1 //===- ScalarReplAggregates.cpp - Scalar Replacement of Aggregates --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This transformation implements the well known scalar replacement of
11 // aggregates transformation. This xform breaks up alloca instructions of
12 // aggregate type (structure or array) into individual alloca instructions for
13 // each member (if possible). Then, if possible, it transforms the individual
14 // alloca instructions into nice clean scalar SSA form.
16 // This combines a simple SRoA algorithm with the Mem2Reg algorithm because
17 // often interact, especially for C++ programs. As such, iterating between
18 // SRoA, then Mem2Reg until we run out of things to promote works well.
20 //===----------------------------------------------------------------------===//
22 #define DEBUG_TYPE "scalarrepl"
23 #include "llvm/Transforms/Scalar.h"
24 #include "llvm/Constants.h"
25 #include "llvm/DerivedTypes.h"
26 #include "llvm/Function.h"
27 #include "llvm/GlobalVariable.h"
28 #include "llvm/Instructions.h"
29 #include "llvm/IntrinsicInst.h"
30 #include "llvm/LLVMContext.h"
31 #include "llvm/Pass.h"
32 #include "llvm/Analysis/Dominators.h"
33 #include "llvm/Target/TargetData.h"
34 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
35 #include "llvm/Transforms/Utils/Local.h"
36 #include "llvm/Support/Debug.h"
37 #include "llvm/Support/ErrorHandling.h"
38 #include "llvm/Support/GetElementPtrTypeIterator.h"
39 #include "llvm/Support/IRBuilder.h"
40 #include "llvm/Support/MathExtras.h"
41 #include "llvm/Support/raw_ostream.h"
42 #include "llvm/ADT/SmallVector.h"
43 #include "llvm/ADT/Statistic.h"
46 STATISTIC(NumReplaced, "Number of allocas broken up");
47 STATISTIC(NumPromoted, "Number of allocas promoted");
48 STATISTIC(NumConverted, "Number of aggregates converted to scalar");
49 STATISTIC(NumGlobals, "Number of allocas copied from constant global");
52 struct SROA : public FunctionPass {
53 static char ID; // Pass identification, replacement for typeid
54 explicit SROA(signed T = -1) : FunctionPass(&ID) {
61 bool runOnFunction(Function &F);
63 bool performScalarRepl(Function &F);
64 bool performPromotion(Function &F);
66 // getAnalysisUsage - This pass does not require any passes, but we know it
67 // will not alter the CFG, so say so.
68 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
69 AU.addRequired<DominatorTree>();
70 AU.addRequired<DominanceFrontier>();
77 /// DeadInsts - Keep track of instructions we have made dead, so that
78 /// we can remove them after we are done working.
79 SmallVector<Value*, 32> DeadInsts;
81 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures
82 /// information about the uses. All these fields are initialized to false
83 /// and set to true when something is learned.
85 /// isUnsafe - This is set to true if the alloca cannot be SROA'd.
88 /// needsCleanup - This is set to true if there is some use of the alloca
89 /// that requires cleanup.
90 bool needsCleanup : 1;
92 /// isMemCpySrc - This is true if this aggregate is memcpy'd from.
95 /// isMemCpyDst - This is true if this aggregate is memcpy'd into.
99 : isUnsafe(false), needsCleanup(false),
100 isMemCpySrc(false), isMemCpyDst(false) {}
103 unsigned SRThreshold;
105 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
107 int isSafeAllocaToScalarRepl(AllocaInst *AI);
109 void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
111 void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset,
113 void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
114 const Type *MemOpType, bool isStore, AllocaInfo &Info);
115 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size);
116 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset,
119 void DoScalarReplacement(AllocaInst *AI,
120 std::vector<AllocaInst*> &WorkList);
121 void DeleteDeadInstructions();
122 void CleanupAllocaUsers(Value *V);
123 AllocaInst *AddNewAlloca(Function &F, const Type *Ty, AllocaInst *Base);
125 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
126 SmallVector<AllocaInst*, 32> &NewElts);
127 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
128 SmallVector<AllocaInst*, 32> &NewElts);
129 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
130 SmallVector<AllocaInst*, 32> &NewElts);
131 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
133 SmallVector<AllocaInst*, 32> &NewElts);
134 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
135 SmallVector<AllocaInst*, 32> &NewElts);
136 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
137 SmallVector<AllocaInst*, 32> &NewElts);
139 bool CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
140 bool &SawVec, uint64_t Offset, unsigned AllocaSize);
141 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
142 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
143 uint64_t Offset, IRBuilder<> &Builder);
144 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
145 uint64_t Offset, IRBuilder<> &Builder);
146 static Instruction *isOnlyCopiedFromConstantGlobal(AllocaInst *AI);
151 static RegisterPass<SROA> X("scalarrepl", "Scalar Replacement of Aggregates");
153 // Public interface to the ScalarReplAggregates pass
154 FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) {
155 return new SROA(Threshold);
159 bool SROA::runOnFunction(Function &F) {
160 TD = getAnalysisIfAvailable<TargetData>();
162 bool Changed = performPromotion(F);
164 // FIXME: ScalarRepl currently depends on TargetData more than it
165 // theoretically needs to. It should be refactored in order to support
166 // target-independent IR. Until this is done, just skip the actual
167 // scalar-replacement portion of this pass.
168 if (!TD) return Changed;
171 bool LocalChange = performScalarRepl(F);
172 if (!LocalChange) break; // No need to repromote if no scalarrepl
174 LocalChange = performPromotion(F);
175 if (!LocalChange) break; // No need to re-scalarrepl if no promotion
182 bool SROA::performPromotion(Function &F) {
183 std::vector<AllocaInst*> Allocas;
184 DominatorTree &DT = getAnalysis<DominatorTree>();
185 DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
187 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
189 bool Changed = false;
194 // Find allocas that are safe to promote, by looking at all instructions in
196 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
197 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
198 if (isAllocaPromotable(AI))
199 Allocas.push_back(AI);
201 if (Allocas.empty()) break;
203 PromoteMemToReg(Allocas, DT, DF);
204 NumPromoted += Allocas.size();
211 /// getNumSAElements - Return the number of elements in the specific struct or
213 static uint64_t getNumSAElements(const Type *T) {
214 if (const StructType *ST = dyn_cast<StructType>(T))
215 return ST->getNumElements();
216 return cast<ArrayType>(T)->getNumElements();
219 // performScalarRepl - This algorithm is a simple worklist driven algorithm,
220 // which runs on all of the malloc/alloca instructions in the function, removing
221 // them if they are only used by getelementptr instructions.
223 bool SROA::performScalarRepl(Function &F) {
224 std::vector<AllocaInst*> WorkList;
226 // Scan the entry basic block, adding any alloca's and mallocs to the worklist
227 BasicBlock &BB = F.getEntryBlock();
228 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
229 if (AllocaInst *A = dyn_cast<AllocaInst>(I))
230 WorkList.push_back(A);
232 // Process the worklist
233 bool Changed = false;
234 while (!WorkList.empty()) {
235 AllocaInst *AI = WorkList.back();
238 // Handle dead allocas trivially. These can be formed by SROA'ing arrays
239 // with unused elements.
240 if (AI->use_empty()) {
241 AI->eraseFromParent();
245 // If this alloca is impossible for us to promote, reject it early.
246 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
249 // Check to see if this allocation is only modified by a memcpy/memmove from
250 // a constant global. If this is the case, we can change all users to use
251 // the constant global instead. This is commonly produced by the CFE by
252 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
253 // is only subsequently read.
254 if (Instruction *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
255 DEBUG(errs() << "Found alloca equal to global: " << *AI << '\n');
256 DEBUG(errs() << " memcpy = " << *TheCopy << '\n');
257 Constant *TheSrc = cast<Constant>(TheCopy->getOperand(2));
258 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
259 TheCopy->eraseFromParent(); // Don't mutate the global.
260 AI->eraseFromParent();
266 // Check to see if we can perform the core SROA transformation. We cannot
267 // transform the allocation instruction if it is an array allocation
268 // (allocations OF arrays are ok though), and an allocation of a scalar
269 // value cannot be decomposed at all.
270 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());
272 // Do not promote [0 x %struct].
273 if (AllocaSize == 0) continue;
275 // Do not promote any struct whose size is too big.
276 if (AllocaSize > SRThreshold) continue;
278 if ((isa<StructType>(AI->getAllocatedType()) ||
279 isa<ArrayType>(AI->getAllocatedType())) &&
280 // Do not promote any struct into more than "32" separate vars.
281 getNumSAElements(AI->getAllocatedType()) <= SRThreshold/4) {
282 // Check that all of the users of the allocation are capable of being
284 switch (isSafeAllocaToScalarRepl(AI)) {
285 default: llvm_unreachable("Unexpected value!");
286 case 0: // Not safe to scalar replace.
288 case 1: // Safe, but requires cleanup/canonicalizations first
289 CleanupAllocaUsers(AI);
291 case 3: // Safe to scalar replace.
292 DoScalarReplacement(AI, WorkList);
298 // If we can turn this aggregate value (potentially with casts) into a
299 // simple scalar value that can be mem2reg'd into a register value.
300 // IsNotTrivial tracks whether this is something that mem2reg could have
301 // promoted itself. If so, we don't want to transform it needlessly. Note
302 // that we can't just check based on the type: the alloca may be of an i32
303 // but that has pointer arithmetic to set byte 3 of it or something.
304 bool IsNotTrivial = false;
305 const Type *VectorTy = 0;
306 bool HadAVector = false;
307 if (CanConvertToScalar(AI, IsNotTrivial, VectorTy, HadAVector,
308 0, unsigned(AllocaSize)) && IsNotTrivial) {
310 // If we were able to find a vector type that can handle this with
311 // insert/extract elements, and if there was at least one use that had
312 // a vector type, promote this to a vector. We don't want to promote
313 // random stuff that doesn't use vectors (e.g. <9 x double>) because then
314 // we just get a lot of insert/extracts. If at least one vector is
315 // involved, then we probably really do have a union of vector/array.
316 if (VectorTy && isa<VectorType>(VectorTy) && HadAVector) {
317 DEBUG(errs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = "
318 << *VectorTy << '\n');
320 // Create and insert the vector alloca.
321 NewAI = new AllocaInst(VectorTy, 0, "", AI->getParent()->begin());
322 ConvertUsesToScalar(AI, NewAI, 0);
324 DEBUG(errs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
326 // Create and insert the integer alloca.
327 const Type *NewTy = IntegerType::get(AI->getContext(), AllocaSize*8);
328 NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
329 ConvertUsesToScalar(AI, NewAI, 0);
332 AI->eraseFromParent();
338 // Otherwise, couldn't process this alloca.
344 /// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
345 /// predicate, do SROA now.
346 void SROA::DoScalarReplacement(AllocaInst *AI,
347 std::vector<AllocaInst*> &WorkList) {
348 DEBUG(errs() << "Found inst to SROA: " << *AI << '\n');
349 SmallVector<AllocaInst*, 32> ElementAllocas;
350 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
351 ElementAllocas.reserve(ST->getNumContainedTypes());
352 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
353 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
355 AI->getName() + "." + Twine(i), AI);
356 ElementAllocas.push_back(NA);
357 WorkList.push_back(NA); // Add to worklist for recursive processing
360 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
361 ElementAllocas.reserve(AT->getNumElements());
362 const Type *ElTy = AT->getElementType();
363 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
364 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
365 AI->getName() + "." + Twine(i), AI);
366 ElementAllocas.push_back(NA);
367 WorkList.push_back(NA); // Add to worklist for recursive processing
371 // Now that we have created the new alloca instructions, rewrite all the
372 // uses of the old alloca.
373 RewriteForScalarRepl(AI, AI, 0, ElementAllocas);
375 // Now erase any instructions that were made dead while rewriting the alloca.
376 DeleteDeadInstructions();
377 AI->eraseFromParent();
382 /// DeleteDeadInstructions - Erase instructions on the DeadInstrs list,
383 /// recursively including all their operands that become trivially dead.
384 void SROA::DeleteDeadInstructions() {
385 while (!DeadInsts.empty()) {
386 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val());
388 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
389 if (Instruction *U = dyn_cast<Instruction>(*OI)) {
390 // Zero out the operand and see if it becomes trivially dead.
391 // (But, don't add allocas to the dead instruction list -- they are
392 // already on the worklist and will be deleted separately.)
394 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U))
395 DeadInsts.push_back(U);
398 I->eraseFromParent();
402 /// isSafeForScalarRepl - Check if instruction I is a safe use with regard to
403 /// performing scalar replacement of alloca AI. The results are flagged in
404 /// the Info parameter. Offset indicates the position within AI that is
405 /// referenced by this instruction.
406 void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
408 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
409 Instruction *User = cast<Instruction>(*UI);
411 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
412 isSafeForScalarRepl(BC, AI, Offset, Info);
413 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
414 uint64_t GEPOffset = Offset;
415 isSafeGEP(GEPI, AI, GEPOffset, Info);
417 isSafeForScalarRepl(GEPI, AI, GEPOffset, Info);
418 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(UI)) {
419 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
421 isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0,
422 UI.getOperandNo() == 1, Info);
425 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
426 if (!LI->isVolatile()) {
427 const Type *LIType = LI->getType();
428 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType),
429 LIType, false, Info);
432 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
433 // Store is ok if storing INTO the pointer, not storing the pointer
434 if (!SI->isVolatile() && SI->getOperand(0) != I) {
435 const Type *SIType = SI->getOperand(0)->getType();
436 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType),
440 } else if (isa<DbgInfoIntrinsic>(UI)) {
441 // If one user is DbgInfoIntrinsic then check if all users are
442 // DbgInfoIntrinsics.
443 if (OnlyUsedByDbgInfoIntrinsics(I)) {
444 Info.needsCleanup = true;
449 DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
452 if (Info.isUnsafe) return;
456 /// isSafeGEP - Check if a GEP instruction can be handled for scalar
457 /// replacement. It is safe when all the indices are constant, in-bounds
458 /// references, and when the resulting offset corresponds to an element within
459 /// the alloca type. The results are flagged in the Info parameter. Upon
460 /// return, Offset is adjusted as specified by the GEP indices.
461 void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI,
462 uint64_t &Offset, AllocaInfo &Info) {
463 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI);
467 // The first GEP index must be zero.
468 if (!isa<ConstantInt>(GEPIt.getOperand()) ||
469 !cast<ConstantInt>(GEPIt.getOperand())->isZero())
470 return MarkUnsafe(Info);
474 // Walk through the GEP type indices, checking the types that this indexes
476 for (; GEPIt != E; ++GEPIt) {
477 // Ignore struct elements, no extra checking needed for these.
478 if (isa<StructType>(*GEPIt))
481 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand());
483 return MarkUnsafe(Info);
485 if (const ArrayType *AT = dyn_cast<ArrayType>(*GEPIt)) {
486 // This GEP indexes an array. Verify that this is an in-range constant
487 // integer. Specifically, consider A[0][i]. We cannot know that the user
488 // isn't doing invalid things like allowing i to index an out-of-range
489 // subscript that accesses A[1]. Because of this, we have to reject SROA
490 // of any accesses into structs where any of the components are variables.
491 if (IdxVal->getZExtValue() >= AT->getNumElements())
492 return MarkUnsafe(Info);
494 const VectorType *VT = cast<VectorType>(*GEPIt);
495 if (IdxVal->getZExtValue() >= VT->getNumElements())
496 return MarkUnsafe(Info);
500 // All the indices are safe. Now compute the offset due to this GEP and
501 // check if the alloca has a component element at that offset.
502 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
503 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
504 &Indices[0], Indices.size());
505 if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0))
509 /// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI
510 /// alloca or has an offset and size that corresponds to a component element
511 /// within it. The offset checked here may have been formed from a GEP with a
512 /// pointer bitcasted to a different type.
513 void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
514 const Type *MemOpType, bool isStore,
516 // Check if this is a load/store of the entire alloca.
517 if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) {
518 bool UsesAggregateType = (MemOpType == AI->getAllocatedType());
519 // This is safe for MemIntrinsics (where MemOpType is 0), integer types
520 // (which are essentially the same as the MemIntrinsics, especially with
521 // regard to copying padding between elements), or references using the
522 // aggregate type of the alloca.
523 if (!MemOpType || isa<IntegerType>(MemOpType) || UsesAggregateType) {
524 if (!UsesAggregateType) {
526 Info.isMemCpyDst = true;
528 Info.isMemCpySrc = true;
533 // Check if the offset/size correspond to a component within the alloca type.
534 const Type *T = AI->getAllocatedType();
535 if (TypeHasComponent(T, Offset, MemSize))
538 return MarkUnsafe(Info);
541 /// TypeHasComponent - Return true if T has a component type with the
542 /// specified offset and size. If Size is zero, do not check the size.
543 bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) {
546 if (const StructType *ST = dyn_cast<StructType>(T)) {
547 const StructLayout *Layout = TD->getStructLayout(ST);
548 unsigned EltIdx = Layout->getElementContainingOffset(Offset);
549 EltTy = ST->getContainedType(EltIdx);
550 EltSize = TD->getTypeAllocSize(EltTy);
551 Offset -= Layout->getElementOffset(EltIdx);
552 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) {
553 EltTy = AT->getElementType();
554 EltSize = TD->getTypeAllocSize(EltTy);
559 if (Offset == 0 && (Size == 0 || EltSize == Size))
561 // Check if the component spans multiple elements.
562 if (Offset + Size > EltSize)
564 return TypeHasComponent(EltTy, Offset, Size);
567 /// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite
568 /// the instruction I, which references it, to use the separate elements.
569 /// Offset indicates the position within AI that is referenced by this
571 void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
572 SmallVector<AllocaInst*, 32> &NewElts) {
573 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
574 Instruction *User = cast<Instruction>(*UI);
576 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
577 RewriteBitCast(BC, AI, Offset, NewElts);
578 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
579 RewriteGEP(GEPI, AI, Offset, NewElts);
580 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
581 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
582 uint64_t MemSize = Length->getZExtValue();
584 MemSize == TD->getTypeAllocSize(AI->getAllocatedType()))
585 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts);
586 // Otherwise the intrinsic can only touch a single element and the
587 // address operand will be updated, so nothing else needs to be done.
588 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
589 const Type *LIType = LI->getType();
590 if (LIType == AI->getAllocatedType()) {
592 // %res = load { i32, i32 }* %alloc
594 // %load.0 = load i32* %alloc.0
595 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0
596 // %load.1 = load i32* %alloc.1
597 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1
598 // (Also works for arrays instead of structs)
599 Value *Insert = UndefValue::get(LIType);
600 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
601 Value *Load = new LoadInst(NewElts[i], "load", LI);
602 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
604 LI->replaceAllUsesWith(Insert);
605 DeadInsts.push_back(LI);
606 } else if (isa<IntegerType>(LIType) &&
607 TD->getTypeAllocSize(LIType) ==
608 TD->getTypeAllocSize(AI->getAllocatedType())) {
609 // If this is a load of the entire alloca to an integer, rewrite it.
610 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
612 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
613 Value *Val = SI->getOperand(0);
614 const Type *SIType = Val->getType();
615 if (SIType == AI->getAllocatedType()) {
617 // store { i32, i32 } %val, { i32, i32 }* %alloc
619 // %val.0 = extractvalue { i32, i32 } %val, 0
620 // store i32 %val.0, i32* %alloc.0
621 // %val.1 = extractvalue { i32, i32 } %val, 1
622 // store i32 %val.1, i32* %alloc.1
623 // (Also works for arrays instead of structs)
624 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
625 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
626 new StoreInst(Extract, NewElts[i], SI);
628 DeadInsts.push_back(SI);
629 } else if (isa<IntegerType>(SIType) &&
630 TD->getTypeAllocSize(SIType) ==
631 TD->getTypeAllocSize(AI->getAllocatedType())) {
632 // If this is a store of the entire alloca from an integer, rewrite it.
633 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
639 /// RewriteBitCast - Update a bitcast reference to the alloca being replaced
640 /// and recursively continue updating all of its uses.
641 void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
642 SmallVector<AllocaInst*, 32> &NewElts) {
643 RewriteForScalarRepl(BC, AI, Offset, NewElts);
644 if (BC->getOperand(0) != AI)
647 // The bitcast references the original alloca. Replace its uses with
648 // references to the first new element alloca.
649 Instruction *Val = NewElts[0];
650 if (Val->getType() != BC->getDestTy()) {
651 Val = new BitCastInst(Val, BC->getDestTy(), "", BC);
654 BC->replaceAllUsesWith(Val);
655 DeadInsts.push_back(BC);
658 /// FindElementAndOffset - Return the index of the element containing Offset
659 /// within the specified type, which must be either a struct or an array.
660 /// Sets T to the type of the element and Offset to the offset within that
661 /// element. IdxTy is set to the type of the index result to be used in a
663 uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset,
664 const Type *&IdxTy) {
666 if (const StructType *ST = dyn_cast<StructType>(T)) {
667 const StructLayout *Layout = TD->getStructLayout(ST);
668 Idx = Layout->getElementContainingOffset(Offset);
669 T = ST->getContainedType(Idx);
670 Offset -= Layout->getElementOffset(Idx);
671 IdxTy = Type::getInt32Ty(T->getContext());
674 const ArrayType *AT = cast<ArrayType>(T);
675 T = AT->getElementType();
676 uint64_t EltSize = TD->getTypeAllocSize(T);
677 Idx = Offset / EltSize;
678 Offset -= Idx * EltSize;
679 IdxTy = Type::getInt64Ty(T->getContext());
683 /// RewriteGEP - Check if this GEP instruction moves the pointer across
684 /// elements of the alloca that are being split apart, and if so, rewrite
685 /// the GEP to be relative to the new element.
686 void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
687 SmallVector<AllocaInst*, 32> &NewElts) {
688 uint64_t OldOffset = Offset;
689 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
690 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
691 &Indices[0], Indices.size());
693 RewriteForScalarRepl(GEPI, AI, Offset, NewElts);
695 const Type *T = AI->getAllocatedType();
697 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy);
698 if (GEPI->getOperand(0) == AI)
699 OldIdx = ~0ULL; // Force the GEP to be rewritten.
701 T = AI->getAllocatedType();
702 uint64_t EltOffset = Offset;
703 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy);
705 // If this GEP does not move the pointer across elements of the alloca
706 // being split, then it does not needs to be rewritten.
710 const Type *i32Ty = Type::getInt32Ty(AI->getContext());
711 SmallVector<Value*, 8> NewArgs;
712 NewArgs.push_back(Constant::getNullValue(i32Ty));
713 while (EltOffset != 0) {
714 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy);
715 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx));
717 Instruction *Val = NewElts[Idx];
718 if (NewArgs.size() > 1) {
719 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(),
720 NewArgs.end(), "", GEPI);
723 if (Val->getType() != GEPI->getType())
724 Val = new BitCastInst(Val, GEPI->getType(), Val->getNameStr(), GEPI);
725 GEPI->replaceAllUsesWith(Val);
726 DeadInsts.push_back(GEPI);
729 /// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI.
730 /// Rewrite it to copy or set the elements of the scalarized memory.
731 void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
733 SmallVector<AllocaInst*, 32> &NewElts) {
734 // If this is a memcpy/memmove, construct the other pointer as the
735 // appropriate type. The "Other" pointer is the pointer that goes to memory
736 // that doesn't have anything to do with the alloca that we are promoting. For
737 // memset, this Value* stays null.
739 LLVMContext &Context = MI->getContext();
740 unsigned MemAlignment = MI->getAlignment();
741 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
742 if (Inst == MTI->getRawDest())
743 OtherPtr = MTI->getRawSource();
745 assert(Inst == MTI->getRawSource());
746 OtherPtr = MTI->getRawDest();
750 // If there is an other pointer, we want to convert it to the same pointer
751 // type as AI has, so we can GEP through it safely.
754 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an
755 // optimization, but it's also required to detect the corner case where
756 // both pointer operands are referencing the same memory, and where
757 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This
758 // function is only called for mem intrinsics that access the whole
759 // aggregate, so non-zero GEPs are not an issue here.)
761 if (BitCastInst *BC = dyn_cast<BitCastInst>(OtherPtr)) {
762 OtherPtr = BC->getOperand(0);
765 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(OtherPtr)) {
766 // All zero GEPs are effectively bitcasts.
767 if (GEP->hasAllZeroIndices()) {
768 OtherPtr = GEP->getOperand(0);
774 // If OtherPtr has already been rewritten, this intrinsic will be dead.
775 if (OtherPtr == NewElts[0])
778 if (ConstantExpr *BCE = dyn_cast<ConstantExpr>(OtherPtr))
779 if (BCE->getOpcode() == Instruction::BitCast)
780 OtherPtr = BCE->getOperand(0);
782 // If the pointer is not the right type, insert a bitcast to the right
784 if (OtherPtr->getType() != AI->getType())
785 OtherPtr = new BitCastInst(OtherPtr, AI->getType(), OtherPtr->getName(),
789 // Process each element of the aggregate.
790 Value *TheFn = MI->getOperand(0);
791 const Type *BytePtrTy = MI->getRawDest()->getType();
792 bool SROADest = MI->getRawDest() == Inst;
794 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext()));
796 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
797 // If this is a memcpy/memmove, emit a GEP of the other element address.
799 unsigned OtherEltAlign = MemAlignment;
801 if (OtherPtr == AI) {
802 OtherElt = NewElts[i];
804 } else if (OtherPtr) {
805 Value *Idx[2] = { Zero,
806 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
807 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2,
808 OtherPtr->getNameStr()+"."+Twine(i),
811 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
812 if (const StructType *ST =
813 dyn_cast<StructType>(OtherPtrTy->getElementType())) {
814 EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
817 cast<SequentialType>(OtherPtr->getType())->getElementType();
818 EltOffset = TD->getTypeAllocSize(EltTy)*i;
821 // The alignment of the other pointer is the guaranteed alignment of the
822 // element, which is affected by both the known alignment of the whole
823 // mem intrinsic and the alignment of the element. If the alignment of
824 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
825 // known alignment is just 4 bytes.
826 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
829 Value *EltPtr = NewElts[i];
830 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
832 // If we got down to a scalar, insert a load or store as appropriate.
833 if (EltTy->isSingleValueType()) {
834 if (isa<MemTransferInst>(MI)) {
836 // From Other to Alloca.
837 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
838 new StoreInst(Elt, EltPtr, MI);
840 // From Alloca to Other.
841 Value *Elt = new LoadInst(EltPtr, "tmp", MI);
842 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
846 assert(isa<MemSetInst>(MI));
848 // If the stored element is zero (common case), just store a null
851 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getOperand(2))) {
853 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0>
855 // If EltTy is a vector type, get the element type.
856 const Type *ValTy = EltTy->getScalarType();
858 // Construct an integer with the right value.
859 unsigned EltSize = TD->getTypeSizeInBits(ValTy);
860 APInt OneVal(EltSize, CI->getZExtValue());
861 APInt TotalVal(OneVal);
863 for (unsigned i = 0; 8*i < EltSize; ++i) {
864 TotalVal = TotalVal.shl(8);
868 // Convert the integer value to the appropriate type.
869 StoreVal = ConstantInt::get(Context, TotalVal);
870 if (isa<PointerType>(ValTy))
871 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
872 else if (ValTy->isFloatingPoint())
873 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
874 assert(StoreVal->getType() == ValTy && "Type mismatch!");
876 // If the requested value was a vector constant, create it.
877 if (EltTy != ValTy) {
878 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
879 SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
880 StoreVal = ConstantVector::get(&Elts[0], NumElts);
883 new StoreInst(StoreVal, EltPtr, MI);
886 // Otherwise, if we're storing a byte variable, use a memset call for
890 // Cast the element pointer to BytePtrTy.
891 if (EltPtr->getType() != BytePtrTy)
892 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getNameStr(), MI);
894 // Cast the other pointer (if we have one) to BytePtrTy.
895 if (OtherElt && OtherElt->getType() != BytePtrTy)
896 OtherElt = new BitCastInst(OtherElt, BytePtrTy,OtherElt->getNameStr(),
899 unsigned EltSize = TD->getTypeAllocSize(EltTy);
901 // Finally, insert the meminst for this element.
902 if (isa<MemTransferInst>(MI)) {
904 SROADest ? EltPtr : OtherElt, // Dest ptr
905 SROADest ? OtherElt : EltPtr, // Src ptr
906 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
908 ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign)
910 CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
912 assert(isa<MemSetInst>(MI));
914 EltPtr, MI->getOperand(2), // Dest, Value,
915 ConstantInt::get(MI->getOperand(3)->getType(), EltSize), // Size
918 CallInst::Create(TheFn, Ops, Ops + 4, "", MI);
921 DeadInsts.push_back(MI);
924 /// RewriteStoreUserOfWholeAlloca - We found a store of an integer that
925 /// overwrites the entire allocation. Extract out the pieces of the stored
926 /// integer and store them individually.
927 void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
928 SmallVector<AllocaInst*, 32> &NewElts){
929 // Extract each element out of the integer according to its structure offset
930 // and store the element value to the individual alloca.
931 Value *SrcVal = SI->getOperand(0);
932 const Type *AllocaEltTy = AI->getAllocatedType();
933 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
935 // Handle tail padding by extending the operand
936 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
937 SrcVal = new ZExtInst(SrcVal,
938 IntegerType::get(SI->getContext(), AllocaSizeBits),
941 DEBUG(errs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI
944 // There are two forms here: AI could be an array or struct. Both cases
945 // have different ways to compute the element offset.
946 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
947 const StructLayout *Layout = TD->getStructLayout(EltSTy);
949 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
950 // Get the number of bits to shift SrcVal to get the value.
951 const Type *FieldTy = EltSTy->getElementType(i);
952 uint64_t Shift = Layout->getElementOffsetInBits(i);
954 if (TD->isBigEndian())
955 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
957 Value *EltVal = SrcVal;
959 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
960 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
961 "sroa.store.elt", SI);
964 // Truncate down to an integer of the right size.
965 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
967 // Ignore zero sized fields like {}, they obviously contain no data.
968 if (FieldSizeBits == 0) continue;
970 if (FieldSizeBits != AllocaSizeBits)
971 EltVal = new TruncInst(EltVal,
972 IntegerType::get(SI->getContext(), FieldSizeBits),
974 Value *DestField = NewElts[i];
975 if (EltVal->getType() == FieldTy) {
976 // Storing to an integer field of this size, just do it.
977 } else if (FieldTy->isFloatingPoint() || isa<VectorType>(FieldTy)) {
978 // Bitcast to the right element type (for fp/vector values).
979 EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
981 // Otherwise, bitcast the dest pointer (for aggregates).
982 DestField = new BitCastInst(DestField,
983 PointerType::getUnqual(EltVal->getType()),
986 new StoreInst(EltVal, DestField, SI);
990 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
991 const Type *ArrayEltTy = ATy->getElementType();
992 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
993 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);
997 if (TD->isBigEndian())
998 Shift = AllocaSizeBits-ElementOffset;
1002 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1003 // Ignore zero sized fields like {}, they obviously contain no data.
1004 if (ElementSizeBits == 0) continue;
1006 Value *EltVal = SrcVal;
1008 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
1009 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
1010 "sroa.store.elt", SI);
1013 // Truncate down to an integer of the right size.
1014 if (ElementSizeBits != AllocaSizeBits)
1015 EltVal = new TruncInst(EltVal,
1016 IntegerType::get(SI->getContext(),
1017 ElementSizeBits),"",SI);
1018 Value *DestField = NewElts[i];
1019 if (EltVal->getType() == ArrayEltTy) {
1020 // Storing to an integer field of this size, just do it.
1021 } else if (ArrayEltTy->isFloatingPoint() || isa<VectorType>(ArrayEltTy)) {
1022 // Bitcast to the right element type (for fp/vector values).
1023 EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
1025 // Otherwise, bitcast the dest pointer (for aggregates).
1026 DestField = new BitCastInst(DestField,
1027 PointerType::getUnqual(EltVal->getType()),
1030 new StoreInst(EltVal, DestField, SI);
1032 if (TD->isBigEndian())
1033 Shift -= ElementOffset;
1035 Shift += ElementOffset;
1039 DeadInsts.push_back(SI);
1042 /// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to
1043 /// an integer. Load the individual pieces to form the aggregate value.
1044 void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
1045 SmallVector<AllocaInst*, 32> &NewElts) {
1046 // Extract each element out of the NewElts according to its structure offset
1047 // and form the result value.
1048 const Type *AllocaEltTy = AI->getAllocatedType();
1049 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
1051 DEBUG(errs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI
1054 // There are two forms here: AI could be an array or struct. Both cases
1055 // have different ways to compute the element offset.
1056 const StructLayout *Layout = 0;
1057 uint64_t ArrayEltBitOffset = 0;
1058 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
1059 Layout = TD->getStructLayout(EltSTy);
1061 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
1062 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
1066 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits));
1068 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1069 // Load the value from the alloca. If the NewElt is an aggregate, cast
1070 // the pointer to an integer of the same size before doing the load.
1071 Value *SrcField = NewElts[i];
1072 const Type *FieldTy =
1073 cast<PointerType>(SrcField->getType())->getElementType();
1074 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
1076 // Ignore zero sized fields like {}, they obviously contain no data.
1077 if (FieldSizeBits == 0) continue;
1079 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(),
1081 if (!isa<IntegerType>(FieldTy) && !FieldTy->isFloatingPoint() &&
1082 !isa<VectorType>(FieldTy))
1083 SrcField = new BitCastInst(SrcField,
1084 PointerType::getUnqual(FieldIntTy),
1086 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);
1088 // If SrcField is a fp or vector of the right size but that isn't an
1089 // integer type, bitcast to an integer so we can shift it.
1090 if (SrcField->getType() != FieldIntTy)
1091 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);
1093 // Zero extend the field to be the same size as the final alloca so that
1094 // we can shift and insert it.
1095 if (SrcField->getType() != ResultVal->getType())
1096 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
1098 // Determine the number of bits to shift SrcField.
1100 if (Layout) // Struct case.
1101 Shift = Layout->getElementOffsetInBits(i);
1103 Shift = i*ArrayEltBitOffset;
1105 if (TD->isBigEndian())
1106 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
1109 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
1110 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
1113 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
1116 // Handle tail padding by truncating the result
1117 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
1118 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);
1120 LI->replaceAllUsesWith(ResultVal);
1121 DeadInsts.push_back(LI);
1124 /// HasPadding - Return true if the specified type has any structure or
1125 /// alignment padding, false otherwise.
1126 static bool HasPadding(const Type *Ty, const TargetData &TD) {
1127 if (const StructType *STy = dyn_cast<StructType>(Ty)) {
1128 const StructLayout *SL = TD.getStructLayout(STy);
1129 unsigned PrevFieldBitOffset = 0;
1130 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1131 unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
1133 // Padding in sub-elements?
1134 if (HasPadding(STy->getElementType(i), TD))
1137 // Check to see if there is any padding between this element and the
1140 unsigned PrevFieldEnd =
1141 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
1142 if (PrevFieldEnd < FieldBitOffset)
1146 PrevFieldBitOffset = FieldBitOffset;
1149 // Check for tail padding.
1150 if (unsigned EltCount = STy->getNumElements()) {
1151 unsigned PrevFieldEnd = PrevFieldBitOffset +
1152 TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
1153 if (PrevFieldEnd < SL->getSizeInBits())
1157 } else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
1158 return HasPadding(ATy->getElementType(), TD);
1159 } else if (const VectorType *VTy = dyn_cast<VectorType>(Ty)) {
1160 return HasPadding(VTy->getElementType(), TD);
1162 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
1165 /// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
1166 /// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
1167 /// or 1 if safe after canonicalization has been performed.
1168 int SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) {
1169 // Loop over the use list of the alloca. We can only transform it if all of
1170 // the users are safe to transform.
1173 isSafeForScalarRepl(AI, AI, 0, Info);
1174 if (Info.isUnsafe) {
1175 DEBUG(errs() << "Cannot transform: " << *AI << '\n');
1179 // Okay, we know all the users are promotable. If the aggregate is a memcpy
1180 // source and destination, we have to be careful. In particular, the memcpy
1181 // could be moving around elements that live in structure padding of the LLVM
1182 // types, but may actually be used. In these cases, we refuse to promote the
1184 if (Info.isMemCpySrc && Info.isMemCpyDst &&
1185 HasPadding(AI->getAllocatedType(), *TD))
1188 // If we require cleanup, return 1, otherwise return 3.
1189 return Info.needsCleanup ? 1 : 3;
1192 /// CleanupAllocaUsers - If SROA reported that it can promote the specified
1193 /// allocation, but only if cleaned up, perform the cleanups required.
1194 void SROA::CleanupAllocaUsers(Value *V) {
1195 for (Value::use_iterator UI = V->use_begin(), E = V->use_end();
1198 Instruction *I = cast<Instruction>(U);
1199 SmallVector<DbgInfoIntrinsic *, 2> DbgInUses;
1200 if (!isa<StoreInst>(I) && OnlyUsedByDbgInfoIntrinsics(I, &DbgInUses)) {
1201 // Safe to remove debug info uses.
1202 while (!DbgInUses.empty()) {
1203 DbgInfoIntrinsic *DI = DbgInUses.back(); DbgInUses.pop_back();
1204 DI->eraseFromParent();
1206 I->eraseFromParent();
1211 /// MergeInType - Add the 'In' type to the accumulated type (Accum) so far at
1212 /// the offset specified by Offset (which is specified in bytes).
1214 /// There are two cases we handle here:
1215 /// 1) A union of vector types of the same size and potentially its elements.
1216 /// Here we turn element accesses into insert/extract element operations.
1217 /// This promotes a <4 x float> with a store of float to the third element
1218 /// into a <4 x float> that uses insert element.
1219 /// 2) A fully general blob of memory, which we turn into some (potentially
1220 /// large) integer type with extract and insert operations where the loads
1221 /// and stores would mutate the memory.
1222 static void MergeInType(const Type *In, uint64_t Offset, const Type *&VecTy,
1223 unsigned AllocaSize, const TargetData &TD,
1224 LLVMContext &Context) {
1225 // If this could be contributing to a vector, analyze it.
1226 if (VecTy != Type::getVoidTy(Context)) { // either null or a vector type.
1228 // If the In type is a vector that is the same size as the alloca, see if it
1229 // matches the existing VecTy.
1230 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
1231 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
1232 // If we're storing/loading a vector of the right size, allow it as a
1233 // vector. If this the first vector we see, remember the type so that
1234 // we know the element size.
1239 } else if (In->isFloatTy() || In->isDoubleTy() ||
1240 (isa<IntegerType>(In) && In->getPrimitiveSizeInBits() >= 8 &&
1241 isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
1242 // If we're accessing something that could be an element of a vector, see
1243 // if the implied vector agrees with what we already have and if Offset is
1244 // compatible with it.
1245 unsigned EltSize = In->getPrimitiveSizeInBits()/8;
1246 if (Offset % EltSize == 0 &&
1247 AllocaSize % EltSize == 0 &&
1249 cast<VectorType>(VecTy)->getElementType()
1250 ->getPrimitiveSizeInBits()/8 == EltSize)) {
1252 VecTy = VectorType::get(In, AllocaSize/EltSize);
1258 // Otherwise, we have a case that we can't handle with an optimized vector
1259 // form. We can still turn this into a large integer.
1260 VecTy = Type::getVoidTy(Context);
1263 /// CanConvertToScalar - V is a pointer. If we can convert the pointee and all
1264 /// its accesses to a single vector type, return true and set VecTy to
1265 /// the new type. If we could convert the alloca into a single promotable
1266 /// integer, return true but set VecTy to VoidTy. Further, if the use is not a
1267 /// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset
1268 /// is the current offset from the base of the alloca being analyzed.
1270 /// If we see at least one access to the value that is as a vector type, set the
1272 bool SROA::CanConvertToScalar(Value *V, bool &IsNotTrivial, const Type *&VecTy,
1273 bool &SawVec, uint64_t Offset,
1274 unsigned AllocaSize) {
1275 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
1276 Instruction *User = cast<Instruction>(*UI);
1278 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1279 // Don't break volatile loads.
1280 if (LI->isVolatile())
1282 MergeInType(LI->getType(), Offset, VecTy,
1283 AllocaSize, *TD, V->getContext());
1284 SawVec |= isa<VectorType>(LI->getType());
1288 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
1289 // Storing the pointer, not into the value?
1290 if (SI->getOperand(0) == V || SI->isVolatile()) return 0;
1291 MergeInType(SI->getOperand(0)->getType(), Offset,
1292 VecTy, AllocaSize, *TD, V->getContext());
1293 SawVec |= isa<VectorType>(SI->getOperand(0)->getType());
1297 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
1298 if (!CanConvertToScalar(BCI, IsNotTrivial, VecTy, SawVec, Offset,
1301 IsNotTrivial = true;
1305 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
1306 // If this is a GEP with a variable indices, we can't handle it.
1307 if (!GEP->hasAllConstantIndices())
1310 // Compute the offset that this GEP adds to the pointer.
1311 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
1312 uint64_t GEPOffset = TD->getIndexedOffset(GEP->getPointerOperandType(),
1313 &Indices[0], Indices.size());
1314 // See if all uses can be converted.
1315 if (!CanConvertToScalar(GEP, IsNotTrivial, VecTy, SawVec,Offset+GEPOffset,
1318 IsNotTrivial = true;
1322 // If this is a constant sized memset of a constant value (e.g. 0) we can
1324 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
1325 // Store of constant value and constant size.
1326 if (isa<ConstantInt>(MSI->getValue()) &&
1327 isa<ConstantInt>(MSI->getLength())) {
1328 IsNotTrivial = true;
1333 // If this is a memcpy or memmove into or out of the whole allocation, we
1334 // can handle it like a load or store of the scalar type.
1335 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
1336 if (ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength()))
1337 if (Len->getZExtValue() == AllocaSize && Offset == 0) {
1338 IsNotTrivial = true;
1343 // Ignore dbg intrinsic.
1344 if (isa<DbgInfoIntrinsic>(User))
1347 // Otherwise, we cannot handle this!
1354 /// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca
1355 /// directly. This happens when we are converting an "integer union" to a
1356 /// single integer scalar, or when we are converting a "vector union" to a
1357 /// vector with insert/extractelement instructions.
1359 /// Offset is an offset from the original alloca, in bits that need to be
1360 /// shifted to the right. By the end of this, there should be no uses of Ptr.
1361 void SROA::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset) {
1362 while (!Ptr->use_empty()) {
1363 Instruction *User = cast<Instruction>(Ptr->use_back());
1365 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
1366 ConvertUsesToScalar(CI, NewAI, Offset);
1367 CI->eraseFromParent();
1371 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
1372 // Compute the offset that this GEP adds to the pointer.
1373 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
1374 uint64_t GEPOffset = TD->getIndexedOffset(GEP->getPointerOperandType(),
1375 &Indices[0], Indices.size());
1376 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
1377 GEP->eraseFromParent();
1381 IRBuilder<> Builder(User->getParent(), User);
1383 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1384 // The load is a bit extract from NewAI shifted right by Offset bits.
1385 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
1387 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
1388 LI->replaceAllUsesWith(NewLoadVal);
1389 LI->eraseFromParent();
1393 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
1394 assert(SI->getOperand(0) != Ptr && "Consistency error!");
1395 // FIXME: Remove once builder has Twine API.
1396 Value *Old = Builder.CreateLoad(NewAI,
1397 (NewAI->getName()+".in").str().c_str());
1398 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
1400 Builder.CreateStore(New, NewAI);
1401 SI->eraseFromParent();
1405 // If this is a constant sized memset of a constant value (e.g. 0) we can
1406 // transform it into a store of the expanded constant value.
1407 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
1408 assert(MSI->getRawDest() == Ptr && "Consistency error!");
1409 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
1410 if (NumBytes != 0) {
1411 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
1413 // Compute the value replicated the right number of times.
1414 APInt APVal(NumBytes*8, Val);
1416 // Splat the value if non-zero.
1418 for (unsigned i = 1; i != NumBytes; ++i)
1419 APVal |= APVal << 8;
1421 // FIXME: Remove once builder has Twine API.
1422 Value *Old = Builder.CreateLoad(NewAI,
1423 (NewAI->getName()+".in").str().c_str());
1424 Value *New = ConvertScalar_InsertValue(
1425 ConstantInt::get(User->getContext(), APVal),
1426 Old, Offset, Builder);
1427 Builder.CreateStore(New, NewAI);
1429 MSI->eraseFromParent();
1433 // If this is a memcpy or memmove into or out of the whole allocation, we
1434 // can handle it like a load or store of the scalar type.
1435 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
1436 assert(Offset == 0 && "must be store to start of alloca");
1438 // If the source and destination are both to the same alloca, then this is
1439 // a noop copy-to-self, just delete it. Otherwise, emit a load and store
1441 AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject());
1443 if (MTI->getSource()->getUnderlyingObject() != OrigAI) {
1444 // Dest must be OrigAI, change this to be a load from the original
1445 // pointer (bitcasted), then a store to our new alloca.
1446 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
1447 Value *SrcPtr = MTI->getSource();
1448 SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
1450 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
1451 SrcVal->setAlignment(MTI->getAlignment());
1452 Builder.CreateStore(SrcVal, NewAI);
1453 } else if (MTI->getDest()->getUnderlyingObject() != OrigAI) {
1454 // Src must be OrigAI, change this to be a load from NewAI then a store
1455 // through the original dest pointer (bitcasted).
1456 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
1457 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");
1459 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
1460 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
1461 NewStore->setAlignment(MTI->getAlignment());
1463 // Noop transfer. Src == Dst
1467 MTI->eraseFromParent();
1471 // If user is a dbg info intrinsic then it is safe to remove it.
1472 if (isa<DbgInfoIntrinsic>(User)) {
1473 User->eraseFromParent();
1477 llvm_unreachable("Unsupported operation!");
1481 /// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
1482 /// or vector value FromVal, extracting the bits from the offset specified by
1483 /// Offset. This returns the value, which is of type ToType.
1485 /// This happens when we are converting an "integer union" to a single
1486 /// integer scalar, or when we are converting a "vector union" to a vector with
1487 /// insert/extractelement instructions.
1489 /// Offset is an offset from the original alloca, in bits that need to be
1490 /// shifted to the right.
1491 Value *SROA::ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
1492 uint64_t Offset, IRBuilder<> &Builder) {
1493 // If the load is of the whole new alloca, no conversion is needed.
1494 if (FromVal->getType() == ToType && Offset == 0)
1497 // If the result alloca is a vector type, this is either an element
1498 // access or a bitcast to another vector type of the same size.
1499 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
1500 if (isa<VectorType>(ToType))
1501 return Builder.CreateBitCast(FromVal, ToType, "tmp");
1503 // Otherwise it must be an element access.
1506 unsigned EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
1507 Elt = Offset/EltSize;
1508 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
1510 // Return the element extracted out of it.
1511 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get(
1512 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp");
1513 if (V->getType() != ToType)
1514 V = Builder.CreateBitCast(V, ToType, "tmp");
1518 // If ToType is a first class aggregate, extract out each of the pieces and
1519 // use insertvalue's to form the FCA.
1520 if (const StructType *ST = dyn_cast<StructType>(ToType)) {
1521 const StructLayout &Layout = *TD->getStructLayout(ST);
1522 Value *Res = UndefValue::get(ST);
1523 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
1524 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
1525 Offset+Layout.getElementOffsetInBits(i),
1527 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
1532 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
1533 uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
1534 Value *Res = UndefValue::get(AT);
1535 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
1536 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
1537 Offset+i*EltSize, Builder);
1538 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
1543 // Otherwise, this must be a union that was converted to an integer value.
1544 const IntegerType *NTy = cast<IntegerType>(FromVal->getType());
1546 // If this is a big-endian system and the load is narrower than the
1547 // full alloca type, we need to do a shift to get the right bits.
1549 if (TD->isBigEndian()) {
1550 // On big-endian machines, the lowest bit is stored at the bit offset
1551 // from the pointer given by getTypeStoreSizeInBits. This matters for
1552 // integers with a bitwidth that is not a multiple of 8.
1553 ShAmt = TD->getTypeStoreSizeInBits(NTy) -
1554 TD->getTypeStoreSizeInBits(ToType) - Offset;
1559 // Note: we support negative bitwidths (with shl) which are not defined.
1560 // We do this to support (f.e.) loads off the end of a structure where
1561 // only some bits are used.
1562 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
1563 FromVal = Builder.CreateLShr(FromVal,
1564 ConstantInt::get(FromVal->getType(),
1566 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
1567 FromVal = Builder.CreateShl(FromVal,
1568 ConstantInt::get(FromVal->getType(),
1571 // Finally, unconditionally truncate the integer to the right width.
1572 unsigned LIBitWidth = TD->getTypeSizeInBits(ToType);
1573 if (LIBitWidth < NTy->getBitWidth())
1575 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(),
1576 LIBitWidth), "tmp");
1577 else if (LIBitWidth > NTy->getBitWidth())
1579 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(),
1580 LIBitWidth), "tmp");
1582 // If the result is an integer, this is a trunc or bitcast.
1583 if (isa<IntegerType>(ToType)) {
1585 } else if (ToType->isFloatingPoint() || isa<VectorType>(ToType)) {
1586 // Just do a bitcast, we know the sizes match up.
1587 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
1589 // Otherwise must be a pointer.
1590 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
1592 assert(FromVal->getType() == ToType && "Didn't convert right?");
1596 /// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
1597 /// or vector value "Old" at the offset specified by Offset.
1599 /// This happens when we are converting an "integer union" to a
1600 /// single integer scalar, or when we are converting a "vector union" to a
1601 /// vector with insert/extractelement instructions.
1603 /// Offset is an offset from the original alloca, in bits that need to be
1604 /// shifted to the right.
1605 Value *SROA::ConvertScalar_InsertValue(Value *SV, Value *Old,
1606 uint64_t Offset, IRBuilder<> &Builder) {
1608 // Convert the stored type to the actual type, shift it left to insert
1609 // then 'or' into place.
1610 const Type *AllocaType = Old->getType();
1611 LLVMContext &Context = Old->getContext();
1613 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
1614 uint64_t VecSize = TD->getTypeAllocSizeInBits(VTy);
1615 uint64_t ValSize = TD->getTypeAllocSizeInBits(SV->getType());
1617 // Changing the whole vector with memset or with an access of a different
1619 if (ValSize == VecSize)
1620 return Builder.CreateBitCast(SV, AllocaType, "tmp");
1622 uint64_t EltSize = TD->getTypeAllocSizeInBits(VTy->getElementType());
1624 // Must be an element insertion.
1625 unsigned Elt = Offset/EltSize;
1627 if (SV->getType() != VTy->getElementType())
1628 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
1630 SV = Builder.CreateInsertElement(Old, SV,
1631 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
1636 // If SV is a first-class aggregate value, insert each value recursively.
1637 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
1638 const StructLayout &Layout = *TD->getStructLayout(ST);
1639 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
1640 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
1641 Old = ConvertScalar_InsertValue(Elt, Old,
1642 Offset+Layout.getElementOffsetInBits(i),
1648 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
1649 uint64_t EltSize = TD->getTypeAllocSizeInBits(AT->getElementType());
1650 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
1651 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
1652 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
1657 // If SV is a float, convert it to the appropriate integer type.
1658 // If it is a pointer, do the same.
1659 unsigned SrcWidth = TD->getTypeSizeInBits(SV->getType());
1660 unsigned DestWidth = TD->getTypeSizeInBits(AllocaType);
1661 unsigned SrcStoreWidth = TD->getTypeStoreSizeInBits(SV->getType());
1662 unsigned DestStoreWidth = TD->getTypeStoreSizeInBits(AllocaType);
1663 if (SV->getType()->isFloatingPoint() || isa<VectorType>(SV->getType()))
1664 SV = Builder.CreateBitCast(SV,
1665 IntegerType::get(SV->getContext(),SrcWidth), "tmp");
1666 else if (isa<PointerType>(SV->getType()))
1667 SV = Builder.CreatePtrToInt(SV, TD->getIntPtrType(SV->getContext()), "tmp");
1669 // Zero extend or truncate the value if needed.
1670 if (SV->getType() != AllocaType) {
1671 if (SV->getType()->getPrimitiveSizeInBits() <
1672 AllocaType->getPrimitiveSizeInBits())
1673 SV = Builder.CreateZExt(SV, AllocaType, "tmp");
1675 // Truncation may be needed if storing more than the alloca can hold
1676 // (undefined behavior).
1677 SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
1678 SrcWidth = DestWidth;
1679 SrcStoreWidth = DestStoreWidth;
1683 // If this is a big-endian system and the store is narrower than the
1684 // full alloca type, we need to do a shift to get the right bits.
1686 if (TD->isBigEndian()) {
1687 // On big-endian machines, the lowest bit is stored at the bit offset
1688 // from the pointer given by getTypeStoreSizeInBits. This matters for
1689 // integers with a bitwidth that is not a multiple of 8.
1690 ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
1695 // Note: we support negative bitwidths (with shr) which are not defined.
1696 // We do this to support (f.e.) stores off the end of a structure where
1697 // only some bits in the structure are set.
1698 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
1699 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
1700 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(),
1703 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
1704 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(),
1706 Mask = Mask.lshr(-ShAmt);
1709 // Mask out the bits we are about to insert from the old value, and or
1711 if (SrcWidth != DestWidth) {
1712 assert(DestWidth > SrcWidth);
1713 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask");
1714 SV = Builder.CreateOr(Old, SV, "ins");
1721 /// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
1722 /// some part of a constant global variable. This intentionally only accepts
1723 /// constant expressions because we don't can't rewrite arbitrary instructions.
1724 static bool PointsToConstantGlobal(Value *V) {
1725 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
1726 return GV->isConstant();
1727 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
1728 if (CE->getOpcode() == Instruction::BitCast ||
1729 CE->getOpcode() == Instruction::GetElementPtr)
1730 return PointsToConstantGlobal(CE->getOperand(0));
1734 /// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
1735 /// pointer to an alloca. Ignore any reads of the pointer, return false if we
1736 /// see any stores or other unknown uses. If we see pointer arithmetic, keep
1737 /// track of whether it moves the pointer (with isOffset) but otherwise traverse
1738 /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
1739 /// the alloca, and if the source pointer is a pointer to a constant global, we
1740 /// can optimize this.
1741 static bool isOnlyCopiedFromConstantGlobal(Value *V, Instruction *&TheCopy,
1743 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
1744 if (LoadInst *LI = dyn_cast<LoadInst>(*UI))
1745 // Ignore non-volatile loads, they are always ok.
1746 if (!LI->isVolatile())
1749 if (BitCastInst *BCI = dyn_cast<BitCastInst>(*UI)) {
1750 // If uses of the bitcast are ok, we are ok.
1751 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
1755 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(*UI)) {
1756 // If the GEP has all zero indices, it doesn't offset the pointer. If it
1757 // doesn't, it does.
1758 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
1759 isOffset || !GEP->hasAllZeroIndices()))
1764 // If this is isn't our memcpy/memmove, reject it as something we can't
1766 if (!isa<MemTransferInst>(*UI))
1769 // If we already have seen a copy, reject the second one.
1770 if (TheCopy) return false;
1772 // If the pointer has been offset from the start of the alloca, we can't
1773 // safely handle this.
1774 if (isOffset) return false;
1776 // If the memintrinsic isn't using the alloca as the dest, reject it.
1777 if (UI.getOperandNo() != 1) return false;
1779 MemIntrinsic *MI = cast<MemIntrinsic>(*UI);
1781 // If the source of the memcpy/move is not a constant global, reject it.
1782 if (!PointsToConstantGlobal(MI->getOperand(2)))
1785 // Otherwise, the transform is safe. Remember the copy instruction.
1791 /// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
1792 /// modified by a copy from a constant global. If we can prove this, we can
1793 /// replace any uses of the alloca with uses of the global directly.
1794 Instruction *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) {
1795 Instruction *TheCopy = 0;
1796 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))