Bug Summary

File:lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
Warning:line 1470, column 28
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/MapVector.h"
16#include "llvm/ADT/SmallString.h"
17#include "llvm/ADT/Statistic.h"
18#include "llvm/Analysis/Loads.h"
19#include "llvm/IR/ConstantRange.h"
20#include "llvm/IR/DataLayout.h"
21#include "llvm/IR/DebugInfo.h"
22#include "llvm/IR/IntrinsicInst.h"
23#include "llvm/IR/LLVMContext.h"
24#include "llvm/IR/MDBuilder.h"
25#include "llvm/Transforms/Utils/BasicBlockUtils.h"
26#include "llvm/Transforms/Utils/Local.h"
27using namespace llvm;
28
29#define DEBUG_TYPE"instcombine" "instcombine"
30
31STATISTIC(NumDeadStore, "Number of dead stores eliminated")static llvm::Statistic NumDeadStore = {"instcombine", "NumDeadStore"
, "Number of dead stores eliminated", {0}, false}
;
32STATISTIC(NumGlobalCopies, "Number of allocas copied from constant global")static llvm::Statistic NumGlobalCopies = {"instcombine", "NumGlobalCopies"
, "Number of allocas copied from constant global", {0}, false
}
;
33
34/// pointsToConstantGlobal - Return true if V (possibly indirectly) points to
35/// some part of a constant global variable. This intentionally only accepts
36/// constant expressions because we can't rewrite arbitrary instructions.
37static bool pointsToConstantGlobal(Value *V) {
38 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
39 return GV->isConstant();
40
41 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V)) {
42 if (CE->getOpcode() == Instruction::BitCast ||
43 CE->getOpcode() == Instruction::AddrSpaceCast ||
44 CE->getOpcode() == Instruction::GetElementPtr)
45 return pointsToConstantGlobal(CE->getOperand(0));
46 }
47 return false;
48}
49
50/// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
51/// pointer to an alloca. Ignore any reads of the pointer, return false if we
52/// see any stores or other unknown uses. If we see pointer arithmetic, keep
53/// track of whether it moves the pointer (with IsOffset) but otherwise traverse
54/// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
55/// the alloca, and if the source pointer is a pointer to a constant global, we
56/// can optimize this.
57static bool
58isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
59 SmallVectorImpl<Instruction *> &ToDelete) {
60 // We track lifetime intrinsics as we encounter them. If we decide to go
61 // ahead and replace the value with the global, this lets the caller quickly
62 // eliminate the markers.
63
64 SmallVector<std::pair<Value *, bool>, 35> ValuesToInspect;
65 ValuesToInspect.emplace_back(V, false);
66 while (!ValuesToInspect.empty()) {
67 auto ValuePair = ValuesToInspect.pop_back_val();
68 const bool IsOffset = ValuePair.second;
69 for (auto &U : ValuePair.first->uses()) {
70 auto *I = cast<Instruction>(U.getUser());
71
72 if (auto *LI = dyn_cast<LoadInst>(I)) {
73 // Ignore non-volatile loads, they are always ok.
74 if (!LI->isSimple()) return false;
75 continue;
76 }
77
78 if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
79 // If uses of the bitcast are ok, we are ok.
80 ValuesToInspect.emplace_back(I, IsOffset);
81 continue;
82 }
83 if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
84 // If the GEP has all zero indices, it doesn't offset the pointer. If it
85 // doesn't, it does.
86 ValuesToInspect.emplace_back(I, IsOffset || !GEP->hasAllZeroIndices());
87 continue;
88 }
89
90 if (auto CS = CallSite(I)) {
91 // If this is the function being called then we treat it like a load and
92 // ignore it.
93 if (CS.isCallee(&U))
94 continue;
95
96 unsigned DataOpNo = CS.getDataOperandNo(&U);
97 bool IsArgOperand = CS.isArgOperand(&U);
98
99 // Inalloca arguments are clobbered by the call.
100 if (IsArgOperand && CS.isInAllocaArgument(DataOpNo))
101 return false;
102
103 // If this is a readonly/readnone call site, then we know it is just a
104 // load (but one that potentially returns the value itself), so we can
105 // ignore it if we know that the value isn't captured.
106 if (CS.onlyReadsMemory() &&
107 (CS.getInstruction()->use_empty() || CS.doesNotCapture(DataOpNo)))
108 continue;
109
110 // If this is being passed as a byval argument, the caller is making a
111 // copy, so it is only a read of the alloca.
112 if (IsArgOperand && CS.isByValArgument(DataOpNo))
113 continue;
114 }
115
116 // Lifetime intrinsics can be handled by the caller.
117 if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
118 if (II->getIntrinsicID() == Intrinsic::lifetime_start ||
119 II->getIntrinsicID() == Intrinsic::lifetime_end) {
120 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!\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 120, __PRETTY_FUNCTION__))
;
121 ToDelete.push_back(II);
122 continue;
123 }
124 }
125
126 // If this is isn't our memcpy/memmove, reject it as something we can't
127 // handle.
128 MemTransferInst *MI = dyn_cast<MemTransferInst>(I);
129 if (!MI)
130 return false;
131
132 // If the transfer is using the alloca as a source of the transfer, then
133 // ignore it since it is a load (unless the transfer is volatile).
134 if (U.getOperandNo() == 1) {
135 if (MI->isVolatile()) return false;
136 continue;
137 }
138
139 // If we already have seen a copy, reject the second one.
140 if (TheCopy) return false;
141
142 // If the pointer has been offset from the start of the alloca, we can't
143 // safely handle this.
144 if (IsOffset) return false;
145
146 // If the memintrinsic isn't using the alloca as the dest, reject it.
147 if (U.getOperandNo() != 0) return false;
148
149 // If the source of the memcpy/move is not a constant global, reject it.
150 if (!pointsToConstantGlobal(MI->getSource()))
151 return false;
152
153 // Otherwise, the transform is safe. Remember the copy instruction.
154 TheCopy = MI;
155 }
156 }
157 return true;
158}
159
160/// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
161/// modified by a copy from a constant global. If we can prove this, we can
162/// replace any uses of the alloca with uses of the global directly.
163static MemTransferInst *
164isOnlyCopiedFromConstantGlobal(AllocaInst *AI,
165 SmallVectorImpl<Instruction *> &ToDelete) {
166 MemTransferInst *TheCopy = nullptr;
167 if (isOnlyCopiedFromConstantGlobal(AI, TheCopy, ToDelete))
168 return TheCopy;
169 return nullptr;
170}
171
172/// Returns true if V is dereferenceable for size of alloca.
173static bool isDereferenceableForAllocaSize(const Value *V, const AllocaInst *AI,
174 const DataLayout &DL) {
175 if (AI->isArrayAllocation())
176 return false;
177 uint64_t AllocaSize = DL.getTypeStoreSize(AI->getAllocatedType());
178 if (!AllocaSize)
179 return false;
180 return isDereferenceableAndAlignedPointer(V, AI->getAlignment(),
181 APInt(64, AllocaSize), DL);
182}
183
184static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
185 // Check for array size of 1 (scalar allocation).
186 if (!AI.isArrayAllocation()) {
187 // i32 1 is the canonical array size for scalar allocations.
188 if (AI.getArraySize()->getType()->isIntegerTy(32))
189 return nullptr;
190
191 // Canonicalize it.
192 Value *V = IC.Builder.getInt32(1);
193 AI.setOperand(0, V);
194 return &AI;
195 }
196
197 // Convert: alloca Ty, C - where C is a constant != 1 into: alloca [C x Ty], 1
198 if (const ConstantInt *C = dyn_cast<ConstantInt>(AI.getArraySize())) {
199 Type *NewTy = ArrayType::get(AI.getAllocatedType(), C->getZExtValue());
200 AllocaInst *New = IC.Builder.CreateAlloca(NewTy, nullptr, AI.getName());
201 New->setAlignment(AI.getAlignment());
202
203 // Scan to the end of the allocation instructions, to skip over a block of
204 // allocas if possible...also skip interleaved debug info
205 //
206 BasicBlock::iterator It(New);
207 while (isa<AllocaInst>(*It) || isa<DbgInfoIntrinsic>(*It))
208 ++It;
209
210 // Now that I is pointing to the first non-allocation-inst in the block,
211 // insert our getelementptr instruction...
212 //
213 Type *IdxTy = IC.getDataLayout().getIntPtrType(AI.getType());
214 Value *NullIdx = Constant::getNullValue(IdxTy);
215 Value *Idx[2] = {NullIdx, NullIdx};
216 Instruction *GEP =
217 GetElementPtrInst::CreateInBounds(New, Idx, New->getName() + ".sub");
218 IC.InsertNewInstBefore(GEP, *It);
219
220 // Now make everything use the getelementptr instead of the original
221 // allocation.
222 return IC.replaceInstUsesWith(AI, GEP);
223 }
224
225 if (isa<UndefValue>(AI.getArraySize()))
226 return IC.replaceInstUsesWith(AI, Constant::getNullValue(AI.getType()));
227
228 // Ensure that the alloca array size argument has type intptr_t, so that
229 // any casting is exposed early.
230 Type *IntPtrTy = IC.getDataLayout().getIntPtrType(AI.getType());
231 if (AI.getArraySize()->getType() != IntPtrTy) {
232 Value *V = IC.Builder.CreateIntCast(AI.getArraySize(), IntPtrTy, false);
233 AI.setOperand(0, V);
234 return &AI;
235 }
236
237 return nullptr;
238}
239
240namespace {
241// If I and V are pointers in different address space, it is not allowed to
242// use replaceAllUsesWith since I and V have different types. A
243// non-target-specific transformation should not use addrspacecast on V since
244// the two address space may be disjoint depending on target.
245//
246// This class chases down uses of the old pointer until reaching the load
247// instructions, then replaces the old pointer in the load instructions with
248// the new pointer. If during the chasing it sees bitcast or GEP, it will
249// create new bitcast or GEP with the new pointer and use them in the load
250// instruction.
251class PointerReplacer {
252public:
253 PointerReplacer(InstCombiner &IC) : IC(IC) {}
254 void replacePointer(Instruction &I, Value *V);
255
256private:
257 void findLoadAndReplace(Instruction &I);
258 void replace(Instruction *I);
259 Value *getReplacement(Value *I);
260
261 SmallVector<Instruction *, 4> Path;
262 MapVector<Value *, Value *> WorkMap;
263 InstCombiner &IC;
264};
265} // end anonymous namespace
266
267void PointerReplacer::findLoadAndReplace(Instruction &I) {
268 for (auto U : I.users()) {
269 auto *Inst = dyn_cast<Instruction>(&*U);
270 if (!Inst)
271 return;
272 DEBUG(dbgs() << "Found pointer user: " << *U << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("instcombine")) { dbgs() << "Found pointer user: " <<
*U << '\n'; } } while (false)
;
273 if (isa<LoadInst>(Inst)) {
274 for (auto P : Path)
275 replace(P);
276 replace(Inst);
277 } else if (isa<GetElementPtrInst>(Inst) || isa<BitCastInst>(Inst)) {
278 Path.push_back(Inst);
279 findLoadAndReplace(*Inst);
280 Path.pop_back();
281 } else {
282 return;
283 }
284 }
285}
286
287Value *PointerReplacer::getReplacement(Value *V) {
288 auto Loc = WorkMap.find(V);
289 if (Loc != WorkMap.end())
290 return Loc->second;
291 return nullptr;
292}
293
294void PointerReplacer::replace(Instruction *I) {
295 if (getReplacement(I))
296 return;
297
298 if (auto *LT = dyn_cast<LoadInst>(I)) {
299 auto *V = getReplacement(LT->getPointerOperand());
300 assert(V && "Operand not replaced")((V && "Operand not replaced") ? static_cast<void>
(0) : __assert_fail ("V && \"Operand not replaced\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 300, __PRETTY_FUNCTION__))
;
301 auto *NewI = new LoadInst(V);
302 NewI->takeName(LT);
303 IC.InsertNewInstWith(NewI, *LT);
304 IC.replaceInstUsesWith(*LT, NewI);
305 WorkMap[LT] = NewI;
306 } else if (auto *GEP = dyn_cast<GetElementPtrInst>(I)) {
307 auto *V = getReplacement(GEP->getPointerOperand());
308 assert(V && "Operand not replaced")((V && "Operand not replaced") ? static_cast<void>
(0) : __assert_fail ("V && \"Operand not replaced\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 308, __PRETTY_FUNCTION__))
;
309 SmallVector<Value *, 8> Indices;
310 Indices.append(GEP->idx_begin(), GEP->idx_end());
311 auto *NewI = GetElementPtrInst::Create(
312 V->getType()->getPointerElementType(), V, Indices);
313 IC.InsertNewInstWith(NewI, *GEP);
314 NewI->takeName(GEP);
315 WorkMap[GEP] = NewI;
316 } else if (auto *BC = dyn_cast<BitCastInst>(I)) {
317 auto *V = getReplacement(BC->getOperand(0));
318 assert(V && "Operand not replaced")((V && "Operand not replaced") ? static_cast<void>
(0) : __assert_fail ("V && \"Operand not replaced\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 318, __PRETTY_FUNCTION__))
;
319 auto *NewT = PointerType::get(BC->getType()->getPointerElementType(),
320 V->getType()->getPointerAddressSpace());
321 auto *NewI = new BitCastInst(V, NewT);
322 IC.InsertNewInstWith(NewI, *BC);
323 NewI->takeName(BC);
324 WorkMap[BC] = NewI;
325 } else {
326 llvm_unreachable("should never reach here")::llvm::llvm_unreachable_internal("should never reach here", "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 326)
;
327 }
328}
329
330void PointerReplacer::replacePointer(Instruction &I, Value *V) {
331#ifndef NDEBUG
332 auto *PT = cast<PointerType>(I.getType());
333 auto *NT = cast<PointerType>(V->getType());
334 assert(PT != NT && PT->getElementType() == NT->getElementType() &&((PT != NT && PT->getElementType() == NT->getElementType
() && "Invalid usage") ? static_cast<void> (0) :
__assert_fail ("PT != NT && PT->getElementType() == NT->getElementType() && \"Invalid usage\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 335, __PRETTY_FUNCTION__))
335 "Invalid usage")((PT != NT && PT->getElementType() == NT->getElementType
() && "Invalid usage") ? static_cast<void> (0) :
__assert_fail ("PT != NT && PT->getElementType() == NT->getElementType() && \"Invalid usage\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 335, __PRETTY_FUNCTION__))
;
336#endif
337 WorkMap[&I] = V;
338 findLoadAndReplace(I);
339}
340
341Instruction *InstCombiner::visitAllocaInst(AllocaInst &AI) {
342 if (auto *I = simplifyAllocaArraySize(*this, AI))
343 return I;
344
345 if (AI.getAllocatedType()->isSized()) {
346 // If the alignment is 0 (unspecified), assign it the preferred alignment.
347 if (AI.getAlignment() == 0)
348 AI.setAlignment(DL.getPrefTypeAlignment(AI.getAllocatedType()));
349
350 // Move all alloca's of zero byte objects to the entry block and merge them
351 // together. Note that we only do this for alloca's, because malloc should
352 // allocate and return a unique pointer, even for a zero byte allocation.
353 if (DL.getTypeAllocSize(AI.getAllocatedType()) == 0) {
354 // For a zero sized alloca there is no point in doing an array allocation.
355 // This is helpful if the array size is a complicated expression not used
356 // elsewhere.
357 if (AI.isArrayAllocation()) {
358 AI.setOperand(0, ConstantInt::get(AI.getArraySize()->getType(), 1));
359 return &AI;
360 }
361
362 // Get the first instruction in the entry block.
363 BasicBlock &EntryBlock = AI.getParent()->getParent()->getEntryBlock();
364 Instruction *FirstInst = EntryBlock.getFirstNonPHIOrDbg();
365 if (FirstInst != &AI) {
366 // If the entry block doesn't start with a zero-size alloca then move
367 // this one to the start of the entry block. There is no problem with
368 // dominance as the array size was forced to a constant earlier already.
369 AllocaInst *EntryAI = dyn_cast<AllocaInst>(FirstInst);
370 if (!EntryAI || !EntryAI->getAllocatedType()->isSized() ||
371 DL.getTypeAllocSize(EntryAI->getAllocatedType()) != 0) {
372 AI.moveBefore(FirstInst);
373 return &AI;
374 }
375
376 // If the alignment of the entry block alloca is 0 (unspecified),
377 // assign it the preferred alignment.
378 if (EntryAI->getAlignment() == 0)
379 EntryAI->setAlignment(
380 DL.getPrefTypeAlignment(EntryAI->getAllocatedType()));
381 // Replace this zero-sized alloca with the one at the start of the entry
382 // block after ensuring that the address will be aligned enough for both
383 // types.
384 unsigned MaxAlign = std::max(EntryAI->getAlignment(),
385 AI.getAlignment());
386 EntryAI->setAlignment(MaxAlign);
387 if (AI.getType() != EntryAI->getType())
388 return new BitCastInst(EntryAI, AI.getType());
389 return replaceInstUsesWith(AI, EntryAI);
390 }
391 }
392 }
393
394 if (AI.getAlignment()) {
395 // Check to see if this allocation is only modified by a memcpy/memmove from
396 // a constant global whose alignment is equal to or exceeds that of the
397 // allocation. If this is the case, we can change all users to use
398 // the constant global instead. This is commonly produced by the CFE by
399 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
400 // is only subsequently read.
401 SmallVector<Instruction *, 4> ToDelete;
402 if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
403 unsigned SourceAlign = getOrEnforceKnownAlignment(
404 Copy->getSource(), AI.getAlignment(), DL, &AI, &AC, &DT);
405 if (AI.getAlignment() <= SourceAlign &&
406 isDereferenceableForAllocaSize(Copy->getSource(), &AI, DL)) {
407 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 (false)
;
408 DEBUG(dbgs() << " memcpy = " << *Copy << '\n')do { if (::llvm::DebugFlag && ::llvm::isCurrentDebugType
("instcombine")) { dbgs() << " memcpy = " << *Copy
<< '\n'; } } while (false)
;
409 for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)
410 eraseInstFromFunction(*ToDelete[i]);
411 Constant *TheSrc = cast<Constant>(Copy->getSource());
412 auto *SrcTy = TheSrc->getType();
413 auto *DestTy = PointerType::get(AI.getType()->getPointerElementType(),
414 SrcTy->getPointerAddressSpace());
415 Constant *Cast =
416 ConstantExpr::getPointerBitCastOrAddrSpaceCast(TheSrc, DestTy);
417 if (AI.getType()->getPointerAddressSpace() ==
418 SrcTy->getPointerAddressSpace()) {
419 Instruction *NewI = replaceInstUsesWith(AI, Cast);
420 eraseInstFromFunction(*Copy);
421 ++NumGlobalCopies;
422 return NewI;
423 } else {
424 PointerReplacer PtrReplacer(*this);
425 PtrReplacer.replacePointer(AI, Cast);
426 ++NumGlobalCopies;
427 }
428 }
429 }
430 }
431
432 // At last, use the generic allocation site handler to aggressively remove
433 // unused allocas.
434 return visitAllocSite(AI);
435}
436
437// Are we allowed to form a atomic load or store of this type?
438static bool isSupportedAtomicType(Type *Ty) {
439 return Ty->isIntegerTy() || Ty->isPointerTy() || Ty->isFloatingPointTy();
440}
441
442/// \brief Helper to combine a load to a new type.
443///
444/// This just does the work of combining a load to a new type. It handles
445/// metadata, etc., and returns the new instruction. The \c NewTy should be the
446/// loaded *value* type. This will convert it to a pointer, cast the operand to
447/// that pointer type, load it, etc.
448///
449/// Note that this will create all of the instructions with whatever insert
450/// point the \c InstCombiner currently is using.
451static LoadInst *combineLoadToNewType(InstCombiner &IC, LoadInst &LI, Type *NewTy,
452 const Twine &Suffix = "") {
453 assert((!LI.isAtomic() || isSupportedAtomicType(NewTy)) &&(((!LI.isAtomic() || isSupportedAtomicType(NewTy)) &&
"can't fold an atomic load to requested type") ? static_cast
<void> (0) : __assert_fail ("(!LI.isAtomic() || isSupportedAtomicType(NewTy)) && \"can't fold an atomic load to requested type\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 454, __PRETTY_FUNCTION__))
454 "can't fold an atomic load to requested type")(((!LI.isAtomic() || isSupportedAtomicType(NewTy)) &&
"can't fold an atomic load to requested type") ? static_cast
<void> (0) : __assert_fail ("(!LI.isAtomic() || isSupportedAtomicType(NewTy)) && \"can't fold an atomic load to requested type\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 454, __PRETTY_FUNCTION__))
;
455
456 Value *Ptr = LI.getPointerOperand();
457 unsigned AS = LI.getPointerAddressSpace();
458 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
459 LI.getAllMetadata(MD);
460
461 LoadInst *NewLoad = IC.Builder.CreateAlignedLoad(
462 IC.Builder.CreateBitCast(Ptr, NewTy->getPointerTo(AS)),
463 LI.getAlignment(), LI.isVolatile(), LI.getName() + Suffix);
464 NewLoad->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
465 MDBuilder MDB(NewLoad->getContext());
466 for (const auto &MDPair : MD) {
467 unsigned ID = MDPair.first;
468 MDNode *N = MDPair.second;
469 // Note, essentially every kind of metadata should be preserved here! This
470 // routine is supposed to clone a load instruction changing *only its type*.
471 // The only metadata it makes sense to drop is metadata which is invalidated
472 // when the pointer type changes. This should essentially never be the case
473 // in LLVM, but we explicitly switch over only known metadata to be
474 // conservatively correct. If you are adding metadata to LLVM which pertains
475 // to loads, you almost certainly want to add it here.
476 switch (ID) {
477 case LLVMContext::MD_dbg:
478 case LLVMContext::MD_tbaa:
479 case LLVMContext::MD_prof:
480 case LLVMContext::MD_fpmath:
481 case LLVMContext::MD_tbaa_struct:
482 case LLVMContext::MD_invariant_load:
483 case LLVMContext::MD_alias_scope:
484 case LLVMContext::MD_noalias:
485 case LLVMContext::MD_nontemporal:
486 case LLVMContext::MD_mem_parallel_loop_access:
487 // All of these directly apply.
488 NewLoad->setMetadata(ID, N);
489 break;
490
491 case LLVMContext::MD_nonnull:
492 copyNonnullMetadata(LI, N, *NewLoad);
493 break;
494 case LLVMContext::MD_align:
495 case LLVMContext::MD_dereferenceable:
496 case LLVMContext::MD_dereferenceable_or_null:
497 // These only directly apply if the new type is also a pointer.
498 if (NewTy->isPointerTy())
499 NewLoad->setMetadata(ID, N);
500 break;
501 case LLVMContext::MD_range:
502 copyRangeMetadata(IC.getDataLayout(), LI, N, *NewLoad);
503 break;
504 }
505 }
506 return NewLoad;
507}
508
509/// \brief Combine a store to a new type.
510///
511/// Returns the newly created store instruction.
512static StoreInst *combineStoreToNewValue(InstCombiner &IC, StoreInst &SI, Value *V) {
513 assert((!SI.isAtomic() || isSupportedAtomicType(V->getType())) &&(((!SI.isAtomic() || isSupportedAtomicType(V->getType())) &&
"can't fold an atomic store of requested type") ? static_cast
<void> (0) : __assert_fail ("(!SI.isAtomic() || isSupportedAtomicType(V->getType())) && \"can't fold an atomic store of requested type\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 514, __PRETTY_FUNCTION__))
514 "can't fold an atomic store of requested type")(((!SI.isAtomic() || isSupportedAtomicType(V->getType())) &&
"can't fold an atomic store of requested type") ? static_cast
<void> (0) : __assert_fail ("(!SI.isAtomic() || isSupportedAtomicType(V->getType())) && \"can't fold an atomic store of requested type\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 514, __PRETTY_FUNCTION__))
;
515
516 Value *Ptr = SI.getPointerOperand();
517 unsigned AS = SI.getPointerAddressSpace();
518 SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
519 SI.getAllMetadata(MD);
520
521 StoreInst *NewStore = IC.Builder.CreateAlignedStore(
522 V, IC.Builder.CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
523 SI.getAlignment(), SI.isVolatile());
524 NewStore->setAtomic(SI.getOrdering(), SI.getSyncScopeID());
525 for (const auto &MDPair : MD) {
526 unsigned ID = MDPair.first;
527 MDNode *N = MDPair.second;
528 // Note, essentially every kind of metadata should be preserved here! This
529 // routine is supposed to clone a store instruction changing *only its
530 // type*. The only metadata it makes sense to drop is metadata which is
531 // invalidated when the pointer type changes. This should essentially
532 // never be the case in LLVM, but we explicitly switch over only known
533 // metadata to be conservatively correct. If you are adding metadata to
534 // LLVM which pertains to stores, you almost certainly want to add it
535 // here.
536 switch (ID) {
537 case LLVMContext::MD_dbg:
538 case LLVMContext::MD_tbaa:
539 case LLVMContext::MD_prof:
540 case LLVMContext::MD_fpmath:
541 case LLVMContext::MD_tbaa_struct:
542 case LLVMContext::MD_alias_scope:
543 case LLVMContext::MD_noalias:
544 case LLVMContext::MD_nontemporal:
545 case LLVMContext::MD_mem_parallel_loop_access:
546 // All of these directly apply.
547 NewStore->setMetadata(ID, N);
548 break;
549
550 case LLVMContext::MD_invariant_load:
551 case LLVMContext::MD_nonnull:
552 case LLVMContext::MD_range:
553 case LLVMContext::MD_align:
554 case LLVMContext::MD_dereferenceable:
555 case LLVMContext::MD_dereferenceable_or_null:
556 // These don't apply for stores.
557 break;
558 }
559 }
560
561 return NewStore;
562}
563
564/// \brief Combine loads to match the type of their uses' value after looking
565/// through intervening bitcasts.
566///
567/// The core idea here is that if the result of a load is used in an operation,
568/// we should load the type most conducive to that operation. For example, when
569/// loading an integer and converting that immediately to a pointer, we should
570/// instead directly load a pointer.
571///
572/// However, this routine must never change the width of a load or the number of
573/// loads as that would introduce a semantic change. This combine is expected to
574/// be a semantic no-op which just allows loads to more closely model the types
575/// of their consuming operations.
576///
577/// Currently, we also refuse to change the precise type used for an atomic load
578/// or a volatile load. This is debatable, and might be reasonable to change
579/// later. However, it is risky in case some backend or other part of LLVM is
580/// relying on the exact type loaded to select appropriate atomic operations.
581static Instruction *combineLoadToOperationType(InstCombiner &IC, LoadInst &LI) {
582 // FIXME: We could probably with some care handle both volatile and ordered
583 // atomic loads here but it isn't clear that this is important.
584 if (!LI.isUnordered())
585 return nullptr;
586
587 if (LI.use_empty())
588 return nullptr;
589
590 // swifterror values can't be bitcasted.
591 if (LI.getPointerOperand()->isSwiftError())
592 return nullptr;
593
594 Type *Ty = LI.getType();
595 const DataLayout &DL = IC.getDataLayout();
596
597 // Try to canonicalize loads which are only ever stored to operate over
598 // integers instead of any other type. We only do this when the loaded type
599 // is sized and has a size exactly the same as its store size and the store
600 // size is a legal integer type.
601 if (!Ty->isIntegerTy() && Ty->isSized() &&
602 DL.isLegalInteger(DL.getTypeStoreSizeInBits(Ty)) &&
603 DL.getTypeStoreSizeInBits(Ty) == DL.getTypeSizeInBits(Ty) &&
604 !DL.isNonIntegralPointerType(Ty)) {
605 if (all_of(LI.users(), [&LI](User *U) {
606 auto *SI = dyn_cast<StoreInst>(U);
607 return SI && SI->getPointerOperand() != &LI &&
608 !SI->getPointerOperand()->isSwiftError();
609 })) {
610 LoadInst *NewLoad = combineLoadToNewType(
611 IC, LI,
612 Type::getIntNTy(LI.getContext(), DL.getTypeStoreSizeInBits(Ty)));
613 // Replace all the stores with stores of the newly loaded value.
614 for (auto UI = LI.user_begin(), UE = LI.user_end(); UI != UE;) {
615 auto *SI = cast<StoreInst>(*UI++);
616 IC.Builder.SetInsertPoint(SI);
617 combineStoreToNewValue(IC, *SI, NewLoad);
618 IC.eraseInstFromFunction(*SI);
619 }
620 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!\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 620, __PRETTY_FUNCTION__))
;
621 // Return the old load so the combiner can delete it safely.
622 return &LI;
623 }
624 }
625
626 // Fold away bit casts of the loaded value by loading the desired type.
627 // We can do this for BitCastInsts as well as casts from and to pointer types,
628 // as long as those are noops (i.e., the source or dest type have the same
629 // bitwidth as the target's pointers).
630 if (LI.hasOneUse())
631 if (auto* CI = dyn_cast<CastInst>(LI.user_back()))
632 if (CI->isNoopCast(DL))
633 if (!LI.isAtomic() || isSupportedAtomicType(CI->getDestTy())) {
634 LoadInst *NewLoad = combineLoadToNewType(IC, LI, CI->getDestTy());
635 CI->replaceAllUsesWith(NewLoad);
636 IC.eraseInstFromFunction(*CI);
637 return &LI;
638 }
639
640 // FIXME: We should also canonicalize loads of vectors when their elements are
641 // cast to other types.
642 return nullptr;
643}
644
645static Instruction *unpackLoadToAggregate(InstCombiner &IC, LoadInst &LI) {
646 // FIXME: We could probably with some care handle both volatile and atomic
647 // stores here but it isn't clear that this is important.
648 if (!LI.isSimple())
649 return nullptr;
650
651 Type *T = LI.getType();
652 if (!T->isAggregateType())
653 return nullptr;
654
655 StringRef Name = LI.getName();
656 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\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 656, __PRETTY_FUNCTION__))
;
657
658 if (auto *ST = dyn_cast<StructType>(T)) {
659 // If the struct only have one element, we unpack.
660 auto NumElements = ST->getNumElements();
661 if (NumElements == 1) {
662 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ST->getTypeAtIndex(0U),
663 ".unpack");
664 AAMDNodes AAMD;
665 LI.getAAMetadata(AAMD);
666 NewLoad->setAAMetadata(AAMD);
667 return IC.replaceInstUsesWith(LI, IC.Builder.CreateInsertValue(
668 UndefValue::get(T), NewLoad, 0, Name));
669 }
670
671 // We don't want to break loads with padding here as we'd loose
672 // the knowledge that padding exists for the rest of the pipeline.
673 const DataLayout &DL = IC.getDataLayout();
674 auto *SL = DL.getStructLayout(ST);
675 if (SL->hasPadding())
676 return nullptr;
677
678 auto Align = LI.getAlignment();
679 if (!Align)
680 Align = DL.getABITypeAlignment(ST);
681
682 auto *Addr = LI.getPointerOperand();
683 auto *IdxType = Type::getInt32Ty(T->getContext());
684 auto *Zero = ConstantInt::get(IdxType, 0);
685
686 Value *V = UndefValue::get(T);
687 for (unsigned i = 0; i < NumElements; i++) {
688 Value *Indices[2] = {
689 Zero,
690 ConstantInt::get(IdxType, i),
691 };
692 auto *Ptr = IC.Builder.CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
693 Name + ".elt");
694 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
695 auto *L = IC.Builder.CreateAlignedLoad(Ptr, EltAlign, Name + ".unpack");
696 // Propagate AA metadata. It'll still be valid on the narrowed load.
697 AAMDNodes AAMD;
698 LI.getAAMetadata(AAMD);
699 L->setAAMetadata(AAMD);
700 V = IC.Builder.CreateInsertValue(V, L, i);
701 }
702
703 V->setName(Name);
704 return IC.replaceInstUsesWith(LI, V);
705 }
706
707 if (auto *AT = dyn_cast<ArrayType>(T)) {
708 auto *ET = AT->getElementType();
709 auto NumElements = AT->getNumElements();
710 if (NumElements == 1) {
711 LoadInst *NewLoad = combineLoadToNewType(IC, LI, ET, ".unpack");
712 AAMDNodes AAMD;
713 LI.getAAMetadata(AAMD);
714 NewLoad->setAAMetadata(AAMD);
715 return IC.replaceInstUsesWith(LI, IC.Builder.CreateInsertValue(
716 UndefValue::get(T), NewLoad, 0, Name));
717 }
718
719 // Bail out if the array is too large. Ideally we would like to optimize
720 // arrays of arbitrary size but this has a terrible impact on compile time.
721 // The threshold here is chosen arbitrarily, maybe needs a little bit of
722 // tuning.
723 if (NumElements > IC.MaxArraySizeForCombine)
724 return nullptr;
725
726 const DataLayout &DL = IC.getDataLayout();
727 auto EltSize = DL.getTypeAllocSize(ET);
728 auto Align = LI.getAlignment();
729 if (!Align)
730 Align = DL.getABITypeAlignment(T);
731
732 auto *Addr = LI.getPointerOperand();
733 auto *IdxType = Type::getInt64Ty(T->getContext());
734 auto *Zero = ConstantInt::get(IdxType, 0);
735
736 Value *V = UndefValue::get(T);
737 uint64_t Offset = 0;
738 for (uint64_t i = 0; i < NumElements; i++) {
739 Value *Indices[2] = {
740 Zero,
741 ConstantInt::get(IdxType, i),
742 };
743 auto *Ptr = IC.Builder.CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
744 Name + ".elt");
745 auto *L = IC.Builder.CreateAlignedLoad(Ptr, MinAlign(Align, Offset),
746 Name + ".unpack");
747 AAMDNodes AAMD;
748 LI.getAAMetadata(AAMD);
749 L->setAAMetadata(AAMD);
750 V = IC.Builder.CreateInsertValue(V, L, i);
751 Offset += EltSize;
752 }
753
754 V->setName(Name);
755 return IC.replaceInstUsesWith(LI, V);
756 }
757
758 return nullptr;
759}
760
761// If we can determine that all possible objects pointed to by the provided
762// pointer value are, not only dereferenceable, but also definitively less than
763// or equal to the provided maximum size, then return true. Otherwise, return
764// false (constant global values and allocas fall into this category).
765//
766// FIXME: This should probably live in ValueTracking (or similar).
767static bool isObjectSizeLessThanOrEq(Value *V, uint64_t MaxSize,
768 const DataLayout &DL) {
769 SmallPtrSet<Value *, 4> Visited;
770 SmallVector<Value *, 4> Worklist(1, V);
771
772 do {
773 Value *P = Worklist.pop_back_val();
774 P = P->stripPointerCasts();
775
776 if (!Visited.insert(P).second)
777 continue;
778
779 if (SelectInst *SI = dyn_cast<SelectInst>(P)) {
780 Worklist.push_back(SI->getTrueValue());
781 Worklist.push_back(SI->getFalseValue());
782 continue;
783 }
784
785 if (PHINode *PN = dyn_cast<PHINode>(P)) {
786 for (Value *IncValue : PN->incoming_values())
787 Worklist.push_back(IncValue);
788 continue;
789 }
790
791 if (GlobalAlias *GA = dyn_cast<GlobalAlias>(P)) {
792 if (GA->isInterposable())
793 return false;
794 Worklist.push_back(GA->getAliasee());
795 continue;
796 }
797
798 // If we know how big this object is, and it is less than MaxSize, continue
799 // searching. Otherwise, return false.
800 if (AllocaInst *AI = dyn_cast<AllocaInst>(P)) {
801 if (!AI->getAllocatedType()->isSized())
802 return false;
803
804 ConstantInt *CS = dyn_cast<ConstantInt>(AI->getArraySize());
805 if (!CS)
806 return false;
807
808 uint64_t TypeSize = DL.getTypeAllocSize(AI->getAllocatedType());
809 // Make sure that, even if the multiplication below would wrap as an
810 // uint64_t, we still do the right thing.
811 if ((CS->getValue().zextOrSelf(128)*APInt(128, TypeSize)).ugt(MaxSize))
812 return false;
813 continue;
814 }
815
816 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(P)) {
817 if (!GV->hasDefinitiveInitializer() || !GV->isConstant())
818 return false;
819
820 uint64_t InitSize = DL.getTypeAllocSize(GV->getValueType());
821 if (InitSize > MaxSize)
822 return false;
823 continue;
824 }
825
826 return false;
827 } while (!Worklist.empty());
828
829 return true;
830}
831
832// If we're indexing into an object of a known size, and the outer index is
833// not a constant, but having any value but zero would lead to undefined
834// behavior, replace it with zero.
835//
836// For example, if we have:
837// @f.a = private unnamed_addr constant [1 x i32] [i32 12], align 4
838// ...
839// %arrayidx = getelementptr inbounds [1 x i32]* @f.a, i64 0, i64 %x
840// ... = load i32* %arrayidx, align 4
841// Then we know that we can replace %x in the GEP with i64 0.
842//
843// FIXME: We could fold any GEP index to zero that would cause UB if it were
844// not zero. Currently, we only handle the first such index. Also, we could
845// also search through non-zero constant indices if we kept track of the
846// offsets those indices implied.
847static bool canReplaceGEPIdxWithZero(InstCombiner &IC, GetElementPtrInst *GEPI,
848 Instruction *MemI, unsigned &Idx) {
849 if (GEPI->getNumOperands() < 2)
850 return false;
851
852 // Find the first non-zero index of a GEP. If all indices are zero, return
853 // one past the last index.
854 auto FirstNZIdx = [](const GetElementPtrInst *GEPI) {
855 unsigned I = 1;
856 for (unsigned IE = GEPI->getNumOperands(); I != IE; ++I) {
857 Value *V = GEPI->getOperand(I);
858 if (const ConstantInt *CI = dyn_cast<ConstantInt>(V))
859 if (CI->isZero())
860 continue;
861
862 break;
863 }
864
865 return I;
866 };
867
868 // Skip through initial 'zero' indices, and find the corresponding pointer
869 // type. See if the next index is not a constant.
870 Idx = FirstNZIdx(GEPI);
871 if (Idx == GEPI->getNumOperands())
872 return false;
873 if (isa<Constant>(GEPI->getOperand(Idx)))
874 return false;
875
876 SmallVector<Value *, 4> Ops(GEPI->idx_begin(), GEPI->idx_begin() + Idx);
877 Type *AllocTy =
878 GetElementPtrInst::getIndexedType(GEPI->getSourceElementType(), Ops);
879 if (!AllocTy || !AllocTy->isSized())
880 return false;
881 const DataLayout &DL = IC.getDataLayout();
882 uint64_t TyAllocSize = DL.getTypeAllocSize(AllocTy);
883
884 // If there are more indices after the one we might replace with a zero, make
885 // sure they're all non-negative. If any of them are negative, the overall
886 // address being computed might be before the base address determined by the
887 // first non-zero index.
888 auto IsAllNonNegative = [&]() {
889 for (unsigned i = Idx+1, e = GEPI->getNumOperands(); i != e; ++i) {
890 KnownBits Known = IC.computeKnownBits(GEPI->getOperand(i), 0, MemI);
891 if (Known.isNonNegative())
892 continue;
893 return false;
894 }
895
896 return true;
897 };
898
899 // FIXME: If the GEP is not inbounds, and there are extra indices after the
900 // one we'll replace, those could cause the address computation to wrap
901 // (rendering the IsAllNonNegative() check below insufficient). We can do
902 // better, ignoring zero indices (and other indices we can prove small
903 // enough not to wrap).
904 if (Idx+1 != GEPI->getNumOperands() && !GEPI->isInBounds())
905 return false;
906
907 // Note that isObjectSizeLessThanOrEq will return true only if the pointer is
908 // also known to be dereferenceable.
909 return isObjectSizeLessThanOrEq(GEPI->getOperand(0), TyAllocSize, DL) &&
910 IsAllNonNegative();
911}
912
913// If we're indexing into an object with a variable index for the memory
914// access, but the object has only one element, we can assume that the index
915// will always be zero. If we replace the GEP, return it.
916template <typename T>
917static Instruction *replaceGEPIdxWithZero(InstCombiner &IC, Value *Ptr,
918 T &MemI) {
919 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr)) {
920 unsigned Idx;
921 if (canReplaceGEPIdxWithZero(IC, GEPI, &MemI, Idx)) {
922 Instruction *NewGEPI = GEPI->clone();
923 NewGEPI->setOperand(Idx,
924 ConstantInt::get(GEPI->getOperand(Idx)->getType(), 0));
925 NewGEPI->insertBefore(GEPI);
926 MemI.setOperand(MemI.getPointerOperandIndex(), NewGEPI);
927 return NewGEPI;
928 }
929 }
930
931 return nullptr;
932}
933
934static bool canSimplifyNullLoadOrGEP(LoadInst &LI, Value *Op) {
935 if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Op)) {
936 const Value *GEPI0 = GEPI->getOperand(0);
937 if (isa<ConstantPointerNull>(GEPI0) && GEPI->getPointerAddressSpace() == 0)
938 return true;
939 }
940 if (isa<UndefValue>(Op) ||
941 (isa<ConstantPointerNull>(Op) && LI.getPointerAddressSpace() == 0))
942 return true;
943 return false;
944}
945
946Instruction *InstCombiner::visitLoadInst(LoadInst &LI) {
947 Value *Op = LI.getOperand(0);
948
949 // Try to canonicalize the loaded type.
950 if (Instruction *Res = combineLoadToOperationType(*this, LI))
951 return Res;
952
953 // Attempt to improve the alignment.
954 unsigned KnownAlign = getOrEnforceKnownAlignment(
955 Op, DL.getPrefTypeAlignment(LI.getType()), DL, &LI, &AC, &DT);
956 unsigned LoadAlign = LI.getAlignment();
957 unsigned EffectiveLoadAlign =
958 LoadAlign != 0 ? LoadAlign : DL.getABITypeAlignment(LI.getType());
959
960 if (KnownAlign > EffectiveLoadAlign)
961 LI.setAlignment(KnownAlign);
962 else if (LoadAlign == 0)
963 LI.setAlignment(EffectiveLoadAlign);
964
965 // Replace GEP indices if possible.
966 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Op, LI)) {
967 Worklist.Add(NewGEPI);
968 return &LI;
969 }
970
971 if (Instruction *Res = unpackLoadToAggregate(*this, LI))
972 return Res;
973
974 // Do really simple store-to-load forwarding and load CSE, to catch cases
975 // where there are several consecutive memory accesses to the same location,
976 // separated by a few arithmetic operations.
977 BasicBlock::iterator BBI(LI);
978 bool IsLoadCSE = false;
979 if (Value *AvailableVal = FindAvailableLoadedValue(
980 &LI, LI.getParent(), BBI, DefMaxInstsToScan, AA, &IsLoadCSE)) {
981 if (IsLoadCSE)
982 combineMetadataForCSE(cast<LoadInst>(AvailableVal), &LI);
983
984 return replaceInstUsesWith(
985 LI, Builder.CreateBitOrPointerCast(AvailableVal, LI.getType(),
986 LI.getName() + ".cast"));
987 }
988
989 // None of the following transforms are legal for volatile/ordered atomic
990 // loads. Most of them do apply for unordered atomics.
991 if (!LI.isUnordered()) return nullptr;
992
993 // load(gep null, ...) -> unreachable
994 // load null/undef -> unreachable
995 // TODO: Consider a target hook for valid address spaces for this xforms.
996 if (canSimplifyNullLoadOrGEP(LI, Op)) {
997 // Insert a new store to null instruction before the load to indicate
998 // that this code is not reachable. We do this instead of inserting
999 // an unreachable instruction directly because we cannot modify the
1000 // CFG.
1001 StoreInst *SI = new StoreInst(UndefValue::get(LI.getType()),
1002 Constant::getNullValue(Op->getType()), &LI);
1003 SI->setDebugLoc(LI.getDebugLoc());
1004 return replaceInstUsesWith(LI, UndefValue::get(LI.getType()));
1005 }
1006
1007 if (Op->hasOneUse()) {
1008 // Change select and PHI nodes to select values instead of addresses: this
1009 // helps alias analysis out a lot, allows many others simplifications, and
1010 // exposes redundancy in the code.
1011 //
1012 // Note that we cannot do the transformation unless we know that the
1013 // introduced loads cannot trap! Something like this is valid as long as
1014 // the condition is always false: load (select bool %C, int* null, int* %G),
1015 // but it would not be valid if we transformed it to load from null
1016 // unconditionally.
1017 //
1018 if (SelectInst *SI = dyn_cast<SelectInst>(Op)) {
1019 // load (select (Cond, &V1, &V2)) --> select(Cond, load &V1, load &V2).
1020 unsigned Align = LI.getAlignment();
1021 if (isSafeToLoadUnconditionally(SI->getOperand(1), Align, DL, SI) &&
1022 isSafeToLoadUnconditionally(SI->getOperand(2), Align, DL, SI)) {
1023 LoadInst *V1 = Builder.CreateLoad(SI->getOperand(1),
1024 SI->getOperand(1)->getName()+".val");
1025 LoadInst *V2 = Builder.CreateLoad(SI->getOperand(2),
1026 SI->getOperand(2)->getName()+".val");
1027 assert(LI.isUnordered() && "implied by above")((LI.isUnordered() && "implied by above") ? static_cast
<void> (0) : __assert_fail ("LI.isUnordered() && \"implied by above\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 1027, __PRETTY_FUNCTION__))
;
1028 V1->setAlignment(Align);
1029 V1->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
1030 V2->setAlignment(Align);
1031 V2->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
1032 return SelectInst::Create(SI->getCondition(), V1, V2);
1033 }
1034
1035 // load (select (cond, null, P)) -> load P
1036 if (isa<ConstantPointerNull>(SI->getOperand(1)) &&
1037 LI.getPointerAddressSpace() == 0) {
1038 LI.setOperand(0, SI->getOperand(2));
1039 return &LI;
1040 }
1041
1042 // load (select (cond, P, null)) -> load P
1043 if (isa<ConstantPointerNull>(SI->getOperand(2)) &&
1044 LI.getPointerAddressSpace() == 0) {
1045 LI.setOperand(0, SI->getOperand(1));
1046 return &LI;
1047 }
1048 }
1049 }
1050 return nullptr;
1051}
1052
1053/// \brief Look for extractelement/insertvalue sequence that acts like a bitcast.
1054///
1055/// \returns underlying value that was "cast", or nullptr otherwise.
1056///
1057/// For example, if we have:
1058///
1059/// %E0 = extractelement <2 x double> %U, i32 0
1060/// %V0 = insertvalue [2 x double] undef, double %E0, 0
1061/// %E1 = extractelement <2 x double> %U, i32 1
1062/// %V1 = insertvalue [2 x double] %V0, double %E1, 1
1063///
1064/// and the layout of a <2 x double> is isomorphic to a [2 x double],
1065/// then %V1 can be safely approximated by a conceptual "bitcast" of %U.
1066/// Note that %U may contain non-undef values where %V1 has undef.
1067static Value *likeBitCastFromVector(InstCombiner &IC, Value *V) {
1068 Value *U = nullptr;
1069 while (auto *IV = dyn_cast<InsertValueInst>(V)) {
1070 auto *E = dyn_cast<ExtractElementInst>(IV->getInsertedValueOperand());
1071 if (!E)
1072 return nullptr;
1073 auto *W = E->getVectorOperand();
1074 if (!U)
1075 U = W;
1076 else if (U != W)
1077 return nullptr;
1078 auto *CI = dyn_cast<ConstantInt>(E->getIndexOperand());
1079 if (!CI || IV->getNumIndices() != 1 || CI->getZExtValue() != *IV->idx_begin())
1080 return nullptr;
1081 V = IV->getAggregateOperand();
1082 }
1083 if (!isa<UndefValue>(V) ||!U)
1084 return nullptr;
1085
1086 auto *UT = cast<VectorType>(U->getType());
1087 auto *VT = V->getType();
1088 // Check that types UT and VT are bitwise isomorphic.
1089 const auto &DL = IC.getDataLayout();
1090 if (DL.getTypeStoreSizeInBits(UT) != DL.getTypeStoreSizeInBits(VT)) {
1091 return nullptr;
1092 }
1093 if (auto *AT = dyn_cast<ArrayType>(VT)) {
1094 if (AT->getNumElements() != UT->getNumElements())
1095 return nullptr;
1096 } else {
1097 auto *ST = cast<StructType>(VT);
1098 if (ST->getNumElements() != UT->getNumElements())
1099 return nullptr;
1100 for (const auto *EltT : ST->elements()) {
1101 if (EltT != UT->getElementType())
1102 return nullptr;
1103 }
1104 }
1105 return U;
1106}
1107
1108/// \brief Combine stores to match the type of value being stored.
1109///
1110/// The core idea here is that the memory does not have any intrinsic type and
1111/// where we can we should match the type of a store to the type of value being
1112/// stored.
1113///
1114/// However, this routine must never change the width of a store or the number of
1115/// stores as that would introduce a semantic change. This combine is expected to
1116/// be a semantic no-op which just allows stores to more closely model the types
1117/// of their incoming values.
1118///
1119/// Currently, we also refuse to change the precise type used for an atomic or
1120/// volatile store. This is debatable, and might be reasonable to change later.
1121/// However, it is risky in case some backend or other part of LLVM is relying
1122/// on the exact type stored to select appropriate atomic operations.
1123///
1124/// \returns true if the store was successfully combined away. This indicates
1125/// the caller must erase the store instruction. We have to let the caller erase
1126/// the store instruction as otherwise there is no way to signal whether it was
1127/// combined or not: IC.EraseInstFromFunction returns a null pointer.
1128static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
1129 // FIXME: We could probably with some care handle both volatile and ordered
1130 // atomic stores here but it isn't clear that this is important.
1131 if (!SI.isUnordered())
1132 return false;
1133
1134 // swifterror values can't be bitcasted.
1135 if (SI.getPointerOperand()->isSwiftError())
1136 return false;
1137
1138 Value *V = SI.getValueOperand();
1139
1140 // Fold away bit casts of the stored value by storing the original type.
1141 if (auto *BC = dyn_cast<BitCastInst>(V)) {
1142 V = BC->getOperand(0);
1143 if (!SI.isAtomic() || isSupportedAtomicType(V->getType())) {
1144 combineStoreToNewValue(IC, SI, V);
1145 return true;
1146 }
1147 }
1148
1149 if (Value *U = likeBitCastFromVector(IC, V))
1150 if (!SI.isAtomic() || isSupportedAtomicType(U->getType())) {
1151 combineStoreToNewValue(IC, SI, U);
1152 return true;
1153 }
1154
1155 // FIXME: We should also canonicalize stores of vectors when their elements
1156 // are cast to other types.
1157 return false;
1158}
1159
1160static bool unpackStoreToAggregate(InstCombiner &IC, StoreInst &SI) {
1161 // FIXME: We could probably with some care handle both volatile and atomic
1162 // stores here but it isn't clear that this is important.
1163 if (!SI.isSimple())
1164 return false;
1165
1166 Value *V = SI.getValueOperand();
1167 Type *T = V->getType();
1168
1169 if (!T->isAggregateType())
1170 return false;
1171
1172 if (auto *ST = dyn_cast<StructType>(T)) {
1173 // If the struct only have one element, we unpack.
1174 unsigned Count = ST->getNumElements();
1175 if (Count == 1) {
1176 V = IC.Builder.CreateExtractValue(V, 0);
1177 combineStoreToNewValue(IC, SI, V);
1178 return true;
1179 }
1180
1181 // We don't want to break loads with padding here as we'd loose
1182 // the knowledge that padding exists for the rest of the pipeline.
1183 const DataLayout &DL = IC.getDataLayout();
1184 auto *SL = DL.getStructLayout(ST);
1185 if (SL->hasPadding())
1186 return false;
1187
1188 auto Align = SI.getAlignment();
1189 if (!Align)
1190 Align = DL.getABITypeAlignment(ST);
1191
1192 SmallString<16> EltName = V->getName();
1193 EltName += ".elt";
1194 auto *Addr = SI.getPointerOperand();
1195 SmallString<16> AddrName = Addr->getName();
1196 AddrName += ".repack";
1197
1198 auto *IdxType = Type::getInt32Ty(ST->getContext());
1199 auto *Zero = ConstantInt::get(IdxType, 0);
1200 for (unsigned i = 0; i < Count; i++) {
1201 Value *Indices[2] = {
1202 Zero,
1203 ConstantInt::get(IdxType, i),
1204 };
1205 auto *Ptr = IC.Builder.CreateInBoundsGEP(ST, Addr, makeArrayRef(Indices),
1206 AddrName);
1207 auto *Val = IC.Builder.CreateExtractValue(V, i, EltName);
1208 auto EltAlign = MinAlign(Align, SL->getElementOffset(i));
1209 llvm::Instruction *NS = IC.Builder.CreateAlignedStore(Val, Ptr, EltAlign);
1210 AAMDNodes AAMD;
1211 SI.getAAMetadata(AAMD);
1212 NS->setAAMetadata(AAMD);
1213 }
1214
1215 return true;
1216 }
1217
1218 if (auto *AT = dyn_cast<ArrayType>(T)) {
1219 // If the array only have one element, we unpack.
1220 auto NumElements = AT->getNumElements();
1221 if (NumElements == 1) {
1222 V = IC.Builder.CreateExtractValue(V, 0);
1223 combineStoreToNewValue(IC, SI, V);
1224 return true;
1225 }
1226
1227 // Bail out if the array is too large. Ideally we would like to optimize
1228 // arrays of arbitrary size but this has a terrible impact on compile time.
1229 // The threshold here is chosen arbitrarily, maybe needs a little bit of
1230 // tuning.
1231 if (NumElements > IC.MaxArraySizeForCombine)
1232 return false;
1233
1234 const DataLayout &DL = IC.getDataLayout();
1235 auto EltSize = DL.getTypeAllocSize(AT->getElementType());
1236 auto Align = SI.getAlignment();
1237 if (!Align)
1238 Align = DL.getABITypeAlignment(T);
1239
1240 SmallString<16> EltName = V->getName();
1241 EltName += ".elt";
1242 auto *Addr = SI.getPointerOperand();
1243 SmallString<16> AddrName = Addr->getName();
1244 AddrName += ".repack";
1245
1246 auto *IdxType = Type::getInt64Ty(T->getContext());
1247 auto *Zero = ConstantInt::get(IdxType, 0);
1248
1249 uint64_t Offset = 0;
1250 for (uint64_t i = 0; i < NumElements; i++) {
1251 Value *Indices[2] = {
1252 Zero,
1253 ConstantInt::get(IdxType, i),
1254 };
1255 auto *Ptr = IC.Builder.CreateInBoundsGEP(AT, Addr, makeArrayRef(Indices),
1256 AddrName);
1257 auto *Val = IC.Builder.CreateExtractValue(V, i, EltName);
1258 auto EltAlign = MinAlign(Align, Offset);
1259 Instruction *NS = IC.Builder.CreateAlignedStore(Val, Ptr, EltAlign);
1260 AAMDNodes AAMD;
1261 SI.getAAMetadata(AAMD);
1262 NS->setAAMetadata(AAMD);
1263 Offset += EltSize;
1264 }
1265
1266 return true;
1267 }
1268
1269 return false;
1270}
1271
1272/// equivalentAddressValues - Test if A and B will obviously have the same
1273/// value. This includes recognizing that %t0 and %t1 will have the same
1274/// value in code like this:
1275/// %t0 = getelementptr \@a, 0, 3
1276/// store i32 0, i32* %t0
1277/// %t1 = getelementptr \@a, 0, 3
1278/// %t2 = load i32* %t1
1279///
1280static bool equivalentAddressValues(Value *A, Value *B) {
1281 // Test if the values are trivially equivalent.
1282 if (A == B) return true;
1283
1284 // Test if the values come form identical arithmetic instructions.
1285 // This uses isIdenticalToWhenDefined instead of isIdenticalTo because
1286 // its only used to compare two uses within the same basic block, which
1287 // means that they'll always either have the same value or one of them
1288 // will have an undefined value.
1289 if (isa<BinaryOperator>(A) ||
1290 isa<CastInst>(A) ||
1291 isa<PHINode>(A) ||
1292 isa<GetElementPtrInst>(A))
1293 if (Instruction *BI = dyn_cast<Instruction>(B))
1294 if (cast<Instruction>(A)->isIdenticalToWhenDefined(BI))
1295 return true;
1296
1297 // Otherwise they may not be equivalent.
1298 return false;
1299}
1300
1301Instruction *InstCombiner::visitStoreInst(StoreInst &SI) {
1302 Value *Val = SI.getOperand(0);
1303 Value *Ptr = SI.getOperand(1);
1304
1305 // Try to canonicalize the stored type.
1306 if (combineStoreToValueType(*this, SI))
1
Taking false branch
1307 return eraseInstFromFunction(SI);
1308
1309 // Attempt to improve the alignment.
1310 unsigned KnownAlign = getOrEnforceKnownAlignment(
1311 Ptr, DL.getPrefTypeAlignment(Val->getType()), DL, &SI, &AC, &DT);
1312 unsigned StoreAlign = SI.getAlignment();
1313 unsigned EffectiveStoreAlign =
1314 StoreAlign != 0 ? StoreAlign : DL.getABITypeAlignment(Val->getType());
2
Assuming 'StoreAlign' is equal to 0
3
'?' condition is false
1315
1316 if (KnownAlign > EffectiveStoreAlign)
4
Taking false branch
1317 SI.setAlignment(KnownAlign);
1318 else if (StoreAlign == 0)
5
Taking true branch
1319 SI.setAlignment(EffectiveStoreAlign);
1320
1321 // Try to canonicalize the stored type.
1322 if (unpackStoreToAggregate(*this, SI))
6
Taking false branch
1323 return eraseInstFromFunction(SI);
1324
1325 // Replace GEP indices if possible.
1326 if (Instruction *NewGEPI = replaceGEPIdxWithZero(*this, Ptr, SI)) {
7
Taking false branch
1327 Worklist.Add(NewGEPI);
1328 return &SI;
1329 }
1330
1331 // Don't hack volatile/ordered stores.
1332 // FIXME: Some bits are legal for ordered atomic stores; needs refactoring.
1333 if (!SI.isUnordered()) return nullptr;
8
Taking false branch
1334
1335 // If the RHS is an alloca with a single use, zapify the store, making the
1336 // alloca dead.
1337 if (Ptr->hasOneUse()) {
9
Assuming the condition is false
10
Taking false branch
1338 if (isa<AllocaInst>(Ptr))
1339 return eraseInstFromFunction(SI);
1340 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Ptr)) {
1341 if (isa<AllocaInst>(GEP->getOperand(0))) {
1342 if (GEP->getOperand(0)->hasOneUse())
1343 return eraseInstFromFunction(SI);
1344 }
1345 }
1346 }
1347
1348 // Do really simple DSE, to catch cases where there are several consecutive
1349 // stores to the same location, separated by a few arithmetic operations. This
1350 // situation often occurs with bitfield accesses.
1351 BasicBlock::iterator BBI(SI);
1352 for (unsigned ScanInsts = 6; BBI != SI.getParent()->begin() && ScanInsts;
11
Loop condition is false. Execution continues on line 1395
1353 --ScanInsts) {
1354 --BBI;
1355 // Don't count debug info directives, lest they affect codegen,
1356 // and we skip pointer-to-pointer bitcasts, which are NOPs.
1357 if (isa<DbgInfoIntrinsic>(BBI) ||
1358 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1359 ScanInsts++;
1360 continue;
1361 }
1362
1363 if (StoreInst *PrevSI = dyn_cast<StoreInst>(BBI)) {
1364 // Prev store isn't volatile, and stores to the same location?
1365 if (PrevSI->isUnordered() && equivalentAddressValues(PrevSI->getOperand(1),
1366 SI.getOperand(1))) {
1367 ++NumDeadStore;
1368 ++BBI;
1369 eraseInstFromFunction(*PrevSI);
1370 continue;
1371 }
1372 break;
1373 }
1374
1375 // If this is a load, we have to stop. However, if the loaded value is from
1376 // the pointer we're loading and is producing the pointer we're storing,
1377 // then *this* store is dead (X = load P; store X -> P).
1378 if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
1379 if (LI == Val && equivalentAddressValues(LI->getOperand(0), Ptr)) {
1380 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\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 1380, __PRETTY_FUNCTION__))
;
1381 return eraseInstFromFunction(SI);
1382 }
1383
1384 // Otherwise, this is a load from some other location. Stores before it
1385 // may not be dead.
1386 break;
1387 }
1388
1389 // Don't skip over loads, throws or things that can modify memory.
1390 if (BBI->mayWriteToMemory() || BBI->mayReadFromMemory() || BBI->mayThrow())
1391 break;
1392 }
1393
1394 // store X, null -> turns into 'unreachable' in SimplifyCFG
1395 if (isa<ConstantPointerNull>(Ptr) && SI.getPointerAddressSpace() == 0) {
1396 if (!isa<UndefValue>(Val)) {
1397 SI.setOperand(0, UndefValue::get(Val->getType()));
1398 if (Instruction *U = dyn_cast<Instruction>(Val))
1399 Worklist.Add(U); // Dropped a use.
1400 }
1401 return nullptr; // Do not modify these!
1402 }
1403
1404 // store undef, Ptr -> noop
1405 if (isa<UndefValue>(Val))
12
Taking false branch
1406 return eraseInstFromFunction(SI);
1407
1408 // If this store is the last instruction in the basic block (possibly
1409 // excepting debug info instructions), and if the block ends with an
1410 // unconditional branch, try to move it to the successor block.
1411 BBI = SI.getIterator();
1412 do {
13
Loop condition is false. Exiting loop
1413 ++BBI;
1414 } while (isa<DbgInfoIntrinsic>(BBI) ||
1415 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy()));
1416 if (BranchInst *BI = dyn_cast<BranchInst>(BBI))
14
Assuming 'BI' is non-null
15
Taking true branch
1417 if (BI->isUnconditional())
16
Taking true branch
1418 if (SimplifyStoreAtEndOfBlock(SI))
17
Calling 'InstCombiner::SimplifyStoreAtEndOfBlock'
1419 return nullptr; // xform done!
1420
1421 return nullptr;
1422}
1423
1424/// SimplifyStoreAtEndOfBlock - Turn things like:
1425/// if () { *P = v1; } else { *P = v2 }
1426/// into a phi node with a store in the successor.
1427///
1428/// Simplify things like:
1429/// *P = v1; if () { *P = v2; }
1430/// into a phi node with a store in the successor.
1431///
1432bool InstCombiner::SimplifyStoreAtEndOfBlock(StoreInst &SI) {
1433 assert(SI.isUnordered() &&((SI.isUnordered() && "this code has not been auditted for volatile or ordered store case"
) ? static_cast<void> (0) : __assert_fail ("SI.isUnordered() && \"this code has not been auditted for volatile or ordered store case\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 1434, __PRETTY_FUNCTION__))
1434 "this code has not been auditted for volatile or ordered store case")((SI.isUnordered() && "this code has not been auditted for volatile or ordered store case"
) ? static_cast<void> (0) : __assert_fail ("SI.isUnordered() && \"this code has not been auditted for volatile or ordered store case\""
, "/build/llvm-toolchain-snapshot-6.0~svn315928/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp"
, 1434, __PRETTY_FUNCTION__))
;
1435
1436 BasicBlock *StoreBB = SI.getParent();
1437
1438 // Check to see if the successor block has exactly two incoming edges. If
1439 // so, see if the other predecessor contains a store to the same location.
1440 // if so, insert a PHI node (if needed) and move the stores down.
1441 BasicBlock *DestBB = StoreBB->getTerminator()->getSuccessor(0);
1442
1443 // Determine whether Dest has exactly two predecessors and, if so, compute
1444 // the other predecessor.
1445 pred_iterator PI = pred_begin(DestBB);
1446 BasicBlock *P = *PI;
1447 BasicBlock *OtherBB = nullptr;
18
'OtherBB' initialized to a null pointer value
1448
1449 if (P != StoreBB)
19
Assuming 'P' is equal to 'StoreBB'
20
Taking false branch
1450 OtherBB = P;
1451
1452 if (++PI == pred_end(DestBB))
21
Assuming the condition is false
22
Taking false branch
1453 return false;
1454
1455 P = *PI;
1456 if (P != StoreBB) {
23
Assuming 'P' is equal to 'StoreBB'
24
Taking false branch
1457 if (OtherBB)
1458 return false;
1459 OtherBB = P;
1460 }
1461 if (++PI != pred_end(DestBB))
25
Assuming the condition is false
26
Taking false branch
1462 return false;
1463
1464 // Bail out if all the relevant blocks aren't distinct (this can happen,
1465 // for example, if SI is in an infinite loop)
1466 if (StoreBB == DestBB || OtherBB == DestBB)
27
Assuming 'StoreBB' is not equal to 'DestBB'
28
Assuming 'OtherBB' is not equal to 'DestBB'
29
Taking false branch
1467 return false;
1468
1469 // Verify that the other block ends in a branch and is not otherwise empty.
1470 BasicBlock::iterator BBI(OtherBB->getTerminator());
30
Called C++ object pointer is null
1471 BranchInst *OtherBr = dyn_cast<BranchInst>(BBI);
1472 if (!OtherBr || BBI == OtherBB->begin())
1473 return false;
1474
1475 // If the other block ends in an unconditional branch, check for the 'if then
1476 // else' case. there is an instruction before the branch.
1477 StoreInst *OtherStore = nullptr;
1478 if (OtherBr->isUnconditional()) {
1479 --BBI;
1480 // Skip over debugging info.
1481 while (isa<DbgInfoIntrinsic>(BBI) ||
1482 (isa<BitCastInst>(BBI) && BBI->getType()->isPointerTy())) {
1483 if (BBI==OtherBB->begin())
1484 return false;
1485 --BBI;
1486 }
1487 // If this isn't a store, isn't a store to the same location, or is not the
1488 // right kind of store, bail out.
1489 OtherStore = dyn_cast<StoreInst>(BBI);
1490 if (!OtherStore || OtherStore->getOperand(1) != SI.getOperand(1) ||
1491 !SI.isSameOperationAs(OtherStore))
1492 return false;
1493 } else {
1494 // Otherwise, the other block ended with a conditional branch. If one of the
1495 // destinations is StoreBB, then we have the if/then case.
1496 if (OtherBr->getSuccessor(0) != StoreBB &&
1497 OtherBr->getSuccessor(1) != StoreBB)
1498 return false;
1499
1500 // Okay, we know that OtherBr now goes to Dest and StoreBB, so this is an
1501 // if/then triangle. See if there is a store to the same ptr as SI that
1502 // lives in OtherBB.
1503 for (;; --BBI) {
1504 // Check to see if we find the matching store.
1505 if ((OtherStore = dyn_cast<StoreInst>(BBI))) {
1506 if (OtherStore->getOperand(1) != SI.getOperand(1) ||
1507 !SI.isSameOperationAs(OtherStore))
1508 return false;
1509 break;
1510 }
1511 // If we find something that may be using or overwriting the stored
1512 // value, or if we run out of instructions, we can't do the xform.
1513 if (BBI->mayReadFromMemory() || BBI->mayThrow() ||
1514 BBI->mayWriteToMemory() || BBI == OtherBB->begin())
1515 return false;
1516 }
1517
1518 // In order to eliminate the store in OtherBr, we have to
1519 // make sure nothing reads or overwrites the stored value in
1520 // StoreBB.
1521 for (BasicBlock::iterator I = StoreBB->begin(); &*I != &SI; ++I) {
1522 // FIXME: This should really be AA driven.
1523 if (I->mayReadFromMemory() || I->mayThrow() || I->mayWriteToMemory())
1524 return false;
1525 }
1526 }
1527
1528 // Insert a PHI node now if we need it.
1529 Value *MergedVal = OtherStore->getOperand(0);
1530 if (MergedVal != SI.getOperand(0)) {
1531 PHINode *PN = PHINode::Create(MergedVal->getType(), 2, "storemerge");
1532 PN->addIncoming(SI.getOperand(0), SI.getParent());
1533 PN->addIncoming(OtherStore->getOperand(0), OtherBB);
1534 MergedVal = InsertNewInstBefore(PN, DestBB->front());
1535 }
1536
1537 // Advance to a place where it is safe to insert the new store and
1538 // insert it.
1539 BBI = DestBB->getFirstInsertionPt();
1540 StoreInst *NewSI = new StoreInst(MergedVal, SI.getOperand(1),
1541 SI.isVolatile(),
1542 SI.getAlignment(),
1543 SI.getOrdering(),
1544 SI.getSyncScopeID());
1545 InsertNewInstBefore(NewSI, *BBI);
1546 // The debug locations of the original instructions might differ; merge them.
1547 NewSI->applyMergedLocation(SI.getDebugLoc(), OtherStore->getDebugLoc());
1548
1549 // If the two stores had AA tags, merge them.
1550 AAMDNodes AATags;
1551 SI.getAAMetadata(AATags);
1552 if (AATags) {
1553 OtherStore->getAAMetadata(AATags, /* Merge = */ true);
1554 NewSI->setAAMetadata(AATags);
1555 }
1556
1557 // Nuke the old stores.
1558 eraseInstFromFunction(SI);
1559 eraseInstFromFunction(*OtherStore);
1560 return true;
1561}