1 //===- InstCombineLoadStoreAlloca.cpp -------------------------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the visit functions for load, store and alloca.
12 //===----------------------------------------------------------------------===//
14 #include "InstCombineInternal.h"
15 #include "llvm/ADT/SmallString.h"
16 #include "llvm/ADT/Statistic.h"
17 #include "llvm/Analysis/Loads.h"
18 #include "llvm/IR/DataLayout.h"
19 #include "llvm/IR/LLVMContext.h"
20 #include "llvm/IR/IntrinsicInst.h"
21 #include "llvm/IR/MDBuilder.h"
22 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
23 #include "llvm/Transforms/Utils/Local.h"
26 #define DEBUG_TYPE "instcombine"
28 STATISTIC(NumDeadStore, "Number of dead stores eliminated");
29 STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global");
31 /// pointsToConstantGlobal - Return true if V (possibly indirectly) points to
32 /// some part of a constant global variable. This intentionally only accepts
33 /// constant expressions because we can't rewrite arbitrary instructions.
34 static bool pointsToConstantGlobal(Value *V) {
35 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
36 return GV->isConstant();
38 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
39 if (CE->getOpcode() == Instruction::BitCast ||
40 CE->getOpcode() == Instruction::AddrSpaceCast ||
41 CE->getOpcode() == Instruction::GetElementPtr)
42 return pointsToConstantGlobal(CE->getOperand(0));
47 /// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
48 /// pointer to an alloca. Ignore any reads of the pointer, return false if we
49 /// see any stores or other unknown uses. If we see pointer arithmetic, keep
50 /// track of whether it moves the pointer (with IsOffset) but otherwise traverse
51 /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
52 /// the alloca, and if the source pointer is a pointer to a constant global, we
53 /// can optimize this.
55 isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
56 SmallVectorImpl<Instruction *> &ToDelete) {
57 // We track lifetime intrinsics as we encounter them. If we decide to go
58 // ahead and replace the value with the global, this lets the caller quickly
59 // eliminate the markers.
61 SmallVector<std::pair<Value *, bool>, 35> ValuesToInspect;
62 ValuesToInspect.push_back(std::make_pair(V, false));
63 while (!ValuesToInspect.empty()) {
64 auto ValuePair = ValuesToInspect.pop_back_val();
65 const bool IsOffset = ValuePair.second;
66 for (auto &U : ValuePair.first->uses()) {
67 Instruction *I = cast<Instruction>(U.getUser());
69 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
70 // Ignore non-volatile loads, they are always ok.
71 if (!LI->isSimple()) return false;
75 if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
76 // If uses of the bitcast are ok, we are ok.
77 ValuesToInspect.push_back(std::make_pair(I, IsOffset));
80 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
81 // If the GEP has all zero indices, it doesn't offset the pointer. If it
83 ValuesToInspect.push_back(
84 std::make_pair(I, IsOffset || !GEP->hasAllZeroIndices()));
88 if (auto CS = CallSite(I)) {
89 // If this is the function being called then we treat it like a load and
94 unsigned DataOpNo = CS.getDataOperandNo(&U);
95 bool IsArgOperand = CS.isArgOperand(&U);
97 // Inalloca arguments are clobbered by the call.
98 if (IsArgOperand && CS.isInAllocaArgument(DataOpNo))
101 // If this is a readonly/readnone call site, then we know it is just a
102 // load (but one that potentially returns the value itself), so we can
103 // ignore it if we know that the value isn't captured.
104 if (CS.onlyReadsMemory() &&
105 (CS.getInstruction()->use_empty() || CS.doesNotCapture(DataOpNo)))
108 // If this is being passed as a byval argument, the caller is making a
109 // copy, so it is only a read of the alloca.
110 if (IsArgOperand && CS.isByValArgument(DataOpNo))
114 // Lifetime intrinsics can be handled by the caller.
115 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
116 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
117 II->getIntrinsicID() == Intrinsic::lifetime_end) {
118 assert(II->use_empty() && "Lifetime markers have no result to use!");
119 ToDelete.push_back(II);
124 // If this is isn't our memcpy/memmove, reject it as something we can't
126 MemTransferInst *MI = dyn_cast<MemTransferInst>(I);
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;
137 // If we already have seen a copy, reject the second one.
138 if (TheCopy) return false;
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;
144 // If the memintrinsic isn't using the alloca as the dest, reject it.
145 if (U.getOperandNo() != 0) return false;
147 // If the source of the memcpy/move is not a constant global, reject it.
148 if (!pointsToConstantGlobal(MI->getSource()))
151 // Otherwise, the transform is safe. Remember the copy instruction.
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 *
162 isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
163 SmallVectorImpl<Instruction *> &ToDelete) {
164 MemTransferInst *TheCopy = nullptr;
165 if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete))
170 static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
171 // Check for array size of 1 (scalar allocation).
172 if (!AI.isArrayAllocation()) {
173 // i32 1 is the canonical array size for scalar allocations.
174 if (AI.getArraySize()->getType()->isIntegerTy(32))
178 Value *V = IC.Builder->getInt32(1);
183 // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
184 if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
185 Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
186 AllocaInst *New = IC.Builder->CreateAlloca(NewTy, nullptr, AI.getName());
187 New->setAlignment(AI.getAlignment());
189 // Scan to the end of the allocation instructions, to skip over a block of
190 // allocas if possible...also skip interleaved debug info
192 BasicBlock::iterator It(New);
193 while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It))
196 // Now that I is pointing to the first non-allocation-inst in the block,
197 // insert our getelementptr instruction...
199 Type *IdxTy = IC.getDataLayout().getIntPtrType(AI.getType());
200 Value *NullIdx = Constant::getNullValue(IdxTy);
201 Value *Idx[2] = {NullIdx, NullIdx};
203 GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub");
204 IC.InsertNewInstBefore(GEP, *It);
206 // Now make everything use the getelementptr instead of the original
208 return IC.replaceInstUsesWith(AI, GEP);
211 if (isa<UndefValue>(AI.getArraySize()))
212 return IC.replaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
214 // Ensure that the alloca array size argument has type intptr_t, so that
215 // any casting is exposed early.
216 Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
217 if (AI.getArraySize()->getType() != IntPtrTy) {
218 Value *V = IC.Builder->CreateIntCast(AI.getArraySize(), IntPtrTy, false);
226 Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
227 if (auto *I = simplifyAllocaArraySize(*this, AI))
230 if (AI.getAllocatedType()->isSized()) {
231 // If the alignment is 0 (unspecified), assign it the preferred alignment.
232 if (AI.getAlignment() == 0)
233 AI.setAlignment(DL.getPrefTypeAlignment(AI.getAllocatedType()));
235 // Move all alloca's of zero byte objects to the entry block and merge them
236 // together. Note that we only do this for alloca's, because malloc should
237 // allocate and return a unique pointer, even for a zero byte allocation.
238 if (DL.getTypeAllocSize(AI.getAllocatedType()) == 0) {
239 // For a zero sized alloca there is no point in doing an array allocation.
240 // This is helpful if the array size is a complicated expression not used
242 if (AI.isArrayAllocation()) {
243 AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1));
247 // Get the first instruction in the entry block.
248 BasicBlock &EntryBlock = AI.getParent()->getParent()->getEntryBlock();
249 Instruction *FirstInst = EntryBlock.getFirstNonPHIOrDbg();
250 if (FirstInst != &AI) {
251 // If the entry block doesn't start with a zero-size alloca then move
252 // this one to the start of the entry block. There is no problem with
253 // dominance as the array size was forced to a constant earlier already.
254 AllocaInst *EntryAI = dyn_cast<AllocaInst>(FirstInst);
255 if (!EntryAI || !EntryAI->getAllocatedType()->isSized() ||
256 DL.getTypeAllocSize(EntryAI->getAllocatedType()) != 0) {
257 AI.moveBefore(FirstInst);
261 // If the alignment of the entry block alloca is 0 (unspecified),
262 // assign it the preferred alignment.
263 if (EntryAI->getAlignment() == 0)
264 EntryAI->setAlignment(
265 DL.getPrefTypeAlignment(EntryAI->getAllocatedType()));
266 // Replace this zero-sized alloca with the one at the start of the entry
267 // block after ensuring that the address will be aligned enough for both
269 unsigned MaxAlign = std::max(EntryAI->getAlignment(),
271 EntryAI->setAlignment(MaxAlign);
272 if (AI.getType() != EntryAI->getType())
273 return new BitCastInst(EntryAI, AI.getType());
274 return replaceInstUsesWith(AI, EntryAI);
279 if (AI.getAlignment()) {
280 // Check to see if this allocation is only modified by a memcpy/memmove from
281 // a constant global whose alignment is equal to or exceeds that of the
282 // allocation. If this is the case, we can change all users to use
283 // the constant global instead. This is commonly produced by the CFE by
284 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
285 // is only subsequently read.
286 SmallVector<Instruction *, 4> ToDelete;
287 if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
288 unsigned SourceAlign = getOrEnforceKnownAlignment(
289 Copy->getSource(), AI.getAlignment(), DL, &AI, AC, DT);
290 if (AI.getAlignment() <= SourceAlign) {
291 DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
292 DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
293 for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
294 eraseInstFromFunction(*ToDelete[i]);
295 Constant *TheSrc = cast<Constant>(Copy->getSource());
297 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, AI.getType());
298 Instruction *NewI = replaceInstUsesWith(AI, Cast);
299 eraseInstFromFunction(*Copy);
306 // At last, use the generic allocation site handler to aggressively remove
308 return visitAllocSite(AI);
311 /// \brief Helper to combine a load to a new type.
313 /// This just does the work of combining a load to a new type. It handles
314 /// metadata, etc., and returns the new instruction. The \c NewTy should be the
315 /// loaded *value* type. This will convert it to a pointer, cast the operand to
316 /// that pointer type, load it, etc.
318 /// Note that this will create all of the instructions with whatever insert
319 /// point the \c InstCombiner currently is using.
320 static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewTy,
321 const Twine &Suffix = "") {
322 Value *Ptr = LI.getPointerOperand();
323 unsigned AS = LI.getPointerAddressSpace();
324 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
325 LI.getAllMetadata(MD);
327 LoadInst *NewLoad = IC.Builder->CreateAlignedLoad(
328 IC.Builder->CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
329 LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
330 NewLoad->setAtomic(LI.getOrdering(), LI.getSynchScope());
331 MDBuilder MDB(NewLoad->getContext());
332 for (const auto &MDPair : MD) {
333 unsigned ID = MDPair.first;
334 MDNode *N = MDPair.second;
335 // Note, essentially every kind of metadata should be preserved here! This
336 // routine is supposed to clone a load instruction changing *only its type*.
337 // The only metadata it makes sense to drop is metadata which is invalidated
338 // when the pointer type changes. This should essentially never be the case
339 // in LLVM, but we explicitly switch over only known metadata to be
340 // conservatively correct. If you are adding metadata to LLVM which pertains
341 // to loads, you almost certainly want to add it here.
343 case LLVMContext::MD_dbg:
344 case LLVMContext::MD_tbaa:
345 case LLVMContext::MD_prof:
346 case LLVMContext::MD_fpmath:
347 case LLVMContext::MD_tbaa_struct:
348 case LLVMContext::MD_invariant_load:
349 case LLVMContext::MD_alias_scope:
350 case LLVMContext::MD_noalias:
351 case LLVMContext::MD_nontemporal:
352 case LLVMContext::MD_mem_parallel_loop_access:
353 // All of these directly apply.
354 NewLoad->setMetadata(ID, N);
357 case LLVMContext::MD_nonnull:
358 // This only directly applies if the new type is also a pointer.
359 if (NewTy->isPointerTy()) {
360 NewLoad->setMetadata(ID, N);
363 // If it's integral now, translate it to !range metadata.
364 if (NewTy->isIntegerTy()) {
365 auto *ITy = cast<IntegerType>(NewTy);
366 auto *NullInt = ConstantExpr::getPtrToInt(
367 ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
369 ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
370 NewLoad->setMetadata(LLVMContext::MD_range,
371 MDB.createRange(NonNullInt, NullInt));
374 case LLVMContext::MD_align:
375 case LLVMContext::MD_dereferenceable:
376 case LLVMContext::MD_dereferenceable_or_null:
377 // These only directly apply if the new type is also a pointer.
378 if (NewTy->isPointerTy())
379 NewLoad->setMetadata(ID, N);
381 case LLVMContext::MD_range:
382 // FIXME: It would be nice to propagate this in some way, but the type
383 // conversions make it hard. If the new type is a pointer, we could
384 // translate it to !nonnull metadata.
391 /// \brief Combine a store to a new type.
393 /// Returns the newly created store instruction.
394 static StoreInst *combineStoreToNewValue(InstCombiner &IC, StoreInst &SI, Value *V) {
395 Value *Ptr = SI.getPointerOperand();
396 unsigned AS = SI.getPointerAddressSpace();
397 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
398 SI.getAllMetadata(MD);
400 StoreInst *NewStore = IC.Builder->CreateAlignedStore(
401 V, IC.Builder->CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
402 SI.getAlignment(), SI.isVolatile());
403 NewStore->setAtomic(SI.getOrdering(), SI.getSynchScope());
404 for (const auto &MDPair : MD) {
405 unsigned ID = MDPair.first;
406 MDNode *N = MDPair.second;
407 // Note, essentially every kind of metadata should be preserved here! This
408 // routine is supposed to clone a store instruction changing *only its
409 // type*. The only metadata it makes sense to drop is metadata which is
410 // invalidated when the pointer type changes. This should essentially
411 // never be the case in LLVM, but we explicitly switch over only known
412 // metadata to be conservatively correct. If you are adding metadata to
413 // LLVM which pertains to stores, you almost certainly want to add it
416 case LLVMContext::MD_dbg:
417 case LLVMContext::MD_tbaa:
418 case LLVMContext::MD_prof:
419 case LLVMContext::MD_fpmath:
420 case LLVMContext::MD_tbaa_struct:
421 case LLVMContext::MD_alias_scope:
422 case LLVMContext::MD_noalias:
423 case LLVMContext::MD_nontemporal:
424 case LLVMContext::MD_mem_parallel_loop_access:
425 // All of these directly apply.
426 NewStore->setMetadata(ID, N);
429 case LLVMContext::MD_invariant_load:
430 case LLVMContext::MD_nonnull:
431 case LLVMContext::MD_range:
432 case LLVMContext::MD_align:
433 case LLVMContext::MD_dereferenceable:
434 case LLVMContext::MD_dereferenceable_or_null:
435 // These don't apply for stores.
443 /// \brief Combine loads to match the type of their uses' value after looking
444 /// through intervening bitcasts.
446 /// The core idea here is that if the result of a load is used in an operation,
447 /// we should load the type most conducive to that operation. For example, when
448 /// loading an integer and converting that immediately to a pointer, we should
449 /// instead directly load a pointer.
451 /// However, this routine must never change the width of a load or the number of
452 /// loads as that would introduce a semantic change. This combine is expected to
453 /// be a semantic no-op which just allows loads to more closely model the types
454 /// of their consuming operations.
456 /// Currently, we also refuse to change the precise type used for an atomic load
457 /// or a volatile load. This is debatable, and might be reasonable to change
458 /// later. However, it is risky in case some backend or other part of LLVM is
459 /// relying on the exact type loaded to select appropriate atomic operations.
460 static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
461 // FIXME: We could probably with some care handle both volatile and ordered
462 // atomic loads here but it isn't clear that this is important.
463 if (!LI.isUnordered())
469 Type *Ty = LI.getType();
470 const DataLayout &DL = IC.getDataLayout();
472 // Try to canonicalize loads which are only ever stored to operate over
473 // integers instead of any other type. We only do this when the loaded type
474 // is sized and has a size exactly the same as its store size and the store
475 // size is a legal integer type.
476 if (!Ty->isIntegerTy() && Ty->isSized() &&
477 DL.isLegalInteger(DL.getTypeStoreSizeInBits(Ty)) &&
478 DL.getTypeStoreSizeInBits(Ty) == DL.getTypeSizeInBits(Ty)) {
479 if (std::all_of(LI.user_begin(), LI.user_end(), [&LI](User *U) {
480 auto *SI = dyn_cast<StoreInst>(U);
481 return SI && SI->getPointerOperand() != &LI;
483 LoadInst *NewLoad = combineLoadToNewType(
485 Type::getIntNTy(LI.getContext(), DL.getTypeStoreSizeInBits(Ty)));
486 // Replace all the stores with stores of the newly loaded value.
487 for (auto UI = LI.user_begin(), UE = LI.user_end(); UI != UE;) {
488 auto *SI = cast<StoreInst>(*UI++);
489 IC.Builder->SetInsertPoint(SI);
490 combineStoreToNewValue(IC, *SI, NewLoad);
491 IC.eraseInstFromFunction(*SI);
493 assert(LI.use_empty() && "Failed to remove all users of the load!");
494 // Return the old load so the combiner can delete it safely.
499 // Fold away bit casts of the loaded value by loading the desired type.
500 // We can do this for BitCastInsts as well as casts from and to pointer types,
501 // as long as those are noops (i.e., the source or dest type have the same
502 // bitwidth as the target's pointers).
504 if (auto* CI = dyn_cast<CastInst>(LI.user_back())) {
505 if (CI->isNoopCast(DL)) {
506 LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
507 CI->replaceAllUsesWith(NewLoad);
508 IC.eraseInstFromFunction(*CI);
513 // FIXME: We should also canonicalize loads of vectors when their elements are
514 // cast to other types.
518 static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
519 // FIXME: We could probably with some care handle both volatile and atomic
520 // stores here but it isn't clear that this is important.
524 Type *T = LI.getType();
525 if (!T->isAggregateType())
528 StringRef Name = LI.getName();
529 assert(LI.getAlignment() && "Alignment must be set at this point");
531 if (auto *ST = dyn_cast<StructType>(T)) {
532 // If the struct only have one element, we unpack.
533 auto NumElements = ST->getNumElements();
534 if (NumElements == 1) {
535 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
537 return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
538 UndefValue::get(T), NewLoad, 0, Name));
541 // We don't want to break loads with padding here as we'd loose
542 // the knowledge that padding exists for the rest of the pipeline.
543 const DataLayout &DL = IC.getDataLayout();
544 auto *SL = DL.getStructLayout(ST);
545 if (SL->hasPadding())
548 auto Align = LI.getAlignment();
550 Align = DL.getABITypeAlignment(ST);
552 auto *Addr = LI.getPointerOperand();
553 auto *IdxType = Type::getInt32Ty(T->getContext());
554 auto *Zero = ConstantInt::get(IdxType, 0);
556 Value *V = UndefValue::get(T);
557 for (unsigned i = 0; i < NumElements; i++) {
558 Value *Indices[2] = {
560 ConstantInt::get(IdxType, i),
562 auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
564 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
565 auto *L = IC.Builder->CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
566 V = IC.Builder->CreateInsertValue(V, L, i);
570 return IC.replaceInstUsesWith(LI, V);
573 if (auto *AT = dyn_cast<ArrayType>(T)) {
574 auto *ET = AT->getElementType();
575 auto NumElements = AT->getNumElements();
576 if (NumElements == 1) {
577 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
578 return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
579 UndefValue::get(T), NewLoad, 0, Name));
582 const DataLayout &DL = IC.getDataLayout();
583 auto EltSize = DL.getTypeAllocSize(ET);
584 auto Align = LI.getAlignment();
586 Align = DL.getABITypeAlignment(T);
588 auto *Addr = LI.getPointerOperand();
589 auto *IdxType = Type::getInt64Ty(T->getContext());
590 auto *Zero = ConstantInt::get(IdxType, 0);
592 Value *V = UndefValue::get(T);
594 for (uint64_t i = 0; i < NumElements; i++) {
595 Value *Indices[2] = {
597 ConstantInt::get(IdxType, i),
599 auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
601 auto *L = IC.Builder->CreateAlignedLoad(Ptr, MinAlign(Align, Offset),
603 V = IC.Builder->CreateInsertValue(V, L, i);
608 return IC.replaceInstUsesWith(LI, V);
614 // If we can determine that all possible objects pointed to by the provided
615 // pointer value are, not only dereferenceable, but also definitively less than
616 // or equal to the provided maximum size, then return true. Otherwise, return
617 // false (constant global values and allocas fall into this category).
619 // FIXME: This should probably live in ValueTracking (or similar).
620 static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize,
621 const DataLayout &DL) {
622 SmallPtrSet<Value *, 4> Visited;
623 SmallVector<Value *, 4> Worklist(1, V);
626 Value *P = Worklist.pop_back_val();
627 P = P->stripPointerCasts();
629 if (!Visited.insert(P).second)
632 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
633 Worklist.push_back(SI->getTrueValue());
634 Worklist.push_back(SI->getFalseValue());
638 if (PHINode *PN = dyn_cast<PHINode>(P)) {
639 for (Value *IncValue : PN->incoming_values())
640 Worklist.push_back(IncValue);
644 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(P)) {
645 if (GA->isInterposable())
647 Worklist.push_back(GA->getAliasee());
651 // If we know how big this object is, and it is less than MaxSize, continue
652 // searching. Otherwise, return false.
653 if (AllocaInst *AI = dyn_cast<AllocaInst>(P)) {
654 if (!AI->getAllocatedType()->isSized())
657 ConstantInt *CS = dyn_cast<ConstantInt>(AI->getArraySize());
661 uint64_t TypeSize = DL.getTypeAllocSize(AI->getAllocatedType());
662 // Make sure that, even if the multiplication below would wrap as an
663 // uint64_t, we still do the right thing.
664 if ((CS->getValue().zextOrSelf(128)*APInt(128, TypeSize)).ugt(MaxSize))
669 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
670 if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
673 uint64_t InitSize = DL.getTypeAllocSize(GV->getValueType());
674 if (InitSize > MaxSize)
680 } while (!Worklist.empty());
685 // If we're indexing into an object of a known size, and the outer index is
686 // not a constant, but having any value but zero would lead to undefined
687 // behavior, replace it with zero.
689 // For example, if we have:
690 // @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
692 // %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x
693 // ... = load i32* %arrayidx, align 4
694 // Then we know that we can replace %x in the GEP with i64 0.
696 // FIXME: We could fold any GEP index to zero that would cause UB if it were
697 // not zero. Currently, we only handle the first such index. Also, we could
698 // also search through non-zero constant indices if we kept track of the
699 // offsets those indices implied.
700 static bool canReplaceGEPIdxWithZero(InstCombiner &IC, GetElementPtrInst *GEPI,
701 Instruction *MemI, unsigned &Idx) {
702 if (GEPI->getNumOperands() < 2)
705 // Find the first non-zero index of a GEP. If all indices are zero, return
706 // one past the last index.
707 auto FirstNZIdx = [](const GetElementPtrInst *GEPI) {
709 for (unsigned IE = GEPI->getNumOperands(); I != IE; ++I) {
710 Value *V = GEPI->getOperand(I);
711 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V))
721 // Skip through initial 'zero' indices, and find the corresponding pointer
722 // type. See if the next index is not a constant.
723 Idx = FirstNZIdx(GEPI);
724 if (Idx == GEPI->getNumOperands())
726 if (isa<Constant>(GEPI->getOperand(Idx)))
729 SmallVector<Value *, 4> Ops(GEPI->idx_begin(), GEPI->idx_begin() + Idx);
731 GetElementPtrInst::getIndexedType(GEPI->getSourceElementType(), Ops);
732 if (!AllocTy || !AllocTy->isSized())
734 const DataLayout &DL = IC.getDataLayout();
735 uint64_t TyAllocSize = DL.getTypeAllocSize(AllocTy);
737 // If there are more indices after the one we might replace with a zero, make
738 // sure they're all non-negative. If any of them are negative, the overall
739 // address being computed might be before the base address determined by the
740 // first non-zero index.
741 auto IsAllNonNegative = [&]() {
742 for (unsigned i = Idx+1, e = GEPI->getNumOperands(); i != e; ++i) {
743 bool KnownNonNegative, KnownNegative;
744 IC.ComputeSignBit(GEPI->getOperand(i), KnownNonNegative,
745 KnownNegative, 0, MemI);
746 if (KnownNonNegative)
754 // FIXME: If the GEP is not inbounds, and there are extra indices after the
755 // one we'll replace, those could cause the address computation to wrap
756 // (rendering the IsAllNonNegative() check below insufficient). We can do
757 // better, ignoring zero indices (and other indices we can prove small
758 // enough not to wrap).
759 if (Idx+1 != GEPI->getNumOperands() && !GEPI->isInBounds())
762 // Note that isObjectSizeLessThanOrEq will return true only if the pointer is
763 // also known to be dereferenceable.
764 return isObjectSizeLessThanOrEq(GEPI->getOperand(0), TyAllocSize, DL) &&
768 // If we're indexing into an object with a variable index for the memory
769 // access, but the object has only one element, we can assume that the index
770 // will always be zero. If we replace the GEP, return it.
771 template <typename T>
772 static Instruction *replaceGEPIdxWithZero(InstCombiner &IC, Value *Ptr,
774 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) {
776 if (canReplaceGEPIdxWithZero(IC, GEPI, &MemI, Idx)) {
777 Instruction *NewGEPI = GEPI->clone();
778 NewGEPI->setOperand(Idx,
779 ConstantInt::get(GEPI->getOperand(Idx)->getType(), 0));
780 NewGEPI->insertBefore(GEPI);
781 MemI.setOperand(MemI.getPointerOperandIndex(), NewGEPI);
789 Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
790 Value *Op = LI.getOperand(0);
792 // Try to canonicalize the loaded type.
793 if (Instruction *Res = combineLoadToOperationType(*this, LI))
796 // Attempt to improve the alignment.
797 unsigned KnownAlign = getOrEnforceKnownAlignment(
798 Op, DL.getPrefTypeAlignment(LI.getType()), DL, &LI, AC, DT);
799 unsigned LoadAlign = LI.getAlignment();
800 unsigned EffectiveLoadAlign =
801 LoadAlign != 0 ? LoadAlign : DL.getABITypeAlignment(LI.getType());
803 if (KnownAlign > EffectiveLoadAlign)
804 LI.setAlignment(KnownAlign);
805 else if (LoadAlign == 0)
806 LI.setAlignment(EffectiveLoadAlign);
808 // Replace GEP indices if possible.
809 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Op, LI)) {
810 Worklist.Add(NewGEPI);
814 if (Instruction *Res = unpackLoadToAggregate(*this, LI))
817 // Do really simple store-to-load forwarding and load CSE, to catch cases
818 // where there are several consecutive memory accesses to the same location,
819 // separated by a few arithmetic operations.
820 BasicBlock::iterator BBI(LI);
822 bool IsLoadCSE = false;
823 if (Value *AvailableVal =
824 FindAvailableLoadedValue(&LI, LI.getParent(), BBI,
825 DefMaxInstsToScan, AA, &AATags, &IsLoadCSE)) {
827 LoadInst *NLI = cast<LoadInst>(AvailableVal);
828 unsigned KnownIDs[] = {
829 LLVMContext::MD_tbaa, LLVMContext::MD_alias_scope,
830 LLVMContext::MD_noalias, LLVMContext::MD_range,
831 LLVMContext::MD_invariant_load, LLVMContext::MD_nonnull,
832 LLVMContext::MD_invariant_group, LLVMContext::MD_align,
833 LLVMContext::MD_dereferenceable,
834 LLVMContext::MD_dereferenceable_or_null};
835 combineMetadata(NLI, &LI, KnownIDs);
838 return replaceInstUsesWith(
839 LI, Builder->CreateBitOrPointerCast(AvailableVal, LI.getType(),
840 LI.getName() + ".cast"));
843 // None of the following transforms are legal for volatile/ordered atomic
844 // loads. Most of them do apply for unordered atomics.
845 if (!LI.isUnordered()) return nullptr;
847 // load(gep null, ...) -> unreachable
848 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
849 const Value *GEPI0 = GEPI->getOperand(0);
850 // TODO: Consider a target hook for valid address spaces for this xform.
851 if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){
852 // Insert a new store to null instruction before the load to indicate
853 // that this code is not reachable. We do this instead of inserting
854 // an unreachable instruction directly because we cannot modify the
856 new StoreInst(UndefValue::get(LI.getType()),
857 Constant::getNullValue(Op->getType()), &LI);
858 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
862 // load null/undef -> unreachable
863 // TODO: Consider a target hook for valid address spaces for this xform.
864 if (isa<UndefValue>(Op) ||
865 (isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) {
866 // Insert a new store to null instruction before the load to indicate that
867 // this code is not reachable. We do this instead of inserting an
868 // unreachable instruction directly because we cannot modify the CFG.
869 new StoreInst(UndefValue::get(LI.getType()),
870 Constant::getNullValue(Op->getType()), &LI);
871 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
874 if (Op->hasOneUse()) {
875 // Change select and PHI nodes to select values instead of addresses: this
876 // helps alias analysis out a lot, allows many others simplifications, and
877 // exposes redundancy in the code.
879 // Note that we cannot do the transformation unless we know that the
880 // introduced loads cannot trap! Something like this is valid as long as
881 // the condition is always false: load (select bool %C, int* null, int* %G),
882 // but it would not be valid if we transformed it to load from null
885 if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
886 // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
887 unsigned Align = LI.getAlignment();
888 if (isSafeToLoadUnconditionally(SI->getOperand(1), Align, DL, SI) &&
889 isSafeToLoadUnconditionally(SI->getOperand(2), Align, DL, SI)) {
890 LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1),
891 SI->getOperand(1)->getName()+".val");
892 LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2),
893 SI->getOperand(2)->getName()+".val");
894 assert(LI.isUnordered() && "implied by above");
895 V1->setAlignment(Align);
896 V1->setAtomic(LI.getOrdering(), LI.getSynchScope());
897 V2->setAlignment(Align);
898 V2->setAtomic(LI.getOrdering(), LI.getSynchScope());
899 return SelectInst::Create(SI->getCondition(), V1, V2);
902 // load (select (cond, null, P)) -> load P
903 if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
904 LI.getPointerAddressSpace() == 0) {
905 LI.setOperand(0, SI->getOperand(2));
909 // load (select (cond, P, null)) -> load P
910 if (isa<ConstantPointerNull>(SI->getOperand(2)) &&
911 LI.getPointerAddressSpace() == 0) {
912 LI.setOperand(0, SI->getOperand(1));
920 /// \brief Look for extractelement/insertvalue sequence that acts like a bitcast.
922 /// \returns underlying value that was "cast", or nullptr otherwise.
924 /// For example, if we have:
926 /// %E0 = extractelement <2 x double> %U, i32 0
927 /// %V0 = insertvalue [2 x double] undef, double %E0, 0
928 /// %E1 = extractelement <2 x double> %U, i32 1
929 /// %V1 = insertvalue [2 x double] %V0, double %E1, 1
931 /// and the layout of a <2 x double> is isomorphic to a [2 x double],
932 /// then %V1 can be safely approximated by a conceptual "bitcast" of %U.
933 /// Note that %U may contain non-undef values where %V1 has undef.
934 static Value *likeBitCastFromVector(InstCombiner &IC, Value *V) {
936 while (auto *IV = dyn_cast<InsertValueInst>(V)) {
937 auto *E = dyn_cast<ExtractElementInst>(IV->getInsertedValueOperand());
940 auto *W = E->getVectorOperand();
945 auto *CI = dyn_cast<ConstantInt>(E->getIndexOperand());
946 if (!CI || IV->getNumIndices() != 1 || CI->getZExtValue() != *IV->idx_begin())
948 V = IV->getAggregateOperand();
950 if (!isa<UndefValue>(V) ||!U)
953 auto *UT = cast<VectorType>(U->getType());
954 auto *VT = V->getType();
955 // Check that types UT and VT are bitwise isomorphic.
956 const auto &DL = IC.getDataLayout();
957 if (DL.getTypeStoreSizeInBits(UT) != DL.getTypeStoreSizeInBits(VT)) {
960 if (auto *AT = dyn_cast<ArrayType>(VT)) {
961 if (AT->getNumElements() != UT->getNumElements())
964 auto *ST = cast<StructType>(VT);
965 if (ST->getNumElements() != UT->getNumElements())
967 for (const auto *EltT : ST->elements()) {
968 if (EltT != UT->getElementType())
975 /// \brief Combine stores to match the type of value being stored.
977 /// The core idea here is that the memory does not have any intrinsic type and
978 /// where we can we should match the type of a store to the type of value being
981 /// However, this routine must never change the width of a store or the number of
982 /// stores as that would introduce a semantic change. This combine is expected to
983 /// be a semantic no-op which just allows stores to more closely model the types
984 /// of their incoming values.
986 /// Currently, we also refuse to change the precise type used for an atomic or
987 /// volatile store. This is debatable, and might be reasonable to change later.
988 /// However, it is risky in case some backend or other part of LLVM is relying
989 /// on the exact type stored to select appropriate atomic operations.
991 /// \returns true if the store was successfully combined away. This indicates
992 /// the caller must erase the store instruction. We have to let the caller erase
993 /// the store instruction as otherwise there is no way to signal whether it was
994 /// combined or not: IC.EraseInstFromFunction returns a null pointer.
995 static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
996 // FIXME: We could probably with some care handle both volatile and ordered
997 // atomic stores here but it isn't clear that this is important.
998 if (!SI.isUnordered())
1001 Value *V = SI.getValueOperand();
1003 // Fold away bit casts of the stored value by storing the original type.
1004 if (auto *BC = dyn_cast<BitCastInst>(V)) {
1005 V = BC->getOperand(0);
1006 combineStoreToNewValue(IC, SI, V);
1010 if (Value *U = likeBitCastFromVector(IC, V)) {
1011 combineStoreToNewValue(IC, SI, U);
1015 // FIXME: We should also canonicalize stores of vectors when their elements
1016 // are cast to other types.
1020 static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
1021 // FIXME: We could probably with some care handle both volatile and atomic
1022 // stores here but it isn't clear that this is important.
1026 Value *V = SI.getValueOperand();
1027 Type *T = V->getType();
1029 if (!T->isAggregateType())
1032 if (auto *ST = dyn_cast<StructType>(T)) {
1033 // If the struct only have one element, we unpack.
1034 unsigned Count = ST->getNumElements();
1036 V = IC.Builder->CreateExtractValue(V, 0);
1037 combineStoreToNewValue(IC, SI, V);
1041 // We don't want to break loads with padding here as we'd loose
1042 // the knowledge that padding exists for the rest of the pipeline.
1043 const DataLayout &DL = IC.getDataLayout();
1044 auto *SL = DL.getStructLayout(ST);
1045 if (SL->hasPadding())
1048 auto Align = SI.getAlignment();
1050 Align = DL.getABITypeAlignment(ST);
1052 SmallString<16> EltName = V->getName();
1054 auto *Addr = SI.getPointerOperand();
1055 SmallString<16> AddrName = Addr->getName();
1056 AddrName += ".repack";
1058 auto *IdxType = Type::getInt32Ty(ST->getContext());
1059 auto *Zero = ConstantInt::get(IdxType, 0);
1060 for (unsigned i = 0; i < Count; i++) {
1061 Value *Indices[2] = {
1063 ConstantInt::get(IdxType, i),
1065 auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
1067 auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
1068 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
1069 IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
1075 if (auto *AT = dyn_cast<ArrayType>(T)) {
1076 // If the array only have one element, we unpack.
1077 auto NumElements = AT->getNumElements();
1078 if (NumElements == 1) {
1079 V = IC.Builder->CreateExtractValue(V, 0);
1080 combineStoreToNewValue(IC, SI, V);
1084 const DataLayout &DL = IC.getDataLayout();
1085 auto EltSize = DL.getTypeAllocSize(AT->getElementType());
1086 auto Align = SI.getAlignment();
1088 Align = DL.getABITypeAlignment(T);
1090 SmallString<16> EltName = V->getName();
1092 auto *Addr = SI.getPointerOperand();
1093 SmallString<16> AddrName = Addr->getName();
1094 AddrName += ".repack";
1096 auto *IdxType = Type::getInt64Ty(T->getContext());
1097 auto *Zero = ConstantInt::get(IdxType, 0);
1099 uint64_t Offset = 0;
1100 for (uint64_t i = 0; i < NumElements; i++) {
1101 Value *Indices[2] = {
1103 ConstantInt::get(IdxType, i),
1105 auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
1107 auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
1108 auto EltAlign = MinAlign(Align, Offset);
1109 IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
1119 /// equivalentAddressValues - Test if A and B will obviously have the same
1120 /// value. This includes recognizing that %t0 and %t1 will have the same
1121 /// value in code like this:
1122 /// %t0 = getelementptr \@a, 0, 3
1123 /// store i32 0, i32* %t0
1124 /// %t1 = getelementptr \@a, 0, 3
1125 /// %t2 = load i32* %t1
1127 static bool equivalentAddressValues(Value *A, Value *B) {
1128 // Test if the values are trivially equivalent.
1129 if (A == B) return true;
1131 // Test if the values come form identical arithmetic instructions.
1132 // This uses isIdenticalToWhenDefined instead of isIdenticalTo because
1133 // its only used to compare two uses within the same basic block, which
1134 // means that they'll always either have the same value or one of them
1135 // will have an undefined value.
1136 if (isa<BinaryOperator>(A) ||
1139 isa<GetElementPtrInst>(A))
1140 if (Instruction *BI = dyn_cast<Instruction>(B))
1141 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
1144 // Otherwise they may not be equivalent.
1148 Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
1149 Value *Val = SI.getOperand(0);
1150 Value *Ptr = SI.getOperand(1);
1152 // Try to canonicalize the stored type.
1153 if (combineStoreToValueType(*this, SI))
1154 return eraseInstFromFunction(SI);
1156 // Attempt to improve the alignment.
1157 unsigned KnownAlign = getOrEnforceKnownAlignment(
1158 Ptr, DL.getPrefTypeAlignment(Val->getType()), DL, &SI, AC, DT);
1159 unsigned StoreAlign = SI.getAlignment();
1160 unsigned EffectiveStoreAlign =
1161 StoreAlign != 0 ? StoreAlign : DL.getABITypeAlignment(Val->getType());
1163 if (KnownAlign > EffectiveStoreAlign)
1164 SI.setAlignment(KnownAlign);
1165 else if (StoreAlign == 0)
1166 SI.setAlignment(EffectiveStoreAlign);
1168 // Try to canonicalize the stored type.
1169 if (unpackStoreToAggregate(*this, SI))
1170 return eraseInstFromFunction(SI);
1172 // Replace GEP indices if possible.
1173 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {
1174 Worklist.Add(NewGEPI);
1178 // Don't hack volatile/ordered stores.
1179 // FIXME: Some bits are legal for ordered atomic stores; needs refactoring.
1180 if (!SI.isUnordered()) return nullptr;
1182 // If the RHS is an alloca with a single use, zapify the store, making the
1184 if (Ptr->hasOneUse()) {
1185 if (isa<AllocaInst>(Ptr))
1186 return eraseInstFromFunction(SI);
1187 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
1188 if (isa<AllocaInst>(GEP->getOperand(0))) {
1189 if (GEP->getOperand(0)->hasOneUse())
1190 return eraseInstFromFunction(SI);
1195 // Do really simple DSE, to catch cases where there are several consecutive
1196 // stores to the same location, separated by a few arithmetic operations. This
1197 // situation often occurs with bitfield accesses.
1198 BasicBlock::iterator BBI(SI);
1199 for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
1202 // Don't count debug info directives, lest they affect codegen,
1203 // and we skip pointer-to-pointer bitcasts, which are NOPs.
1204 if (isa<DbgInfoIntrinsic>(BBI) ||
1205 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1210 if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
1211 // Prev store isn't volatile, and stores to the same location?
1212 if (PrevSI->isUnordered() && equivalentAddressValues(PrevSI->getOperand(1),
1213 SI.getOperand(1))) {
1216 eraseInstFromFunction(*PrevSI);
1222 // If this is a load, we have to stop. However, if the loaded value is from
1223 // the pointer we're loading and is producing the pointer we're storing,
1224 // then *this* store is dead (X = load P; store X -> P).
1225 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
1226 if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr)) {
1227 assert(SI.isUnordered() && "can't eliminate ordering operation");
1228 return eraseInstFromFunction(SI);
1231 // Otherwise, this is a load from some other location. Stores before it
1236 // Don't skip over loads or things that can modify memory.
1237 if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory())
1241 // store X, null -> turns into 'unreachable' in SimplifyCFG
1242 if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
1243 if (!isa<UndefValue>(Val)) {
1244 SI.setOperand(0, UndefValue::get(Val->getType()));
1245 if (Instruction *U = dyn_cast<Instruction>(Val))
1246 Worklist.Add(U); // Dropped a use.
1248 return nullptr; // Do not modify these!
1251 // store undef, Ptr -> noop
1252 if (isa<UndefValue>(Val))
1253 return eraseInstFromFunction(SI);
1255 // If this store is the last instruction in the basic block (possibly
1256 // excepting debug info instructions), and if the block ends with an
1257 // unconditional branch, try to move it to the successor block.
1258 BBI = SI.getIterator();
1261 } while (isa<DbgInfoIntrinsic>(BBI) ||
1262 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
1263 if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
1264 if (BI->isUnconditional())
1265 if (SimplifyStoreAtEndOfBlock(SI))
1266 return nullptr; // xform done!
1271 /// SimplifyStoreAtEndOfBlock - Turn things like:
1272 /// if () { *P = v1; } else { *P = v2 }
1273 /// into a phi node with a store in the successor.
1275 /// Simplify things like:
1276 /// *P = v1; if () { *P = v2; }
1277 /// into a phi node with a store in the successor.
1279 bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
1280 assert(SI.isUnordered() &&
1281 "this code has not been auditted for volatile or ordered store case");
1283 BasicBlock *StoreBB = SI.getParent();
1285 // Check to see if the successor block has exactly two incoming edges. If
1286 // so, see if the other predecessor contains a store to the same location.
1287 // if so, insert a PHI node (if needed) and move the stores down.
1288 BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
1290 // Determine whether Dest has exactly two predecessors and, if so, compute
1291 // the other predecessor.
1292 pred_iterator PI = pred_begin(DestBB);
1293 BasicBlock *P = *PI;
1294 BasicBlock *OtherBB = nullptr;
1299 if (++PI == pred_end(DestBB))
1308 if (++PI != pred_end(DestBB))
1311 // Bail out if all the relevant blocks aren't distinct (this can happen,
1312 // for example, if SI is in an infinite loop)
1313 if (StoreBB == DestBB || OtherBB == DestBB)
1316 // Verify that the other block ends in a branch and is not otherwise empty.
1317 BasicBlock::iterator BBI(OtherBB->getTerminator());
1318 BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
1319 if (!OtherBr || BBI == OtherBB->begin())
1322 // If the other block ends in an unconditional branch, check for the 'if then
1323 // else' case. there is an instruction before the branch.
1324 StoreInst *OtherStore = nullptr;
1325 if (OtherBr->isUnconditional()) {
1327 // Skip over debugging info.
1328 while (isa<DbgInfoIntrinsic>(BBI) ||
1329 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1330 if (BBI==OtherBB->begin())
1334 // If this isn't a store, isn't a store to the same location, or is not the
1335 // right kind of store, bail out.
1336 OtherStore = dyn_cast<StoreInst>(BBI);
1337 if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
1338 !SI.isSameOperationAs(OtherStore))
1341 // Otherwise, the other block ended with a conditional branch. If one of the
1342 // destinations is StoreBB, then we have the if/then case.
1343 if (OtherBr->getSuccessor(0) != StoreBB &&
1344 OtherBr->getSuccessor(1) != StoreBB)
1347 // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
1348 // if/then triangle. See if there is a store to the same ptr as SI that
1349 // lives in OtherBB.
1351 // Check to see if we find the matching store.
1352 if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
1353 if (OtherStore->getOperand(1) != SI.getOperand(1) ||
1354 !SI.isSameOperationAs(OtherStore))
1358 // If we find something that may be using or overwriting the stored
1359 // value, or if we run out of instructions, we can't do the xform.
1360 if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
1361 BBI == OtherBB->begin())
1365 // In order to eliminate the store in OtherBr, we have to
1366 // make sure nothing reads or overwrites the stored value in
1368 for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
1369 // FIXME: This should really be AA driven.
1370 if (I->mayReadFromMemory() || I->mayWriteToMemory())
1375 // Insert a PHI node now if we need it.
1376 Value *MergedVal = OtherStore->getOperand(0);
1377 if (MergedVal != SI.getOperand(0)) {
1378 PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge");
1379 PN->addIncoming(SI.getOperand(0), SI.getParent());
1380 PN->addIncoming(OtherStore->getOperand(0), OtherBB);
1381 MergedVal = InsertNewInstBefore(PN, DestBB->front());
1384 // Advance to a place where it is safe to insert the new store and
1386 BBI = DestBB->getFirstInsertionPt();
1387 StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1),
1391 SI.getSynchScope());
1392 InsertNewInstBefore(NewSI, *BBI);
1393 NewSI->setDebugLoc(OtherStore->getDebugLoc());
1395 // If the two stores had AA tags, merge them.
1397 SI.getAAMetadata(AATags);
1399 OtherStore->getAAMetadata(AATags, /* Merge = */ true);
1400 NewSI->setAAMetadata(AATags);
1403 // Nuke the old stores.
1404 eraseInstFromFunction(SI);
1405 eraseInstFromFunction(*OtherStore);