this isn't a store, isn't a store to the same location, or is not the
1571 // right kind of store, bail out.
1572 OtherStore = dyn_cast<StoreInst>(BBI);
1573 if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
1574 !SI.isSameOperationAs(OtherStore))
1575 return false;
1576 } else {
1577 // Otherwise, the other block ended with a conditional branch. If one of the
1578 // destinations is StoreBB, then we have the if/then case.
1579 if (OtherBr->getSuccessor(0) != StoreBB &&
1580 OtherBr->getSuccessor(1) != StoreBB)
1581 return false;
1582
1583 // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
1584 // if/then triangle. See if there is a store to the same ptr as SI that
1585 // lives in OtherBB.
1586 for (;; --BBI) {
1587 // Check to see if we find the matching store.
1588 if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
1589 if (OtherStore->getOperand(1) != SI.getOperand(1) ||
1590 !SI.isSameOperationAs(OtherStore))
1591 return false;
1592 break;
1593 }
1594 // If we find something that may be using or overwriting the stored
1595 // value, or if we run out of instructions, we can't do the transform.
1596 if (BBI->mayReadFromMemory() || BBI->mayThrow() ||
1597 BBI->mayWriteToMemory() || BBI == OtherBB->begin())
1598 return false;
1599 }
1600
1601 // In order to eliminate the store in OtherBr, we have to make sure nothing
1602 // reads or overwrites the stored value in StoreBB.
1603 for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
1604 // FIXME: This should really be AA driven.
1605 if (I->mayReadFromMemory() || I->mayThrow() || I->mayWriteToMemory())
1606 return false;
1607 }
1608 }
1609
1610 // Insert a PHI node now if we need it.
1611 Value *MergedVal = OtherStore->getOperand(0);
1612 // The debug locations of the original instructions might differ. Merge them.
1613 DebugLoc MergedLoc = DILocation::getMergedLocation(SI.getDebugLoc(),
1614 OtherStore->getDebugLoc());
1615 if (MergedVal != SI.getOperand(0)) {
1616 PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge");
1617 PN->addIncoming(SI.getOperand(0), SI.getParent());
1618 PN->addIncoming(OtherStore->getOperand(0), OtherBB);
1619 MergedVal = InsertNewInstBefore(PN, DestBB->front());
1620 PN->setDebugLoc(MergedLoc);
1621 }
1622
1623 // Advance to a place where it is safe to insert the new store and insert it.
1624 BBI = DestBB->getFirstInsertionPt();
1625 StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1),
1626 SI.isVolatile(), SI.getAlignment(),
1627 SI.getOrdering(), SI.getSyncScopeID());
1628 InsertNewInstBefore(NewSI, *BBI);
1629 NewSI->setDebugLoc(MergedLoc);
1630
1631 // If the two stores had AA tags, merge them.
1632 AAMDNodes AATags;
1633 SI.getAAMetadata(AATags);
1634 if (AATags) {
1635 OtherStore->getAAMetadata(AATags, /* Merge = */ true);
1636 NewSI->setAAMetadata(AATags);
1637 }
1638
1639 // Nuke the old stores.
1640 eraseInstFromFunction(SI);
1641 eraseInstFromFunction(*OtherStore);
1642 return true;
1643 }
1644