Bug Summary

File:lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
Location:line 1251, column 28
Description:Called C++ object pointer is null

Annotated Source Code

1//===- InstCombineLoadStoreAlloca.cpp -------------------------------------===//
2//
3// The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file implements the visit functions for load, store and alloca.
11//
12//===----------------------------------------------------------------------===//
13
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"
24using namespace llvm;
25
26#define DEBUG_TYPE"instcombine" "instcombine"
27
28STATISTIC(NumDeadStore, "Number of dead stores eliminated")static llvm::Statistic NumDeadStore = { "instcombine", "Number of dead stores eliminated"
, 0, 0 };
29STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global")static llvm::Statistic NumGlobalCopies = { "instcombine", "Number of allocas copied from constant global"
, 0, 0 };
30
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.
34static bool pointsToConstantGlobal(Value *V) {
35 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
36 return GV->isConstant();
37
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));
43 }
44 return false;
45}
46
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.
54static bool
55isOnlyCopiedFromConstantGlobal(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.
60
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());
68
69 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
70 // Ignore non-volatile loads, they are always ok.
71 if (!LI->isSimple()) return false;
72 continue;
73 }
74
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));
78 continue;
79 }
80 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
81 // If the GEP has all zero indices, it doesn't offset the pointer. If it
82 // doesn't, it does.
83 ValuesToInspect.push_back(
84 std::make_pair(I, IsOffset || !GEP->hasAllZeroIndices()));
85 continue;
86 }
87
88 if (auto CS = CallSite(I)) {
89 // If this is the function being called then we treat it like a load and
90 // ignore it.
91 if (CS.isCallee(&U))
92 continue;
93
94 unsigned DataOpNo = CS.getDataOperandNo(&U);
95 bool IsArgOperand = CS.isArgOperand(&U);
96
97 // Inalloca arguments are clobbered by the call.
98 if (IsArgOperand && CS.isInAllocaArgument(DataOpNo))
99 return false;
100
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)))
106 continue;
107
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))
111 continue;
112 }
113
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!")((II->use_empty() && "Lifetime markers have no result to use!"
) ? static_cast<void> (0) : __assert_fail ("II->use_empty() && \"Lifetime markers have no result to use!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.9~svn266909/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 118, __PRETTY_FUNCTION__));
119 ToDelete.push_back(II);
120 continue;
121 }
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.
161static MemTransferInst *
162isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
163 SmallVectorImpl<Instruction *> &ToDelete) {
164 MemTransferInst *TheCopy = nullptr;
165 if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete))
166 return TheCopy;
167 return nullptr;
168}
169
170static 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))
175 return nullptr;
176
177 // Canonicalize it.
178 Value *V = IC.Builder->getInt32(1);
179 AI.setOperand(0, V);
180 return &AI;
181 }
182
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());
188
189 // Scan to the end of the allocation instructions, to skip over a block of
190 // allocas if possible...also skip interleaved debug info
191 //
192 BasicBlock::iterator It(New);
193 while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It))
194 ++It;
195
196 // Now that I is pointing to the first non-allocation-inst in the block,
197 // insert our getelementptr instruction...
198 //
199 Type *IdxTy = IC.getDataLayout().getIntPtrType(AI.getType());
200 Value *NullIdx = Constant::getNullValue(IdxTy);
201 Value *Idx[2] = {NullIdx, NullIdx};
202 Instruction *GEP =
203 GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub");
204 IC.InsertNewInstBefore(GEP, *It);
205
206 // Now make everything use the getelementptr instead of the original
207 // allocation.
208 return IC.replaceInstUsesWith(AI, GEP);
209 }
210
211 if (isa<UndefValue>(AI.getArraySize()))
212 return IC.replaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
213
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);
219 AI.setOperand(0, V);
220 return &AI;
221 }
222
223 return nullptr;
224}
225
226Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
227 if (auto *I = simplifyAllocaArraySize(*this, AI))
228 return I;
229
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()));
234
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
241 // elsewhere.
242 if (AI.isArrayAllocation()) {
243 AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1));
244 return &AI;
245 }
246
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);
258 return &AI;
259 }
260
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
268 // types.
269 unsigned MaxAlign = std::max(EntryAI->getAlignment(),
270 AI.getAlignment());
271 EntryAI->setAlignment(MaxAlign);
272 if (AI.getType() != EntryAI->getType())
273 return new BitCastInst(EntryAI, AI.getType());
274 return replaceInstUsesWith(AI, EntryAI);
275 }
276 }
277 }
278
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')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("instcombine")) { dbgs() << "Found alloca equal to global: "
<< AI << '\n'; } } while (0);
292 DEBUG(dbgs() << " memcpy = " << *Copy << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("instcombine")) { dbgs() << " memcpy = " << *Copy
<< '\n'; } } while (0);
293 for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
294 eraseInstFromFunction(*ToDelete[i]);
295 Constant *TheSrc = cast<Constant>(Copy->getSource());
296 Constant *Cast
297 = ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, AI.getType());
298 Instruction *NewI = replaceInstUsesWith(AI, Cast);
299 eraseInstFromFunction(*Copy);
300 ++NumGlobalCopies;
301 return NewI;
302 }
303 }
304 }
305
306 // At last, use the generic allocation site handler to aggressively remove
307 // unused allocas.
308 return visitAllocSite(AI);
309}
310
311/// \brief Helper to combine a load to a new type.
312///
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.
317///
318/// Note that this will create all of the instructions with whatever insert
319/// point the \c InstCombiner currently is using.
320static 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);
326
327 LoadInst *NewLoad = IC.Builder->CreateAlignedLoad(
328 IC.Builder->CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
329 LI.getAlignment(), LI.getName() + Suffix);
330 MDBuilder MDB(NewLoad->getContext());
331 for (const auto &MDPair : MD) {
332 unsigned ID = MDPair.first;
333 MDNode *N = MDPair.second;
334 // Note, essentially every kind of metadata should be preserved here! This
335 // routine is supposed to clone a load instruction changing *only its type*.
336 // The only metadata it makes sense to drop is metadata which is invalidated
337 // when the pointer type changes. This should essentially never be the case
338 // in LLVM, but we explicitly switch over only known metadata to be
339 // conservatively correct. If you are adding metadata to LLVM which pertains
340 // to loads, you almost certainly want to add it here.
341 switch (ID) {
342 case LLVMContext::MD_dbg:
343 case LLVMContext::MD_tbaa:
344 case LLVMContext::MD_prof:
345 case LLVMContext::MD_fpmath:
346 case LLVMContext::MD_tbaa_struct:
347 case LLVMContext::MD_invariant_load:
348 case LLVMContext::MD_alias_scope:
349 case LLVMContext::MD_noalias:
350 case LLVMContext::MD_nontemporal:
351 case LLVMContext::MD_mem_parallel_loop_access:
352 // All of these directly apply.
353 NewLoad->setMetadata(ID, N);
354 break;
355
356 case LLVMContext::MD_nonnull:
357 // This only directly applies if the new type is also a pointer.
358 if (NewTy->isPointerTy()) {
359 NewLoad->setMetadata(ID, N);
360 break;
361 }
362 // If it's integral now, translate it to !range metadata.
363 if (NewTy->isIntegerTy()) {
364 auto *ITy = cast<IntegerType>(NewTy);
365 auto *NullInt = ConstantExpr::getPtrToInt(
366 ConstantPointerNull::get(cast<PointerType>(Ptr->getType())), ITy);
367 auto *NonNullInt =
368 ConstantExpr::getAdd(NullInt, ConstantInt::get(ITy, 1));
369 NewLoad->setMetadata(LLVMContext::MD_range,
370 MDB.createRange(NonNullInt, NullInt));
371 }
372 break;
373 case LLVMContext::MD_align:
374 case LLVMContext::MD_dereferenceable:
375 case LLVMContext::MD_dereferenceable_or_null:
376 // These only directly apply if the new type is also a pointer.
377 if (NewTy->isPointerTy())
378 NewLoad->setMetadata(ID, N);
379 break;
380 case LLVMContext::MD_range:
381 // FIXME: It would be nice to propagate this in some way, but the type
382 // conversions make it hard. If the new type is a pointer, we could
383 // translate it to !nonnull metadata.
384 break;
385 }
386 }
387 return NewLoad;
388}
389
390/// \brief Combine a store to a new type.
391///
392/// Returns the newly created store instruction.
393static StoreInst *combineStoreToNewValue(InstCombiner &IC, StoreInst &SI, Value *V) {
394 Value *Ptr = SI.getPointerOperand();
395 unsigned AS = SI.getPointerAddressSpace();
396 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
397 SI.getAllMetadata(MD);
398
399 StoreInst *NewStore = IC.Builder->CreateAlignedStore(
400 V, IC.Builder->CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
401 SI.getAlignment());
402 for (const auto &MDPair : MD) {
403 unsigned ID = MDPair.first;
404 MDNode *N = MDPair.second;
405 // Note, essentially every kind of metadata should be preserved here! This
406 // routine is supposed to clone a store instruction changing *only its
407 // type*. The only metadata it makes sense to drop is metadata which is
408 // invalidated when the pointer type changes. This should essentially
409 // never be the case in LLVM, but we explicitly switch over only known
410 // metadata to be conservatively correct. If you are adding metadata to
411 // LLVM which pertains to stores, you almost certainly want to add it
412 // here.
413 switch (ID) {
414 case LLVMContext::MD_dbg:
415 case LLVMContext::MD_tbaa:
416 case LLVMContext::MD_prof:
417 case LLVMContext::MD_fpmath:
418 case LLVMContext::MD_tbaa_struct:
419 case LLVMContext::MD_alias_scope:
420 case LLVMContext::MD_noalias:
421 case LLVMContext::MD_nontemporal:
422 case LLVMContext::MD_mem_parallel_loop_access:
423 // All of these directly apply.
424 NewStore->setMetadata(ID, N);
425 break;
426
427 case LLVMContext::MD_invariant_load:
428 case LLVMContext::MD_nonnull:
429 case LLVMContext::MD_range:
430 case LLVMContext::MD_align:
431 case LLVMContext::MD_dereferenceable:
432 case LLVMContext::MD_dereferenceable_or_null:
433 // These don't apply for stores.
434 break;
435 }
436 }
437
438 return NewStore;
439}
440
441/// \brief Combine loads to match the type of value their uses after looking
442/// through intervening bitcasts.
443///
444/// The core idea here is that if the result of a load is used in an operation,
445/// we should load the type most conducive to that operation. For example, when
446/// loading an integer and converting that immediately to a pointer, we should
447/// instead directly load a pointer.
448///
449/// However, this routine must never change the width of a load or the number of
450/// loads as that would introduce a semantic change. This combine is expected to
451/// be a semantic no-op which just allows loads to more closely model the types
452/// of their consuming operations.
453///
454/// Currently, we also refuse to change the precise type used for an atomic load
455/// or a volatile load. This is debatable, and might be reasonable to change
456/// later. However, it is risky in case some backend or other part of LLVM is
457/// relying on the exact type loaded to select appropriate atomic operations.
458static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
459 // FIXME: We could probably with some care handle both volatile and atomic
460 // loads here but it isn't clear that this is important.
461 if (!LI.isSimple())
462 return nullptr;
463
464 if (LI.use_empty())
465 return nullptr;
466
467 Type *Ty = LI.getType();
468 const DataLayout &DL = IC.getDataLayout();
469
470 // Try to canonicalize loads which are only ever stored to operate over
471 // integers instead of any other type. We only do this when the loaded type
472 // is sized and has a size exactly the same as its store size and the store
473 // size is a legal integer type.
474 if (!Ty->isIntegerTy() && Ty->isSized() &&
475 DL.isLegalInteger(DL.getTypeStoreSizeInBits(Ty)) &&
476 DL.getTypeStoreSizeInBits(Ty) == DL.getTypeSizeInBits(Ty)) {
477 if (std::all_of(LI.user_begin(), LI.user_end(), [&LI](User *U) {
478 auto *SI = dyn_cast<StoreInst>(U);
479 return SI && SI->getPointerOperand() != &LI;
480 })) {
481 LoadInst *NewLoad = combineLoadToNewType(
482 IC, LI,
483 Type::getIntNTy(LI.getContext(), DL.getTypeStoreSizeInBits(Ty)));
484 // Replace all the stores with stores of the newly loaded value.
485 for (auto UI = LI.user_begin(), UE = LI.user_end(); UI != UE;) {
486 auto *SI = cast<StoreInst>(*UI++);
487 IC.Builder->SetInsertPoint(SI);
488 combineStoreToNewValue(IC, *SI, NewLoad);
489 IC.eraseInstFromFunction(*SI);
490 }
491 assert(LI.use_empty() && "Failed to remove all users of the load!")((LI.use_empty() && "Failed to remove all users of the load!"
) ? static_cast<void> (0) : __assert_fail ("LI.use_empty() && \"Failed to remove all users of the load!\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.9~svn266909/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 491, __PRETTY_FUNCTION__));
492 // Return the old load so the combiner can delete it safely.
493 return &LI;
494 }
495 }
496
497 // Fold away bit casts of the loaded value by loading the desired type.
498 // We can do this for BitCastInsts as well as casts from and to pointer types,
499 // as long as those are noops (i.e., the source or dest type have the same
500 // bitwidth as the target's pointers).
501 if (LI.hasOneUse())
502 if (auto* CI = dyn_cast<CastInst>(LI.user_back())) {
503 if (CI->isNoopCast(DL)) {
504 LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
505 CI->replaceAllUsesWith(NewLoad);
506 IC.eraseInstFromFunction(*CI);
507 return &LI;
508 }
509 }
510
511 // FIXME: We should also canonicalize loads of vectors when their elements are
512 // cast to other types.
513 return nullptr;
514}
515
516static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
517 // FIXME: We could probably with some care handle both volatile and atomic
518 // stores here but it isn't clear that this is important.
519 if (!LI.isSimple())
520 return nullptr;
521
522 Type *T = LI.getType();
523 if (!T->isAggregateType())
524 return nullptr;
525
526 StringRef Name = LI.getName();
527 assert(LI.getAlignment() && "Alignment must be set at this point")((LI.getAlignment() && "Alignment must be set at this point"
) ? static_cast<void> (0) : __assert_fail ("LI.getAlignment() && \"Alignment must be set at this point\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.9~svn266909/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 527, __PRETTY_FUNCTION__));
528
529 if (auto *ST = dyn_cast<StructType>(T)) {
530 // If the struct only have one element, we unpack.
531 auto NumElements = ST->getNumElements();
532 if (NumElements == 1) {
533 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
534 ".unpack");
535 return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
536 UndefValue::get(T), NewLoad, 0, Name));
537 }
538
539 // We don't want to break loads with padding here as we'd loose
540 // the knowledge that padding exists for the rest of the pipeline.
541 const DataLayout &DL = IC.getDataLayout();
542 auto *SL = DL.getStructLayout(ST);
543 if (SL->hasPadding())
544 return nullptr;
545
546 auto Align = LI.getAlignment();
547 if (!Align)
548 Align = DL.getABITypeAlignment(ST);
549
550 auto *Addr = LI.getPointerOperand();
551 auto *IdxType = Type::getInt32Ty(T->getContext());
552 auto *Zero = ConstantInt::get(IdxType, 0);
553
554 Value *V = UndefValue::get(T);
555 for (unsigned i = 0; i < NumElements; i++) {
556 Value *Indices[2] = {
557 Zero,
558 ConstantInt::get(IdxType, i),
559 };
560 auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
561 Name + ".elt");
562 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
563 auto *L = IC.Builder->CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
564 V = IC.Builder->CreateInsertValue(V, L, i);
565 }
566
567 V->setName(Name);
568 return IC.replaceInstUsesWith(LI, V);
569 }
570
571 if (auto *AT = dyn_cast<ArrayType>(T)) {
572 auto *ET = AT->getElementType();
573 auto NumElements = AT->getNumElements();
574 if (NumElements == 1) {
575 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
576 return IC.replaceInstUsesWith(LI, IC.Builder->CreateInsertValue(
577 UndefValue::get(T), NewLoad, 0, Name));
578 }
579
580 const DataLayout &DL = IC.getDataLayout();
581 auto EltSize = DL.getTypeAllocSize(ET);
582 auto Align = LI.getAlignment();
583 if (!Align)
584 Align = DL.getABITypeAlignment(T);
585
586 auto *Addr = LI.getPointerOperand();
587 auto *IdxType = Type::getInt64Ty(T->getContext());
588 auto *Zero = ConstantInt::get(IdxType, 0);
589
590 Value *V = UndefValue::get(T);
591 uint64_t Offset = 0;
592 for (uint64_t i = 0; i < NumElements; i++) {
593 Value *Indices[2] = {
594 Zero,
595 ConstantInt::get(IdxType, i),
596 };
597 auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
598 Name + ".elt");
599 auto *L = IC.Builder->CreateAlignedLoad(Ptr, MinAlign(Align, Offset),
600 Name + ".unpack");
601 V = IC.Builder->CreateInsertValue(V, L, i);
602 Offset += EltSize;
603 }
604
605 V->setName(Name);
606 return IC.replaceInstUsesWith(LI, V);
607 }
608
609 return nullptr;
610}
611
612// If we can determine that all possible objects pointed to by the provided
613// pointer value are, not only dereferenceable, but also definitively less than
614// or equal to the provided maximum size, then return true. Otherwise, return
615// false (constant global values and allocas fall into this category).
616//
617// FIXME: This should probably live in ValueTracking (or similar).
618static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize,
619 const DataLayout &DL) {
620 SmallPtrSet<Value *, 4> Visited;
621 SmallVector<Value *, 4> Worklist(1, V);
622
623 do {
624 Value *P = Worklist.pop_back_val();
625 P = P->stripPointerCasts();
626
627 if (!Visited.insert(P).second)
628 continue;
629
630 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
631 Worklist.push_back(SI->getTrueValue());
632 Worklist.push_back(SI->getFalseValue());
633 continue;
634 }
635
636 if (PHINode *PN = dyn_cast<PHINode>(P)) {
637 for (Value *IncValue : PN->incoming_values())
638 Worklist.push_back(IncValue);
639 continue;
640 }
641
642 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(P)) {
643 if (GA->isInterposable())
644 return false;
645 Worklist.push_back(GA->getAliasee());
646 continue;
647 }
648
649 // If we know how big this object is, and it is less than MaxSize, continue
650 // searching. Otherwise, return false.
651 if (AllocaInst *AI = dyn_cast<AllocaInst>(P)) {
652 if (!AI->getAllocatedType()->isSized())
653 return false;
654
655 ConstantInt *CS = dyn_cast<ConstantInt>(AI->getArraySize());
656 if (!CS)
657 return false;
658
659 uint64_t TypeSize = DL.getTypeAllocSize(AI->getAllocatedType());
660 // Make sure that, even if the multiplication below would wrap as an
661 // uint64_t, we still do the right thing.
662 if ((CS->getValue().zextOrSelf(128)*APInt(128, TypeSize)).ugt(MaxSize))
663 return false;
664 continue;
665 }
666
667 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
668 if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
669 return false;
670
671 uint64_t InitSize = DL.getTypeAllocSize(GV->getValueType());
672 if (InitSize > MaxSize)
673 return false;
674 continue;
675 }
676
677 return false;
678 } while (!Worklist.empty());
679
680 return true;
681}
682
683// If we're indexing into an object of a known size, and the outer index is
684// not a constant, but having any value but zero would lead to undefined
685// behavior, replace it with zero.
686//
687// For example, if we have:
688// @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
689// ...
690// %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x
691// ... = load i32* %arrayidx, align 4
692// Then we know that we can replace %x in the GEP with i64 0.
693//
694// FIXME: We could fold any GEP index to zero that would cause UB if it were
695// not zero. Currently, we only handle the first such index. Also, we could
696// also search through non-zero constant indices if we kept track of the
697// offsets those indices implied.
698static bool canReplaceGEPIdxWithZero(InstCombiner &IC, GetElementPtrInst *GEPI,
699 Instruction *MemI, unsigned &Idx) {
700 if (GEPI->getNumOperands() < 2)
701 return false;
702
703 // Find the first non-zero index of a GEP. If all indices are zero, return
704 // one past the last index.
705 auto FirstNZIdx = [](const GetElementPtrInst *GEPI) {
706 unsigned I = 1;
707 for (unsigned IE = GEPI->getNumOperands(); I != IE; ++I) {
708 Value *V = GEPI->getOperand(I);
709 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V))
710 if (CI->isZero())
711 continue;
712
713 break;
714 }
715
716 return I;
717 };
718
719 // Skip through initial 'zero' indices, and find the corresponding pointer
720 // type. See if the next index is not a constant.
721 Idx = FirstNZIdx(GEPI);
722 if (Idx == GEPI->getNumOperands())
723 return false;
724 if (isa<Constant>(GEPI->getOperand(Idx)))
725 return false;
726
727 SmallVector<Value *, 4> Ops(GEPI->idx_begin(), GEPI->idx_begin() + Idx);
728 Type *AllocTy =
729 GetElementPtrInst::getIndexedType(GEPI->getSourceElementType(), Ops);
730 if (!AllocTy || !AllocTy->isSized())
731 return false;
732 const DataLayout &DL = IC.getDataLayout();
733 uint64_t TyAllocSize = DL.getTypeAllocSize(AllocTy);
734
735 // If there are more indices after the one we might replace with a zero, make
736 // sure they're all non-negative. If any of them are negative, the overall
737 // address being computed might be before the base address determined by the
738 // first non-zero index.
739 auto IsAllNonNegative = [&]() {
740 for (unsigned i = Idx+1, e = GEPI->getNumOperands(); i != e; ++i) {
741 bool KnownNonNegative, KnownNegative;
742 IC.ComputeSignBit(GEPI->getOperand(i), KnownNonNegative,
743 KnownNegative, 0, MemI);
744 if (KnownNonNegative)
745 continue;
746 return false;
747 }
748
749 return true;
750 };
751
752 // FIXME: If the GEP is not inbounds, and there are extra indices after the
753 // one we'll replace, those could cause the address computation to wrap
754 // (rendering the IsAllNonNegative() check below insufficient). We can do
755 // better, ignoring zero indices (and other indices we can prove small
756 // enough not to wrap).
757 if (Idx+1 != GEPI->getNumOperands() && !GEPI->isInBounds())
758 return false;
759
760 // Note that isObjectSizeLessThanOrEq will return true only if the pointer is
761 // also known to be dereferenceable.
762 return isObjectSizeLessThanOrEq(GEPI->getOperand(0), TyAllocSize, DL) &&
763 IsAllNonNegative();
764}
765
766// If we're indexing into an object with a variable index for the memory
767// access, but the object has only one element, we can assume that the index
768// will always be zero. If we replace the GEP, return it.
769template <typename T>
770static Instruction *replaceGEPIdxWithZero(InstCombiner &IC, Value *Ptr,
771 T &MemI) {
772 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) {
773 unsigned Idx;
774 if (canReplaceGEPIdxWithZero(IC, GEPI, &MemI, Idx)) {
775 Instruction *NewGEPI = GEPI->clone();
776 NewGEPI->setOperand(Idx,
777 ConstantInt::get(GEPI->getOperand(Idx)->getType(), 0));
778 NewGEPI->insertBefore(GEPI);
779 MemI.setOperand(MemI.getPointerOperandIndex(), NewGEPI);
780 return NewGEPI;
781 }
782 }
783
784 return nullptr;
785}
786
787Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
788 Value *Op = LI.getOperand(0);
789
790 // Try to canonicalize the loaded type.
791 if (Instruction *Res = combineLoadToOperationType(*this, LI))
792 return Res;
793
794 // Attempt to improve the alignment.
795 unsigned KnownAlign = getOrEnforceKnownAlignment(
796 Op, DL.getPrefTypeAlignment(LI.getType()), DL, &LI, AC, DT);
797 unsigned LoadAlign = LI.getAlignment();
798 unsigned EffectiveLoadAlign =
799 LoadAlign != 0 ? LoadAlign : DL.getABITypeAlignment(LI.getType());
800
801 if (KnownAlign > EffectiveLoadAlign)
802 LI.setAlignment(KnownAlign);
803 else if (LoadAlign == 0)
804 LI.setAlignment(EffectiveLoadAlign);
805
806 // Replace GEP indices if possible.
807 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Op, LI)) {
808 Worklist.Add(NewGEPI);
809 return &LI;
810 }
811
812 // None of the following transforms are legal for volatile/atomic loads.
813 // FIXME: Some of it is okay for atomic loads; needs refactoring.
814 if (!LI.isSimple()) return nullptr;
815
816 if (Instruction *Res = unpackLoadToAggregate(*this, LI))
817 return Res;
818
819 // Do really simple store-to-load forwarding and load CSE, to catch cases
820 // where there are several consecutive memory accesses to the same location,
821 // separated by a few arithmetic operations.
822 BasicBlock::iterator BBI(LI);
823 AAMDNodes AATags;
824 if (Value *AvailableVal =
825 FindAvailableLoadedValue(&LI, LI.getParent(), BBI,
826 DefMaxInstsToScan, AA, &AATags)) {
827 if (LoadInst *NLI = dyn_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);
836 };
837
838 return replaceInstUsesWith(
839 LI, Builder->CreateBitOrPointerCast(AvailableVal, LI.getType(),
840 LI.getName() + ".cast"));
841 }
842
843 // load(gep null, ...) -> unreachable
844 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
845 const Value *GEPI0 = GEPI->getOperand(0);
846 // TODO: Consider a target hook for valid address spaces for this xform.
847 if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0){
848 // Insert a new store to null instruction before the load to indicate
849 // that this code is not reachable. We do this instead of inserting
850 // an unreachable instruction directly because we cannot modify the
851 // CFG.
852 new StoreInst(UndefValue::get(LI.getType()),
853 Constant::getNullValue(Op->getType()), &LI);
854 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
855 }
856 }
857
858 // load null/undef -> unreachable
859 // TODO: Consider a target hook for valid address spaces for this xform.
860 if (isa<UndefValue>(Op) ||
861 (isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0)) {
862 // Insert a new store to null instruction before the load to indicate that
863 // this code is not reachable. We do this instead of inserting an
864 // unreachable instruction directly because we cannot modify the CFG.
865 new StoreInst(UndefValue::get(LI.getType()),
866 Constant::getNullValue(Op->getType()), &LI);
867 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
868 }
869
870 if (Op->hasOneUse()) {
871 // Change select and PHI nodes to select values instead of addresses: this
872 // helps alias analysis out a lot, allows many others simplifications, and
873 // exposes redundancy in the code.
874 //
875 // Note that we cannot do the transformation unless we know that the
876 // introduced loads cannot trap! Something like this is valid as long as
877 // the condition is always false: load (select bool %C, int* null, int* %G),
878 // but it would not be valid if we transformed it to load from null
879 // unconditionally.
880 //
881 if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
882 // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
883 unsigned Align = LI.getAlignment();
884 if (isSafeToLoadUnconditionally(SI->getOperand(1), Align, SI) &&
885 isSafeToLoadUnconditionally(SI->getOperand(2), Align, SI)) {
886 LoadInst *V1 = Builder->CreateLoad(SI->getOperand(1),
887 SI->getOperand(1)->getName()+".val");
888 LoadInst *V2 = Builder->CreateLoad(SI->getOperand(2),
889 SI->getOperand(2)->getName()+".val");
890 V1->setAlignment(Align);
891 V2->setAlignment(Align);
892 return SelectInst::Create(SI->getCondition(), V1, V2);
893 }
894
895 // load (select (cond, null, P)) -> load P
896 if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
897 LI.getPointerAddressSpace() == 0) {
898 LI.setOperand(0, SI->getOperand(2));
899 return &LI;
900 }
901
902 // load (select (cond, P, null)) -> load P
903 if (isa<ConstantPointerNull>(SI->getOperand(2)) &&
904 LI.getPointerAddressSpace() == 0) {
905 LI.setOperand(0, SI->getOperand(1));
906 return &LI;
907 }
908 }
909 }
910 return nullptr;
911}
912
913/// \brief Combine stores to match the type of value being stored.
914///
915/// The core idea here is that the memory does not have any intrinsic type and
916/// where we can we should match the type of a store to the type of value being
917/// stored.
918///
919/// However, this routine must never change the width of a store or the number of
920/// stores as that would introduce a semantic change. This combine is expected to
921/// be a semantic no-op which just allows stores to more closely model the types
922/// of their incoming values.
923///
924/// Currently, we also refuse to change the precise type used for an atomic or
925/// volatile store. This is debatable, and might be reasonable to change later.
926/// However, it is risky in case some backend or other part of LLVM is relying
927/// on the exact type stored to select appropriate atomic operations.
928///
929/// \returns true if the store was successfully combined away. This indicates
930/// the caller must erase the store instruction. We have to let the caller erase
931/// the store instruction as otherwise there is no way to signal whether it was
932/// combined or not: IC.EraseInstFromFunction returns a null pointer.
933static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
934 // FIXME: We could probably with some care handle both volatile and atomic
935 // stores here but it isn't clear that this is important.
936 if (!SI.isSimple())
937 return false;
938
939 Value *V = SI.getValueOperand();
940
941 // Fold away bit casts of the stored value by storing the original type.
942 if (auto *BC = dyn_cast<BitCastInst>(V)) {
943 V = BC->getOperand(0);
944 combineStoreToNewValue(IC, SI, V);
945 return true;
946 }
947
948 // FIXME: We should also canonicalize loads of vectors when their elements are
949 // cast to other types.
950 return false;
951}
952
953static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
954 // FIXME: We could probably with some care handle both volatile and atomic
955 // stores here but it isn't clear that this is important.
956 if (!SI.isSimple())
957 return false;
958
959 Value *V = SI.getValueOperand();
960 Type *T = V->getType();
961
962 if (!T->isAggregateType())
963 return false;
964
965 if (auto *ST = dyn_cast<StructType>(T)) {
966 // If the struct only have one element, we unpack.
967 unsigned Count = ST->getNumElements();
968 if (Count == 1) {
969 V = IC.Builder->CreateExtractValue(V, 0);
970 combineStoreToNewValue(IC, SI, V);
971 return true;
972 }
973
974 // We don't want to break loads with padding here as we'd loose
975 // the knowledge that padding exists for the rest of the pipeline.
976 const DataLayout &DL = IC.getDataLayout();
977 auto *SL = DL.getStructLayout(ST);
978 if (SL->hasPadding())
979 return false;
980
981 auto Align = SI.getAlignment();
982 if (!Align)
983 Align = DL.getABITypeAlignment(ST);
984
985 SmallString<16> EltName = V->getName();
986 EltName += ".elt";
987 auto *Addr = SI.getPointerOperand();
988 SmallString<16> AddrName = Addr->getName();
989 AddrName += ".repack";
990
991 auto *IdxType = Type::getInt32Ty(ST->getContext());
992 auto *Zero = ConstantInt::get(IdxType, 0);
993 for (unsigned i = 0; i < Count; i++) {
994 Value *Indices[2] = {
995 Zero,
996 ConstantInt::get(IdxType, i),
997 };
998 auto *Ptr = IC.Builder->CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
999 AddrName);
1000 auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
1001 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
1002 IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
1003 }
1004
1005 return true;
1006 }
1007
1008 if (auto *AT = dyn_cast<ArrayType>(T)) {
1009 // If the array only have one element, we unpack.
1010 auto NumElements = AT->getNumElements();
1011 if (NumElements == 1) {
1012 V = IC.Builder->CreateExtractValue(V, 0);
1013 combineStoreToNewValue(IC, SI, V);
1014 return true;
1015 }
1016
1017 const DataLayout &DL = IC.getDataLayout();
1018 auto EltSize = DL.getTypeAllocSize(AT->getElementType());
1019 auto Align = SI.getAlignment();
1020 if (!Align)
1021 Align = DL.getABITypeAlignment(T);
1022
1023 SmallString<16> EltName = V->getName();
1024 EltName += ".elt";
1025 auto *Addr = SI.getPointerOperand();
1026 SmallString<16> AddrName = Addr->getName();
1027 AddrName += ".repack";
1028
1029 auto *IdxType = Type::getInt64Ty(T->getContext());
1030 auto *Zero = ConstantInt::get(IdxType, 0);
1031
1032 uint64_t Offset = 0;
1033 for (uint64_t i = 0; i < NumElements; i++) {
1034 Value *Indices[2] = {
1035 Zero,
1036 ConstantInt::get(IdxType, i),
1037 };
1038 auto *Ptr = IC.Builder->CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
1039 AddrName);
1040 auto *Val = IC.Builder->CreateExtractValue(V, i, EltName);
1041 auto EltAlign = MinAlign(Align, Offset);
1042 IC.Builder->CreateAlignedStore(Val, Ptr, EltAlign);
1043 Offset += EltSize;
1044 }
1045
1046 return true;
1047 }
1048
1049 return false;
1050}
1051
1052/// equivalentAddressValues - Test if A and B will obviously have the same
1053/// value. This includes recognizing that %t0 and %t1 will have the same
1054/// value in code like this:
1055/// %t0 = getelementptr \@a, 0, 3
1056/// store i32 0, i32* %t0
1057/// %t1 = getelementptr \@a, 0, 3
1058/// %t2 = load i32* %t1
1059///
1060static bool equivalentAddressValues(Value *A, Value *B) {
1061 // Test if the values are trivially equivalent.
1062 if (A == B) return true;
1063
1064 // Test if the values come form identical arithmetic instructions.
1065 // This uses isIdenticalToWhenDefined instead of isIdenticalTo because
1066 // its only used to compare two uses within the same basic block, which
1067 // means that they'll always either have the same value or one of them
1068 // will have an undefined value.
1069 if (isa<BinaryOperator>(A) ||
1070 isa<CastInst>(A) ||
1071 isa<PHINode>(A) ||
1072 isa<GetElementPtrInst>(A))
1073 if (Instruction *BI = dyn_cast<Instruction>(B))
1074 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
1075 return true;
1076
1077 // Otherwise they may not be equivalent.
1078 return false;
1079}
1080
1081Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
1082 Value *Val = SI.getOperand(0);
1083 Value *Ptr = SI.getOperand(1);
1084
1085 // Try to canonicalize the stored type.
1086 if (combineStoreToValueType(*this, SI))
1087 return eraseInstFromFunction(SI);
1088
1089 // Attempt to improve the alignment.
1090 unsigned KnownAlign = getOrEnforceKnownAlignment(
1091 Ptr, DL.getPrefTypeAlignment(Val->getType()), DL, &SI, AC, DT);
1092 unsigned StoreAlign = SI.getAlignment();
1093 unsigned EffectiveStoreAlign =
1094 StoreAlign != 0 ? StoreAlign : DL.getABITypeAlignment(Val->getType());
1095
1096 if (KnownAlign > EffectiveStoreAlign)
1097 SI.setAlignment(KnownAlign);
1098 else if (StoreAlign == 0)
1099 SI.setAlignment(EffectiveStoreAlign);
1100
1101 // Try to canonicalize the stored type.
1102 if (unpackStoreToAggregate(*this, SI))
1103 return eraseInstFromFunction(SI);
1104
1105 // Replace GEP indices if possible.
1106 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {
1107 Worklist.Add(NewGEPI);
1108 return &SI;
1109 }
1110
1111 // Don't hack volatile/ordered stores.
1112 // FIXME: Some bits are legal for ordered atomic stores; needs refactoring.
1113 if (!SI.isUnordered()) return nullptr;
1114
1115 // If the RHS is an alloca with a single use, zapify the store, making the
1116 // alloca dead.
1117 if (Ptr->hasOneUse()) {
1118 if (isa<AllocaInst>(Ptr))
1119 return eraseInstFromFunction(SI);
1120 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
1121 if (isa<AllocaInst>(GEP->getOperand(0))) {
1122 if (GEP->getOperand(0)->hasOneUse())
1123 return eraseInstFromFunction(SI);
1124 }
1125 }
1126 }
1127
1128 // Do really simple DSE, to catch cases where there are several consecutive
1129 // stores to the same location, separated by a few arithmetic operations. This
1130 // situation often occurs with bitfield accesses.
1131 BasicBlock::iterator BBI(SI);
1132 for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
1133 --ScanInsts) {
1134 --BBI;
1135 // Don't count debug info directives, lest they affect codegen,
1136 // and we skip pointer-to-pointer bitcasts, which are NOPs.
1137 if (isa<DbgInfoIntrinsic>(BBI) ||
1138 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1139 ScanInsts++;
1140 continue;
1141 }
1142
1143 if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
1144 // Prev store isn't volatile, and stores to the same location?
1145 if (PrevSI->isUnordered() && equivalentAddressValues(PrevSI->getOperand(1),
1146 SI.getOperand(1))) {
1147 ++NumDeadStore;
1148 ++BBI;
1149 eraseInstFromFunction(*PrevSI);
1150 continue;
1151 }
1152 break;
1153 }
1154
1155 // If this is a load, we have to stop. However, if the loaded value is from
1156 // the pointer we're loading and is producing the pointer we're storing,
1157 // then *this* store is dead (X = load P; store X -> P).
1158 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
1159 if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr)) {
1160 assert(SI.isUnordered() && "can't eliminate ordering operation")((SI.isUnordered() && "can't eliminate ordering operation"
) ? static_cast<void> (0) : __assert_fail ("SI.isUnordered() && \"can't eliminate ordering operation\""
, "/tmp/buildd/llvm-toolchain-snapshot-3.9~svn266909/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 1160, __PRETTY_FUNCTION__));
1161 return eraseInstFromFunction(SI);
1162 }
1163
1164 // Otherwise, this is a load from some other location. Stores before it
1165 // may not be dead.
1166 break;
1167 }
1168
1169 // Don't skip over loads or things that can modify memory.
1170 if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory())
1171 break;
1172 }
1173
1174 // store X, null -> turns into 'unreachable' in SimplifyCFG
1175 if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
1176 if (!isa<UndefValue>(Val)) {
1177 SI.setOperand(0, UndefValue::get(Val->getType()));
1178 if (Instruction *U = dyn_cast<Instruction>(Val))
1179 Worklist.Add(U); // Dropped a use.
1180 }
1181 return nullptr; // Do not modify these!
1182 }
1183
1184 // store undef, Ptr -> noop
1185 if (isa<UndefValue>(Val))
1186 return eraseInstFromFunction(SI);
1187
1188 // The code below needs to be audited and adjusted for unordered atomics
1189 if (!SI.isSimple())
1190 return nullptr;
1191
1192 // If this store is the last instruction in the basic block (possibly
1193 // excepting debug info instructions), and if the block ends with an
1194 // unconditional branch, try to move it to the successor block.
1195 BBI = SI.getIterator();
1196 do {
1197 ++BBI;
1198 } while (isa<DbgInfoIntrinsic>(BBI) ||
1199 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
1200 if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
1201 if (BI->isUnconditional())
1202 if (SimplifyStoreAtEndOfBlock(SI))
1203 return nullptr; // xform done!
1204
1205 return nullptr;
1206}
1207
1208/// SimplifyStoreAtEndOfBlock - Turn things like:
1209/// if () { *P = v1; } else { *P = v2 }
1210/// into a phi node with a store in the successor.
1211///
1212/// Simplify things like:
1213/// *P = v1; if () { *P = v2; }
1214/// into a phi node with a store in the successor.
1215///
1216bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
1217 BasicBlock *StoreBB = SI.getParent();
1218
1219 // Check to see if the successor block has exactly two incoming edges. If
1220 // so, see if the other predecessor contains a store to the same location.
1221 // if so, insert a PHI node (if needed) and move the stores down.
1222 BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
1223
1224 // Determine whether Dest has exactly two predecessors and, if so, compute
1225 // the other predecessor.
1226 pred_iterator PI = pred_begin(DestBB);
1227 BasicBlock *P = *PI;
1228 BasicBlock *OtherBB = nullptr;
1
'OtherBB' initialized to a null pointer value
→
1229
1230 if (P != StoreBB)
2
←
Assuming 'P' is equal to 'StoreBB'
→
3
←
Taking false branch
→
1231 OtherBB = P;
1232
1233 if (++PI == pred_end(DestBB))
4
←
Taking false branch
→
1234 return false;
1235
1236 P = *PI;
1237 if (P != StoreBB) {
5
←
Assuming 'P' is equal to 'StoreBB'
→
6
←
Taking false branch
→
1238 if (OtherBB)
1239 return false;
1240 OtherBB = P;
1241 }
1242 if (++PI != pred_end(DestBB))
7
←
Taking false branch
→
1243 return false;
1244
1245 // Bail out if all the relevant blocks aren't distinct (this can happen,
1246 // for example, if SI is in an infinite loop)
1247 if (StoreBB == DestBB || OtherBB == DestBB)
8
←
Assuming 'StoreBB' is not equal to 'DestBB'
→
9
←
Assuming 'OtherBB' is not equal to 'DestBB'
→
10
←
Taking false branch
→
1248 return false;
1249
1250 // Verify that the other block ends in a branch and is not otherwise empty.
1251 BasicBlock::iterator BBI(OtherBB->getTerminator());
11
←
Called C++ object pointer is null
1252 BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
1253 if (!OtherBr || BBI == OtherBB->begin())
1254 return false;
1255
1256 // If the other block ends in an unconditional branch, check for the 'if then
1257 // else' case. there is an instruction before the branch.
1258 StoreInst *OtherStore = nullptr;
1259 if (OtherBr->isUnconditional()) {
1260 --BBI;
1261 // Skip over debugging info.
1262 while (isa<DbgInfoIntrinsic>(BBI) ||
1263 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1264 if (BBI==OtherBB->begin())
1265 return false;
1266 --BBI;
1267 }
1268 // If this isn't a store, isn't a store to the same location, or is not the
1269 // right kind of store, bail out.
1270 OtherStore = dyn_cast<StoreInst>(BBI);
1271 if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
1272 !SI.isSameOperationAs(OtherStore))
1273 return false;
1274 } else {
1275 // Otherwise, the other block ended with a conditional branch. If one of the
1276 // destinations is StoreBB, then we have the if/then case.
1277 if (OtherBr->getSuccessor(0) != StoreBB &&
1278 OtherBr->getSuccessor(1) != StoreBB)
1279 return false;
1280
1281 // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
1282 // if/then triangle. See if there is a store to the same ptr as SI that
1283 // lives in OtherBB.
1284 for (;; --BBI) {
1285 // Check to see if we find the matching store.
1286 if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
1287 if (OtherStore->getOperand(1) != SI.getOperand(1) ||
1288 !SI.isSameOperationAs(OtherStore))
1289 return false;
1290 break;
1291 }
1292 // If we find something that may be using or overwriting the stored
1293 // value, or if we run out of instructions, we can't do the xform.
1294 if (BBI->mayReadFromMemory() || BBI->mayWriteToMemory() ||
1295 BBI == OtherBB->begin())
1296 return false;
1297 }
1298
1299 // In order to eliminate the store in OtherBr, we have to
1300 // make sure nothing reads or overwrites the stored value in
1301 // StoreBB.
1302 for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
1303 // FIXME: This should really be AA driven.
1304 if (I->mayReadFromMemory() || I->mayWriteToMemory())
1305 return false;
1306 }
1307 }
1308
1309 // Insert a PHI node now if we need it.
1310 Value *MergedVal = OtherStore->getOperand(0);
1311 if (MergedVal != SI.getOperand(0)) {
1312 PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge");
1313 PN->addIncoming(SI.getOperand(0), SI.getParent());
1314 PN->addIncoming(OtherStore->getOperand(0), OtherBB);
1315 MergedVal = InsertNewInstBefore(PN, DestBB->front());
1316 }
1317
1318 // Advance to a place where it is safe to insert the new store and
1319 // insert it.
1320 BBI = DestBB->getFirstInsertionPt();
1321 StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1),
1322 SI.isVolatile(),
1323 SI.getAlignment(),
1324 SI.getOrdering(),
1325 SI.getSynchScope());
1326 InsertNewInstBefore(NewSI, *BBI);
1327 NewSI->setDebugLoc(OtherStore->getDebugLoc());
1328
1329 // If the two stores had AA tags, merge them.
1330 AAMDNodes AATags;
1331 SI.getAAMetadata(AATags);
1332 if (AATags) {
1333 OtherStore->getAAMetadata(AATags, /* Merge = */ true);
1334 NewSI->setAAMetadata(AATags);
1335 }
1336
1337 // Nuke the old stores.
1338 eraseInstFromFunction(SI);
1339 eraseInstFromFunction(*OtherStore);
1340 return true;
1341}