1 //===- SROA.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. It tries to identify promotable elements of an
12 /// aggregate alloca, and promote them to registers. It will also try to
13 /// convert uses of an element (or set of elements) of an alloca into a vector
14 /// or bitfield-style integer scalar if appropriate.
16 /// It works to do this with minimal slicing of the alloca so that regions
17 /// which are merely transferred in and out of external memory remain unchanged
18 /// and are not decomposed to scalar code.
20 /// Because this also performs alloca promotion, it can be thought of as also
21 /// serving the purpose of SSA formation. The algorithm iterates on the
22 /// function until all opportunities for promotion have been realized.
24 //===----------------------------------------------------------------------===//
26 #define DEBUG_TYPE "sroa"
27 #include "llvm/Transforms/Scalar.h"
28 #include "llvm/Constants.h"
29 #include "llvm/DIBuilder.h"
30 #include "llvm/DebugInfo.h"
31 #include "llvm/DerivedTypes.h"
32 #include "llvm/Function.h"
33 #include "llvm/GlobalVariable.h"
34 #include "llvm/IRBuilder.h"
35 #include "llvm/Instructions.h"
36 #include "llvm/IntrinsicInst.h"
37 #include "llvm/LLVMContext.h"
38 #include "llvm/Module.h"
39 #include "llvm/Operator.h"
40 #include "llvm/Pass.h"
41 #include "llvm/ADT/SetVector.h"
42 #include "llvm/ADT/SmallVector.h"
43 #include "llvm/ADT/Statistic.h"
44 #include "llvm/ADT/STLExtras.h"
45 #include "llvm/ADT/TinyPtrVector.h"
46 #include "llvm/Analysis/Dominators.h"
47 #include "llvm/Analysis/Loads.h"
48 #include "llvm/Analysis/ValueTracking.h"
49 #include "llvm/Support/CallSite.h"
50 #include "llvm/Support/Debug.h"
51 #include "llvm/Support/ErrorHandling.h"
52 #include "llvm/Support/GetElementPtrTypeIterator.h"
53 #include "llvm/Support/InstVisitor.h"
54 #include "llvm/Support/MathExtras.h"
55 #include "llvm/Support/ValueHandle.h"
56 #include "llvm/Support/raw_ostream.h"
57 #include "llvm/Target/TargetData.h"
58 #include "llvm/Transforms/Utils/Local.h"
59 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
60 #include "llvm/Transforms/Utils/SSAUpdater.h"
63 STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
64 STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced");
65 STATISTIC(NumPromoted, "Number of allocas promoted to SSA values");
66 STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion");
67 STATISTIC(NumDeleted, "Number of instructions deleted");
68 STATISTIC(NumVectorized, "Number of vectorized aggregates");
71 /// \brief Alloca partitioning representation.
73 /// This class represents a partitioning of an alloca into slices, and
74 /// information about the nature of uses of each slice of the alloca. The goal
75 /// is that this information is sufficient to decide if and how to split the
76 /// alloca apart and replace slices with scalars. It is also intended that this
77 /// structure can capture the relevant information needed both to decide about
78 /// and to enact these transformations.
79 class AllocaPartitioning {
81 /// \brief A common base class for representing a half-open byte range.
83 /// \brief The beginning offset of the range.
86 /// \brief The ending offset, not included in the range.
89 ByteRange() : BeginOffset(), EndOffset() {}
90 ByteRange(uint64_t BeginOffset, uint64_t EndOffset)
91 : BeginOffset(BeginOffset), EndOffset(EndOffset) {}
93 /// \brief Support for ordering ranges.
95 /// This provides an ordering over ranges such that start offsets are
96 /// always increasing, and within equal start offsets, the end offsets are
97 /// decreasing. Thus the spanning range comes first in a cluster with the
98 /// same start position.
99 bool operator<(const ByteRange &RHS) const {
100 if (BeginOffset < RHS.BeginOffset) return true;
101 if (BeginOffset > RHS.BeginOffset) return false;
102 if (EndOffset > RHS.EndOffset) return true;
106 /// \brief Support comparison with a single offset to allow binary searches.
107 bool operator<(uint64_t RHSOffset) const {
108 return BeginOffset < RHSOffset;
111 bool operator==(const ByteRange &RHS) const {
112 return BeginOffset == RHS.BeginOffset && EndOffset == RHS.EndOffset;
114 bool operator!=(const ByteRange &RHS) const { return !operator==(RHS); }
117 /// \brief A partition of an alloca.
119 /// This structure represents a contiguous partition of the alloca. These are
120 /// formed by examining the uses of the alloca. During formation, they may
121 /// overlap but once an AllocaPartitioning is built, the Partitions within it
122 /// are all disjoint.
123 struct Partition : public ByteRange {
124 /// \brief Whether this partition is splittable into smaller partitions.
126 /// We flag partitions as splittable when they are formed entirely due to
127 /// accesses by trivially splittable operations such as memset and memcpy.
129 /// FIXME: At some point we should consider loads and stores of FCAs to be
130 /// splittable and eagerly split them into scalar values.
133 Partition() : ByteRange(), IsSplittable() {}
134 Partition(uint64_t BeginOffset, uint64_t EndOffset, bool IsSplittable)
135 : ByteRange(BeginOffset, EndOffset), IsSplittable(IsSplittable) {}
138 /// \brief A particular use of a partition of the alloca.
140 /// This structure is used to associate uses of a partition with it. They
141 /// mark the range of bytes which are referenced by a particular instruction,
142 /// and includes a handle to the user itself and the pointer value in use.
143 /// The bounds of these uses are determined by intersecting the bounds of the
144 /// memory use itself with a particular partition. As a consequence there is
145 /// intentionally overlap between various uses of the same partition.
146 struct PartitionUse : public ByteRange {
147 /// \brief The user of this range of the alloca.
148 AssertingVH<Instruction> User;
150 /// \brief The particular pointer value derived from this alloca in use.
151 AssertingVH<Instruction> Ptr;
153 PartitionUse() : ByteRange(), User(), Ptr() {}
154 PartitionUse(uint64_t BeginOffset, uint64_t EndOffset,
155 Instruction *User, Instruction *Ptr)
156 : ByteRange(BeginOffset, EndOffset), User(User), Ptr(Ptr) {}
159 /// \brief Construct a partitioning of a particular alloca.
161 /// Construction does most of the work for partitioning the alloca. This
162 /// performs the necessary walks of users and builds a partitioning from it.
163 AllocaPartitioning(const TargetData &TD, AllocaInst &AI);
165 /// \brief Test whether a pointer to the allocation escapes our analysis.
167 /// If this is true, the partitioning is never fully built and should be
169 bool isEscaped() const { return PointerEscapingInstr; }
171 /// \brief Support for iterating over the partitions.
173 typedef SmallVectorImpl<Partition>::iterator iterator;
174 iterator begin() { return Partitions.begin(); }
175 iterator end() { return Partitions.end(); }
177 typedef SmallVectorImpl<Partition>::const_iterator const_iterator;
178 const_iterator begin() const { return Partitions.begin(); }
179 const_iterator end() const { return Partitions.end(); }
182 /// \brief Support for iterating over and manipulating a particular
183 /// partition's uses.
185 /// The iteration support provided for uses is more limited, but also
186 /// includes some manipulation routines to support rewriting the uses of
187 /// partitions during SROA.
189 typedef SmallVectorImpl<PartitionUse>::iterator use_iterator;
190 use_iterator use_begin(unsigned Idx) { return Uses[Idx].begin(); }
191 use_iterator use_begin(const_iterator I) { return Uses[I - begin()].begin(); }
192 use_iterator use_end(unsigned Idx) { return Uses[Idx].end(); }
193 use_iterator use_end(const_iterator I) { return Uses[I - begin()].end(); }
194 void use_insert(unsigned Idx, use_iterator UI, const PartitionUse &U) {
195 Uses[Idx].insert(UI, U);
197 void use_insert(const_iterator I, use_iterator UI, const PartitionUse &U) {
198 Uses[I - begin()].insert(UI, U);
200 void use_erase(unsigned Idx, use_iterator UI) { Uses[Idx].erase(UI); }
201 void use_erase(const_iterator I, use_iterator UI) {
202 Uses[I - begin()].erase(UI);
205 typedef SmallVectorImpl<PartitionUse>::const_iterator const_use_iterator;
206 const_use_iterator use_begin(unsigned Idx) const { return Uses[Idx].begin(); }
207 const_use_iterator use_begin(const_iterator I) const {
208 return Uses[I - begin()].begin();
210 const_use_iterator use_end(unsigned Idx) const { return Uses[Idx].end(); }
211 const_use_iterator use_end(const_iterator I) const {
212 return Uses[I - begin()].end();
216 /// \brief Allow iterating the dead users for this alloca.
218 /// These are instructions which will never actually use the alloca as they
219 /// are outside the allocated range. They are safe to replace with undef and
222 typedef SmallVectorImpl<Instruction *>::const_iterator dead_user_iterator;
223 dead_user_iterator dead_user_begin() const { return DeadUsers.begin(); }
224 dead_user_iterator dead_user_end() const { return DeadUsers.end(); }
227 /// \brief Allow iterating the dead expressions referring to this alloca.
229 /// These are operands which have cannot actually be used to refer to the
230 /// alloca as they are outside its range and the user doesn't correct for
231 /// that. These mostly consist of PHI node inputs and the like which we just
232 /// need to replace with undef.
234 typedef SmallVectorImpl<Use *>::const_iterator dead_op_iterator;
235 dead_op_iterator dead_op_begin() const { return DeadOperands.begin(); }
236 dead_op_iterator dead_op_end() const { return DeadOperands.end(); }
239 /// \brief MemTransferInst auxiliary data.
240 /// This struct provides some auxiliary data about memory transfer
241 /// intrinsics such as memcpy and memmove. These intrinsics can use two
242 /// different ranges within the same alloca, and provide other challenges to
243 /// correctly represent. We stash extra data to help us untangle this
244 /// after the partitioning is complete.
245 struct MemTransferOffsets {
246 uint64_t DestBegin, DestEnd;
247 uint64_t SourceBegin, SourceEnd;
250 MemTransferOffsets getMemTransferOffsets(MemTransferInst &II) const {
251 return MemTransferInstData.lookup(&II);
254 /// \brief Map from a PHI or select operand back to a partition.
256 /// When manipulating PHI nodes or selects, they can use more than one
257 /// partition of an alloca. We store a special mapping to allow finding the
258 /// partition referenced by each of these operands, if any.
259 iterator findPartitionForPHIOrSelectOperand(Instruction &I, Value *Op) {
260 SmallDenseMap<std::pair<Instruction *, Value *>,
261 std::pair<unsigned, unsigned> >::const_iterator MapIt
262 = PHIOrSelectOpMap.find(std::make_pair(&I, Op));
263 if (MapIt == PHIOrSelectOpMap.end())
266 return begin() + MapIt->second.first;
269 /// \brief Map from a PHI or select operand back to the specific use of
272 /// Similar to mapping these operands back to the partitions, this maps
273 /// directly to the use structure of that partition.
274 use_iterator findPartitionUseForPHIOrSelectOperand(Instruction &I,
276 SmallDenseMap<std::pair<Instruction *, Value *>,
277 std::pair<unsigned, unsigned> >::const_iterator MapIt
278 = PHIOrSelectOpMap.find(std::make_pair(&I, Op));
279 assert(MapIt != PHIOrSelectOpMap.end());
280 return Uses[MapIt->second.first].begin() + MapIt->second.second;
283 /// \brief Compute a common type among the uses of a particular partition.
285 /// This routines walks all of the uses of a particular partition and tries
286 /// to find a common type between them. Untyped operations such as memset and
287 /// memcpy are ignored.
288 Type *getCommonType(iterator I) const;
290 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
291 void print(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const;
292 void printUsers(raw_ostream &OS, const_iterator I,
293 StringRef Indent = " ") const;
294 void print(raw_ostream &OS) const;
295 void LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED dump(const_iterator I) const;
296 void LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED dump() const;
300 template <typename DerivedT, typename RetT = void> class BuilderBase;
301 class PartitionBuilder;
302 friend class AllocaPartitioning::PartitionBuilder;
304 friend class AllocaPartitioning::UseBuilder;
306 /// \brief Handle to alloca instruction to simplify method interfaces.
309 /// \brief The instruction responsible for this alloca having no partitioning.
311 /// When an instruction (potentially) escapes the pointer to the alloca, we
312 /// store a pointer to that here and abort trying to partition the alloca.
313 /// This will be null if the alloca is partitioned successfully.
314 Instruction *PointerEscapingInstr;
316 /// \brief The partitions of the alloca.
318 /// We store a vector of the partitions over the alloca here. This vector is
319 /// sorted by increasing begin offset, and then by decreasing end offset. See
320 /// the Partition inner class for more details. Initially (during
321 /// construction) there are overlaps, but we form a disjoint sequence of
322 /// partitions while finishing construction and a fully constructed object is
323 /// expected to always have this as a disjoint space.
324 SmallVector<Partition, 8> Partitions;
326 /// \brief The uses of the partitions.
328 /// This is essentially a mapping from each partition to a list of uses of
329 /// that partition. The mapping is done with a Uses vector that has the exact
330 /// same number of entries as the partition vector. Each entry is itself
331 /// a vector of the uses.
332 SmallVector<SmallVector<PartitionUse, 2>, 8> Uses;
334 /// \brief Instructions which will become dead if we rewrite the alloca.
336 /// Note that these are not separated by partition. This is because we expect
337 /// a partitioned alloca to be completely rewritten or not rewritten at all.
338 /// If rewritten, all these instructions can simply be removed and replaced
339 /// with undef as they come from outside of the allocated space.
340 SmallVector<Instruction *, 8> DeadUsers;
342 /// \brief Operands which will become dead if we rewrite the alloca.
344 /// These are operands that in their particular use can be replaced with
345 /// undef when we rewrite the alloca. These show up in out-of-bounds inputs
346 /// to PHI nodes and the like. They aren't entirely dead (there might be
347 /// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we
348 /// want to swap this particular input for undef to simplify the use lists of
350 SmallVector<Use *, 8> DeadOperands;
352 /// \brief The underlying storage for auxiliary memcpy and memset info.
353 SmallDenseMap<MemTransferInst *, MemTransferOffsets, 4> MemTransferInstData;
355 /// \brief A side datastructure used when building up the partitions and uses.
357 /// This mapping is only really used during the initial building of the
358 /// partitioning so that we can retain information about PHI and select nodes
360 SmallDenseMap<Instruction *, std::pair<uint64_t, bool> > PHIOrSelectSizes;
362 /// \brief Auxiliary information for particular PHI or select operands.
363 SmallDenseMap<std::pair<Instruction *, Value *>,
364 std::pair<unsigned, unsigned>, 4> PHIOrSelectOpMap;
366 /// \brief A utility routine called from the constructor.
368 /// This does what it says on the tin. It is the key of the alloca partition
369 /// splitting and merging. After it is called we have the desired disjoint
370 /// collection of partitions.
371 void splitAndMergePartitions();
375 template <typename DerivedT, typename RetT>
376 class AllocaPartitioning::BuilderBase
377 : public InstVisitor<DerivedT, RetT> {
379 BuilderBase(const TargetData &TD, AllocaInst &AI, AllocaPartitioning &P)
381 AllocSize(TD.getTypeAllocSize(AI.getAllocatedType())),
387 const TargetData &TD;
388 const uint64_t AllocSize;
389 AllocaPartitioning &P;
395 SmallVector<OffsetUse, 8> Queue;
397 // The active offset and use while visiting.
401 void enqueueUsers(Instruction &I, uint64_t UserOffset) {
402 SmallPtrSet<User *, 8> UserSet;
403 for (Value::use_iterator UI = I.use_begin(), UE = I.use_end();
405 if (!UserSet.insert(*UI))
408 OffsetUse OU = { &UI.getUse(), UserOffset };
413 bool computeConstantGEPOffset(GetElementPtrInst &GEPI, uint64_t &GEPOffset) {
415 for (gep_type_iterator GTI = gep_type_begin(GEPI), GTE = gep_type_end(GEPI);
417 ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
423 // Handle a struct index, which adds its field offset to the pointer.
424 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
425 unsigned ElementIdx = OpC->getZExtValue();
426 const StructLayout *SL = TD.getStructLayout(STy);
427 GEPOffset += SL->getElementOffset(ElementIdx);
432 += OpC->getZExtValue() * TD.getTypeAllocSize(GTI.getIndexedType());
437 Value *foldSelectInst(SelectInst &SI) {
438 // If the condition being selected on is a constant or the same value is
439 // being selected between, fold the select. Yes this does (rarely) happen
441 if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition()))
442 return SI.getOperand(1+CI->isZero());
443 if (SI.getOperand(1) == SI.getOperand(2)) {
444 assert(*U == SI.getOperand(1));
445 return SI.getOperand(1);
451 /// \brief Builder for the alloca partitioning.
453 /// This class builds an alloca partitioning by recursively visiting the uses
454 /// of an alloca and splitting the partitions for each load and store at each
456 class AllocaPartitioning::PartitionBuilder
457 : public BuilderBase<PartitionBuilder, bool> {
458 friend class InstVisitor<PartitionBuilder, bool>;
460 SmallDenseMap<Instruction *, unsigned> MemTransferPartitionMap;
463 PartitionBuilder(const TargetData &TD, AllocaInst &AI, AllocaPartitioning &P)
464 : BuilderBase<PartitionBuilder, bool>(TD, AI, P) {}
466 /// \brief Run the builder over the allocation.
468 // Note that we have to re-evaluate size on each trip through the loop as
469 // the queue grows at the tail.
470 for (unsigned Idx = 0; Idx < Queue.size(); ++Idx) {
472 Offset = Queue[Idx].Offset;
473 if (!visit(cast<Instruction>(U->getUser())))
480 bool markAsEscaping(Instruction &I) {
481 P.PointerEscapingInstr = &I;
485 void insertUse(Instruction &I, uint64_t Size, bool IsSplittable = false) {
486 uint64_t BeginOffset = Offset, EndOffset = Offset + Size;
488 // Completely skip uses which start outside of the allocation.
489 if (BeginOffset >= AllocSize) {
490 DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
491 << " which starts past the end of the " << AllocSize
493 << " alloca: " << P.AI << "\n"
494 << " use: " << I << "\n");
498 // Clamp the size to the allocation.
499 if (EndOffset > AllocSize) {
500 DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @" << Offset
501 << " to remain within the " << AllocSize << " byte alloca:\n"
502 << " alloca: " << P.AI << "\n"
503 << " use: " << I << "\n");
504 EndOffset = AllocSize;
507 // See if we can just add a user onto the last slot currently occupied.
508 if (!P.Partitions.empty() &&
509 P.Partitions.back().BeginOffset == BeginOffset &&
510 P.Partitions.back().EndOffset == EndOffset) {
511 P.Partitions.back().IsSplittable &= IsSplittable;
515 Partition New(BeginOffset, EndOffset, IsSplittable);
516 P.Partitions.push_back(New);
519 bool handleLoadOrStore(Type *Ty, Instruction &I) {
520 uint64_t Size = TD.getTypeStoreSize(Ty);
522 // If this memory access can be shown to *statically* extend outside the
523 // bounds of of the allocation, it's behavior is undefined, so simply
524 // ignore it. Note that this is more strict than the generic clamping
525 // behavior of insertUse. We also try to handle cases which might run the
527 // FIXME: We should instead consider the pointer to have escaped if this
528 // function is being instrumented for addressing bugs or race conditions.
529 if (Offset >= AllocSize || Size > AllocSize || Offset + Size > AllocSize) {
530 DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte "
531 << (isa<LoadInst>(I) ? "load" : "store") << " @" << Offset
532 << " which extends past the end of the " << AllocSize
534 << " alloca: " << P.AI << "\n"
535 << " use: " << I << "\n");
543 bool visitBitCastInst(BitCastInst &BC) {
544 enqueueUsers(BC, Offset);
548 bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
550 if (!computeConstantGEPOffset(GEPI, GEPOffset))
551 return markAsEscaping(GEPI);
553 enqueueUsers(GEPI, GEPOffset);
557 bool visitLoadInst(LoadInst &LI) {
558 return handleLoadOrStore(LI.getType(), LI);
561 bool visitStoreInst(StoreInst &SI) {
562 if (SI.getOperand(0) == *U)
563 return markAsEscaping(SI);
565 return handleLoadOrStore(SI.getOperand(0)->getType(), SI);
569 bool visitMemSetInst(MemSetInst &II) {
570 assert(II.getRawDest() == *U && "Pointer use is not the destination?");
571 ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
572 insertUse(II, Length ? Length->getZExtValue() : AllocSize - Offset, Length);
576 bool visitMemTransferInst(MemTransferInst &II) {
577 ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
578 uint64_t Size = Length ? Length->getZExtValue() : AllocSize - Offset;
580 // Zero-length mem transfer intrinsics can be ignored entirely.
583 MemTransferOffsets &Offsets = P.MemTransferInstData[&II];
585 // Only intrinsics with a constant length can be split.
586 Offsets.IsSplittable = Length;
588 if (*U != II.getRawDest()) {
589 assert(*U == II.getRawSource());
590 Offsets.SourceBegin = Offset;
591 Offsets.SourceEnd = Offset + Size;
593 Offsets.DestBegin = Offset;
594 Offsets.DestEnd = Offset + Size;
597 insertUse(II, Size, Offsets.IsSplittable);
598 unsigned NewIdx = P.Partitions.size() - 1;
600 SmallDenseMap<Instruction *, unsigned>::const_iterator PMI;
601 bool Inserted = false;
602 llvm::tie(PMI, Inserted)
603 = MemTransferPartitionMap.insert(std::make_pair(&II, NewIdx));
604 if (!Inserted && Offsets.IsSplittable) {
605 // We've found a memory transfer intrinsic which refers to the alloca as
606 // both a source and dest. We refuse to split these to simplify splitting
607 // logic. If possible, SROA will still split them into separate allocas
608 // and then re-analyze.
609 Offsets.IsSplittable = false;
610 P.Partitions[PMI->second].IsSplittable = false;
611 P.Partitions[NewIdx].IsSplittable = false;
617 // Disable SRoA for any intrinsics except for lifetime invariants.
618 // FIXME: What about debug instrinsics? This matches old behavior, but
619 // doesn't make sense.
620 bool visitIntrinsicInst(IntrinsicInst &II) {
621 if (II.getIntrinsicID() == Intrinsic::lifetime_start ||
622 II.getIntrinsicID() == Intrinsic::lifetime_end) {
623 ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
624 uint64_t Size = std::min(AllocSize - Offset, Length->getLimitedValue());
625 insertUse(II, Size, true);
629 return markAsEscaping(II);
632 Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) {
633 // We consider any PHI or select that results in a direct load or store of
634 // the same offset to be a viable use for partitioning purposes. These uses
635 // are considered unsplittable and the size is the maximum loaded or stored
637 SmallPtrSet<Instruction *, 4> Visited;
638 SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
639 Visited.insert(Root);
640 Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
642 Instruction *I, *UsedI;
643 llvm::tie(UsedI, I) = Uses.pop_back_val();
645 if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
646 Size = std::max(Size, TD.getTypeStoreSize(LI->getType()));
649 if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
650 Value *Op = SI->getOperand(0);
653 Size = std::max(Size, TD.getTypeStoreSize(Op->getType()));
657 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
658 if (!GEP->hasAllZeroIndices())
660 } else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) &&
661 !isa<SelectInst>(I)) {
665 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE;
667 if (Visited.insert(cast<Instruction>(*UI)))
668 Uses.push_back(std::make_pair(I, cast<Instruction>(*UI)));
669 } while (!Uses.empty());
674 bool visitPHINode(PHINode &PN) {
675 // See if we already have computed info on this node.
676 std::pair<uint64_t, bool> &PHIInfo = P.PHIOrSelectSizes[&PN];
678 PHIInfo.second = true;
679 insertUse(PN, PHIInfo.first);
683 // Check for an unsafe use of the PHI node.
684 if (Instruction *EscapingI = hasUnsafePHIOrSelectUse(&PN, PHIInfo.first))
685 return markAsEscaping(*EscapingI);
687 insertUse(PN, PHIInfo.first);
691 bool visitSelectInst(SelectInst &SI) {
692 if (Value *Result = foldSelectInst(SI)) {
694 // If the result of the constant fold will be the pointer, recurse
695 // through the select as if we had RAUW'ed it.
696 enqueueUsers(SI, Offset);
701 // See if we already have computed info on this node.
702 std::pair<uint64_t, bool> &SelectInfo = P.PHIOrSelectSizes[&SI];
703 if (SelectInfo.first) {
704 SelectInfo.second = true;
705 insertUse(SI, SelectInfo.first);
709 // Check for an unsafe use of the PHI node.
710 if (Instruction *EscapingI = hasUnsafePHIOrSelectUse(&SI, SelectInfo.first))
711 return markAsEscaping(*EscapingI);
713 insertUse(SI, SelectInfo.first);
717 /// \brief Disable SROA entirely if there are unhandled users of the alloca.
718 bool visitInstruction(Instruction &I) { return markAsEscaping(I); }
722 /// \brief Use adder for the alloca partitioning.
724 /// This class adds the uses of an alloca to all of the partitions which they
725 /// use. For splittable partitions, this can end up doing essentially a linear
726 /// walk of the partitions, but the number of steps remains bounded by the
727 /// total result instruction size:
728 /// - The number of partitions is a result of the number unsplittable
729 /// instructions using the alloca.
730 /// - The number of users of each partition is at worst the total number of
731 /// splittable instructions using the alloca.
732 /// Thus we will produce N * M instructions in the end, where N are the number
733 /// of unsplittable uses and M are the number of splittable. This visitor does
734 /// the exact same number of updates to the partitioning.
736 /// In the more common case, this visitor will leverage the fact that the
737 /// partition space is pre-sorted, and do a logarithmic search for the
738 /// partition needed, making the total visit a classical ((N + M) * log(N))
739 /// complexity operation.
740 class AllocaPartitioning::UseBuilder : public BuilderBase<UseBuilder> {
741 friend class InstVisitor<UseBuilder>;
743 /// \brief Set to de-duplicate dead instructions found in the use walk.
744 SmallPtrSet<Instruction *, 4> VisitedDeadInsts;
747 UseBuilder(const TargetData &TD, AllocaInst &AI, AllocaPartitioning &P)
748 : BuilderBase<UseBuilder>(TD, AI, P) {}
750 /// \brief Run the builder over the allocation.
752 // Note that we have to re-evaluate size on each trip through the loop as
753 // the queue grows at the tail.
754 for (unsigned Idx = 0; Idx < Queue.size(); ++Idx) {
756 Offset = Queue[Idx].Offset;
757 this->visit(cast<Instruction>(U->getUser()));
762 void markAsDead(Instruction &I) {
763 if (VisitedDeadInsts.insert(&I))
764 P.DeadUsers.push_back(&I);
767 void insertUse(uint64_t Size, Instruction &User) {
768 uint64_t BeginOffset = Offset, EndOffset = Offset + Size;
770 // If the use extends outside of the allocation, record it as a dead use
771 // for elimination later.
772 if (BeginOffset >= AllocSize || Size == 0)
773 return markAsDead(User);
775 // Bound the use by the size of the allocation.
776 if (EndOffset > AllocSize)
777 EndOffset = AllocSize;
779 // NB: This only works if we have zero overlapping partitions.
780 iterator B = std::lower_bound(P.begin(), P.end(), BeginOffset);
781 if (B != P.begin() && llvm::prior(B)->EndOffset > BeginOffset)
783 for (iterator I = B, E = P.end(); I != E && I->BeginOffset < EndOffset;
785 PartitionUse NewUse(std::max(I->BeginOffset, BeginOffset),
786 std::min(I->EndOffset, EndOffset),
787 &User, cast<Instruction>(*U));
788 P.Uses[I - P.begin()].push_back(NewUse);
789 if (isa<PHINode>(U->getUser()) || isa<SelectInst>(U->getUser()))
790 P.PHIOrSelectOpMap[std::make_pair(&User, U->get())]
791 = std::make_pair(I - P.begin(), P.Uses[I - P.begin()].size() - 1);
795 void handleLoadOrStore(Type *Ty, Instruction &I) {
796 uint64_t Size = TD.getTypeStoreSize(Ty);
798 // If this memory access can be shown to *statically* extend outside the
799 // bounds of of the allocation, it's behavior is undefined, so simply
800 // ignore it. Note that this is more strict than the generic clamping
801 // behavior of insertUse.
802 if (Offset >= AllocSize || Size > AllocSize || Offset + Size > AllocSize)
803 return markAsDead(I);
808 void visitBitCastInst(BitCastInst &BC) {
810 return markAsDead(BC);
812 enqueueUsers(BC, Offset);
815 void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
816 if (GEPI.use_empty())
817 return markAsDead(GEPI);
820 if (!computeConstantGEPOffset(GEPI, GEPOffset))
821 llvm_unreachable("Unable to compute constant offset for use");
823 enqueueUsers(GEPI, GEPOffset);
826 void visitLoadInst(LoadInst &LI) {
827 handleLoadOrStore(LI.getType(), LI);
830 void visitStoreInst(StoreInst &SI) {
831 handleLoadOrStore(SI.getOperand(0)->getType(), SI);
834 void visitMemSetInst(MemSetInst &II) {
835 ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
836 insertUse(Length ? Length->getZExtValue() : AllocSize - Offset, II);
839 void visitMemTransferInst(MemTransferInst &II) {
840 ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
841 insertUse(Length ? Length->getZExtValue() : AllocSize - Offset, II);
844 void visitIntrinsicInst(IntrinsicInst &II) {
845 assert(II.getIntrinsicID() == Intrinsic::lifetime_start ||
846 II.getIntrinsicID() == Intrinsic::lifetime_end);
848 ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
849 insertUse(std::min(AllocSize - Offset, Length->getLimitedValue()), II);
852 void insertPHIOrSelect(Instruction &User) {
853 uint64_t Size = P.PHIOrSelectSizes.lookup(&User).first;
855 // For PHI and select operands outside the alloca, we can't nuke the entire
856 // phi or select -- the other side might still be relevant, so we special
857 // case them here and use a separate structure to track the operands
858 // themselves which should be replaced with undef.
859 if (Offset >= AllocSize) {
860 P.DeadOperands.push_back(U);
864 insertUse(Size, User);
866 void visitPHINode(PHINode &PN) {
868 return markAsDead(PN);
870 insertPHIOrSelect(PN);
872 void visitSelectInst(SelectInst &SI) {
874 return markAsDead(SI);
876 if (Value *Result = foldSelectInst(SI)) {
878 // If the result of the constant fold will be the pointer, recurse
879 // through the select as if we had RAUW'ed it.
880 enqueueUsers(SI, Offset);
885 insertPHIOrSelect(SI);
888 /// \brief Unreachable, we've already visited the alloca once.
889 void visitInstruction(Instruction &I) {
890 llvm_unreachable("Unhandled instruction in use builder.");
894 void AllocaPartitioning::splitAndMergePartitions() {
895 size_t NumDeadPartitions = 0;
897 // Track the range of splittable partitions that we pass when accumulating
898 // overlapping unsplittable partitions.
899 uint64_t SplitEndOffset = 0ull;
901 Partition New(0ull, 0ull, false);
903 for (unsigned i = 0, j = i, e = Partitions.size(); i != e; i = j) {
906 if (!Partitions[i].IsSplittable || New.BeginOffset == New.EndOffset) {
907 assert(New.BeginOffset == New.EndOffset);
910 assert(New.IsSplittable);
911 New.EndOffset = std::max(New.EndOffset, Partitions[i].EndOffset);
913 assert(New.BeginOffset != New.EndOffset);
915 // Scan the overlapping partitions.
916 while (j != e && New.EndOffset > Partitions[j].BeginOffset) {
917 // If the new partition we are forming is splittable, stop at the first
918 // unsplittable partition.
919 if (New.IsSplittable && !Partitions[j].IsSplittable)
922 // Grow the new partition to include any equally splittable range. 'j' is
923 // always equally splittable when New is splittable, but when New is not
924 // splittable, we may subsume some (or part of some) splitable partition
925 // without growing the new one.
926 if (New.IsSplittable == Partitions[j].IsSplittable) {
927 New.EndOffset = std::max(New.EndOffset, Partitions[j].EndOffset);
929 assert(!New.IsSplittable);
930 assert(Partitions[j].IsSplittable);
931 SplitEndOffset = std::max(SplitEndOffset, Partitions[j].EndOffset);
934 Partitions[j].BeginOffset = Partitions[j].EndOffset = UINT64_MAX;
939 // If the new partition is splittable, chop off the end as soon as the
940 // unsplittable subsequent partition starts and ensure we eventually cover
941 // the splittable area.
942 if (j != e && New.IsSplittable) {
943 SplitEndOffset = std::max(SplitEndOffset, New.EndOffset);
944 New.EndOffset = std::min(New.EndOffset, Partitions[j].BeginOffset);
947 // Add the new partition if it differs from the original one and is
948 // non-empty. We can end up with an empty partition here if it was
949 // splittable but there is an unsplittable one that starts at the same
951 if (New != Partitions[i]) {
952 if (New.BeginOffset != New.EndOffset)
953 Partitions.push_back(New);
954 // Mark the old one for removal.
955 Partitions[i].BeginOffset = Partitions[i].EndOffset = UINT64_MAX;
959 New.BeginOffset = New.EndOffset;
960 if (!New.IsSplittable) {
961 New.EndOffset = std::max(New.EndOffset, SplitEndOffset);
962 if (j != e && !Partitions[j].IsSplittable)
963 New.EndOffset = std::min(New.EndOffset, Partitions[j].BeginOffset);
964 New.IsSplittable = true;
965 // If there is a trailing splittable partition which won't be fused into
966 // the next splittable partition go ahead and add it onto the partitions
968 if (New.BeginOffset < New.EndOffset &&
969 (j == e || !Partitions[j].IsSplittable ||
970 New.EndOffset < Partitions[j].BeginOffset)) {
971 Partitions.push_back(New);
972 New.BeginOffset = New.EndOffset = 0ull;
977 // Re-sort the partitions now that they have been split and merged into
978 // disjoint set of partitions. Also remove any of the dead partitions we've
979 // replaced in the process.
980 std::sort(Partitions.begin(), Partitions.end());
981 if (NumDeadPartitions) {
982 assert(Partitions.back().BeginOffset == UINT64_MAX);
983 assert(Partitions.back().EndOffset == UINT64_MAX);
984 assert((ptrdiff_t)NumDeadPartitions ==
985 std::count(Partitions.begin(), Partitions.end(), Partitions.back()));
987 Partitions.erase(Partitions.end() - NumDeadPartitions, Partitions.end());
990 AllocaPartitioning::AllocaPartitioning(const TargetData &TD, AllocaInst &AI)
991 : AI(AI), PointerEscapingInstr(0) {
992 PartitionBuilder PB(TD, AI, *this);
996 if (Partitions.size() > 1) {
997 // Sort the uses. This arranges for the offsets to be in ascending order,
998 // and the sizes to be in descending order.
999 std::sort(Partitions.begin(), Partitions.end());
1001 // Intersect splittability for all partitions with equal offsets and sizes.
1002 // Then remove all but the first so that we have a sequence of non-equal but
1003 // potentially overlapping partitions.
1004 for (iterator I = Partitions.begin(), J = I, E = Partitions.end(); I != E;
1007 while (J != E && *I == *J) {
1008 I->IsSplittable &= J->IsSplittable;
1012 Partitions.erase(std::unique(Partitions.begin(), Partitions.end()),
1015 // Split splittable and merge unsplittable partitions into a disjoint set
1016 // of partitions over the used space of the allocation.
1017 splitAndMergePartitions();
1020 // Now build up the user lists for each of these disjoint partitions by
1021 // re-walking the recursive users of the alloca.
1022 Uses.resize(Partitions.size());
1023 UseBuilder UB(TD, AI, *this);
1025 for (iterator I = Partitions.begin(), E = Partitions.end(); I != E; ++I)
1026 std::stable_sort(use_begin(I), use_end(I));
1029 Type *AllocaPartitioning::getCommonType(iterator I) const {
1031 for (const_use_iterator UI = use_begin(I), UE = use_end(I); UI != UE; ++UI) {
1032 if (isa<MemIntrinsic>(*UI->User))
1034 if (UI->BeginOffset != I->BeginOffset || UI->EndOffset != I->EndOffset)
1038 if (LoadInst *LI = dyn_cast<LoadInst>(&*UI->User)) {
1039 UserTy = LI->getType();
1040 } else if (StoreInst *SI = dyn_cast<StoreInst>(&*UI->User)) {
1041 UserTy = SI->getValueOperand()->getType();
1042 } else if (SelectInst *SI = dyn_cast<SelectInst>(&*UI->User)) {
1043 if (PointerType *PtrTy = dyn_cast<PointerType>(SI->getType()))
1044 UserTy = PtrTy->getElementType();
1045 } else if (PHINode *PN = dyn_cast<PHINode>(&*UI->User)) {
1046 if (PointerType *PtrTy = dyn_cast<PointerType>(PN->getType()))
1047 UserTy = PtrTy->getElementType();
1050 if (Ty && Ty != UserTy)
1058 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1060 void AllocaPartitioning::print(raw_ostream &OS, const_iterator I,
1061 StringRef Indent) const {
1062 OS << Indent << "partition #" << (I - begin())
1063 << " [" << I->BeginOffset << "," << I->EndOffset << ")"
1064 << (I->IsSplittable ? " (splittable)" : "")
1065 << (Uses[I - begin()].empty() ? " (zero uses)" : "")
1069 void AllocaPartitioning::printUsers(raw_ostream &OS, const_iterator I,
1070 StringRef Indent) const {
1071 for (const_use_iterator UI = use_begin(I), UE = use_end(I);
1073 OS << Indent << " [" << UI->BeginOffset << "," << UI->EndOffset << ") "
1074 << "used by: " << *UI->User << "\n";
1075 if (MemTransferInst *II = dyn_cast<MemTransferInst>(&*UI->User)) {
1076 const MemTransferOffsets &MTO = MemTransferInstData.lookup(II);
1078 if (!MTO.IsSplittable)
1079 IsDest = UI->BeginOffset == MTO.DestBegin;
1081 IsDest = MTO.DestBegin != 0u;
1082 OS << Indent << " (original " << (IsDest ? "dest" : "source") << ": "
1083 << "[" << (IsDest ? MTO.DestBegin : MTO.SourceBegin)
1084 << "," << (IsDest ? MTO.DestEnd : MTO.SourceEnd) << ")\n";
1089 void AllocaPartitioning::print(raw_ostream &OS) const {
1090 if (PointerEscapingInstr) {
1091 OS << "No partitioning for alloca: " << AI << "\n"
1092 << " A pointer to this alloca escaped by:\n"
1093 << " " << *PointerEscapingInstr << "\n";
1097 OS << "Partitioning of alloca: " << AI << "\n";
1099 for (const_iterator I = begin(), E = end(); I != E; ++I, ++Num) {
1105 void AllocaPartitioning::dump(const_iterator I) const { print(dbgs(), I); }
1106 void AllocaPartitioning::dump() const { print(dbgs()); }
1108 #endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
1112 /// \brief An optimization pass providing Scalar Replacement of Aggregates.
1114 /// This pass takes allocations which can be completely analyzed (that is, they
1115 /// don't escape) and tries to turn them into scalar SSA values. There are
1116 /// a few steps to this process.
1118 /// 1) It takes allocations of aggregates and analyzes the ways in which they
1119 /// are used to try to split them into smaller allocations, ideally of
1120 /// a single scalar data type. It will split up memcpy and memset accesses
1121 /// as necessary and try to isolate invidual scalar accesses.
1122 /// 2) It will transform accesses into forms which are suitable for SSA value
1123 /// promotion. This can be replacing a memset with a scalar store of an
1124 /// integer value, or it can involve speculating operations on a PHI or
1125 /// select to be a PHI or select of the results.
1126 /// 3) Finally, this will try to detect a pattern of accesses which map cleanly
1127 /// onto insert and extract operations on a vector value, and convert them to
1128 /// this form. By doing so, it will enable promotion of vector aggregates to
1129 /// SSA vector values.
1130 class SROA : public FunctionPass {
1132 const TargetData *TD;
1135 /// \brief Worklist of alloca instructions to simplify.
1137 /// Each alloca in the function is added to this. Each new alloca formed gets
1138 /// added to it as well to recursively simplify unless that alloca can be
1139 /// directly promoted. Finally, each time we rewrite a use of an alloca other
1140 /// the one being actively rewritten, we add it back onto the list if not
1141 /// already present to ensure it is re-visited.
1142 SetVector<AllocaInst *, SmallVector<AllocaInst *, 16> > Worklist;
1144 /// \brief A collection of instructions to delete.
1145 /// We try to batch deletions to simplify code and make things a bit more
1147 SmallVector<Instruction *, 8> DeadInsts;
1149 /// \brief A set to prevent repeatedly marking an instruction split into many
1150 /// uses as dead. Only used to guard insertion into DeadInsts.
1151 SmallPtrSet<Instruction *, 4> DeadSplitInsts;
1153 /// \brief A set of deleted alloca instructions.
1155 /// These pointers are *no longer valid* as they have been deleted. They are
1156 /// used to remove deleted allocas from the list of promotable allocas.
1157 SmallPtrSet<AllocaInst *, 4> DeletedAllocas;
1159 /// \brief A collection of alloca instructions we can directly promote.
1160 std::vector<AllocaInst *> PromotableAllocas;
1163 SROA() : FunctionPass(ID), C(0), TD(0), DT(0) {
1164 initializeSROAPass(*PassRegistry::getPassRegistry());
1166 bool runOnFunction(Function &F);
1167 void getAnalysisUsage(AnalysisUsage &AU) const;
1169 const char *getPassName() const { return "SROA"; }
1173 friend class AllocaPartitionRewriter;
1174 friend class AllocaPartitionVectorRewriter;
1176 bool rewriteAllocaPartition(AllocaInst &AI,
1177 AllocaPartitioning &P,
1178 AllocaPartitioning::iterator PI);
1179 bool splitAlloca(AllocaInst &AI, AllocaPartitioning &P);
1180 bool runOnAlloca(AllocaInst &AI);
1181 void deleteDeadInstructions();
1187 FunctionPass *llvm::createSROAPass() {
1191 INITIALIZE_PASS_BEGIN(SROA, "sroa", "Scalar Replacement Of Aggregates",
1193 INITIALIZE_PASS_DEPENDENCY(DominatorTree)
1194 INITIALIZE_PASS_END(SROA, "sroa", "Scalar Replacement Of Aggregates",
1197 /// \brief Accumulate the constant offsets in a GEP into a single APInt offset.
1199 /// If the provided GEP is all-constant, the total byte offset formed by the
1200 /// GEP is computed and Offset is set to it. If the GEP has any non-constant
1201 /// operands, the function returns false and the value of Offset is unmodified.
1202 static bool accumulateGEPOffsets(const TargetData &TD, GEPOperator &GEP,
1204 APInt GEPOffset(Offset.getBitWidth(), 0);
1205 for (gep_type_iterator GTI = gep_type_begin(GEP), GTE = gep_type_end(GEP);
1206 GTI != GTE; ++GTI) {
1207 ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
1210 if (OpC->isZero()) continue;
1212 // Handle a struct index, which adds its field offset to the pointer.
1213 if (StructType *STy = dyn_cast<StructType>(*GTI)) {
1214 unsigned ElementIdx = OpC->getZExtValue();
1215 const StructLayout *SL = TD.getStructLayout(STy);
1216 GEPOffset += APInt(Offset.getBitWidth(),
1217 SL->getElementOffset(ElementIdx));
1221 APInt TypeSize(Offset.getBitWidth(),
1222 TD.getTypeAllocSize(GTI.getIndexedType()));
1223 if (VectorType *VTy = dyn_cast<VectorType>(*GTI)) {
1224 assert((VTy->getScalarSizeInBits() % 8) == 0 &&
1225 "vector element size is not a multiple of 8, cannot GEP over it");
1226 TypeSize = VTy->getScalarSizeInBits() / 8;
1229 GEPOffset += OpC->getValue().sextOrTrunc(Offset.getBitWidth()) * TypeSize;
1235 /// \brief Build a GEP out of a base pointer and indices.
1237 /// This will return the BasePtr if that is valid, or build a new GEP
1238 /// instruction using the IRBuilder if GEP-ing is needed.
1239 static Value *buildGEP(IRBuilder<> &IRB, Value *BasePtr,
1240 SmallVectorImpl<Value *> &Indices,
1241 const Twine &Prefix) {
1242 if (Indices.empty())
1245 // A single zero index is a no-op, so check for this and avoid building a GEP
1247 if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
1250 return IRB.CreateInBoundsGEP(BasePtr, Indices, Prefix + ".idx");
1253 /// \brief Get a natural GEP off of the BasePtr walking through Ty toward
1254 /// TargetTy without changing the offset of the pointer.
1256 /// This routine assumes we've already established a properly offset GEP with
1257 /// Indices, and arrived at the Ty type. The goal is to continue to GEP with
1258 /// zero-indices down through type layers until we find one the same as
1259 /// TargetTy. If we can't find one with the same type, we at least try to use
1260 /// one with the same size. If none of that works, we just produce the GEP as
1261 /// indicated by Indices to have the correct offset.
1262 static Value *getNaturalGEPWithType(IRBuilder<> &IRB, const TargetData &TD,
1263 Value *BasePtr, Type *Ty, Type *TargetTy,
1264 SmallVectorImpl<Value *> &Indices,
1265 const Twine &Prefix) {
1267 return buildGEP(IRB, BasePtr, Indices, Prefix);
1269 // See if we can descend into a struct and locate a field with the correct
1271 unsigned NumLayers = 0;
1272 Type *ElementTy = Ty;
1274 if (ElementTy->isPointerTy())
1276 if (SequentialType *SeqTy = dyn_cast<SequentialType>(ElementTy)) {
1277 ElementTy = SeqTy->getElementType();
1278 Indices.push_back(IRB.getInt(APInt(TD.getPointerSizeInBits(), 0)));
1279 } else if (StructType *STy = dyn_cast<StructType>(ElementTy)) {
1280 ElementTy = *STy->element_begin();
1281 Indices.push_back(IRB.getInt32(0));
1286 } while (ElementTy != TargetTy);
1287 if (ElementTy != TargetTy)
1288 Indices.erase(Indices.end() - NumLayers, Indices.end());
1290 return buildGEP(IRB, BasePtr, Indices, Prefix);
1293 /// \brief Recursively compute indices for a natural GEP.
1295 /// This is the recursive step for getNaturalGEPWithOffset that walks down the
1296 /// element types adding appropriate indices for the GEP.
1297 static Value *getNaturalGEPRecursively(IRBuilder<> &IRB, const TargetData &TD,
1298 Value *Ptr, Type *Ty, APInt &Offset,
1300 SmallVectorImpl<Value *> &Indices,
1301 const Twine &Prefix) {
1303 return getNaturalGEPWithType(IRB, TD, Ptr, Ty, TargetTy, Indices, Prefix);
1305 // We can't recurse through pointer types.
1306 if (Ty->isPointerTy())
1309 if (VectorType *VecTy = dyn_cast<VectorType>(Ty)) {
1310 unsigned ElementSizeInBits = VecTy->getScalarSizeInBits();
1311 if (ElementSizeInBits % 8)
1312 return 0; // GEPs over multiple of 8 size vector elements are invalid.
1313 APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
1314 APInt NumSkippedElements = Offset.udiv(ElementSize);
1315 if (NumSkippedElements.ugt(VecTy->getNumElements()))
1317 Offset -= NumSkippedElements * ElementSize;
1318 Indices.push_back(IRB.getInt(NumSkippedElements));
1319 return getNaturalGEPRecursively(IRB, TD, Ptr, VecTy->getElementType(),
1320 Offset, TargetTy, Indices, Prefix);
1323 if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
1324 Type *ElementTy = ArrTy->getElementType();
1325 APInt ElementSize(Offset.getBitWidth(), TD.getTypeAllocSize(ElementTy));
1326 APInt NumSkippedElements = Offset.udiv(ElementSize);
1327 if (NumSkippedElements.ugt(ArrTy->getNumElements()))
1330 Offset -= NumSkippedElements * ElementSize;
1331 Indices.push_back(IRB.getInt(NumSkippedElements));
1332 return getNaturalGEPRecursively(IRB, TD, Ptr, ElementTy, Offset, TargetTy,
1336 StructType *STy = dyn_cast<StructType>(Ty);
1340 const StructLayout *SL = TD.getStructLayout(STy);
1341 uint64_t StructOffset = Offset.getZExtValue();
1342 if (StructOffset > SL->getSizeInBytes())
1344 unsigned Index = SL->getElementContainingOffset(StructOffset);
1345 Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index));
1346 Type *ElementTy = STy->getElementType(Index);
1347 if (Offset.uge(TD.getTypeAllocSize(ElementTy)))
1348 return 0; // The offset points into alignment padding.
1350 Indices.push_back(IRB.getInt32(Index));
1351 return getNaturalGEPRecursively(IRB, TD, Ptr, ElementTy, Offset, TargetTy,
1355 /// \brief Get a natural GEP from a base pointer to a particular offset and
1356 /// resulting in a particular type.
1358 /// The goal is to produce a "natural" looking GEP that works with the existing
1359 /// composite types to arrive at the appropriate offset and element type for
1360 /// a pointer. TargetTy is the element type the returned GEP should point-to if
1361 /// possible. We recurse by decreasing Offset, adding the appropriate index to
1362 /// Indices, and setting Ty to the result subtype.
1364 /// If no natural GEP can be constructed, this function returns null.
1365 static Value *getNaturalGEPWithOffset(IRBuilder<> &IRB, const TargetData &TD,
1366 Value *Ptr, APInt Offset, Type *TargetTy,
1367 SmallVectorImpl<Value *> &Indices,
1368 const Twine &Prefix) {
1369 PointerType *Ty = cast<PointerType>(Ptr->getType());
1371 // Don't consider any GEPs through an i8* as natural unless the TargetTy is
1373 if (Ty == IRB.getInt8PtrTy() && TargetTy->isIntegerTy(8))
1376 Type *ElementTy = Ty->getElementType();
1377 APInt ElementSize(Offset.getBitWidth(), TD.getTypeAllocSize(ElementTy));
1378 if (ElementSize == 0)
1379 return 0; // Zero-length arrays can't help us build a natural GEP.
1380 APInt NumSkippedElements = Offset.udiv(ElementSize);
1382 Offset -= NumSkippedElements * ElementSize;
1383 Indices.push_back(IRB.getInt(NumSkippedElements));
1384 return getNaturalGEPRecursively(IRB, TD, Ptr, ElementTy, Offset, TargetTy,
1388 /// \brief Compute an adjusted pointer from Ptr by Offset bytes where the
1389 /// resulting pointer has PointerTy.
1391 /// This tries very hard to compute a "natural" GEP which arrives at the offset
1392 /// and produces the pointer type desired. Where it cannot, it will try to use
1393 /// the natural GEP to arrive at the offset and bitcast to the type. Where that
1394 /// fails, it will try to use an existing i8* and GEP to the byte offset and
1395 /// bitcast to the type.
1397 /// The strategy for finding the more natural GEPs is to peel off layers of the
1398 /// pointer, walking back through bit casts and GEPs, searching for a base
1399 /// pointer from which we can compute a natural GEP with the desired
1400 /// properities. The algorithm tries to fold as many constant indices into
1401 /// a single GEP as possible, thus making each GEP more independent of the
1402 /// surrounding code.
1403 static Value *getAdjustedPtr(IRBuilder<> &IRB, const TargetData &TD,
1404 Value *Ptr, APInt Offset, Type *PointerTy,
1405 const Twine &Prefix) {
1406 // Even though we don't look through PHI nodes, we could be called on an
1407 // instruction in an unreachable block, which may be on a cycle.
1408 SmallPtrSet<Value *, 4> Visited;
1409 Visited.insert(Ptr);
1410 SmallVector<Value *, 4> Indices;
1412 // We may end up computing an offset pointer that has the wrong type. If we
1413 // never are able to compute one directly that has the correct type, we'll
1414 // fall back to it, so keep it around here.
1415 Value *OffsetPtr = 0;
1417 // Remember any i8 pointer we come across to re-use if we need to do a raw
1420 APInt Int8PtrOffset(Offset.getBitWidth(), 0);
1422 Type *TargetTy = PointerTy->getPointerElementType();
1425 // First fold any existing GEPs into the offset.
1426 while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
1427 APInt GEPOffset(Offset.getBitWidth(), 0);
1428 if (!accumulateGEPOffsets(TD, *GEP, GEPOffset))
1430 Offset += GEPOffset;
1431 Ptr = GEP->getPointerOperand();
1432 if (!Visited.insert(Ptr))
1436 // See if we can perform a natural GEP here.
1438 if (Value *P = getNaturalGEPWithOffset(IRB, TD, Ptr, Offset, TargetTy,
1440 if (P->getType() == PointerTy) {
1441 // Zap any offset pointer that we ended up computing in previous rounds.
1442 if (OffsetPtr && OffsetPtr->use_empty())
1443 if (Instruction *I = dyn_cast<Instruction>(OffsetPtr))
1444 I->eraseFromParent();
1452 // Stash this pointer if we've found an i8*.
1453 if (Ptr->getType()->isIntegerTy(8)) {
1455 Int8PtrOffset = Offset;
1458 // Peel off a layer of the pointer and update the offset appropriately.
1459 if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
1460 Ptr = cast<Operator>(Ptr)->getOperand(0);
1461 } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
1462 if (GA->mayBeOverridden())
1464 Ptr = GA->getAliasee();
1468 assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!");
1469 } while (Visited.insert(Ptr));
1473 Int8Ptr = IRB.CreateBitCast(Ptr, IRB.getInt8PtrTy(),
1474 Prefix + ".raw_cast");
1475 Int8PtrOffset = Offset;
1478 OffsetPtr = Int8PtrOffset == 0 ? Int8Ptr :
1479 IRB.CreateInBoundsGEP(Int8Ptr, IRB.getInt(Int8PtrOffset),
1480 Prefix + ".raw_idx");
1484 // On the off chance we were targeting i8*, guard the bitcast here.
1485 if (Ptr->getType() != PointerTy)
1486 Ptr = IRB.CreateBitCast(Ptr, PointerTy, Prefix + ".cast");
1491 /// \brief Test whether the given alloca partition can be promoted to a vector.
1493 /// This is a quick test to check whether we can rewrite a particular alloca
1494 /// partition (and its newly formed alloca) into a vector alloca with only
1495 /// whole-vector loads and stores such that it could be promoted to a vector
1496 /// SSA value. We only can ensure this for a limited set of operations, and we
1497 /// don't want to do the rewrites unless we are confident that the result will
1498 /// be promotable, so we have an early test here.
1499 static bool isVectorPromotionViable(const TargetData &TD,
1501 AllocaPartitioning &P,
1502 uint64_t PartitionBeginOffset,
1503 uint64_t PartitionEndOffset,
1504 AllocaPartitioning::const_use_iterator I,
1505 AllocaPartitioning::const_use_iterator E) {
1506 VectorType *Ty = dyn_cast<VectorType>(AllocaTy);
1510 uint64_t VecSize = TD.getTypeSizeInBits(Ty);
1511 uint64_t ElementSize = Ty->getScalarSizeInBits();
1513 // While the definition of LLVM vectors is bitpacked, we don't support sizes
1514 // that aren't byte sized.
1515 if (ElementSize % 8)
1517 assert((VecSize % 8) == 0 && "vector size not a multiple of element size?");
1521 for (; I != E; ++I) {
1522 uint64_t BeginOffset = I->BeginOffset - PartitionBeginOffset;
1523 uint64_t BeginIndex = BeginOffset / ElementSize;
1524 if (BeginIndex * ElementSize != BeginOffset ||
1525 BeginIndex >= Ty->getNumElements())
1527 uint64_t EndOffset = I->EndOffset - PartitionBeginOffset;
1528 uint64_t EndIndex = EndOffset / ElementSize;
1529 if (EndIndex * ElementSize != EndOffset ||
1530 EndIndex > Ty->getNumElements())
1533 // FIXME: We should build shuffle vector instructions to handle
1534 // non-element-sized accesses.
1535 if ((EndOffset - BeginOffset) != ElementSize &&
1536 (EndOffset - BeginOffset) != VecSize)
1539 if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(&*I->User)) {
1540 if (MI->isVolatile())
1542 if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(&*I->User)) {
1543 const AllocaPartitioning::MemTransferOffsets &MTO
1544 = P.getMemTransferOffsets(*MTI);
1545 if (!MTO.IsSplittable)
1548 } else if (I->Ptr->getType()->getPointerElementType()->isStructTy()) {
1549 // Disable vector promotion when there are loads or stores of an FCA.
1551 } else if (!isa<LoadInst>(*I->User) && !isa<StoreInst>(*I->User)) {
1559 /// \brief Visitor to rewrite instructions using a partition of an alloca to
1560 /// use a new alloca.
1562 /// Also implements the rewriting to vector-based accesses when the partition
1563 /// passes the isVectorPromotionViable predicate. Most of the rewriting logic
1565 class AllocaPartitionRewriter : public InstVisitor<AllocaPartitionRewriter,
1567 // Befriend the base class so it can delegate to private visit methods.
1568 friend class llvm::InstVisitor<AllocaPartitionRewriter, bool>;
1570 const TargetData &TD;
1571 AllocaPartitioning &P;
1573 AllocaInst &OldAI, &NewAI;
1574 const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
1576 // If we are rewriting an alloca partition which can be written as pure
1577 // vector operations, we stash extra information here. When VecTy is
1578 // non-null, we have some strict guarantees about the rewriten alloca:
1579 // - The new alloca is exactly the size of the vector type here.
1580 // - The accesses all either map to the entire vector or to a single
1582 // - The set of accessing instructions is only one of those handled above
1583 // in isVectorPromotionViable. Generally these are the same access kinds
1584 // which are promotable via mem2reg.
1587 uint64_t ElementSize;
1589 // The offset of the partition user currently being rewritten.
1590 uint64_t BeginOffset, EndOffset;
1591 Instruction *OldPtr;
1593 // The name prefix to use when rewriting instructions for this alloca.
1594 std::string NamePrefix;
1597 AllocaPartitionRewriter(const TargetData &TD, AllocaPartitioning &P,
1598 AllocaPartitioning::iterator PI,
1599 SROA &Pass, AllocaInst &OldAI, AllocaInst &NewAI,
1600 uint64_t NewBeginOffset, uint64_t NewEndOffset)
1601 : TD(TD), P(P), Pass(Pass),
1602 OldAI(OldAI), NewAI(NewAI),
1603 NewAllocaBeginOffset(NewBeginOffset),
1604 NewAllocaEndOffset(NewEndOffset),
1605 VecTy(), ElementTy(), ElementSize(),
1606 BeginOffset(), EndOffset() {
1609 /// \brief Visit the users of the alloca partition and rewrite them.
1610 bool visitUsers(AllocaPartitioning::const_use_iterator I,
1611 AllocaPartitioning::const_use_iterator E) {
1612 if (isVectorPromotionViable(TD, NewAI.getAllocatedType(), P,
1613 NewAllocaBeginOffset, NewAllocaEndOffset,
1616 VecTy = cast<VectorType>(NewAI.getAllocatedType());
1617 ElementTy = VecTy->getElementType();
1618 assert((VecTy->getScalarSizeInBits() % 8) == 0 &&
1619 "Only multiple-of-8 sized vector elements are viable");
1620 ElementSize = VecTy->getScalarSizeInBits() / 8;
1622 bool CanSROA = true;
1623 for (; I != E; ++I) {
1624 BeginOffset = I->BeginOffset;
1625 EndOffset = I->EndOffset;
1627 NamePrefix = (Twine(NewAI.getName()) + "." + Twine(BeginOffset)).str();
1628 CanSROA &= visit(I->User);
1640 // Every instruction which can end up as a user must have a rewrite rule.
1641 bool visitInstruction(Instruction &I) {
1642 DEBUG(dbgs() << " !!!! Cannot rewrite: " << I << "\n");
1643 llvm_unreachable("No rewrite rule for this instruction!");
1646 Twine getName(const Twine &Suffix) {
1647 return NamePrefix + Suffix;
1650 Value *getAdjustedAllocaPtr(IRBuilder<> &IRB, Type *PointerTy) {
1651 assert(BeginOffset >= NewAllocaBeginOffset);
1652 APInt Offset(TD.getPointerSizeInBits(), BeginOffset - NewAllocaBeginOffset);
1653 return getAdjustedPtr(IRB, TD, &NewAI, Offset, PointerTy, getName(""));
1656 ConstantInt *getIndex(IRBuilder<> &IRB, uint64_t Offset) {
1657 assert(VecTy && "Can only call getIndex when rewriting a vector");
1658 uint64_t RelOffset = Offset - NewAllocaBeginOffset;
1659 assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds");
1660 uint32_t Index = RelOffset / ElementSize;
1661 assert(Index * ElementSize == RelOffset);
1662 return IRB.getInt32(Index);
1665 void deleteIfTriviallyDead(Value *V) {
1666 Instruction *I = cast<Instruction>(V);
1667 if (isInstructionTriviallyDead(I))
1668 Pass.DeadInsts.push_back(I);
1671 Value *getValueCast(IRBuilder<> &IRB, Value *V, Type *Ty) {
1672 if (V->getType()->isIntegerTy() && Ty->isPointerTy())
1673 return IRB.CreateIntToPtr(V, Ty);
1674 if (V->getType()->isPointerTy() && Ty->isIntegerTy())
1675 return IRB.CreatePtrToInt(V, Ty);
1677 return IRB.CreateBitCast(V, Ty);
1680 bool rewriteVectorizedLoadInst(IRBuilder<> &IRB, LoadInst &LI, Value *OldOp) {
1682 if (LI.getType() == VecTy->getElementType() ||
1683 BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset) {
1685 = IRB.CreateExtractElement(IRB.CreateLoad(&NewAI, getName(".load")),
1686 getIndex(IRB, BeginOffset),
1687 getName(".extract"));
1689 Result = IRB.CreateLoad(&NewAI, getName(".load"));
1691 if (Result->getType() != LI.getType())
1692 Result = getValueCast(IRB, Result, LI.getType());
1693 LI.replaceAllUsesWith(Result);
1694 Pass.DeadInsts.push_back(&LI);
1696 DEBUG(dbgs() << " to: " << *Result << "\n");
1700 bool visitLoadInst(LoadInst &LI) {
1701 DEBUG(dbgs() << " original: " << LI << "\n");
1702 Value *OldOp = LI.getOperand(0);
1703 assert(OldOp == OldPtr);
1704 IRBuilder<> IRB(&LI);
1707 return rewriteVectorizedLoadInst(IRB, LI, OldOp);
1709 Value *NewPtr = getAdjustedAllocaPtr(IRB,
1710 LI.getPointerOperand()->getType());
1711 LI.setOperand(0, NewPtr);
1712 DEBUG(dbgs() << " to: " << LI << "\n");
1714 deleteIfTriviallyDead(OldOp);
1715 return NewPtr == &NewAI && !LI.isVolatile();
1718 bool rewriteVectorizedStoreInst(IRBuilder<> &IRB, StoreInst &SI,
1720 Value *V = SI.getValueOperand();
1721 if (V->getType() == ElementTy ||
1722 BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset) {
1723 if (V->getType() != ElementTy)
1724 V = getValueCast(IRB, V, ElementTy);
1725 V = IRB.CreateInsertElement(IRB.CreateLoad(&NewAI, getName(".load")), V,
1726 getIndex(IRB, BeginOffset),
1727 getName(".insert"));
1728 } else if (V->getType() != VecTy) {
1729 V = getValueCast(IRB, V, VecTy);
1731 StoreInst *Store = IRB.CreateStore(V, &NewAI);
1732 Pass.DeadInsts.push_back(&SI);
1735 DEBUG(dbgs() << " to: " << *Store << "\n");
1739 bool visitStoreInst(StoreInst &SI) {
1740 DEBUG(dbgs() << " original: " << SI << "\n");
1741 Value *OldOp = SI.getOperand(1);
1742 assert(OldOp == OldPtr);
1743 IRBuilder<> IRB(&SI);
1746 return rewriteVectorizedStoreInst(IRB, SI, OldOp);
1748 Value *NewPtr = getAdjustedAllocaPtr(IRB,
1749 SI.getPointerOperand()->getType());
1750 SI.setOperand(1, NewPtr);
1751 DEBUG(dbgs() << " to: " << SI << "\n");
1753 deleteIfTriviallyDead(OldOp);
1754 return NewPtr == &NewAI && !SI.isVolatile();
1757 bool visitMemSetInst(MemSetInst &II) {
1758 DEBUG(dbgs() << " original: " << II << "\n");
1759 IRBuilder<> IRB(&II);
1760 assert(II.getRawDest() == OldPtr);
1762 // If the memset has a variable size, it cannot be split, just adjust the
1763 // pointer to the new alloca.
1764 if (!isa<Constant>(II.getLength())) {
1765 II.setDest(getAdjustedAllocaPtr(IRB, II.getRawDest()->getType()));
1766 deleteIfTriviallyDead(OldPtr);
1770 // Record this instruction for deletion.
1771 if (Pass.DeadSplitInsts.insert(&II))
1772 Pass.DeadInsts.push_back(&II);
1774 Type *AllocaTy = NewAI.getAllocatedType();
1775 Type *ScalarTy = AllocaTy->getScalarType();
1777 // If this doesn't map cleanly onto the alloca type, and that type isn't
1778 // a single value type, just emit a memset.
1779 if (!VecTy && (BeginOffset != NewAllocaBeginOffset ||
1780 EndOffset != NewAllocaEndOffset ||
1781 !AllocaTy->isSingleValueType() ||
1782 !TD.isLegalInteger(TD.getTypeSizeInBits(ScalarTy)))) {
1783 Type *SizeTy = II.getLength()->getType();
1784 Constant *Size = ConstantInt::get(SizeTy, EndOffset - BeginOffset);
1787 = IRB.CreateMemSet(getAdjustedAllocaPtr(IRB,
1788 II.getRawDest()->getType()),
1789 II.getValue(), Size, II.getAlignment(),
1792 DEBUG(dbgs() << " to: " << *New << "\n");
1796 // If we can represent this as a simple value, we have to build the actual
1797 // value to store, which requires expanding the byte present in memset to
1798 // a sensible representation for the alloca type. This is essentially
1799 // splatting the byte to a sufficiently wide integer, bitcasting to the
1800 // desired scalar type, and splatting it across any desired vector type.
1801 Value *V = II.getValue();
1802 IntegerType *VTy = cast<IntegerType>(V->getType());
1803 Type *IntTy = Type::getIntNTy(VTy->getContext(),
1804 TD.getTypeSizeInBits(ScalarTy));
1805 if (TD.getTypeSizeInBits(ScalarTy) > VTy->getBitWidth())
1806 V = IRB.CreateMul(IRB.CreateZExt(V, IntTy, getName(".zext")),
1807 ConstantExpr::getUDiv(
1808 Constant::getAllOnesValue(IntTy),
1809 ConstantExpr::getZExt(
1810 Constant::getAllOnesValue(V->getType()),
1812 getName(".isplat"));
1813 if (V->getType() != ScalarTy) {
1814 if (ScalarTy->isPointerTy())
1815 V = IRB.CreateIntToPtr(V, ScalarTy);
1816 else if (ScalarTy->isPrimitiveType() || ScalarTy->isVectorTy())
1817 V = IRB.CreateBitCast(V, ScalarTy);
1818 else if (ScalarTy->isIntegerTy())
1819 llvm_unreachable("Computed different integer types with equal widths");
1821 llvm_unreachable("Invalid scalar type");
1824 // If this is an element-wide memset of a vectorizable alloca, insert it.
1825 if (VecTy && (BeginOffset > NewAllocaBeginOffset ||
1826 EndOffset < NewAllocaEndOffset)) {
1827 StoreInst *Store = IRB.CreateStore(
1828 IRB.CreateInsertElement(IRB.CreateLoad(&NewAI, getName(".load")), V,
1829 getIndex(IRB, BeginOffset),
1830 getName(".insert")),
1833 DEBUG(dbgs() << " to: " << *Store << "\n");
1837 // Splat to a vector if needed.
1838 if (VectorType *VecTy = dyn_cast<VectorType>(AllocaTy)) {
1839 VectorType *SplatSourceTy = VectorType::get(V->getType(), 1);
1840 V = IRB.CreateShuffleVector(
1841 IRB.CreateInsertElement(UndefValue::get(SplatSourceTy), V,
1842 IRB.getInt32(0), getName(".vsplat.insert")),
1843 UndefValue::get(SplatSourceTy),
1844 ConstantVector::getSplat(VecTy->getNumElements(), IRB.getInt32(0)),
1845 getName(".vsplat.shuffle"));
1846 assert(V->getType() == VecTy);
1849 Value *New = IRB.CreateStore(V, &NewAI, II.isVolatile());
1851 DEBUG(dbgs() << " to: " << *New << "\n");
1852 return !II.isVolatile();
1855 bool visitMemTransferInst(MemTransferInst &II) {
1856 // Rewriting of memory transfer instructions can be a bit tricky. We break
1857 // them into two categories: split intrinsics and unsplit intrinsics.
1859 DEBUG(dbgs() << " original: " << II << "\n");
1860 IRBuilder<> IRB(&II);
1862 assert(II.getRawSource() == OldPtr || II.getRawDest() == OldPtr);
1863 bool IsDest = II.getRawDest() == OldPtr;
1865 const AllocaPartitioning::MemTransferOffsets &MTO
1866 = P.getMemTransferOffsets(II);
1868 // For unsplit intrinsics, we simply modify the source and destination
1869 // pointers in place. This isn't just an optimization, it is a matter of
1870 // correctness. With unsplit intrinsics we may be dealing with transfers
1871 // within a single alloca before SROA ran, or with transfers that have
1872 // a variable length. We may also be dealing with memmove instead of
1873 // memcpy, and so simply updating the pointers is the necessary for us to
1874 // update both source and dest of a single call.
1875 if (!MTO.IsSplittable) {
1876 Value *OldOp = IsDest ? II.getRawDest() : II.getRawSource();
1878 II.setDest(getAdjustedAllocaPtr(IRB, II.getRawDest()->getType()));
1880 II.setSource(getAdjustedAllocaPtr(IRB, II.getRawSource()->getType()));
1882 DEBUG(dbgs() << " to: " << II << "\n");
1883 deleteIfTriviallyDead(OldOp);
1886 // For split transfer intrinsics we have an incredibly useful assurance:
1887 // the source and destination do not reside within the same alloca, and at
1888 // least one of them does not escape. This means that we can replace
1889 // memmove with memcpy, and we don't need to worry about all manner of
1890 // downsides to splitting and transforming the operations.
1892 // Compute the relative offset within the transfer.
1893 unsigned IntPtrWidth = TD.getPointerSizeInBits();
1894 APInt RelOffset(IntPtrWidth, BeginOffset - (IsDest ? MTO.DestBegin
1895 : MTO.SourceBegin));
1897 // If this doesn't map cleanly onto the alloca type, and that type isn't
1898 // a single value type, just emit a memcpy.
1900 = !VecTy && (BeginOffset != NewAllocaBeginOffset ||
1901 EndOffset != NewAllocaEndOffset ||
1902 !NewAI.getAllocatedType()->isSingleValueType());
1904 // If we're just going to emit a memcpy, the alloca hasn't changed, and the
1905 // size hasn't been shrunk based on analysis of the viable range, this is
1907 if (EmitMemCpy && &OldAI == &NewAI) {
1908 uint64_t OrigBegin = IsDest ? MTO.DestBegin : MTO.SourceBegin;
1909 uint64_t OrigEnd = IsDest ? MTO.DestEnd : MTO.SourceEnd;
1910 // Ensure the start lines up.
1911 assert(BeginOffset == OrigBegin);
1913 // Rewrite the size as needed.
1914 if (EndOffset != OrigEnd)
1915 II.setLength(ConstantInt::get(II.getLength()->getType(),
1916 EndOffset - BeginOffset));
1919 // Record this instruction for deletion.
1920 if (Pass.DeadSplitInsts.insert(&II))
1921 Pass.DeadInsts.push_back(&II);
1923 bool IsVectorElement = VecTy && (BeginOffset > NewAllocaBeginOffset ||
1924 EndOffset < NewAllocaEndOffset);
1926 Type *OtherPtrTy = IsDest ? II.getRawSource()->getType()
1927 : II.getRawDest()->getType();
1929 OtherPtrTy = IsVectorElement ? VecTy->getElementType()->getPointerTo()
1932 // Compute the other pointer, folding as much as possible to produce
1933 // a single, simple GEP in most cases.
1934 Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest();
1935 OtherPtr = getAdjustedPtr(IRB, TD, OtherPtr, RelOffset, OtherPtrTy,
1936 getName("." + OtherPtr->getName()));
1938 // Strip all inbounds GEPs and pointer casts to try to dig out any root
1939 // alloca that should be re-examined after rewriting this instruction.
1941 = dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets()))
1942 Pass.Worklist.insert(AI);
1946 = getAdjustedAllocaPtr(IRB, IsDest ? II.getRawDest()->getType()
1947 : II.getRawSource()->getType());
1948 Type *SizeTy = II.getLength()->getType();
1949 Constant *Size = ConstantInt::get(SizeTy, EndOffset - BeginOffset);
1951 CallInst *New = IRB.CreateMemCpy(IsDest ? OurPtr : OtherPtr,
1952 IsDest ? OtherPtr : OurPtr,
1953 Size, II.getAlignment(),
1956 DEBUG(dbgs() << " to: " << *New << "\n");
1960 Value *SrcPtr = OtherPtr;
1961 Value *DstPtr = &NewAI;
1963 std::swap(SrcPtr, DstPtr);
1966 if (IsVectorElement && !IsDest) {
1967 // We have to extract rather than load.
1968 Src = IRB.CreateExtractElement(IRB.CreateLoad(SrcPtr,
1969 getName(".copyload")),
1970 getIndex(IRB, BeginOffset),
1971 getName(".copyextract"));
1973 Src = IRB.CreateLoad(SrcPtr, II.isVolatile(), getName(".copyload"));
1976 if (IsVectorElement && IsDest) {
1977 // We have to insert into a loaded copy before storing.
1978 Src = IRB.CreateInsertElement(IRB.CreateLoad(&NewAI, getName(".load")),
1979 Src, getIndex(IRB, BeginOffset),
1980 getName(".insert"));
1983 Value *Store = IRB.CreateStore(Src, DstPtr, II.isVolatile());
1985 DEBUG(dbgs() << " to: " << *Store << "\n");
1986 return !II.isVolatile();
1989 bool visitIntrinsicInst(IntrinsicInst &II) {
1990 assert(II.getIntrinsicID() == Intrinsic::lifetime_start ||
1991 II.getIntrinsicID() == Intrinsic::lifetime_end);
1992 DEBUG(dbgs() << " original: " << II << "\n");
1993 IRBuilder<> IRB(&II);
1994 assert(II.getArgOperand(1) == OldPtr);
1996 // Record this instruction for deletion.
1997 if (Pass.DeadSplitInsts.insert(&II))
1998 Pass.DeadInsts.push_back(&II);
2001 = ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
2002 EndOffset - BeginOffset);
2003 Value *Ptr = getAdjustedAllocaPtr(IRB, II.getArgOperand(1)->getType());
2005 if (II.getIntrinsicID() == Intrinsic::lifetime_start)
2006 New = IRB.CreateLifetimeStart(Ptr, Size);
2008 New = IRB.CreateLifetimeEnd(Ptr, Size);
2010 DEBUG(dbgs() << " to: " << *New << "\n");
2014 /// PHI instructions that use an alloca and are subsequently loaded can be
2015 /// rewritten to load both input pointers in the pred blocks and then PHI the
2016 /// results, allowing the load of the alloca to be promoted.
2018 /// %P2 = phi [i32* %Alloca, i32* %Other]
2019 /// %V = load i32* %P2
2021 /// %V1 = load i32* %Alloca -> will be mem2reg'd
2023 /// %V2 = load i32* %Other
2025 /// %V = phi [i32 %V1, i32 %V2]
2027 /// We can do this to a select if its only uses are loads and if the operand
2028 /// to the select can be loaded unconditionally.
2030 /// FIXME: This should be hoisted into a generic utility, likely in
2031 /// Transforms/Util/Local.h
2032 bool isSafePHIToSpeculate(PHINode &PN, SmallVectorImpl<LoadInst *> &Loads) {
2033 // For now, we can only do this promotion if the load is in the same block
2034 // as the PHI, and if there are no stores between the phi and load.
2035 // TODO: Allow recursive phi users.
2036 // TODO: Allow stores.
2037 BasicBlock *BB = PN.getParent();
2038 unsigned MaxAlign = 0;
2039 for (Value::use_iterator UI = PN.use_begin(), UE = PN.use_end();
2041 LoadInst *LI = dyn_cast<LoadInst>(*UI);
2042 if (LI == 0 || !LI->isSimple()) return false;
2044 // For now we only allow loads in the same block as the PHI. This is
2045 // a common case that happens when instcombine merges two loads through
2047 if (LI->getParent() != BB) return false;
2049 // Ensure that there are no instructions between the PHI and the load that
2051 for (BasicBlock::iterator BBI = &PN; &*BBI != LI; ++BBI)
2052 if (BBI->mayWriteToMemory())
2055 MaxAlign = std::max(MaxAlign, LI->getAlignment());
2056 Loads.push_back(LI);
2059 // We can only transform this if it is safe to push the loads into the
2060 // predecessor blocks. The only thing to watch out for is that we can't put
2061 // a possibly trapping load in the predecessor if it is a critical edge.
2062 for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num;
2064 TerminatorInst *TI = PN.getIncomingBlock(Idx)->getTerminator();
2065 Value *InVal = PN.getIncomingValue(Idx);
2067 // If the value is produced by the terminator of the predecessor (an
2068 // invoke) or it has side-effects, there is no valid place to put a load
2069 // in the predecessor.
2070 if (TI == InVal || TI->mayHaveSideEffects())
2073 // If the predecessor has a single successor, then the edge isn't
2075 if (TI->getNumSuccessors() == 1)
2078 // If this pointer is always safe to load, or if we can prove that there
2079 // is already a load in the block, then we can move the load to the pred
2081 if (InVal->isDereferenceablePointer() ||
2082 isSafeToLoadUnconditionally(InVal, TI, MaxAlign, &TD))
2091 bool visitPHINode(PHINode &PN) {
2092 DEBUG(dbgs() << " original: " << PN << "\n");
2093 // We would like to compute a new pointer in only one place, but have it be
2094 // as local as possible to the PHI. To do that, we re-use the location of
2095 // the old pointer, which necessarily must be in the right position to
2096 // dominate the PHI.
2097 IRBuilder<> PtrBuilder(cast<Instruction>(OldPtr));
2099 SmallVector<LoadInst *, 4> Loads;
2100 if (!isSafePHIToSpeculate(PN, Loads)) {
2101 Value *NewPtr = getAdjustedAllocaPtr(PtrBuilder, OldPtr->getType());
2102 // Replace the operands which were using the old pointer.
2103 User::op_iterator OI = PN.op_begin(), OE = PN.op_end();
2104 for (; OI != OE; ++OI)
2108 DEBUG(dbgs() << " to: " << PN << "\n");
2109 deleteIfTriviallyDead(OldPtr);
2112 assert(!Loads.empty());
2114 Type *LoadTy = cast<PointerType>(PN.getType())->getElementType();
2115 IRBuilder<> PHIBuilder(&PN);
2116 PHINode *NewPN = PHIBuilder.CreatePHI(LoadTy, PN.getNumIncomingValues());
2117 NewPN->takeName(&PN);
2119 // Get the TBAA tag and alignment to use from one of the loads. It doesn't
2120 // matter which one we get and if any differ, it doesn't matter.
2121 LoadInst *SomeLoad = cast<LoadInst>(Loads.back());
2122 MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa);
2123 unsigned Align = SomeLoad->getAlignment();
2124 Value *NewPtr = getAdjustedAllocaPtr(PtrBuilder, OldPtr->getType());
2126 // Rewrite all loads of the PN to use the new PHI.
2128 LoadInst *LI = Loads.pop_back_val();
2129 LI->replaceAllUsesWith(NewPN);
2130 Pass.DeadInsts.push_back(LI);
2131 } while (!Loads.empty());
2133 // Inject loads into all of the pred blocks.
2134 for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
2135 BasicBlock *Pred = PN.getIncomingBlock(Idx);
2136 TerminatorInst *TI = Pred->getTerminator();
2137 Value *InVal = PN.getIncomingValue(Idx);
2138 IRBuilder<> PredBuilder(TI);
2140 // Map the value to the new alloca pointer if this was the old alloca
2142 bool ThisOperand = InVal == OldPtr;
2147 = PredBuilder.CreateLoad(InVal, getName(".sroa.speculate." +
2149 ++NumLoadsSpeculated;
2150 Load->setAlignment(Align);
2152 Load->setMetadata(LLVMContext::MD_tbaa, TBAATag);
2153 NewPN->addIncoming(Load, Pred);
2157 Instruction *OtherPtr = dyn_cast<Instruction>(InVal);
2159 // No uses to rewrite.
2162 // Try to lookup and rewrite any partition uses corresponding to this phi
2164 AllocaPartitioning::iterator PI
2165 = P.findPartitionForPHIOrSelectOperand(PN, OtherPtr);
2166 if (PI != P.end()) {
2167 // If the other pointer is within the partitioning, replace the PHI in
2168 // its uses with the load we just speculated, or add another load for
2169 // it to rewrite if we've already replaced the PHI.
2170 AllocaPartitioning::use_iterator UI
2171 = P.findPartitionUseForPHIOrSelectOperand(PN, OtherPtr);
2172 if (isa<PHINode>(*UI->User))
2175 AllocaPartitioning::PartitionUse OtherUse = *UI;
2176 OtherUse.User = Load;
2177 P.use_insert(PI, std::upper_bound(UI, P.use_end(PI), OtherUse),
2182 DEBUG(dbgs() << " speculated to: " << *NewPN << "\n");
2183 return NewPtr == &NewAI;
2186 /// Select instructions that use an alloca and are subsequently loaded can be
2187 /// rewritten to load both input pointers and then select between the result,
2188 /// allowing the load of the alloca to be promoted.
2190 /// %P2 = select i1 %cond, i32* %Alloca, i32* %Other
2191 /// %V = load i32* %P2
2193 /// %V1 = load i32* %Alloca -> will be mem2reg'd
2194 /// %V2 = load i32* %Other
2195 /// %V = select i1 %cond, i32 %V1, i32 %V2
2197 /// We can do this to a select if its only uses are loads and if the operand
2198 /// to the select can be loaded unconditionally.
2199 bool isSafeSelectToSpeculate(SelectInst &SI,
2200 SmallVectorImpl<LoadInst *> &Loads) {
2201 Value *TValue = SI.getTrueValue();
2202 Value *FValue = SI.getFalseValue();
2203 bool TDerefable = TValue->isDereferenceablePointer();
2204 bool FDerefable = FValue->isDereferenceablePointer();
2206 for (Value::use_iterator UI = SI.use_begin(), UE = SI.use_end();
2208 LoadInst *LI = dyn_cast<LoadInst>(*UI);
2209 if (LI == 0 || !LI->isSimple()) return false;
2211 // Both operands to the select need to be dereferencable, either
2212 // absolutely (e.g. allocas) or at this point because we can see other
2214 if (!TDerefable && !isSafeToLoadUnconditionally(TValue, LI,
2215 LI->getAlignment(), &TD))
2217 if (!FDerefable && !isSafeToLoadUnconditionally(FValue, LI,
2218 LI->getAlignment(), &TD))
2220 Loads.push_back(LI);
2226 bool visitSelectInst(SelectInst &SI) {
2227 DEBUG(dbgs() << " original: " << SI << "\n");
2228 IRBuilder<> IRB(&SI);
2230 // Find the operand we need to rewrite here.
2231 bool IsTrueVal = SI.getTrueValue() == OldPtr;
2233 assert(SI.getFalseValue() != OldPtr && "Pointer is both operands!");
2235 assert(SI.getFalseValue() == OldPtr && "Pointer isn't an operand!");
2236 Value *NewPtr = getAdjustedAllocaPtr(IRB, OldPtr->getType());
2238 // If the select isn't safe to speculate, just use simple logic to emit it.
2239 SmallVector<LoadInst *, 4> Loads;
2240 if (!isSafeSelectToSpeculate(SI, Loads)) {
2241 SI.setOperand(IsTrueVal ? 1 : 2, NewPtr);
2242 DEBUG(dbgs() << " to: " << SI << "\n");
2243 deleteIfTriviallyDead(OldPtr);
2247 Value *OtherPtr = IsTrueVal ? SI.getFalseValue() : SI.getTrueValue();
2248 AllocaPartitioning::iterator PI
2249 = P.findPartitionForPHIOrSelectOperand(SI, OtherPtr);
2250 AllocaPartitioning::PartitionUse OtherUse;
2251 if (PI != P.end()) {
2252 // If the other pointer is within the partitioning, remove the select
2253 // from its uses. We'll add in the new loads below.
2254 AllocaPartitioning::use_iterator UI
2255 = P.findPartitionUseForPHIOrSelectOperand(SI, OtherPtr);
2257 P.use_erase(PI, UI);
2260 Value *TV = IsTrueVal ? NewPtr : SI.getTrueValue();
2261 Value *FV = IsTrueVal ? SI.getFalseValue() : NewPtr;
2262 // Replace the loads of the select with a select of two loads.
2263 while (!Loads.empty()) {
2264 LoadInst *LI = Loads.pop_back_val();
2266 IRB.SetInsertPoint(LI);
2268 IRB.CreateLoad(TV, getName("." + LI->getName() + ".true"));
2270 IRB.CreateLoad(FV, getName("." + LI->getName() + ".false"));
2271 NumLoadsSpeculated += 2;
2272 if (PI != P.end()) {
2273 LoadInst *OtherLoad = IsTrueVal ? FL : TL;
2274 assert(OtherUse.Ptr == OtherLoad->getOperand(0));
2275 OtherUse.User = OtherLoad;
2276 P.use_insert(PI, P.use_end(PI), OtherUse);
2279 // Transfer alignment and TBAA info if present.
2280 TL->setAlignment(LI->getAlignment());
2281 FL->setAlignment(LI->getAlignment());
2282 if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) {
2283 TL->setMetadata(LLVMContext::MD_tbaa, Tag);
2284 FL->setMetadata(LLVMContext::MD_tbaa, Tag);
2287 Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL);
2289 DEBUG(dbgs() << " speculated to: " << *V << "\n");
2290 LI->replaceAllUsesWith(V);
2291 Pass.DeadInsts.push_back(LI);
2294 std::stable_sort(P.use_begin(PI), P.use_end(PI));
2296 deleteIfTriviallyDead(OldPtr);
2297 return NewPtr == &NewAI;
2303 /// \brief Try to find a partition of the aggregate type passed in for a given
2304 /// offset and size.
2306 /// This recurses through the aggregate type and tries to compute a subtype
2307 /// based on the offset and size. When the offset and size span a sub-section
2308 /// of an array, it will even compute a new array type for that sub-section.
2309 static Type *getTypePartition(const TargetData &TD, Type *Ty,
2310 uint64_t Offset, uint64_t Size) {
2311 if (Offset == 0 && TD.getTypeAllocSize(Ty) == Size)
2314 if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) {
2315 // We can't partition pointers...
2316 if (SeqTy->isPointerTy())
2319 Type *ElementTy = SeqTy->getElementType();
2320 uint64_t ElementSize = TD.getTypeAllocSize(ElementTy);
2321 uint64_t NumSkippedElements = Offset / ElementSize;
2322 if (ArrayType *ArrTy = dyn_cast<ArrayType>(SeqTy))
2323 if (NumSkippedElements >= ArrTy->getNumElements())
2325 if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy))
2326 if (NumSkippedElements >= VecTy->getNumElements())
2328 Offset -= NumSkippedElements * ElementSize;
2330 // First check if we need to recurse.
2331 if (Offset > 0 || Size < ElementSize) {
2332 // Bail if the partition ends in a different array element.
2333 if ((Offset + Size) > ElementSize)
2335 // Recurse through the element type trying to peel off offset bytes.
2336 return getTypePartition(TD, ElementTy, Offset, Size);
2338 assert(Offset == 0);
2340 if (Size == ElementSize)
2342 assert(Size > ElementSize);
2343 uint64_t NumElements = Size / ElementSize;
2344 if (NumElements * ElementSize != Size)
2346 return ArrayType::get(ElementTy, NumElements);
2349 StructType *STy = dyn_cast<StructType>(Ty);
2353 const StructLayout *SL = TD.getStructLayout(STy);
2354 if (Offset > SL->getSizeInBytes())
2356 uint64_t EndOffset = Offset + Size;
2357 if (EndOffset > SL->getSizeInBytes())
2360 unsigned Index = SL->getElementContainingOffset(Offset);
2361 if (SL->getElementOffset(Index) != Offset)
2362 return 0; // Inside of padding.
2363 Offset -= SL->getElementOffset(Index);
2365 Type *ElementTy = STy->getElementType(Index);
2366 uint64_t ElementSize = TD.getTypeAllocSize(ElementTy);
2367 if (Offset >= ElementSize)
2368 return 0; // The offset points into alignment padding.
2370 // See if any partition must be contained by the element.
2371 if (Offset > 0 || Size < ElementSize) {
2372 if ((Offset + Size) > ElementSize)
2374 // Bail if this is a poniter element, we can't recurse through them.
2375 if (ElementTy->isPointerTy())
2377 return getTypePartition(TD, ElementTy, Offset, Size);
2379 assert(Offset == 0);
2381 if (Size == ElementSize)
2384 StructType::element_iterator EI = STy->element_begin() + Index,
2385 EE = STy->element_end();
2386 if (EndOffset < SL->getSizeInBytes()) {
2387 unsigned EndIndex = SL->getElementContainingOffset(EndOffset);
2388 if (Index == EndIndex)
2389 return 0; // Within a single element and its padding.
2390 assert(Index < EndIndex);
2391 assert(Index + EndIndex <= STy->getNumElements());
2392 EE = STy->element_begin() + EndIndex;
2395 // Try to build up a sub-structure.
2396 SmallVector<Type *, 4> ElementTys;
2398 ElementTys.push_back(*EI++);
2400 StructType *SubTy = StructType::get(STy->getContext(), ElementTys,
2402 const StructLayout *SubSL = TD.getStructLayout(SubTy);
2403 if (Size == SubSL->getSizeInBytes())
2406 // FIXME: We could potentially recurse down through the last element in the
2407 // sub-struct to find a natural end point.
2411 /// \brief Rewrite an alloca partition's users.
2413 /// This routine drives both of the rewriting goals of the SROA pass. It tries
2414 /// to rewrite uses of an alloca partition to be conducive for SSA value
2415 /// promotion. If the partition needs a new, more refined alloca, this will
2416 /// build that new alloca, preserving as much type information as possible, and
2417 /// rewrite the uses of the old alloca to point at the new one and have the
2418 /// appropriate new offsets. It also evaluates how successful the rewrite was
2419 /// at enabling promotion and if it was successful queues the alloca to be
2421 bool SROA::rewriteAllocaPartition(AllocaInst &AI,
2422 AllocaPartitioning &P,
2423 AllocaPartitioning::iterator PI) {
2424 uint64_t AllocaSize = PI->EndOffset - PI->BeginOffset;
2425 if (P.use_begin(PI) == P.use_end(PI))
2426 return false; // No live uses left of this partition.
2428 // Try to compute a friendly type for this partition of the alloca. This
2429 // won't always succeed, in which case we fall back to a legal integer type
2430 // or an i8 array of an appropriate size.
2432 if (Type *PartitionTy = P.getCommonType(PI))
2433 if (TD->getTypeAllocSize(PartitionTy) >= AllocaSize)
2434 AllocaTy = PartitionTy;
2436 if (Type *PartitionTy = getTypePartition(*TD, AI.getAllocatedType(),
2437 PI->BeginOffset, AllocaSize))
2438 AllocaTy = PartitionTy;
2440 (AllocaTy->isArrayTy() &&
2441 AllocaTy->getArrayElementType()->isIntegerTy())) &&
2442 TD->isLegalInteger(AllocaSize * 8))
2443 AllocaTy = Type::getIntNTy(*C, AllocaSize * 8);
2445 AllocaTy = ArrayType::get(Type::getInt8Ty(*C), AllocaSize);
2446 assert(TD->getTypeAllocSize(AllocaTy) >= AllocaSize);
2448 // Check for the case where we're going to rewrite to a new alloca of the
2449 // exact same type as the original, and with the same access offsets. In that
2450 // case, re-use the existing alloca, but still run through the rewriter to
2451 // performe phi and select speculation.
2453 if (AllocaTy == AI.getAllocatedType()) {
2454 assert(PI->BeginOffset == 0 &&
2455 "Non-zero begin offset but same alloca type");
2456 assert(PI == P.begin() && "Begin offset is zero on later partition");
2459 // FIXME: The alignment here is overly conservative -- we could in many
2460 // cases get away with much weaker alignment constraints.
2461 NewAI = new AllocaInst(AllocaTy, 0, AI.getAlignment(),
2462 AI.getName() + ".sroa." + Twine(PI - P.begin()),
2467 DEBUG(dbgs() << "Rewriting alloca partition "
2468 << "[" << PI->BeginOffset << "," << PI->EndOffset << ") to: "
2471 AllocaPartitionRewriter Rewriter(*TD, P, PI, *this, AI, *NewAI,
2472 PI->BeginOffset, PI->EndOffset);
2473 DEBUG(dbgs() << " rewriting ");
2474 DEBUG(P.print(dbgs(), PI, ""));
2475 if (Rewriter.visitUsers(P.use_begin(PI), P.use_end(PI))) {
2476 DEBUG(dbgs() << " and queuing for promotion\n");
2477 PromotableAllocas.push_back(NewAI);
2478 } else if (NewAI != &AI) {
2479 // If we can't promote the alloca, iterate on it to check for new
2480 // refinements exposed by splitting the current alloca. Don't iterate on an
2481 // alloca which didn't actually change and didn't get promoted.
2482 Worklist.insert(NewAI);
2487 /// \brief Walks the partitioning of an alloca rewriting uses of each partition.
2488 bool SROA::splitAlloca(AllocaInst &AI, AllocaPartitioning &P) {
2489 bool Changed = false;
2490 for (AllocaPartitioning::iterator PI = P.begin(), PE = P.end(); PI != PE;
2492 Changed |= rewriteAllocaPartition(AI, P, PI);
2497 /// \brief Analyze an alloca for SROA.
2499 /// This analyzes the alloca to ensure we can reason about it, builds
2500 /// a partitioning of the alloca, and then hands it off to be split and
2501 /// rewritten as needed.
2502 bool SROA::runOnAlloca(AllocaInst &AI) {
2503 DEBUG(dbgs() << "SROA alloca: " << AI << "\n");
2504 ++NumAllocasAnalyzed;
2506 // Special case dead allocas, as they're trivial.
2507 if (AI.use_empty()) {
2508 AI.eraseFromParent();
2512 // Skip alloca forms that this analysis can't handle.
2513 if (AI.isArrayAllocation() || !AI.getAllocatedType()->isSized() ||
2514 TD->getTypeAllocSize(AI.getAllocatedType()) == 0)
2517 // First check if this is a non-aggregate type that we should simply promote.
2518 if (!AI.getAllocatedType()->isAggregateType() && isAllocaPromotable(&AI)) {
2519 DEBUG(dbgs() << " Trivially scalar type, queuing for promotion...\n");
2520 PromotableAllocas.push_back(&AI);
2524 // Build the partition set using a recursive instruction-visiting builder.
2525 AllocaPartitioning P(*TD, AI);
2526 DEBUG(P.print(dbgs()));
2530 // No partitions to split. Leave the dead alloca for a later pass to clean up.
2531 if (P.begin() == P.end())
2534 // Delete all the dead users of this alloca before splitting and rewriting it.
2535 bool Changed = false;
2536 for (AllocaPartitioning::dead_user_iterator DI = P.dead_user_begin(),
2537 DE = P.dead_user_end();
2540 (*DI)->replaceAllUsesWith(UndefValue::get((*DI)->getType()));
2541 DeadInsts.push_back(*DI);
2543 for (AllocaPartitioning::dead_op_iterator DO = P.dead_op_begin(),
2544 DE = P.dead_op_end();
2547 // Clobber the use with an undef value.
2548 **DO = UndefValue::get(OldV->getType());
2549 if (Instruction *OldI = dyn_cast<Instruction>(OldV))
2550 if (isInstructionTriviallyDead(OldI)) {
2552 DeadInsts.push_back(OldI);
2556 return splitAlloca(AI, P) || Changed;
2559 void SROA::deleteDeadInstructions() {
2560 DeadSplitInsts.clear();
2561 while (!DeadInsts.empty()) {
2562 Instruction *I = DeadInsts.pop_back_val();
2563 DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
2565 for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
2566 if (Instruction *U = dyn_cast<Instruction>(*OI)) {
2567 // Zero out the operand and see if it becomes trivially dead.
2569 if (isInstructionTriviallyDead(U))
2570 DeadInsts.push_back(U);
2573 if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
2574 DeletedAllocas.insert(AI);
2577 I->eraseFromParent();
2582 /// \brief A predicate to test whether an alloca belongs to a set.
2583 class IsAllocaInSet {
2584 typedef SmallPtrSet<AllocaInst *, 4> SetType;
2588 IsAllocaInSet(const SetType &Set) : Set(Set) {}
2589 bool operator()(AllocaInst *AI) { return Set.count(AI); }
2593 bool SROA::runOnFunction(Function &F) {
2594 DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
2595 C = &F.getContext();
2596 TD = getAnalysisIfAvailable<TargetData>();
2598 DEBUG(dbgs() << " Skipping SROA -- no target data!\n");
2601 DT = &getAnalysis<DominatorTree>();
2603 BasicBlock &EntryBB = F.getEntryBlock();
2604 for (BasicBlock::iterator I = EntryBB.begin(), E = llvm::prior(EntryBB.end());
2606 if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
2607 Worklist.insert(AI);
2609 bool Changed = false;
2610 while (!Worklist.empty()) {
2611 Changed |= runOnAlloca(*Worklist.pop_back_val());
2612 deleteDeadInstructions();
2613 if (!DeletedAllocas.empty()) {
2614 PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(),
2615 PromotableAllocas.end(),
2616 IsAllocaInSet(DeletedAllocas)),
2617 PromotableAllocas.end());
2618 DeletedAllocas.clear();
2622 if (!PromotableAllocas.empty()) {
2623 DEBUG(dbgs() << "Promoting allocas with mem2reg...\n");
2624 PromoteMemToReg(PromotableAllocas, *DT);
2626 NumPromoted += PromotableAllocas.size();
2627 PromotableAllocas.clear();
2633 void SROA::getAnalysisUsage(AnalysisUsage &AU) const {
2634 AU.addRequired<DominatorTree>();
2635 AU.setPreservesCFG();