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llvm-6502/lib/Transforms/Scalar/SROA.cpp
Benjamin Kramer 7f80b75b96 Drop spurious handle in comment. 
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2013-09-22 11:24:58 +00:00

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//===- SROA.cpp - Scalar Replacement Of Aggregates ------------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
/// \file
/// This transformation implements the well known scalar replacement of
/// aggregates transformation. It tries to identify promotable elements of an
/// aggregate alloca, and promote them to registers. It will also try to
/// convert uses of an element (or set of elements) of an alloca into a vector
/// or bitfield-style integer scalar if appropriate.
///
/// It works to do this with minimal slicing of the alloca so that regions
/// which are merely transferred in and out of external memory remain unchanged
/// and are not decomposed to scalar code.
///
/// Because this also performs alloca promotion, it can be thought of as also
/// serving the purpose of SSA formation. The algorithm iterates on the
/// function until all opportunities for promotion have been realized.
///
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "sroa"
#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/PtrUseVisitor.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/DIBuilder.h"
#include "llvm/DebugInfo.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.h"
#include "llvm/InstVisitor.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Transforms/Utils/PromoteMemToReg.h"
#include "llvm/Transforms/Utils/SSAUpdater.h"
using namespace llvm;
STATISTIC(NumAllocasAnalyzed, "Number of allocas analyzed for replacement");
STATISTIC(NumAllocaPartitions, "Number of alloca partitions formed");
STATISTIC(MaxPartitionsPerAlloca, "Maximum number of partitions per alloca");
STATISTIC(NumAllocaPartitionUses, "Number of alloca partition uses rewritten");
STATISTIC(MaxUsesPerAllocaPartition, "Maximum number of uses of a partition");
STATISTIC(NumNewAllocas, "Number of new, smaller allocas introduced");
STATISTIC(NumPromoted, "Number of allocas promoted to SSA values");
STATISTIC(NumLoadsSpeculated, "Number of loads speculated to allow promotion");
STATISTIC(NumDeleted, "Number of instructions deleted");
STATISTIC(NumVectorized, "Number of vectorized aggregates");
/// Hidden option to force the pass to not use DomTree and mem2reg, instead
/// forming SSA values through the SSAUpdater infrastructure.
static cl::opt<bool>
ForceSSAUpdater("force-ssa-updater", cl::init(false), cl::Hidden);
namespace {
/// \brief A custom IRBuilder inserter which prefixes all names if they are
/// preserved.
template <bool preserveNames = true>
class IRBuilderPrefixedInserter :
public IRBuilderDefaultInserter<preserveNames> {
std::string Prefix;
public:
void SetNamePrefix(const Twine &P) { Prefix = P.str(); }
protected:
void InsertHelper(Instruction *I, const Twine &Name, BasicBlock *BB,
BasicBlock::iterator InsertPt) const {
IRBuilderDefaultInserter<preserveNames>::InsertHelper(
I, Name.isTriviallyEmpty() ? Name : Prefix + Name, BB, InsertPt);
}
};
// Specialization for not preserving the name is trivial.
template <>
class IRBuilderPrefixedInserter<false> :
public IRBuilderDefaultInserter<false> {
public:
void SetNamePrefix(const Twine &P) {}
};
/// \brief Provide a typedef for IRBuilder that drops names in release builds.
#ifndef NDEBUG
typedef llvm::IRBuilder<true, ConstantFolder,
IRBuilderPrefixedInserter<true> > IRBuilderTy;
#else
typedef llvm::IRBuilder<false, ConstantFolder,
IRBuilderPrefixedInserter<false> > IRBuilderTy;
#endif
}
namespace {
/// \brief A used slice of an alloca.
///
/// This structure represents a slice of an alloca used by some instruction. It
/// stores both the begin and end offsets of this use, a pointer to the use
/// itself, and a flag indicating whether we can classify the use as splittable
/// or not when forming partitions of the alloca.
class Slice {
/// \brief The beginning offset of the range.
uint64_t BeginOffset;
/// \brief The ending offset, not included in the range.
uint64_t EndOffset;
/// \brief Storage for both the use of this slice and whether it can be
/// split.
PointerIntPair<Use *, 1, bool> UseAndIsSplittable;
public:
Slice() : BeginOffset(), EndOffset() {}
Slice(uint64_t BeginOffset, uint64_t EndOffset, Use *U, bool IsSplittable)
: BeginOffset(BeginOffset), EndOffset(EndOffset),
UseAndIsSplittable(U, IsSplittable) {}
uint64_t beginOffset() const { return BeginOffset; }
uint64_t endOffset() const { return EndOffset; }
bool isSplittable() const { return UseAndIsSplittable.getInt(); }
void makeUnsplittable() { UseAndIsSplittable.setInt(false); }
Use *getUse() const { return UseAndIsSplittable.getPointer(); }
bool isDead() const { return getUse() == 0; }
void kill() { UseAndIsSplittable.setPointer(0); }
/// \brief Support for ordering ranges.
///
/// This provides an ordering over ranges such that start offsets are
/// always increasing, and within equal start offsets, the end offsets are
/// decreasing. Thus the spanning range comes first in a cluster with the
/// same start position.
bool operator<(const Slice &RHS) const {
if (beginOffset() < RHS.beginOffset()) return true;
if (beginOffset() > RHS.beginOffset()) return false;
if (isSplittable() != RHS.isSplittable()) return !isSplittable();
if (endOffset() > RHS.endOffset()) return true;
return false;
}
/// \brief Support comparison with a single offset to allow binary searches.
friend LLVM_ATTRIBUTE_UNUSED bool operator<(const Slice &LHS,
uint64_t RHSOffset) {
return LHS.beginOffset() < RHSOffset;
}
friend LLVM_ATTRIBUTE_UNUSED bool operator<(uint64_t LHSOffset,
const Slice &RHS) {
return LHSOffset < RHS.beginOffset();
}
bool operator==(const Slice &RHS) const {
return isSplittable() == RHS.isSplittable() &&
beginOffset() == RHS.beginOffset() && endOffset() == RHS.endOffset();
}
bool operator!=(const Slice &RHS) const { return !operator==(RHS); }
};
} // end anonymous namespace
namespace llvm {
template <typename T> struct isPodLike;
template <> struct isPodLike<Slice> {
static const bool value = true;
};
}
namespace {
/// \brief Representation of the alloca slices.
///
/// This class represents the slices of an alloca which are formed by its
/// various uses. If a pointer escapes, we can't fully build a representation
/// for the slices used and we reflect that in this structure. The uses are
/// stored, sorted by increasing beginning offset and with unsplittable slices
/// starting at a particular offset before splittable slices.
class AllocaSlices {
public:
/// \brief Construct the slices of a particular alloca.
AllocaSlices(const DataLayout &DL, AllocaInst &AI);
/// \brief Test whether a pointer to the allocation escapes our analysis.
///
/// If this is true, the slices are never fully built and should be
/// ignored.
bool isEscaped() const { return PointerEscapingInstr; }
/// \brief Support for iterating over the slices.
/// @{
typedef SmallVectorImpl<Slice>::iterator iterator;
iterator begin() { return Slices.begin(); }
iterator end() { return Slices.end(); }
typedef SmallVectorImpl<Slice>::const_iterator const_iterator;
const_iterator begin() const { return Slices.begin(); }
const_iterator end() const { return Slices.end(); }
/// @}
/// \brief Allow iterating the dead users for this alloca.
///
/// These are instructions which will never actually use the alloca as they
/// are outside the allocated range. They are safe to replace with undef and
/// delete.
/// @{
typedef SmallVectorImpl<Instruction *>::const_iterator dead_user_iterator;
dead_user_iterator dead_user_begin() const { return DeadUsers.begin(); }
dead_user_iterator dead_user_end() const { return DeadUsers.end(); }
/// @}
/// \brief Allow iterating the dead expressions referring to this alloca.
///
/// These are operands which have cannot actually be used to refer to the
/// alloca as they are outside its range and the user doesn't correct for
/// that. These mostly consist of PHI node inputs and the like which we just
/// need to replace with undef.
/// @{
typedef SmallVectorImpl<Use *>::const_iterator dead_op_iterator;
dead_op_iterator dead_op_begin() const { return DeadOperands.begin(); }
dead_op_iterator dead_op_end() const { return DeadOperands.end(); }
/// @}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void print(raw_ostream &OS, const_iterator I, StringRef Indent = " ") const;
void printSlice(raw_ostream &OS, const_iterator I,
StringRef Indent = " ") const;
void printUse(raw_ostream &OS, const_iterator I,
StringRef Indent = " ") const;
void print(raw_ostream &OS) const;
void LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED dump(const_iterator I) const;
void LLVM_ATTRIBUTE_NOINLINE LLVM_ATTRIBUTE_USED dump() const;
#endif
private:
template <typename DerivedT, typename RetT = void> class BuilderBase;
class SliceBuilder;
friend class AllocaSlices::SliceBuilder;
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// \brief Handle to alloca instruction to simplify method interfaces.
AllocaInst &AI;
#endif
/// \brief The instruction responsible for this alloca not having a known set
/// of slices.
///
/// When an instruction (potentially) escapes the pointer to the alloca, we
/// store a pointer to that here and abort trying to form slices of the
/// alloca. This will be null if the alloca slices are analyzed successfully.
Instruction *PointerEscapingInstr;
/// \brief The slices of the alloca.
///
/// We store a vector of the slices formed by uses of the alloca here. This
/// vector is sorted by increasing begin offset, and then the unsplittable
/// slices before the splittable ones. See the Slice inner class for more
/// details.
SmallVector<Slice, 8> Slices;
/// \brief Instructions which will become dead if we rewrite the alloca.
///
/// Note that these are not separated by slice. This is because we expect an
/// alloca to be completely rewritten or not rewritten at all. If rewritten,
/// all these instructions can simply be removed and replaced with undef as
/// they come from outside of the allocated space.
SmallVector<Instruction *, 8> DeadUsers;
/// \brief Operands which will become dead if we rewrite the alloca.
///
/// These are operands that in their particular use can be replaced with
/// undef when we rewrite the alloca. These show up in out-of-bounds inputs
/// to PHI nodes and the like. They aren't entirely dead (there might be
/// a GEP back into the bounds using it elsewhere) and nor is the PHI, but we
/// want to swap this particular input for undef to simplify the use lists of
/// the alloca.
SmallVector<Use *, 8> DeadOperands;
};
}
static Value *foldSelectInst(SelectInst &SI) {
// If the condition being selected on is a constant or the same value is
// being selected between, fold the select. Yes this does (rarely) happen
// early on.
if (ConstantInt *CI = dyn_cast<ConstantInt>(SI.getCondition()))
return SI.getOperand(1+CI->isZero());
if (SI.getOperand(1) == SI.getOperand(2))
return SI.getOperand(1);
return 0;
}
/// \brief Builder for the alloca slices.
///
/// This class builds a set of alloca slices by recursively visiting the uses
/// of an alloca and making a slice for each load and store at each offset.
class AllocaSlices::SliceBuilder : public PtrUseVisitor<SliceBuilder> {
friend class PtrUseVisitor<SliceBuilder>;
friend class InstVisitor<SliceBuilder>;
typedef PtrUseVisitor<SliceBuilder> Base;
const uint64_t AllocSize;
AllocaSlices &S;
SmallDenseMap<Instruction *, unsigned> MemTransferSliceMap;
SmallDenseMap<Instruction *, uint64_t> PHIOrSelectSizes;
/// \brief Set to de-duplicate dead instructions found in the use walk.
SmallPtrSet<Instruction *, 4> VisitedDeadInsts;
public:
SliceBuilder(const DataLayout &DL, AllocaInst &AI, AllocaSlices &S)
: PtrUseVisitor<SliceBuilder>(DL),
AllocSize(DL.getTypeAllocSize(AI.getAllocatedType())), S(S) {}
private:
void markAsDead(Instruction &I) {
if (VisitedDeadInsts.insert(&I))
S.DeadUsers.push_back(&I);
}
void insertUse(Instruction &I, const APInt &Offset, uint64_t Size,
bool IsSplittable = false) {
// Completely skip uses which have a zero size or start either before or
// past the end of the allocation.
if (Size == 0 || Offset.isNegative() || Offset.uge(AllocSize)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
<< " which has zero size or starts outside of the "
<< AllocSize << " byte alloca:\n"
<< " alloca: " << S.AI << "\n"
<< " use: " << I << "\n");
return markAsDead(I);
}
uint64_t BeginOffset = Offset.getZExtValue();
uint64_t EndOffset = BeginOffset + Size;
// Clamp the end offset to the end of the allocation. Note that this is
// formulated to handle even the case where "BeginOffset + Size" overflows.
// This may appear superficially to be something we could ignore entirely,
// but that is not so! There may be widened loads or PHI-node uses where
// some instructions are dead but not others. We can't completely ignore
// them, and so have to record at least the information here.
assert(AllocSize >= BeginOffset); // Established above.
if (Size > AllocSize - BeginOffset) {
DEBUG(dbgs() << "WARNING: Clamping a " << Size << " byte use @" << Offset
<< " to remain within the " << AllocSize << " byte alloca:\n"
<< " alloca: " << S.AI << "\n"
<< " use: " << I << "\n");
EndOffset = AllocSize;
}
S.Slices.push_back(Slice(BeginOffset, EndOffset, U, IsSplittable));
}
void visitBitCastInst(BitCastInst &BC) {
if (BC.use_empty())
return markAsDead(BC);
return Base::visitBitCastInst(BC);
}
void visitGetElementPtrInst(GetElementPtrInst &GEPI) {
if (GEPI.use_empty())
return markAsDead(GEPI);
return Base::visitGetElementPtrInst(GEPI);
}
void handleLoadOrStore(Type *Ty, Instruction &I, const APInt &Offset,
uint64_t Size, bool IsVolatile) {
// We allow splitting of loads and stores where the type is an integer type
// and cover the entire alloca. This prevents us from splitting over
// eagerly.
// FIXME: In the great blue eventually, we should eagerly split all integer
// loads and stores, and then have a separate step that merges adjacent
// alloca partitions into a single partition suitable for integer widening.
// Or we should skip the merge step and rely on GVN and other passes to
// merge adjacent loads and stores that survive mem2reg.
bool IsSplittable =
Ty->isIntegerTy() && !IsVolatile && Offset == 0 && Size >= AllocSize;
insertUse(I, Offset, Size, IsSplittable);
}
void visitLoadInst(LoadInst &LI) {
assert((!LI.isSimple() || LI.getType()->isSingleValueType()) &&
"All simple FCA loads should have been pre-split");
if (!IsOffsetKnown)
return PI.setAborted(&LI);
uint64_t Size = DL.getTypeStoreSize(LI.getType());
return handleLoadOrStore(LI.getType(), LI, Offset, Size, LI.isVolatile());
}
void visitStoreInst(StoreInst &SI) {
Value *ValOp = SI.getValueOperand();
if (ValOp == *U)
return PI.setEscapedAndAborted(&SI);
if (!IsOffsetKnown)
return PI.setAborted(&SI);
uint64_t Size = DL.getTypeStoreSize(ValOp->getType());
// If this memory access can be shown to *statically* extend outside the
// bounds of of the allocation, it's behavior is undefined, so simply
// ignore it. Note that this is more strict than the generic clamping
// behavior of insertUse. We also try to handle cases which might run the
// risk of overflow.
// FIXME: We should instead consider the pointer to have escaped if this
// function is being instrumented for addressing bugs or race conditions.
if (Offset.isNegative() || Size > AllocSize ||
Offset.ugt(AllocSize - Size)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte store @" << Offset
<< " which extends past the end of the " << AllocSize
<< " byte alloca:\n"
<< " alloca: " << S.AI << "\n"
<< " use: " << SI << "\n");
return markAsDead(SI);
}
assert((!SI.isSimple() || ValOp->getType()->isSingleValueType()) &&
"All simple FCA stores should have been pre-split");
handleLoadOrStore(ValOp->getType(), SI, Offset, Size, SI.isVolatile());
}
void visitMemSetInst(MemSetInst &II) {
assert(II.getRawDest() == *U && "Pointer use is not the destination?");
ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
if ((Length && Length->getValue() == 0) ||
(IsOffsetKnown && !Offset.isNegative() && Offset.uge(AllocSize)))
// Zero-length mem transfer intrinsics can be ignored entirely.
return markAsDead(II);
if (!IsOffsetKnown)
return PI.setAborted(&II);
insertUse(II, Offset,
Length ? Length->getLimitedValue()
: AllocSize - Offset.getLimitedValue(),
(bool)Length);
}
void visitMemTransferInst(MemTransferInst &II) {
ConstantInt *Length = dyn_cast<ConstantInt>(II.getLength());
if ((Length && Length->getValue() == 0) ||
(IsOffsetKnown && !Offset.isNegative() && Offset.uge(AllocSize)))
// Zero-length mem transfer intrinsics can be ignored entirely.
return markAsDead(II);
if (!IsOffsetKnown)
return PI.setAborted(&II);
uint64_t RawOffset = Offset.getLimitedValue();
uint64_t Size = Length ? Length->getLimitedValue()
: AllocSize - RawOffset;
// Check for the special case where the same exact value is used for both
// source and dest.
if (*U == II.getRawDest() && *U == II.getRawSource()) {
// For non-volatile transfers this is a no-op.
if (!II.isVolatile())
return markAsDead(II);
return insertUse(II, Offset, Size, /*IsSplittable=*/false);
}
// If we have seen both source and destination for a mem transfer, then
// they both point to the same alloca.
bool Inserted;
SmallDenseMap<Instruction *, unsigned>::iterator MTPI;
llvm::tie(MTPI, Inserted) =
MemTransferSliceMap.insert(std::make_pair(&II, S.Slices.size()));
unsigned PrevIdx = MTPI->second;
if (!Inserted) {
Slice &PrevP = S.Slices[PrevIdx];
// Check if the begin offsets match and this is a non-volatile transfer.
// In that case, we can completely elide the transfer.
if (!II.isVolatile() && PrevP.beginOffset() == RawOffset) {
PrevP.kill();
return markAsDead(II);
}
// Otherwise we have an offset transfer within the same alloca. We can't
// split those.
PrevP.makeUnsplittable();
}
// Insert the use now that we've fixed up the splittable nature.
insertUse(II, Offset, Size, /*IsSplittable=*/Inserted && Length);
// Check that we ended up with a valid index in the map.
assert(S.Slices[PrevIdx].getUse()->getUser() == &II &&
"Map index doesn't point back to a slice with this user.");
}
// Disable SRoA for any intrinsics except for lifetime invariants.
// FIXME: What about debug intrinsics? This matches old behavior, but
// doesn't make sense.
void visitIntrinsicInst(IntrinsicInst &II) {
if (!IsOffsetKnown)
return PI.setAborted(&II);
if (II.getIntrinsicID() == Intrinsic::lifetime_start ||
II.getIntrinsicID() == Intrinsic::lifetime_end) {
ConstantInt *Length = cast<ConstantInt>(II.getArgOperand(0));
uint64_t Size = std::min(AllocSize - Offset.getLimitedValue(),
Length->getLimitedValue());
insertUse(II, Offset, Size, true);
return;
}
Base::visitIntrinsicInst(II);
}
Instruction *hasUnsafePHIOrSelectUse(Instruction *Root, uint64_t &Size) {
// We consider any PHI or select that results in a direct load or store of
// the same offset to be a viable use for slicing purposes. These uses
// are considered unsplittable and the size is the maximum loaded or stored
// size.
SmallPtrSet<Instruction *, 4> Visited;
SmallVector<std::pair<Instruction *, Instruction *>, 4> Uses;
Visited.insert(Root);
Uses.push_back(std::make_pair(cast<Instruction>(*U), Root));
// If there are no loads or stores, the access is dead. We mark that as
// a size zero access.
Size = 0;
do {
Instruction *I, *UsedI;
llvm::tie(UsedI, I) = Uses.pop_back_val();
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
Size = std::max(Size, DL.getTypeStoreSize(LI->getType()));
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
Value *Op = SI->getOperand(0);
if (Op == UsedI)
return SI;
Size = std::max(Size, DL.getTypeStoreSize(Op->getType()));
continue;
}
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(I)) {
if (!GEP->hasAllZeroIndices())
return GEP;
} else if (!isa<BitCastInst>(I) && !isa<PHINode>(I) &&
!isa<SelectInst>(I)) {
return I;
}
for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE;
++UI)
if (Visited.insert(cast<Instruction>(*UI)))
Uses.push_back(std::make_pair(I, cast<Instruction>(*UI)));
} while (!Uses.empty());
return 0;
}
void visitPHINode(PHINode &PN) {
if (PN.use_empty())
return markAsDead(PN);
if (!IsOffsetKnown)
return PI.setAborted(&PN);
// See if we already have computed info on this node.
uint64_t &PHISize = PHIOrSelectSizes[&PN];
if (!PHISize) {
// This is a new PHI node, check for an unsafe use of the PHI node.
if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&PN, PHISize))
return PI.setAborted(UnsafeI);
}
// For PHI and select operands outside the alloca, we can't nuke the entire
// phi or select -- the other side might still be relevant, so we special
// case them here and use a separate structure to track the operands
// themselves which should be replaced with undef.
// FIXME: This should instead be escaped in the event we're instrumenting
// for address sanitization.
if ((Offset.isNegative() && (-Offset).uge(PHISize)) ||
(!Offset.isNegative() && Offset.uge(AllocSize))) {
S.DeadOperands.push_back(U);
return;
}
insertUse(PN, Offset, PHISize);
}
void visitSelectInst(SelectInst &SI) {
if (SI.use_empty())
return markAsDead(SI);
if (Value *Result = foldSelectInst(SI)) {
if (Result == *U)
// If the result of the constant fold will be the pointer, recurse
// through the select as if we had RAUW'ed it.
enqueueUsers(SI);
else
// Otherwise the operand to the select is dead, and we can replace it
// with undef.
S.DeadOperands.push_back(U);
return;
}
if (!IsOffsetKnown)
return PI.setAborted(&SI);
// See if we already have computed info on this node.
uint64_t &SelectSize = PHIOrSelectSizes[&SI];
if (!SelectSize) {
// This is a new Select, check for an unsafe use of it.
if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&SI, SelectSize))
return PI.setAborted(UnsafeI);
}
// For PHI and select operands outside the alloca, we can't nuke the entire
// phi or select -- the other side might still be relevant, so we special
// case them here and use a separate structure to track the operands
// themselves which should be replaced with undef.
// FIXME: This should instead be escaped in the event we're instrumenting
// for address sanitization.
if ((Offset.isNegative() && Offset.uge(SelectSize)) ||
(!Offset.isNegative() && Offset.uge(AllocSize))) {
S.DeadOperands.push_back(U);
return;
}
insertUse(SI, Offset, SelectSize);
}
/// \brief Disable SROA entirely if there are unhandled users of the alloca.
void visitInstruction(Instruction &I) {
PI.setAborted(&I);
}
};
AllocaSlices::AllocaSlices(const DataLayout &DL, AllocaInst &AI)
:
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
AI(AI),
#endif
PointerEscapingInstr(0) {
SliceBuilder PB(DL, AI, *this);
SliceBuilder::PtrInfo PtrI = PB.visitPtr(AI);
if (PtrI.isEscaped() || PtrI.isAborted()) {
// FIXME: We should sink the escape vs. abort info into the caller nicely,
// possibly by just storing the PtrInfo in the AllocaSlices.
PointerEscapingInstr = PtrI.getEscapingInst() ? PtrI.getEscapingInst()
: PtrI.getAbortingInst();
assert(PointerEscapingInstr && "Did not track a bad instruction");
return;
}
Slices.erase(std::remove_if(Slices.begin(), Slices.end(),
std::mem_fun_ref(&Slice::isDead)),
Slices.end());
// Sort the uses. This arranges for the offsets to be in ascending order,
// and the sizes to be in descending order.
std::sort(Slices.begin(), Slices.end());
}
#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
void AllocaSlices::print(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
printSlice(OS, I, Indent);
printUse(OS, I, Indent);
}
void AllocaSlices::printSlice(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
OS << Indent << "[" << I->beginOffset() << "," << I->endOffset() << ")"
<< " slice #" << (I - begin())
<< (I->isSplittable() ? " (splittable)" : "") << "\n";
}
void AllocaSlices::printUse(raw_ostream &OS, const_iterator I,
StringRef Indent) const {
OS << Indent << " used by: " << *I->getUse()->getUser() << "\n";
}
void AllocaSlices::print(raw_ostream &OS) const {
if (PointerEscapingInstr) {
OS << "Can't analyze slices for alloca: " << AI << "\n"
<< " A pointer to this alloca escaped by:\n"
<< " " << *PointerEscapingInstr << "\n";
return;
}
OS << "Slices of alloca: " << AI << "\n";
for (const_iterator I = begin(), E = end(); I != E; ++I)
print(OS, I);
}
void AllocaSlices::dump(const_iterator I) const { print(dbgs(), I); }
void AllocaSlices::dump() const { print(dbgs()); }
#endif // !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
namespace {
/// \brief Implementation of LoadAndStorePromoter for promoting allocas.
///
/// This subclass of LoadAndStorePromoter adds overrides to handle promoting
/// the loads and stores of an alloca instruction, as well as updating its
/// debug information. This is used when a domtree is unavailable and thus
/// mem2reg in its full form can't be used to handle promotion of allocas to
/// scalar values.
class AllocaPromoter : public LoadAndStorePromoter {
AllocaInst &AI;
DIBuilder &DIB;
SmallVector<DbgDeclareInst *, 4> DDIs;
SmallVector<DbgValueInst *, 4> DVIs;
public:
AllocaPromoter(const SmallVectorImpl<Instruction *> &Insts, SSAUpdater &S,
AllocaInst &AI, DIBuilder &DIB)
: LoadAndStorePromoter(Insts, S), AI(AI), DIB(DIB) {}
void run(const SmallVectorImpl<Instruction*> &Insts) {
// Retain the debug information attached to the alloca for use when
// rewriting loads and stores.
if (MDNode *DebugNode = MDNode::getIfExists(AI.getContext(), &AI)) {
for (Value::use_iterator UI = DebugNode->use_begin(),
UE = DebugNode->use_end();
UI != UE; ++UI)
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(*UI))
DDIs.push_back(DDI);
else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(*UI))
DVIs.push_back(DVI);
}
LoadAndStorePromoter::run(Insts);
// While we have the debug information, clear it off of the alloca. The
// caller takes care of deleting the alloca.
while (!DDIs.empty())
DDIs.pop_back_val()->eraseFromParent();
while (!DVIs.empty())
DVIs.pop_back_val()->eraseFromParent();
}
virtual bool isInstInList(Instruction *I,
const SmallVectorImpl<Instruction*> &Insts) const {
Value *Ptr;
if (LoadInst *LI = dyn_cast<LoadInst>(I))
Ptr = LI->getOperand(0);
else
Ptr = cast<StoreInst>(I)->getPointerOperand();
// Only used to detect cycles, which will be rare and quickly found as
// we're walking up a chain of defs rather than down through uses.
SmallPtrSet<Value *, 4> Visited;
do {
if (Ptr == &AI)
return true;
if (BitCastInst *BCI = dyn_cast<BitCastInst>(Ptr))
Ptr = BCI->getOperand(0);
else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(Ptr))
Ptr = GEPI->getPointerOperand();
else
return false;
} while (Visited.insert(Ptr));
return false;
}
virtual void updateDebugInfo(Instruction *Inst) const {
for (SmallVectorImpl<DbgDeclareInst *>::const_iterator I = DDIs.begin(),
E = DDIs.end(); I != E; ++I) {
DbgDeclareInst *DDI = *I;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
else if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
}
for (SmallVectorImpl<DbgValueInst *>::const_iterator I = DVIs.begin(),
E = DVIs.end(); I != E; ++I) {
DbgValueInst *DVI = *I;
Value *Arg = 0;
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
// If an argument is zero extended then use argument directly. The ZExt
// may be zapped by an optimization pass in future.
if (ZExtInst *ZExt = dyn_cast<ZExtInst>(SI->getOperand(0)))
Arg = dyn_cast<Argument>(ZExt->getOperand(0));
else if (SExtInst *SExt = dyn_cast<SExtInst>(SI->getOperand(0)))
Arg = dyn_cast<Argument>(SExt->getOperand(0));
if (!Arg)
Arg = SI->getValueOperand();
} else if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
Arg = LI->getPointerOperand();
} else {
continue;
}
Instruction *DbgVal =
DIB.insertDbgValueIntrinsic(Arg, 0, DIVariable(DVI->getVariable()),
Inst);
DbgVal->setDebugLoc(DVI->getDebugLoc());
}
}
};
} // end anon namespace
namespace {
/// \brief An optimization pass providing Scalar Replacement of Aggregates.
///
/// This pass takes allocations which can be completely analyzed (that is, they
/// don't escape) and tries to turn them into scalar SSA values. There are
/// a few steps to this process.
///
/// 1) It takes allocations of aggregates and analyzes the ways in which they
/// are used to try to split them into smaller allocations, ideally of
/// a single scalar data type. It will split up memcpy and memset accesses
/// as necessary and try to isolate individual scalar accesses.
/// 2) It will transform accesses into forms which are suitable for SSA value
/// promotion. This can be replacing a memset with a scalar store of an
/// integer value, or it can involve speculating operations on a PHI or
/// select to be a PHI or select of the results.
/// 3) Finally, this will try to detect a pattern of accesses which map cleanly
/// onto insert and extract operations on a vector value, and convert them to
/// this form. By doing so, it will enable promotion of vector aggregates to
/// SSA vector values.
class SROA : public FunctionPass {
const bool RequiresDomTree;
LLVMContext *C;
const DataLayout *DL;
DominatorTree *DT;
/// \brief Worklist of alloca instructions to simplify.
///
/// Each alloca in the function is added to this. Each new alloca formed gets
/// added to it as well to recursively simplify unless that alloca can be
/// directly promoted. Finally, each time we rewrite a use of an alloca other
/// the one being actively rewritten, we add it back onto the list if not
/// already present to ensure it is re-visited.
SetVector<AllocaInst *, SmallVector<AllocaInst *, 16> > Worklist;
/// \brief A collection of instructions to delete.
/// We try to batch deletions to simplify code and make things a bit more
/// efficient.
SetVector<Instruction *, SmallVector<Instruction *, 8> > DeadInsts;
/// \brief Post-promotion worklist.
///
/// Sometimes we discover an alloca which has a high probability of becoming
/// viable for SROA after a round of promotion takes place. In those cases,
/// the alloca is enqueued here for re-processing.
///
/// Note that we have to be very careful to clear allocas out of this list in
/// the event they are deleted.
SetVector<AllocaInst *, SmallVector<AllocaInst *, 16> > PostPromotionWorklist;
/// \brief A collection of alloca instructions we can directly promote.
std::vector<AllocaInst *> PromotableAllocas;
/// \brief A worklist of PHIs to speculate prior to promoting allocas.
///
/// All of these PHIs have been checked for the safety of speculation and by
/// being speculated will allow promoting allocas currently in the promotable
/// queue.
SetVector<PHINode *, SmallVector<PHINode *, 2> > SpeculatablePHIs;
/// \brief A worklist of select instructions to speculate prior to promoting
/// allocas.
///
/// All of these select instructions have been checked for the safety of
/// speculation and by being speculated will allow promoting allocas
/// currently in the promotable queue.
SetVector<SelectInst *, SmallVector<SelectInst *, 2> > SpeculatableSelects;
public:
SROA(bool RequiresDomTree = true)
: FunctionPass(ID), RequiresDomTree(RequiresDomTree),
C(0), DL(0), DT(0) {
initializeSROAPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F);
void getAnalysisUsage(AnalysisUsage &AU) const;
const char *getPassName() const { return "SROA"; }
static char ID;
private:
friend class PHIOrSelectSpeculator;
friend class AllocaSliceRewriter;
bool rewritePartition(AllocaInst &AI, AllocaSlices &S,
AllocaSlices::iterator B, AllocaSlices::iterator E,
int64_t BeginOffset, int64_t EndOffset,
ArrayRef<AllocaSlices::iterator> SplitUses);
bool splitAlloca(AllocaInst &AI, AllocaSlices &S);
bool runOnAlloca(AllocaInst &AI);
void deleteDeadInstructions(SmallPtrSet<AllocaInst *, 4> &DeletedAllocas);
bool promoteAllocas(Function &F);
};
}
char SROA::ID = 0;
FunctionPass *llvm::createSROAPass(bool RequiresDomTree) {
return new SROA(RequiresDomTree);
}
INITIALIZE_PASS_BEGIN(SROA, "sroa", "Scalar Replacement Of Aggregates",
false, false)
INITIALIZE_PASS_DEPENDENCY(DominatorTree)
INITIALIZE_PASS_END(SROA, "sroa", "Scalar Replacement Of Aggregates",
false, false)
/// Walk the range of a partitioning looking for a common type to cover this
/// sequence of slices.
static Type *findCommonType(AllocaSlices::const_iterator B,
AllocaSlices::const_iterator E,
uint64_t EndOffset) {
Type *Ty = 0;
for (AllocaSlices::const_iterator I = B; I != E; ++I) {
Use *U = I->getUse();
if (isa<IntrinsicInst>(*U->getUser()))
continue;
if (I->beginOffset() != B->beginOffset() || I->endOffset() != EndOffset)
continue;
Type *UserTy = 0;
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser()))
UserTy = LI->getType();
else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser()))
UserTy = SI->getValueOperand()->getType();
else
return 0; // Bail if we have weird uses.
if (IntegerType *ITy = dyn_cast<IntegerType>(UserTy)) {
// If the type is larger than the partition, skip it. We only encounter
// this for split integer operations where we want to use the type of the
// entity causing the split.
if (ITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
continue;
// If we have found an integer type use covering the alloca, use that
// regardless of the other types, as integers are often used for a
// "bucket
// of bits" type.
return ITy;
}
if (Ty && Ty != UserTy)
return 0;
Ty = UserTy;
}
return Ty;
}
/// PHI instructions that use an alloca and are subsequently loaded can be
/// rewritten to load both input pointers in the pred blocks and then PHI the
/// results, allowing the load of the alloca to be promoted.
/// From this:
/// %P2 = phi [i32* %Alloca, i32* %Other]
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// ...
/// %V2 = load i32* %Other
/// ...
/// %V = phi [i32 %V1, i32 %V2]
///
/// We can do this to a select if its only uses are loads and if the operands
/// to the select can be loaded unconditionally.
///
/// FIXME: This should be hoisted into a generic utility, likely in
/// Transforms/Util/Local.h
static bool isSafePHIToSpeculate(PHINode &PN,
const DataLayout *DL = 0) {
// For now, we can only do this promotion if the load is in the same block
// as the PHI, and if there are no stores between the phi and load.
// TODO: Allow recursive phi users.
// TODO: Allow stores.
BasicBlock *BB = PN.getParent();
unsigned MaxAlign = 0;
bool HaveLoad = false;
for (Value::use_iterator UI = PN.use_begin(), UE = PN.use_end(); UI != UE;
++UI) {
LoadInst *LI = dyn_cast<LoadInst>(*UI);
if (LI == 0 || !LI->isSimple())
return false;
// For now we only allow loads in the same block as the PHI. This is
// a common case that happens when instcombine merges two loads through
// a PHI.
if (LI->getParent() != BB)
return false;
// Ensure that there are no instructions between the PHI and the load that
// could store.
for (BasicBlock::iterator BBI = &PN; &*BBI != LI; ++BBI)
if (BBI->mayWriteToMemory())
return false;
MaxAlign = std::max(MaxAlign, LI->getAlignment());
HaveLoad = true;
}
if (!HaveLoad)
return false;
// We can only transform this if it is safe to push the loads into the
// predecessor blocks. The only thing to watch out for is that we can't put
// a possibly trapping load in the predecessor if it is a critical edge.
for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
TerminatorInst *TI = PN.getIncomingBlock(Idx)->getTerminator();
Value *InVal = PN.getIncomingValue(Idx);
// If the value is produced by the terminator of the predecessor (an
// invoke) or it has side-effects, there is no valid place to put a load
// in the predecessor.
if (TI == InVal || TI->mayHaveSideEffects())
return false;
// If the predecessor has a single successor, then the edge isn't
// critical.
if (TI->getNumSuccessors() == 1)
continue;
// If this pointer is always safe to load, or if we can prove that there
// is already a load in the block, then we can move the load to the pred
// block.
if (InVal->isDereferenceablePointer() ||
isSafeToLoadUnconditionally(InVal, TI, MaxAlign, DL))
continue;
return false;
}
return true;
}
static void speculatePHINodeLoads(PHINode &PN) {
DEBUG(dbgs() << " original: " << PN << "\n");
Type *LoadTy = cast<PointerType>(PN.getType())->getElementType();
IRBuilderTy PHIBuilder(&PN);
PHINode *NewPN = PHIBuilder.CreatePHI(LoadTy, PN.getNumIncomingValues(),
PN.getName() + ".sroa.speculated");
// Get the TBAA tag and alignment to use from one of the loads. It doesn't
// matter which one we get and if any differ.
LoadInst *SomeLoad = cast<LoadInst>(*PN.use_begin());
MDNode *TBAATag = SomeLoad->getMetadata(LLVMContext::MD_tbaa);
unsigned Align = SomeLoad->getAlignment();
// Rewrite all loads of the PN to use the new PHI.
while (!PN.use_empty()) {
LoadInst *LI = cast<LoadInst>(*PN.use_begin());
LI->replaceAllUsesWith(NewPN);
LI->eraseFromParent();
}
// Inject loads into all of the pred blocks.
for (unsigned Idx = 0, Num = PN.getNumIncomingValues(); Idx != Num; ++Idx) {
BasicBlock *Pred = PN.getIncomingBlock(Idx);
TerminatorInst *TI = Pred->getTerminator();
Value *InVal = PN.getIncomingValue(Idx);
IRBuilderTy PredBuilder(TI);
LoadInst *Load = PredBuilder.CreateLoad(
InVal, (PN.getName() + ".sroa.speculate.load." + Pred->getName()));
++NumLoadsSpeculated;
Load->setAlignment(Align);
if (TBAATag)
Load->setMetadata(LLVMContext::MD_tbaa, TBAATag);
NewPN->addIncoming(Load, Pred);
}
DEBUG(dbgs() << " speculated to: " << *NewPN << "\n");
PN.eraseFromParent();
}
/// Select instructions that use an alloca and are subsequently loaded can be
/// rewritten to load both input pointers and then select between the result,
/// allowing the load of the alloca to be promoted.
/// From this:
/// %P2 = select i1 %cond, i32* %Alloca, i32* %Other
/// %V = load i32* %P2
/// to:
/// %V1 = load i32* %Alloca -> will be mem2reg'd
/// %V2 = load i32* %Other
/// %V = select i1 %cond, i32 %V1, i32 %V2
///
/// We can do this to a select if its only uses are loads and if the operand
/// to the select can be loaded unconditionally.
static bool isSafeSelectToSpeculate(SelectInst &SI, const DataLayout *DL = 0) {
Value *TValue = SI.getTrueValue();
Value *FValue = SI.getFalseValue();
bool TDerefable = TValue->isDereferenceablePointer();
bool FDerefable = FValue->isDereferenceablePointer();
for (Value::use_iterator UI = SI.use_begin(), UE = SI.use_end(); UI != UE;
++UI) {
LoadInst *LI = dyn_cast<LoadInst>(*UI);
if (LI == 0 || !LI->isSimple())
return false;
// Both operands to the select need to be dereferencable, either
// absolutely (e.g. allocas) or at this point because we can see other
// accesses to it.
if (!TDerefable &&
!isSafeToLoadUnconditionally(TValue, LI, LI->getAlignment(), DL))
return false;
if (!FDerefable &&
!isSafeToLoadUnconditionally(FValue, LI, LI->getAlignment(), DL))
return false;
}
return true;
}
static void speculateSelectInstLoads(SelectInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
IRBuilderTy IRB(&SI);
Value *TV = SI.getTrueValue();
Value *FV = SI.getFalseValue();
// Replace the loads of the select with a select of two loads.
while (!SI.use_empty()) {
LoadInst *LI = cast<LoadInst>(*SI.use_begin());
assert(LI->isSimple() && "We only speculate simple loads");
IRB.SetInsertPoint(LI);
LoadInst *TL =
IRB.CreateLoad(TV, LI->getName() + ".sroa.speculate.load.true");
LoadInst *FL =
IRB.CreateLoad(FV, LI->getName() + ".sroa.speculate.load.false");
NumLoadsSpeculated += 2;
// Transfer alignment and TBAA info if present.
TL->setAlignment(LI->getAlignment());
FL->setAlignment(LI->getAlignment());
if (MDNode *Tag = LI->getMetadata(LLVMContext::MD_tbaa)) {
TL->setMetadata(LLVMContext::MD_tbaa, Tag);
FL->setMetadata(LLVMContext::MD_tbaa, Tag);
}
Value *V = IRB.CreateSelect(SI.getCondition(), TL, FL,
LI->getName() + ".sroa.speculated");
DEBUG(dbgs() << " speculated to: " << *V << "\n");
LI->replaceAllUsesWith(V);
LI->eraseFromParent();
}
SI.eraseFromParent();
}
/// \brief Build a GEP out of a base pointer and indices.
///
/// This will return the BasePtr if that is valid, or build a new GEP
/// instruction using the IRBuilder if GEP-ing is needed.
static Value *buildGEP(IRBuilderTy &IRB, Value *BasePtr,
SmallVectorImpl<Value *> &Indices) {
if (Indices.empty())
return BasePtr;
// A single zero index is a no-op, so check for this and avoid building a GEP
// in that case.
if (Indices.size() == 1 && cast<ConstantInt>(Indices.back())->isZero())
return BasePtr;
return IRB.CreateInBoundsGEP(BasePtr, Indices, "idx");
}
/// \brief Get a natural GEP off of the BasePtr walking through Ty toward
/// TargetTy without changing the offset of the pointer.
///
/// This routine assumes we've already established a properly offset GEP with
/// Indices, and arrived at the Ty type. The goal is to continue to GEP with
/// zero-indices down through type layers until we find one the same as
/// TargetTy. If we can't find one with the same type, we at least try to use
/// one with the same size. If none of that works, we just produce the GEP as
/// indicated by Indices to have the correct offset.
static Value *getNaturalGEPWithType(IRBuilderTy &IRB, const DataLayout &DL,
Value *BasePtr, Type *Ty, Type *TargetTy,
SmallVectorImpl<Value *> &Indices) {
if (Ty == TargetTy)
return buildGEP(IRB, BasePtr, Indices);
// See if we can descend into a struct and locate a field with the correct
// type.
unsigned NumLayers = 0;
Type *ElementTy = Ty;
do {
if (ElementTy->isPointerTy())
break;
if (SequentialType *SeqTy = dyn_cast<SequentialType>(ElementTy)) {
ElementTy = SeqTy->getElementType();
// Note that we use the default address space as this index is over an
// array or a vector, not a pointer.
Indices.push_back(IRB.getInt(APInt(DL.getPointerSizeInBits(0), 0)));
} else if (StructType *STy = dyn_cast<StructType>(ElementTy)) {
if (STy->element_begin() == STy->element_end())
break; // Nothing left to descend into.
ElementTy = *STy->element_begin();
Indices.push_back(IRB.getInt32(0));
} else {
break;
}
++NumLayers;
} while (ElementTy != TargetTy);
if (ElementTy != TargetTy)
Indices.erase(Indices.end() - NumLayers, Indices.end());
return buildGEP(IRB, BasePtr, Indices);
}
/// \brief Recursively compute indices for a natural GEP.
///
/// This is the recursive step for getNaturalGEPWithOffset that walks down the
/// element types adding appropriate indices for the GEP.
static Value *getNaturalGEPRecursively(IRBuilderTy &IRB, const DataLayout &DL,
Value *Ptr, Type *Ty, APInt &Offset,
Type *TargetTy,
SmallVectorImpl<Value *> &Indices) {
if (Offset == 0)
return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices);
// We can't recurse through pointer types.
if (Ty->isPointerTy())
return 0;
// We try to analyze GEPs over vectors here, but note that these GEPs are
// extremely poorly defined currently. The long-term goal is to remove GEPing
// over a vector from the IR completely.
if (VectorType *VecTy = dyn_cast<VectorType>(Ty)) {
unsigned ElementSizeInBits = DL.getTypeSizeInBits(VecTy->getScalarType());
if (ElementSizeInBits % 8)
return 0; // GEPs over non-multiple of 8 size vector elements are invalid.
APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(VecTy->getNumElements()))
return 0;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(),
Offset, TargetTy, Indices);
}
if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
Type *ElementTy = ArrTy->getElementType();
APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(ArrTy->getNumElements()))
return 0;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return 0;
const StructLayout *SL = DL.getStructLayout(STy);
uint64_t StructOffset = Offset.getZExtValue();
if (StructOffset >= SL->getSizeInBytes())
return 0;
unsigned Index = SL->getElementContainingOffset(StructOffset);
Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index));
Type *ElementTy = STy->getElementType(Index);
if (Offset.uge(DL.getTypeAllocSize(ElementTy)))
return 0; // The offset points into alignment padding.
Indices.push_back(IRB.getInt32(Index));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices);
}
/// \brief Get a natural GEP from a base pointer to a particular offset and
/// resulting in a particular type.
///
/// The goal is to produce a "natural" looking GEP that works with the existing
/// composite types to arrive at the appropriate offset and element type for
/// a pointer. TargetTy is the element type the returned GEP should point-to if
/// possible. We recurse by decreasing Offset, adding the appropriate index to
/// Indices, and setting Ty to the result subtype.
///
/// If no natural GEP can be constructed, this function returns null.
static Value *getNaturalGEPWithOffset(IRBuilderTy &IRB, const DataLayout &DL,
Value *Ptr, APInt Offset, Type *TargetTy,
SmallVectorImpl<Value *> &Indices) {
PointerType *Ty = cast<PointerType>(Ptr->getType());
// Don't consider any GEPs through an i8* as natural unless the TargetTy is
// an i8.
if (Ty == IRB.getInt8PtrTy() && TargetTy->isIntegerTy(8))
return 0;
Type *ElementTy = Ty->getElementType();
if (!ElementTy->isSized())
return 0; // We can't GEP through an unsized element.
APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
if (ElementSize == 0)
return 0; // Zero-length arrays can't help us build a natural GEP.
APInt NumSkippedElements = Offset.sdiv(ElementSize);
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices);
}
/// \brief Compute an adjusted pointer from Ptr by Offset bytes where the
/// resulting pointer has PointerTy.
///
/// This tries very hard to compute a "natural" GEP which arrives at the offset
/// and produces the pointer type desired. Where it cannot, it will try to use
/// the natural GEP to arrive at the offset and bitcast to the type. Where that
/// fails, it will try to use an existing i8* and GEP to the byte offset and
/// bitcast to the type.
///
/// The strategy for finding the more natural GEPs is to peel off layers of the
/// pointer, walking back through bit casts and GEPs, searching for a base
/// pointer from which we can compute a natural GEP with the desired
/// properties. The algorithm tries to fold as many constant indices into
/// a single GEP as possible, thus making each GEP more independent of the
/// surrounding code.
static Value *getAdjustedPtr(IRBuilderTy &IRB, const DataLayout &DL,
Value *Ptr, APInt Offset, Type *PointerTy) {
// Even though we don't look through PHI nodes, we could be called on an
// instruction in an unreachable block, which may be on a cycle.
SmallPtrSet<Value *, 4> Visited;
Visited.insert(Ptr);
SmallVector<Value *, 4> Indices;
// We may end up computing an offset pointer that has the wrong type. If we
// never are able to compute one directly that has the correct type, we'll
// fall back to it, so keep it around here.
Value *OffsetPtr = 0;
// Remember any i8 pointer we come across to re-use if we need to do a raw
// byte offset.
Value *Int8Ptr = 0;
APInt Int8PtrOffset(Offset.getBitWidth(), 0);
Type *TargetTy = PointerTy->getPointerElementType();
do {
// First fold any existing GEPs into the offset.
while (GEPOperator *GEP = dyn_cast<GEPOperator>(Ptr)) {
APInt GEPOffset(Offset.getBitWidth(), 0);
if (!GEP->accumulateConstantOffset(DL, GEPOffset))
break;
Offset += GEPOffset;
Ptr = GEP->getPointerOperand();
if (!Visited.insert(Ptr))
break;
}
// See if we can perform a natural GEP here.
Indices.clear();
if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
Indices)) {
if (P->getType() == PointerTy) {
// Zap any offset pointer that we ended up computing in previous rounds.
if (OffsetPtr && OffsetPtr->use_empty())
if (Instruction *I = dyn_cast<Instruction>(OffsetPtr))
I->eraseFromParent();
return P;
}
if (!OffsetPtr) {
OffsetPtr = P;
}
}
// Stash this pointer if we've found an i8*.
if (Ptr->getType()->isIntegerTy(8)) {
Int8Ptr = Ptr;
Int8PtrOffset = Offset;
}
// Peel off a layer of the pointer and update the offset appropriately.
if (Operator::getOpcode(Ptr) == Instruction::BitCast) {
Ptr = cast<Operator>(Ptr)->getOperand(0);
} else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(Ptr)) {
if (GA->mayBeOverridden())
break;
Ptr = GA->getAliasee();
} else {
break;
}
assert(Ptr->getType()->isPointerTy() && "Unexpected operand type!");
} while (Visited.insert(Ptr));
if (!OffsetPtr) {
if (!Int8Ptr) {
Int8Ptr = IRB.CreateBitCast(Ptr, IRB.getInt8PtrTy(),
"raw_cast");
Int8PtrOffset = Offset;
}
OffsetPtr = Int8PtrOffset == 0 ? Int8Ptr :
IRB.CreateInBoundsGEP(Int8Ptr, IRB.getInt(Int8PtrOffset),
"raw_idx");
}
Ptr = OffsetPtr;
// On the off chance we were targeting i8*, guard the bitcast here.
if (Ptr->getType() != PointerTy)
Ptr = IRB.CreateBitCast(Ptr, PointerTy, "cast");
return Ptr;
}
/// \brief Test whether we can convert a value from the old to the new type.
///
/// This predicate should be used to guard calls to convertValue in order to
/// ensure that we only try to convert viable values. The strategy is that we
/// will peel off single element struct and array wrappings to get to an
/// underlying value, and convert that value.
static bool canConvertValue(const DataLayout &DL, Type *OldTy, Type *NewTy) {
if (OldTy == NewTy)
return true;
if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy))
if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy))
if (NewITy->getBitWidth() >= OldITy->getBitWidth())
return true;
if (DL.getTypeSizeInBits(NewTy) != DL.getTypeSizeInBits(OldTy))
return false;
if (!NewTy->isSingleValueType() || !OldTy->isSingleValueType())
return false;
// We can convert pointers to integers and vice-versa. Same for vectors
// of pointers and integers.
OldTy = OldTy->getScalarType();
NewTy = NewTy->getScalarType();
if (NewTy->isPointerTy() || OldTy->isPointerTy()) {
if (NewTy->isPointerTy() && OldTy->isPointerTy())
return true;
if (NewTy->isIntegerTy() || OldTy->isIntegerTy())
return true;
return false;
}
return true;
}
/// \brief Generic routine to convert an SSA value to a value of a different
/// type.
///
/// This will try various different casting techniques, such as bitcasts,
/// inttoptr, and ptrtoint casts. Use the \c canConvertValue predicate to test
/// two types for viability with this routine.
static Value *convertValue(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
Type *NewTy) {
Type *OldTy = V->getType();
assert(canConvertValue(DL, OldTy, NewTy) && "Value not convertable to type");
if (OldTy == NewTy)
return V;
if (IntegerType *OldITy = dyn_cast<IntegerType>(OldTy))
if (IntegerType *NewITy = dyn_cast<IntegerType>(NewTy))
if (NewITy->getBitWidth() > OldITy->getBitWidth())
return IRB.CreateZExt(V, NewITy);
// See if we need inttoptr for this type pair. A cast involving both scalars
// and vectors requires and additional bitcast.
if (OldTy->getScalarType()->isIntegerTy() &&
NewTy->getScalarType()->isPointerTy()) {
// Expand <2 x i32> to i8* --> <2 x i32> to i64 to i8*
if (OldTy->isVectorTy() && !NewTy->isVectorTy())
return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
NewTy);
// Expand i128 to <2 x i8*> --> i128 to <2 x i64> to <2 x i8*>
if (!OldTy->isVectorTy() && NewTy->isVectorTy())
return IRB.CreateIntToPtr(IRB.CreateBitCast(V, DL.getIntPtrType(NewTy)),
NewTy);
return IRB.CreateIntToPtr(V, NewTy);
}
// See if we need ptrtoint for this type pair. A cast involving both scalars
// and vectors requires and additional bitcast.
if (OldTy->getScalarType()->isPointerTy() &&
NewTy->getScalarType()->isIntegerTy()) {
// Expand <2 x i8*> to i128 --> <2 x i8*> to <2 x i64> to i128
if (OldTy->isVectorTy() && !NewTy->isVectorTy())
return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
NewTy);
// Expand i8* to <2 x i32> --> i8* to i64 to <2 x i32>
if (!OldTy->isVectorTy() && NewTy->isVectorTy())
return IRB.CreateBitCast(IRB.CreatePtrToInt(V, DL.getIntPtrType(OldTy)),
NewTy);
return IRB.CreatePtrToInt(V, NewTy);
}
return IRB.CreateBitCast(V, NewTy);
}
/// \brief Test whether the given slice use can be promoted to a vector.
///
/// This function is called to test each entry in a partioning which is slated
/// for a single slice.
static bool isVectorPromotionViableForSlice(
const DataLayout &DL, AllocaSlices &S, uint64_t SliceBeginOffset,
uint64_t SliceEndOffset, VectorType *Ty, uint64_t ElementSize,
AllocaSlices::const_iterator I) {
// First validate the slice offsets.
uint64_t BeginOffset =
std::max(I->beginOffset(), SliceBeginOffset) - SliceBeginOffset;
uint64_t BeginIndex = BeginOffset / ElementSize;
if (BeginIndex * ElementSize != BeginOffset ||
BeginIndex >= Ty->getNumElements())
return false;
uint64_t EndOffset =
std::min(I->endOffset(), SliceEndOffset) - SliceBeginOffset;
uint64_t EndIndex = EndOffset / ElementSize;
if (EndIndex * ElementSize != EndOffset || EndIndex > Ty->getNumElements())
return false;
assert(EndIndex > BeginIndex && "Empty vector!");
uint64_t NumElements = EndIndex - BeginIndex;
Type *SliceTy =
(NumElements == 1) ? Ty->getElementType()
: VectorType::get(Ty->getElementType(), NumElements);
Type *SplitIntTy =
Type::getIntNTy(Ty->getContext(), NumElements * ElementSize * 8);
Use *U = I->getUse();
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
if (MI->isVolatile())
return false;
if (!I->isSplittable())
return false; // Skip any unsplittable intrinsics.
} else if (U->get()->getType()->getPointerElementType()->isStructTy()) {
// Disable vector promotion when there are loads or stores of an FCA.
return false;
} else if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
if (LI->isVolatile())
return false;
Type *LTy = LI->getType();
if (SliceBeginOffset > I->beginOffset() ||
SliceEndOffset < I->endOffset()) {
assert(LTy->isIntegerTy());
LTy = SplitIntTy;
}
if (!canConvertValue(DL, SliceTy, LTy))
return false;
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
if (SI->isVolatile())
return false;
Type *STy = SI->getValueOperand()->getType();
if (SliceBeginOffset > I->beginOffset() ||
SliceEndOffset < I->endOffset()) {
assert(STy->isIntegerTy());
STy = SplitIntTy;
}
if (!canConvertValue(DL, STy, SliceTy))
return false;
} else {
return false;
}
return true;
}
/// \brief Test whether the given alloca partitioning and range of slices can be
/// promoted to a vector.
///
/// This is a quick test to check whether we can rewrite a particular alloca
/// partition (and its newly formed alloca) into a vector alloca with only
/// whole-vector loads and stores such that it could be promoted to a vector
/// SSA value. We only can ensure this for a limited set of operations, and we
/// don't want to do the rewrites unless we are confident that the result will
/// be promotable, so we have an early test here.
static bool
isVectorPromotionViable(const DataLayout &DL, Type *AllocaTy, AllocaSlices &S,
uint64_t SliceBeginOffset, uint64_t SliceEndOffset,
AllocaSlices::const_iterator I,
AllocaSlices::const_iterator E,
ArrayRef<AllocaSlices::iterator> SplitUses) {
VectorType *Ty = dyn_cast<VectorType>(AllocaTy);
if (!Ty)
return false;
uint64_t ElementSize = DL.getTypeSizeInBits(Ty->getScalarType());
// While the definition of LLVM vectors is bitpacked, we don't support sizes
// that aren't byte sized.
if (ElementSize % 8)
return false;
assert((DL.getTypeSizeInBits(Ty) % 8) == 0 &&
"vector size not a multiple of element size?");
ElementSize /= 8;
for (; I != E; ++I)
if (!isVectorPromotionViableForSlice(DL, S, SliceBeginOffset,
SliceEndOffset, Ty, ElementSize, I))
return false;
for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
SUE = SplitUses.end();
SUI != SUE; ++SUI)
if (!isVectorPromotionViableForSlice(DL, S, SliceBeginOffset,
SliceEndOffset, Ty, ElementSize, *SUI))
return false;
return true;
}
/// \brief Test whether a slice of an alloca is valid for integer widening.
///
/// This implements the necessary checking for the \c isIntegerWideningViable
/// test below on a single slice of the alloca.
static bool isIntegerWideningViableForSlice(const DataLayout &DL,
Type *AllocaTy,
uint64_t AllocBeginOffset,
uint64_t Size, AllocaSlices &S,
AllocaSlices::const_iterator I,
bool &WholeAllocaOp) {
uint64_t RelBegin = I->beginOffset() - AllocBeginOffset;
uint64_t RelEnd = I->endOffset() - AllocBeginOffset;
// We can't reasonably handle cases where the load or store extends past
// the end of the aloca's type and into its padding.
if (RelEnd > Size)
return false;
Use *U = I->getUse();
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
if (LI->isVolatile())
return false;
if (RelBegin == 0 && RelEnd == Size)
WholeAllocaOp = true;
if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) {
if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
return false;
} else if (RelBegin != 0 || RelEnd != Size ||
!canConvertValue(DL, AllocaTy, LI->getType())) {
// Non-integer loads need to be convertible from the alloca type so that
// they are promotable.
return false;
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
Type *ValueTy = SI->getValueOperand()->getType();
if (SI->isVolatile())
return false;
if (RelBegin == 0 && RelEnd == Size)
WholeAllocaOp = true;
if (IntegerType *ITy = dyn_cast<IntegerType>(ValueTy)) {
if (ITy->getBitWidth() < DL.getTypeStoreSizeInBits(ITy))
return false;
} else if (RelBegin != 0 || RelEnd != Size ||
!canConvertValue(DL, ValueTy, AllocaTy)) {
// Non-integer stores need to be convertible to the alloca type so that
// they are promotable.
return false;
}
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
if (MI->isVolatile() || !isa<Constant>(MI->getLength()))
return false;
if (!I->isSplittable())
return false; // Skip any unsplittable intrinsics.
} else if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(U->getUser())) {
if (II->getIntrinsicID() != Intrinsic::lifetime_start &&
II->getIntrinsicID() != Intrinsic::lifetime_end)
return false;
} else {
return false;
}
return true;
}
/// \brief Test whether the given alloca partition's integer operations can be
/// widened to promotable ones.
///
/// This is a quick test to check whether we can rewrite the integer loads and
/// stores to a particular alloca into wider loads and stores and be able to
/// promote the resulting alloca.
static bool
isIntegerWideningViable(const DataLayout &DL, Type *AllocaTy,
uint64_t AllocBeginOffset, AllocaSlices &S,
AllocaSlices::const_iterator I,
AllocaSlices::const_iterator E,
ArrayRef<AllocaSlices::iterator> SplitUses) {
uint64_t SizeInBits = DL.getTypeSizeInBits(AllocaTy);
// Don't create integer types larger than the maximum bitwidth.
if (SizeInBits > IntegerType::MAX_INT_BITS)
return false;
// Don't try to handle allocas with bit-padding.
if (SizeInBits != DL.getTypeStoreSizeInBits(AllocaTy))
return false;
// We need to ensure that an integer type with the appropriate bitwidth can
// be converted to the alloca type, whatever that is. We don't want to force
// the alloca itself to have an integer type if there is a more suitable one.
Type *IntTy = Type::getIntNTy(AllocaTy->getContext(), SizeInBits);
if (!canConvertValue(DL, AllocaTy, IntTy) ||
!canConvertValue(DL, IntTy, AllocaTy))
return false;
uint64_t Size = DL.getTypeStoreSize(AllocaTy);
// While examining uses, we ensure that the alloca has a covering load or
// store. We don't want to widen the integer operations only to fail to
// promote due to some other unsplittable entry (which we may make splittable
// later). However, if there are only splittable uses, go ahead and assume
// that we cover the alloca.
bool WholeAllocaOp = (I != E) ? false : DL.isLegalInteger(SizeInBits);
for (; I != E; ++I)
if (!isIntegerWideningViableForSlice(DL, AllocaTy, AllocBeginOffset, Size,
S, I, WholeAllocaOp))
return false;
for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
SUE = SplitUses.end();
SUI != SUE; ++SUI)
if (!isIntegerWideningViableForSlice(DL, AllocaTy, AllocBeginOffset, Size,
S, *SUI, WholeAllocaOp))
return false;
return WholeAllocaOp;
}
static Value *extractInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *V,
IntegerType *Ty, uint64_t Offset,
const Twine &Name) {
DEBUG(dbgs() << " start: " << *V << "\n");
IntegerType *IntTy = cast<IntegerType>(V->getType());
assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
"Element extends past full value");
uint64_t ShAmt = 8*Offset;
if (DL.isBigEndian())
ShAmt = 8*(DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
if (ShAmt) {
V = IRB.CreateLShr(V, ShAmt, Name + ".shift");
DEBUG(dbgs() << " shifted: " << *V << "\n");
}
assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
"Cannot extract to a larger integer!");
if (Ty != IntTy) {
V = IRB.CreateTrunc(V, Ty, Name + ".trunc");
DEBUG(dbgs() << " trunced: " << *V << "\n");
}
return V;
}
static Value *insertInteger(const DataLayout &DL, IRBuilderTy &IRB, Value *Old,
Value *V, uint64_t Offset, const Twine &Name) {
IntegerType *IntTy = cast<IntegerType>(Old->getType());
IntegerType *Ty = cast<IntegerType>(V->getType());
assert(Ty->getBitWidth() <= IntTy->getBitWidth() &&
"Cannot insert a larger integer!");
DEBUG(dbgs() << " start: " << *V << "\n");
if (Ty != IntTy) {
V = IRB.CreateZExt(V, IntTy, Name + ".ext");
DEBUG(dbgs() << " extended: " << *V << "\n");
}
assert(DL.getTypeStoreSize(Ty) + Offset <= DL.getTypeStoreSize(IntTy) &&
"Element store outside of alloca store");
uint64_t ShAmt = 8*Offset;
if (DL.isBigEndian())
ShAmt = 8*(DL.getTypeStoreSize(IntTy) - DL.getTypeStoreSize(Ty) - Offset);
if (ShAmt) {
V = IRB.CreateShl(V, ShAmt, Name + ".shift");
DEBUG(dbgs() << " shifted: " << *V << "\n");
}
if (ShAmt || Ty->getBitWidth() < IntTy->getBitWidth()) {
APInt Mask = ~Ty->getMask().zext(IntTy->getBitWidth()).shl(ShAmt);
Old = IRB.CreateAnd(Old, Mask, Name + ".mask");
DEBUG(dbgs() << " masked: " << *Old << "\n");
V = IRB.CreateOr(Old, V, Name + ".insert");
DEBUG(dbgs() << " inserted: " << *V << "\n");
}
return V;
}
static Value *extractVector(IRBuilderTy &IRB, Value *V,
unsigned BeginIndex, unsigned EndIndex,
const Twine &Name) {
VectorType *VecTy = cast<VectorType>(V->getType());
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
if (NumElements == VecTy->getNumElements())
return V;
if (NumElements == 1) {
V = IRB.CreateExtractElement(V, IRB.getInt32(BeginIndex),
Name + ".extract");
DEBUG(dbgs() << " extract: " << *V << "\n");
return V;
}
SmallVector<Constant*, 8> Mask;
Mask.reserve(NumElements);
for (unsigned i = BeginIndex; i != EndIndex; ++i)
Mask.push_back(IRB.getInt32(i));
V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
ConstantVector::get(Mask),
Name + ".extract");
DEBUG(dbgs() << " shuffle: " << *V << "\n");
return V;
}
static Value *insertVector(IRBuilderTy &IRB, Value *Old, Value *V,
unsigned BeginIndex, const Twine &Name) {
VectorType *VecTy = cast<VectorType>(Old->getType());
assert(VecTy && "Can only insert a vector into a vector");
VectorType *Ty = dyn_cast<VectorType>(V->getType());
if (!Ty) {
// Single element to insert.
V = IRB.CreateInsertElement(Old, V, IRB.getInt32(BeginIndex),
Name + ".insert");
DEBUG(dbgs() << " insert: " << *V << "\n");
return V;
}
assert(Ty->getNumElements() <= VecTy->getNumElements() &&
"Too many elements!");
if (Ty->getNumElements() == VecTy->getNumElements()) {
assert(V->getType() == VecTy && "Vector type mismatch");
return V;
}
unsigned EndIndex = BeginIndex + Ty->getNumElements();
// When inserting a smaller vector into the larger to store, we first
// use a shuffle vector to widen it with undef elements, and then
// a second shuffle vector to select between the loaded vector and the
// incoming vector.
SmallVector<Constant*, 8> Mask;
Mask.reserve(VecTy->getNumElements());
for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
if (i >= BeginIndex && i < EndIndex)
Mask.push_back(IRB.getInt32(i - BeginIndex));
else
Mask.push_back(UndefValue::get(IRB.getInt32Ty()));
V = IRB.CreateShuffleVector(V, UndefValue::get(V->getType()),
ConstantVector::get(Mask),
Name + ".expand");
DEBUG(dbgs() << " shuffle: " << *V << "\n");
Mask.clear();
for (unsigned i = 0; i != VecTy->getNumElements(); ++i)
Mask.push_back(IRB.getInt1(i >= BeginIndex && i < EndIndex));
V = IRB.CreateSelect(ConstantVector::get(Mask), V, Old, Name + "blend");
DEBUG(dbgs() << " blend: " << *V << "\n");
return V;
}
namespace {
/// \brief Visitor to rewrite instructions using p particular slice of an alloca
/// to use a new alloca.
///
/// Also implements the rewriting to vector-based accesses when the partition
/// passes the isVectorPromotionViable predicate. Most of the rewriting logic
/// lives here.
class AllocaSliceRewriter : public InstVisitor<AllocaSliceRewriter, bool> {
// Befriend the base class so it can delegate to private visit methods.
friend class llvm::InstVisitor<AllocaSliceRewriter, bool>;
typedef llvm::InstVisitor<AllocaSliceRewriter, bool> Base;
const DataLayout &DL;
AllocaSlices &S;
SROA &Pass;
AllocaInst &OldAI, &NewAI;
const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
Type *NewAllocaTy;
// If we are rewriting an alloca partition which can be written as pure
// vector operations, we stash extra information here. When VecTy is
// non-null, we have some strict guarantees about the rewritten alloca:
// - The new alloca is exactly the size of the vector type here.
// - The accesses all either map to the entire vector or to a single
// element.
// - The set of accessing instructions is only one of those handled above
// in isVectorPromotionViable. Generally these are the same access kinds
// which are promotable via mem2reg.
VectorType *VecTy;
Type *ElementTy;
uint64_t ElementSize;
// This is a convenience and flag variable that will be null unless the new
// alloca's integer operations should be widened to this integer type due to
// passing isIntegerWideningViable above. If it is non-null, the desired
// integer type will be stored here for easy access during rewriting.
IntegerType *IntTy;
// The offset of the slice currently being rewritten.
uint64_t BeginOffset, EndOffset;
bool IsSplittable;
bool IsSplit;
Use *OldUse;
Instruction *OldPtr;
// Output members carrying state about the result of visiting and rewriting
// the slice of the alloca.
bool IsUsedByRewrittenSpeculatableInstructions;
// Utility IR builder, whose name prefix is setup for each visited use, and
// the insertion point is set to point to the user.
IRBuilderTy IRB;
public:
AllocaSliceRewriter(const DataLayout &DL, AllocaSlices &S, SROA &Pass,
AllocaInst &OldAI, AllocaInst &NewAI,
uint64_t NewBeginOffset, uint64_t NewEndOffset,
bool IsVectorPromotable = false,
bool IsIntegerPromotable = false)
: DL(DL), S(S), Pass(Pass), OldAI(OldAI), NewAI(NewAI),
NewAllocaBeginOffset(NewBeginOffset), NewAllocaEndOffset(NewEndOffset),
NewAllocaTy(NewAI.getAllocatedType()),
VecTy(IsVectorPromotable ? cast<VectorType>(NewAllocaTy) : 0),
ElementTy(VecTy ? VecTy->getElementType() : 0),
ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy) / 8 : 0),
IntTy(IsIntegerPromotable
? Type::getIntNTy(
NewAI.getContext(),
DL.getTypeSizeInBits(NewAI.getAllocatedType()))
: 0),
BeginOffset(), EndOffset(), IsSplittable(), IsSplit(), OldUse(),
OldPtr(), IsUsedByRewrittenSpeculatableInstructions(false),
IRB(NewAI.getContext(), ConstantFolder()) {
if (VecTy) {
assert((DL.getTypeSizeInBits(ElementTy) % 8) == 0 &&
"Only multiple-of-8 sized vector elements are viable");
++NumVectorized;
}
assert((!IsVectorPromotable && !IsIntegerPromotable) ||
IsVectorPromotable != IsIntegerPromotable);
}
bool visit(AllocaSlices::const_iterator I) {
bool CanSROA = true;
BeginOffset = I->beginOffset();
EndOffset = I->endOffset();
IsSplittable = I->isSplittable();
IsSplit =
BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset;
OldUse = I->getUse();
OldPtr = cast<Instruction>(OldUse->get());
Instruction *OldUserI = cast<Instruction>(OldUse->getUser());
IRB.SetInsertPoint(OldUserI);
IRB.SetCurrentDebugLocation(OldUserI->getDebugLoc());
IRB.SetNamePrefix(Twine(NewAI.getName()) + "." + Twine(BeginOffset) + ".");
CanSROA &= visit(cast<Instruction>(OldUse->getUser()));
if (VecTy || IntTy)
assert(CanSROA);
return CanSROA;
}
/// \brief Query whether this slice is used by speculatable instructions after
/// rewriting.
///
/// These instructions (PHIs and Selects currently) require the alloca slice
/// to run back through the rewriter. Thus, they are promotable, but not on
/// this iteration. This is distinct from a slice which is unpromotable for
/// some other reason, in which case we don't even want to perform the
/// speculation. This can be querried at any time and reflects whether (at
/// that point) a visit call has rewritten a speculatable instruction on the
/// current slice.
bool isUsedByRewrittenSpeculatableInstructions() const {
return IsUsedByRewrittenSpeculatableInstructions;
}
private:
// Make sure the other visit overloads are visible.
using Base::visit;
// Every instruction which can end up as a user must have a rewrite rule.
bool visitInstruction(Instruction &I) {
DEBUG(dbgs() << " !!!! Cannot rewrite: " << I << "\n");
llvm_unreachable("No rewrite rule for this instruction!");
}
Value *getAdjustedAllocaPtr(IRBuilderTy &IRB, uint64_t Offset,
Type *PointerTy) {
assert(Offset >= NewAllocaBeginOffset);
return getAdjustedPtr(IRB, DL, &NewAI, APInt(DL.getPointerSizeInBits(),
Offset - NewAllocaBeginOffset),
PointerTy);
}
/// \brief Compute suitable alignment to access an offset into the new alloca.
unsigned getOffsetAlign(uint64_t Offset) {
unsigned NewAIAlign = NewAI.getAlignment();
if (!NewAIAlign)
NewAIAlign = DL.getABITypeAlignment(NewAI.getAllocatedType());
return MinAlign(NewAIAlign, Offset);
}
/// \brief Compute suitable alignment to access a type at an offset of the
/// new alloca.
///
/// \returns zero if the type's ABI alignment is a suitable alignment,
/// otherwise returns the maximal suitable alignment.
unsigned getOffsetTypeAlign(Type *Ty, uint64_t Offset) {
unsigned Align = getOffsetAlign(Offset);
return Align == DL.getABITypeAlignment(Ty) ? 0 : Align;
}
unsigned getIndex(uint64_t Offset) {
assert(VecTy && "Can only call getIndex when rewriting a vector");
uint64_t RelOffset = Offset - NewAllocaBeginOffset;
assert(RelOffset / ElementSize < UINT32_MAX && "Index out of bounds");
uint32_t Index = RelOffset / ElementSize;
assert(Index * ElementSize == RelOffset);
return Index;
}
void deleteIfTriviallyDead(Value *V) {
Instruction *I = cast<Instruction>(V);
if (isInstructionTriviallyDead(I))
Pass.DeadInsts.insert(I);
}
Value *rewriteVectorizedLoadInst(uint64_t NewBeginOffset,
uint64_t NewEndOffset) {
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"load");
return extractVector(IRB, V, BeginIndex, EndIndex, "vec");
}
Value *rewriteIntegerLoad(LoadInst &LI, uint64_t NewBeginOffset,
uint64_t NewEndOffset) {
assert(IntTy && "We cannot insert an integer to the alloca");
assert(!LI.isVolatile());
Value *V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"load");
V = convertValue(DL, IRB, V, IntTy);
assert(NewBeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
if (Offset > 0 || NewEndOffset < NewAllocaEndOffset)
V = extractInteger(DL, IRB, V, cast<IntegerType>(LI.getType()), Offset,
"extract");
return V;
}
bool visitLoadInst(LoadInst &LI) {
DEBUG(dbgs() << " original: " << LI << "\n");
Value *OldOp = LI.getOperand(0);
assert(OldOp == OldPtr);
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
uint64_t NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
uint64_t NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
uint64_t Size = NewEndOffset - NewBeginOffset;
Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), Size * 8)
: LI.getType();
bool IsPtrAdjusted = false;
Value *V;
if (VecTy) {
V = rewriteVectorizedLoadInst(NewBeginOffset, NewEndOffset);
} else if (IntTy && LI.getType()->isIntegerTy()) {
V = rewriteIntegerLoad(LI, NewBeginOffset, NewEndOffset);
} else if (NewBeginOffset == NewAllocaBeginOffset &&
canConvertValue(DL, NewAllocaTy, LI.getType())) {
V = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
LI.isVolatile(), "load");
} else {
Type *LTy = TargetTy->getPointerTo();
V = IRB.CreateAlignedLoad(
getAdjustedAllocaPtr(IRB, NewBeginOffset, LTy),
getOffsetTypeAlign(TargetTy, NewBeginOffset - NewAllocaBeginOffset),
LI.isVolatile(), "load");
IsPtrAdjusted = true;
}
V = convertValue(DL, IRB, V, TargetTy);
if (IsSplit) {
assert(!LI.isVolatile());
assert(LI.getType()->isIntegerTy() &&
"Only integer type loads and stores are split");
assert(Size < DL.getTypeStoreSize(LI.getType()) &&
"Split load isn't smaller than original load");
assert(LI.getType()->getIntegerBitWidth() ==
DL.getTypeStoreSizeInBits(LI.getType()) &&
"Non-byte-multiple bit width");
// Move the insertion point just past the load so that we can refer to it.
IRB.SetInsertPoint(llvm::next(BasicBlock::iterator(&LI)));
// Create a placeholder value with the same type as LI to use as the
// basis for the new value. This allows us to replace the uses of LI with
// the computed value, and then replace the placeholder with LI, leaving
// LI only used for this computation.
Value *Placeholder
= new LoadInst(UndefValue::get(LI.getType()->getPointerTo()));
V = insertInteger(DL, IRB, Placeholder, V, NewBeginOffset,
"insert");
LI.replaceAllUsesWith(V);
Placeholder->replaceAllUsesWith(&LI);
delete Placeholder;
} else {
LI.replaceAllUsesWith(V);
}
Pass.DeadInsts.insert(&LI);
deleteIfTriviallyDead(OldOp);
DEBUG(dbgs() << " to: " << *V << "\n");
return !LI.isVolatile() && !IsPtrAdjusted;
}
bool rewriteVectorizedStoreInst(Value *V, StoreInst &SI, Value *OldOp,
uint64_t NewBeginOffset,
uint64_t NewEndOffset) {
if (V->getType() != VecTy) {
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
Type *SliceTy =
(NumElements == 1) ? ElementTy
: VectorType::get(ElementTy, NumElements);
if (V->getType() != SliceTy)
V = convertValue(DL, IRB, V, SliceTy);
// Mix in the existing elements.
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"load");
V = insertVector(IRB, Old, V, BeginIndex, "vec");
}
StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
Pass.DeadInsts.insert(&SI);
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return true;
}
bool rewriteIntegerStore(Value *V, StoreInst &SI,
uint64_t NewBeginOffset, uint64_t NewEndOffset) {
assert(IntTy && "We cannot extract an integer from the alloca");
assert(!SI.isVolatile());
if (DL.getTypeSizeInBits(V->getType()) != IntTy->getBitWidth()) {
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"oldload");
Old = convertValue(DL, IRB, Old, IntTy);
assert(BeginOffset >= NewAllocaBeginOffset && "Out of bounds offset");
uint64_t Offset = BeginOffset - NewAllocaBeginOffset;
V = insertInteger(DL, IRB, Old, SI.getValueOperand(), Offset,
"insert");
}
V = convertValue(DL, IRB, V, NewAllocaTy);
StoreInst *Store = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment());
Pass.DeadInsts.insert(&SI);
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return true;
}
bool visitStoreInst(StoreInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
Value *OldOp = SI.getOperand(1);
assert(OldOp == OldPtr);
Value *V = SI.getValueOperand();
// Strip all inbounds GEPs and pointer casts to try to dig out any root
// alloca that should be re-examined after promoting this alloca.
if (V->getType()->isPointerTy())
if (AllocaInst *AI = dyn_cast<AllocaInst>(V->stripInBoundsOffsets()))
Pass.PostPromotionWorklist.insert(AI);
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
uint64_t NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
uint64_t NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
uint64_t Size = NewEndOffset - NewBeginOffset;
if (Size < DL.getTypeStoreSize(V->getType())) {
assert(!SI.isVolatile());
assert(V->getType()->isIntegerTy() &&
"Only integer type loads and stores are split");
assert(V->getType()->getIntegerBitWidth() ==
DL.getTypeStoreSizeInBits(V->getType()) &&
"Non-byte-multiple bit width");
IntegerType *NarrowTy = Type::getIntNTy(SI.getContext(), Size * 8);
V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset,
"extract");
}
if (VecTy)
return rewriteVectorizedStoreInst(V, SI, OldOp, NewBeginOffset,
NewEndOffset);
if (IntTy && V->getType()->isIntegerTy())
return rewriteIntegerStore(V, SI, NewBeginOffset, NewEndOffset);
StoreInst *NewSI;
if (NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset &&
canConvertValue(DL, V->getType(), NewAllocaTy)) {
V = convertValue(DL, IRB, V, NewAllocaTy);
NewSI = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
SI.isVolatile());
} else {
Value *NewPtr = getAdjustedAllocaPtr(IRB, NewBeginOffset,
V->getType()->getPointerTo());
NewSI = IRB.CreateAlignedStore(
V, NewPtr, getOffsetTypeAlign(
V->getType(), NewBeginOffset - NewAllocaBeginOffset),
SI.isVolatile());
}
(void)NewSI;
Pass.DeadInsts.insert(&SI);
deleteIfTriviallyDead(OldOp);
DEBUG(dbgs() << " to: " << *NewSI << "\n");
return NewSI->getPointerOperand() == &NewAI && !SI.isVolatile();
}
/// \brief Compute an integer value from splatting an i8 across the given
/// number of bytes.
///
/// Note that this routine assumes an i8 is a byte. If that isn't true, don't
/// call this routine.
/// FIXME: Heed the advice above.
///
/// \param V The i8 value to splat.
/// \param Size The number of bytes in the output (assuming i8 is one byte)
Value *getIntegerSplat(Value *V, unsigned Size) {
assert(Size > 0 && "Expected a positive number of bytes.");
IntegerType *VTy = cast<IntegerType>(V->getType());
assert(VTy->getBitWidth() == 8 && "Expected an i8 value for the byte");
if (Size == 1)
return V;
Type *SplatIntTy = Type::getIntNTy(VTy->getContext(), Size*8);
V = IRB.CreateMul(IRB.CreateZExt(V, SplatIntTy, "zext"),
ConstantExpr::getUDiv(
Constant::getAllOnesValue(SplatIntTy),
ConstantExpr::getZExt(
Constant::getAllOnesValue(V->getType()),
SplatIntTy)),
"isplat");
return V;
}
/// \brief Compute a vector splat for a given element value.
Value *getVectorSplat(Value *V, unsigned NumElements) {
V = IRB.CreateVectorSplat(NumElements, V, "vsplat");
DEBUG(dbgs() << " splat: " << *V << "\n");
return V;
}
bool visitMemSetInst(MemSetInst &II) {
DEBUG(dbgs() << " original: " << II << "\n");
assert(II.getRawDest() == OldPtr);
// If the memset has a variable size, it cannot be split, just adjust the
// pointer to the new alloca.
if (!isa<Constant>(II.getLength())) {
assert(!IsSplit);
assert(BeginOffset >= NewAllocaBeginOffset);
II.setDest(
getAdjustedAllocaPtr(IRB, BeginOffset, II.getRawDest()->getType()));
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(ConstantInt::get(CstTy, getOffsetAlign(BeginOffset)));
deleteIfTriviallyDead(OldPtr);
return false;
}
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
Type *AllocaTy = NewAI.getAllocatedType();
Type *ScalarTy = AllocaTy->getScalarType();
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
uint64_t NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
uint64_t NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
uint64_t SliceOffset = NewBeginOffset - NewAllocaBeginOffset;
// If this doesn't map cleanly onto the alloca type, and that type isn't
// a single value type, just emit a memset.
if (!VecTy && !IntTy &&
(BeginOffset > NewAllocaBeginOffset ||
EndOffset < NewAllocaEndOffset ||
!AllocaTy->isSingleValueType() ||
!DL.isLegalInteger(DL.getTypeSizeInBits(ScalarTy)) ||
DL.getTypeSizeInBits(ScalarTy)%8 != 0)) {
Type *SizeTy = II.getLength()->getType();
Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
CallInst *New = IRB.CreateMemSet(
getAdjustedAllocaPtr(IRB, NewBeginOffset, II.getRawDest()->getType()),
II.getValue(), Size, getOffsetAlign(SliceOffset), II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return false;
}
// If we can represent this as a simple value, we have to build the actual
// value to store, which requires expanding the byte present in memset to
// a sensible representation for the alloca type. This is essentially
// splatting the byte to a sufficiently wide integer, splatting it across
// any desired vector width, and bitcasting to the final type.
Value *V;
if (VecTy) {
// If this is a memset of a vectorized alloca, insert it.
assert(ElementTy == ScalarTy);
unsigned BeginIndex = getIndex(NewBeginOffset);
unsigned EndIndex = getIndex(NewEndOffset);
assert(EndIndex > BeginIndex && "Empty vector!");
unsigned NumElements = EndIndex - BeginIndex;
assert(NumElements <= VecTy->getNumElements() && "Too many elements!");
Value *Splat =
getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ElementTy) / 8);
Splat = convertValue(DL, IRB, Splat, ElementTy);
if (NumElements > 1)
Splat = getVectorSplat(Splat, NumElements);
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"oldload");
V = insertVector(IRB, Old, Splat, BeginIndex, "vec");
} else if (IntTy) {
// If this is a memset on an alloca where we can widen stores, insert the
// set integer.
assert(!II.isVolatile());
uint64_t Size = NewEndOffset - NewBeginOffset;
V = getIntegerSplat(II.getValue(), Size);
if (IntTy && (BeginOffset != NewAllocaBeginOffset ||
EndOffset != NewAllocaBeginOffset)) {
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"oldload");
Old = convertValue(DL, IRB, Old, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
V = insertInteger(DL, IRB, Old, V, Offset, "insert");
} else {
assert(V->getType() == IntTy &&
"Wrong type for an alloca wide integer!");
}
V = convertValue(DL, IRB, V, AllocaTy);
} else {
// Established these invariants above.
assert(NewBeginOffset == NewAllocaBeginOffset);
assert(NewEndOffset == NewAllocaEndOffset);
V = getIntegerSplat(II.getValue(), DL.getTypeSizeInBits(ScalarTy) / 8);
if (VectorType *AllocaVecTy = dyn_cast<VectorType>(AllocaTy))
V = getVectorSplat(V, AllocaVecTy->getNumElements());
V = convertValue(DL, IRB, V, AllocaTy);
}
Value *New = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return !II.isVolatile();
}
bool visitMemTransferInst(MemTransferInst &II) {
// Rewriting of memory transfer instructions can be a bit tricky. We break
// them into two categories: split intrinsics and unsplit intrinsics.
DEBUG(dbgs() << " original: " << II << "\n");
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
uint64_t NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
uint64_t NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
assert(II.getRawSource() == OldPtr || II.getRawDest() == OldPtr);
bool IsDest = II.getRawDest() == OldPtr;
// Compute the relative offset within the transfer.
unsigned IntPtrWidth = DL.getPointerSizeInBits();
APInt RelOffset(IntPtrWidth, NewBeginOffset - BeginOffset);
unsigned Align = II.getAlignment();
uint64_t SliceOffset = NewBeginOffset - NewAllocaBeginOffset;
if (Align > 1)
Align =
MinAlign(RelOffset.zextOrTrunc(64).getZExtValue(),
MinAlign(II.getAlignment(), getOffsetAlign(SliceOffset)));
// For unsplit intrinsics, we simply modify the source and destination
// pointers in place. This isn't just an optimization, it is a matter of
// correctness. With unsplit intrinsics we may be dealing with transfers
// within a single alloca before SROA ran, or with transfers that have
// a variable length. We may also be dealing with memmove instead of
// memcpy, and so simply updating the pointers is the necessary for us to
// update both source and dest of a single call.
if (!IsSplittable) {
Value *OldOp = IsDest ? II.getRawDest() : II.getRawSource();
if (IsDest)
II.setDest(
getAdjustedAllocaPtr(IRB, BeginOffset, II.getRawDest()->getType()));
else
II.setSource(getAdjustedAllocaPtr(IRB, BeginOffset,
II.getRawSource()->getType()));
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(ConstantInt::get(CstTy, Align));
DEBUG(dbgs() << " to: " << II << "\n");
deleteIfTriviallyDead(OldOp);
return false;
}
// For split transfer intrinsics we have an incredibly useful assurance:
// the source and destination do not reside within the same alloca, and at
// least one of them does not escape. This means that we can replace
// memmove with memcpy, and we don't need to worry about all manner of
// downsides to splitting and transforming the operations.
// If this doesn't map cleanly onto the alloca type, and that type isn't
// a single value type, just emit a memcpy.
bool EmitMemCpy
= !VecTy && !IntTy && (BeginOffset > NewAllocaBeginOffset ||
EndOffset < NewAllocaEndOffset ||
!NewAI.getAllocatedType()->isSingleValueType());
// If we're just going to emit a memcpy, the alloca hasn't changed, and the
// size hasn't been shrunk based on analysis of the viable range, this is
// a no-op.
if (EmitMemCpy && &OldAI == &NewAI) {
// Ensure the start lines up.
assert(NewBeginOffset == BeginOffset);
// Rewrite the size as needed.
if (NewEndOffset != EndOffset)
II.setLength(ConstantInt::get(II.getLength()->getType(),
NewEndOffset - NewBeginOffset));
return false;
}
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
// Strip all inbounds GEPs and pointer casts to try to dig out any root
// alloca that should be re-examined after rewriting this instruction.
Value *OtherPtr = IsDest ? II.getRawSource() : II.getRawDest();
if (AllocaInst *AI
= dyn_cast<AllocaInst>(OtherPtr->stripInBoundsOffsets()))
Pass.Worklist.insert(AI);
if (EmitMemCpy) {
Type *OtherPtrTy = IsDest ? II.getRawSource()->getType()
: II.getRawDest()->getType();
// Compute the other pointer, folding as much as possible to produce
// a single, simple GEP in most cases.
OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy);
Value *OurPtr = getAdjustedAllocaPtr(
IRB, NewBeginOffset,
IsDest ? II.getRawDest()->getType() : II.getRawSource()->getType());
Type *SizeTy = II.getLength()->getType();
Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
CallInst *New = IRB.CreateMemCpy(IsDest ? OurPtr : OtherPtr,
IsDest ? OtherPtr : OurPtr,
Size, Align, II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return false;
}
// Note that we clamp the alignment to 1 here as a 0 alignment for a memcpy
// is equivalent to 1, but that isn't true if we end up rewriting this as
// a load or store.
if (!Align)
Align = 1;
bool IsWholeAlloca = NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset;
uint64_t Size = NewEndOffset - NewBeginOffset;
unsigned BeginIndex = VecTy ? getIndex(NewBeginOffset) : 0;
unsigned EndIndex = VecTy ? getIndex(NewEndOffset) : 0;
unsigned NumElements = EndIndex - BeginIndex;
IntegerType *SubIntTy
= IntTy ? Type::getIntNTy(IntTy->getContext(), Size*8) : 0;
Type *OtherPtrTy = NewAI.getType();
if (VecTy && !IsWholeAlloca) {
if (NumElements == 1)
OtherPtrTy = VecTy->getElementType();
else
OtherPtrTy = VectorType::get(VecTy->getElementType(), NumElements);
OtherPtrTy = OtherPtrTy->getPointerTo();
} else if (IntTy && !IsWholeAlloca) {
OtherPtrTy = SubIntTy->getPointerTo();
}
Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, RelOffset, OtherPtrTy);
Value *DstPtr = &NewAI;
if (!IsDest)
std::swap(SrcPtr, DstPtr);
Value *Src;
if (VecTy && !IsWholeAlloca && !IsDest) {
Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"load");
Src = extractVector(IRB, Src, BeginIndex, EndIndex, "vec");
} else if (IntTy && !IsWholeAlloca && !IsDest) {
Src = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"load");
Src = convertValue(DL, IRB, Src, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
Src = extractInteger(DL, IRB, Src, SubIntTy, Offset, "extract");
} else {
Src = IRB.CreateAlignedLoad(SrcPtr, Align, II.isVolatile(),
"copyload");
}
if (VecTy && !IsWholeAlloca && IsDest) {
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"oldload");
Src = insertVector(IRB, Old, Src, BeginIndex, "vec");
} else if (IntTy && !IsWholeAlloca && IsDest) {
Value *Old = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
"oldload");
Old = convertValue(DL, IRB, Old, IntTy);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
Src = insertInteger(DL, IRB, Old, Src, Offset, "insert");
Src = convertValue(DL, IRB, Src, NewAllocaTy);
}
StoreInst *Store = cast<StoreInst>(
IRB.CreateAlignedStore(Src, DstPtr, Align, II.isVolatile()));
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
return !II.isVolatile();
}
bool visitIntrinsicInst(IntrinsicInst &II) {
assert(II.getIntrinsicID() == Intrinsic::lifetime_start ||
II.getIntrinsicID() == Intrinsic::lifetime_end);
DEBUG(dbgs() << " original: " << II << "\n");
assert(II.getArgOperand(1) == OldPtr);
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
uint64_t NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
uint64_t NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
ConstantInt *Size
= ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
NewEndOffset - NewBeginOffset);
Value *Ptr =
getAdjustedAllocaPtr(IRB, NewBeginOffset, II.getArgOperand(1)->getType());
Value *New;
if (II.getIntrinsicID() == Intrinsic::lifetime_start)
New = IRB.CreateLifetimeStart(Ptr, Size);
else
New = IRB.CreateLifetimeEnd(Ptr, Size);
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return true;
}
bool visitPHINode(PHINode &PN) {
DEBUG(dbgs() << " original: " << PN << "\n");
assert(BeginOffset >= NewAllocaBeginOffset && "PHIs are unsplittable");
assert(EndOffset <= NewAllocaEndOffset && "PHIs are unsplittable");
// We would like to compute a new pointer in only one place, but have it be
// as local as possible to the PHI. To do that, we re-use the location of
// the old pointer, which necessarily must be in the right position to
// dominate the PHI.
IRBuilderTy PtrBuilder(OldPtr);
PtrBuilder.SetNamePrefix(Twine(NewAI.getName()) + "." + Twine(BeginOffset) +
".");
Value *NewPtr =
getAdjustedAllocaPtr(PtrBuilder, BeginOffset, OldPtr->getType());
// Replace the operands which were using the old pointer.
std::replace(PN.op_begin(), PN.op_end(), cast<Value>(OldPtr), NewPtr);
DEBUG(dbgs() << " to: " << PN << "\n");
deleteIfTriviallyDead(OldPtr);
// Check whether we can speculate this PHI node, and if so remember that
// fact and queue it up for another iteration after the speculation
// occurs.
if (isSafePHIToSpeculate(PN, &DL)) {
Pass.SpeculatablePHIs.insert(&PN);
IsUsedByRewrittenSpeculatableInstructions = true;
return true;
}
return false; // PHIs can't be promoted on their own.
}
bool visitSelectInst(SelectInst &SI) {
DEBUG(dbgs() << " original: " << SI << "\n");
assert((SI.getTrueValue() == OldPtr || SI.getFalseValue() == OldPtr) &&
"Pointer isn't an operand!");
assert(BeginOffset >= NewAllocaBeginOffset && "Selects are unsplittable");
assert(EndOffset <= NewAllocaEndOffset && "Selects are unsplittable");
Value *NewPtr = getAdjustedAllocaPtr(IRB, BeginOffset, OldPtr->getType());
// Replace the operands which were using the old pointer.
if (SI.getOperand(1) == OldPtr)
SI.setOperand(1, NewPtr);
if (SI.getOperand(2) == OldPtr)
SI.setOperand(2, NewPtr);
DEBUG(dbgs() << " to: " << SI << "\n");
deleteIfTriviallyDead(OldPtr);
// Check whether we can speculate this select instruction, and if so
// remember that fact and queue it up for another iteration after the
// speculation occurs.
if (isSafeSelectToSpeculate(SI, &DL)) {
Pass.SpeculatableSelects.insert(&SI);
IsUsedByRewrittenSpeculatableInstructions = true;
return true;
}
return false; // Selects can't be promoted on their own.
}
};
}
namespace {
/// \brief Visitor to rewrite aggregate loads and stores as scalar.
///
/// This pass aggressively rewrites all aggregate loads and stores on
/// a particular pointer (or any pointer derived from it which we can identify)
/// with scalar loads and stores.
class AggLoadStoreRewriter : public InstVisitor<AggLoadStoreRewriter, bool> {
// Befriend the base class so it can delegate to private visit methods.
friend class llvm::InstVisitor<AggLoadStoreRewriter, bool>;
const DataLayout &DL;
/// Queue of pointer uses to analyze and potentially rewrite.
SmallVector<Use *, 8> Queue;
/// Set to prevent us from cycling with phi nodes and loops.
SmallPtrSet<User *, 8> Visited;
/// The current pointer use being rewritten. This is used to dig up the used
/// value (as opposed to the user).
Use *U;
public:
AggLoadStoreRewriter(const DataLayout &DL) : DL(DL) {}
/// Rewrite loads and stores through a pointer and all pointers derived from
/// it.
bool rewrite(Instruction &I) {
DEBUG(dbgs() << " Rewriting FCA loads and stores...\n");
enqueueUsers(I);
bool Changed = false;
while (!Queue.empty()) {
U = Queue.pop_back_val();
Changed |= visit(cast<Instruction>(U->getUser()));
}
return Changed;
}
private:
/// Enqueue all the users of the given instruction for further processing.
/// This uses a set to de-duplicate users.
void enqueueUsers(Instruction &I) {
for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE;
++UI)
if (Visited.insert(*UI))
Queue.push_back(&UI.getUse());
}
// Conservative default is to not rewrite anything.
bool visitInstruction(Instruction &I) { return false; }
/// \brief Generic recursive split emission class.
template <typename Derived>
class OpSplitter {
protected:
/// The builder used to form new instructions.
IRBuilderTy IRB;
/// The indices which to be used with insert- or extractvalue to select the
/// appropriate value within the aggregate.
SmallVector<unsigned, 4> Indices;
/// The indices to a GEP instruction which will move Ptr to the correct slot
/// within the aggregate.
SmallVector<Value *, 4> GEPIndices;
/// The base pointer of the original op, used as a base for GEPing the
/// split operations.
Value *Ptr;
/// Initialize the splitter with an insertion point, Ptr and start with a
/// single zero GEP index.
OpSplitter(Instruction *InsertionPoint, Value *Ptr)
: IRB(InsertionPoint), GEPIndices(1, IRB.getInt32(0)), Ptr(Ptr) {}
public:
/// \brief Generic recursive split emission routine.
///
/// This method recursively splits an aggregate op (load or store) into
/// scalar or vector ops. It splits recursively until it hits a single value
/// and emits that single value operation via the template argument.
///
/// The logic of this routine relies on GEPs and insertvalue and
/// extractvalue all operating with the same fundamental index list, merely
/// formatted differently (GEPs need actual values).
///
/// \param Ty The type being split recursively into smaller ops.
/// \param Agg The aggregate value being built up or stored, depending on
/// whether this is splitting a load or a store respectively.
void emitSplitOps(Type *Ty, Value *&Agg, const Twine &Name) {
if (Ty->isSingleValueType())
return static_cast<Derived *>(this)->emitFunc(Ty, Agg, Name);
if (ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
unsigned OldSize = Indices.size();
(void)OldSize;
for (unsigned Idx = 0, Size = ATy->getNumElements(); Idx != Size;
++Idx) {
assert(Indices.size() == OldSize && "Did not return to the old size");
Indices.push_back(Idx);
GEPIndices.push_back(IRB.getInt32(Idx));
emitSplitOps(ATy->getElementType(), Agg, Name + "." + Twine(Idx));
GEPIndices.pop_back();
Indices.pop_back();
}
return;
}
if (StructType *STy = dyn_cast<StructType>(Ty)) {
unsigned OldSize = Indices.size();
(void)OldSize;
for (unsigned Idx = 0, Size = STy->getNumElements(); Idx != Size;
++Idx) {
assert(Indices.size() == OldSize && "Did not return to the old size");
Indices.push_back(Idx);
GEPIndices.push_back(IRB.getInt32(Idx));
emitSplitOps(STy->getElementType(Idx), Agg, Name + "." + Twine(Idx));
GEPIndices.pop_back();
Indices.pop_back();
}
return;
}
llvm_unreachable("Only arrays and structs are aggregate loadable types");
}
};
struct LoadOpSplitter : public OpSplitter<LoadOpSplitter> {
LoadOpSplitter(Instruction *InsertionPoint, Value *Ptr)
: OpSplitter<LoadOpSplitter>(InsertionPoint, Ptr) {}
/// Emit a leaf load of a single value. This is called at the leaves of the
/// recursive emission to actually load values.
void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
assert(Ty->isSingleValueType());
// Load the single value and insert it using the indices.
Value *GEP = IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep");
Value *Load = IRB.CreateLoad(GEP, Name + ".load");
Agg = IRB.CreateInsertValue(Agg, Load, Indices, Name + ".insert");
DEBUG(dbgs() << " to: " << *Load << "\n");
}
};
bool visitLoadInst(LoadInst &LI) {
assert(LI.getPointerOperand() == *U);
if (!LI.isSimple() || LI.getType()->isSingleValueType())
return false;
// We have an aggregate being loaded, split it apart.
DEBUG(dbgs() << " original: " << LI << "\n");
LoadOpSplitter Splitter(&LI, *U);
Value *V = UndefValue::get(LI.getType());
Splitter.emitSplitOps(LI.getType(), V, LI.getName() + ".fca");
LI.replaceAllUsesWith(V);
LI.eraseFromParent();
return true;
}
struct StoreOpSplitter : public OpSplitter<StoreOpSplitter> {
StoreOpSplitter(Instruction *InsertionPoint, Value *Ptr)
: OpSplitter<StoreOpSplitter>(InsertionPoint, Ptr) {}
/// Emit a leaf store of a single value. This is called at the leaves of the
/// recursive emission to actually produce stores.
void emitFunc(Type *Ty, Value *&Agg, const Twine &Name) {
assert(Ty->isSingleValueType());
// Extract the single value and store it using the indices.
Value *Store = IRB.CreateStore(
IRB.CreateExtractValue(Agg, Indices, Name + ".extract"),
IRB.CreateInBoundsGEP(Ptr, GEPIndices, Name + ".gep"));
(void)Store;
DEBUG(dbgs() << " to: " << *Store << "\n");
}
};
bool visitStoreInst(StoreInst &SI) {
if (!SI.isSimple() || SI.getPointerOperand() != *U)
return false;
Value *V = SI.getValueOperand();
if (V->getType()->isSingleValueType())
return false;
// We have an aggregate being stored, split it apart.
DEBUG(dbgs() << " original: " << SI << "\n");
StoreOpSplitter Splitter(&SI, *U);
Splitter.emitSplitOps(V->getType(), V, V->getName() + ".fca");
SI.eraseFromParent();
return true;
}
bool visitBitCastInst(BitCastInst &BC) {
enqueueUsers(BC);
return false;
}
bool visitGetElementPtrInst(GetElementPtrInst &GEPI) {
enqueueUsers(GEPI);
return false;
}
bool visitPHINode(PHINode &PN) {
enqueueUsers(PN);
return false;
}
bool visitSelectInst(SelectInst &SI) {
enqueueUsers(SI);
return false;
}
};
}
/// \brief Strip aggregate type wrapping.
///
/// This removes no-op aggregate types wrapping an underlying type. It will
/// strip as many layers of types as it can without changing either the type
/// size or the allocated size.
static Type *stripAggregateTypeWrapping(const DataLayout &DL, Type *Ty) {
if (Ty->isSingleValueType())
return Ty;
uint64_t AllocSize = DL.getTypeAllocSize(Ty);
uint64_t TypeSize = DL.getTypeSizeInBits(Ty);
Type *InnerTy;
if (ArrayType *ArrTy = dyn_cast<ArrayType>(Ty)) {
InnerTy = ArrTy->getElementType();
} else if (StructType *STy = dyn_cast<StructType>(Ty)) {
const StructLayout *SL = DL.getStructLayout(STy);
unsigned Index = SL->getElementContainingOffset(0);
InnerTy = STy->getElementType(Index);
} else {
return Ty;
}
if (AllocSize > DL.getTypeAllocSize(InnerTy) ||
TypeSize > DL.getTypeSizeInBits(InnerTy))
return Ty;
return stripAggregateTypeWrapping(DL, InnerTy);
}
/// \brief Try to find a partition of the aggregate type passed in for a given
/// offset and size.
///
/// This recurses through the aggregate type and tries to compute a subtype
/// based on the offset and size. When the offset and size span a sub-section
/// of an array, it will even compute a new array type for that sub-section,
/// and the same for structs.
///
/// Note that this routine is very strict and tries to find a partition of the
/// type which produces the *exact* right offset and size. It is not forgiving
/// when the size or offset cause either end of type-based partition to be off.
/// Also, this is a best-effort routine. It is reasonable to give up and not
/// return a type if necessary.
static Type *getTypePartition(const DataLayout &DL, Type *Ty,
uint64_t Offset, uint64_t Size) {
if (Offset == 0 && DL.getTypeAllocSize(Ty) == Size)
return stripAggregateTypeWrapping(DL, Ty);
if (Offset > DL.getTypeAllocSize(Ty) ||
(DL.getTypeAllocSize(Ty) - Offset) < Size)
return 0;
if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) {
// We can't partition pointers...
if (SeqTy->isPointerTy())
return 0;
Type *ElementTy = SeqTy->getElementType();
uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
uint64_t NumSkippedElements = Offset / ElementSize;
if (ArrayType *ArrTy = dyn_cast<ArrayType>(SeqTy)) {
if (NumSkippedElements >= ArrTy->getNumElements())
return 0;
} else if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy)) {
if (NumSkippedElements >= VecTy->getNumElements())
return 0;
}
Offset -= NumSkippedElements * ElementSize;
// First check if we need to recurse.
if (Offset > 0 || Size < ElementSize) {
// Bail if the partition ends in a different array element.
if ((Offset + Size) > ElementSize)
return 0;
// Recurse through the element type trying to peel off offset bytes.
return getTypePartition(DL, ElementTy, Offset, Size);
}
assert(Offset == 0);
if (Size == ElementSize)
return stripAggregateTypeWrapping(DL, ElementTy);
assert(Size > ElementSize);
uint64_t NumElements = Size / ElementSize;
if (NumElements * ElementSize != Size)
return 0;
return ArrayType::get(ElementTy, NumElements);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return 0;
const StructLayout *SL = DL.getStructLayout(STy);
if (Offset >= SL->getSizeInBytes())
return 0;
uint64_t EndOffset = Offset + Size;
if (EndOffset > SL->getSizeInBytes())
return 0;
unsigned Index = SL->getElementContainingOffset(Offset);
Offset -= SL->getElementOffset(Index);
Type *ElementTy = STy->getElementType(Index);
uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
if (Offset >= ElementSize)
return 0; // The offset points into alignment padding.
// See if any partition must be contained by the element.
if (Offset > 0 || Size < ElementSize) {
if ((Offset + Size) > ElementSize)
return 0;
return getTypePartition(DL, ElementTy, Offset, Size);
}
assert(Offset == 0);
if (Size == ElementSize)
return stripAggregateTypeWrapping(DL, ElementTy);
StructType::element_iterator EI = STy->element_begin() + Index,
EE = STy->element_end();
if (EndOffset < SL->getSizeInBytes()) {
unsigned EndIndex = SL->getElementContainingOffset(EndOffset);
if (Index == EndIndex)
return 0; // Within a single element and its padding.
// Don't try to form "natural" types if the elements don't line up with the
// expected size.
// FIXME: We could potentially recurse down through the last element in the
// sub-struct to find a natural end point.
if (SL->getElementOffset(EndIndex) != EndOffset)
return 0;
assert(Index < EndIndex);
EE = STy->element_begin() + EndIndex;
}
// Try to build up a sub-structure.
StructType *SubTy = StructType::get(STy->getContext(), makeArrayRef(EI, EE),
STy->isPacked());
const StructLayout *SubSL = DL.getStructLayout(SubTy);
if (Size != SubSL->getSizeInBytes())
return 0; // The sub-struct doesn't have quite the size needed.
return SubTy;
}
/// \brief Rewrite an alloca partition's users.
///
/// This routine drives both of the rewriting goals of the SROA pass. It tries
/// to rewrite uses of an alloca partition to be conducive for SSA value
/// promotion. If the partition needs a new, more refined alloca, this will
/// build that new alloca, preserving as much type information as possible, and
/// rewrite the uses of the old alloca to point at the new one and have the
/// appropriate new offsets. It also evaluates how successful the rewrite was
/// at enabling promotion and if it was successful queues the alloca to be
/// promoted.
bool SROA::rewritePartition(AllocaInst &AI, AllocaSlices &S,
AllocaSlices::iterator B, AllocaSlices::iterator E,
int64_t BeginOffset, int64_t EndOffset,
ArrayRef<AllocaSlices::iterator> SplitUses) {
assert(BeginOffset < EndOffset);
uint64_t SliceSize = EndOffset - BeginOffset;
// Try to compute a friendly type for this partition of the alloca. This
// won't always succeed, in which case we fall back to a legal integer type
// or an i8 array of an appropriate size.
Type *SliceTy = 0;
if (Type *CommonUseTy = findCommonType(B, E, EndOffset))
if (DL->getTypeAllocSize(CommonUseTy) >= SliceSize)
SliceTy = CommonUseTy;
if (!SliceTy)
if (Type *TypePartitionTy = getTypePartition(*DL, AI.getAllocatedType(),
BeginOffset, SliceSize))
SliceTy = TypePartitionTy;
if ((!SliceTy || (SliceTy->isArrayTy() &&
SliceTy->getArrayElementType()->isIntegerTy())) &&
DL->isLegalInteger(SliceSize * 8))
SliceTy = Type::getIntNTy(*C, SliceSize * 8);
if (!SliceTy)
SliceTy = ArrayType::get(Type::getInt8Ty(*C), SliceSize);
assert(DL->getTypeAllocSize(SliceTy) >= SliceSize);
bool IsVectorPromotable = isVectorPromotionViable(
*DL, SliceTy, S, BeginOffset, EndOffset, B, E, SplitUses);
bool IsIntegerPromotable =
!IsVectorPromotable &&
isIntegerWideningViable(*DL, SliceTy, BeginOffset, S, B, E, SplitUses);
// Check for the case where we're going to rewrite to a new alloca of the
// exact same type as the original, and with the same access offsets. In that
// case, re-use the existing alloca, but still run through the rewriter to
// perform phi and select speculation.
AllocaInst *NewAI;
if (SliceTy == AI.getAllocatedType()) {
assert(BeginOffset == 0 &&
"Non-zero begin offset but same alloca type");
NewAI = &AI;
// FIXME: We should be able to bail at this point with "nothing changed".
// FIXME: We might want to defer PHI speculation until after here.
} else {
unsigned Alignment = AI.getAlignment();
if (!Alignment) {
// The minimum alignment which users can rely on when the explicit
// alignment is omitted or zero is that required by the ABI for this
// type.
Alignment = DL->getABITypeAlignment(AI.getAllocatedType());
}
Alignment = MinAlign(Alignment, BeginOffset);
// If we will get at least this much alignment from the type alone, leave
// the alloca's alignment unconstrained.
if (Alignment <= DL->getABITypeAlignment(SliceTy))
Alignment = 0;
NewAI = new AllocaInst(SliceTy, 0, Alignment,
AI.getName() + ".sroa." + Twine(B - S.begin()), &AI);
++NumNewAllocas;
}
DEBUG(dbgs() << "Rewriting alloca partition "
<< "[" << BeginOffset << "," << EndOffset << ") to: " << *NewAI
<< "\n");
// Track the high watermark on several worklists that are only relevant for
// promoted allocas. We will reset it to this point if the alloca is not in
// fact scheduled for promotion.
unsigned PPWOldSize = PostPromotionWorklist.size();
unsigned SPOldSize = SpeculatablePHIs.size();
unsigned SSOldSize = SpeculatableSelects.size();
unsigned NumUses = 0;
AllocaSliceRewriter Rewriter(*DL, S, *this, AI, *NewAI, BeginOffset,
EndOffset, IsVectorPromotable,
IsIntegerPromotable);
bool Promotable = true;
for (ArrayRef<AllocaSlices::iterator>::const_iterator SUI = SplitUses.begin(),
SUE = SplitUses.end();
SUI != SUE; ++SUI) {
DEBUG(dbgs() << " rewriting split ");
DEBUG(S.printSlice(dbgs(), *SUI, ""));
Promotable &= Rewriter.visit(*SUI);
++NumUses;
}
for (AllocaSlices::iterator I = B; I != E; ++I) {
DEBUG(dbgs() << " rewriting ");
DEBUG(S.printSlice(dbgs(), I, ""));
Promotable &= Rewriter.visit(I);
++NumUses;
}
NumAllocaPartitionUses += NumUses;
MaxUsesPerAllocaPartition =
std::max<unsigned>(NumUses, MaxUsesPerAllocaPartition);
if (Promotable && !Rewriter.isUsedByRewrittenSpeculatableInstructions()) {
DEBUG(dbgs() << " and queuing for promotion\n");
PromotableAllocas.push_back(NewAI);
} else if (NewAI != &AI ||
(Promotable &&
Rewriter.isUsedByRewrittenSpeculatableInstructions())) {
// If we can't promote the alloca, iterate on it to check for new
// refinements exposed by splitting the current alloca. Don't iterate on an
// alloca which didn't actually change and didn't get promoted.
//
// Alternatively, if we could promote the alloca but have speculatable
// instructions then we will speculate them after finishing our processing
// of the original alloca. Mark the new one for re-visiting in the next
// iteration so the speculated operations can be rewritten.
//
// FIXME: We should actually track whether the rewriter changed anything.
Worklist.insert(NewAI);
}
// Drop any post-promotion work items if promotion didn't happen.
if (!Promotable) {
while (PostPromotionWorklist.size() > PPWOldSize)
PostPromotionWorklist.pop_back();
while (SpeculatablePHIs.size() > SPOldSize)
SpeculatablePHIs.pop_back();
while (SpeculatableSelects.size() > SSOldSize)
SpeculatableSelects.pop_back();
}
return true;
}
namespace {
struct IsSliceEndLessOrEqualTo {
uint64_t UpperBound;
IsSliceEndLessOrEqualTo(uint64_t UpperBound) : UpperBound(UpperBound) {}
bool operator()(const AllocaSlices::iterator &I) {
return I->endOffset() <= UpperBound;
}
};
}
static void
removeFinishedSplitUses(SmallVectorImpl<AllocaSlices::iterator> &SplitUses,
uint64_t &MaxSplitUseEndOffset, uint64_t Offset) {
if (Offset >= MaxSplitUseEndOffset) {
SplitUses.clear();
MaxSplitUseEndOffset = 0;
return;
}
size_t SplitUsesOldSize = SplitUses.size();
SplitUses.erase(std::remove_if(SplitUses.begin(), SplitUses.end(),
IsSliceEndLessOrEqualTo(Offset)),
SplitUses.end());
if (SplitUsesOldSize == SplitUses.size())
return;
// Recompute the max. While this is linear, so is remove_if.
MaxSplitUseEndOffset = 0;
for (SmallVectorImpl<AllocaSlices::iterator>::iterator
SUI = SplitUses.begin(),
SUE = SplitUses.end();
SUI != SUE; ++SUI)
MaxSplitUseEndOffset = std::max((*SUI)->endOffset(), MaxSplitUseEndOffset);
}
/// \brief Walks the slices of an alloca and form partitions based on them,
/// rewriting each of their uses.
bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &S) {
if (S.begin() == S.end())
return false;
unsigned NumPartitions = 0;
bool Changed = false;
SmallVector<AllocaSlices::iterator, 4> SplitUses;
uint64_t MaxSplitUseEndOffset = 0;
uint64_t BeginOffset = S.begin()->beginOffset();
for (AllocaSlices::iterator SI = S.begin(), SJ = llvm::next(SI), SE = S.end();
SI != SE; SI = SJ) {
uint64_t MaxEndOffset = SI->endOffset();
if (!SI->isSplittable()) {
// When we're forming an unsplittable region, it must always start at the
// first slice and will extend through its end.
assert(BeginOffset == SI->beginOffset());
// Form a partition including all of the overlapping slices with this
// unsplittable slice.
while (SJ != SE && SJ->beginOffset() < MaxEndOffset) {
if (!SJ->isSplittable())
MaxEndOffset = std::max(MaxEndOffset, SJ->endOffset());
++SJ;
}
} else {
assert(SI->isSplittable()); // Established above.
// Collect all of the overlapping splittable slices.
while (SJ != SE && SJ->beginOffset() < MaxEndOffset &&
SJ->isSplittable()) {
MaxEndOffset = std::max(MaxEndOffset, SJ->endOffset());
++SJ;
}
// Back up MaxEndOffset and SJ if we ended the span early when
// encountering an unsplittable slice.
if (SJ != SE && SJ->beginOffset() < MaxEndOffset) {
assert(!SJ->isSplittable());
MaxEndOffset = SJ->beginOffset();
}
}
// Check if we have managed to move the end offset forward yet. If so,
// we'll have to rewrite uses and erase old split uses.
if (BeginOffset < MaxEndOffset) {
// Rewrite a sequence of overlapping slices.
Changed |=
rewritePartition(AI, S, SI, SJ, BeginOffset, MaxEndOffset, SplitUses);
++NumPartitions;
removeFinishedSplitUses(SplitUses, MaxSplitUseEndOffset, MaxEndOffset);
}
// Accumulate all the splittable slices from the [SI,SJ) region which
// overlap going forward.
for (AllocaSlices::iterator SK = SI; SK != SJ; ++SK)
if (SK->isSplittable() && SK->endOffset() > MaxEndOffset) {
SplitUses.push_back(SK);
MaxSplitUseEndOffset = std::max(SK->endOffset(), MaxSplitUseEndOffset);
}
// If we're already at the end and we have no split uses, we're done.
if (SJ == SE && SplitUses.empty())
break;
// If we have no split uses or no gap in offsets, we're ready to move to
// the next slice.
if (SplitUses.empty() || (SJ != SE && MaxEndOffset == SJ->beginOffset())) {
BeginOffset = SJ->beginOffset();
continue;
}
// Even if we have split slices, if the next slice is splittable and the
// split slices reach it, we can simply set up the beginning offset of the
// next iteration to bridge between them.
if (SJ != SE && SJ->isSplittable() &&
MaxSplitUseEndOffset > SJ->beginOffset()) {
BeginOffset = MaxEndOffset;
continue;
}
// Otherwise, we have a tail of split slices. Rewrite them with an empty
// range of slices.
uint64_t PostSplitEndOffset =
SJ == SE ? MaxSplitUseEndOffset : SJ->beginOffset();
Changed |= rewritePartition(AI, S, SJ, SJ, MaxEndOffset, PostSplitEndOffset,
SplitUses);
++NumPartitions;
if (SJ == SE)
break; // Skip the rest, we don't need to do any cleanup.
removeFinishedSplitUses(SplitUses, MaxSplitUseEndOffset,
PostSplitEndOffset);
// Now just reset the begin offset for the next iteration.
BeginOffset = SJ->beginOffset();
}
NumAllocaPartitions += NumPartitions;
MaxPartitionsPerAlloca =
std::max<unsigned>(NumPartitions, MaxPartitionsPerAlloca);
return Changed;
}
/// \brief Analyze an alloca for SROA.
///
/// This analyzes the alloca to ensure we can reason about it, builds
/// the slices of the alloca, and then hands it off to be split and
/// rewritten as needed.
bool SROA::runOnAlloca(AllocaInst &AI) {
DEBUG(dbgs() << "SROA alloca: " << AI << "\n");
++NumAllocasAnalyzed;
// Special case dead allocas, as they're trivial.
if (AI.use_empty()) {
AI.eraseFromParent();
return true;
}
// Skip alloca forms that this analysis can't handle.
if (AI.isArrayAllocation() || !AI.getAllocatedType()->isSized() ||
DL->getTypeAllocSize(AI.getAllocatedType()) == 0)
return false;
bool Changed = false;
// First, split any FCA loads and stores touching this alloca to promote
// better splitting and promotion opportunities.
AggLoadStoreRewriter AggRewriter(*DL);
Changed |= AggRewriter.rewrite(AI);
// Build the slices using a recursive instruction-visiting builder.
AllocaSlices S(*DL, AI);
DEBUG(S.print(dbgs()));
if (S.isEscaped())
return Changed;
// Delete all the dead users of this alloca before splitting and rewriting it.
for (AllocaSlices::dead_user_iterator DI = S.dead_user_begin(),
DE = S.dead_user_end();
DI != DE; ++DI) {
Changed = true;
(*DI)->replaceAllUsesWith(UndefValue::get((*DI)->getType()));
DeadInsts.insert(*DI);
}
for (AllocaSlices::dead_op_iterator DO = S.dead_op_begin(),
DE = S.dead_op_end();
DO != DE; ++DO) {
Value *OldV = **DO;
// Clobber the use with an undef value.
**DO = UndefValue::get(OldV->getType());
if (Instruction *OldI = dyn_cast<Instruction>(OldV))
if (isInstructionTriviallyDead(OldI)) {
Changed = true;
DeadInsts.insert(OldI);
}
}
// No slices to split. Leave the dead alloca for a later pass to clean up.
if (S.begin() == S.end())
return Changed;
Changed |= splitAlloca(AI, S);
DEBUG(dbgs() << " Speculating PHIs\n");
while (!SpeculatablePHIs.empty())
speculatePHINodeLoads(*SpeculatablePHIs.pop_back_val());
DEBUG(dbgs() << " Speculating Selects\n");
while (!SpeculatableSelects.empty())
speculateSelectInstLoads(*SpeculatableSelects.pop_back_val());
return Changed;
}
/// \brief Delete the dead instructions accumulated in this run.
///
/// Recursively deletes the dead instructions we've accumulated. This is done
/// at the very end to maximize locality of the recursive delete and to
/// minimize the problems of invalidated instruction pointers as such pointers
/// are used heavily in the intermediate stages of the algorithm.
///
/// We also record the alloca instructions deleted here so that they aren't
/// subsequently handed to mem2reg to promote.
void SROA::deleteDeadInstructions(SmallPtrSet<AllocaInst*, 4> &DeletedAllocas) {
while (!DeadInsts.empty()) {
Instruction *I = DeadInsts.pop_back_val();
DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
I->replaceAllUsesWith(UndefValue::get(I->getType()));
for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
if (Instruction *U = dyn_cast<Instruction>(*OI)) {
// Zero out the operand and see if it becomes trivially dead.
*OI = 0;
if (isInstructionTriviallyDead(U))
DeadInsts.insert(U);
}
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
DeletedAllocas.insert(AI);
++NumDeleted;
I->eraseFromParent();
}
}
static void enqueueUsersInWorklist(Instruction &I,
SmallVectorImpl<Instruction *> &Worklist,
SmallPtrSet<Instruction *, 8> &Visited) {
for (Value::use_iterator UI = I.use_begin(), UE = I.use_end(); UI != UE;
++UI)
if (Visited.insert(cast<Instruction>(*UI)))
Worklist.push_back(cast<Instruction>(*UI));
}
/// \brief Promote the allocas, using the best available technique.
///
/// This attempts to promote whatever allocas have been identified as viable in
/// the PromotableAllocas list. If that list is empty, there is nothing to do.
/// If there is a domtree available, we attempt to promote using the full power
/// of mem2reg. Otherwise, we build and use the AllocaPromoter above which is
/// based on the SSAUpdater utilities. This function returns whether any
/// promotion occurred.
bool SROA::promoteAllocas(Function &F) {
if (PromotableAllocas.empty())
return false;
NumPromoted += PromotableAllocas.size();
if (DT && !ForceSSAUpdater) {
DEBUG(dbgs() << "Promoting allocas with mem2reg...\n");
PromoteMemToReg(PromotableAllocas, *DT);
PromotableAllocas.clear();
return true;
}
DEBUG(dbgs() << "Promoting allocas with SSAUpdater...\n");
SSAUpdater SSA;
DIBuilder DIB(*F.getParent());
SmallVector<Instruction *, 64> Insts;
// We need a worklist to walk the uses of each alloca.
SmallVector<Instruction *, 8> Worklist;
SmallPtrSet<Instruction *, 8> Visited;
SmallVector<Instruction *, 32> DeadInsts;
for (unsigned Idx = 0, Size = PromotableAllocas.size(); Idx != Size; ++Idx) {
AllocaInst *AI = PromotableAllocas[Idx];
Insts.clear();
Worklist.clear();
Visited.clear();
enqueueUsersInWorklist(*AI, Worklist, Visited);
while (!Worklist.empty()) {
Instruction *I = Worklist.pop_back_val();
// FIXME: Currently the SSAUpdater infrastructure doesn't reason about
// lifetime intrinsics and so we strip them (and the bitcasts+GEPs
// leading to them) here. Eventually it should use them to optimize the
// scalar values produced.
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
assert(II->getIntrinsicID() == Intrinsic::lifetime_start ||
II->getIntrinsicID() == Intrinsic::lifetime_end);
II->eraseFromParent();
continue;
}
// Push the loads and stores we find onto the list. SROA will already
// have validated that all loads and stores are viable candidates for
// promotion.
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
assert(LI->getType() == AI->getAllocatedType());
Insts.push_back(LI);
continue;
}
if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
assert(SI->getValueOperand()->getType() == AI->getAllocatedType());
Insts.push_back(SI);
continue;
}
// For everything else, we know that only no-op bitcasts and GEPs will
// make it this far, just recurse through them and recall them for later
// removal.
DeadInsts.push_back(I);
enqueueUsersInWorklist(*I, Worklist, Visited);
}
AllocaPromoter(Insts, SSA, *AI, DIB).run(Insts);
while (!DeadInsts.empty())
DeadInsts.pop_back_val()->eraseFromParent();
AI->eraseFromParent();
}
PromotableAllocas.clear();
return true;
}
namespace {
/// \brief A predicate to test whether an alloca belongs to a set.
class IsAllocaInSet {
typedef SmallPtrSet<AllocaInst *, 4> SetType;
const SetType &Set;
public:
typedef AllocaInst *argument_type;
IsAllocaInSet(const SetType &Set) : Set(Set) {}
bool operator()(AllocaInst *AI) const { return Set.count(AI); }
};
}
bool SROA::runOnFunction(Function &F) {
DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
C = &F.getContext();
DL = getAnalysisIfAvailable<DataLayout>();
if (!DL) {
DEBUG(dbgs() << " Skipping SROA -- no target data!\n");
return false;
}
DT = getAnalysisIfAvailable<DominatorTree>();
BasicBlock &EntryBB = F.getEntryBlock();
for (BasicBlock::iterator I = EntryBB.begin(), E = llvm::prior(EntryBB.end());
I != E; ++I)
if (AllocaInst *AI = dyn_cast<AllocaInst>(I))
Worklist.insert(AI);
bool Changed = false;
// A set of deleted alloca instruction pointers which should be removed from
// the list of promotable allocas.
SmallPtrSet<AllocaInst *, 4> DeletedAllocas;
do {
while (!Worklist.empty()) {
Changed |= runOnAlloca(*Worklist.pop_back_val());
deleteDeadInstructions(DeletedAllocas);
// Remove the deleted allocas from various lists so that we don't try to
// continue processing them.
if (!DeletedAllocas.empty()) {
Worklist.remove_if(IsAllocaInSet(DeletedAllocas));
PostPromotionWorklist.remove_if(IsAllocaInSet(DeletedAllocas));
PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(),
PromotableAllocas.end(),
IsAllocaInSet(DeletedAllocas)),
PromotableAllocas.end());
DeletedAllocas.clear();
}
}
Changed |= promoteAllocas(F);
Worklist = PostPromotionWorklist;
PostPromotionWorklist.clear();
} while (!Worklist.empty());
return Changed;
}
void SROA::getAnalysisUsage(AnalysisUsage &AU) const {
if (RequiresDomTree)
AU.addRequired<DominatorTree>();
AU.setPreservesCFG();
}
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