LLVM API Documentation

SROA.cpp
Go to the documentation of this file.
00001 //===- SROA.cpp - Scalar Replacement Of Aggregates ------------------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 /// \file
00010 /// This transformation implements the well known scalar replacement of
00011 /// aggregates transformation. It tries to identify promotable elements of an
00012 /// aggregate alloca, and promote them to registers. It will also try to
00013 /// convert uses of an element (or set of elements) of an alloca into a vector
00014 /// or bitfield-style integer scalar if appropriate.
00015 ///
00016 /// It works to do this with minimal slicing of the alloca so that regions
00017 /// which are merely transferred in and out of external memory remain unchanged
00018 /// and are not decomposed to scalar code.
00019 ///
00020 /// Because this also performs alloca promotion, it can be thought of as also
00021 /// serving the purpose of SSA formation. The algorithm iterates on the
00022 /// function until all opportunities for promotion have been realized.
00023 ///
00024 //===----------------------------------------------------------------------===//
00025 
00026 #include "llvm/Transforms/Scalar.h"
00027 #include "llvm/ADT/STLExtras.h"
00028 #include "llvm/ADT/SetVector.h"
00029 #include "llvm/ADT/SmallVector.h"
00030 #include "llvm/ADT/Statistic.h"
00031 #include "llvm/Analysis/AssumptionTracker.h"
00032 #include "llvm/Analysis/Loads.h"
00033 #include "llvm/Analysis/PtrUseVisitor.h"
00034 #include "llvm/Analysis/ValueTracking.h"
00035 #include "llvm/IR/Constants.h"
00036 #include "llvm/IR/DIBuilder.h"
00037 #include "llvm/IR/DataLayout.h"
00038 #include "llvm/IR/DebugInfo.h"
00039 #include "llvm/IR/DerivedTypes.h"
00040 #include "llvm/IR/Dominators.h"
00041 #include "llvm/IR/Function.h"
00042 #include "llvm/IR/IRBuilder.h"
00043 #include "llvm/IR/InstVisitor.h"
00044 #include "llvm/IR/Instructions.h"
00045 #include "llvm/IR/IntrinsicInst.h"
00046 #include "llvm/IR/LLVMContext.h"
00047 #include "llvm/IR/Operator.h"
00048 #include "llvm/Pass.h"
00049 #include "llvm/Support/CommandLine.h"
00050 #include "llvm/Support/Compiler.h"
00051 #include "llvm/Support/Debug.h"
00052 #include "llvm/Support/ErrorHandling.h"
00053 #include "llvm/Support/MathExtras.h"
00054 #include "llvm/Support/TimeValue.h"
00055 #include "llvm/Support/raw_ostream.h"
00056 #include "llvm/Transforms/Utils/Local.h"
00057 #include "llvm/Transforms/Utils/PromoteMemToReg.h"
00058 #include "llvm/Transforms/Utils/SSAUpdater.h"
00059 
00060 #if __cplusplus >= 201103L && !defined(NDEBUG)
00061 // We only use this for a debug check in C++11
00062 #include <random>
00063 #endif
00064 
00065 using namespace llvm;
00066 
00067 #define DEBUG_TYPE "sroa"
00068 
00069 STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
00070 STATISTIC(NumAllocaPartitions, "Number of alloca partitions formed");
00071 STATISTIC(MaxPartitionsPerAlloca, "Maximum number of partitions per alloca");
00072 STATISTIC(NumAllocaPartitionUses, "Number of alloca partition uses rewritten");
00073 STATISTIC(MaxUsesPerAllocaPartition, "Maximum number of uses of a partition");
00074 STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced");
00075 STATISTIC(NumPromoted, "Number of allocas promoted to SSA values");
00076 STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion");
00077 STATISTIC(NumDeleted, "Number of instructions deleted");
00078 STATISTIC(NumVectorized, "Number of vectorized aggregates");
00079 
00080 /// Hidden option to force the pass to not use DomTree and mem2reg, instead
00081 /// forming SSA values through the SSAUpdater infrastructure.
00082 static cl::opt<bool>
00083 ForceSSAUpdater("force-ssa-updater", cl::init(false), cl::Hidden);
00084 
00085 /// Hidden option to enable randomly shuffling the slices to help uncover
00086 /// instability in their order.
00087 static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
00088                                              cl::init(false), cl::Hidden);
00089 
00090 /// Hidden option to experiment with completely strict handling of inbounds
00091 /// GEPs.
00092 static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds",
00093                                         cl::init(false), cl::Hidden);
00094 
00095 namespace {
00096 /// \brief A custom IRBuilder inserter which prefixes all names if they are
00097 /// preserved.
00098 template <bool preserveNames = true>
00099 class IRBuilderPrefixedInserter :
00100     public IRBuilderDefaultInserter<preserveNames> {
00101   std::string Prefix;
00102 
00103 public:
00104   void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
00105 
00106 protected:
00107   void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
00108                     BasicBlock::iterator InsertPt) const {
00109     IRBuilderDefaultInserter<preserveNames>::InsertHelper(
00110         I, Name.isTriviallyEmpty() ? Name : Prefix + Name, BB, InsertPt);
00111   }
00112 };
00113 
00114 // Specialization for not preserving the name is trivial.
00115 template <>
00116 class IRBuilderPrefixedInserter<false> :
00117     public IRBuilderDefaultInserter<false> {
00118 public:
00119   void SetNamePrefix(const Twine &P) {}
00120 };
00121 
00122 /// \brief Provide a typedef for IRBuilder that drops names in release builds.
00123 #ifndef NDEBUG
00124 typedef llvm::IRBuilder<true, ConstantFolder,
00125                         IRBuilderPrefixedInserter<true> > IRBuilderTy;
00126 #else
00127 typedef llvm::IRBuilder<false, ConstantFolder,
00128                         IRBuilderPrefixedInserter<false> > IRBuilderTy;
00129 #endif
00130 }
00131 
00132 namespace {
00133 /// \brief A used slice of an alloca.
00134 ///
00135 /// This structure represents a slice of an alloca used by some instruction. It
00136 /// stores both the begin and end offsets of this use, a pointer to the use
00137 /// itself, and a flag indicating whether we can classify the use as splittable
00138 /// or not when forming partitions of the alloca.
00139 class Slice {
00140   /// \brief The beginning offset of the range.
00141   uint64_t BeginOffset;
00142 
00143   /// \brief The ending offset, not included in the range.
00144   uint64_t EndOffset;
00145 
00146   /// \brief Storage for both the use of this slice and whether it can be
00147   /// split.
00148   PointerIntPair<Use *, 1, bool> UseAndIsSplittable;
00149 
00150 public:
00151   Slice() : BeginOffset(), EndOffset() {}
00152   Slice(uint64_t BeginOffset, uint64_t EndOffset, Use *U, bool IsSplittable)
00153       : BeginOffset(BeginOffset), EndOffset(EndOffset),
00154         UseAndIsSplittable(U, IsSplittable) {}
00155 
00156   uint64_t beginOffset() const { return BeginOffset; }
00157   uint64_t endOffset() const { return EndOffset; }
00158 
00159   bool isSplittable() const { return UseAndIsSplittable.getInt(); }
00160   void makeUnsplittable() { UseAndIsSplittable.setInt(false); }
00161 
00162   Use *getUse() const { return UseAndIsSplittable.getPointer(); }
00163 
00164   bool isDead() const { return getUse() == nullptr; }
00165   void kill() { UseAndIsSplittable.setPointer(nullptr); }
00166 
00167   /// \brief Support for ordering ranges.
00168   ///
00169   /// This provides an ordering over ranges such that start offsets are
00170   /// always increasing, and within equal start offsets, the end offsets are
00171   /// decreasing. Thus the spanning range comes first in a cluster with the
00172   /// same start position.
00173   bool operator<(const Slice &RHS) const {
00174     if (beginOffset() < RHS.beginOffset()) return true;
00175     if (beginOffset() > RHS.beginOffset()) return false;
00176     if (isSplittable() != RHS.isSplittable()) return !isSplittable();
00177     if (endOffset() > RHS.endOffset()) return true;
00178     return false;
00179   }
00180 
00181   /// \brief Support comparison with a single offset to allow binary searches.
00182   friend LLVM_ATTRIBUTE_UNUSED bool operator<(const Slice &LHS,
00183                                               uint64_t RHSOffset) {
00184     return LHS.beginOffset() < RHSOffset;
00185   }
00186   friend LLVM_ATTRIBUTE_UNUSED bool operator<(uint64_t LHSOffset,
00187                                               const Slice &RHS) {
00188     return LHSOffset < RHS.beginOffset();
00189   }
00190 
00191   bool operator==(const Slice &RHS) const {
00192     return isSplittable() == RHS.isSplittable() &&
00193            beginOffset() == RHS.beginOffset() && endOffset() == RHS.endOffset();
00194   }
00195   bool operator!=(const Slice &RHS) const { return !operator==(RHS); }
00196 };
00197 } // end anonymous namespace
00198 
00199 namespace llvm {
00200 template <typename T> struct isPodLike;
00201 template <> struct isPodLike<Slice> {
00202    static const bool value = true;
00203 };
00204 }
00205 
00206 namespace {
00207 /// \brief Representation of the alloca slices.
00208 ///
00209 /// This class represents the slices of an alloca which are formed by its
00210 /// various uses. If a pointer escapes, we can't fully build a representation
00211 /// for the slices used and we reflect that in this structure. The uses are
00212 /// stored, sorted by increasing beginning offset and with unsplittable slices
00213 /// starting at a particular offset before splittable slices.
00214 class AllocaSlices {
00215 public:
00216   /// \brief Construct the slices of a particular alloca.
00217   AllocaSlices(const DataLayout &DL, AllocaInst &AI);
00218 
00219   /// \brief Test whether a pointer to the allocation escapes our analysis.
00220   ///
00221   /// If this is true, the slices are never fully built and should be
00222   /// ignored.
00223   bool isEscaped() const { return PointerEscapingInstr; }
00224 
00225   /// \brief Support for iterating over the slices.
00226   /// @{
00227   typedef SmallVectorImpl<Slice>::iterator iterator;
00228   iterator begin() { return Slices.begin(); }
00229   iterator end() { return Slices.end(); }
00230 
00231   typedef SmallVectorImpl<Slice>::const_iterator const_iterator;
00232   const_iterator begin() const { return Slices.begin(); }
00233   const_iterator end() const { return Slices.end(); }
00234   /// @}
00235 
00236   /// \brief Allow iterating the dead users for this alloca.
00237   ///
00238   /// These are instructions which will never actually use the alloca as they
00239   /// are outside the allocated range. They are safe to replace with undef and
00240   /// delete.
00241   /// @{
00242   typedef SmallVectorImpl<Instruction *>::const_iterator dead_user_iterator;
00243   dead_user_iterator dead_user_begin() const { return DeadUsers.begin(); }
00244   dead_user_iterator dead_user_end() const { return DeadUsers.end(); }
00245   /// @}
00246 
00247   /// \brief Allow iterating the dead expressions referring to this alloca.
00248   ///
00249   /// These are operands which have cannot actually be used to refer to the
00250   /// alloca as they are outside its range and the user doesn't correct for
00251   /// that. These mostly consist of PHI node inputs and the like which we just
00252   /// need to replace with undef.
00253   /// @{
00254   typedef SmallVectorImpl<Use *>::const_iterator dead_op_iterator;
00255   dead_op_iterator dead_op_begin() const { return DeadOperands.begin(); }
00256   dead_op_iterator dead_op_end() const { return DeadOperands.end(); }
00257   /// @}
00258 
00259 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
00260   void print(raw_ostream &OS, const_iterator I, StringRef Indent = "  ") const;
00261   void printSlice(raw_ostream &OS, const_iterator I,
00262                   StringRef Indent = "  ") const;
00263   void printUse(raw_ostream &OS, const_iterator I,
00264                 StringRef Indent = "  ") const;
00265   void print(raw_ostream &OS) const;
00266   void dump(const_iterator I) const;
00267   void dump() const;
00268 #endif
00269 
00270 private:
00271   template <typename DerivedT, typename RetT = void> class BuilderBase;
00272   class SliceBuilder;
00273   friend class AllocaSlices::SliceBuilder;
00274 
00275 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
00276   /// \brief Handle to alloca instruction to simplify method interfaces.
00277   AllocaInst &AI;
00278 #endif
00279 
00280   /// \brief The instruction responsible for this alloca not having a known set
00281   /// of slices.
00282   ///
00283   /// When an instruction (potentially) escapes the pointer to the alloca, we
00284   /// store a pointer to that here and abort trying to form slices of the
00285   /// alloca. This will be null if the alloca slices are analyzed successfully.
00286   Instruction *PointerEscapingInstr;
00287 
00288   /// \brief The slices of the alloca.
00289   ///
00290   /// We store a vector of the slices formed by uses of the alloca here. This
00291   /// vector is sorted by increasing begin offset, and then the unsplittable
00292   /// slices before the splittable ones. See the Slice inner class for more
00293   /// details.
00294   SmallVector<Slice, 8> Slices;
00295 
00296   /// \brief Instructions which will become dead if we rewrite the alloca.
00297   ///
00298   /// Note that these are not separated by slice. This is because we expect an
00299   /// alloca to be completely rewritten or not rewritten at all. If rewritten,
00300   /// all these instructions can simply be removed and replaced with undef as
00301   /// they come from outside of the allocated space.
00302   SmallVector<Instruction *, 8> DeadUsers;
00303 
00304   /// \brief Operands which will become dead if we rewrite the alloca.
00305   ///
00306   /// These are operands that in their particular use can be replaced with
00307   /// undef when we rewrite the alloca. These show up in out-of-bounds inputs
00308   /// to PHI nodes and the like. They aren't entirely dead (there might be
00309   /// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we
00310   /// want to swap this particular input for undef to simplify the use lists of
00311   /// the alloca.
00312   SmallVector<Use *, 8> DeadOperands;
00313 };
00314 }
00315 
00316 static Value *foldSelectInst(SelectInst &SI) {
00317   // If the condition being selected on is a constant or the same value is
00318   // being selected between, fold the select. Yes this does (rarely) happen
00319   // early on.
00320   if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition()))
00321     return SI.getOperand(1+CI->isZero());
00322   if (SI.getOperand(1) == SI.getOperand(2))
00323     return SI.getOperand(1);
00324 
00325   return nullptr;
00326 }
00327 
00328 /// \brief A helper that folds a PHI node or a select.
00329 static Value *foldPHINodeOrSelectInst(Instruction &I) {
00330   if (PHINode *PN = dyn_cast<PHINode>(&I)) {
00331     // If PN merges together the same value, return that value.
00332     return PN->hasConstantValue();
00333   }
00334   return foldSelectInst(cast<SelectInst>(I));
00335 }
00336 
00337 /// \brief Builder for the alloca slices.
00338 ///
00339 /// This class builds a set of alloca slices by recursively visiting the uses
00340 /// of an alloca and making a slice for each load and store at each offset.
00341 class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> {
00342   friend class PtrUseVisitor<SliceBuilder>;
00343   friend class InstVisitor<SliceBuilder>;
00344   typedef PtrUseVisitor<SliceBuilder> Base;
00345 
00346   const uint64_t AllocSize;
00347   AllocaSlices &S;
00348 
00349   SmallDenseMap<Instruction *, unsigned> MemTransferSliceMap;
00350   SmallDenseMap<Instruction *, uint64_t> PHIOrSelectSizes;
00351 
00352   /// \brief Set to de-duplicate dead instructions found in the use walk.
00353   SmallPtrSet<Instruction *, 4> VisitedDeadInsts;
00354 
00355 public:
00356   SliceBuilder(const DataLayout &DL, AllocaInst &AI, AllocaSlices &S)
00357       : PtrUseVisitor<SliceBuilder>(DL),
00358         AllocSize(DL.getTypeAllocSize(AI.getAllocatedType())), S(S) {}
00359 
00360 private:
00361   void markAsDead(Instruction &I) {
00362     if (VisitedDeadInsts.insert(&I))
00363       S.DeadUsers.push_back(&I);
00364   }
00365 
00366   void insertUse(Instruction &I, const APInt &Offset, uint64_t Size,
00367                  bool IsSplittable = false) {
00368     // Completely skip uses which have a zero size or start either before or
00369     // past the end of the allocation.
00370     if (Size == 0 || Offset.uge(AllocSize)) {
00371       DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
00372                    << " which has zero size or starts outside of the "
00373                    << AllocSize << " byte alloca:\n"
00374                    << "    alloca: " << S.AI << "\n"
00375                    << "       use: " << I << "\n");
00376       return markAsDead(I);
00377     }
00378 
00379     uint64_t BeginOffset = Offset.getZExtValue();
00380     uint64_t EndOffset = BeginOffset + Size;
00381 
00382     // Clamp the end offset to the end of the allocation. Note that this is
00383     // formulated to handle even the case where "BeginOffset + Size" overflows.
00384     // This may appear superficially to be something we could ignore entirely,
00385     // but that is not so! There may be widened loads or PHI-node uses where
00386     // some instructions are dead but not others. We can't completely ignore
00387     // them, and so have to record at least the information here.
00388     assert(AllocSize >= BeginOffset); // Established above.
00389     if (Size > AllocSize - BeginOffset) {
00390       DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @" << Offset
00391                    << " to remain within the " << AllocSize << " byte alloca:\n"
00392                    << "    alloca: " << S.AI << "\n"
00393                    << "       use: " << I << "\n");
00394       EndOffset = AllocSize;
00395     }
00396 
00397     S.Slices.push_back(Slice(BeginOffset, EndOffset, U, IsSplittable));
00398   }
00399 
00400   void visitBitCastInst(BitCastInst &BC) {
00401     if (BC.use_empty())
00402       return markAsDead(BC);
00403 
00404     return Base::visitBitCastInst(BC);
00405   }
00406 
00407   void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
00408     if (GEPI.use_empty())
00409       return markAsDead(GEPI);
00410 
00411     if (SROAStrictInbounds && GEPI.isInBounds()) {
00412       // FIXME: This is a manually un-factored variant of the basic code inside
00413       // of GEPs with checking of the inbounds invariant specified in the
00414       // langref in a very strict sense. If we ever want to enable
00415       // SROAStrictInbounds, this code should be factored cleanly into
00416       // PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds
00417       // by writing out the code here where we have tho underlying allocation
00418       // size readily available.
00419       APInt GEPOffset = Offset;
00420       for (gep_type_iterator GTI = gep_type_begin(GEPI),
00421                              GTE = gep_type_end(GEPI);
00422            GTI != GTE; ++GTI) {
00423         ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
00424         if (!OpC)
00425           break;
00426 
00427         // Handle a struct index, which adds its field offset to the pointer.
00428         if (StructType *STy = dyn_cast<StructType>(*GTI)) {
00429           unsigned ElementIdx = OpC->getZExtValue();
00430           const StructLayout *SL = DL.getStructLayout(STy);
00431           GEPOffset +=
00432               APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx));
00433         } else {
00434           // For array or vector indices, scale the index by the size of the type.
00435           APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
00436           GEPOffset += Index * APInt(Offset.getBitWidth(),
00437                                      DL.getTypeAllocSize(GTI.getIndexedType()));
00438         }
00439 
00440         // If this index has computed an intermediate pointer which is not
00441         // inbounds, then the result of the GEP is a poison value and we can
00442         // delete it and all uses.
00443         if (GEPOffset.ugt(AllocSize))
00444           return markAsDead(GEPI);
00445       }
00446     }
00447 
00448     return Base::visitGetElementPtrInst(GEPI);
00449   }
00450 
00451   void handleLoadOrStore(Type *Ty, Instruction &I, const APInt &Offset,
00452                          uint64_t Size, bool IsVolatile) {
00453     // We allow splitting of loads and stores where the type is an integer type
00454     // and cover the entire alloca. This prevents us from splitting over
00455     // eagerly.
00456     // FIXME: In the great blue eventually, we should eagerly split all integer
00457     // loads and stores, and then have a separate step that merges adjacent
00458     // alloca partitions into a single partition suitable for integer widening.
00459     // Or we should skip the merge step and rely on GVN and other passes to
00460     // merge adjacent loads and stores that survive mem2reg.
00461     bool IsSplittable =
00462         Ty->isIntegerTy() && !IsVolatile && Offset == 0 && Size >= AllocSize;
00463 
00464     insertUse(I, Offset, Size, IsSplittable);
00465   }
00466 
00467   void visitLoadInst(LoadInst &LI) {
00468     assert((!LI.isSimple() || LI.getType()->isSingleValueType()) &&
00469            "All simple FCA loads should have been pre-split");
00470 
00471     if (!IsOffsetKnown)
00472       return PI.setAborted(&LI);
00473 
00474     uint64_t Size = DL.getTypeStoreSize(LI.getType());
00475     return handleLoadOrStore(LI.getType(), LI, Offset, Size, LI.isVolatile());
00476   }
00477 
00478   void visitStoreInst(StoreInst &SI) {
00479     Value *ValOp = SI.getValueOperand();
00480     if (ValOp == *U)
00481       return PI.setEscapedAndAborted(&SI);
00482     if (!IsOffsetKnown)
00483       return PI.setAborted(&SI);
00484 
00485     uint64_t Size = DL.getTypeStoreSize(ValOp->getType());
00486 
00487     // If this memory access can be shown to *statically* extend outside the
00488     // bounds of of the allocation, it's behavior is undefined, so simply
00489     // ignore it. Note that this is more strict than the generic clamping
00490     // behavior of insertUse. We also try to handle cases which might run the
00491     // risk of overflow.
00492     // FIXME: We should instead consider the pointer to have escaped if this
00493     // function is being instrumented for addressing bugs or race conditions.
00494     if (Size > AllocSize || Offset.ugt(AllocSize - Size)) {
00495       DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte store @" << Offset
00496                    << " which extends past the end of the " << AllocSize
00497                    << " byte alloca:\n"
00498                    << "    alloca: " << S.AI << "\n"
00499                    << "       use: " << SI << "\n");
00500       return markAsDead(SI);
00501     }
00502 
00503     assert((!SI.isSimple() || ValOp->getType()->isSingleValueType()) &&
00504            "All simple FCA stores should have been pre-split");
00505     handleLoadOrStore(ValOp->getType(), SI, Offset, Size, SI.isVolatile());
00506   }
00507 
00508 
00509   void visitMemSetInst(MemSetInst &II) {
00510     assert(II.getRawDest() == *U && "Pointer use is not the destination?");
00511     ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
00512     if ((Length && Length->getValue() == 0) ||
00513         (IsOffsetKnown && Offset.uge(AllocSize)))
00514       // Zero-length mem transfer intrinsics can be ignored entirely.
00515       return markAsDead(II);
00516 
00517     if (!IsOffsetKnown)
00518       return PI.setAborted(&II);
00519 
00520     insertUse(II, Offset,
00521               Length ? Length->getLimitedValue()
00522                      : AllocSize - Offset.getLimitedValue(),
00523               (bool)Length);
00524   }
00525 
00526   void visitMemTransferInst(MemTransferInst &II) {
00527     ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
00528     if (Length && Length->getValue() == 0)
00529       // Zero-length mem transfer intrinsics can be ignored entirely.
00530       return markAsDead(II);
00531 
00532     // Because we can visit these intrinsics twice, also check to see if the
00533     // first time marked this instruction as dead. If so, skip it.
00534     if (VisitedDeadInsts.count(&II))
00535       return;
00536 
00537     if (!IsOffsetKnown)
00538       return PI.setAborted(&II);
00539 
00540     // This side of the transfer is completely out-of-bounds, and so we can
00541     // nuke the entire transfer. However, we also need to nuke the other side
00542     // if already added to our partitions.
00543     // FIXME: Yet another place we really should bypass this when
00544     // instrumenting for ASan.
00545     if (Offset.uge(AllocSize)) {
00546       SmallDenseMap<Instruction *, unsigned>::iterator MTPI = MemTransferSliceMap.find(&II);
00547       if (MTPI != MemTransferSliceMap.end())
00548         S.Slices[MTPI->second].kill();
00549       return markAsDead(II);
00550     }
00551 
00552     uint64_t RawOffset = Offset.getLimitedValue();
00553     uint64_t Size = Length ? Length->getLimitedValue()
00554                            : AllocSize - RawOffset;
00555 
00556     // Check for the special case where the same exact value is used for both
00557     // source and dest.
00558     if (*U == II.getRawDest() && *U == II.getRawSource()) {
00559       // For non-volatile transfers this is a no-op.
00560       if (!II.isVolatile())
00561         return markAsDead(II);
00562 
00563       return insertUse(II, Offset, Size, /*IsSplittable=*/false);
00564     }
00565 
00566     // If we have seen both source and destination for a mem transfer, then
00567     // they both point to the same alloca.
00568     bool Inserted;
00569     SmallDenseMap<Instruction *, unsigned>::iterator MTPI;
00570     std::tie(MTPI, Inserted) =
00571         MemTransferSliceMap.insert(std::make_pair(&II, S.Slices.size()));
00572     unsigned PrevIdx = MTPI->second;
00573     if (!Inserted) {
00574       Slice &PrevP = S.Slices[PrevIdx];
00575 
00576       // Check if the begin offsets match and this is a non-volatile transfer.
00577       // In that case, we can completely elide the transfer.
00578       if (!II.isVolatile() && PrevP.beginOffset() == RawOffset) {
00579         PrevP.kill();
00580         return markAsDead(II);
00581       }
00582 
00583       // Otherwise we have an offset transfer within the same alloca. We can't
00584       // split those.
00585       PrevP.makeUnsplittable();
00586     }
00587 
00588     // Insert the use now that we've fixed up the splittable nature.
00589     insertUse(II, Offset, Size, /*IsSplittable=*/Inserted && Length);
00590 
00591     // Check that we ended up with a valid index in the map.
00592     assert(S.Slices[PrevIdx].getUse()->getUser() == &II &&
00593            "Map index doesn't point back to a slice with this user.");
00594   }
00595 
00596   // Disable SRoA for any intrinsics except for lifetime invariants.
00597   // FIXME: What about debug intrinsics? This matches old behavior, but
00598   // doesn't make sense.
00599   void visitIntrinsicInst(IntrinsicInst &II) {
00600     if (!IsOffsetKnown)
00601       return PI.setAborted(&II);
00602 
00603     if (II.getIntrinsicID() == Intrinsic::lifetime_start ||
00604         II.getIntrinsicID() == Intrinsic::lifetime_end) {
00605       ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
00606       uint64_t Size = std::min(AllocSize - Offset.getLimitedValue(),
00607                                Length->getLimitedValue());
00608       insertUse(II, Offset, Size, true);
00609       return;
00610     }
00611 
00612     Base::visitIntrinsicInst(II);
00613   }
00614 
00615   Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) {
00616     // We consider any PHI or select that results in a direct load or store of
00617     // the same offset to be a viable use for slicing purposes. These uses
00618     // are considered unsplittable and the size is the maximum loaded or stored
00619     // size.
00620     SmallPtrSet<Instruction *, 4> Visited;
00621     SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
00622     Visited.insert(Root);
00623     Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
00624     // If there are no loads or stores, the access is dead. We mark that as
00625     // a size zero access.
00626     Size = 0;
00627     do {
00628       Instruction *I, *UsedI;
00629       std::tie(UsedI, I) = Uses.pop_back_val();
00630 
00631       if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
00632         Size = std::max(Size, DL.getTypeStoreSize(LI->getType()));
00633         continue;
00634       }
00635       if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
00636         Value *Op = SI->getOperand(0);
00637         if (Op == UsedI)
00638           return SI;
00639         Size = std::max(Size, DL.getTypeStoreSize(Op->getType()));
00640         continue;
00641       }
00642 
00643       if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
00644         if (!GEP->hasAllZeroIndices())
00645           return GEP;
00646       } else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) &&
00647                  !isa<SelectInst>(I)) {
00648         return I;
00649       }
00650 
00651       for (User *U : I->users())
00652         if (Visited.insert(cast<Instruction>(U)))
00653           Uses.push_back(std::make_pair(I, cast<Instruction>(U)));
00654     } while (!Uses.empty());
00655 
00656     return nullptr;
00657   }
00658 
00659   void visitPHINodeOrSelectInst(Instruction &I) {
00660     assert(isa<PHINode>(I) || isa<SelectInst>(I));
00661     if (I.use_empty())
00662       return markAsDead(I);
00663 
00664     // TODO: We could use SimplifyInstruction here to fold PHINodes and
00665     // SelectInsts. However, doing so requires to change the current
00666     // dead-operand-tracking mechanism. For instance, suppose neither loading
00667     // from %U nor %other traps. Then "load (select undef, %U, %other)" does not
00668     // trap either.  However, if we simply replace %U with undef using the
00669     // current dead-operand-tracking mechanism, "load (select undef, undef,
00670     // %other)" may trap because the select may return the first operand
00671     // "undef".
00672     if (Value *Result = foldPHINodeOrSelectInst(I)) {
00673       if (Result == *U)
00674         // If the result of the constant fold will be the pointer, recurse
00675         // through the PHI/select as if we had RAUW'ed it.
00676         enqueueUsers(I);
00677       else
00678         // Otherwise the operand to the PHI/select is dead, and we can replace
00679         // it with undef.
00680         S.DeadOperands.push_back(U);
00681 
00682       return;
00683     }
00684 
00685     if (!IsOffsetKnown)
00686       return PI.setAborted(&I);
00687 
00688     // See if we already have computed info on this node.
00689     uint64_t &Size = PHIOrSelectSizes[&I];
00690     if (!Size) {
00691       // This is a new PHI/Select, check for an unsafe use of it.
00692       if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&I, Size))
00693         return PI.setAborted(UnsafeI);
00694     }
00695 
00696     // For PHI and select operands outside the alloca, we can't nuke the entire
00697     // phi or select -- the other side might still be relevant, so we special
00698     // case them here and use a separate structure to track the operands
00699     // themselves which should be replaced with undef.
00700     // FIXME: This should instead be escaped in the event we're instrumenting
00701     // for address sanitization.
00702     if (Offset.uge(AllocSize)) {
00703       S.DeadOperands.push_back(U);
00704       return;
00705     }
00706 
00707     insertUse(I, Offset, Size);
00708   }
00709 
00710   void visitPHINode(PHINode &PN) {
00711     visitPHINodeOrSelectInst(PN);
00712   }
00713 
00714   void visitSelectInst(SelectInst &SI) {
00715     visitPHINodeOrSelectInst(SI);
00716   }
00717 
00718   /// \brief Disable SROA entirely if there are unhandled users of the alloca.
00719   void visitInstruction(Instruction &I) {
00720     PI.setAborted(&I);
00721   }
00722 };
00723 
00724 AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI)
00725     :
00726 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
00727       AI(AI),
00728 #endif
00729       PointerEscapingInstr(nullptr) {
00730   SliceBuilder PB(DL, AI, *this);
00731   SliceBuilder::PtrInfo PtrI = PB.visitPtr(AI);
00732   if (PtrI.isEscaped() || PtrI.isAborted()) {
00733     // FIXME: We should sink the escape vs. abort info into the caller nicely,
00734     // possibly by just storing the PtrInfo in the AllocaSlices.
00735     PointerEscapingInstr = PtrI.getEscapingInst() ? PtrI.getEscapingInst()
00736                                                   : PtrI.getAbortingInst();
00737     assert(PointerEscapingInstr && "Did not track a bad instruction");
00738     return;
00739   }
00740 
00741   Slices.erase(std::remove_if(Slices.begin(), Slices.end(),
00742                               std::mem_fun_ref(&Slice::isDead)),
00743                Slices.end());
00744 
00745 #if __cplusplus >= 201103L && !defined(NDEBUG)
00746   if (SROARandomShuffleSlices) {
00747     std::mt19937 MT(static_cast<unsigned>(sys::TimeValue::now().msec()));
00748     std::shuffle(Slices.begin(), Slices.end(), MT);
00749   }
00750 #endif
00751 
00752   // Sort the uses. This arranges for the offsets to be in ascending order,
00753   // and the sizes to be in descending order.
00754   std::sort(Slices.begin(), Slices.end());
00755 }
00756 
00757 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
00758 
00759 void AllocaSlices::print(raw_ostream &OS, const_iterator I,
00760                          StringRef Indent) const {
00761   printSlice(OS, I, Indent);
00762   printUse(OS, I, Indent);
00763 }
00764 
00765 void AllocaSlices::printSlice(raw_ostream &OS, const_iterator I,
00766                               StringRef Indent) const {
00767   OS << Indent << "[" << I->beginOffset() << "," << I->endOffset() << ")"
00768      << " slice #" << (I - begin())
00769      << (I->isSplittable() ? " (splittable)" : "") << "\n";
00770 }
00771 
00772 void AllocaSlices::printUse(raw_ostream &OS, const_iterator I,
00773                             StringRef Indent) const {
00774   OS << Indent << "  used by: " << *I->getUse()->getUser() << "\n";
00775 }
00776 
00777 void AllocaSlices::print(raw_ostream &OS) const {
00778   if (PointerEscapingInstr) {
00779     OS << "Can't analyze slices for alloca: " << AI << "\n"
00780        << "  A pointer to this alloca escaped by:\n"
00781        << "  " << *PointerEscapingInstr << "\n";
00782     return;
00783   }
00784 
00785   OS << "Slices of alloca: " << AI << "\n";
00786   for (const_iterator I = begin(), E = end(); I != E; ++I)
00787     print(OS, I);
00788 }
00789 
00790 LLVM_DUMP_METHOD void AllocaSlices::dump(const_iterator I) const {
00791   print(dbgs(), I);
00792 }
00793 LLVM_DUMP_METHOD void AllocaSlices::dump() const { print(dbgs()); }
00794 
00795 #endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
00796 
00797 namespace {
00798 /// \brief Implementation of LoadAndStorePromoter for promoting allocas.
00799 ///
00800 /// This subclass of LoadAndStorePromoter adds overrides to handle promoting
00801 /// the loads and stores of an alloca instruction, as well as updating its
00802 /// debug information. This is used when a domtree is unavailable and thus
00803 /// mem2reg in its full form can't be used to handle promotion of allocas to
00804 /// scalar values.
00805 class AllocaPromoter : public LoadAndStorePromoter {
00806   AllocaInst &AI;
00807   DIBuilder &DIB;
00808 
00809   SmallVector<DbgDeclareInst *, 4> DDIs;
00810   SmallVector<DbgValueInst *, 4> DVIs;
00811 
00812 public:
00813   AllocaPromoter(const SmallVectorImpl<Instruction *> &Insts, SSAUpdater &S,
00814                  AllocaInst &AI, DIBuilder &DIB)
00815       : LoadAndStorePromoter(Insts, S), AI(AI), DIB(DIB) {}
00816 
00817   void run(const SmallVectorImpl<Instruction*> &Insts) {
00818     // Retain the debug information attached to the alloca for use when
00819     // rewriting loads and stores.
00820     if (MDNode *DebugNode = MDNode::getIfExists(AI.getContext(), &AI)) {
00821       for (User *U : DebugNode->users())
00822         if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
00823           DDIs.push_back(DDI);
00824         else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
00825           DVIs.push_back(DVI);
00826     }
00827 
00828     LoadAndStorePromoter::run(Insts);
00829 
00830     // While we have the debug information, clear it off of the alloca. The
00831     // caller takes care of deleting the alloca.
00832     while (!DDIs.empty())
00833       DDIs.pop_back_val()->eraseFromParent();
00834     while (!DVIs.empty())
00835       DVIs.pop_back_val()->eraseFromParent();
00836   }
00837 
00838   bool isInstInList(Instruction *I,
00839                     const SmallVectorImpl<Instruction*> &Insts) const override {
00840     Value *Ptr;
00841     if (LoadInst *LI = dyn_cast<LoadInst>(I))
00842       Ptr = LI->getOperand(0);
00843     else
00844       Ptr = cast<StoreInst>(I)->getPointerOperand();
00845 
00846     // Only used to detect cycles, which will be rare and quickly found as
00847     // we're walking up a chain of defs rather than down through uses.
00848     SmallPtrSet<Value *, 4> Visited;
00849 
00850     do {
00851       if (Ptr == &AI)
00852         return true;
00853 
00854       if (BitCastInst *BCI = dyn_cast<BitCastInst>(Ptr))
00855         Ptr = BCI->getOperand(0);
00856       else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr))
00857         Ptr = GEPI->getPointerOperand();
00858       else
00859         return false;
00860 
00861     } while (Visited.insert(Ptr));
00862 
00863     return false;
00864   }
00865 
00866   void updateDebugInfo(Instruction *Inst) const override {
00867     for (SmallVectorImpl<DbgDeclareInst *>::const_iterator I = DDIs.begin(),
00868            E = DDIs.end(); I != E; ++I) {
00869       DbgDeclareInst *DDI = *I;
00870       if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
00871         ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
00872       else if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
00873         ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
00874     }
00875     for (SmallVectorImpl<DbgValueInst *>::const_iterator I = DVIs.begin(),
00876            E = DVIs.end(); I != E; ++I) {
00877       DbgValueInst *DVI = *I;
00878       Value *Arg = nullptr;
00879       if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
00880         // If an argument is zero extended then use argument directly. The ZExt
00881         // may be zapped by an optimization pass in future.
00882         if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
00883           Arg = dyn_cast<Argument>(ZExt->getOperand(0));
00884         else if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
00885           Arg = dyn_cast<Argument>(SExt->getOperand(0));
00886         if (!Arg)
00887           Arg = SI->getValueOperand();
00888       } else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
00889         Arg = LI->getPointerOperand();
00890       } else {
00891         continue;
00892       }
00893       Instruction *DbgVal =
00894           DIB.insertDbgValueIntrinsic(Arg, 0, DIVariable(DVI->getVariable()),
00895                                       DIExpression(DVI->getExpression()), Inst);
00896       DbgVal->setDebugLoc(DVI->getDebugLoc());
00897     }
00898   }
00899 };
00900 } // end anon namespace
00901 
00902 
00903 namespace {
00904 /// \brief An optimization pass providing Scalar Replacement of Aggregates.
00905 ///
00906 /// This pass takes allocations which can be completely analyzed (that is, they
00907 /// don't escape) and tries to turn them into scalar SSA values. There are
00908 /// a few steps to this process.
00909 ///
00910 /// 1) It takes allocations of aggregates and analyzes the ways in which they
00911 ///    are used to try to split them into smaller allocations, ideally of
00912 ///    a single scalar data type. It will split up memcpy and memset accesses
00913 ///    as necessary and try to isolate individual scalar accesses.
00914 /// 2) It will transform accesses into forms which are suitable for SSA value
00915 ///    promotion. This can be replacing a memset with a scalar store of an
00916 ///    integer value, or it can involve speculating operations on a PHI or
00917 ///    select to be a PHI or select of the results.
00918 /// 3) Finally, this will try to detect a pattern of accesses which map cleanly
00919 ///    onto insert and extract operations on a vector value, and convert them to
00920 ///    this form. By doing so, it will enable promotion of vector aggregates to
00921 ///    SSA vector values.
00922 class SROA : public FunctionPass {
00923   const bool RequiresDomTree;
00924 
00925   LLVMContext *C;
00926   const DataLayout *DL;
00927   DominatorTree *DT;
00928   AssumptionTracker *AT;
00929 
00930   /// \brief Worklist of alloca instructions to simplify.
00931   ///
00932   /// Each alloca in the function is added to this. Each new alloca formed gets
00933   /// added to it as well to recursively simplify unless that alloca can be
00934   /// directly promoted. Finally, each time we rewrite a use of an alloca other
00935   /// the one being actively rewritten, we add it back onto the list if not
00936   /// already present to ensure it is re-visited.
00937   SetVector<AllocaInst *, SmallVector<AllocaInst *, 16> > Worklist;
00938 
00939   /// \brief A collection of instructions to delete.
00940   /// We try to batch deletions to simplify code and make things a bit more
00941   /// efficient.
00942   SetVector<Instruction *, SmallVector<Instruction *, 8> > DeadInsts;
00943 
00944   /// \brief Post-promotion worklist.
00945   ///
00946   /// Sometimes we discover an alloca which has a high probability of becoming
00947   /// viable for SROA after a round of promotion takes place. In those cases,
00948   /// the alloca is enqueued here for re-processing.
00949   ///
00950   /// Note that we have to be very careful to clear allocas out of this list in
00951   /// the event they are deleted.
00952   SetVector<AllocaInst *, SmallVector<AllocaInst *, 16> > PostPromotionWorklist;
00953 
00954   /// \brief A collection of alloca instructions we can directly promote.
00955   std::vector<AllocaInst *> PromotableAllocas;
00956 
00957   /// \brief A worklist of PHIs to speculate prior to promoting allocas.
00958   ///
00959   /// All of these PHIs have been checked for the safety of speculation and by
00960   /// being speculated will allow promoting allocas currently in the promotable
00961   /// queue.
00962   SetVector<PHINode *, SmallVector<PHINode *, 2> > SpeculatablePHIs;
00963 
00964   /// \brief A worklist of select instructions to speculate prior to promoting
00965   /// allocas.
00966   ///
00967   /// All of these select instructions have been checked for the safety of
00968   /// speculation and by being speculated will allow promoting allocas
00969   /// currently in the promotable queue.
00970   SetVector<SelectInst *, SmallVector<SelectInst *, 2> > SpeculatableSelects;
00971 
00972 public:
00973   SROA(bool RequiresDomTree = true)
00974       : FunctionPass(ID), RequiresDomTree(RequiresDomTree),
00975         C(nullptr), DL(nullptr), DT(nullptr) {
00976     initializeSROAPass(*PassRegistry::getPassRegistry());
00977   }
00978   bool runOnFunction(Function &F) override;
00979   void getAnalysisUsage(AnalysisUsage &AU) const override;
00980 
00981   const char *getPassName() const override { return "SROA"; }
00982   static char ID;
00983 
00984 private:
00985   friend class PHIOrSelectSpeculator;
00986   friend class AllocaSliceRewriter;
00987 
00988   bool rewritePartition(AllocaInst &AI, AllocaSlices &S,
00989                         AllocaSlices::iterator B, AllocaSlices::iterator E,
00990                         int64_t BeginOffset, int64_t EndOffset,
00991                         ArrayRef<AllocaSlices::iterator> SplitUses);
00992   bool splitAlloca(AllocaInst &AI, AllocaSlices &S);
00993   bool runOnAlloca(AllocaInst &AI);
00994   void clobberUse(Use &U);
00995   void deleteDeadInstructions(SmallPtrSetImpl<AllocaInst *> &DeletedAllocas);
00996   bool promoteAllocas(Function &F);
00997 };
00998 }
00999 
01000 char SROA::ID = 0;
01001 
01002 FunctionPass *llvm::createSROAPass(bool RequiresDomTree) {
01003   return new SROA(RequiresDomTree);
01004 }
01005 
01006 INITIALIZE_PASS_BEGIN(SROA, "sroa", "Scalar Replacement Of Aggregates",
01007                       false, false)
01008 INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
01009 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
01010 INITIALIZE_PASS_END(SROA, "sroa", "Scalar Replacement Of Aggregates",
01011                     false, false)
01012 
01013 /// Walk the range of a partitioning looking for a common type to cover this
01014 /// sequence of slices.
01015 static Type *findCommonType(AllocaSlices::const_iterator B,
01016                             AllocaSlices::const_iterator E,
01017                             uint64_t EndOffset) {
01018   Type *Ty = nullptr;
01019   bool TyIsCommon = true;
01020   IntegerType *ITy = nullptr;
01021 
01022   // Note that we need to look at *every* alloca slice's Use to ensure we
01023   // always get consistent results regardless of the order of slices.
01024   for (AllocaSlices::const_iterator I = B; I != E; ++I) {
01025     Use *U = I->getUse();
01026     if (isa<IntrinsicInst>(*U->getUser()))
01027       continue;
01028     if (I->beginOffset() != B->beginOffset() || I->endOffset() != EndOffset)
01029       continue;
01030 
01031     Type *UserTy = nullptr;
01032     if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
01033       UserTy = LI->getType();
01034     } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
01035       UserTy = SI->getValueOperand()->getType();
01036     }
01037 
01038     if (IntegerType *UserITy = dyn_cast_or_null<IntegerType>(UserTy)) {
01039       // If the type is larger than the partition, skip it. We only encounter
01040       // this for split integer operations where we want to use the type of the
01041       // entity causing the split. Also skip if the type is not a byte width
01042       // multiple.
01043       if (UserITy->getBitWidth() % 8 != 0 ||
01044           UserITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
01045         continue;
01046 
01047       // Track the largest bitwidth integer type used in this way in case there
01048       // is no common type.
01049       if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
01050         ITy = UserITy;
01051     }
01052 
01053     // To avoid depending on the order of slices, Ty and TyIsCommon must not
01054     // depend on types skipped above.
01055     if (!UserTy || (Ty && Ty != UserTy))
01056       TyIsCommon = false; // Give up on anything but an iN type.
01057     else
01058       Ty = UserTy;
01059   }
01060 
01061   return TyIsCommon ? Ty : ITy;
01062 }
01063 
01064 /// PHI instructions that use an alloca and are subsequently loaded can be
01065 /// rewritten to load both input pointers in the pred blocks and then PHI the
01066 /// results, allowing the load of the alloca to be promoted.
01067 /// From this:
01068 ///   %P2 = phi [i32* %Alloca, i32* %Other]
01069 ///   %V = load i32* %P2
01070 /// to:
01071 ///   %V1 = load i32* %Alloca      -> will be mem2reg'd
01072 ///   ...
01073 ///   %V2 = load i32* %Other
01074 ///   ...
01075 ///   %V = phi [i32 %V1, i32 %V2]
01076 ///
01077 /// We can do this to a select if its only uses are loads and if the operands
01078 /// to the select can be loaded unconditionally.
01079 ///
01080 /// FIXME: This should be hoisted into a generic utility, likely in
01081 /// Transforms/Util/Local.h
01082 static bool isSafePHIToSpeculate(PHINode &PN,
01083                                  const DataLayout *DL = nullptr) {
01084   // For now, we can only do this promotion if the load is in the same block
01085   // as the PHI, and if there are no stores between the phi and load.
01086   // TODO: Allow recursive phi users.
01087   // TODO: Allow stores.
01088   BasicBlock *BB = PN.getParent();
01089   unsigned MaxAlign = 0;
01090   bool HaveLoad = false;
01091   for (User *U : PN.users()) {
01092     LoadInst *LI = dyn_cast<LoadInst>(U);
01093     if (!LI || !LI->isSimple())
01094       return false;
01095 
01096     // For now we only allow loads in the same block as the PHI.  This is
01097     // a common case that happens when instcombine merges two loads through
01098     // a PHI.
01099     if (LI->getParent() != BB)
01100       return false;
01101 
01102     // Ensure that there are no instructions between the PHI and the load that
01103     // could store.
01104     for (BasicBlock::iterator BBI = &PN; &*BBI != LI; ++BBI)
01105       if (BBI->mayWriteToMemory())
01106         return false;
01107 
01108     MaxAlign = std::max(MaxAlign, LI->getAlignment());
01109     HaveLoad = true;
01110   }
01111 
01112   if (!HaveLoad)
01113     return false;
01114 
01115   // We can only transform this if it is safe to push the loads into the
01116   // predecessor blocks. The only thing to watch out for is that we can't put
01117   // a possibly trapping load in the predecessor if it is a critical edge.
01118   for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
01119     TerminatorInst *TI = PN.getIncomingBlock(Idx)->getTerminator();
01120     Value *InVal = PN.getIncomingValue(Idx);
01121 
01122     // If the value is produced by the terminator of the predecessor (an
01123     // invoke) or it has side-effects, there is no valid place to put a load
01124     // in the predecessor.
01125     if (TI == InVal || TI->mayHaveSideEffects())
01126       return false;
01127 
01128     // If the predecessor has a single successor, then the edge isn't
01129     // critical.
01130     if (TI->getNumSuccessors() == 1)
01131       continue;
01132 
01133     // If this pointer is always safe to load, or if we can prove that there
01134     // is already a load in the block, then we can move the load to the pred
01135     // block.
01136     if (InVal->isDereferenceablePointer(DL) ||
01137         isSafeToLoadUnconditionally(InVal, TI, MaxAlign, DL))
01138       continue;
01139 
01140     return false;
01141   }
01142 
01143   return true;
01144 }
01145 
01146 static void speculatePHINodeLoads(PHINode &PN) {
01147   DEBUG(dbgs() << "    original: " << PN << "\n");
01148 
01149   Type *LoadTy = cast<PointerType>(PN.getType())->getElementType();
01150   IRBuilderTy PHIBuilder(&PN);
01151   PHINode *NewPN = PHIBuilder.CreatePHI(LoadTy, PN.getNumIncomingValues(),
01152                                         PN.getName() + ".sroa.speculated");
01153 
01154   // Get the AA tags and alignment to use from one of the loads.  It doesn't
01155   // matter which one we get and if any differ.
01156   LoadInst *SomeLoad = cast<LoadInst>(PN.user_back());
01157 
01158   AAMDNodes AATags;
01159   SomeLoad->getAAMetadata(AATags);
01160   unsigned Align = SomeLoad->getAlignment();
01161 
01162   // Rewrite all loads of the PN to use the new PHI.
01163   while (!PN.use_empty()) {
01164     LoadInst *LI = cast<LoadInst>(PN.user_back());
01165     LI->replaceAllUsesWith(NewPN);
01166     LI->eraseFromParent();
01167   }
01168 
01169   // Inject loads into all of the pred blocks.
01170   for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
01171     BasicBlock *Pred = PN.getIncomingBlock(Idx);
01172     TerminatorInst *TI = Pred->getTerminator();
01173     Value *InVal = PN.getIncomingValue(Idx);
01174     IRBuilderTy PredBuilder(TI);
01175 
01176     LoadInst *Load = PredBuilder.CreateLoad(
01177         InVal, (PN.getName() + ".sroa.speculate.load." + Pred->getName()));
01178     ++NumLoadsSpeculated;
01179     Load->setAlignment(Align);
01180     if (AATags)
01181       Load->setAAMetadata(AATags);
01182     NewPN->addIncoming(Load, Pred);
01183   }
01184 
01185   DEBUG(dbgs() << "          speculated to: " << *NewPN << "\n");
01186   PN.eraseFromParent();
01187 }
01188 
01189 /// Select instructions that use an alloca and are subsequently loaded can be
01190 /// rewritten to load both input pointers and then select between the result,
01191 /// allowing the load of the alloca to be promoted.
01192 /// From this:
01193 ///   %P2 = select i1 %cond, i32* %Alloca, i32* %Other
01194 ///   %V = load i32* %P2
01195 /// to:
01196 ///   %V1 = load i32* %Alloca      -> will be mem2reg'd
01197 ///   %V2 = load i32* %Other
01198 ///   %V = select i1 %cond, i32 %V1, i32 %V2
01199 ///
01200 /// We can do this to a select if its only uses are loads and if the operand
01201 /// to the select can be loaded unconditionally.
01202 static bool isSafeSelectToSpeculate(SelectInst &SI,
01203                                     const DataLayout *DL = nullptr) {
01204   Value *TValue = SI.getTrueValue();
01205   Value *FValue = SI.getFalseValue();
01206   bool TDerefable = TValue->isDereferenceablePointer(DL);
01207   bool FDerefable = FValue->isDereferenceablePointer(DL);
01208 
01209   for (User *U : SI.users()) {
01210     LoadInst *LI = dyn_cast<LoadInst>(U);
01211     if (!LI || !LI->isSimple())
01212       return false;
01213 
01214     // Both operands to the select need to be dereferencable, either
01215     // absolutely (e.g. allocas) or at this point because we can see other
01216     // accesses to it.
01217     if (!TDerefable &&
01218         !isSafeToLoadUnconditionally(TValue, LI, LI->getAlignment(), DL))
01219       return false;
01220     if (!FDerefable &&
01221         !isSafeToLoadUnconditionally(FValue, LI, LI->getAlignment(), DL))
01222       return false;
01223   }
01224 
01225   return true;
01226 }
01227 
01228 static void speculateSelectInstLoads(SelectInst &SI) {
01229   DEBUG(dbgs() << "    original: " << SI << "\n");
01230 
01231   IRBuilderTy IRB(&SI);
01232   Value *TV = SI.getTrueValue();
01233   Value *FV = SI.getFalseValue();
01234   // Replace the loads of the select with a select of two loads.
01235   while (!SI.use_empty()) {
01236     LoadInst *LI = cast<LoadInst>(SI.user_back());
01237     assert(LI->isSimple() && "We only speculate simple loads");
01238 
01239     IRB.SetInsertPoint(LI);
01240     LoadInst *TL =
01241         IRB.CreateLoad(TV, LI->getName() + ".sroa.speculate.load.true");
01242     LoadInst *FL =
01243         IRB.CreateLoad(FV, LI->getName() + ".sroa.speculate.load.false");
01244     NumLoadsSpeculated += 2;
01245 
01246     // Transfer alignment and AA info if present.
01247     TL->setAlignment(LI->getAlignment());
01248     FL->setAlignment(LI->getAlignment());
01249 
01250     AAMDNodes Tags;
01251     LI->getAAMetadata(Tags);
01252     if (Tags) {
01253       TL->setAAMetadata(Tags);
01254       FL->setAAMetadata(Tags);
01255     }
01256 
01257     Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL,
01258                                 LI->getName() + ".sroa.speculated");
01259 
01260     DEBUG(dbgs() << "          speculated to: " << *V << "\n");
01261     LI->replaceAllUsesWith(V);
01262     LI->eraseFromParent();
01263   }
01264   SI.eraseFromParent();
01265 }
01266 
01267 /// \brief Build a GEP out of a base pointer and indices.
01268 ///
01269 /// This will return the BasePtr if that is valid, or build a new GEP
01270 /// instruction using the IRBuilder if GEP-ing is needed.
01271 static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
01272                        SmallVectorImpl<Value *> &Indices, Twine NamePrefix) {
01273   if (Indices.empty())
01274     return BasePtr;
01275 
01276   // A single zero index is a no-op, so check for this and avoid building a GEP
01277   // in that case.
01278   if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
01279     return BasePtr;
01280 
01281   return IRB.CreateInBoundsGEP(BasePtr, Indices, NamePrefix + "sroa_idx");
01282 }
01283 
01284 /// \brief Get a natural GEP off of the BasePtr walking through Ty toward
01285 /// TargetTy without changing the offset of the pointer.
01286 ///
01287 /// This routine assumes we've already established a properly offset GEP with
01288 /// Indices, and arrived at the Ty type. The goal is to continue to GEP with
01289 /// zero-indices down through type layers until we find one the same as
01290 /// TargetTy. If we can't find one with the same type, we at least try to use
01291 /// one with the same size. If none of that works, we just produce the GEP as
01292 /// indicated by Indices to have the correct offset.
01293 static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
01294                                     Value *BasePtr, Type *Ty, Type *TargetTy,
01295                                     SmallVectorImpl<Value *> &Indices,
01296                                     Twine NamePrefix) {
01297   if (Ty == TargetTy)
01298     return buildGEP(IRB, BasePtr, Indices, NamePrefix);
01299 
01300   // Pointer size to use for the indices.
01301   unsigned PtrSize = DL.getPointerTypeSizeInBits(BasePtr->getType());
01302 
01303   // See if we can descend into a struct and locate a field with the correct
01304   // type.
01305   unsigned NumLayers = 0;
01306   Type *ElementTy = Ty;
01307   do {
01308     if (ElementTy->isPointerTy())
01309       break;
01310 
01311     if (ArrayType *ArrayTy = dyn_cast<ArrayType>(ElementTy)) {
01312       ElementTy = ArrayTy->getElementType();
01313       Indices.push_back(IRB.getIntN(PtrSize, 0));
01314     } else if (VectorType *VectorTy = dyn_cast<VectorType>(ElementTy)) {
01315       ElementTy = VectorTy->getElementType();
01316       Indices.push_back(IRB.getInt32(0));
01317     } else if (StructType *STy = dyn_cast<StructType>(ElementTy)) {
01318       if (STy->element_begin() == STy->element_end())
01319         break; // Nothing left to descend into.
01320       ElementTy = *STy->element_begin();
01321       Indices.push_back(IRB.getInt32(0));
01322     } else {
01323       break;
01324     }
01325     ++NumLayers;
01326   } while (ElementTy != TargetTy);
01327   if (ElementTy != TargetTy)
01328     Indices.erase(Indices.end() - NumLayers, Indices.end());
01329 
01330   return buildGEP(IRB, BasePtr, Indices, NamePrefix);
01331 }
01332 
01333 /// \brief Recursively compute indices for a natural GEP.
01334 ///
01335 /// This is the recursive step for getNaturalGEPWithOffset that walks down the
01336 /// element types adding appropriate indices for the GEP.
01337 static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
01338                                        Value *Ptr, Type *Ty, APInt &Offset,
01339                                        Type *TargetTy,
01340                                        SmallVectorImpl<Value *> &Indices,
01341                                        Twine NamePrefix) {
01342   if (Offset == 0)
01343     return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices, NamePrefix);
01344 
01345   // We can't recurse through pointer types.
01346   if (Ty->isPointerTy())
01347     return nullptr;
01348 
01349   // We try to analyze GEPs over vectors here, but note that these GEPs are
01350   // extremely poorly defined currently. The long-term goal is to remove GEPing
01351   // over a vector from the IR completely.
01352   if (VectorType *VecTy = dyn_cast<VectorType>(Ty)) {
01353     unsigned ElementSizeInBits = DL.getTypeSizeInBits(VecTy->getScalarType());
01354     if (ElementSizeInBits % 8 != 0) {
01355       // GEPs over non-multiple of 8 size vector elements are invalid.
01356       return nullptr;
01357     }
01358     APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
01359     APInt NumSkippedElements = Offset.sdiv(ElementSize);
01360     if (NumSkippedElements.ugt(VecTy->getNumElements()))
01361       return nullptr;
01362     Offset -= NumSkippedElements * ElementSize;
01363     Indices.push_back(IRB.getInt(NumSkippedElements));
01364     return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(),
01365                                     Offset, TargetTy, Indices, NamePrefix);
01366   }
01367 
01368   if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
01369     Type *ElementTy = ArrTy->getElementType();
01370     APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
01371     APInt NumSkippedElements = Offset.sdiv(ElementSize);
01372     if (NumSkippedElements.ugt(ArrTy->getNumElements()))
01373       return nullptr;
01374 
01375     Offset -= NumSkippedElements * ElementSize;
01376     Indices.push_back(IRB.getInt(NumSkippedElements));
01377     return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
01378                                     Indices, NamePrefix);
01379   }
01380 
01381   StructType *STy = dyn_cast<StructType>(Ty);
01382   if (!STy)
01383     return nullptr;
01384 
01385   const StructLayout *SL = DL.getStructLayout(STy);
01386   uint64_t StructOffset = Offset.getZExtValue();
01387   if (StructOffset >= SL->getSizeInBytes())
01388     return nullptr;
01389   unsigned Index = SL->getElementContainingOffset(StructOffset);
01390   Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index));
01391   Type *ElementTy = STy->getElementType(Index);
01392   if (Offset.uge(DL.getTypeAllocSize(ElementTy)))
01393     return nullptr; // The offset points into alignment padding.
01394 
01395   Indices.push_back(IRB.getInt32(Index));
01396   return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
01397                                   Indices, NamePrefix);
01398 }
01399 
01400 /// \brief Get a natural GEP from a base pointer to a particular offset and
01401 /// resulting in a particular type.
01402 ///
01403 /// The goal is to produce a "natural" looking GEP that works with the existing
01404 /// composite types to arrive at the appropriate offset and element type for
01405 /// a pointer. TargetTy is the element type the returned GEP should point-to if
01406 /// possible. We recurse by decreasing Offset, adding the appropriate index to
01407 /// Indices, and setting Ty to the result subtype.
01408 ///
01409 /// If no natural GEP can be constructed, this function returns null.
01410 static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
01411                                       Value *Ptr, APInt Offset, Type *TargetTy,
01412                                       SmallVectorImpl<Value *> &Indices,
01413                                       Twine NamePrefix) {
01414   PointerType *Ty = cast<PointerType>(Ptr->getType());
01415 
01416   // Don't consider any GEPs through an i8* as natural unless the TargetTy is
01417   // an i8.
01418   if (Ty == IRB.getInt8PtrTy(Ty->getAddressSpace()) && TargetTy->isIntegerTy(8))
01419     return nullptr;
01420 
01421   Type *ElementTy = Ty->getElementType();
01422   if (!ElementTy->isSized())
01423     return nullptr; // We can't GEP through an unsized element.
01424   APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
01425   if (ElementSize == 0)
01426     return nullptr; // Zero-length arrays can't help us build a natural GEP.
01427   APInt NumSkippedElements = Offset.sdiv(ElementSize);
01428 
01429   Offset -= NumSkippedElements * ElementSize;
01430   Indices.push_back(IRB.getInt(NumSkippedElements));
01431   return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
01432                                   Indices, NamePrefix);
01433 }
01434 
01435 /// \brief Compute an adjusted pointer from Ptr by Offset bytes where the
01436 /// resulting pointer has PointerTy.
01437 ///
01438 /// This tries very hard to compute a "natural" GEP which arrives at the offset
01439 /// and produces the pointer type desired. Where it cannot, it will try to use
01440 /// the natural GEP to arrive at the offset and bitcast to the type. Where that
01441 /// fails, it will try to use an existing i8* and GEP to the byte offset and
01442 /// bitcast to the type.
01443 ///
01444 /// The strategy for finding the more natural GEPs is to peel off layers of the
01445 /// pointer, walking back through bit casts and GEPs, searching for a base
01446 /// pointer from which we can compute a natural GEP with the desired
01447 /// properties. The algorithm tries to fold as many constant indices into
01448 /// a single GEP as possible, thus making each GEP more independent of the
01449 /// surrounding code.
01450 static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL, Value *Ptr,
01451                              APInt Offset, Type *PointerTy,
01452                              Twine NamePrefix) {
01453   // Even though we don't look through PHI nodes, we could be called on an
01454   // instruction in an unreachable block, which may be on a cycle.
01455   SmallPtrSet<Value *, 4> Visited;
01456   Visited.insert(Ptr);
01457   SmallVector<Value *, 4> Indices;
01458 
01459   // We may end up computing an offset pointer that has the wrong type. If we
01460   // never are able to compute one directly that has the correct type, we'll
01461   // fall back to it, so keep it around here.
01462   Value *OffsetPtr = nullptr;
01463 
01464   // Remember any i8 pointer we come across to re-use if we need to do a raw
01465   // byte offset.
01466   Value *Int8Ptr = nullptr;
01467   APInt Int8PtrOffset(Offset.getBitWidth(), 0);
01468 
01469   Type *TargetTy = PointerTy->getPointerElementType();
01470 
01471   do {
01472     // First fold any existing GEPs into the offset.
01473     while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
01474       APInt GEPOffset(Offset.getBitWidth(), 0);
01475       if (!GEP->accumulateConstantOffset(DL, GEPOffset))
01476         break;
01477       Offset += GEPOffset;
01478       Ptr = GEP->getPointerOperand();
01479       if (!Visited.insert(Ptr))
01480         break;
01481     }
01482 
01483     // See if we can perform a natural GEP here.
01484     Indices.clear();
01485     if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
01486                                            Indices, NamePrefix)) {
01487       if (P->getType() == PointerTy) {
01488         // Zap any offset pointer that we ended up computing in previous rounds.
01489         if (OffsetPtr && OffsetPtr->use_empty())
01490           if (Instruction *I = dyn_cast<Instruction>(OffsetPtr))
01491             I->eraseFromParent();
01492         return P;
01493       }
01494       if (!OffsetPtr) {
01495         OffsetPtr = P;
01496       }
01497     }
01498 
01499     // Stash this pointer if we've found an i8*.
01500     if (Ptr->getType()->isIntegerTy(8)) {
01501       Int8Ptr = Ptr;
01502       Int8PtrOffset = Offset;
01503     }
01504 
01505     // Peel off a layer of the pointer and update the offset appropriately.
01506     if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
01507       Ptr = cast<Operator>(Ptr)->getOperand(0);
01508     } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
01509       if (GA->mayBeOverridden())
01510         break;
01511       Ptr = GA->getAliasee();
01512     } else {
01513       break;
01514     }
01515     assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!");
01516   } while (Visited.insert(Ptr));
01517 
01518   if (!OffsetPtr) {
01519     if (!Int8Ptr) {
01520       Int8Ptr = IRB.CreateBitCast(
01521           Ptr, IRB.getInt8PtrTy(PointerTy->getPointerAddressSpace()),
01522           NamePrefix + "sroa_raw_cast");
01523       Int8PtrOffset = Offset;
01524     }
01525 
01526     OffsetPtr = Int8PtrOffset == 0 ? Int8Ptr :
01527       IRB.CreateInBoundsGEP(Int8Ptr, IRB.getInt(Int8PtrOffset),
01528                             NamePrefix + "sroa_raw_idx");
01529   }
01530   Ptr = OffsetPtr;
01531 
01532   // On the off chance we were targeting i8*, guard the bitcast here.
01533   if (Ptr->getType() != PointerTy)
01534     Ptr = IRB.CreateBitCast(Ptr, PointerTy, NamePrefix + "sroa_cast");
01535 
01536   return Ptr;
01537 }
01538 
01539 /// \brief Test whether we can convert a value from the old to the new type.
01540 ///
01541 /// This predicate should be used to guard calls to convertValue in order to
01542 /// ensure that we only try to convert viable values. The strategy is that we
01543 /// will peel off single element struct and array wrappings to get to an
01544 /// underlying value, and convert that value.
01545 static bool canConvertValue(const DataLayout &DL, Type *OldTy, Type *NewTy) {
01546   if (OldTy == NewTy)
01547     return true;
01548   if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy))
01549     if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy))
01550       if (NewITy->getBitWidth() >= OldITy->getBitWidth())
01551         return true;
01552   if (DL.getTypeSizeInBits(NewTy) != DL.getTypeSizeInBits(OldTy))
01553     return false;
01554   if (!NewTy->isSingleValueType() || !OldTy->isSingleValueType())
01555     return false;
01556 
01557   // We can convert pointers to integers and vice-versa. Same for vectors
01558   // of pointers and integers.
01559   OldTy = OldTy->getScalarType();
01560   NewTy = NewTy->getScalarType();
01561   if (NewTy->isPointerTy() || OldTy->isPointerTy()) {
01562     if (NewTy->isPointerTy() && OldTy->isPointerTy())
01563       return true;
01564     if (NewTy->isIntegerTy() || OldTy->isIntegerTy())
01565       return true;
01566     return false;
01567   }
01568 
01569   return true;
01570 }
01571 
01572 /// \brief Generic routine to convert an SSA value to a value of a different
01573 /// type.
01574 ///
01575 /// This will try various different casting techniques, such as bitcasts,
01576 /// inttoptr, and ptrtoint casts. Use the \c canConvertValue predicate to test
01577 /// two types for viability with this routine.
01578 static Value *convertValue(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
01579                            Type *NewTy) {
01580   Type *OldTy = V->getType();
01581   assert(canConvertValue(DL, OldTy, NewTy) && "Value not convertable to type");
01582 
01583   if (OldTy == NewTy)
01584     return V;
01585 
01586   if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy))
01587     if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy))
01588       if (NewITy->getBitWidth() > OldITy->getBitWidth())
01589         return IRB.CreateZExt(V, NewITy);
01590 
01591   // See if we need inttoptr for this type pair. A cast involving both scalars
01592   // and vectors requires and additional bitcast.
01593   if (OldTy->getScalarType()->isIntegerTy() &&
01594       NewTy->getScalarType()->isPointerTy()) {
01595     // Expand <2 x i32> to i8* --> <2 x i32> to i64 to i8*
01596     if (OldTy->isVectorTy() && !NewTy->isVectorTy())
01597       return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
01598                                 NewTy);
01599 
01600     // Expand i128 to <2 x i8*> --> i128 to <2 x i64> to <2 x i8*>
01601     if (!OldTy->isVectorTy() && NewTy->isVectorTy())
01602       return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
01603                                 NewTy);
01604 
01605     return IRB.CreateIntToPtr(V, NewTy);
01606   }
01607 
01608   // See if we need ptrtoint for this type pair. A cast involving both scalars
01609   // and vectors requires and additional bitcast.
01610   if (OldTy->getScalarType()->isPointerTy() &&
01611       NewTy->getScalarType()->isIntegerTy()) {
01612     // Expand <2 x i8*> to i128 --> <2 x i8*> to <2 x i64> to i128
01613     if (OldTy->isVectorTy() && !NewTy->isVectorTy())
01614       return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
01615                                NewTy);
01616 
01617     // Expand i8* to <2 x i32> --> i8* to i64 to <2 x i32>
01618     if (!OldTy->isVectorTy() && NewTy->isVectorTy())
01619       return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
01620                                NewTy);
01621 
01622     return IRB.CreatePtrToInt(V, NewTy);
01623   }
01624 
01625   return IRB.CreateBitCast(V, NewTy);
01626 }
01627 
01628 /// \brief Test whether the given slice use can be promoted to a vector.
01629 ///
01630 /// This function is called to test each entry in a partioning which is slated
01631 /// for a single slice.
01632 static bool isVectorPromotionViableForSlice(
01633     const DataLayout &DL, AllocaSlices &S, uint64_t SliceBeginOffset,
01634     uint64_t SliceEndOffset, VectorType *Ty, uint64_t ElementSize,
01635     AllocaSlices::const_iterator I) {
01636   // First validate the slice offsets.
01637   uint64_t BeginOffset =
01638       std::max(I->beginOffset(), SliceBeginOffset) - SliceBeginOffset;
01639   uint64_t BeginIndex = BeginOffset / ElementSize;
01640   if (BeginIndex * ElementSize != BeginOffset ||
01641       BeginIndex >= Ty->getNumElements())
01642     return false;
01643   uint64_t EndOffset =
01644       std::min(I->endOffset(), SliceEndOffset) - SliceBeginOffset;
01645   uint64_t EndIndex = EndOffset / ElementSize;
01646   if (EndIndex * ElementSize != EndOffset || EndIndex > Ty->getNumElements())
01647     return false;
01648 
01649   assert(EndIndex > BeginIndex && "Empty vector!");
01650   uint64_t NumElements = EndIndex - BeginIndex;
01651   Type *SliceTy =
01652       (NumElements == 1) ? Ty->getElementType()
01653                          : VectorType::get(Ty->getElementType(), NumElements);
01654 
01655   Type *SplitIntTy =
01656       Type::getIntNTy(Ty->getContext(), NumElements * ElementSize * 8);
01657 
01658   Use *U = I->getUse();
01659 
01660   if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
01661     if (MI->isVolatile())
01662       return false;
01663     if (!I->isSplittable())
01664       return false; // Skip any unsplittable intrinsics.
01665   } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
01666     if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
01667         II->getIntrinsicID() != Intrinsic::lifetime_end)
01668       return false;
01669   } else if (U->get()->getType()->getPointerElementType()->isStructTy()) {
01670     // Disable vector promotion when there are loads or stores of an FCA.
01671     return false;
01672   } else if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
01673     if (LI->isVolatile())
01674       return false;
01675     Type *LTy = LI->getType();
01676     if (SliceBeginOffset > I->beginOffset() ||
01677         SliceEndOffset < I->endOffset()) {
01678       assert(LTy->isIntegerTy());
01679       LTy = SplitIntTy;
01680     }
01681     if (!canConvertValue(DL, SliceTy, LTy))
01682       return false;
01683   } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
01684     if (SI->isVolatile())
01685       return false;
01686     Type *STy = SI->getValueOperand()->getType();
01687     if (SliceBeginOffset > I->beginOffset() ||
01688         SliceEndOffset < I->endOffset()) {
01689       assert(STy->isIntegerTy());
01690       STy = SplitIntTy;
01691     }
01692     if (!canConvertValue(DL, STy, SliceTy))
01693       return false;
01694   } else {
01695     return false;
01696   }
01697 
01698   return true;
01699 }
01700 
01701 /// \brief Test whether the given alloca partitioning and range of slices can be
01702 /// promoted to a vector.
01703 ///
01704 /// This is a quick test to check whether we can rewrite a particular alloca
01705 /// partition (and its newly formed alloca) into a vector alloca with only
01706 /// whole-vector loads and stores such that it could be promoted to a vector
01707 /// SSA value. We only can ensure this for a limited set of operations, and we
01708 /// don't want to do the rewrites unless we are confident that the result will
01709 /// be promotable, so we have an early test here.
01710 static bool
01711 isVectorPromotionViable(const DataLayout &DL, Type *AllocaTy, AllocaSlices &S,
01712                         uint64_t SliceBeginOffset, uint64_t SliceEndOffset,
01713                         AllocaSlices::const_iterator I,
01714                         AllocaSlices::const_iterator E,
01715                         ArrayRef<AllocaSlices::iterator> SplitUses) {
01716   VectorType *Ty = dyn_cast<VectorType>(AllocaTy);
01717   if (!Ty)
01718     return false;
01719 
01720   uint64_t ElementSize = DL.getTypeSizeInBits(Ty->getScalarType());
01721 
01722   // While the definition of LLVM vectors is bitpacked, we don't support sizes
01723   // that aren't byte sized.
01724   if (ElementSize % 8)
01725     return false;
01726   assert((DL.getTypeSizeInBits(Ty) % 8) == 0 &&
01727          "vector size not a multiple of element size?");
01728   ElementSize /= 8;
01729 
01730   for (; I != E; ++I)
01731     if (!isVectorPromotionViableForSlice(DL, S, SliceBeginOffset,
01732                                          SliceEndOffset, Ty, ElementSize, I))
01733       return false;
01734 
01735   for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
01736                                                         SUE = SplitUses.end();
01737        SUI != SUE; ++SUI)
01738     if (!isVectorPromotionViableForSlice(DL, S, SliceBeginOffset,
01739                                          SliceEndOffset, Ty, ElementSize, *SUI))
01740       return false;
01741 
01742   return true;
01743 }
01744 
01745 /// \brief Test whether a slice of an alloca is valid for integer widening.
01746 ///
01747 /// This implements the necessary checking for the \c isIntegerWideningViable
01748 /// test below on a single slice of the alloca.
01749 static bool isIntegerWideningViableForSlice(const DataLayout &DL,
01750                                             Type *AllocaTy,
01751                                             uint64_t AllocBeginOffset,
01752                                             uint64_t Size, AllocaSlices &S,
01753                                             AllocaSlices::const_iterator I,
01754                                             bool &WholeAllocaOp) {
01755   uint64_t RelBegin = I->beginOffset() - AllocBeginOffset;
01756   uint64_t RelEnd = I->endOffset() - AllocBeginOffset;
01757 
01758   // We can't reasonably handle cases where the load or store extends past
01759   // the end of the aloca's type and into its padding.
01760   if (RelEnd > Size)
01761     return false;
01762 
01763   Use *U = I->getUse();
01764 
01765   if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
01766     if (LI->isVolatile())
01767       return false;
01768     if (RelBegin == 0 && RelEnd == Size)
01769       WholeAllocaOp = true;
01770     if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) {
01771       if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
01772         return false;
01773     } else if (RelBegin != 0 || RelEnd != Size ||
01774                !canConvertValue(DL, AllocaTy, LI->getType())) {
01775       // Non-integer loads need to be convertible from the alloca type so that
01776       // they are promotable.
01777       return false;
01778     }
01779   } else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
01780     Type *ValueTy = SI->getValueOperand()->getType();
01781     if (SI->isVolatile())
01782       return false;
01783     if (RelBegin == 0 && RelEnd == Size)
01784       WholeAllocaOp = true;
01785     if (IntegerType *ITy = dyn_cast<IntegerType>(ValueTy)) {
01786       if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
01787         return false;
01788     } else if (RelBegin != 0 || RelEnd != Size ||
01789                !canConvertValue(DL, ValueTy, AllocaTy)) {
01790       // Non-integer stores need to be convertible to the alloca type so that
01791       // they are promotable.
01792       return false;
01793     }
01794   } else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
01795     if (MI->isVolatile() || !isa<Constant>(MI->getLength()))
01796       return false;
01797     if (!I->isSplittable())
01798       return false; // Skip any unsplittable intrinsics.
01799   } else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
01800     if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
01801         II->getIntrinsicID() != Intrinsic::lifetime_end)
01802       return false;
01803   } else {
01804     return false;
01805   }
01806 
01807   return true;
01808 }
01809 
01810 /// \brief Test whether the given alloca partition's integer operations can be
01811 /// widened to promotable ones.
01812 ///
01813 /// This is a quick test to check whether we can rewrite the integer loads and
01814 /// stores to a particular alloca into wider loads and stores and be able to
01815 /// promote the resulting alloca.
01816 static bool
01817 isIntegerWideningViable(const DataLayout &DL, Type *AllocaTy,
01818                         uint64_t AllocBeginOffset, AllocaSlices &S,
01819                         AllocaSlices::const_iterator I,
01820                         AllocaSlices::const_iterator E,
01821                         ArrayRef<AllocaSlices::iterator> SplitUses) {
01822   uint64_t SizeInBits = DL.getTypeSizeInBits(AllocaTy);
01823   // Don't create integer types larger than the maximum bitwidth.
01824   if (SizeInBits > IntegerType::MAX_INT_BITS)
01825     return false;
01826 
01827   // Don't try to handle allocas with bit-padding.
01828   if (SizeInBits != DL.getTypeStoreSizeInBits(AllocaTy))
01829     return false;
01830 
01831   // We need to ensure that an integer type with the appropriate bitwidth can
01832   // be converted to the alloca type, whatever that is. We don't want to force
01833   // the alloca itself to have an integer type if there is a more suitable one.
01834   Type *IntTy = Type::getIntNTy(AllocaTy->getContext(), SizeInBits);
01835   if (!canConvertValue(DL, AllocaTy, IntTy) ||
01836       !canConvertValue(DL, IntTy, AllocaTy))
01837     return false;
01838 
01839   uint64_t Size = DL.getTypeStoreSize(AllocaTy);
01840 
01841   // While examining uses, we ensure that the alloca has a covering load or
01842   // store. We don't want to widen the integer operations only to fail to
01843   // promote due to some other unsplittable entry (which we may make splittable
01844   // later). However, if there are only splittable uses, go ahead and assume
01845   // that we cover the alloca.
01846   bool WholeAllocaOp = (I != E) ? false : DL.isLegalInteger(SizeInBits);
01847 
01848   for (; I != E; ++I)
01849     if (!isIntegerWideningViableForSlice(DL, AllocaTy, AllocBeginOffset, Size,
01850                                          S, I, WholeAllocaOp))
01851       return false;
01852 
01853   for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
01854                                                         SUE = SplitUses.end();
01855        SUI != SUE; ++SUI)
01856     if (!isIntegerWideningViableForSlice(DL, AllocaTy, AllocBeginOffset, Size,
01857                                          S, *SUI, WholeAllocaOp))
01858       return false;
01859 
01860   return WholeAllocaOp;
01861 }
01862 
01863 static Value *extractInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
01864                              IntegerType *Ty, uint64_t Offset,
01865                              const Twine &Name) {
01866   DEBUG(dbgs() << "       start: " << *V << "\n");
01867   IntegerType *IntTy = cast<IntegerType>(V->getType());
01868   assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
01869          "Element extends past full value");
01870   uint64_t ShAmt = 8*Offset;
01871   if (DL.isBigEndian())
01872     ShAmt = 8*(DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
01873   if (ShAmt) {
01874     V = IRB.CreateLShr(V, ShAmt, Name + ".shift");
01875     DEBUG(dbgs() << "     shifted: " << *V << "\n");
01876   }
01877   assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
01878          "Cannot extract to a larger integer!");
01879   if (Ty != IntTy) {
01880     V = IRB.CreateTrunc(V, Ty, Name + ".trunc");
01881     DEBUG(dbgs() << "     trunced: " << *V << "\n");
01882   }
01883   return V;
01884 }
01885 
01886 static Value *insertInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *Old,
01887                             Value *V, uint64_t Offset, const Twine &Name) {
01888   IntegerType *IntTy = cast<IntegerType>(Old->getType());
01889   IntegerType *Ty = cast<IntegerType>(V->getType());
01890   assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
01891          "Cannot insert a larger integer!");
01892   DEBUG(dbgs() << "       start: " << *V << "\n");
01893   if (Ty != IntTy) {
01894     V = IRB.CreateZExt(V, IntTy, Name + ".ext");
01895     DEBUG(dbgs() << "    extended: " << *V << "\n");
01896   }
01897   assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
01898          "Element store outside of alloca store");
01899   uint64_t ShAmt = 8*Offset;
01900   if (DL.isBigEndian())
01901     ShAmt = 8*(DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
01902   if (ShAmt) {
01903     V = IRB.CreateShl(V, ShAmt, Name + ".shift");
01904     DEBUG(dbgs() << "     shifted: " << *V << "\n");
01905   }
01906 
01907   if (ShAmt || Ty->getBitWidth() < IntTy->getBitWidth()) {
01908     APInt Mask = ~Ty->getMask().zext(IntTy->getBitWidth()).shl(ShAmt);
01909     Old = IRB.CreateAnd(Old, Mask, Name + ".mask");
01910     DEBUG(dbgs() << "      masked: " << *Old << "\n");
01911     V = IRB.CreateOr(Old, V, Name + ".insert");
01912     DEBUG(dbgs() << "    inserted: " << *V << "\n");
01913   }
01914   return V;
01915 }
01916 
01917 static Value *extractVector(IRBuilderTy &IRB, Value *V,
01918                             unsigned BeginIndex, unsigned EndIndex,
01919                             const Twine &Name) {
01920   VectorType *VecTy = cast<VectorType>(V->getType());
01921   unsigned NumElements = EndIndex - BeginIndex;
01922   assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
01923 
01924   if (NumElements == VecTy->getNumElements())
01925     return V;
01926 
01927   if (NumElements == 1) {
01928     V = IRB.CreateExtractElement(V, IRB.getInt32(BeginIndex),
01929                                  Name + ".extract");
01930     DEBUG(dbgs() << "     extract: " << *V << "\n");
01931     return V;
01932   }
01933 
01934   SmallVector<Constant*, 8> Mask;
01935   Mask.reserve(NumElements);
01936   for (unsigned i = BeginIndex; i != EndIndex; ++i)
01937     Mask.push_back(IRB.getInt32(i));
01938   V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
01939                               ConstantVector::get(Mask),
01940                               Name + ".extract");
01941   DEBUG(dbgs() << "     shuffle: " << *V << "\n");
01942   return V;
01943 }
01944 
01945 static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V,
01946                            unsigned BeginIndex, const Twine &Name) {
01947   VectorType *VecTy = cast<VectorType>(Old->getType());
01948   assert(VecTy && "Can only insert a vector into a vector");
01949 
01950   VectorType *Ty = dyn_cast<VectorType>(V->getType());
01951   if (!Ty) {
01952     // Single element to insert.
01953     V = IRB.CreateInsertElement(Old, V, IRB.getInt32(BeginIndex),
01954                                 Name + ".insert");
01955     DEBUG(dbgs() <<  "     insert: " << *V << "\n");
01956     return V;
01957   }
01958 
01959   assert(Ty->getNumElements() <= VecTy->getNumElements() &&
01960          "Too many elements!");
01961   if (Ty->getNumElements() == VecTy->getNumElements()) {
01962     assert(V->getType() == VecTy && "Vector type mismatch");
01963     return V;
01964   }
01965   unsigned EndIndex = BeginIndex + Ty->getNumElements();
01966 
01967   // When inserting a smaller vector into the larger to store, we first
01968   // use a shuffle vector to widen it with undef elements, and then
01969   // a second shuffle vector to select between the loaded vector and the
01970   // incoming vector.
01971   SmallVector<Constant*, 8> Mask;
01972   Mask.reserve(VecTy->getNumElements());
01973   for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
01974     if (i >= BeginIndex && i < EndIndex)
01975       Mask.push_back(IRB.getInt32(i - BeginIndex));
01976     else
01977       Mask.push_back(UndefValue::get(IRB.getInt32Ty()));
01978   V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
01979                               ConstantVector::get(Mask),
01980                               Name + ".expand");
01981   DEBUG(dbgs() << "    shuffle: " << *V << "\n");
01982 
01983   Mask.clear();
01984   for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
01985     Mask.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex));
01986 
01987   V = IRB.CreateSelect(ConstantVector::get(Mask), V, Old, Name + "blend");
01988 
01989   DEBUG(dbgs() << "    blend: " << *V << "\n");
01990   return V;
01991 }
01992 
01993 namespace {
01994 /// \brief Visitor to rewrite instructions using p particular slice of an alloca
01995 /// to use a new alloca.
01996 ///
01997 /// Also implements the rewriting to vector-based accesses when the partition
01998 /// passes the isVectorPromotionViable predicate. Most of the rewriting logic
01999 /// lives here.
02000 class AllocaSliceRewriter : public InstVisitor<AllocaSliceRewriter, bool> {
02001   // Befriend the base class so it can delegate to private visit methods.
02002   friend class llvm::InstVisitor<AllocaSliceRewriter, bool>;
02003   typedef llvm::InstVisitor<AllocaSliceRewriter, bool> Base;
02004 
02005   const DataLayout &DL;
02006   AllocaSlices &S;
02007   SROA &Pass;
02008   AllocaInst &OldAI, &NewAI;
02009   const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
02010   Type *NewAllocaTy;
02011 
02012   // If we are rewriting an alloca partition which can be written as pure
02013   // vector operations, we stash extra information here. When VecTy is
02014   // non-null, we have some strict guarantees about the rewritten alloca:
02015   //   - The new alloca is exactly the size of the vector type here.
02016   //   - The accesses all either map to the entire vector or to a single
02017   //     element.
02018   //   - The set of accessing instructions is only one of those handled above
02019   //     in isVectorPromotionViable. Generally these are the same access kinds
02020   //     which are promotable via mem2reg.
02021   VectorType *VecTy;
02022   Type *ElementTy;
02023   uint64_t ElementSize;
02024 
02025   // This is a convenience and flag variable that will be null unless the new
02026   // alloca's integer operations should be widened to this integer type due to
02027   // passing isIntegerWideningViable above. If it is non-null, the desired
02028   // integer type will be stored here for easy access during rewriting.
02029   IntegerType *IntTy;
02030 
02031   // The original offset of the slice currently being rewritten relative to
02032   // the original alloca.
02033   uint64_t BeginOffset, EndOffset;
02034   // The new offsets of the slice currently being rewritten relative to the
02035   // original alloca.
02036   uint64_t NewBeginOffset, NewEndOffset;
02037 
02038   uint64_t SliceSize;
02039   bool IsSplittable;
02040   bool IsSplit;
02041   Use *OldUse;
02042   Instruction *OldPtr;
02043 
02044   // Track post-rewrite users which are PHI nodes and Selects.
02045   SmallPtrSetImpl<PHINode *> &PHIUsers;
02046   SmallPtrSetImpl<SelectInst *> &SelectUsers;
02047 
02048   // Utility IR builder, whose name prefix is setup for each visited use, and
02049   // the insertion point is set to point to the user.
02050   IRBuilderTy IRB;
02051 
02052 public:
02053   AllocaSliceRewriter(const DataLayout &DL, AllocaSlices &S, SROA &Pass,
02054                       AllocaInst &OldAI, AllocaInst &NewAI,
02055                       uint64_t NewAllocaBeginOffset,
02056                       uint64_t NewAllocaEndOffset, bool IsVectorPromotable,
02057                       bool IsIntegerPromotable,
02058                       SmallPtrSetImpl<PHINode *> &PHIUsers,
02059                       SmallPtrSetImpl<SelectInst *> &SelectUsers)
02060       : DL(DL), S(S), Pass(Pass), OldAI(OldAI), NewAI(NewAI),
02061         NewAllocaBeginOffset(NewAllocaBeginOffset),
02062         NewAllocaEndOffset(NewAllocaEndOffset),
02063         NewAllocaTy(NewAI.getAllocatedType()),
02064         VecTy(IsVectorPromotable ? cast<VectorType>(NewAllocaTy) : nullptr),
02065         ElementTy(VecTy ? VecTy->getElementType() : nullptr),
02066         ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy) / 8 : 0),
02067         IntTy(IsIntegerPromotable
02068                   ? Type::getIntNTy(
02069                         NewAI.getContext(),
02070                         DL.getTypeSizeInBits(NewAI.getAllocatedType()))
02071                   : nullptr),
02072         BeginOffset(), EndOffset(), IsSplittable(), IsSplit(), OldUse(),
02073         OldPtr(), PHIUsers(PHIUsers), SelectUsers(SelectUsers),
02074         IRB(NewAI.getContext(), ConstantFolder()) {
02075     if (VecTy) {
02076       assert((DL.getTypeSizeInBits(ElementTy) % 8) == 0 &&
02077              "Only multiple-of-8 sized vector elements are viable");
02078       ++NumVectorized;
02079     }
02080     assert((!IsVectorPromotable && !IsIntegerPromotable) ||
02081            IsVectorPromotable != IsIntegerPromotable);
02082   }
02083 
02084   bool visit(AllocaSlices::const_iterator I) {
02085     bool CanSROA = true;
02086     BeginOffset = I->beginOffset();
02087     EndOffset = I->endOffset();
02088     IsSplittable = I->isSplittable();
02089     IsSplit =
02090         BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset;
02091 
02092     // Compute the intersecting offset range.
02093     assert(BeginOffset < NewAllocaEndOffset);
02094     assert(EndOffset > NewAllocaBeginOffset);
02095     NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
02096     NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
02097 
02098     SliceSize = NewEndOffset - NewBeginOffset;
02099 
02100     OldUse = I->getUse();
02101     OldPtr = cast<Instruction>(OldUse->get());
02102 
02103     Instruction *OldUserI = cast<Instruction>(OldUse->getUser());
02104     IRB.SetInsertPoint(OldUserI);
02105     IRB.SetCurrentDebugLocation(OldUserI->getDebugLoc());
02106     IRB.SetNamePrefix(Twine(NewAI.getName()) + "." + Twine(BeginOffset) + ".");
02107 
02108     CanSROA &= visit(cast<Instruction>(OldUse->getUser()));
02109     if (VecTy || IntTy)
02110       assert(CanSROA);
02111     return CanSROA;
02112   }
02113 
02114 private:
02115   // Make sure the other visit overloads are visible.
02116   using Base::visit;
02117 
02118   // Every instruction which can end up as a user must have a rewrite rule.
02119   bool visitInstruction(Instruction &I) {
02120     DEBUG(dbgs() << "    !!!! Cannot rewrite: " << I << "\n");
02121     llvm_unreachable("No rewrite rule for this instruction!");
02122   }
02123 
02124   Value *getNewAllocaSlicePtr(IRBuilderTy &IRB, Type *PointerTy) {
02125     // Note that the offset computation can use BeginOffset or NewBeginOffset
02126     // interchangeably for unsplit slices.
02127     assert(IsSplit || BeginOffset == NewBeginOffset);
02128     uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
02129 
02130 #ifndef NDEBUG
02131     StringRef OldName = OldPtr->getName();
02132     // Skip through the last '.sroa.' component of the name.
02133     size_t LastSROAPrefix = OldName.rfind(".sroa.");
02134     if (LastSROAPrefix != StringRef::npos) {
02135       OldName = OldName.substr(LastSROAPrefix + strlen(".sroa."));
02136       // Look for an SROA slice index.
02137       size_t IndexEnd = OldName.find_first_not_of("0123456789");
02138       if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') {
02139         // Strip the index and look for the offset.
02140         OldName = OldName.substr(IndexEnd + 1);
02141         size_t OffsetEnd = OldName.find_first_not_of("0123456789");
02142         if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.')
02143           // Strip the offset.
02144           OldName = OldName.substr(OffsetEnd + 1);
02145       }
02146     }
02147     // Strip any SROA suffixes as well.
02148     OldName = OldName.substr(0, OldName.find(".sroa_"));
02149 #endif
02150 
02151     return getAdjustedPtr(IRB, DL, &NewAI,
02152                           APInt(DL.getPointerSizeInBits(), Offset), PointerTy,
02153 #ifndef NDEBUG
02154                           Twine(OldName) + "."
02155 #else
02156                           Twine()
02157 #endif
02158                           );
02159   }
02160 
02161   /// \brief Compute suitable alignment to access this slice of the *new* alloca.
02162   ///
02163   /// You can optionally pass a type to this routine and if that type's ABI
02164   /// alignment is itself suitable, this will return zero.
02165   unsigned getSliceAlign(Type *Ty = nullptr) {
02166     unsigned NewAIAlign = NewAI.getAlignment();
02167     if (!NewAIAlign)
02168       NewAIAlign = DL.getABITypeAlignment(NewAI.getAllocatedType());
02169     unsigned Align = MinAlign(NewAIAlign, NewBeginOffset - NewAllocaBeginOffset);
02170     return (Ty && Align == DL.getABITypeAlignment(Ty)) ? 0 : Align;
02171   }
02172 
02173   unsigned getIndex(uint64_t Offset) {
02174     assert(VecTy && "Can only call getIndex when rewriting a vector");
02175     uint64_t RelOffset = Offset - NewAllocaBeginOffset;
02176     assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds");
02177     uint32_t Index = RelOffset / ElementSize;
02178     assert(Index * ElementSize == RelOffset);
02179     return Index;
02180   }
02181 
02182   void deleteIfTriviallyDead(Value *V) {
02183     Instruction *I = cast<Instruction>(V);
02184     if (isInstructionTriviallyDead(I))
02185       Pass.DeadInsts.insert(I);
02186   }
02187 
02188   Value *rewriteVectorizedLoadInst() {
02189     unsigned BeginIndex = getIndex(NewBeginOffset);
02190     unsigned EndIndex = getIndex(NewEndOffset);
02191     assert(EndIndex > BeginIndex && "Empty vector!");
02192 
02193     Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02194                                      "load");
02195     return extractVector(IRB, V, BeginIndex, EndIndex, "vec");
02196   }
02197 
02198   Value *rewriteIntegerLoad(LoadInst &LI) {
02199     assert(IntTy && "We cannot insert an integer to the alloca");
02200     assert(!LI.isVolatile());
02201     Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02202                                      "load");
02203     V = convertValue(DL, IRB, V, IntTy);
02204     assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
02205     uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
02206     if (Offset > 0 || NewEndOffset < NewAllocaEndOffset)
02207       V = extractInteger(DL, IRB, V, cast<IntegerType>(LI.getType()), Offset,
02208                          "extract");
02209     return V;
02210   }
02211 
02212   bool visitLoadInst(LoadInst &LI) {
02213     DEBUG(dbgs() << "    original: " << LI << "\n");
02214     Value *OldOp = LI.getOperand(0);
02215     assert(OldOp == OldPtr);
02216 
02217     Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), SliceSize * 8)
02218                              : LI.getType();
02219     bool IsPtrAdjusted = false;
02220     Value *V;
02221     if (VecTy) {
02222       V = rewriteVectorizedLoadInst();
02223     } else if (IntTy && LI.getType()->isIntegerTy()) {
02224       V = rewriteIntegerLoad(LI);
02225     } else if (NewBeginOffset == NewAllocaBeginOffset &&
02226                canConvertValue(DL, NewAllocaTy, LI.getType())) {
02227       V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02228                                 LI.isVolatile(), LI.getName());
02229     } else {
02230       Type *LTy = TargetTy->getPointerTo();
02231       V = IRB.CreateAlignedLoad(getNewAllocaSlicePtr(IRB, LTy),
02232                                 getSliceAlign(TargetTy), LI.isVolatile(),
02233                                 LI.getName());
02234       IsPtrAdjusted = true;
02235     }
02236     V = convertValue(DL, IRB, V, TargetTy);
02237 
02238     if (IsSplit) {
02239       assert(!LI.isVolatile());
02240       assert(LI.getType()->isIntegerTy() &&
02241              "Only integer type loads and stores are split");
02242       assert(SliceSize < DL.getTypeStoreSize(LI.getType()) &&
02243              "Split load isn't smaller than original load");
02244       assert(LI.getType()->getIntegerBitWidth() ==
02245              DL.getTypeStoreSizeInBits(LI.getType()) &&
02246              "Non-byte-multiple bit width");
02247       // Move the insertion point just past the load so that we can refer to it.
02248       IRB.SetInsertPoint(std::next(BasicBlock::iterator(&LI)));
02249       // Create a placeholder value with the same type as LI to use as the
02250       // basis for the new value. This allows us to replace the uses of LI with
02251       // the computed value, and then replace the placeholder with LI, leaving
02252       // LI only used for this computation.
02253       Value *Placeholder
02254         = new LoadInst(UndefValue::get(LI.getType()->getPointerTo()));
02255       V = insertInteger(DL, IRB, Placeholder, V, NewBeginOffset,
02256                         "insert");
02257       LI.replaceAllUsesWith(V);
02258       Placeholder->replaceAllUsesWith(&LI);
02259       delete Placeholder;
02260     } else {
02261       LI.replaceAllUsesWith(V);
02262     }
02263 
02264     Pass.DeadInsts.insert(&LI);
02265     deleteIfTriviallyDead(OldOp);
02266     DEBUG(dbgs() << "          to: " << *V << "\n");
02267     return !LI.isVolatile() && !IsPtrAdjusted;
02268   }
02269 
02270   bool rewriteVectorizedStoreInst(Value *V, StoreInst &SI, Value *OldOp) {
02271     if (V->getType() != VecTy) {
02272       unsigned BeginIndex = getIndex(NewBeginOffset);
02273       unsigned EndIndex = getIndex(NewEndOffset);
02274       assert(EndIndex > BeginIndex && "Empty vector!");
02275       unsigned NumElements = EndIndex - BeginIndex;
02276       assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
02277       Type *SliceTy =
02278           (NumElements == 1) ? ElementTy
02279                              : VectorType::get(ElementTy, NumElements);
02280       if (V->getType() != SliceTy)
02281         V = convertValue(DL, IRB, V, SliceTy);
02282 
02283       // Mix in the existing elements.
02284       Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02285                                          "load");
02286       V = insertVector(IRB, Old, V, BeginIndex, "vec");
02287     }
02288     StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
02289     Pass.DeadInsts.insert(&SI);
02290 
02291     (void)Store;
02292     DEBUG(dbgs() << "          to: " << *Store << "\n");
02293     return true;
02294   }
02295 
02296   bool rewriteIntegerStore(Value *V, StoreInst &SI) {
02297     assert(IntTy && "We cannot extract an integer from the alloca");
02298     assert(!SI.isVolatile());
02299     if (DL.getTypeSizeInBits(V->getType()) != IntTy->getBitWidth()) {
02300       Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02301                                          "oldload");
02302       Old = convertValue(DL, IRB, Old, IntTy);
02303       assert(BeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
02304       uint64_t Offset = BeginOffset - NewAllocaBeginOffset;
02305       V = insertInteger(DL, IRB, Old, SI.getValueOperand(), Offset,
02306                         "insert");
02307     }
02308     V = convertValue(DL, IRB, V, NewAllocaTy);
02309     StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
02310     Pass.DeadInsts.insert(&SI);
02311     (void)Store;
02312     DEBUG(dbgs() << "          to: " << *Store << "\n");
02313     return true;
02314   }
02315 
02316   bool visitStoreInst(StoreInst &SI) {
02317     DEBUG(dbgs() << "    original: " << SI << "\n");
02318     Value *OldOp = SI.getOperand(1);
02319     assert(OldOp == OldPtr);
02320 
02321     Value *V = SI.getValueOperand();
02322 
02323     // Strip all inbounds GEPs and pointer casts to try to dig out any root
02324     // alloca that should be re-examined after promoting this alloca.
02325     if (V->getType()->isPointerTy())
02326       if (AllocaInst *AI = dyn_cast<AllocaInst>(V->stripInBoundsOffsets()))
02327         Pass.PostPromotionWorklist.insert(AI);
02328 
02329     if (SliceSize < DL.getTypeStoreSize(V->getType())) {
02330       assert(!SI.isVolatile());
02331       assert(V->getType()->isIntegerTy() &&
02332              "Only integer type loads and stores are split");
02333       assert(V->getType()->getIntegerBitWidth() ==
02334              DL.getTypeStoreSizeInBits(V->getType()) &&
02335              "Non-byte-multiple bit width");
02336       IntegerType *NarrowTy = Type::getIntNTy(SI.getContext(), SliceSize * 8);
02337       V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset,
02338                          "extract");
02339     }
02340 
02341     if (VecTy)
02342       return rewriteVectorizedStoreInst(V, SI, OldOp);
02343     if (IntTy && V->getType()->isIntegerTy())
02344       return rewriteIntegerStore(V, SI);
02345 
02346     StoreInst *NewSI;
02347     if (NewBeginOffset == NewAllocaBeginOffset &&
02348         NewEndOffset == NewAllocaEndOffset &&
02349         canConvertValue(DL, V->getType(), NewAllocaTy)) {
02350       V = convertValue(DL, IRB, V, NewAllocaTy);
02351       NewSI = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
02352                                      SI.isVolatile());
02353     } else {
02354       Value *NewPtr = getNewAllocaSlicePtr(IRB, V->getType()->getPointerTo());
02355       NewSI = IRB.CreateAlignedStore(V, NewPtr, getSliceAlign(V->getType()),
02356                                      SI.isVolatile());
02357     }
02358     (void)NewSI;
02359     Pass.DeadInsts.insert(&SI);
02360     deleteIfTriviallyDead(OldOp);
02361 
02362     DEBUG(dbgs() << "          to: " << *NewSI << "\n");
02363     return NewSI->getPointerOperand() == &NewAI && !SI.isVolatile();
02364   }
02365 
02366   /// \brief Compute an integer value from splatting an i8 across the given
02367   /// number of bytes.
02368   ///
02369   /// Note that this routine assumes an i8 is a byte. If that isn't true, don't
02370   /// call this routine.
02371   /// FIXME: Heed the advice above.
02372   ///
02373   /// \param V The i8 value to splat.
02374   /// \param Size The number of bytes in the output (assuming i8 is one byte)
02375   Value *getIntegerSplat(Value *V, unsigned Size) {
02376     assert(Size > 0 && "Expected a positive number of bytes.");
02377     IntegerType *VTy = cast<IntegerType>(V->getType());
02378     assert(VTy->getBitWidth() == 8 && "Expected an i8 value for the byte");
02379     if (Size == 1)
02380       return V;
02381 
02382     Type *SplatIntTy = Type::getIntNTy(VTy->getContext(), Size*8);
02383     V = IRB.CreateMul(IRB.CreateZExt(V, SplatIntTy, "zext"),
02384                       ConstantExpr::getUDiv(
02385                         Constant::getAllOnesValue(SplatIntTy),
02386                         ConstantExpr::getZExt(
02387                           Constant::getAllOnesValue(V->getType()),
02388                           SplatIntTy)),
02389                       "isplat");
02390     return V;
02391   }
02392 
02393   /// \brief Compute a vector splat for a given element value.
02394   Value *getVectorSplat(Value *V, unsigned NumElements) {
02395     V = IRB.CreateVectorSplat(NumElements, V, "vsplat");
02396     DEBUG(dbgs() << "       splat: " << *V << "\n");
02397     return V;
02398   }
02399 
02400   bool visitMemSetInst(MemSetInst &II) {
02401     DEBUG(dbgs() << "    original: " << II << "\n");
02402     assert(II.getRawDest() == OldPtr);
02403 
02404     // If the memset has a variable size, it cannot be split, just adjust the
02405     // pointer to the new alloca.
02406     if (!isa<Constant>(II.getLength())) {
02407       assert(!IsSplit);
02408       assert(NewBeginOffset == BeginOffset);
02409       II.setDest(getNewAllocaSlicePtr(IRB, OldPtr->getType()));
02410       Type *CstTy = II.getAlignmentCst()->getType();
02411       II.setAlignment(ConstantInt::get(CstTy, getSliceAlign()));
02412 
02413       deleteIfTriviallyDead(OldPtr);
02414       return false;
02415     }
02416 
02417     // Record this instruction for deletion.
02418     Pass.DeadInsts.insert(&II);
02419 
02420     Type *AllocaTy = NewAI.getAllocatedType();
02421     Type *ScalarTy = AllocaTy->getScalarType();
02422 
02423     // If this doesn't map cleanly onto the alloca type, and that type isn't
02424     // a single value type, just emit a memset.
02425     if (!VecTy && !IntTy &&
02426         (BeginOffset > NewAllocaBeginOffset ||
02427          EndOffset < NewAllocaEndOffset ||
02428          SliceSize != DL.getTypeStoreSize(AllocaTy) ||
02429          !AllocaTy->isSingleValueType() ||
02430          !DL.isLegalInteger(DL.getTypeSizeInBits(ScalarTy)) ||
02431          DL.getTypeSizeInBits(ScalarTy)%8 != 0)) {
02432       Type *SizeTy = II.getLength()->getType();
02433       Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
02434       CallInst *New = IRB.CreateMemSet(
02435           getNewAllocaSlicePtr(IRB, OldPtr->getType()), II.getValue(), Size,
02436           getSliceAlign(), II.isVolatile());
02437       (void)New;
02438       DEBUG(dbgs() << "          to: " << *New << "\n");
02439       return false;
02440     }
02441 
02442     // If we can represent this as a simple value, we have to build the actual
02443     // value to store, which requires expanding the byte present in memset to
02444     // a sensible representation for the alloca type. This is essentially
02445     // splatting the byte to a sufficiently wide integer, splatting it across
02446     // any desired vector width, and bitcasting to the final type.
02447     Value *V;
02448 
02449     if (VecTy) {
02450       // If this is a memset of a vectorized alloca, insert it.
02451       assert(ElementTy == ScalarTy);
02452 
02453       unsigned BeginIndex = getIndex(NewBeginOffset);
02454       unsigned EndIndex = getIndex(NewEndOffset);
02455       assert(EndIndex > BeginIndex && "Empty vector!");
02456       unsigned NumElements = EndIndex - BeginIndex;
02457       assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
02458 
02459       Value *Splat =
02460           getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ElementTy) / 8);
02461       Splat = convertValue(DL, IRB, Splat, ElementTy);
02462       if (NumElements > 1)
02463         Splat = getVectorSplat(Splat, NumElements);
02464 
02465       Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02466                                          "oldload");
02467       V = insertVector(IRB, Old, Splat, BeginIndex, "vec");
02468     } else if (IntTy) {
02469       // If this is a memset on an alloca where we can widen stores, insert the
02470       // set integer.
02471       assert(!II.isVolatile());
02472 
02473       uint64_t Size = NewEndOffset - NewBeginOffset;
02474       V = getIntegerSplat(II.getValue(), Size);
02475 
02476       if (IntTy && (BeginOffset != NewAllocaBeginOffset ||
02477                     EndOffset != NewAllocaBeginOffset)) {
02478         Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02479                                            "oldload");
02480         Old = convertValue(DL, IRB, Old, IntTy);
02481         uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
02482         V = insertInteger(DL, IRB, Old, V, Offset, "insert");
02483       } else {
02484         assert(V->getType() == IntTy &&
02485                "Wrong type for an alloca wide integer!");
02486       }
02487       V = convertValue(DL, IRB, V, AllocaTy);
02488     } else {
02489       // Established these invariants above.
02490       assert(NewBeginOffset == NewAllocaBeginOffset);
02491       assert(NewEndOffset == NewAllocaEndOffset);
02492 
02493       V = getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ScalarTy) / 8);
02494       if (VectorType *AllocaVecTy = dyn_cast<VectorType>(AllocaTy))
02495         V = getVectorSplat(V, AllocaVecTy->getNumElements());
02496 
02497       V = convertValue(DL, IRB, V, AllocaTy);
02498     }
02499 
02500     Value *New = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
02501                                         II.isVolatile());
02502     (void)New;
02503     DEBUG(dbgs() << "          to: " << *New << "\n");
02504     return !II.isVolatile();
02505   }
02506 
02507   bool visitMemTransferInst(MemTransferInst &II) {
02508     // Rewriting of memory transfer instructions can be a bit tricky. We break
02509     // them into two categories: split intrinsics and unsplit intrinsics.
02510 
02511     DEBUG(dbgs() << "    original: " << II << "\n");
02512 
02513     bool IsDest = &II.getRawDestUse() == OldUse;
02514     assert((IsDest && II.getRawDest() == OldPtr) ||
02515            (!IsDest && II.getRawSource() == OldPtr));
02516 
02517     unsigned SliceAlign = getSliceAlign();
02518 
02519     // For unsplit intrinsics, we simply modify the source and destination
02520     // pointers in place. This isn't just an optimization, it is a matter of
02521     // correctness. With unsplit intrinsics we may be dealing with transfers
02522     // within a single alloca before SROA ran, or with transfers that have
02523     // a variable length. We may also be dealing with memmove instead of
02524     // memcpy, and so simply updating the pointers is the necessary for us to
02525     // update both source and dest of a single call.
02526     if (!IsSplittable) {
02527       Value *AdjustedPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
02528       if (IsDest)
02529         II.setDest(AdjustedPtr);
02530       else
02531         II.setSource(AdjustedPtr);
02532 
02533       if (II.getAlignment() > SliceAlign) {
02534         Type *CstTy = II.getAlignmentCst()->getType();
02535         II.setAlignment(
02536             ConstantInt::get(CstTy, MinAlign(II.getAlignment(), SliceAlign)));
02537       }
02538 
02539       DEBUG(dbgs() << "          to: " << II << "\n");
02540       deleteIfTriviallyDead(OldPtr);
02541       return false;
02542     }
02543     // For split transfer intrinsics we have an incredibly useful assurance:
02544     // the source and destination do not reside within the same alloca, and at
02545     // least one of them does not escape. This means that we can replace
02546     // memmove with memcpy, and we don't need to worry about all manner of
02547     // downsides to splitting and transforming the operations.
02548 
02549     // If this doesn't map cleanly onto the alloca type, and that type isn't
02550     // a single value type, just emit a memcpy.
02551     bool EmitMemCpy =
02552         !VecTy && !IntTy &&
02553         (BeginOffset > NewAllocaBeginOffset || EndOffset < NewAllocaEndOffset ||
02554          SliceSize != DL.getTypeStoreSize(NewAI.getAllocatedType()) ||
02555          !NewAI.getAllocatedType()->isSingleValueType());
02556 
02557     // If we're just going to emit a memcpy, the alloca hasn't changed, and the
02558     // size hasn't been shrunk based on analysis of the viable range, this is
02559     // a no-op.
02560     if (EmitMemCpy && &OldAI == &NewAI) {
02561       // Ensure the start lines up.
02562       assert(NewBeginOffset == BeginOffset);
02563 
02564       // Rewrite the size as needed.
02565       if (NewEndOffset != EndOffset)
02566         II.setLength(ConstantInt::get(II.getLength()->getType(),
02567                                       NewEndOffset - NewBeginOffset));
02568       return false;
02569     }
02570     // Record this instruction for deletion.
02571     Pass.DeadInsts.insert(&II);
02572 
02573     // Strip all inbounds GEPs and pointer casts to try to dig out any root
02574     // alloca that should be re-examined after rewriting this instruction.
02575     Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest();
02576     if (AllocaInst *AI
02577           = dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets())) {
02578       assert(AI != &OldAI && AI != &NewAI &&
02579              "Splittable transfers cannot reach the same alloca on both ends.");
02580       Pass.Worklist.insert(AI);
02581     }
02582 
02583     Type *OtherPtrTy = OtherPtr->getType();
02584     unsigned OtherAS = OtherPtrTy->getPointerAddressSpace();
02585 
02586     // Compute the relative offset for the other pointer within the transfer.
02587     unsigned IntPtrWidth = DL.getPointerSizeInBits(OtherAS);
02588     APInt OtherOffset(IntPtrWidth, NewBeginOffset - BeginOffset);
02589     unsigned OtherAlign = MinAlign(II.getAlignment() ? II.getAlignment() : 1,
02590                                    OtherOffset.zextOrTrunc(64).getZExtValue());
02591 
02592     if (EmitMemCpy) {
02593       // Compute the other pointer, folding as much as possible to produce
02594       // a single, simple GEP in most cases.
02595       OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
02596                                 OtherPtr->getName() + ".");
02597 
02598       Value *OurPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
02599       Type *SizeTy = II.getLength()->getType();
02600       Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
02601 
02602       CallInst *New = IRB.CreateMemCpy(
02603           IsDest ? OurPtr : OtherPtr, IsDest ? OtherPtr : OurPtr, Size,
02604           MinAlign(SliceAlign, OtherAlign), II.isVolatile());
02605       (void)New;
02606       DEBUG(dbgs() << "          to: " << *New << "\n");
02607       return false;
02608     }
02609 
02610     bool IsWholeAlloca = NewBeginOffset == NewAllocaBeginOffset &&
02611                          NewEndOffset == NewAllocaEndOffset;
02612     uint64_t Size = NewEndOffset - NewBeginOffset;
02613     unsigned BeginIndex = VecTy ? getIndex(NewBeginOffset) : 0;
02614     unsigned EndIndex = VecTy ? getIndex(NewEndOffset) : 0;
02615     unsigned NumElements = EndIndex - BeginIndex;
02616     IntegerType *SubIntTy
02617       = IntTy ? Type::getIntNTy(IntTy->getContext(), Size*8) : nullptr;
02618 
02619     // Reset the other pointer type to match the register type we're going to
02620     // use, but using the address space of the original other pointer.
02621     if (VecTy && !IsWholeAlloca) {
02622       if (NumElements == 1)
02623         OtherPtrTy = VecTy->getElementType();
02624       else
02625         OtherPtrTy = VectorType::get(VecTy->getElementType(), NumElements);
02626 
02627       OtherPtrTy = OtherPtrTy->getPointerTo(OtherAS);
02628     } else if (IntTy && !IsWholeAlloca) {
02629       OtherPtrTy = SubIntTy->getPointerTo(OtherAS);
02630     } else {
02631       OtherPtrTy = NewAllocaTy->getPointerTo(OtherAS);
02632     }
02633 
02634     Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
02635                                    OtherPtr->getName() + ".");
02636     unsigned SrcAlign = OtherAlign;
02637     Value *DstPtr = &NewAI;
02638     unsigned DstAlign = SliceAlign;
02639     if (!IsDest) {
02640       std::swap(SrcPtr, DstPtr);
02641       std::swap(SrcAlign, DstAlign);
02642     }
02643 
02644     Value *Src;
02645     if (VecTy && !IsWholeAlloca && !IsDest) {
02646       Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02647                                   "load");
02648       Src = extractVector(IRB, Src, BeginIndex, EndIndex, "vec");
02649     } else if (IntTy && !IsWholeAlloca && !IsDest) {
02650       Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02651                                   "load");
02652       Src = convertValue(DL, IRB, Src, IntTy);
02653       uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
02654       Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract");
02655     } else {
02656       Src = IRB.CreateAlignedLoad(SrcPtr, SrcAlign, II.isVolatile(),
02657                                   "copyload");
02658     }
02659 
02660     if (VecTy && !IsWholeAlloca && IsDest) {
02661       Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02662                                          "oldload");
02663       Src = insertVector(IRB, Old, Src, BeginIndex, "vec");
02664     } else if (IntTy && !IsWholeAlloca && IsDest) {
02665       Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
02666                                          "oldload");
02667       Old = convertValue(DL, IRB, Old, IntTy);
02668       uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
02669       Src = insertInteger(DL, IRB, Old, Src, Offset, "insert");
02670       Src = convertValue(DL, IRB, Src, NewAllocaTy);
02671     }
02672 
02673     StoreInst *Store = cast<StoreInst>(
02674         IRB.CreateAlignedStore(Src, DstPtr, DstAlign, II.isVolatile()));
02675     (void)Store;
02676     DEBUG(dbgs() << "          to: " << *Store << "\n");
02677     return !II.isVolatile();
02678   }
02679 
02680   bool visitIntrinsicInst(IntrinsicInst &II) {
02681     assert(II.getIntrinsicID() == Intrinsic::lifetime_start ||
02682            II.getIntrinsicID() == Intrinsic::lifetime_end);
02683     DEBUG(dbgs() << "    original: " << II << "\n");
02684     assert(II.getArgOperand(1) == OldPtr);
02685 
02686     // Record this instruction for deletion.
02687     Pass.DeadInsts.insert(&II);
02688 
02689     ConstantInt *Size
02690       = ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
02691                          NewEndOffset - NewBeginOffset);
02692     Value *Ptr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
02693     Value *New;
02694     if (II.getIntrinsicID() == Intrinsic::lifetime_start)
02695       New = IRB.CreateLifetimeStart(Ptr, Size);
02696     else
02697       New = IRB.CreateLifetimeEnd(Ptr, Size);
02698 
02699     (void)New;
02700     DEBUG(dbgs() << "          to: " << *New << "\n");
02701     return true;
02702   }
02703 
02704   bool visitPHINode(PHINode &PN) {
02705     DEBUG(dbgs() << "    original: " << PN << "\n");
02706     assert(BeginOffset >= NewAllocaBeginOffset && "PHIs are unsplittable");
02707     assert(EndOffset <= NewAllocaEndOffset && "PHIs are unsplittable");
02708 
02709     // We would like to compute a new pointer in only one place, but have it be
02710     // as local as possible to the PHI. To do that, we re-use the location of
02711     // the old pointer, which necessarily must be in the right position to
02712     // dominate the PHI.
02713     IRBuilderTy PtrBuilder(IRB);
02714     if (isa<PHINode>(OldPtr))
02715       PtrBuilder.SetInsertPoint(OldPtr->getParent()->getFirstInsertionPt());
02716     else
02717       PtrBuilder.SetInsertPoint(OldPtr);
02718     PtrBuilder.SetCurrentDebugLocation(OldPtr->getDebugLoc());
02719 
02720     Value *NewPtr = getNewAllocaSlicePtr(PtrBuilder, OldPtr->getType());
02721     // Replace the operands which were using the old pointer.
02722     std::replace(PN.op_begin(), PN.op_end(), cast<Value>(OldPtr), NewPtr);
02723 
02724     DEBUG(dbgs() << "          to: " << PN << "\n");
02725     deleteIfTriviallyDead(OldPtr);
02726 
02727     // PHIs can't be promoted on their own, but often can be speculated. We
02728     // check the speculation outside of the rewriter so that we see the
02729     // fully-rewritten alloca.
02730     PHIUsers.insert(&PN);
02731     return true;
02732   }
02733 
02734   bool visitSelectInst(SelectInst &SI) {
02735     DEBUG(dbgs() << "    original: " << SI << "\n");
02736     assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) &&
02737            "Pointer isn't an operand!");
02738     assert(BeginOffset >= NewAllocaBeginOffset && "Selects are unsplittable");
02739     assert(EndOffset <= NewAllocaEndOffset && "Selects are unsplittable");
02740 
02741     Value *NewPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
02742     // Replace the operands which were using the old pointer.
02743     if (SI.getOperand(1) == OldPtr)
02744       SI.setOperand(1, NewPtr);
02745     if (SI.getOperand(2) == OldPtr)
02746       SI.setOperand(2, NewPtr);
02747 
02748     DEBUG(dbgs() << "          to: " << SI << "\n");
02749     deleteIfTriviallyDead(OldPtr);
02750 
02751     // Selects can't be promoted on their own, but often can be speculated. We
02752     // check the speculation outside of the rewriter so that we see the
02753     // fully-rewritten alloca.
02754     SelectUsers.insert(&SI);
02755     return true;
02756   }
02757 
02758 };
02759 }
02760 
02761 namespace {
02762 /// \brief Visitor to rewrite aggregate loads and stores as scalar.
02763 ///
02764 /// This pass aggressively rewrites all aggregate loads and stores on
02765 /// a particular pointer (or any pointer derived from it which we can identify)
02766 /// with scalar loads and stores.
02767 class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
02768   // Befriend the base class so it can delegate to private visit methods.
02769   friend class llvm::InstVisitor<AggLoadStoreRewriter, bool>;
02770 
02771   const DataLayout &DL;
02772 
02773   /// Queue of pointer uses to analyze and potentially rewrite.
02774   SmallVector<Use *, 8> Queue;
02775 
02776   /// Set to prevent us from cycling with phi nodes and loops.
02777   SmallPtrSet<User *, 8> Visited;
02778 
02779   /// The current pointer use being rewritten. This is used to dig up the used
02780   /// value (as opposed to the user).
02781   Use *U;
02782 
02783 public:
02784   AggLoadStoreRewriter(const DataLayout &DL) : DL(DL) {}
02785 
02786   /// Rewrite loads and stores through a pointer and all pointers derived from
02787   /// it.
02788   bool rewrite(Instruction &I) {
02789     DEBUG(dbgs() << "  Rewriting FCA loads and stores...\n");
02790     enqueueUsers(I);
02791     bool Changed = false;
02792     while (!Queue.empty()) {
02793       U = Queue.pop_back_val();
02794       Changed |= visit(cast<Instruction>(U->getUser()));
02795     }
02796     return Changed;
02797   }
02798 
02799 private:
02800   /// Enqueue all the users of the given instruction for further processing.
02801   /// This uses a set to de-duplicate users.
02802   void enqueueUsers(Instruction &I) {
02803     for (Use &U : I.uses())
02804       if (Visited.insert(U.getUser()))
02805         Queue.push_back(&U);
02806   }
02807 
02808   // Conservative default is to not rewrite anything.
02809   bool visitInstruction(Instruction &I) { return false; }
02810 
02811   /// \brief Generic recursive split emission class.
02812   template <typename Derived>
02813   class OpSplitter {
02814   protected:
02815     /// The builder used to form new instructions.
02816     IRBuilderTy IRB;
02817     /// The indices which to be used with insert- or extractvalue to select the
02818     /// appropriate value within the aggregate.
02819     SmallVector<unsigned, 4> Indices;
02820     /// The indices to a GEP instruction which will move Ptr to the correct slot
02821     /// within the aggregate.
02822     SmallVector<Value *, 4> GEPIndices;
02823     /// The base pointer of the original op, used as a base for GEPing the
02824     /// split operations.
02825     Value *Ptr;
02826 
02827     /// Initialize the splitter with an insertion point, Ptr and start with a
02828     /// single zero GEP index.
02829     OpSplitter(Instruction *InsertionPoint, Value *Ptr)
02830       : IRB(InsertionPoint), GEPIndices(1, IRB.getInt32(0)), Ptr(Ptr) {}
02831 
02832   public:
02833     /// \brief Generic recursive split emission routine.
02834     ///
02835     /// This method recursively splits an aggregate op (load or store) into
02836     /// scalar or vector ops. It splits recursively until it hits a single value
02837     /// and emits that single value operation via the template argument.
02838     ///
02839     /// The logic of this routine relies on GEPs and insertvalue and
02840     /// extractvalue all operating with the same fundamental index list, merely
02841     /// formatted differently (GEPs need actual values).
02842     ///
02843     /// \param Ty  The type being split recursively into smaller ops.
02844     /// \param Agg The aggregate value being built up or stored, depending on
02845     /// whether this is splitting a load or a store respectively.
02846     void emitSplitOps(Type *Ty, Value *&Agg, const Twine &Name) {
02847       if (Ty->isSingleValueType())
02848         return static_cast<Derived *>(this)->emitFunc(Ty, Agg, Name);
02849 
02850       if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
02851         unsigned OldSize = Indices.size();
02852         (void)OldSize;
02853         for (unsigned Idx = 0, Size = ATy->getNumElements(); Idx != Size;
02854              ++Idx) {
02855           assert(Indices.size() == OldSize && "Did not return to the old size");
02856           Indices.push_back(Idx);
02857           GEPIndices.push_back(IRB.getInt32(Idx));
02858           emitSplitOps(ATy->getElementType(), Agg, Name + "." + Twine(Idx));
02859           GEPIndices.pop_back();
02860           Indices.pop_back();
02861         }
02862         return;
02863       }
02864 
02865       if (StructType *STy = dyn_cast<StructType>(Ty)) {
02866         unsigned OldSize = Indices.size();
02867         (void)OldSize;
02868         for (unsigned Idx = 0, Size = STy->getNumElements(); Idx != Size;
02869              ++Idx) {
02870           assert(Indices.size() == OldSize && "Did not return to the old size");
02871           Indices.push_back(Idx);
02872           GEPIndices.push_back(IRB.getInt32(Idx));
02873           emitSplitOps(STy->getElementType(Idx), Agg, Name + "." + Twine(Idx));
02874           GEPIndices.pop_back();
02875           Indices.pop_back();
02876         }
02877         return;
02878       }
02879 
02880       llvm_unreachable("Only arrays and structs are aggregate loadable types");
02881     }
02882   };
02883 
02884   struct LoadOpSplitter : public OpSplitter<LoadOpSplitter> {
02885     LoadOpSplitter(Instruction *InsertionPoint, Value *Ptr)
02886       : OpSplitter<LoadOpSplitter>(InsertionPoint, Ptr) {}
02887 
02888     /// Emit a leaf load of a single value. This is called at the leaves of the
02889     /// recursive emission to actually load values.
02890     void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
02891       assert(Ty->isSingleValueType());
02892       // Load the single value and insert it using the indices.
02893       Value *GEP = IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep");
02894       Value *Load = IRB.CreateLoad(GEP, Name + ".load");
02895       Agg = IRB.CreateInsertValue(Agg, Load, Indices, Name + ".insert");
02896       DEBUG(dbgs() << "          to: " << *Load << "\n");
02897     }
02898   };
02899 
02900   bool visitLoadInst(LoadInst &LI) {
02901     assert(LI.getPointerOperand() == *U);
02902     if (!LI.isSimple() || LI.getType()->isSingleValueType())
02903       return false;
02904 
02905     // We have an aggregate being loaded, split it apart.
02906     DEBUG(dbgs() << "    original: " << LI << "\n");
02907     LoadOpSplitter Splitter(&LI, *U);
02908     Value *V = UndefValue::get(LI.getType());
02909     Splitter.emitSplitOps(LI.getType(), V, LI.getName() + ".fca");
02910     LI.replaceAllUsesWith(V);
02911     LI.eraseFromParent();
02912     return true;
02913   }
02914 
02915   struct StoreOpSplitter : public OpSplitter<StoreOpSplitter> {
02916     StoreOpSplitter(Instruction *InsertionPoint, Value *Ptr)
02917       : OpSplitter<StoreOpSplitter>(InsertionPoint, Ptr) {}
02918 
02919     /// Emit a leaf store of a single value. This is called at the leaves of the
02920     /// recursive emission to actually produce stores.
02921     void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
02922       assert(Ty->isSingleValueType());
02923       // Extract the single value and store it using the indices.
02924       Value *Store = IRB.CreateStore(
02925         IRB.CreateExtractValue(Agg, Indices, Name + ".extract"),
02926         IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep"));
02927       (void)Store;
02928       DEBUG(dbgs() << "          to: " << *Store << "\n");
02929     }
02930   };
02931 
02932   bool visitStoreInst(StoreInst &SI) {
02933     if (!SI.isSimple() || SI.getPointerOperand() != *U)
02934       return false;
02935     Value *V = SI.getValueOperand();
02936     if (V->getType()->isSingleValueType())
02937       return false;
02938 
02939     // We have an aggregate being stored, split it apart.
02940     DEBUG(dbgs() << "    original: " << SI << "\n");
02941     StoreOpSplitter Splitter(&SI, *U);
02942     Splitter.emitSplitOps(V->getType(), V, V->getName() + ".fca");
02943     SI.eraseFromParent();
02944     return true;
02945   }
02946 
02947   bool visitBitCastInst(BitCastInst &BC) {
02948     enqueueUsers(BC);
02949     return false;
02950   }
02951 
02952   bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
02953     enqueueUsers(GEPI);
02954     return false;
02955   }
02956 
02957   bool visitPHINode(PHINode &PN) {
02958     enqueueUsers(PN);
02959     return false;
02960   }
02961 
02962   bool visitSelectInst(SelectInst &SI) {
02963     enqueueUsers(SI);
02964     return false;
02965   }
02966 };
02967 }
02968 
02969 /// \brief Strip aggregate type wrapping.
02970 ///
02971 /// This removes no-op aggregate types wrapping an underlying type. It will
02972 /// strip as many layers of types as it can without changing either the type
02973 /// size or the allocated size.
02974 static Type *stripAggregateTypeWrapping(const DataLayout &DL, Type *Ty) {
02975   if (Ty->isSingleValueType())
02976     return Ty;
02977 
02978   uint64_t AllocSize = DL.getTypeAllocSize(Ty);
02979   uint64_t TypeSize = DL.getTypeSizeInBits(Ty);
02980 
02981   Type *InnerTy;
02982   if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
02983     InnerTy = ArrTy->getElementType();
02984   } else if (StructType *STy = dyn_cast<StructType>(Ty)) {
02985     const StructLayout *SL = DL.getStructLayout(STy);
02986     unsigned Index = SL->getElementContainingOffset(0);
02987     InnerTy = STy->getElementType(Index);
02988   } else {
02989     return Ty;
02990   }
02991 
02992   if (AllocSize > DL.getTypeAllocSize(InnerTy) ||
02993       TypeSize > DL.getTypeSizeInBits(InnerTy))
02994     return Ty;
02995 
02996   return stripAggregateTypeWrapping(DL, InnerTy);
02997 }
02998 
02999 /// \brief Try to find a partition of the aggregate type passed in for a given
03000 /// offset and size.
03001 ///
03002 /// This recurses through the aggregate type and tries to compute a subtype
03003 /// based on the offset and size. When the offset and size span a sub-section
03004 /// of an array, it will even compute a new array type for that sub-section,
03005 /// and the same for structs.
03006 ///
03007 /// Note that this routine is very strict and tries to find a partition of the
03008 /// type which produces the *exact* right offset and size. It is not forgiving
03009 /// when the size or offset cause either end of type-based partition to be off.
03010 /// Also, this is a best-effort routine. It is reasonable to give up and not
03011 /// return a type if necessary.
03012 static Type *getTypePartition(const DataLayout &DL, Type *Ty,
03013                               uint64_t Offset, uint64_t Size) {
03014   if (Offset == 0 && DL.getTypeAllocSize(Ty) == Size)
03015     return stripAggregateTypeWrapping(DL, Ty);
03016   if (Offset > DL.getTypeAllocSize(Ty) ||
03017       (DL.getTypeAllocSize(Ty) - Offset) < Size)
03018     return nullptr;
03019 
03020   if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) {
03021     // We can't partition pointers...
03022     if (SeqTy->isPointerTy())
03023       return nullptr;
03024 
03025     Type *ElementTy = SeqTy->getElementType();
03026     uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
03027     uint64_t NumSkippedElements = Offset / ElementSize;
03028     if (ArrayType *ArrTy = dyn_cast<ArrayType>(SeqTy)) {
03029       if (NumSkippedElements >= ArrTy->getNumElements())
03030         return nullptr;
03031     } else if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy)) {
03032       if (NumSkippedElements >= VecTy->getNumElements())
03033         return nullptr;
03034     }
03035     Offset -= NumSkippedElements * ElementSize;
03036 
03037     // First check if we need to recurse.
03038     if (Offset > 0 || Size < ElementSize) {
03039       // Bail if the partition ends in a different array element.
03040       if ((Offset + Size) > ElementSize)
03041         return nullptr;
03042       // Recurse through the element type trying to peel off offset bytes.
03043       return getTypePartition(DL, ElementTy, Offset, Size);
03044     }
03045     assert(Offset == 0);
03046 
03047     if (Size == ElementSize)
03048       return stripAggregateTypeWrapping(DL, ElementTy);
03049     assert(Size > ElementSize);
03050     uint64_t NumElements = Size / ElementSize;
03051     if (NumElements * ElementSize != Size)
03052       return nullptr;
03053     return ArrayType::get(ElementTy, NumElements);
03054   }
03055 
03056   StructType *STy = dyn_cast<StructType>(Ty);
03057   if (!STy)
03058     return nullptr;
03059 
03060   const StructLayout *SL = DL.getStructLayout(STy);
03061   if (Offset >= SL->getSizeInBytes())
03062     return nullptr;
03063   uint64_t EndOffset = Offset + Size;
03064   if (EndOffset > SL->getSizeInBytes())
03065     return nullptr;
03066 
03067   unsigned Index = SL->getElementContainingOffset(Offset);
03068   Offset -= SL->getElementOffset(Index);
03069 
03070   Type *ElementTy = STy->getElementType(Index);
03071   uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
03072   if (Offset >= ElementSize)
03073     return nullptr; // The offset points into alignment padding.
03074 
03075   // See if any partition must be contained by the element.
03076   if (Offset > 0 || Size < ElementSize) {
03077     if ((Offset + Size) > ElementSize)
03078       return nullptr;
03079     return getTypePartition(DL, ElementTy, Offset, Size);
03080   }
03081   assert(Offset == 0);
03082 
03083   if (Size == ElementSize)
03084     return stripAggregateTypeWrapping(DL, ElementTy);
03085 
03086   StructType::element_iterator EI = STy->element_begin() + Index,
03087                                EE = STy->element_end();
03088   if (EndOffset < SL->getSizeInBytes()) {
03089     unsigned EndIndex = SL->getElementContainingOffset(EndOffset);
03090     if (Index == EndIndex)
03091       return nullptr; // Within a single element and its padding.
03092 
03093     // Don't try to form "natural" types if the elements don't line up with the
03094     // expected size.
03095     // FIXME: We could potentially recurse down through the last element in the
03096     // sub-struct to find a natural end point.
03097     if (SL->getElementOffset(EndIndex) != EndOffset)
03098       return nullptr;
03099 
03100     assert(Index < EndIndex);
03101     EE = STy->element_begin() + EndIndex;
03102   }
03103 
03104   // Try to build up a sub-structure.
03105   StructType *SubTy = StructType::get(STy->getContext(), makeArrayRef(EI, EE),
03106                                       STy->isPacked());
03107   const StructLayout *SubSL = DL.getStructLayout(SubTy);
03108   if (Size != SubSL->getSizeInBytes())
03109     return nullptr; // The sub-struct doesn't have quite the size needed.
03110 
03111   return SubTy;
03112 }
03113 
03114 /// \brief Rewrite an alloca partition's users.
03115 ///
03116 /// This routine drives both of the rewriting goals of the SROA pass. It tries
03117 /// to rewrite uses of an alloca partition to be conducive for SSA value
03118 /// promotion. If the partition needs a new, more refined alloca, this will
03119 /// build that new alloca, preserving as much type information as possible, and
03120 /// rewrite the uses of the old alloca to point at the new one and have the
03121 /// appropriate new offsets. It also evaluates how successful the rewrite was
03122 /// at enabling promotion and if it was successful queues the alloca to be
03123 /// promoted.
03124 bool SROA::rewritePartition(AllocaInst &AI, AllocaSlices &S,
03125                             AllocaSlices::iterator B, AllocaSlices::iterator E,
03126                             int64_t BeginOffset, int64_t EndOffset,
03127                             ArrayRef<AllocaSlices::iterator> SplitUses) {
03128   assert(BeginOffset < EndOffset);
03129   uint64_t SliceSize = EndOffset - BeginOffset;
03130 
03131   // Try to compute a friendly type for this partition of the alloca. This
03132   // won't always succeed, in which case we fall back to a legal integer type
03133   // or an i8 array of an appropriate size.
03134   Type *SliceTy = nullptr;
03135   if (Type *CommonUseTy = findCommonType(B, E, EndOffset))
03136     if (DL->getTypeAllocSize(CommonUseTy) >= SliceSize)
03137       SliceTy = CommonUseTy;
03138   if (!SliceTy)
03139     if (Type *TypePartitionTy = getTypePartition(*DL, AI.getAllocatedType(),
03140                                                  BeginOffset, SliceSize))
03141       SliceTy = TypePartitionTy;
03142   if ((!SliceTy || (SliceTy->isArrayTy() &&
03143                     SliceTy->getArrayElementType()->isIntegerTy())) &&
03144       DL->isLegalInteger(SliceSize * 8))
03145     SliceTy = Type::getIntNTy(*C, SliceSize * 8);
03146   if (!SliceTy)
03147     SliceTy = ArrayType::get(Type::getInt8Ty(*C), SliceSize);
03148   assert(DL->getTypeAllocSize(SliceTy) >= SliceSize);
03149 
03150   bool IsVectorPromotable = isVectorPromotionViable(
03151       *DL, SliceTy, S, BeginOffset, EndOffset, B, E, SplitUses);
03152 
03153   bool IsIntegerPromotable =
03154       !IsVectorPromotable &&
03155       isIntegerWideningViable(*DL, SliceTy, BeginOffset, S, B, E, SplitUses);
03156 
03157   // Check for the case where we're going to rewrite to a new alloca of the
03158   // exact same type as the original, and with the same access offsets. In that
03159   // case, re-use the existing alloca, but still run through the rewriter to
03160   // perform phi and select speculation.
03161   AllocaInst *NewAI;
03162   if (SliceTy == AI.getAllocatedType()) {
03163     assert(BeginOffset == 0 &&
03164            "Non-zero begin offset but same alloca type");
03165     NewAI = &AI;
03166     // FIXME: We should be able to bail at this point with "nothing changed".
03167     // FIXME: We might want to defer PHI speculation until after here.
03168   } else {
03169     unsigned Alignment = AI.getAlignment();
03170     if (!Alignment) {
03171       // The minimum alignment which users can rely on when the explicit
03172       // alignment is omitted or zero is that required by the ABI for this
03173       // type.
03174       Alignment = DL->getABITypeAlignment(AI.getAllocatedType());
03175     }
03176     Alignment = MinAlign(Alignment, BeginOffset);
03177     // If we will get at least this much alignment from the type alone, leave
03178     // the alloca's alignment unconstrained.
03179     if (Alignment <= DL->getABITypeAlignment(SliceTy))
03180       Alignment = 0;
03181     NewAI = new AllocaInst(SliceTy, nullptr, Alignment,
03182                            AI.getName() + ".sroa." + Twine(B - S.begin()), &AI);
03183     ++NumNewAllocas;
03184   }
03185 
03186   DEBUG(dbgs() << "Rewriting alloca partition "
03187                << "[" << BeginOffset << "," << EndOffset << ") to: " << *NewAI
03188                << "\n");
03189 
03190   // Track the high watermark on the worklist as it is only relevant for
03191   // promoted allocas. We will reset it to this point if the alloca is not in
03192   // fact scheduled for promotion.
03193   unsigned PPWOldSize = PostPromotionWorklist.size();
03194   unsigned NumUses = 0;
03195   SmallPtrSet<PHINode *, 8> PHIUsers;
03196   SmallPtrSet<SelectInst *, 8> SelectUsers;
03197 
03198   AllocaSliceRewriter Rewriter(*DL, S, *this, AI, *NewAI, BeginOffset,
03199                                EndOffset, IsVectorPromotable,
03200                                IsIntegerPromotable, PHIUsers, SelectUsers);
03201   bool Promotable = true;
03202   for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
03203                                                         SUE = SplitUses.end();
03204        SUI != SUE; ++SUI) {
03205     DEBUG(dbgs() << "  rewriting split ");
03206     DEBUG(S.printSlice(dbgs(), *SUI, ""));
03207     Promotable &= Rewriter.visit(*SUI);
03208     ++NumUses;
03209   }
03210   for (AllocaSlices::iterator I = B; I != E; ++I) {
03211     DEBUG(dbgs() << "  rewriting ");
03212     DEBUG(S.printSlice(dbgs(), I, ""));
03213     Promotable &= Rewriter.visit(I);
03214     ++NumUses;
03215   }
03216 
03217   NumAllocaPartitionUses += NumUses;
03218   MaxUsesPerAllocaPartition =
03219       std::max<unsigned>(NumUses, MaxUsesPerAllocaPartition);
03220 
03221   // Now that we've processed all the slices in the new partition, check if any
03222   // PHIs or Selects would block promotion.
03223   for (SmallPtrSetImpl<PHINode *>::iterator I = PHIUsers.begin(),
03224                                             E = PHIUsers.end();
03225        I != E; ++I)
03226     if (!isSafePHIToSpeculate(**I, DL)) {
03227       Promotable = false;
03228       PHIUsers.clear();
03229       SelectUsers.clear();
03230       break;
03231     }
03232   for (SmallPtrSetImpl<SelectInst *>::iterator I = SelectUsers.begin(),
03233                                                E = SelectUsers.end();
03234        I != E; ++I)
03235     if (!isSafeSelectToSpeculate(**I, DL)) {
03236       Promotable = false;
03237       PHIUsers.clear();
03238       SelectUsers.clear();
03239       break;
03240     }
03241 
03242   if (Promotable) {
03243     if (PHIUsers.empty() && SelectUsers.empty()) {
03244       // Promote the alloca.
03245       PromotableAllocas.push_back(NewAI);
03246     } else {
03247       // If we have either PHIs or Selects to speculate, add them to those
03248       // worklists and re-queue the new alloca so that we promote in on the
03249       // next iteration.
03250       for (SmallPtrSetImpl<PHINode *>::iterator I = PHIUsers.begin(),
03251                                                 E = PHIUsers.end();
03252            I != E; ++I)
03253         SpeculatablePHIs.insert(*I);
03254       for (SmallPtrSetImpl<SelectInst *>::iterator I = SelectUsers.begin(),
03255                                                    E = SelectUsers.end();
03256            I != E; ++I)
03257         SpeculatableSelects.insert(*I);
03258       Worklist.insert(NewAI);
03259     }
03260   } else {
03261     // If we can't promote the alloca, iterate on it to check for new
03262     // refinements exposed by splitting the current alloca. Don't iterate on an
03263     // alloca which didn't actually change and didn't get promoted.
03264     if (NewAI != &AI)
03265       Worklist.insert(NewAI);
03266 
03267     // Drop any post-promotion work items if promotion didn't happen.
03268     while (PostPromotionWorklist.size() > PPWOldSize)
03269       PostPromotionWorklist.pop_back();
03270   }
03271 
03272   return true;
03273 }
03274 
03275 static void
03276 removeFinishedSplitUses(SmallVectorImpl<AllocaSlices::iterator> &SplitUses,
03277                         uint64_t &MaxSplitUseEndOffset, uint64_t Offset) {
03278   if (Offset >= MaxSplitUseEndOffset) {
03279     SplitUses.clear();
03280     MaxSplitUseEndOffset = 0;
03281     return;
03282   }
03283 
03284   size_t SplitUsesOldSize = SplitUses.size();
03285   SplitUses.erase(std::remove_if(SplitUses.begin(), SplitUses.end(),
03286                                  [Offset](const AllocaSlices::iterator &I) {
03287                     return I->endOffset() <= Offset;
03288                   }),
03289                   SplitUses.end());
03290   if (SplitUsesOldSize == SplitUses.size())
03291     return;
03292 
03293   // Recompute the max. While this is linear, so is remove_if.
03294   MaxSplitUseEndOffset = 0;
03295   for (SmallVectorImpl<AllocaSlices::iterator>::iterator
03296            SUI = SplitUses.begin(),
03297            SUE = SplitUses.end();
03298        SUI != SUE; ++SUI)
03299     MaxSplitUseEndOffset = std::max((*SUI)->endOffset(), MaxSplitUseEndOffset);
03300 }
03301 
03302 /// \brief Walks the slices of an alloca and form partitions based on them,
03303 /// rewriting each of their uses.
03304 bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &S) {
03305   if (S.begin() == S.end())
03306     return false;
03307 
03308   unsigned NumPartitions = 0;
03309   bool Changed = false;
03310   SmallVector<AllocaSlices::iterator, 4> SplitUses;
03311   uint64_t MaxSplitUseEndOffset = 0;
03312 
03313   uint64_t BeginOffset = S.begin()->beginOffset();
03314 
03315   for (AllocaSlices::iterator SI = S.begin(), SJ = std::next(SI), SE = S.end();
03316        SI != SE; SI = SJ) {
03317     uint64_t MaxEndOffset = SI->endOffset();
03318 
03319     if (!SI->isSplittable()) {
03320       // When we're forming an unsplittable region, it must always start at the
03321       // first slice and will extend through its end.
03322       assert(BeginOffset == SI->beginOffset());
03323 
03324       // Form a partition including all of the overlapping slices with this
03325       // unsplittable slice.
03326       while (SJ != SE && SJ->beginOffset() < MaxEndOffset) {
03327         if (!SJ->isSplittable())
03328           MaxEndOffset = std::max(MaxEndOffset, SJ->endOffset());
03329         ++SJ;
03330       }
03331     } else {
03332       assert(SI->isSplittable()); // Established above.
03333 
03334       // Collect all of the overlapping splittable slices.
03335       while (SJ != SE && SJ->beginOffset() < MaxEndOffset &&
03336              SJ->isSplittable()) {
03337         MaxEndOffset = std::max(MaxEndOffset, SJ->endOffset());
03338         ++SJ;
03339       }
03340 
03341       // Back up MaxEndOffset and SJ if we ended the span early when
03342       // encountering an unsplittable slice.
03343       if (SJ != SE && SJ->beginOffset() < MaxEndOffset) {
03344         assert(!SJ->isSplittable());
03345         MaxEndOffset = SJ->beginOffset();
03346       }
03347     }
03348 
03349     // Check if we have managed to move the end offset forward yet. If so,
03350     // we'll have to rewrite uses and erase old split uses.
03351     if (BeginOffset < MaxEndOffset) {
03352       // Rewrite a sequence of overlapping slices.
03353       Changed |=
03354           rewritePartition(AI, S, SI, SJ, BeginOffset, MaxEndOffset, SplitUses);
03355       ++NumPartitions;
03356 
03357       removeFinishedSplitUses(SplitUses, MaxSplitUseEndOffset, MaxEndOffset);
03358     }
03359 
03360     // Accumulate all the splittable slices from the [SI,SJ) region which
03361     // overlap going forward.
03362     for (AllocaSlices::iterator SK = SI; SK != SJ; ++SK)
03363       if (SK->isSplittable() && SK->endOffset() > MaxEndOffset) {
03364         SplitUses.push_back(SK);
03365         MaxSplitUseEndOffset = std::max(SK->endOffset(), MaxSplitUseEndOffset);
03366       }
03367 
03368     // If we're already at the end and we have no split uses, we're done.
03369     if (SJ == SE && SplitUses.empty())
03370       break;
03371 
03372     // If we have no split uses or no gap in offsets, we're ready to move to
03373     // the next slice.
03374     if (SplitUses.empty() || (SJ != SE && MaxEndOffset == SJ->beginOffset())) {
03375       BeginOffset = SJ->beginOffset();
03376       continue;
03377     }
03378 
03379     // Even if we have split slices, if the next slice is splittable and the
03380     // split slices reach it, we can simply set up the beginning offset of the
03381     // next iteration to bridge between them.
03382     if (SJ != SE && SJ->isSplittable() &&
03383         MaxSplitUseEndOffset > SJ->beginOffset()) {
03384       BeginOffset = MaxEndOffset;
03385       continue;
03386     }
03387 
03388     // Otherwise, we have a tail of split slices. Rewrite them with an empty
03389     // range of slices.
03390     uint64_t PostSplitEndOffset =
03391         SJ == SE ? MaxSplitUseEndOffset : SJ->beginOffset();
03392 
03393     Changed |= rewritePartition(AI, S, SJ, SJ, MaxEndOffset, PostSplitEndOffset,
03394                                 SplitUses);
03395     ++NumPartitions;
03396 
03397     if (SJ == SE)
03398       break; // Skip the rest, we don't need to do any cleanup.
03399 
03400     removeFinishedSplitUses(SplitUses, MaxSplitUseEndOffset,
03401                             PostSplitEndOffset);
03402 
03403     // Now just reset the begin offset for the next iteration.
03404     BeginOffset = SJ->beginOffset();
03405   }
03406 
03407   NumAllocaPartitions += NumPartitions;
03408   MaxPartitionsPerAlloca =
03409       std::max<unsigned>(NumPartitions, MaxPartitionsPerAlloca);
03410 
03411   return Changed;
03412 }
03413 
03414 /// \brief Clobber a use with undef, deleting the used value if it becomes dead.
03415 void SROA::clobberUse(Use &U) {
03416   Value *OldV = U;
03417   // Replace the use with an undef value.
03418   U = UndefValue::get(OldV->getType());
03419 
03420   // Check for this making an instruction dead. We have to garbage collect
03421   // all the dead instructions to ensure the uses of any alloca end up being
03422   // minimal.
03423   if (Instruction *OldI = dyn_cast<Instruction>(OldV))
03424     if (isInstructionTriviallyDead(OldI)) {
03425       DeadInsts.insert(OldI);
03426     }
03427 }
03428 
03429 /// \brief Analyze an alloca for SROA.
03430 ///
03431 /// This analyzes the alloca to ensure we can reason about it, builds
03432 /// the slices of the alloca, and then hands it off to be split and
03433 /// rewritten as needed.
03434 bool SROA::runOnAlloca(AllocaInst &AI) {
03435   DEBUG(dbgs() << "SROA alloca: " << AI << "\n");
03436   ++NumAllocasAnalyzed;
03437 
03438   // Special case dead allocas, as they're trivial.
03439   if (AI.use_empty()) {
03440     AI.eraseFromParent();
03441     return true;
03442   }
03443 
03444   // Skip alloca forms that this analysis can't handle.
03445   if (AI.isArrayAllocation() || !AI.getAllocatedType()->isSized() ||
03446       DL->getTypeAllocSize(AI.getAllocatedType()) == 0)
03447     return false;
03448 
03449   bool Changed = false;
03450 
03451   // First, split any FCA loads and stores touching this alloca to promote
03452   // better splitting and promotion opportunities.
03453   AggLoadStoreRewriter AggRewriter(*DL);
03454   Changed |= AggRewriter.rewrite(AI);
03455 
03456   // Build the slices using a recursive instruction-visiting builder.
03457   AllocaSlices S(*DL, AI);
03458   DEBUG(S.print(dbgs()));
03459   if (S.isEscaped())
03460     return Changed;
03461 
03462   // Delete all the dead users of this alloca before splitting and rewriting it.
03463   for (AllocaSlices::dead_user_iterator DI = S.dead_user_begin(),
03464                                         DE = S.dead_user_end();
03465        DI != DE; ++DI) {
03466     // Free up everything used by this instruction.
03467     for (Use &DeadOp : (*DI)->operands())
03468       clobberUse(DeadOp);
03469 
03470     // Now replace the uses of this instruction.
03471     (*DI)->replaceAllUsesWith(UndefValue::get((*DI)->getType()));
03472 
03473     // And mark it for deletion.
03474     DeadInsts.insert(*DI);
03475     Changed = true;
03476   }
03477   for (AllocaSlices::dead_op_iterator DO = S.dead_op_begin(),
03478                                       DE = S.dead_op_end();
03479        DO != DE; ++DO) {
03480     clobberUse(**DO);
03481     Changed = true;
03482   }
03483 
03484   // No slices to split. Leave the dead alloca for a later pass to clean up.
03485   if (S.begin() == S.end())
03486     return Changed;
03487 
03488   Changed |= splitAlloca(AI, S);
03489 
03490   DEBUG(dbgs() << "  Speculating PHIs\n");
03491   while (!SpeculatablePHIs.empty())
03492     speculatePHINodeLoads(*SpeculatablePHIs.pop_back_val());
03493 
03494   DEBUG(dbgs() << "  Speculating Selects\n");
03495   while (!SpeculatableSelects.empty())
03496     speculateSelectInstLoads(*SpeculatableSelects.pop_back_val());
03497 
03498   return Changed;
03499 }
03500 
03501 /// \brief Delete the dead instructions accumulated in this run.
03502 ///
03503 /// Recursively deletes the dead instructions we've accumulated. This is done
03504 /// at the very end to maximize locality of the recursive delete and to
03505 /// minimize the problems of invalidated instruction pointers as such pointers
03506 /// are used heavily in the intermediate stages of the algorithm.
03507 ///
03508 /// We also record the alloca instructions deleted here so that they aren't
03509 /// subsequently handed to mem2reg to promote.
03510 void SROA::deleteDeadInstructions(SmallPtrSetImpl<AllocaInst*> &DeletedAllocas) {
03511   while (!DeadInsts.empty()) {
03512     Instruction *I = DeadInsts.pop_back_val();
03513     DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
03514 
03515     I->replaceAllUsesWith(UndefValue::get(I->getType()));
03516 
03517     for (Use &Operand : I->operands())
03518       if (Instruction *U = dyn_cast<Instruction>(Operand)) {
03519         // Zero out the operand and see if it becomes trivially dead.
03520         Operand = nullptr;
03521         if (isInstructionTriviallyDead(U))
03522           DeadInsts.insert(U);
03523       }
03524 
03525     if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
03526       DeletedAllocas.insert(AI);
03527 
03528     ++NumDeleted;
03529     I->eraseFromParent();
03530   }
03531 }
03532 
03533 static void enqueueUsersInWorklist(Instruction &I,
03534                                    SmallVectorImpl<Instruction *> &Worklist,
03535                                    SmallPtrSetImpl<Instruction *> &Visited) {
03536   for (User *U : I.users())
03537     if (Visited.insert(cast<Instruction>(U)))
03538       Worklist.push_back(cast<Instruction>(U));
03539 }
03540 
03541 /// \brief Promote the allocas, using the best available technique.
03542 ///
03543 /// This attempts to promote whatever allocas have been identified as viable in
03544 /// the PromotableAllocas list. If that list is empty, there is nothing to do.
03545 /// If there is a domtree available, we attempt to promote using the full power
03546 /// of mem2reg. Otherwise, we build and use the AllocaPromoter above which is
03547 /// based on the SSAUpdater utilities. This function returns whether any
03548 /// promotion occurred.
03549 bool SROA::promoteAllocas(Function &F) {
03550   if (PromotableAllocas.empty())
03551     return false;
03552 
03553   NumPromoted += PromotableAllocas.size();
03554 
03555   if (DT && !ForceSSAUpdater) {
03556     DEBUG(dbgs() << "Promoting allocas with mem2reg...\n");
03557     PromoteMemToReg(PromotableAllocas, *DT, nullptr, AT);
03558     PromotableAllocas.clear();
03559     return true;
03560   }
03561 
03562   DEBUG(dbgs() << "Promoting allocas with SSAUpdater...\n");
03563   SSAUpdater SSA;
03564   DIBuilder DIB(*F.getParent());
03565   SmallVector<Instruction *, 64> Insts;
03566 
03567   // We need a worklist to walk the uses of each alloca.
03568   SmallVector<Instruction *, 8> Worklist;
03569   SmallPtrSet<Instruction *, 8> Visited;
03570   SmallVector<Instruction *, 32> DeadInsts;
03571 
03572   for (unsigned Idx = 0, Size = PromotableAllocas.size(); Idx != Size; ++Idx) {
03573     AllocaInst *AI = PromotableAllocas[Idx];
03574     Insts.clear();
03575     Worklist.clear();
03576     Visited.clear();
03577 
03578     enqueueUsersInWorklist(*AI, Worklist, Visited);
03579 
03580     while (!Worklist.empty()) {
03581       Instruction *I = Worklist.pop_back_val();
03582 
03583       // FIXME: Currently the SSAUpdater infrastructure doesn't reason about
03584       // lifetime intrinsics and so we strip them (and the bitcasts+GEPs
03585       // leading to them) here. Eventually it should use them to optimize the
03586       // scalar values produced.
03587       if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
03588         assert(II->getIntrinsicID() == Intrinsic::lifetime_start ||
03589                II->getIntrinsicID() == Intrinsic::lifetime_end);
03590         II->eraseFromParent();
03591         continue;
03592       }
03593 
03594       // Push the loads and stores we find onto the list. SROA will already
03595       // have validated that all loads and stores are viable candidates for
03596       // promotion.
03597       if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
03598         assert(LI->getType() == AI->getAllocatedType());
03599         Insts.push_back(LI);
03600         continue;
03601       }
03602       if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
03603         assert(SI->getValueOperand()->getType() == AI->getAllocatedType());
03604         Insts.push_back(SI);
03605         continue;
03606       }
03607 
03608       // For everything else, we know that only no-op bitcasts and GEPs will
03609       // make it this far, just recurse through them and recall them for later
03610       // removal.
03611       DeadInsts.push_back(I);
03612       enqueueUsersInWorklist(*I, Worklist, Visited);
03613     }
03614     AllocaPromoter(Insts, SSA, *AI, DIB).run(Insts);
03615     while (!DeadInsts.empty())
03616       DeadInsts.pop_back_val()->eraseFromParent();
03617     AI->eraseFromParent();
03618   }
03619 
03620   PromotableAllocas.clear();
03621   return true;
03622 }
03623 
03624 bool SROA::runOnFunction(Function &F) {
03625   if (skipOptnoneFunction(F))
03626     return false;
03627 
03628   DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
03629   C = &F.getContext();
03630   DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
03631   if (!DLP) {
03632     DEBUG(dbgs() << "  Skipping SROA -- no target data!\n");
03633     return false;
03634   }
03635   DL = &DLP->getDataLayout();
03636   DominatorTreeWrapperPass *DTWP =
03637       getAnalysisIfAvailable<DominatorTreeWrapperPass>();
03638   DT = DTWP ? &DTWP->getDomTree() : nullptr;
03639   AT = &getAnalysis<AssumptionTracker>();
03640 
03641   BasicBlock &EntryBB = F.getEntryBlock();
03642   for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(EntryBB.end());
03643        I != E; ++I)
03644     if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
03645       Worklist.insert(AI);
03646 
03647   bool Changed = false;
03648   // A set of deleted alloca instruction pointers which should be removed from
03649   // the list of promotable allocas.
03650   SmallPtrSet<AllocaInst *, 4> DeletedAllocas;
03651 
03652   do {
03653     while (!Worklist.empty()) {
03654       Changed |= runOnAlloca(*Worklist.pop_back_val());
03655       deleteDeadInstructions(DeletedAllocas);
03656 
03657       // Remove the deleted allocas from various lists so that we don't try to
03658       // continue processing them.
03659       if (!DeletedAllocas.empty()) {
03660         auto IsInSet = [&](AllocaInst *AI) {
03661           return DeletedAllocas.count(AI);
03662         };
03663         Worklist.remove_if(IsInSet);
03664         PostPromotionWorklist.remove_if(IsInSet);
03665         PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(),
03666                                                PromotableAllocas.end(),
03667                                                IsInSet),
03668                                 PromotableAllocas.end());
03669         DeletedAllocas.clear();
03670       }
03671     }
03672 
03673     Changed |= promoteAllocas(F);
03674 
03675     Worklist = PostPromotionWorklist;
03676     PostPromotionWorklist.clear();
03677   } while (!Worklist.empty());
03678 
03679   return Changed;
03680 }
03681 
03682 void SROA::getAnalysisUsage(AnalysisUsage &AU) const {
03683   AU.addRequired<AssumptionTracker>();
03684   if (RequiresDomTree)
03685     AU.addRequired<DominatorTreeWrapperPass>();
03686   AU.setPreservesCFG();
03687 }