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/Module.h"
32 #include "llvm/Pass.h"
33 #include "llvm/Analysis/Dominators.h"
34 #include "llvm/Target/TargetData.h"
35 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
36 #include "llvm/Transforms/Utils/Local.h"
37 #include "llvm/Support/Debug.h"
38 #include "llvm/Support/ErrorHandling.h"
39 #include "llvm/Support/GetElementPtrTypeIterator.h"
40 #include "llvm/Support/IRBuilder.h"
41 #include "llvm/Support/MathExtras.h"
42 #include "llvm/Support/raw_ostream.h"
43 #include "llvm/ADT/SmallVector.h"
44 #include "llvm/ADT/Statistic.h"
47 STATISTIC(NumReplaced, "Number of allocas broken up");
48 STATISTIC(NumPromoted, "Number of allocas promoted");
49 STATISTIC(NumConverted, "Number of aggregates converted to scalar");
50 STATISTIC(NumGlobals, "Number of allocas copied from constant global");
53 struct SROA : public FunctionPass {
54 static char ID; // Pass identification, replacement for typeid
55 explicit SROA(signed T = -1) : FunctionPass(ID) {
62 bool runOnFunction(Function &F);
64 bool performScalarRepl(Function &F);
65 bool performPromotion(Function &F);
67 // getAnalysisUsage - This pass does not require any passes, but we know it
68 // will not alter the CFG, so say so.
69 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
70 AU.addRequired<DominatorTree>();
71 AU.addRequired<DominanceFrontier>();
78 /// DeadInsts - Keep track of instructions we have made dead, so that
79 /// we can remove them after we are done working.
80 SmallVector<Value*, 32> DeadInsts;
82 /// AllocaInfo - When analyzing uses of an alloca instruction, this captures
83 /// information about the uses. All these fields are initialized to false
84 /// and set to true when something is learned.
86 /// isUnsafe - This is set to true if the alloca cannot be SROA'd.
89 /// isMemCpySrc - This is true if this aggregate is memcpy'd from.
92 /// isMemCpyDst - This is true if this aggregate is memcpy'd into.
96 : isUnsafe(false), isMemCpySrc(false), isMemCpyDst(false) {}
101 void MarkUnsafe(AllocaInfo &I) { I.isUnsafe = true; }
103 bool isSafeAllocaToScalarRepl(AllocaInst *AI);
105 void isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
107 void isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t &Offset,
109 void isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
110 const Type *MemOpType, bool isStore, AllocaInfo &Info);
111 bool TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size);
112 uint64_t FindElementAndOffset(const Type *&T, uint64_t &Offset,
115 void DoScalarReplacement(AllocaInst *AI,
116 std::vector<AllocaInst*> &WorkList);
117 void DeleteDeadInstructions();
119 void RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
120 SmallVector<AllocaInst*, 32> &NewElts);
121 void RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
122 SmallVector<AllocaInst*, 32> &NewElts);
123 void RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
124 SmallVector<AllocaInst*, 32> &NewElts);
125 void RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
127 SmallVector<AllocaInst*, 32> &NewElts);
128 void RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
129 SmallVector<AllocaInst*, 32> &NewElts);
130 void RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
131 SmallVector<AllocaInst*, 32> &NewElts);
133 static MemTransferInst *isOnlyCopiedFromConstantGlobal(AllocaInst *AI);
138 INITIALIZE_PASS(SROA, "scalarrepl",
139 "Scalar Replacement of Aggregates", false, false);
141 // Public interface to the ScalarReplAggregates pass
142 FunctionPass *llvm::createScalarReplAggregatesPass(signed int Threshold) {
143 return new SROA(Threshold);
147 //===----------------------------------------------------------------------===//
148 // Convert To Scalar Optimization.
149 //===----------------------------------------------------------------------===//
152 /// ConvertToScalarInfo - This class implements the "Convert To Scalar"
153 /// optimization, which scans the uses of an alloca and determines if it can
154 /// rewrite it in terms of a single new alloca that can be mem2reg'd.
155 class ConvertToScalarInfo {
156 /// AllocaSize - The size of the alloca being considered.
158 const TargetData &TD;
160 /// IsNotTrivial - This is set to true if there is some access to the object
161 /// which means that mem2reg can't promote it.
164 /// VectorTy - This tracks the type that we should promote the vector to if
165 /// it is possible to turn it into a vector. This starts out null, and if it
166 /// isn't possible to turn into a vector type, it gets set to VoidTy.
167 const Type *VectorTy;
169 /// HadAVector - True if there is at least one vector access to the alloca.
170 /// We don't want to turn random arrays into vectors and use vector element
171 /// insert/extract, but if there are element accesses to something that is
172 /// also declared as a vector, we do want to promote to a vector.
176 explicit ConvertToScalarInfo(unsigned Size, const TargetData &td)
177 : AllocaSize(Size), TD(td) {
178 IsNotTrivial = false;
183 AllocaInst *TryConvert(AllocaInst *AI);
186 bool CanConvertToScalar(Value *V, uint64_t Offset);
187 void MergeInType(const Type *In, uint64_t Offset);
188 void ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI, uint64_t Offset);
190 Value *ConvertScalar_ExtractValue(Value *NV, const Type *ToType,
191 uint64_t Offset, IRBuilder<> &Builder);
192 Value *ConvertScalar_InsertValue(Value *StoredVal, Value *ExistingVal,
193 uint64_t Offset, IRBuilder<> &Builder);
195 } // end anonymous namespace.
198 /// IsVerbotenVectorType - Return true if this is a vector type ScalarRepl isn't
199 /// allowed to form. We do this to avoid MMX types, which is a complete hack,
200 /// but is required until the backend is fixed.
201 static bool IsVerbotenVectorType(const VectorType *VTy, const Instruction *I) {
202 StringRef Triple(I->getParent()->getParent()->getParent()->getTargetTriple());
203 if (!Triple.startswith("i386") &&
204 !Triple.startswith("x86_64"))
207 // Reject all the MMX vector types.
208 switch (VTy->getNumElements()) {
209 default: return false;
210 case 1: return VTy->getElementType()->isIntegerTy(64);
211 case 2: return VTy->getElementType()->isIntegerTy(32);
212 case 4: return VTy->getElementType()->isIntegerTy(16);
213 case 8: return VTy->getElementType()->isIntegerTy(8);
218 /// TryConvert - Analyze the specified alloca, and if it is safe to do so,
219 /// rewrite it to be a new alloca which is mem2reg'able. This returns the new
220 /// alloca if possible or null if not.
221 AllocaInst *ConvertToScalarInfo::TryConvert(AllocaInst *AI) {
222 // If we can't convert this scalar, or if mem2reg can trivially do it, bail
224 if (!CanConvertToScalar(AI, 0) || !IsNotTrivial)
227 // If we were able to find a vector type that can handle this with
228 // insert/extract elements, and if there was at least one use that had
229 // a vector type, promote this to a vector. We don't want to promote
230 // random stuff that doesn't use vectors (e.g. <9 x double>) because then
231 // we just get a lot of insert/extracts. If at least one vector is
232 // involved, then we probably really do have a union of vector/array.
234 if (VectorTy && VectorTy->isVectorTy() && HadAVector &&
235 !IsVerbotenVectorType(cast<VectorType>(VectorTy), AI)) {
236 DEBUG(dbgs() << "CONVERT TO VECTOR: " << *AI << "\n TYPE = "
237 << *VectorTy << '\n');
238 NewTy = VectorTy; // Use the vector type.
240 DEBUG(dbgs() << "CONVERT TO SCALAR INTEGER: " << *AI << "\n");
241 // Create and insert the integer alloca.
242 NewTy = IntegerType::get(AI->getContext(), AllocaSize*8);
244 AllocaInst *NewAI = new AllocaInst(NewTy, 0, "", AI->getParent()->begin());
245 ConvertUsesToScalar(AI, NewAI, 0);
249 /// MergeInType - Add the 'In' type to the accumulated vector type (VectorTy)
250 /// so far at the offset specified by Offset (which is specified in bytes).
252 /// There are two cases we handle here:
253 /// 1) A union of vector types of the same size and potentially its elements.
254 /// Here we turn element accesses into insert/extract element operations.
255 /// This promotes a <4 x float> with a store of float to the third element
256 /// into a <4 x float> that uses insert element.
257 /// 2) A fully general blob of memory, which we turn into some (potentially
258 /// large) integer type with extract and insert operations where the loads
259 /// and stores would mutate the memory. We mark this by setting VectorTy
261 void ConvertToScalarInfo::MergeInType(const Type *In, uint64_t Offset) {
262 // If we already decided to turn this into a blob of integer memory, there is
263 // nothing to be done.
264 if (VectorTy && VectorTy->isVoidTy())
267 // If this could be contributing to a vector, analyze it.
269 // If the In type is a vector that is the same size as the alloca, see if it
270 // matches the existing VecTy.
271 if (const VectorType *VInTy = dyn_cast<VectorType>(In)) {
272 // Remember if we saw a vector type.
275 if (VInTy->getBitWidth()/8 == AllocaSize && Offset == 0) {
276 // If we're storing/loading a vector of the right size, allow it as a
277 // vector. If this the first vector we see, remember the type so that
278 // we know the element size. If this is a subsequent access, ignore it
279 // even if it is a differing type but the same size. Worst case we can
280 // bitcast the resultant vectors.
285 } else if (In->isFloatTy() || In->isDoubleTy() ||
286 (In->isIntegerTy() && In->getPrimitiveSizeInBits() >= 8 &&
287 isPowerOf2_32(In->getPrimitiveSizeInBits()))) {
288 // If we're accessing something that could be an element of a vector, see
289 // if the implied vector agrees with what we already have and if Offset is
290 // compatible with it.
291 unsigned EltSize = In->getPrimitiveSizeInBits()/8;
292 if (Offset % EltSize == 0 && AllocaSize % EltSize == 0 &&
294 cast<VectorType>(VectorTy)->getElementType()
295 ->getPrimitiveSizeInBits()/8 == EltSize)) {
297 VectorTy = VectorType::get(In, AllocaSize/EltSize);
302 // Otherwise, we have a case that we can't handle with an optimized vector
303 // form. We can still turn this into a large integer.
304 VectorTy = Type::getVoidTy(In->getContext());
307 /// CanConvertToScalar - V is a pointer. If we can convert the pointee and all
308 /// its accesses to a single vector type, return true and set VecTy to
309 /// the new type. If we could convert the alloca into a single promotable
310 /// integer, return true but set VecTy to VoidTy. Further, if the use is not a
311 /// completely trivial use that mem2reg could promote, set IsNotTrivial. Offset
312 /// is the current offset from the base of the alloca being analyzed.
314 /// If we see at least one access to the value that is as a vector type, set the
316 bool ConvertToScalarInfo::CanConvertToScalar(Value *V, uint64_t Offset) {
317 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
318 Instruction *User = cast<Instruction>(*UI);
320 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
321 // Don't break volatile loads.
322 if (LI->isVolatile())
324 MergeInType(LI->getType(), Offset);
328 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
329 // Storing the pointer, not into the value?
330 if (SI->getOperand(0) == V || SI->isVolatile()) return false;
331 MergeInType(SI->getOperand(0)->getType(), Offset);
335 if (BitCastInst *BCI = dyn_cast<BitCastInst>(User)) {
336 IsNotTrivial = true; // Can't be mem2reg'd.
337 if (!CanConvertToScalar(BCI, Offset))
342 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
343 // If this is a GEP with a variable indices, we can't handle it.
344 if (!GEP->hasAllConstantIndices())
347 // Compute the offset that this GEP adds to the pointer.
348 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
349 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
350 &Indices[0], Indices.size());
351 // See if all uses can be converted.
352 if (!CanConvertToScalar(GEP, Offset+GEPOffset))
354 IsNotTrivial = true; // Can't be mem2reg'd.
358 // If this is a constant sized memset of a constant value (e.g. 0) we can
360 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
361 // Store of constant value and constant size.
362 if (!isa<ConstantInt>(MSI->getValue()) ||
363 !isa<ConstantInt>(MSI->getLength()))
365 IsNotTrivial = true; // Can't be mem2reg'd.
369 // If this is a memcpy or memmove into or out of the whole allocation, we
370 // can handle it like a load or store of the scalar type.
371 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
372 ConstantInt *Len = dyn_cast<ConstantInt>(MTI->getLength());
373 if (Len == 0 || Len->getZExtValue() != AllocaSize || Offset != 0)
376 IsNotTrivial = true; // Can't be mem2reg'd.
380 // Otherwise, we cannot handle this!
387 /// ConvertUsesToScalar - Convert all of the users of Ptr to use the new alloca
388 /// directly. This happens when we are converting an "integer union" to a
389 /// single integer scalar, or when we are converting a "vector union" to a
390 /// vector with insert/extractelement instructions.
392 /// Offset is an offset from the original alloca, in bits that need to be
393 /// shifted to the right. By the end of this, there should be no uses of Ptr.
394 void ConvertToScalarInfo::ConvertUsesToScalar(Value *Ptr, AllocaInst *NewAI,
396 while (!Ptr->use_empty()) {
397 Instruction *User = cast<Instruction>(Ptr->use_back());
399 if (BitCastInst *CI = dyn_cast<BitCastInst>(User)) {
400 ConvertUsesToScalar(CI, NewAI, Offset);
401 CI->eraseFromParent();
405 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(User)) {
406 // Compute the offset that this GEP adds to the pointer.
407 SmallVector<Value*, 8> Indices(GEP->op_begin()+1, GEP->op_end());
408 uint64_t GEPOffset = TD.getIndexedOffset(GEP->getPointerOperandType(),
409 &Indices[0], Indices.size());
410 ConvertUsesToScalar(GEP, NewAI, Offset+GEPOffset*8);
411 GEP->eraseFromParent();
415 IRBuilder<> Builder(User->getParent(), User);
417 if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
418 // The load is a bit extract from NewAI shifted right by Offset bits.
419 Value *LoadedVal = Builder.CreateLoad(NewAI, "tmp");
421 = ConvertScalar_ExtractValue(LoadedVal, LI->getType(), Offset, Builder);
422 LI->replaceAllUsesWith(NewLoadVal);
423 LI->eraseFromParent();
427 if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
428 assert(SI->getOperand(0) != Ptr && "Consistency error!");
429 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
430 Value *New = ConvertScalar_InsertValue(SI->getOperand(0), Old, Offset,
432 Builder.CreateStore(New, NewAI);
433 SI->eraseFromParent();
435 // If the load we just inserted is now dead, then the inserted store
436 // overwrote the entire thing.
437 if (Old->use_empty())
438 Old->eraseFromParent();
442 // If this is a constant sized memset of a constant value (e.g. 0) we can
443 // transform it into a store of the expanded constant value.
444 if (MemSetInst *MSI = dyn_cast<MemSetInst>(User)) {
445 assert(MSI->getRawDest() == Ptr && "Consistency error!");
446 unsigned NumBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
448 unsigned Val = cast<ConstantInt>(MSI->getValue())->getZExtValue();
450 // Compute the value replicated the right number of times.
451 APInt APVal(NumBytes*8, Val);
453 // Splat the value if non-zero.
455 for (unsigned i = 1; i != NumBytes; ++i)
458 Instruction *Old = Builder.CreateLoad(NewAI, NewAI->getName()+".in");
459 Value *New = ConvertScalar_InsertValue(
460 ConstantInt::get(User->getContext(), APVal),
461 Old, Offset, Builder);
462 Builder.CreateStore(New, NewAI);
464 // If the load we just inserted is now dead, then the memset overwrote
466 if (Old->use_empty())
467 Old->eraseFromParent();
469 MSI->eraseFromParent();
473 // If this is a memcpy or memmove into or out of the whole allocation, we
474 // can handle it like a load or store of the scalar type.
475 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(User)) {
476 assert(Offset == 0 && "must be store to start of alloca");
478 // If the source and destination are both to the same alloca, then this is
479 // a noop copy-to-self, just delete it. Otherwise, emit a load and store
481 AllocaInst *OrigAI = cast<AllocaInst>(Ptr->getUnderlyingObject(0));
483 if (MTI->getSource()->getUnderlyingObject(0) != OrigAI) {
484 // Dest must be OrigAI, change this to be a load from the original
485 // pointer (bitcasted), then a store to our new alloca.
486 assert(MTI->getRawDest() == Ptr && "Neither use is of pointer?");
487 Value *SrcPtr = MTI->getSource();
488 SrcPtr = Builder.CreateBitCast(SrcPtr, NewAI->getType());
490 LoadInst *SrcVal = Builder.CreateLoad(SrcPtr, "srcval");
491 SrcVal->setAlignment(MTI->getAlignment());
492 Builder.CreateStore(SrcVal, NewAI);
493 } else if (MTI->getDest()->getUnderlyingObject(0) != OrigAI) {
494 // Src must be OrigAI, change this to be a load from NewAI then a store
495 // through the original dest pointer (bitcasted).
496 assert(MTI->getRawSource() == Ptr && "Neither use is of pointer?");
497 LoadInst *SrcVal = Builder.CreateLoad(NewAI, "srcval");
499 Value *DstPtr = Builder.CreateBitCast(MTI->getDest(), NewAI->getType());
500 StoreInst *NewStore = Builder.CreateStore(SrcVal, DstPtr);
501 NewStore->setAlignment(MTI->getAlignment());
503 // Noop transfer. Src == Dst
506 MTI->eraseFromParent();
510 llvm_unreachable("Unsupported operation!");
514 /// ConvertScalar_ExtractValue - Extract a value of type ToType from an integer
515 /// or vector value FromVal, extracting the bits from the offset specified by
516 /// Offset. This returns the value, which is of type ToType.
518 /// This happens when we are converting an "integer union" to a single
519 /// integer scalar, or when we are converting a "vector union" to a vector with
520 /// insert/extractelement instructions.
522 /// Offset is an offset from the original alloca, in bits that need to be
523 /// shifted to the right.
524 Value *ConvertToScalarInfo::
525 ConvertScalar_ExtractValue(Value *FromVal, const Type *ToType,
526 uint64_t Offset, IRBuilder<> &Builder) {
527 // If the load is of the whole new alloca, no conversion is needed.
528 if (FromVal->getType() == ToType && Offset == 0)
531 // If the result alloca is a vector type, this is either an element
532 // access or a bitcast to another vector type of the same size.
533 if (const VectorType *VTy = dyn_cast<VectorType>(FromVal->getType())) {
534 if (ToType->isVectorTy())
535 return Builder.CreateBitCast(FromVal, ToType, "tmp");
537 // Otherwise it must be an element access.
540 unsigned EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
541 Elt = Offset/EltSize;
542 assert(EltSize*Elt == Offset && "Invalid modulus in validity checking");
544 // Return the element extracted out of it.
545 Value *V = Builder.CreateExtractElement(FromVal, ConstantInt::get(
546 Type::getInt32Ty(FromVal->getContext()), Elt), "tmp");
547 if (V->getType() != ToType)
548 V = Builder.CreateBitCast(V, ToType, "tmp");
552 // If ToType is a first class aggregate, extract out each of the pieces and
553 // use insertvalue's to form the FCA.
554 if (const StructType *ST = dyn_cast<StructType>(ToType)) {
555 const StructLayout &Layout = *TD.getStructLayout(ST);
556 Value *Res = UndefValue::get(ST);
557 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
558 Value *Elt = ConvertScalar_ExtractValue(FromVal, ST->getElementType(i),
559 Offset+Layout.getElementOffsetInBits(i),
561 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
566 if (const ArrayType *AT = dyn_cast<ArrayType>(ToType)) {
567 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
568 Value *Res = UndefValue::get(AT);
569 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
570 Value *Elt = ConvertScalar_ExtractValue(FromVal, AT->getElementType(),
571 Offset+i*EltSize, Builder);
572 Res = Builder.CreateInsertValue(Res, Elt, i, "tmp");
577 // Otherwise, this must be a union that was converted to an integer value.
578 const IntegerType *NTy = cast<IntegerType>(FromVal->getType());
580 // If this is a big-endian system and the load is narrower than the
581 // full alloca type, we need to do a shift to get the right bits.
583 if (TD.isBigEndian()) {
584 // On big-endian machines, the lowest bit is stored at the bit offset
585 // from the pointer given by getTypeStoreSizeInBits. This matters for
586 // integers with a bitwidth that is not a multiple of 8.
587 ShAmt = TD.getTypeStoreSizeInBits(NTy) -
588 TD.getTypeStoreSizeInBits(ToType) - Offset;
593 // Note: we support negative bitwidths (with shl) which are not defined.
594 // We do this to support (f.e.) loads off the end of a structure where
595 // only some bits are used.
596 if (ShAmt > 0 && (unsigned)ShAmt < NTy->getBitWidth())
597 FromVal = Builder.CreateLShr(FromVal,
598 ConstantInt::get(FromVal->getType(),
600 else if (ShAmt < 0 && (unsigned)-ShAmt < NTy->getBitWidth())
601 FromVal = Builder.CreateShl(FromVal,
602 ConstantInt::get(FromVal->getType(),
605 // Finally, unconditionally truncate the integer to the right width.
606 unsigned LIBitWidth = TD.getTypeSizeInBits(ToType);
607 if (LIBitWidth < NTy->getBitWidth())
609 Builder.CreateTrunc(FromVal, IntegerType::get(FromVal->getContext(),
611 else if (LIBitWidth > NTy->getBitWidth())
613 Builder.CreateZExt(FromVal, IntegerType::get(FromVal->getContext(),
616 // If the result is an integer, this is a trunc or bitcast.
617 if (ToType->isIntegerTy()) {
619 } else if (ToType->isFloatingPointTy() || ToType->isVectorTy()) {
620 // Just do a bitcast, we know the sizes match up.
621 FromVal = Builder.CreateBitCast(FromVal, ToType, "tmp");
623 // Otherwise must be a pointer.
624 FromVal = Builder.CreateIntToPtr(FromVal, ToType, "tmp");
626 assert(FromVal->getType() == ToType && "Didn't convert right?");
630 /// ConvertScalar_InsertValue - Insert the value "SV" into the existing integer
631 /// or vector value "Old" at the offset specified by Offset.
633 /// This happens when we are converting an "integer union" to a
634 /// single integer scalar, or when we are converting a "vector union" to a
635 /// vector with insert/extractelement instructions.
637 /// Offset is an offset from the original alloca, in bits that need to be
638 /// shifted to the right.
639 Value *ConvertToScalarInfo::
640 ConvertScalar_InsertValue(Value *SV, Value *Old,
641 uint64_t Offset, IRBuilder<> &Builder) {
642 // Convert the stored type to the actual type, shift it left to insert
643 // then 'or' into place.
644 const Type *AllocaType = Old->getType();
645 LLVMContext &Context = Old->getContext();
647 if (const VectorType *VTy = dyn_cast<VectorType>(AllocaType)) {
648 uint64_t VecSize = TD.getTypeAllocSizeInBits(VTy);
649 uint64_t ValSize = TD.getTypeAllocSizeInBits(SV->getType());
651 // Changing the whole vector with memset or with an access of a different
653 if (ValSize == VecSize)
654 return Builder.CreateBitCast(SV, AllocaType, "tmp");
656 uint64_t EltSize = TD.getTypeAllocSizeInBits(VTy->getElementType());
658 // Must be an element insertion.
659 unsigned Elt = Offset/EltSize;
661 if (SV->getType() != VTy->getElementType())
662 SV = Builder.CreateBitCast(SV, VTy->getElementType(), "tmp");
664 SV = Builder.CreateInsertElement(Old, SV,
665 ConstantInt::get(Type::getInt32Ty(SV->getContext()), Elt),
670 // If SV is a first-class aggregate value, insert each value recursively.
671 if (const StructType *ST = dyn_cast<StructType>(SV->getType())) {
672 const StructLayout &Layout = *TD.getStructLayout(ST);
673 for (unsigned i = 0, e = ST->getNumElements(); i != e; ++i) {
674 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
675 Old = ConvertScalar_InsertValue(Elt, Old,
676 Offset+Layout.getElementOffsetInBits(i),
682 if (const ArrayType *AT = dyn_cast<ArrayType>(SV->getType())) {
683 uint64_t EltSize = TD.getTypeAllocSizeInBits(AT->getElementType());
684 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
685 Value *Elt = Builder.CreateExtractValue(SV, i, "tmp");
686 Old = ConvertScalar_InsertValue(Elt, Old, Offset+i*EltSize, Builder);
691 // If SV is a float, convert it to the appropriate integer type.
692 // If it is a pointer, do the same.
693 unsigned SrcWidth = TD.getTypeSizeInBits(SV->getType());
694 unsigned DestWidth = TD.getTypeSizeInBits(AllocaType);
695 unsigned SrcStoreWidth = TD.getTypeStoreSizeInBits(SV->getType());
696 unsigned DestStoreWidth = TD.getTypeStoreSizeInBits(AllocaType);
697 if (SV->getType()->isFloatingPointTy() || SV->getType()->isVectorTy())
698 SV = Builder.CreateBitCast(SV,
699 IntegerType::get(SV->getContext(),SrcWidth), "tmp");
700 else if (SV->getType()->isPointerTy())
701 SV = Builder.CreatePtrToInt(SV, TD.getIntPtrType(SV->getContext()), "tmp");
703 // Zero extend or truncate the value if needed.
704 if (SV->getType() != AllocaType) {
705 if (SV->getType()->getPrimitiveSizeInBits() <
706 AllocaType->getPrimitiveSizeInBits())
707 SV = Builder.CreateZExt(SV, AllocaType, "tmp");
709 // Truncation may be needed if storing more than the alloca can hold
710 // (undefined behavior).
711 SV = Builder.CreateTrunc(SV, AllocaType, "tmp");
712 SrcWidth = DestWidth;
713 SrcStoreWidth = DestStoreWidth;
717 // If this is a big-endian system and the store is narrower than the
718 // full alloca type, we need to do a shift to get the right bits.
720 if (TD.isBigEndian()) {
721 // On big-endian machines, the lowest bit is stored at the bit offset
722 // from the pointer given by getTypeStoreSizeInBits. This matters for
723 // integers with a bitwidth that is not a multiple of 8.
724 ShAmt = DestStoreWidth - SrcStoreWidth - Offset;
729 // Note: we support negative bitwidths (with shr) which are not defined.
730 // We do this to support (f.e.) stores off the end of a structure where
731 // only some bits in the structure are set.
732 APInt Mask(APInt::getLowBitsSet(DestWidth, SrcWidth));
733 if (ShAmt > 0 && (unsigned)ShAmt < DestWidth) {
734 SV = Builder.CreateShl(SV, ConstantInt::get(SV->getType(),
737 } else if (ShAmt < 0 && (unsigned)-ShAmt < DestWidth) {
738 SV = Builder.CreateLShr(SV, ConstantInt::get(SV->getType(),
740 Mask = Mask.lshr(-ShAmt);
743 // Mask out the bits we are about to insert from the old value, and or
745 if (SrcWidth != DestWidth) {
746 assert(DestWidth > SrcWidth);
747 Old = Builder.CreateAnd(Old, ConstantInt::get(Context, ~Mask), "mask");
748 SV = Builder.CreateOr(Old, SV, "ins");
754 //===----------------------------------------------------------------------===//
756 //===----------------------------------------------------------------------===//
759 bool SROA::runOnFunction(Function &F) {
760 TD = getAnalysisIfAvailable<TargetData>();
762 bool Changed = performPromotion(F);
764 // FIXME: ScalarRepl currently depends on TargetData more than it
765 // theoretically needs to. It should be refactored in order to support
766 // target-independent IR. Until this is done, just skip the actual
767 // scalar-replacement portion of this pass.
768 if (!TD) return Changed;
771 bool LocalChange = performScalarRepl(F);
772 if (!LocalChange) break; // No need to repromote if no scalarrepl
774 LocalChange = performPromotion(F);
775 if (!LocalChange) break; // No need to re-scalarrepl if no promotion
782 bool SROA::performPromotion(Function &F) {
783 std::vector<AllocaInst*> Allocas;
784 DominatorTree &DT = getAnalysis<DominatorTree>();
785 DominanceFrontier &DF = getAnalysis<DominanceFrontier>();
787 BasicBlock &BB = F.getEntryBlock(); // Get the entry node for the function
789 bool Changed = false;
794 // Find allocas that are safe to promote, by looking at all instructions in
796 for (BasicBlock::iterator I = BB.begin(), E = --BB.end(); I != E; ++I)
797 if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) // Is it an alloca?
798 if (isAllocaPromotable(AI))
799 Allocas.push_back(AI);
801 if (Allocas.empty()) break;
803 PromoteMemToReg(Allocas, DT, DF);
804 NumPromoted += Allocas.size();
812 /// ShouldAttemptScalarRepl - Decide if an alloca is a good candidate for
813 /// SROA. It must be a struct or array type with a small number of elements.
814 static bool ShouldAttemptScalarRepl(AllocaInst *AI) {
815 const Type *T = AI->getAllocatedType();
816 // Do not promote any struct into more than 32 separate vars.
817 if (const StructType *ST = dyn_cast<StructType>(T))
818 return ST->getNumElements() <= 32;
819 // Arrays are much less likely to be safe for SROA; only consider
820 // them if they are very small.
821 if (const ArrayType *AT = dyn_cast<ArrayType>(T))
822 return AT->getNumElements() <= 8;
827 // performScalarRepl - This algorithm is a simple worklist driven algorithm,
828 // which runs on all of the malloc/alloca instructions in the function, removing
829 // them if they are only used by getelementptr instructions.
831 bool SROA::performScalarRepl(Function &F) {
832 std::vector<AllocaInst*> WorkList;
834 // Scan the entry basic block, adding allocas to the worklist.
835 BasicBlock &BB = F.getEntryBlock();
836 for (BasicBlock::iterator I = BB.begin(), E = BB.end(); I != E; ++I)
837 if (AllocaInst *A = dyn_cast<AllocaInst>(I))
838 WorkList.push_back(A);
840 // Process the worklist
841 bool Changed = false;
842 while (!WorkList.empty()) {
843 AllocaInst *AI = WorkList.back();
846 // Handle dead allocas trivially. These can be formed by SROA'ing arrays
847 // with unused elements.
848 if (AI->use_empty()) {
849 AI->eraseFromParent();
854 // If this alloca is impossible for us to promote, reject it early.
855 if (AI->isArrayAllocation() || !AI->getAllocatedType()->isSized())
858 // Check to see if this allocation is only modified by a memcpy/memmove from
859 // a constant global. If this is the case, we can change all users to use
860 // the constant global instead. This is commonly produced by the CFE by
861 // constructs like "void foo() { int A[] = {1,2,3,4,5,6,7,8,9...}; }" if 'A'
862 // is only subsequently read.
863 if (MemTransferInst *TheCopy = isOnlyCopiedFromConstantGlobal(AI)) {
864 DEBUG(dbgs() << "Found alloca equal to global: " << *AI << '\n');
865 DEBUG(dbgs() << " memcpy = " << *TheCopy << '\n');
866 Constant *TheSrc = cast<Constant>(TheCopy->getSource());
867 AI->replaceAllUsesWith(ConstantExpr::getBitCast(TheSrc, AI->getType()));
868 TheCopy->eraseFromParent(); // Don't mutate the global.
869 AI->eraseFromParent();
875 // Check to see if we can perform the core SROA transformation. We cannot
876 // transform the allocation instruction if it is an array allocation
877 // (allocations OF arrays are ok though), and an allocation of a scalar
878 // value cannot be decomposed at all.
879 uint64_t AllocaSize = TD->getTypeAllocSize(AI->getAllocatedType());
881 // Do not promote [0 x %struct].
882 if (AllocaSize == 0) continue;
884 // Do not promote any struct whose size is too big.
885 if (AllocaSize > SRThreshold) continue;
887 // If the alloca looks like a good candidate for scalar replacement, and if
888 // all its users can be transformed, then split up the aggregate into its
889 // separate elements.
890 if (ShouldAttemptScalarRepl(AI) && isSafeAllocaToScalarRepl(AI)) {
891 DoScalarReplacement(AI, WorkList);
896 // If we can turn this aggregate value (potentially with casts) into a
897 // simple scalar value that can be mem2reg'd into a register value.
898 // IsNotTrivial tracks whether this is something that mem2reg could have
899 // promoted itself. If so, we don't want to transform it needlessly. Note
900 // that we can't just check based on the type: the alloca may be of an i32
901 // but that has pointer arithmetic to set byte 3 of it or something.
902 if (AllocaInst *NewAI =
903 ConvertToScalarInfo((unsigned)AllocaSize, *TD).TryConvert(AI)) {
905 AI->eraseFromParent();
911 // Otherwise, couldn't process this alloca.
917 /// DoScalarReplacement - This alloca satisfied the isSafeAllocaToScalarRepl
918 /// predicate, do SROA now.
919 void SROA::DoScalarReplacement(AllocaInst *AI,
920 std::vector<AllocaInst*> &WorkList) {
921 DEBUG(dbgs() << "Found inst to SROA: " << *AI << '\n');
922 SmallVector<AllocaInst*, 32> ElementAllocas;
923 if (const StructType *ST = dyn_cast<StructType>(AI->getAllocatedType())) {
924 ElementAllocas.reserve(ST->getNumContainedTypes());
925 for (unsigned i = 0, e = ST->getNumContainedTypes(); i != e; ++i) {
926 AllocaInst *NA = new AllocaInst(ST->getContainedType(i), 0,
928 AI->getName() + "." + Twine(i), AI);
929 ElementAllocas.push_back(NA);
930 WorkList.push_back(NA); // Add to worklist for recursive processing
933 const ArrayType *AT = cast<ArrayType>(AI->getAllocatedType());
934 ElementAllocas.reserve(AT->getNumElements());
935 const Type *ElTy = AT->getElementType();
936 for (unsigned i = 0, e = AT->getNumElements(); i != e; ++i) {
937 AllocaInst *NA = new AllocaInst(ElTy, 0, AI->getAlignment(),
938 AI->getName() + "." + Twine(i), AI);
939 ElementAllocas.push_back(NA);
940 WorkList.push_back(NA); // Add to worklist for recursive processing
944 // Now that we have created the new alloca instructions, rewrite all the
945 // uses of the old alloca.
946 RewriteForScalarRepl(AI, AI, 0, ElementAllocas);
948 // Now erase any instructions that were made dead while rewriting the alloca.
949 DeleteDeadInstructions();
950 AI->eraseFromParent();
955 /// DeleteDeadInstructions - Erase instructions on the DeadInstrs list,
956 /// recursively including all their operands that become trivially dead.
957 void SROA::DeleteDeadInstructions() {
958 while (!DeadInsts.empty()) {
959 Instruction *I = cast<Instruction>(DeadInsts.pop_back_val());
961 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
962 if (Instruction *U = dyn_cast<Instruction>(*OI)) {
963 // Zero out the operand and see if it becomes trivially dead.
964 // (But, don't add allocas to the dead instruction list -- they are
965 // already on the worklist and will be deleted separately.)
967 if (isInstructionTriviallyDead(U) && !isa<AllocaInst>(U))
968 DeadInsts.push_back(U);
971 I->eraseFromParent();
975 /// isSafeForScalarRepl - Check if instruction I is a safe use with regard to
976 /// performing scalar replacement of alloca AI. The results are flagged in
977 /// the Info parameter. Offset indicates the position within AI that is
978 /// referenced by this instruction.
979 void SROA::isSafeForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
981 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
982 Instruction *User = cast<Instruction>(*UI);
984 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
985 isSafeForScalarRepl(BC, AI, Offset, Info);
986 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
987 uint64_t GEPOffset = Offset;
988 isSafeGEP(GEPI, AI, GEPOffset, Info);
990 isSafeForScalarRepl(GEPI, AI, GEPOffset, Info);
991 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
992 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
994 isSafeMemAccess(AI, Offset, Length->getZExtValue(), 0,
995 UI.getOperandNo() == 0, Info);
998 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
999 if (!LI->isVolatile()) {
1000 const Type *LIType = LI->getType();
1001 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(LIType),
1002 LIType, false, Info);
1005 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
1006 // Store is ok if storing INTO the pointer, not storing the pointer
1007 if (!SI->isVolatile() && SI->getOperand(0) != I) {
1008 const Type *SIType = SI->getOperand(0)->getType();
1009 isSafeMemAccess(AI, Offset, TD->getTypeAllocSize(SIType),
1010 SIType, true, Info);
1014 DEBUG(errs() << " Transformation preventing inst: " << *User << '\n');
1017 if (Info.isUnsafe) return;
1021 /// isSafeGEP - Check if a GEP instruction can be handled for scalar
1022 /// replacement. It is safe when all the indices are constant, in-bounds
1023 /// references, and when the resulting offset corresponds to an element within
1024 /// the alloca type. The results are flagged in the Info parameter. Upon
1025 /// return, Offset is adjusted as specified by the GEP indices.
1026 void SROA::isSafeGEP(GetElementPtrInst *GEPI, AllocaInst *AI,
1027 uint64_t &Offset, AllocaInfo &Info) {
1028 gep_type_iterator GEPIt = gep_type_begin(GEPI), E = gep_type_end(GEPI);
1032 // Walk through the GEP type indices, checking the types that this indexes
1034 for (; GEPIt != E; ++GEPIt) {
1035 // Ignore struct elements, no extra checking needed for these.
1036 if ((*GEPIt)->isStructTy())
1039 ConstantInt *IdxVal = dyn_cast<ConstantInt>(GEPIt.getOperand());
1041 return MarkUnsafe(Info);
1044 // Compute the offset due to this GEP and check if the alloca has a
1045 // component element at that offset.
1046 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
1047 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
1048 &Indices[0], Indices.size());
1049 if (!TypeHasComponent(AI->getAllocatedType(), Offset, 0))
1053 /// isSafeMemAccess - Check if a load/store/memcpy operates on the entire AI
1054 /// alloca or has an offset and size that corresponds to a component element
1055 /// within it. The offset checked here may have been formed from a GEP with a
1056 /// pointer bitcasted to a different type.
1057 void SROA::isSafeMemAccess(AllocaInst *AI, uint64_t Offset, uint64_t MemSize,
1058 const Type *MemOpType, bool isStore,
1060 // Check if this is a load/store of the entire alloca.
1061 if (Offset == 0 && MemSize == TD->getTypeAllocSize(AI->getAllocatedType())) {
1062 bool UsesAggregateType = (MemOpType == AI->getAllocatedType());
1063 // This is safe for MemIntrinsics (where MemOpType is 0), integer types
1064 // (which are essentially the same as the MemIntrinsics, especially with
1065 // regard to copying padding between elements), or references using the
1066 // aggregate type of the alloca.
1067 if (!MemOpType || MemOpType->isIntegerTy() || UsesAggregateType) {
1068 if (!UsesAggregateType) {
1070 Info.isMemCpyDst = true;
1072 Info.isMemCpySrc = true;
1077 // Check if the offset/size correspond to a component within the alloca type.
1078 const Type *T = AI->getAllocatedType();
1079 if (TypeHasComponent(T, Offset, MemSize))
1082 return MarkUnsafe(Info);
1085 /// TypeHasComponent - Return true if T has a component type with the
1086 /// specified offset and size. If Size is zero, do not check the size.
1087 bool SROA::TypeHasComponent(const Type *T, uint64_t Offset, uint64_t Size) {
1090 if (const StructType *ST = dyn_cast<StructType>(T)) {
1091 const StructLayout *Layout = TD->getStructLayout(ST);
1092 unsigned EltIdx = Layout->getElementContainingOffset(Offset);
1093 EltTy = ST->getContainedType(EltIdx);
1094 EltSize = TD->getTypeAllocSize(EltTy);
1095 Offset -= Layout->getElementOffset(EltIdx);
1096 } else if (const ArrayType *AT = dyn_cast<ArrayType>(T)) {
1097 EltTy = AT->getElementType();
1098 EltSize = TD->getTypeAllocSize(EltTy);
1099 if (Offset >= AT->getNumElements() * EltSize)
1105 if (Offset == 0 && (Size == 0 || EltSize == Size))
1107 // Check if the component spans multiple elements.
1108 if (Offset + Size > EltSize)
1110 return TypeHasComponent(EltTy, Offset, Size);
1113 /// RewriteForScalarRepl - Alloca AI is being split into NewElts, so rewrite
1114 /// the instruction I, which references it, to use the separate elements.
1115 /// Offset indicates the position within AI that is referenced by this
1117 void SROA::RewriteForScalarRepl(Instruction *I, AllocaInst *AI, uint64_t Offset,
1118 SmallVector<AllocaInst*, 32> &NewElts) {
1119 for (Value::use_iterator UI = I->use_begin(), E = I->use_end(); UI!=E; ++UI) {
1120 Instruction *User = cast<Instruction>(*UI);
1122 if (BitCastInst *BC = dyn_cast<BitCastInst>(User)) {
1123 RewriteBitCast(BC, AI, Offset, NewElts);
1124 } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(User)) {
1125 RewriteGEP(GEPI, AI, Offset, NewElts);
1126 } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(User)) {
1127 ConstantInt *Length = dyn_cast<ConstantInt>(MI->getLength());
1128 uint64_t MemSize = Length->getZExtValue();
1130 MemSize == TD->getTypeAllocSize(AI->getAllocatedType()))
1131 RewriteMemIntrinUserOfAlloca(MI, I, AI, NewElts);
1132 // Otherwise the intrinsic can only touch a single element and the
1133 // address operand will be updated, so nothing else needs to be done.
1134 } else if (LoadInst *LI = dyn_cast<LoadInst>(User)) {
1135 const Type *LIType = LI->getType();
1136 if (LIType == AI->getAllocatedType()) {
1138 // %res = load { i32, i32 }* %alloc
1140 // %load.0 = load i32* %alloc.0
1141 // %insert.0 insertvalue { i32, i32 } zeroinitializer, i32 %load.0, 0
1142 // %load.1 = load i32* %alloc.1
1143 // %insert = insertvalue { i32, i32 } %insert.0, i32 %load.1, 1
1144 // (Also works for arrays instead of structs)
1145 Value *Insert = UndefValue::get(LIType);
1146 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1147 Value *Load = new LoadInst(NewElts[i], "load", LI);
1148 Insert = InsertValueInst::Create(Insert, Load, i, "insert", LI);
1150 LI->replaceAllUsesWith(Insert);
1151 DeadInsts.push_back(LI);
1152 } else if (LIType->isIntegerTy() &&
1153 TD->getTypeAllocSize(LIType) ==
1154 TD->getTypeAllocSize(AI->getAllocatedType())) {
1155 // If this is a load of the entire alloca to an integer, rewrite it.
1156 RewriteLoadUserOfWholeAlloca(LI, AI, NewElts);
1158 } else if (StoreInst *SI = dyn_cast<StoreInst>(User)) {
1159 Value *Val = SI->getOperand(0);
1160 const Type *SIType = Val->getType();
1161 if (SIType == AI->getAllocatedType()) {
1163 // store { i32, i32 } %val, { i32, i32 }* %alloc
1165 // %val.0 = extractvalue { i32, i32 } %val, 0
1166 // store i32 %val.0, i32* %alloc.0
1167 // %val.1 = extractvalue { i32, i32 } %val, 1
1168 // store i32 %val.1, i32* %alloc.1
1169 // (Also works for arrays instead of structs)
1170 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1171 Value *Extract = ExtractValueInst::Create(Val, i, Val->getName(), SI);
1172 new StoreInst(Extract, NewElts[i], SI);
1174 DeadInsts.push_back(SI);
1175 } else if (SIType->isIntegerTy() &&
1176 TD->getTypeAllocSize(SIType) ==
1177 TD->getTypeAllocSize(AI->getAllocatedType())) {
1178 // If this is a store of the entire alloca from an integer, rewrite it.
1179 RewriteStoreUserOfWholeAlloca(SI, AI, NewElts);
1185 /// RewriteBitCast - Update a bitcast reference to the alloca being replaced
1186 /// and recursively continue updating all of its uses.
1187 void SROA::RewriteBitCast(BitCastInst *BC, AllocaInst *AI, uint64_t Offset,
1188 SmallVector<AllocaInst*, 32> &NewElts) {
1189 RewriteForScalarRepl(BC, AI, Offset, NewElts);
1190 if (BC->getOperand(0) != AI)
1193 // The bitcast references the original alloca. Replace its uses with
1194 // references to the first new element alloca.
1195 Instruction *Val = NewElts[0];
1196 if (Val->getType() != BC->getDestTy()) {
1197 Val = new BitCastInst(Val, BC->getDestTy(), "", BC);
1200 BC->replaceAllUsesWith(Val);
1201 DeadInsts.push_back(BC);
1204 /// FindElementAndOffset - Return the index of the element containing Offset
1205 /// within the specified type, which must be either a struct or an array.
1206 /// Sets T to the type of the element and Offset to the offset within that
1207 /// element. IdxTy is set to the type of the index result to be used in a
1208 /// GEP instruction.
1209 uint64_t SROA::FindElementAndOffset(const Type *&T, uint64_t &Offset,
1210 const Type *&IdxTy) {
1212 if (const StructType *ST = dyn_cast<StructType>(T)) {
1213 const StructLayout *Layout = TD->getStructLayout(ST);
1214 Idx = Layout->getElementContainingOffset(Offset);
1215 T = ST->getContainedType(Idx);
1216 Offset -= Layout->getElementOffset(Idx);
1217 IdxTy = Type::getInt32Ty(T->getContext());
1220 const ArrayType *AT = cast<ArrayType>(T);
1221 T = AT->getElementType();
1222 uint64_t EltSize = TD->getTypeAllocSize(T);
1223 Idx = Offset / EltSize;
1224 Offset -= Idx * EltSize;
1225 IdxTy = Type::getInt64Ty(T->getContext());
1229 /// RewriteGEP - Check if this GEP instruction moves the pointer across
1230 /// elements of the alloca that are being split apart, and if so, rewrite
1231 /// the GEP to be relative to the new element.
1232 void SROA::RewriteGEP(GetElementPtrInst *GEPI, AllocaInst *AI, uint64_t Offset,
1233 SmallVector<AllocaInst*, 32> &NewElts) {
1234 uint64_t OldOffset = Offset;
1235 SmallVector<Value*, 8> Indices(GEPI->op_begin() + 1, GEPI->op_end());
1236 Offset += TD->getIndexedOffset(GEPI->getPointerOperandType(),
1237 &Indices[0], Indices.size());
1239 RewriteForScalarRepl(GEPI, AI, Offset, NewElts);
1241 const Type *T = AI->getAllocatedType();
1243 uint64_t OldIdx = FindElementAndOffset(T, OldOffset, IdxTy);
1244 if (GEPI->getOperand(0) == AI)
1245 OldIdx = ~0ULL; // Force the GEP to be rewritten.
1247 T = AI->getAllocatedType();
1248 uint64_t EltOffset = Offset;
1249 uint64_t Idx = FindElementAndOffset(T, EltOffset, IdxTy);
1251 // If this GEP does not move the pointer across elements of the alloca
1252 // being split, then it does not needs to be rewritten.
1256 const Type *i32Ty = Type::getInt32Ty(AI->getContext());
1257 SmallVector<Value*, 8> NewArgs;
1258 NewArgs.push_back(Constant::getNullValue(i32Ty));
1259 while (EltOffset != 0) {
1260 uint64_t EltIdx = FindElementAndOffset(T, EltOffset, IdxTy);
1261 NewArgs.push_back(ConstantInt::get(IdxTy, EltIdx));
1263 Instruction *Val = NewElts[Idx];
1264 if (NewArgs.size() > 1) {
1265 Val = GetElementPtrInst::CreateInBounds(Val, NewArgs.begin(),
1266 NewArgs.end(), "", GEPI);
1267 Val->takeName(GEPI);
1269 if (Val->getType() != GEPI->getType())
1270 Val = new BitCastInst(Val, GEPI->getType(), Val->getName(), GEPI);
1271 GEPI->replaceAllUsesWith(Val);
1272 DeadInsts.push_back(GEPI);
1275 /// RewriteMemIntrinUserOfAlloca - MI is a memcpy/memset/memmove from or to AI.
1276 /// Rewrite it to copy or set the elements of the scalarized memory.
1277 void SROA::RewriteMemIntrinUserOfAlloca(MemIntrinsic *MI, Instruction *Inst,
1279 SmallVector<AllocaInst*, 32> &NewElts) {
1280 // If this is a memcpy/memmove, construct the other pointer as the
1281 // appropriate type. The "Other" pointer is the pointer that goes to memory
1282 // that doesn't have anything to do with the alloca that we are promoting. For
1283 // memset, this Value* stays null.
1284 Value *OtherPtr = 0;
1285 unsigned MemAlignment = MI->getAlignment();
1286 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI)) { // memmove/memcopy
1287 if (Inst == MTI->getRawDest())
1288 OtherPtr = MTI->getRawSource();
1290 assert(Inst == MTI->getRawSource());
1291 OtherPtr = MTI->getRawDest();
1295 // If there is an other pointer, we want to convert it to the same pointer
1296 // type as AI has, so we can GEP through it safely.
1298 unsigned AddrSpace =
1299 cast<PointerType>(OtherPtr->getType())->getAddressSpace();
1301 // Remove bitcasts and all-zero GEPs from OtherPtr. This is an
1302 // optimization, but it's also required to detect the corner case where
1303 // both pointer operands are referencing the same memory, and where
1304 // OtherPtr may be a bitcast or GEP that currently being rewritten. (This
1305 // function is only called for mem intrinsics that access the whole
1306 // aggregate, so non-zero GEPs are not an issue here.)
1307 OtherPtr = OtherPtr->stripPointerCasts();
1309 // Copying the alloca to itself is a no-op: just delete it.
1310 if (OtherPtr == AI || OtherPtr == NewElts[0]) {
1311 // This code will run twice for a no-op memcpy -- once for each operand.
1312 // Put only one reference to MI on the DeadInsts list.
1313 for (SmallVector<Value*, 32>::const_iterator I = DeadInsts.begin(),
1314 E = DeadInsts.end(); I != E; ++I)
1315 if (*I == MI) return;
1316 DeadInsts.push_back(MI);
1320 // If the pointer is not the right type, insert a bitcast to the right
1323 PointerType::get(AI->getType()->getElementType(), AddrSpace);
1325 if (OtherPtr->getType() != NewTy)
1326 OtherPtr = new BitCastInst(OtherPtr, NewTy, OtherPtr->getName(), MI);
1329 // Process each element of the aggregate.
1330 Value *TheFn = MI->getCalledValue();
1331 const Type *BytePtrTy = MI->getRawDest()->getType();
1332 bool SROADest = MI->getRawDest() == Inst;
1334 Constant *Zero = Constant::getNullValue(Type::getInt32Ty(MI->getContext()));
1336 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1337 // If this is a memcpy/memmove, emit a GEP of the other element address.
1338 Value *OtherElt = 0;
1339 unsigned OtherEltAlign = MemAlignment;
1342 Value *Idx[2] = { Zero,
1343 ConstantInt::get(Type::getInt32Ty(MI->getContext()), i) };
1344 OtherElt = GetElementPtrInst::CreateInBounds(OtherPtr, Idx, Idx + 2,
1345 OtherPtr->getName()+"."+Twine(i),
1348 const PointerType *OtherPtrTy = cast<PointerType>(OtherPtr->getType());
1349 const Type *OtherTy = OtherPtrTy->getElementType();
1350 if (const StructType *ST = dyn_cast<StructType>(OtherTy)) {
1351 EltOffset = TD->getStructLayout(ST)->getElementOffset(i);
1353 const Type *EltTy = cast<SequentialType>(OtherTy)->getElementType();
1354 EltOffset = TD->getTypeAllocSize(EltTy)*i;
1357 // The alignment of the other pointer is the guaranteed alignment of the
1358 // element, which is affected by both the known alignment of the whole
1359 // mem intrinsic and the alignment of the element. If the alignment of
1360 // the memcpy (f.e.) is 32 but the element is at a 4-byte offset, then the
1361 // known alignment is just 4 bytes.
1362 OtherEltAlign = (unsigned)MinAlign(OtherEltAlign, EltOffset);
1365 Value *EltPtr = NewElts[i];
1366 const Type *EltTy = cast<PointerType>(EltPtr->getType())->getElementType();
1368 // If we got down to a scalar, insert a load or store as appropriate.
1369 if (EltTy->isSingleValueType()) {
1370 if (isa<MemTransferInst>(MI)) {
1372 // From Other to Alloca.
1373 Value *Elt = new LoadInst(OtherElt, "tmp", false, OtherEltAlign, MI);
1374 new StoreInst(Elt, EltPtr, MI);
1376 // From Alloca to Other.
1377 Value *Elt = new LoadInst(EltPtr, "tmp", MI);
1378 new StoreInst(Elt, OtherElt, false, OtherEltAlign, MI);
1382 assert(isa<MemSetInst>(MI));
1384 // If the stored element is zero (common case), just store a null
1387 if (ConstantInt *CI = dyn_cast<ConstantInt>(MI->getArgOperand(1))) {
1389 StoreVal = Constant::getNullValue(EltTy); // 0.0, null, 0, <0,0>
1391 // If EltTy is a vector type, get the element type.
1392 const Type *ValTy = EltTy->getScalarType();
1394 // Construct an integer with the right value.
1395 unsigned EltSize = TD->getTypeSizeInBits(ValTy);
1396 APInt OneVal(EltSize, CI->getZExtValue());
1397 APInt TotalVal(OneVal);
1399 for (unsigned i = 0; 8*i < EltSize; ++i) {
1400 TotalVal = TotalVal.shl(8);
1404 // Convert the integer value to the appropriate type.
1405 StoreVal = ConstantInt::get(CI->getContext(), TotalVal);
1406 if (ValTy->isPointerTy())
1407 StoreVal = ConstantExpr::getIntToPtr(StoreVal, ValTy);
1408 else if (ValTy->isFloatingPointTy())
1409 StoreVal = ConstantExpr::getBitCast(StoreVal, ValTy);
1410 assert(StoreVal->getType() == ValTy && "Type mismatch!");
1412 // If the requested value was a vector constant, create it.
1413 if (EltTy != ValTy) {
1414 unsigned NumElts = cast<VectorType>(ValTy)->getNumElements();
1415 SmallVector<Constant*, 16> Elts(NumElts, StoreVal);
1416 StoreVal = ConstantVector::get(&Elts[0], NumElts);
1419 new StoreInst(StoreVal, EltPtr, MI);
1422 // Otherwise, if we're storing a byte variable, use a memset call for
1426 // Cast the element pointer to BytePtrTy.
1427 if (EltPtr->getType() != BytePtrTy)
1428 EltPtr = new BitCastInst(EltPtr, BytePtrTy, EltPtr->getName(), MI);
1430 // Cast the other pointer (if we have one) to BytePtrTy.
1431 if (OtherElt && OtherElt->getType() != BytePtrTy) {
1432 // Preserve address space of OtherElt
1433 const PointerType* OtherPTy = cast<PointerType>(OtherElt->getType());
1434 const PointerType* PTy = cast<PointerType>(BytePtrTy);
1435 if (OtherPTy->getElementType() != PTy->getElementType()) {
1436 Type *NewOtherPTy = PointerType::get(PTy->getElementType(),
1437 OtherPTy->getAddressSpace());
1438 OtherElt = new BitCastInst(OtherElt, NewOtherPTy,
1439 OtherElt->getNameStr(), MI);
1443 unsigned EltSize = TD->getTypeAllocSize(EltTy);
1445 // Finally, insert the meminst for this element.
1446 if (isa<MemTransferInst>(MI)) {
1448 SROADest ? EltPtr : OtherElt, // Dest ptr
1449 SROADest ? OtherElt : EltPtr, // Src ptr
1450 ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
1452 ConstantInt::get(Type::getInt32Ty(MI->getContext()), OtherEltAlign),
1453 MI->getVolatileCst()
1455 // In case we fold the address space overloaded memcpy of A to B
1456 // with memcpy of B to C, change the function to be a memcpy of A to C.
1457 const Type *Tys[] = { Ops[0]->getType(), Ops[1]->getType(),
1458 Ops[2]->getType() };
1459 Module *M = MI->getParent()->getParent()->getParent();
1460 TheFn = Intrinsic::getDeclaration(M, MI->getIntrinsicID(), Tys, 3);
1461 CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
1463 assert(isa<MemSetInst>(MI));
1465 EltPtr, MI->getArgOperand(1), // Dest, Value,
1466 ConstantInt::get(MI->getArgOperand(2)->getType(), EltSize), // Size
1468 ConstantInt::get(Type::getInt1Ty(MI->getContext()), 0) // isVolatile
1470 const Type *Tys[] = { Ops[0]->getType(), Ops[2]->getType() };
1471 Module *M = MI->getParent()->getParent()->getParent();
1472 TheFn = Intrinsic::getDeclaration(M, Intrinsic::memset, Tys, 2);
1473 CallInst::Create(TheFn, Ops, Ops + 5, "", MI);
1476 DeadInsts.push_back(MI);
1479 /// RewriteStoreUserOfWholeAlloca - We found a store of an integer that
1480 /// overwrites the entire allocation. Extract out the pieces of the stored
1481 /// integer and store them individually.
1482 void SROA::RewriteStoreUserOfWholeAlloca(StoreInst *SI, AllocaInst *AI,
1483 SmallVector<AllocaInst*, 32> &NewElts){
1484 // Extract each element out of the integer according to its structure offset
1485 // and store the element value to the individual alloca.
1486 Value *SrcVal = SI->getOperand(0);
1487 const Type *AllocaEltTy = AI->getAllocatedType();
1488 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
1490 // Handle tail padding by extending the operand
1491 if (TD->getTypeSizeInBits(SrcVal->getType()) != AllocaSizeBits)
1492 SrcVal = new ZExtInst(SrcVal,
1493 IntegerType::get(SI->getContext(), AllocaSizeBits),
1496 DEBUG(dbgs() << "PROMOTING STORE TO WHOLE ALLOCA: " << *AI << '\n' << *SI
1499 // There are two forms here: AI could be an array or struct. Both cases
1500 // have different ways to compute the element offset.
1501 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
1502 const StructLayout *Layout = TD->getStructLayout(EltSTy);
1504 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1505 // Get the number of bits to shift SrcVal to get the value.
1506 const Type *FieldTy = EltSTy->getElementType(i);
1507 uint64_t Shift = Layout->getElementOffsetInBits(i);
1509 if (TD->isBigEndian())
1510 Shift = AllocaSizeBits-Shift-TD->getTypeAllocSizeInBits(FieldTy);
1512 Value *EltVal = SrcVal;
1514 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
1515 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
1516 "sroa.store.elt", SI);
1519 // Truncate down to an integer of the right size.
1520 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
1522 // Ignore zero sized fields like {}, they obviously contain no data.
1523 if (FieldSizeBits == 0) continue;
1525 if (FieldSizeBits != AllocaSizeBits)
1526 EltVal = new TruncInst(EltVal,
1527 IntegerType::get(SI->getContext(), FieldSizeBits),
1529 Value *DestField = NewElts[i];
1530 if (EltVal->getType() == FieldTy) {
1531 // Storing to an integer field of this size, just do it.
1532 } else if (FieldTy->isFloatingPointTy() || FieldTy->isVectorTy()) {
1533 // Bitcast to the right element type (for fp/vector values).
1534 EltVal = new BitCastInst(EltVal, FieldTy, "", SI);
1536 // Otherwise, bitcast the dest pointer (for aggregates).
1537 DestField = new BitCastInst(DestField,
1538 PointerType::getUnqual(EltVal->getType()),
1541 new StoreInst(EltVal, DestField, SI);
1545 const ArrayType *ATy = cast<ArrayType>(AllocaEltTy);
1546 const Type *ArrayEltTy = ATy->getElementType();
1547 uint64_t ElementOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
1548 uint64_t ElementSizeBits = TD->getTypeSizeInBits(ArrayEltTy);
1552 if (TD->isBigEndian())
1553 Shift = AllocaSizeBits-ElementOffset;
1557 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1558 // Ignore zero sized fields like {}, they obviously contain no data.
1559 if (ElementSizeBits == 0) continue;
1561 Value *EltVal = SrcVal;
1563 Value *ShiftVal = ConstantInt::get(EltVal->getType(), Shift);
1564 EltVal = BinaryOperator::CreateLShr(EltVal, ShiftVal,
1565 "sroa.store.elt", SI);
1568 // Truncate down to an integer of the right size.
1569 if (ElementSizeBits != AllocaSizeBits)
1570 EltVal = new TruncInst(EltVal,
1571 IntegerType::get(SI->getContext(),
1572 ElementSizeBits),"",SI);
1573 Value *DestField = NewElts[i];
1574 if (EltVal->getType() == ArrayEltTy) {
1575 // Storing to an integer field of this size, just do it.
1576 } else if (ArrayEltTy->isFloatingPointTy() ||
1577 ArrayEltTy->isVectorTy()) {
1578 // Bitcast to the right element type (for fp/vector values).
1579 EltVal = new BitCastInst(EltVal, ArrayEltTy, "", SI);
1581 // Otherwise, bitcast the dest pointer (for aggregates).
1582 DestField = new BitCastInst(DestField,
1583 PointerType::getUnqual(EltVal->getType()),
1586 new StoreInst(EltVal, DestField, SI);
1588 if (TD->isBigEndian())
1589 Shift -= ElementOffset;
1591 Shift += ElementOffset;
1595 DeadInsts.push_back(SI);
1598 /// RewriteLoadUserOfWholeAlloca - We found a load of the entire allocation to
1599 /// an integer. Load the individual pieces to form the aggregate value.
1600 void SROA::RewriteLoadUserOfWholeAlloca(LoadInst *LI, AllocaInst *AI,
1601 SmallVector<AllocaInst*, 32> &NewElts) {
1602 // Extract each element out of the NewElts according to its structure offset
1603 // and form the result value.
1604 const Type *AllocaEltTy = AI->getAllocatedType();
1605 uint64_t AllocaSizeBits = TD->getTypeAllocSizeInBits(AllocaEltTy);
1607 DEBUG(dbgs() << "PROMOTING LOAD OF WHOLE ALLOCA: " << *AI << '\n' << *LI
1610 // There are two forms here: AI could be an array or struct. Both cases
1611 // have different ways to compute the element offset.
1612 const StructLayout *Layout = 0;
1613 uint64_t ArrayEltBitOffset = 0;
1614 if (const StructType *EltSTy = dyn_cast<StructType>(AllocaEltTy)) {
1615 Layout = TD->getStructLayout(EltSTy);
1617 const Type *ArrayEltTy = cast<ArrayType>(AllocaEltTy)->getElementType();
1618 ArrayEltBitOffset = TD->getTypeAllocSizeInBits(ArrayEltTy);
1622 Constant::getNullValue(IntegerType::get(LI->getContext(), AllocaSizeBits));
1624 for (unsigned i = 0, e = NewElts.size(); i != e; ++i) {
1625 // Load the value from the alloca. If the NewElt is an aggregate, cast
1626 // the pointer to an integer of the same size before doing the load.
1627 Value *SrcField = NewElts[i];
1628 const Type *FieldTy =
1629 cast<PointerType>(SrcField->getType())->getElementType();
1630 uint64_t FieldSizeBits = TD->getTypeSizeInBits(FieldTy);
1632 // Ignore zero sized fields like {}, they obviously contain no data.
1633 if (FieldSizeBits == 0) continue;
1635 const IntegerType *FieldIntTy = IntegerType::get(LI->getContext(),
1637 if (!FieldTy->isIntegerTy() && !FieldTy->isFloatingPointTy() &&
1638 !FieldTy->isVectorTy())
1639 SrcField = new BitCastInst(SrcField,
1640 PointerType::getUnqual(FieldIntTy),
1642 SrcField = new LoadInst(SrcField, "sroa.load.elt", LI);
1644 // If SrcField is a fp or vector of the right size but that isn't an
1645 // integer type, bitcast to an integer so we can shift it.
1646 if (SrcField->getType() != FieldIntTy)
1647 SrcField = new BitCastInst(SrcField, FieldIntTy, "", LI);
1649 // Zero extend the field to be the same size as the final alloca so that
1650 // we can shift and insert it.
1651 if (SrcField->getType() != ResultVal->getType())
1652 SrcField = new ZExtInst(SrcField, ResultVal->getType(), "", LI);
1654 // Determine the number of bits to shift SrcField.
1656 if (Layout) // Struct case.
1657 Shift = Layout->getElementOffsetInBits(i);
1659 Shift = i*ArrayEltBitOffset;
1661 if (TD->isBigEndian())
1662 Shift = AllocaSizeBits-Shift-FieldIntTy->getBitWidth();
1665 Value *ShiftVal = ConstantInt::get(SrcField->getType(), Shift);
1666 SrcField = BinaryOperator::CreateShl(SrcField, ShiftVal, "", LI);
1669 // Don't create an 'or x, 0' on the first iteration.
1670 if (!isa<Constant>(ResultVal) ||
1671 !cast<Constant>(ResultVal)->isNullValue())
1672 ResultVal = BinaryOperator::CreateOr(SrcField, ResultVal, "", LI);
1674 ResultVal = SrcField;
1677 // Handle tail padding by truncating the result
1678 if (TD->getTypeSizeInBits(LI->getType()) != AllocaSizeBits)
1679 ResultVal = new TruncInst(ResultVal, LI->getType(), "", LI);
1681 LI->replaceAllUsesWith(ResultVal);
1682 DeadInsts.push_back(LI);
1685 /// HasPadding - Return true if the specified type has any structure or
1686 /// alignment padding, false otherwise.
1687 static bool HasPadding(const Type *Ty, const TargetData &TD) {
1688 if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty))
1689 return HasPadding(ATy->getElementType(), TD);
1691 if (const VectorType *VTy = dyn_cast<VectorType>(Ty))
1692 return HasPadding(VTy->getElementType(), TD);
1694 if (const StructType *STy = dyn_cast<StructType>(Ty)) {
1695 const StructLayout *SL = TD.getStructLayout(STy);
1696 unsigned PrevFieldBitOffset = 0;
1697 for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
1698 unsigned FieldBitOffset = SL->getElementOffsetInBits(i);
1700 // Padding in sub-elements?
1701 if (HasPadding(STy->getElementType(i), TD))
1704 // Check to see if there is any padding between this element and the
1707 unsigned PrevFieldEnd =
1708 PrevFieldBitOffset+TD.getTypeSizeInBits(STy->getElementType(i-1));
1709 if (PrevFieldEnd < FieldBitOffset)
1713 PrevFieldBitOffset = FieldBitOffset;
1716 // Check for tail padding.
1717 if (unsigned EltCount = STy->getNumElements()) {
1718 unsigned PrevFieldEnd = PrevFieldBitOffset +
1719 TD.getTypeSizeInBits(STy->getElementType(EltCount-1));
1720 if (PrevFieldEnd < SL->getSizeInBits())
1725 return TD.getTypeSizeInBits(Ty) != TD.getTypeAllocSizeInBits(Ty);
1728 /// isSafeStructAllocaToScalarRepl - Check to see if the specified allocation of
1729 /// an aggregate can be broken down into elements. Return 0 if not, 3 if safe,
1730 /// or 1 if safe after canonicalization has been performed.
1731 bool SROA::isSafeAllocaToScalarRepl(AllocaInst *AI) {
1732 // Loop over the use list of the alloca. We can only transform it if all of
1733 // the users are safe to transform.
1736 isSafeForScalarRepl(AI, AI, 0, Info);
1737 if (Info.isUnsafe) {
1738 DEBUG(dbgs() << "Cannot transform: " << *AI << '\n');
1742 // Okay, we know all the users are promotable. If the aggregate is a memcpy
1743 // source and destination, we have to be careful. In particular, the memcpy
1744 // could be moving around elements that live in structure padding of the LLVM
1745 // types, but may actually be used. In these cases, we refuse to promote the
1747 if (Info.isMemCpySrc && Info.isMemCpyDst &&
1748 HasPadding(AI->getAllocatedType(), *TD))
1756 /// PointsToConstantGlobal - Return true if V (possibly indirectly) points to
1757 /// some part of a constant global variable. This intentionally only accepts
1758 /// constant expressions because we don't can't rewrite arbitrary instructions.
1759 static bool PointsToConstantGlobal(Value *V) {
1760 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(V))
1761 return GV->isConstant();
1762 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
1763 if (CE->getOpcode() == Instruction::BitCast ||
1764 CE->getOpcode() == Instruction::GetElementPtr)
1765 return PointsToConstantGlobal(CE->getOperand(0));
1769 /// isOnlyCopiedFromConstantGlobal - Recursively walk the uses of a (derived)
1770 /// pointer to an alloca. Ignore any reads of the pointer, return false if we
1771 /// see any stores or other unknown uses. If we see pointer arithmetic, keep
1772 /// track of whether it moves the pointer (with isOffset) but otherwise traverse
1773 /// the uses. If we see a memcpy/memmove that targets an unoffseted pointer to
1774 /// the alloca, and if the source pointer is a pointer to a constant global, we
1775 /// can optimize this.
1776 static bool isOnlyCopiedFromConstantGlobal(Value *V, MemTransferInst *&TheCopy,
1778 for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI!=E; ++UI) {
1779 User *U = cast<Instruction>(*UI);
1781 if (LoadInst *LI = dyn_cast<LoadInst>(U))
1782 // Ignore non-volatile loads, they are always ok.
1783 if (!LI->isVolatile())
1786 if (BitCastInst *BCI = dyn_cast<BitCastInst>(U)) {
1787 // If uses of the bitcast are ok, we are ok.
1788 if (!isOnlyCopiedFromConstantGlobal(BCI, TheCopy, isOffset))
1792 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
1793 // If the GEP has all zero indices, it doesn't offset the pointer. If it
1794 // doesn't, it does.
1795 if (!isOnlyCopiedFromConstantGlobal(GEP, TheCopy,
1796 isOffset || !GEP->hasAllZeroIndices()))
1801 // If this is isn't our memcpy/memmove, reject it as something we can't
1803 MemTransferInst *MI = dyn_cast<MemTransferInst>(U);
1807 // If we already have seen a copy, reject the second one.
1808 if (TheCopy) return false;
1810 // If the pointer has been offset from the start of the alloca, we can't
1811 // safely handle this.
1812 if (isOffset) return false;
1814 // If the memintrinsic isn't using the alloca as the dest, reject it.
1815 if (UI.getOperandNo() != 0) return false;
1817 // If the source of the memcpy/move is not a constant global, reject it.
1818 if (!PointsToConstantGlobal(MI->getSource()))
1821 // Otherwise, the transform is safe. Remember the copy instruction.
1827 /// isOnlyCopiedFromConstantGlobal - Return true if the specified alloca is only
1828 /// modified by a copy from a constant global. If we can prove this, we can
1829 /// replace any uses of the alloca with uses of the global directly.
1830 MemTransferInst *SROA::isOnlyCopiedFromConstantGlobal(AllocaInst *AI) {
1831 MemTransferInst *TheCopy = 0;
1832 if (::isOnlyCopiedFromConstantGlobal(AI, TheCopy, false))