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llvm-6502/lib/Transforms/Scalar/SROA.cpp
Chandler Carruth 2cf40d1ae5 [SROA] Fix a nasty pile of bugs to do with big-endian, different alloca 
types and loads, loads or stores widened past the size of an alloca,
etc.

This started off with a bug report about big-endian behavior with
bitfields and loads and stores to a { i32, i24 } struct. An initial
attempt to fix this was sent for review in D10357, but that didn't
really get to the root of the problem.

The core issue was that canConvertValue and convertValue in SROA were
handling different bitwidth integers by doing a zext of the integer. It
wouldn't do a trunc though, only a zext! This would in turn lead SROA to
form an i24 load from an i24 alloca, zext it to i32, and then use it.
This would at least produce the wrong value for big-endian systems.

One of my many false starts here was to correct the computation for
big-endian systems by shifting. But this doesn't actually work because
the original code has a 64-bit store to the entire 8 bytes, and a 32-bit
load of the last 4 bytes, and because the alloc size is 8 bytes, we
can't lose that last (least significant if bigendian) byte! The real
problem here is that we're forming an i24 load in SROA which is actually
not sufficiently wide to load all of the necessary bits here. The source
has an i32 load, and SROA needs to form that as well.

The straightforward way to do this is to disable the zext logic in
canConvertValue and convertValue, forcing us to actually load all
32-bits. This seems like a really good change, but it in turn breaks
several other parts of SROA.

First in the chain of knock-on failures, we had places where we were
doing integer-widening promotion even though some of the integer loads
or stores extended *past the end* of the alloca's memory! There was even
a comment about preventing this, but it only prevented the case where
the type had a different bit size from its store size. So I added checks
to handle the cases where we actually have a widened load or store and
to avoid trying to special integer widening promotion in those cases.

Second, we actually rely on the ability to promote in the face of loads
past the end of an alloca! This is important so that we can (for
example) speculate loads around PHI nodes to do more promotion. The bits
loaded are garbage, but as long as they aren't used and the alignment is
suitable high (which it wasn't in the test case!) this is "fine". And we
can't stop promoting here, lots of things stop working well if we do. So
we need to add specific logic to handle the extension (and truncation)
case, but *only* where that extension or truncation are over bytes that
*are outside the alloca's allocated storage* and thus totally bogus to
load or store.

And of course, once we add back this correct handling of extension or
truncation, we need to correctly handle bigendian systems to avoid
re-introducing the exact bug that started us off on this chain of misery
in the first place, but this time even more subtle as it only happens
along speculated loads atop a PHI node.

I've ported an existing test for PHI speculation to the big-endian test
file and checked that we get that part correct, and I've added several
more interesting big-endian test cases that should help check that we're
getting this correct.

Fun times.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242869 91177308-0d34-0410-b5e6-96231b3b80d8
2015-07-22 03:32:42 +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.
///
//===----------------------------------------------------------------------===//
#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/AssumptionCache.h"
#include "llvm/Analysis/Loads.h"
#include "llvm/Analysis/PtrUseVisitor.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DebugInfo.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstVisitor.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Operator.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/TimeValue.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"
#if __cplusplus >= 201103L && !defined(NDEBUG)
// We only use this for a debug check in C++11
#include <random>
#endif
using namespace llvm;
#define DEBUG_TYPE "sroa"
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);
/// Hidden option to enable randomly shuffling the slices to help uncover
/// instability in their order.
static cl::opt<bool> SROARandomShuffleSlices("sroa-random-shuffle-slices",
cl::init(false), cl::Hidden);
/// Hidden option to experiment with completely strict handling of inbounds
/// GEPs.
static cl::opt<bool> SROAStrictInbounds("sroa-strict-inbounds", 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() == nullptr; }
void kill() { UseAndIsSplittable.setPointer(nullptr); }
/// \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;
typedef iterator_range<iterator> range;
iterator begin() { return Slices.begin(); }
iterator end() { return Slices.end(); }
typedef SmallVectorImpl<Slice>::const_iterator const_iterator;
typedef iterator_range<const_iterator> const_range;
const_iterator begin() const { return Slices.begin(); }
const_iterator end() const { return Slices.end(); }
/// @}
/// \brief Erase a range of slices.
void erase(iterator Start, iterator Stop) { Slices.erase(Start, Stop); }
/// \brief Insert new slices for this alloca.
///
/// This moves the slices into the alloca's slices collection, and re-sorts
/// everything so that the usual ordering properties of the alloca's slices
/// hold.
void insert(ArrayRef<Slice> NewSlices) {
int OldSize = Slices.size();
Slices.append(NewSlices.begin(), NewSlices.end());
auto SliceI = Slices.begin() + OldSize;
std::sort(SliceI, Slices.end());
std::inplace_merge(Slices.begin(), SliceI, Slices.end());
}
// Forward declare an iterator to befriend it.
class partition_iterator;
/// \brief A partition of the slices.
///
/// An ephemeral representation for a range of slices which can be viewed as
/// a partition of the alloca. This range represents a span of the alloca's
/// memory which cannot be split, and provides access to all of the slices
/// overlapping some part of the partition.
///
/// Objects of this type are produced by traversing the alloca's slices, but
/// are only ephemeral and not persistent.
class Partition {
private:
friend class AllocaSlices;
friend class AllocaSlices::partition_iterator;
/// \brief The begining and ending offsets of the alloca for this partition.
uint64_t BeginOffset, EndOffset;
/// \brief The start end end iterators of this partition.
iterator SI, SJ;
/// \brief A collection of split slice tails overlapping the partition.
SmallVector<Slice *, 4> SplitTails;
/// \brief Raw constructor builds an empty partition starting and ending at
/// the given iterator.
Partition(iterator SI) : SI(SI), SJ(SI) {}
public:
/// \brief The start offset of this partition.
///
/// All of the contained slices start at or after this offset.
uint64_t beginOffset() const { return BeginOffset; }
/// \brief The end offset of this partition.
///
/// All of the contained slices end at or before this offset.
uint64_t endOffset() const { return EndOffset; }
/// \brief The size of the partition.
///
/// Note that this can never be zero.
uint64_t size() const {
assert(BeginOffset < EndOffset && "Partitions must span some bytes!");
return EndOffset - BeginOffset;
}
/// \brief Test whether this partition contains no slices, and merely spans
/// a region occupied by split slices.
bool empty() const { return SI == SJ; }
/// \name Iterate slices that start within the partition.
/// These may be splittable or unsplittable. They have a begin offset >= the
/// partition begin offset.
/// @{
// FIXME: We should probably define a "concat_iterator" helper and use that
// to stitch together pointee_iterators over the split tails and the
// contiguous iterators of the partition. That would give a much nicer
// interface here. We could then additionally expose filtered iterators for
// split, unsplit, and unsplittable splices based on the usage patterns.
iterator begin() const { return SI; }
iterator end() const { return SJ; }
/// @}
/// \brief Get the sequence of split slice tails.
///
/// These tails are of slices which start before this partition but are
/// split and overlap into the partition. We accumulate these while forming
/// partitions.
ArrayRef<Slice *> splitSliceTails() const { return SplitTails; }
};
/// \brief An iterator over partitions of the alloca's slices.
///
/// This iterator implements the core algorithm for partitioning the alloca's
/// slices. It is a forward iterator as we don't support backtracking for
/// efficiency reasons, and re-use a single storage area to maintain the
/// current set of split slices.
///
/// It is templated on the slice iterator type to use so that it can operate
/// with either const or non-const slice iterators.
class partition_iterator
: public iterator_facade_base<partition_iterator,
std::forward_iterator_tag, Partition> {
friend class AllocaSlices;
/// \brief Most of the state for walking the partitions is held in a class
/// with a nice interface for examining them.
Partition P;
/// \brief We need to keep the end of the slices to know when to stop.
AllocaSlices::iterator SE;
/// \brief We also need to keep track of the maximum split end offset seen.
/// FIXME: Do we really?
uint64_t MaxSplitSliceEndOffset;
/// \brief Sets the partition to be empty at given iterator, and sets the
/// end iterator.
partition_iterator(AllocaSlices::iterator SI, AllocaSlices::iterator SE)
: P(SI), SE(SE), MaxSplitSliceEndOffset(0) {
// If not already at the end, advance our state to form the initial
// partition.
if (SI != SE)
advance();
}
/// \brief Advance the iterator to the next partition.
///
/// Requires that the iterator not be at the end of the slices.
void advance() {
assert((P.SI != SE || !P.SplitTails.empty()) &&
"Cannot advance past the end of the slices!");
// Clear out any split uses which have ended.
if (!P.SplitTails.empty()) {
if (P.EndOffset >= MaxSplitSliceEndOffset) {
// If we've finished all splits, this is easy.
P.SplitTails.clear();
MaxSplitSliceEndOffset = 0;
} else {
// Remove the uses which have ended in the prior partition. This
// cannot change the max split slice end because we just checked that
// the prior partition ended prior to that max.
P.SplitTails.erase(
std::remove_if(
P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) { return S->endOffset() <= P.EndOffset; }),
P.SplitTails.end());
assert(std::any_of(P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) {
return S->endOffset() == MaxSplitSliceEndOffset;
}) &&
"Could not find the current max split slice offset!");
assert(std::all_of(P.SplitTails.begin(), P.SplitTails.end(),
[&](Slice *S) {
return S->endOffset() <= MaxSplitSliceEndOffset;
}) &&
"Max split slice end offset is not actually the max!");
}
}
// If P.SI is already at the end, then we've cleared the split tail and
// now have an end iterator.
if (P.SI == SE) {
assert(P.SplitTails.empty() && "Failed to clear the split slices!");
return;
}
// If we had a non-empty partition previously, set up the state for
// subsequent partitions.
if (P.SI != P.SJ) {
// Accumulate all the splittable slices which started in the old
// partition into the split list.
for (Slice &S : P)
if (S.isSplittable() && S.endOffset() > P.EndOffset) {
P.SplitTails.push_back(&S);
MaxSplitSliceEndOffset =
std::max(S.endOffset(), MaxSplitSliceEndOffset);
}
// Start from the end of the previous partition.
P.SI = P.SJ;
// If P.SI is now at the end, we at most have a tail of split slices.
if (P.SI == SE) {
P.BeginOffset = P.EndOffset;
P.EndOffset = MaxSplitSliceEndOffset;
return;
}
// If the we have split slices and the next slice is after a gap and is
// not splittable immediately form an empty partition for the split
// slices up until the next slice begins.
if (!P.SplitTails.empty() && P.SI->beginOffset() != P.EndOffset &&
!P.SI->isSplittable()) {
P.BeginOffset = P.EndOffset;
P.EndOffset = P.SI->beginOffset();
return;
}
}
// OK, we need to consume new slices. Set the end offset based on the
// current slice, and step SJ past it. The beginning offset of the
// parttion is the beginning offset of the next slice unless we have
// pre-existing split slices that are continuing, in which case we begin
// at the prior end offset.
P.BeginOffset = P.SplitTails.empty() ? P.SI->beginOffset() : P.EndOffset;
P.EndOffset = P.SI->endOffset();
++P.SJ;
// There are two strategies to form a partition based on whether the
// partition starts with an unsplittable slice or a splittable slice.
if (!P.SI->isSplittable()) {
// When we're forming an unsplittable region, it must always start at
// the first slice and will extend through its end.
assert(P.BeginOffset == P.SI->beginOffset());
// Form a partition including all of the overlapping slices with this
// unsplittable slice.
while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
if (!P.SJ->isSplittable())
P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
++P.SJ;
}
// We have a partition across a set of overlapping unsplittable
// partitions.
return;
}
// If we're starting with a splittable slice, then we need to form
// a synthetic partition spanning it and any other overlapping splittable
// splices.
assert(P.SI->isSplittable() && "Forming a splittable partition!");
// Collect all of the overlapping splittable slices.
while (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset &&
P.SJ->isSplittable()) {
P.EndOffset = std::max(P.EndOffset, P.SJ->endOffset());
++P.SJ;
}
// Back upiP.EndOffset if we ended the span early when encountering an
// unsplittable slice. This synthesizes the early end offset of
// a partition spanning only splittable slices.
if (P.SJ != SE && P.SJ->beginOffset() < P.EndOffset) {
assert(!P.SJ->isSplittable());
P.EndOffset = P.SJ->beginOffset();
}
}
public:
bool operator==(const partition_iterator &RHS) const {
assert(SE == RHS.SE &&
"End iterators don't match between compared partition iterators!");
// The observed positions of partitions is marked by the P.SI iterator and
// the emptyness of the split slices. The latter is only relevant when
// P.SI == SE, as the end iterator will additionally have an empty split
// slices list, but the prior may have the same P.SI and a tail of split
// slices.
if (P.SI == RHS.P.SI &&
P.SplitTails.empty() == RHS.P.SplitTails.empty()) {
assert(P.SJ == RHS.P.SJ &&
"Same set of slices formed two different sized partitions!");
assert(P.SplitTails.size() == RHS.P.SplitTails.size() &&
"Same slice position with differently sized non-empty split "
"slice tails!");
return true;
}
return false;
}
partition_iterator &operator++() {
advance();
return *this;
}
Partition &operator*() { return P; }
};
/// \brief A forward range over the partitions of the alloca's slices.
///
/// This accesses an iterator range over the partitions of the alloca's
/// slices. It computes these partitions on the fly based on the overlapping
/// offsets of the slices and the ability to split them. It will visit "empty"
/// partitions to cover regions of the alloca only accessed via split
/// slices.
iterator_range<partition_iterator> partitions() {
return make_range(partition_iterator(begin(), end()),
partition_iterator(end(), end()));
}
/// \brief Access the dead users for this alloca.
ArrayRef<Instruction *> getDeadUsers() const { return DeadUsers; }
/// \brief Access the dead operands 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.
ArrayRef<Use *> getDeadOperands() const { return DeadOperands; }
#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 dump(const_iterator I) const;
void 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 nullptr;
}
/// \brief A helper that folds a PHI node or a select.
static Value *foldPHINodeOrSelectInst(Instruction &I) {
if (PHINode *PN = dyn_cast<PHINode>(&I)) {
// If PN merges together the same value, return that value.
return PN->hasConstantValue();
}
return foldSelectInst(cast<SelectInst>(I));
}
/// \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 &AS;
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 &AS)
: PtrUseVisitor<SliceBuilder>(DL),
AllocSize(DL.getTypeAllocSize(AI.getAllocatedType())), AS(AS) {}
private:
void markAsDead(Instruction &I) {
if (VisitedDeadInsts.insert(&I).second)
AS.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.uge(AllocSize)) {
DEBUG(dbgs() << "WARNING: Ignoring " << Size << " byte use @" << Offset
<< " which has zero size or starts outside of the "
<< AllocSize << " byte alloca:\n"
<< " alloca: " << AS.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: " << AS.AI << "\n"
<< " use: " << I << "\n");
EndOffset = AllocSize;
}
AS.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);
if (SROAStrictInbounds && GEPI.isInBounds()) {
// FIXME: This is a manually un-factored variant of the basic code inside
// of GEPs with checking of the inbounds invariant specified in the
// langref in a very strict sense. If we ever want to enable
// SROAStrictInbounds, this code should be factored cleanly into
// PtrUseVisitor, but it is easier to experiment with SROAStrictInbounds
// by writing out the code here where we have tho underlying allocation
// size readily available.
APInt GEPOffset = Offset;
const DataLayout &DL = GEPI.getModule()->getDataLayout();
for (gep_type_iterator GTI = gep_type_begin(GEPI),
GTE = gep_type_end(GEPI);
GTI != GTE; ++GTI) {
ConstantInt *OpC = dyn_cast<ConstantInt>(GTI.getOperand());
if (!OpC)
break;
// Handle a struct index, which adds its field offset to the pointer.
if (StructType *STy = dyn_cast<StructType>(*GTI)) {
unsigned ElementIdx = OpC->getZExtValue();
const StructLayout *SL = DL.getStructLayout(STy);
GEPOffset +=
APInt(Offset.getBitWidth(), SL->getElementOffset(ElementIdx));
} else {
// For array or vector indices, scale the index by the size of the
// type.
APInt Index = OpC->getValue().sextOrTrunc(Offset.getBitWidth());
GEPOffset += Index * APInt(Offset.getBitWidth(),
DL.getTypeAllocSize(GTI.getIndexedType()));
}
// If this index has computed an intermediate pointer which is not
// inbounds, then the result of the GEP is a poison value and we can
// delete it and all uses.
if (GEPOffset.ugt(AllocSize))
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 non-volatile loads and stores where the type is an
// integer type. These may be used to implement 'memcpy' or other "transfer
// of bits" patterns.
bool IsSplittable = Ty->isIntegerTy() && !IsVolatile;
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);
const DataLayout &DL = LI.getModule()->getDataLayout();
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);
const DataLayout &DL = SI.getModule()->getDataLayout();
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 (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: " << AS.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.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)
// Zero-length mem transfer intrinsics can be ignored entirely.
return markAsDead(II);
// Because we can visit these intrinsics twice, also check to see if the
// first time marked this instruction as dead. If so, skip it.
if (VisitedDeadInsts.count(&II))
return;
if (!IsOffsetKnown)
return PI.setAborted(&II);
// This side of the transfer is completely out-of-bounds, and so we can
// nuke the entire transfer. However, we also need to nuke the other side
// if already added to our partitions.
// FIXME: Yet another place we really should bypass this when
// instrumenting for ASan.
if (Offset.uge(AllocSize)) {
SmallDenseMap<Instruction *, unsigned>::iterator MTPI =
MemTransferSliceMap.find(&II);
if (MTPI != MemTransferSliceMap.end())
AS.Slices[MTPI->second].kill();
return markAsDead(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;
std::tie(MTPI, Inserted) =
MemTransferSliceMap.insert(std::make_pair(&II, AS.Slices.size()));
unsigned PrevIdx = MTPI->second;
if (!Inserted) {
Slice &PrevP = AS.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(AS.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));
const DataLayout &DL = Root->getModule()->getDataLayout();
// 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;
std::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 (User *U : I->users())
if (Visited.insert(cast<Instruction>(U)).second)
Uses.push_back(std::make_pair(I, cast<Instruction>(U)));
} while (!Uses.empty());
return nullptr;
}
void visitPHINodeOrSelectInst(Instruction &I) {
assert(isa<PHINode>(I) || isa<SelectInst>(I));
if (I.use_empty())
return markAsDead(I);
// TODO: We could use SimplifyInstruction here to fold PHINodes and
// SelectInsts. However, doing so requires to change the current
// dead-operand-tracking mechanism. For instance, suppose neither loading
// from %U nor %other traps. Then "load (select undef, %U, %other)" does not
// trap either. However, if we simply replace %U with undef using the
// current dead-operand-tracking mechanism, "load (select undef, undef,
// %other)" may trap because the select may return the first operand
// "undef".
if (Value *Result = foldPHINodeOrSelectInst(I)) {
if (Result == *U)
// If the result of the constant fold will be the pointer, recurse
// through the PHI/select as if we had RAUW'ed it.
enqueueUsers(I);
else
// Otherwise the operand to the PHI/select is dead, and we can replace
// it with undef.
AS.DeadOperands.push_back(U);
return;
}
if (!IsOffsetKnown)
return PI.setAborted(&I);
// See if we already have computed info on this node.
uint64_t &Size = PHIOrSelectSizes[&I];
if (!Size) {
// This is a new PHI/Select, check for an unsafe use of it.
if (Instruction *UnsafeI = hasUnsafePHIOrSelectUse(&I, Size))
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.uge(AllocSize)) {
AS.DeadOperands.push_back(U);
return;
}
insertUse(I, Offset, Size);
}
void visitPHINode(PHINode &PN) { visitPHINodeOrSelectInst(PN); }
void visitSelectInst(SelectInst &SI) { visitPHINodeOrSelectInst(SI); }
/// \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(nullptr) {
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(),
[](const Slice &S) {
return S.isDead();
}),
Slices.end());
#if __cplusplus >= 201103L && !defined(NDEBUG)
if (SROARandomShuffleSlices) {
std::mt19937 MT(static_cast<unsigned>(sys::TimeValue::now().msec()));
std::shuffle(Slices.begin(), Slices.end(), MT);
}
#endif
// 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);
OS << "\n";
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)" : "");
}
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);
}
LLVM_DUMP_METHOD void AllocaSlices::dump(const_iterator I) const {
print(dbgs(), I);
}
LLVM_DUMP_METHOD 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(ArrayRef<const 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 (auto *L = LocalAsMetadata::getIfExists(&AI)) {
if (auto *DINode = MetadataAsValue::getIfExists(AI.getContext(), L)) {
for (User *U : DINode->users())
if (DbgDeclareInst *DDI = dyn_cast<DbgDeclareInst>(U))
DDIs.push_back(DDI);
else if (DbgValueInst *DVI = dyn_cast<DbgValueInst>(U))
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();
}
bool
isInstInList(Instruction *I,
const SmallVectorImpl<Instruction *> &Insts) const override {
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).second);
return false;
}
void updateDebugInfo(Instruction *Inst) const override {
for (DbgDeclareInst *DDI : DDIs)
if (StoreInst *SI = dyn_cast<StoreInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, SI, DIB);
else if (LoadInst *LI = dyn_cast<LoadInst>(Inst))
ConvertDebugDeclareToDebugValue(DDI, LI, DIB);
for (DbgValueInst *DVI : DVIs) {
Value *Arg = nullptr;
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;
}
DIB.insertDbgValueIntrinsic(Arg, 0, DVI->getVariable(),
DVI->getExpression(), DVI->getDebugLoc(),
Inst);
}
}
};
} // 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;
DominatorTree *DT;
AssumptionCache *AC;
/// \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(nullptr),
DT(nullptr) {
initializeSROAPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override;
void getAnalysisUsage(AnalysisUsage &AU) const override;
const char *getPassName() const override { return "SROA"; }
static char ID;
private:
friend class PHIOrSelectSpeculator;
friend class AllocaSliceRewriter;
bool presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS);
AllocaInst *rewritePartition(AllocaInst &AI, AllocaSlices &AS,
AllocaSlices::Partition &P);
bool splitAlloca(AllocaInst &AI, AllocaSlices &AS);
bool runOnAlloca(AllocaInst &AI);
void clobberUse(Use &U);
void deleteDeadInstructions(SmallPtrSetImpl<AllocaInst *> &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(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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 = nullptr;
bool TyIsCommon = true;
IntegerType *ITy = nullptr;
// Note that we need to look at *every* alloca slice's Use to ensure we
// always get consistent results regardless of the order of slices.
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 = nullptr;
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
UserTy = LI->getType();
} else if (StoreInst *SI = dyn_cast<StoreInst>(U->getUser())) {
UserTy = SI->getValueOperand()->getType();
}
if (IntegerType *UserITy = dyn_cast_or_null<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. Also skip if the type is not a byte width
// multiple.
if (UserITy->getBitWidth() % 8 != 0 ||
UserITy->getBitWidth() / 8 > (EndOffset - B->beginOffset()))
continue;
// Track the largest bitwidth integer type used in this way in case there
// is no common type.
if (!ITy || ITy->getBitWidth() < UserITy->getBitWidth())
ITy = UserITy;
}
// To avoid depending on the order of slices, Ty and TyIsCommon must not
// depend on types skipped above.
if (!UserTy || (Ty && Ty != UserTy))
TyIsCommon = false; // Give up on anything but an iN type.
else
Ty = UserTy;
}
return TyIsCommon ? Ty : ITy;
}
/// 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) {
// 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 (User *U : PN.users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !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;
const DataLayout &DL = PN.getModule()->getDataLayout();
// 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 (isDereferenceablePointer(InVal, DL) ||
isSafeToLoadUnconditionally(InVal, TI, MaxAlign))
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 AA tags 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.user_back());
AAMDNodes AATags;
SomeLoad->getAAMetadata(AATags);
unsigned Align = SomeLoad->getAlignment();
// Rewrite all loads of the PN to use the new PHI.
while (!PN.use_empty()) {
LoadInst *LI = cast<LoadInst>(PN.user_back());
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 (AATags)
Load->setAAMetadata(AATags);
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) {
Value *TValue = SI.getTrueValue();
Value *FValue = SI.getFalseValue();
const DataLayout &DL = SI.getModule()->getDataLayout();
bool TDerefable = isDereferenceablePointer(TValue, DL);
bool FDerefable = isDereferenceablePointer(FValue, DL);
for (User *U : SI.users()) {
LoadInst *LI = dyn_cast<LoadInst>(U);
if (!LI || !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()))
return false;
if (!FDerefable &&
!isSafeToLoadUnconditionally(FValue, LI, LI->getAlignment()))
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.user_back());
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 AA info if present.
TL->setAlignment(LI->getAlignment());
FL->setAlignment(LI->getAlignment());
AAMDNodes Tags;
LI->getAAMetadata(Tags);
if (Tags) {
TL->setAAMetadata(Tags);
FL->setAAMetadata(Tags);
}
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, Twine NamePrefix) {
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(nullptr, BasePtr, Indices,
NamePrefix + "sroa_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,
Twine NamePrefix) {
if (Ty == TargetTy)
return buildGEP(IRB, BasePtr, Indices, NamePrefix);
// Pointer size to use for the indices.
unsigned PtrSize = DL.getPointerTypeSizeInBits(BasePtr->getType());
// 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 (ArrayType *ArrayTy = dyn_cast<ArrayType>(ElementTy)) {
ElementTy = ArrayTy->getElementType();
Indices.push_back(IRB.getIntN(PtrSize, 0));
} else if (VectorType *VectorTy = dyn_cast<VectorType>(ElementTy)) {
ElementTy = VectorTy->getElementType();
Indices.push_back(IRB.getInt32(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, NamePrefix);
}
/// \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,
Twine NamePrefix) {
if (Offset == 0)
return getNaturalGEPWithType(IRB, DL, Ptr, Ty, TargetTy, Indices,
NamePrefix);
// We can't recurse through pointer types.
if (Ty->isPointerTy())
return nullptr;
// 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 != 0) {
// GEPs over non-multiple of 8 size vector elements are invalid.
return nullptr;
}
APInt ElementSize(Offset.getBitWidth(), ElementSizeInBits / 8);
APInt NumSkippedElements = Offset.sdiv(ElementSize);
if (NumSkippedElements.ugt(VecTy->getNumElements()))
return nullptr;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, VecTy->getElementType(),
Offset, TargetTy, Indices, NamePrefix);
}
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 nullptr;
Offset -= NumSkippedElements * ElementSize;
Indices.push_back(IRB.getInt(NumSkippedElements));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices, NamePrefix);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return nullptr;
const StructLayout *SL = DL.getStructLayout(STy);
uint64_t StructOffset = Offset.getZExtValue();
if (StructOffset >= SL->getSizeInBytes())
return nullptr;
unsigned Index = SL->getElementContainingOffset(StructOffset);
Offset -= APInt(Offset.getBitWidth(), SL->getElementOffset(Index));
Type *ElementTy = STy->getElementType(Index);
if (Offset.uge(DL.getTypeAllocSize(ElementTy)))
return nullptr; // The offset points into alignment padding.
Indices.push_back(IRB.getInt32(Index));
return getNaturalGEPRecursively(IRB, DL, Ptr, ElementTy, Offset, TargetTy,
Indices, NamePrefix);
}
/// \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,
Twine NamePrefix) {
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(Ty->getAddressSpace()) && TargetTy->isIntegerTy(8))
return nullptr;
Type *ElementTy = Ty->getElementType();
if (!ElementTy->isSized())
return nullptr; // We can't GEP through an unsized element.
APInt ElementSize(Offset.getBitWidth(), DL.getTypeAllocSize(ElementTy));
if (ElementSize == 0)
return nullptr; // 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, NamePrefix);
}
/// \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, Twine NamePrefix) {
// 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 and the base it was computed from around here.
Value *OffsetPtr = nullptr;
Value *OffsetBasePtr;
// Remember any i8 pointer we come across to re-use if we need to do a raw
// byte offset.
Value *Int8Ptr = nullptr;
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).second)
break;
}
// See if we can perform a natural GEP here.
Indices.clear();
if (Value *P = getNaturalGEPWithOffset(IRB, DL, Ptr, Offset, TargetTy,
Indices, NamePrefix)) {
// If we have a new natural pointer at the offset, clear out any old
// offset pointer we computed. Unless it is the base pointer or
// a non-instruction, we built a GEP we don't need. Zap it.
if (OffsetPtr && OffsetPtr != OffsetBasePtr)
if (Instruction *I = dyn_cast<Instruction>(OffsetPtr)) {
assert(I->use_empty() && "Built a GEP with uses some how!");
I->eraseFromParent();
}
OffsetPtr = P;
OffsetBasePtr = Ptr;
// If we also found a pointer of the right type, we're done.
if (P->getType() == PointerTy)
return 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).second);
if (!OffsetPtr) {
if (!Int8Ptr) {
Int8Ptr = IRB.CreateBitCast(
Ptr, IRB.getInt8PtrTy(PointerTy->getPointerAddressSpace()),
NamePrefix + "sroa_raw_cast");
Int8PtrOffset = Offset;
}
OffsetPtr = Int8PtrOffset == 0
? Int8Ptr
: IRB.CreateInBoundsGEP(IRB.getInt8Ty(), Int8Ptr,
IRB.getInt(Int8PtrOffset),
NamePrefix + "sroa_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, NamePrefix + "sroa_cast");
return Ptr;
}
/// \brief Compute the adjusted alignment for a load or store from an offset.
static unsigned getAdjustedAlignment(Instruction *I, uint64_t Offset,
const DataLayout &DL) {
unsigned Alignment;
Type *Ty;
if (auto *LI = dyn_cast<LoadInst>(I)) {
Alignment = LI->getAlignment();
Ty = LI->getType();
} else if (auto *SI = dyn_cast<StoreInst>(I)) {
Alignment = SI->getAlignment();
Ty = SI->getValueOperand()->getType();
} else {
llvm_unreachable("Only loads and stores are allowed!");
}
if (!Alignment)
Alignment = DL.getABITypeAlignment(Ty);
return MinAlign(Alignment, Offset);
}
/// \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;
// For integer types, we can't handle any bit-width differences. This would
// break both vector conversions with extension and introduce endianness
// issues when in conjunction with loads and stores.
if (isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) {
assert(cast<IntegerType>(OldTy)->getBitWidth() !=
cast<IntegerType>(NewTy)->getBitWidth() &&
"We can't have the same bitwidth for different int types");
return false;
}
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;
assert(!(isa<IntegerType>(OldTy) && isa<IntegerType>(NewTy)) &&
"Integer types must be the exact same to convert.");
// 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(AllocaSlices::Partition &P,
const Slice &S, VectorType *Ty,
uint64_t ElementSize,
const DataLayout &DL) {
// First validate the slice offsets.
uint64_t BeginOffset =
std::max(S.beginOffset(), P.beginOffset()) - P.beginOffset();
uint64_t BeginIndex = BeginOffset / ElementSize;
if (BeginIndex * ElementSize != BeginOffset ||
BeginIndex >= Ty->getNumElements())
return false;
uint64_t EndOffset =
std::min(S.endOffset(), P.endOffset()) - P.beginOffset();
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 = S.getUse();
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(U->getUser())) {
if (MI->isVolatile())
return false;
if (!S.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 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 (P.beginOffset() > S.beginOffset() || P.endOffset() < S.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 (P.beginOffset() > S.beginOffset() || P.endOffset() < S.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 VectorType *isVectorPromotionViable(AllocaSlices::Partition &P,
const DataLayout &DL) {
// Collect the candidate types for vector-based promotion. Also track whether
// we have different element types.
SmallVector<VectorType *, 4> CandidateTys;
Type *CommonEltTy = nullptr;
bool HaveCommonEltTy = true;
auto CheckCandidateType = [&](Type *Ty) {
if (auto *VTy = dyn_cast<VectorType>(Ty)) {
CandidateTys.push_back(VTy);
if (!CommonEltTy)
CommonEltTy = VTy->getElementType();
else if (CommonEltTy != VTy->getElementType())
HaveCommonEltTy = false;
}
};
// Consider any loads or stores that are the exact size of the slice.
for (const Slice &S : P)
if (S.beginOffset() == P.beginOffset() &&
S.endOffset() == P.endOffset()) {
if (auto *LI = dyn_cast<LoadInst>(S.getUse()->getUser()))
CheckCandidateType(LI->getType());
else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser()))
CheckCandidateType(SI->getValueOperand()->getType());
}
// If we didn't find a vector type, nothing to do here.
if (CandidateTys.empty())
return nullptr;
// Remove non-integer vector types if we had multiple common element types.
// FIXME: It'd be nice to replace them with integer vector types, but we can't
// do that until all the backends are known to produce good code for all
// integer vector types.
if (!HaveCommonEltTy) {
CandidateTys.erase(std::remove_if(CandidateTys.begin(), CandidateTys.end(),
[](VectorType *VTy) {
return !VTy->getElementType()->isIntegerTy();
}),
CandidateTys.end());
// If there were no integer vector types, give up.
if (CandidateTys.empty())
return nullptr;
// Rank the remaining candidate vector types. This is easy because we know
// they're all integer vectors. We sort by ascending number of elements.
auto RankVectorTypes = [&DL](VectorType *RHSTy, VectorType *LHSTy) {
assert(DL.getTypeSizeInBits(RHSTy) == DL.getTypeSizeInBits(LHSTy) &&
"Cannot have vector types of different sizes!");
assert(RHSTy->getElementType()->isIntegerTy() &&
"All non-integer types eliminated!");
assert(LHSTy->getElementType()->isIntegerTy() &&
"All non-integer types eliminated!");
return RHSTy->getNumElements() < LHSTy->getNumElements();
};
std::sort(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes);
CandidateTys.erase(
std::unique(CandidateTys.begin(), CandidateTys.end(), RankVectorTypes),
CandidateTys.end());
} else {
// The only way to have the same element type in every vector type is to
// have the same vector type. Check that and remove all but one.
#ifndef NDEBUG
for (VectorType *VTy : CandidateTys) {
assert(VTy->getElementType() == CommonEltTy &&
"Unaccounted for element type!");
assert(VTy == CandidateTys[0] &&
"Different vector types with the same element type!");
}
#endif
CandidateTys.resize(1);
}
// Try each vector type, and return the one which works.
auto CheckVectorTypeForPromotion = [&](VectorType *VTy) {
uint64_t ElementSize = DL.getTypeSizeInBits(VTy->getElementType());
// 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(VTy) % 8) == 0 &&
"vector size not a multiple of element size?");
ElementSize /= 8;
for (const Slice &S : P)
if (!isVectorPromotionViableForSlice(P, S, VTy, ElementSize, DL))
return false;
for (const Slice *S : P.splitSliceTails())
if (!isVectorPromotionViableForSlice(P, *S, VTy, ElementSize, DL))
return false;
return true;
};
for (VectorType *VTy : CandidateTys)
if (CheckVectorTypeForPromotion(VTy))
return VTy;
return nullptr;
}
/// \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 Slice &S,
uint64_t AllocBeginOffset,
Type *AllocaTy,
const DataLayout &DL,
bool &WholeAllocaOp) {
uint64_t Size = DL.getTypeStoreSize(AllocaTy);
uint64_t RelBegin = S.beginOffset() - AllocBeginOffset;
uint64_t RelEnd = S.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 = S.getUse();
if (LoadInst *LI = dyn_cast<LoadInst>(U->getUser())) {
if (LI->isVolatile())
return false;
// We can't handle loads that extend past the allocated memory.
if (DL.getTypeStoreSize(LI->getType()) > Size)
return false;
// Note that we don't count vector loads or stores as whole-alloca
// operations which enable integer widening because we would prefer to use
// vector widening instead.
if (!isa<VectorType>(LI->getType()) && 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;
// We can't handle stores that extend past the allocated memory.
if (DL.getTypeStoreSize(ValueTy) > Size)
return false;
// Note that we don't count vector loads or stores as whole-alloca
// operations which enable integer widening because we would prefer to use
// vector widening instead.
if (!isa<VectorType>(ValueTy) && 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 (!S.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(AllocaSlices::Partition &P, Type *AllocaTy,
const DataLayout &DL) {
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;
// 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.
// FIXME: We shouldn't consider split slices that happen to start in the
// partition here...
bool WholeAllocaOp =
P.begin() != P.end() ? false : DL.isLegalInteger(SizeInBits);
for (const Slice &S : P)
if (!isIntegerWideningViableForSlice(S, P.beginOffset(), AllocaTy, DL,
WholeAllocaOp))
return false;
for (const Slice *S : P.splitSliceTails())
if (!isIntegerWideningViableForSlice(*S, P.beginOffset(), AllocaTy, DL,
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 &AS;
SROA &Pass;
AllocaInst &OldAI, &NewAI;
const uint64_t NewAllocaBeginOffset, NewAllocaEndOffset;
Type *NewAllocaTy;
// 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;
// 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;
// The original offset of the slice currently being rewritten relative to
// the original alloca.
uint64_t BeginOffset, EndOffset;
// The new offsets of the slice currently being rewritten relative to the
// original alloca.
uint64_t NewBeginOffset, NewEndOffset;
uint64_t SliceSize;
bool IsSplittable;
bool IsSplit;
Use *OldUse;
Instruction *OldPtr;
// Track post-rewrite users which are PHI nodes and Selects.
SmallPtrSetImpl<PHINode *> &PHIUsers;
SmallPtrSetImpl<SelectInst *> &SelectUsers;
// 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 &AS, SROA &Pass,
AllocaInst &OldAI, AllocaInst &NewAI,
uint64_t NewAllocaBeginOffset,
uint64_t NewAllocaEndOffset, bool IsIntegerPromotable,
VectorType *PromotableVecTy,
SmallPtrSetImpl<PHINode *> &PHIUsers,
SmallPtrSetImpl<SelectInst *> &SelectUsers)
: DL(DL), AS(AS), Pass(Pass), OldAI(OldAI), NewAI(NewAI),
NewAllocaBeginOffset(NewAllocaBeginOffset),
NewAllocaEndOffset(NewAllocaEndOffset),
NewAllocaTy(NewAI.getAllocatedType()),
IntTy(IsIntegerPromotable
? Type::getIntNTy(
NewAI.getContext(),
DL.getTypeSizeInBits(NewAI.getAllocatedType()))
: nullptr),
VecTy(PromotableVecTy),
ElementTy(VecTy ? VecTy->getElementType() : nullptr),
ElementSize(VecTy ? DL.getTypeSizeInBits(ElementTy) / 8 : 0),
BeginOffset(), EndOffset(), IsSplittable(), IsSplit(), OldUse(),
OldPtr(), PHIUsers(PHIUsers), SelectUsers(SelectUsers),
IRB(NewAI.getContext(), ConstantFolder()) {
if (VecTy) {
assert((DL.getTypeSizeInBits(ElementTy) % 8) == 0 &&
"Only multiple-of-8 sized vector elements are viable");
++NumVectorized;
}
assert((!IntTy && !VecTy) || (IntTy && !VecTy) || (!IntTy && VecTy));
}
bool visit(AllocaSlices::const_iterator I) {
bool CanSROA = true;
BeginOffset = I->beginOffset();
EndOffset = I->endOffset();
IsSplittable = I->isSplittable();
IsSplit =
BeginOffset < NewAllocaBeginOffset || EndOffset > NewAllocaEndOffset;
DEBUG(dbgs() << " rewriting " << (IsSplit ? "split " : ""));
DEBUG(AS.printSlice(dbgs(), I, ""));
DEBUG(dbgs() << "\n");
// Compute the intersecting offset range.
assert(BeginOffset < NewAllocaEndOffset);
assert(EndOffset > NewAllocaBeginOffset);
NewBeginOffset = std::max(BeginOffset, NewAllocaBeginOffset);
NewEndOffset = std::min(EndOffset, NewAllocaEndOffset);
SliceSize = NewEndOffset - NewBeginOffset;
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;
}
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 *getNewAllocaSlicePtr(IRBuilderTy &IRB, Type *PointerTy) {
// Note that the offset computation can use BeginOffset or NewBeginOffset
// interchangeably for unsplit slices.
assert(IsSplit || BeginOffset == NewBeginOffset);
uint64_t Offset = NewBeginOffset - NewAllocaBeginOffset;
#ifndef NDEBUG
StringRef OldName = OldPtr->getName();
// Skip through the last '.sroa.' component of the name.
size_t LastSROAPrefix = OldName.rfind(".sroa.");
if (LastSROAPrefix != StringRef::npos) {
OldName = OldName.substr(LastSROAPrefix + strlen(".sroa."));
// Look for an SROA slice index.
size_t IndexEnd = OldName.find_first_not_of("0123456789");
if (IndexEnd != StringRef::npos && OldName[IndexEnd] == '.') {
// Strip the index and look for the offset.
OldName = OldName.substr(IndexEnd + 1);
size_t OffsetEnd = OldName.find_first_not_of("0123456789");
if (OffsetEnd != StringRef::npos && OldName[OffsetEnd] == '.')
// Strip the offset.
OldName = OldName.substr(OffsetEnd + 1);
}
}
// Strip any SROA suffixes as well.
OldName = OldName.substr(0, OldName.find(".sroa_"));
#endif
return getAdjustedPtr(IRB, DL, &NewAI,
APInt(DL.getPointerSizeInBits(), Offset), PointerTy,
#ifndef NDEBUG
Twine(OldName) + "."
#else
Twine()
#endif
);
}
/// \brief Compute suitable alignment to access this slice of the *new*
/// alloca.
///
/// You can optionally pass a type to this routine and if that type's ABI
/// alignment is itself suitable, this will return zero.
unsigned getSliceAlign(Type *Ty = nullptr) {
unsigned NewAIAlign = NewAI.getAlignment();
if (!NewAIAlign)
NewAIAlign = DL.getABITypeAlignment(NewAI.getAllocatedType());
unsigned Align =
MinAlign(NewAIAlign, NewBeginOffset - NewAllocaBeginOffset);
return (Ty && 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() {
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) {
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);
Type *TargetTy = IsSplit ? Type::getIntNTy(LI.getContext(), SliceSize * 8)
: LI.getType();
const bool IsLoadPastEnd = DL.getTypeStoreSize(TargetTy) > SliceSize;
bool IsPtrAdjusted = false;
Value *V;
if (VecTy) {
V = rewriteVectorizedLoadInst();
} else if (IntTy && LI.getType()->isIntegerTy()) {
V = rewriteIntegerLoad(LI);
} else if (NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset &&
(canConvertValue(DL, NewAllocaTy, TargetTy) ||
(IsLoadPastEnd && NewAllocaTy->isIntegerTy() &&
TargetTy->isIntegerTy()))) {
LoadInst *NewLI = IRB.CreateAlignedLoad(&NewAI, NewAI.getAlignment(),
LI.isVolatile(), LI.getName());
if (LI.isVolatile())
NewLI->setAtomic(LI.getOrdering(), LI.getSynchScope());
V = NewLI;
// If this is an integer load past the end of the slice (which means the
// bytes outside the slice are undef or this load is dead) just forcibly
// fix the integer size with correct handling of endianness.
if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
if (auto *TITy = dyn_cast<IntegerType>(TargetTy))
if (AITy->getBitWidth() < TITy->getBitWidth()) {
V = IRB.CreateZExt(V, TITy, "load.ext");
if (DL.isBigEndian())
V = IRB.CreateShl(V, TITy->getBitWidth() - AITy->getBitWidth(),
"endian_shift");
}
} else {
Type *LTy = TargetTy->getPointerTo();
LoadInst *NewLI = IRB.CreateAlignedLoad(getNewAllocaSlicePtr(IRB, LTy),
getSliceAlign(TargetTy),
LI.isVolatile(), LI.getName());
if (LI.isVolatile())
NewLI->setAtomic(LI.getOrdering(), LI.getSynchScope());
V = NewLI;
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(SliceSize < 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(std::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 - BeginOffset,
"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) {
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) {
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);
if (SliceSize < 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(), SliceSize * 8);
V = extractInteger(DL, IRB, V, NarrowTy, NewBeginOffset - BeginOffset,
"extract");
}
if (VecTy)
return rewriteVectorizedStoreInst(V, SI, OldOp);
if (IntTy && V->getType()->isIntegerTy())
return rewriteIntegerStore(V, SI);
const bool IsStorePastEnd = DL.getTypeStoreSize(V->getType()) > SliceSize;
StoreInst *NewSI;
if (NewBeginOffset == NewAllocaBeginOffset &&
NewEndOffset == NewAllocaEndOffset &&
(canConvertValue(DL, V->getType(), NewAllocaTy) ||
(IsStorePastEnd && NewAllocaTy->isIntegerTy() &&
V->getType()->isIntegerTy()))) {
// If this is an integer store past the end of slice (and thus the bytes
// past that point are irrelevant or this is unreachable), truncate the
// value prior to storing.
if (auto *VITy = dyn_cast<IntegerType>(V->getType()))
if (auto *AITy = dyn_cast<IntegerType>(NewAllocaTy))
if (VITy->getBitWidth() > AITy->getBitWidth()) {
if (DL.isBigEndian())
V = IRB.CreateLShr(V, VITy->getBitWidth() - AITy->getBitWidth(),
"endian_shift");
V = IRB.CreateTrunc(V, AITy, "load.trunc");
}
V = convertValue(DL, IRB, V, NewAllocaTy);
NewSI = IRB.CreateAlignedStore(V, &NewAI, NewAI.getAlignment(),
SI.isVolatile());
} else {
Value *NewPtr = getNewAllocaSlicePtr(IRB, V->getType()->getPointerTo());
NewSI = IRB.CreateAlignedStore(V, NewPtr, getSliceAlign(V->getType()),
SI.isVolatile());
}
if (SI.isVolatile())
NewSI->setAtomic(SI.getOrdering(), SI.getSynchScope());
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(NewBeginOffset == BeginOffset);
II.setDest(getNewAllocaSlicePtr(IRB, OldPtr->getType()));
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(ConstantInt::get(CstTy, getSliceAlign()));
deleteIfTriviallyDead(OldPtr);
return false;
}
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
Type *AllocaTy = NewAI.getAllocatedType();
Type *ScalarTy = AllocaTy->getScalarType();
// 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 ||
SliceSize != DL.getTypeStoreSize(AllocaTy) ||
!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(
getNewAllocaSlicePtr(IRB, OldPtr->getType()), II.getValue(), Size,
getSliceAlign(), 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");
bool IsDest = &II.getRawDestUse() == OldUse;
assert((IsDest && II.getRawDest() == OldPtr) ||
(!IsDest && II.getRawSource() == OldPtr));
unsigned SliceAlign = getSliceAlign();
// 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 *AdjustedPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
if (IsDest)
II.setDest(AdjustedPtr);
else
II.setSource(AdjustedPtr);
if (II.getAlignment() > SliceAlign) {
Type *CstTy = II.getAlignmentCst()->getType();
II.setAlignment(
ConstantInt::get(CstTy, MinAlign(II.getAlignment(), SliceAlign)));
}
DEBUG(dbgs() << " to: " << II << "\n");
deleteIfTriviallyDead(OldPtr);
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 ||
SliceSize != DL.getTypeStoreSize(NewAI.getAllocatedType()) ||
!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())) {
assert(AI != &OldAI && AI != &NewAI &&
"Splittable transfers cannot reach the same alloca on both ends.");
Pass.Worklist.insert(AI);
}
Type *OtherPtrTy = OtherPtr->getType();
unsigned OtherAS = OtherPtrTy->getPointerAddressSpace();
// Compute the relative offset for the other pointer within the transfer.
unsigned IntPtrWidth = DL.getPointerSizeInBits(OtherAS);
APInt OtherOffset(IntPtrWidth, NewBeginOffset - BeginOffset);
unsigned OtherAlign = MinAlign(II.getAlignment() ? II.getAlignment() : 1,
OtherOffset.zextOrTrunc(64).getZExtValue());
if (EmitMemCpy) {
// Compute the other pointer, folding as much as possible to produce
// a single, simple GEP in most cases.
OtherPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
OtherPtr->getName() + ".");
Value *OurPtr = getNewAllocaSlicePtr(IRB, OldPtr->getType());
Type *SizeTy = II.getLength()->getType();
Constant *Size = ConstantInt::get(SizeTy, NewEndOffset - NewBeginOffset);
CallInst *New = IRB.CreateMemCpy(
IsDest ? OurPtr : OtherPtr, IsDest ? OtherPtr : OurPtr, Size,
MinAlign(SliceAlign, OtherAlign), II.isVolatile());
(void)New;
DEBUG(dbgs() << " to: " << *New << "\n");
return false;
}
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) : nullptr;
// Reset the other pointer type to match the register type we're going to
// use, but using the address space of the original other pointer.
if (VecTy && !IsWholeAlloca) {
if (NumElements == 1)
OtherPtrTy = VecTy->getElementType();
else
OtherPtrTy = VectorType::get(VecTy->getElementType(), NumElements);
OtherPtrTy = OtherPtrTy->getPointerTo(OtherAS);
} else if (IntTy && !IsWholeAlloca) {
OtherPtrTy = SubIntTy->getPointerTo(OtherAS);
} else {
OtherPtrTy = NewAllocaTy->getPointerTo(OtherAS);
}
Value *SrcPtr = getAdjustedPtr(IRB, DL, OtherPtr, OtherOffset, OtherPtrTy,
OtherPtr->getName() + ".");
unsigned SrcAlign = OtherAlign;
Value *DstPtr = &NewAI;
unsigned DstAlign = SliceAlign;
if (!IsDest) {
std::swap(SrcPtr, DstPtr);
std::swap(SrcAlign, DstAlign);
}
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, SrcAlign, 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, DstAlign, 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);
// Record this instruction for deletion.
Pass.DeadInsts.insert(&II);
ConstantInt *Size =
ConstantInt::get(cast<IntegerType>(II.getArgOperand(0)->getType()),
NewEndOffset - NewBeginOffset);
Value *Ptr = getNewAllocaSlicePtr(IRB, OldPtr->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(IRB);
if (isa<PHINode>(OldPtr))
PtrBuilder.SetInsertPoint(OldPtr->getParent()->getFirstInsertionPt());
else
PtrBuilder.SetInsertPoint(OldPtr);
PtrBuilder.SetCurrentDebugLocation(OldPtr->getDebugLoc());
Value *NewPtr = getNewAllocaSlicePtr(PtrBuilder, 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);
// PHIs can't be promoted on their own, but often can be speculated. We
// check the speculation outside of the rewriter so that we see the
// fully-rewritten alloca.
PHIUsers.insert(&PN);
return true;
}
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 = getNewAllocaSlicePtr(IRB, 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);
// Selects can't be promoted on their own, but often can be speculated. We
// check the speculation outside of the rewriter so that we see the
// fully-rewritten alloca.
SelectUsers.insert(&SI);
return true;
}
};
}
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 (Use &U : I.uses())
if (Visited.insert(U.getUser()).second)
Queue.push_back(&U);
}
// 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(nullptr, 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(nullptr, 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 nullptr;
if (SequentialType *SeqTy = dyn_cast<SequentialType>(Ty)) {
// We can't partition pointers...
if (SeqTy->isPointerTy())
return nullptr;
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 nullptr;
} else if (VectorType *VecTy = dyn_cast<VectorType>(SeqTy)) {
if (NumSkippedElements >= VecTy->getNumElements())
return nullptr;
}
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 nullptr;
// 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 nullptr;
return ArrayType::get(ElementTy, NumElements);
}
StructType *STy = dyn_cast<StructType>(Ty);
if (!STy)
return nullptr;
const StructLayout *SL = DL.getStructLayout(STy);
if (Offset >= SL->getSizeInBytes())
return nullptr;
uint64_t EndOffset = Offset + Size;
if (EndOffset > SL->getSizeInBytes())
return nullptr;
unsigned Index = SL->getElementContainingOffset(Offset);
Offset -= SL->getElementOffset(Index);
Type *ElementTy = STy->getElementType(Index);
uint64_t ElementSize = DL.getTypeAllocSize(ElementTy);
if (Offset >= ElementSize)
return nullptr; // 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 nullptr;
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 nullptr; // 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 nullptr;
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 nullptr; // The sub-struct doesn't have quite the size needed.
return SubTy;
}
/// \brief Pre-split loads and stores to simplify rewriting.
///
/// We want to break up the splittable load+store pairs as much as
/// possible. This is important to do as a preprocessing step, as once we
/// start rewriting the accesses to partitions of the alloca we lose the
/// necessary information to correctly split apart paired loads and stores
/// which both point into this alloca. The case to consider is something like
/// the following:
///
/// %a = alloca [12 x i8]
/// %gep1 = getelementptr [12 x i8]* %a, i32 0, i32 0
/// %gep2 = getelementptr [12 x i8]* %a, i32 0, i32 4
/// %gep3 = getelementptr [12 x i8]* %a, i32 0, i32 8
/// %iptr1 = bitcast i8* %gep1 to i64*
/// %iptr2 = bitcast i8* %gep2 to i64*
/// %fptr1 = bitcast i8* %gep1 to float*
/// %fptr2 = bitcast i8* %gep2 to float*
/// %fptr3 = bitcast i8* %gep3 to float*
/// store float 0.0, float* %fptr1
/// store float 1.0, float* %fptr2
/// %v = load i64* %iptr1
/// store i64 %v, i64* %iptr2
/// %f1 = load float* %fptr2
/// %f2 = load float* %fptr3
///
/// Here we want to form 3 partitions of the alloca, each 4 bytes large, and
/// promote everything so we recover the 2 SSA values that should have been
/// there all along.
///
/// \returns true if any changes are made.
bool SROA::presplitLoadsAndStores(AllocaInst &AI, AllocaSlices &AS) {
DEBUG(dbgs() << "Pre-splitting loads and stores\n");
// Track the loads and stores which are candidates for pre-splitting here, in
// the order they first appear during the partition scan. These give stable
// iteration order and a basis for tracking which loads and stores we
// actually split.
SmallVector<LoadInst *, 4> Loads;
SmallVector<StoreInst *, 4> Stores;
// We need to accumulate the splits required of each load or store where we
// can find them via a direct lookup. This is important to cross-check loads
// and stores against each other. We also track the slice so that we can kill
// all the slices that end up split.
struct SplitOffsets {
Slice *S;
std::vector<uint64_t> Splits;
};
SmallDenseMap<Instruction *, SplitOffsets, 8> SplitOffsetsMap;
// Track loads out of this alloca which cannot, for any reason, be pre-split.
// This is important as we also cannot pre-split stores of those loads!
// FIXME: This is all pretty gross. It means that we can be more aggressive
// in pre-splitting when the load feeding the store happens to come from
// a separate alloca. Put another way, the effectiveness of SROA would be
// decreased by a frontend which just concatenated all of its local allocas
// into one big flat alloca. But defeating such patterns is exactly the job
// SROA is tasked with! Sadly, to not have this discrepancy we would have
// change store pre-splitting to actually force pre-splitting of the load
// that feeds it *and all stores*. That makes pre-splitting much harder, but
// maybe it would make it more principled?
SmallPtrSet<LoadInst *, 8> UnsplittableLoads;
DEBUG(dbgs() << " Searching for candidate loads and stores\n");
for (auto &P : AS.partitions()) {
for (Slice &S : P) {
Instruction *I = cast<Instruction>(S.getUse()->getUser());
if (!S.isSplittable() ||S.endOffset() <= P.endOffset()) {
// If this was a load we have to track that it can't participate in any
// pre-splitting!
if (auto *LI = dyn_cast<LoadInst>(I))
UnsplittableLoads.insert(LI);
continue;
}
assert(P.endOffset() > S.beginOffset() &&
"Empty or backwards partition!");
// Determine if this is a pre-splittable slice.
if (auto *LI = dyn_cast<LoadInst>(I)) {
assert(!LI->isVolatile() && "Cannot split volatile loads!");
// The load must be used exclusively to store into other pointers for
// us to be able to arbitrarily pre-split it. The stores must also be
// simple to avoid changing semantics.
auto IsLoadSimplyStored = [](LoadInst *LI) {
for (User *LU : LI->users()) {
auto *SI = dyn_cast<StoreInst>(LU);
if (!SI || !SI->isSimple())
return false;
}
return true;
};
if (!IsLoadSimplyStored(LI)) {
UnsplittableLoads.insert(LI);
continue;
}
Loads.push_back(LI);
} else if (auto *SI = dyn_cast<StoreInst>(S.getUse()->getUser())) {
if (!SI ||
S.getUse() != &SI->getOperandUse(SI->getPointerOperandIndex()))
continue;
auto *StoredLoad = dyn_cast<LoadInst>(SI->getValueOperand());
if (!StoredLoad || !StoredLoad->isSimple())
continue;
assert(!SI->isVolatile() && "Cannot split volatile stores!");
Stores.push_back(SI);
} else {
// Other uses cannot be pre-split.
continue;
}
// Record the initial split.
DEBUG(dbgs() << " Candidate: " << *I << "\n");
auto &Offsets = SplitOffsetsMap[I];
assert(Offsets.Splits.empty() &&
"Should not have splits the first time we see an instruction!");
Offsets.S = &S;
Offsets.Splits.push_back(P.endOffset() - S.beginOffset());
}
// Now scan the already split slices, and add a split for any of them which
// we're going to pre-split.
for (Slice *S : P.splitSliceTails()) {
auto SplitOffsetsMapI =
SplitOffsetsMap.find(cast<Instruction>(S->getUse()->getUser()));
if (SplitOffsetsMapI == SplitOffsetsMap.end())
continue;
auto &Offsets = SplitOffsetsMapI->second;
assert(Offsets.S == S && "Found a mismatched slice!");
assert(!Offsets.Splits.empty() &&
"Cannot have an empty set of splits on the second partition!");
assert(Offsets.Splits.back() ==
P.beginOffset() - Offsets.S->beginOffset() &&
"Previous split does not end where this one begins!");
// Record each split. The last partition's end isn't needed as the size
// of the slice dictates that.
if (S->endOffset() > P.endOffset())
Offsets.Splits.push_back(P.endOffset() - Offsets.S->beginOffset());
}
}
// We may have split loads where some of their stores are split stores. For
// such loads and stores, we can only pre-split them if their splits exactly
// match relative to their starting offset. We have to verify this prior to
// any rewriting.
Stores.erase(
std::remove_if(Stores.begin(), Stores.end(),
[&UnsplittableLoads, &SplitOffsetsMap](StoreInst *SI) {
// Lookup the load we are storing in our map of split
// offsets.
auto *LI = cast<LoadInst>(SI->getValueOperand());
// If it was completely unsplittable, then we're done,
// and this store can't be pre-split.
if (UnsplittableLoads.count(LI))
return true;
auto LoadOffsetsI = SplitOffsetsMap.find(LI);
if (LoadOffsetsI == SplitOffsetsMap.end())
return false; // Unrelated loads are definitely safe.
auto &LoadOffsets = LoadOffsetsI->second;
// Now lookup the store's offsets.
auto &StoreOffsets = SplitOffsetsMap[SI];
// If the relative offsets of each split in the load and
// store match exactly, then we can split them and we
// don't need to remove them here.
if (LoadOffsets.Splits == StoreOffsets.Splits)
return false;
DEBUG(dbgs()
<< " Mismatched splits for load and store:\n"
<< " " << *LI << "\n"
<< " " << *SI << "\n");
// We've found a store and load that we need to split
// with mismatched relative splits. Just give up on them
// and remove both instructions from our list of
// candidates.
UnsplittableLoads.insert(LI);
return true;
}),
Stores.end());
// Now we have to go *back* through all te stores, because a later store may
// have caused an earlier store's load to become unsplittable and if it is
// unsplittable for the later store, then we can't rely on it being split in
// the earlier store either.
Stores.erase(std::remove_if(Stores.begin(), Stores.end(),
[&UnsplittableLoads](StoreInst *SI) {
auto *LI =
cast<LoadInst>(SI->getValueOperand());
return UnsplittableLoads.count(LI);
}),
Stores.end());
// Once we've established all the loads that can't be split for some reason,
// filter any that made it into our list out.
Loads.erase(std::remove_if(Loads.begin(), Loads.end(),
[&UnsplittableLoads](LoadInst *LI) {
return UnsplittableLoads.count(LI);
}),
Loads.end());
// If no loads or stores are left, there is no pre-splitting to be done for
// this alloca.
if (Loads.empty() && Stores.empty())
return false;
// From here on, we can't fail and will be building new accesses, so rig up
// an IR builder.
IRBuilderTy IRB(&AI);
// Collect the new slices which we will merge into the alloca slices.
SmallVector<Slice, 4> NewSlices;
// Track any allocas we end up splitting loads and stores for so we iterate
// on them.
SmallPtrSet<AllocaInst *, 4> ResplitPromotableAllocas;
// At this point, we have collected all of the loads and stores we can
// pre-split, and the specific splits needed for them. We actually do the
// splitting in a specific order in order to handle when one of the loads in
// the value operand to one of the stores.
//
// First, we rewrite all of the split loads, and just accumulate each split
// load in a parallel structure. We also build the slices for them and append
// them to the alloca slices.
SmallDenseMap<LoadInst *, std::vector<LoadInst *>, 1> SplitLoadsMap;
std::vector<LoadInst *> SplitLoads;
const DataLayout &DL = AI.getModule()->getDataLayout();
for (LoadInst *LI : Loads) {
SplitLoads.clear();
IntegerType *Ty = cast<IntegerType>(LI->getType());
uint64_t LoadSize = Ty->getBitWidth() / 8;
assert(LoadSize > 0 && "Cannot have a zero-sized integer load!");
auto &Offsets = SplitOffsetsMap[LI];
assert(LoadSize == Offsets.S->endOffset() - Offsets.S->beginOffset() &&
"Slice size should always match load size exactly!");
uint64_t BaseOffset = Offsets.S->beginOffset();
assert(BaseOffset + LoadSize > BaseOffset &&
"Cannot represent alloca access size using 64-bit integers!");
Instruction *BasePtr = cast<Instruction>(LI->getPointerOperand());
IRB.SetInsertPoint(BasicBlock::iterator(LI));
DEBUG(dbgs() << " Splitting load: " << *LI << "\n");
uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
int Idx = 0, Size = Offsets.Splits.size();
for (;;) {
auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8);
auto *PartPtrTy = PartTy->getPointerTo(LI->getPointerAddressSpace());
LoadInst *PLoad = IRB.CreateAlignedLoad(
getAdjustedPtr(IRB, DL, BasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, BasePtr->getName() + "."),
getAdjustedAlignment(LI, PartOffset, DL), /*IsVolatile*/ false,
LI->getName());
// Append this load onto the list of split loads so we can find it later
// to rewrite the stores.
SplitLoads.push_back(PLoad);
// Now build a new slice for the alloca.
NewSlices.push_back(
Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
&PLoad->getOperandUse(PLoad->getPointerOperandIndex()),
/*IsSplittable*/ false));
DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset()
<< ", " << NewSlices.back().endOffset() << "): " << *PLoad
<< "\n");
// See if we've handled all the splits.
if (Idx >= Size)
break;
// Setup the next partition.
PartOffset = Offsets.Splits[Idx];
++Idx;
PartSize = (Idx < Size ? Offsets.Splits[Idx] : LoadSize) - PartOffset;
}
// Now that we have the split loads, do the slow walk over all uses of the
// load and rewrite them as split stores, or save the split loads to use
// below if the store is going to be split there anyways.
bool DeferredStores = false;
for (User *LU : LI->users()) {
StoreInst *SI = cast<StoreInst>(LU);
if (!Stores.empty() && SplitOffsetsMap.count(SI)) {
DeferredStores = true;
DEBUG(dbgs() << " Deferred splitting of store: " << *SI << "\n");
continue;
}
Value *StoreBasePtr = SI->getPointerOperand();
IRB.SetInsertPoint(BasicBlock::iterator(SI));
DEBUG(dbgs() << " Splitting store of load: " << *SI << "\n");
for (int Idx = 0, Size = SplitLoads.size(); Idx < Size; ++Idx) {
LoadInst *PLoad = SplitLoads[Idx];
uint64_t PartOffset = Idx == 0 ? 0 : Offsets.Splits[Idx - 1];
auto *PartPtrTy =
PLoad->getType()->getPointerTo(SI->getPointerAddressSpace());
StoreInst *PStore = IRB.CreateAlignedStore(
PLoad, getAdjustedPtr(IRB, DL, StoreBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, StoreBasePtr->getName() + "."),
getAdjustedAlignment(SI, PartOffset, DL), /*IsVolatile*/ false);
(void)PStore;
DEBUG(dbgs() << " +" << PartOffset << ":" << *PStore << "\n");
}
// We want to immediately iterate on any allocas impacted by splitting
// this store, and we have to track any promotable alloca (indicated by
// a direct store) as needing to be resplit because it is no longer
// promotable.
if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(StoreBasePtr)) {
ResplitPromotableAllocas.insert(OtherAI);
Worklist.insert(OtherAI);
} else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
StoreBasePtr->stripInBoundsOffsets())) {
Worklist.insert(OtherAI);
}
// Mark the original store as dead.
DeadInsts.insert(SI);
}
// Save the split loads if there are deferred stores among the users.
if (DeferredStores)
SplitLoadsMap.insert(std::make_pair(LI, std::move(SplitLoads)));
// Mark the original load as dead and kill the original slice.
DeadInsts.insert(LI);
Offsets.S->kill();
}
// Second, we rewrite all of the split stores. At this point, we know that
// all loads from this alloca have been split already. For stores of such
// loads, we can simply look up the pre-existing split loads. For stores of
// other loads, we split those loads first and then write split stores of
// them.
for (StoreInst *SI : Stores) {
auto *LI = cast<LoadInst>(SI->getValueOperand());
IntegerType *Ty = cast<IntegerType>(LI->getType());
uint64_t StoreSize = Ty->getBitWidth() / 8;
assert(StoreSize > 0 && "Cannot have a zero-sized integer store!");
auto &Offsets = SplitOffsetsMap[SI];
assert(StoreSize == Offsets.S->endOffset() - Offsets.S->beginOffset() &&
"Slice size should always match load size exactly!");
uint64_t BaseOffset = Offsets.S->beginOffset();
assert(BaseOffset + StoreSize > BaseOffset &&
"Cannot represent alloca access size using 64-bit integers!");
Value *LoadBasePtr = LI->getPointerOperand();
Instruction *StoreBasePtr = cast<Instruction>(SI->getPointerOperand());
DEBUG(dbgs() << " Splitting store: " << *SI << "\n");
// Check whether we have an already split load.
auto SplitLoadsMapI = SplitLoadsMap.find(LI);
std::vector<LoadInst *> *SplitLoads = nullptr;
if (SplitLoadsMapI != SplitLoadsMap.end()) {
SplitLoads = &SplitLoadsMapI->second;
assert(SplitLoads->size() == Offsets.Splits.size() + 1 &&
"Too few split loads for the number of splits in the store!");
} else {
DEBUG(dbgs() << " of load: " << *LI << "\n");
}
uint64_t PartOffset = 0, PartSize = Offsets.Splits.front();
int Idx = 0, Size = Offsets.Splits.size();
for (;;) {
auto *PartTy = Type::getIntNTy(Ty->getContext(), PartSize * 8);
auto *PartPtrTy = PartTy->getPointerTo(SI->getPointerAddressSpace());
// Either lookup a split load or create one.
LoadInst *PLoad;
if (SplitLoads) {
PLoad = (*SplitLoads)[Idx];
} else {
IRB.SetInsertPoint(BasicBlock::iterator(LI));
PLoad = IRB.CreateAlignedLoad(
getAdjustedPtr(IRB, DL, LoadBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, LoadBasePtr->getName() + "."),
getAdjustedAlignment(LI, PartOffset, DL), /*IsVolatile*/ false,
LI->getName());
}
// And store this partition.
IRB.SetInsertPoint(BasicBlock::iterator(SI));
StoreInst *PStore = IRB.CreateAlignedStore(
PLoad, getAdjustedPtr(IRB, DL, StoreBasePtr,
APInt(DL.getPointerSizeInBits(), PartOffset),
PartPtrTy, StoreBasePtr->getName() + "."),
getAdjustedAlignment(SI, PartOffset, DL), /*IsVolatile*/ false);
// Now build a new slice for the alloca.
NewSlices.push_back(
Slice(BaseOffset + PartOffset, BaseOffset + PartOffset + PartSize,
&PStore->getOperandUse(PStore->getPointerOperandIndex()),
/*IsSplittable*/ false));
DEBUG(dbgs() << " new slice [" << NewSlices.back().beginOffset()
<< ", " << NewSlices.back().endOffset() << "): " << *PStore
<< "\n");
if (!SplitLoads) {
DEBUG(dbgs() << " of split load: " << *PLoad << "\n");
}
// See if we've finished all the splits.
if (Idx >= Size)
break;
// Setup the next partition.
PartOffset = Offsets.Splits[Idx];
++Idx;
PartSize = (Idx < Size ? Offsets.Splits[Idx] : StoreSize) - PartOffset;
}
// We want to immediately iterate on any allocas impacted by splitting
// this load, which is only relevant if it isn't a load of this alloca and
// thus we didn't already split the loads above. We also have to keep track
// of any promotable allocas we split loads on as they can no longer be
// promoted.
if (!SplitLoads) {
if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(LoadBasePtr)) {
assert(OtherAI != &AI && "We can't re-split our own alloca!");
ResplitPromotableAllocas.insert(OtherAI);
Worklist.insert(OtherAI);
} else if (AllocaInst *OtherAI = dyn_cast<AllocaInst>(
LoadBasePtr->stripInBoundsOffsets())) {
assert(OtherAI != &AI && "We can't re-split our own alloca!");
Worklist.insert(OtherAI);
}
}
// Mark the original store as dead now that we've split it up and kill its
// slice. Note that we leave the original load in place unless this store
// was its ownly use. It may in turn be split up if it is an alloca load
// for some other alloca, but it may be a normal load. This may introduce
// redundant loads, but where those can be merged the rest of the optimizer
// should handle the merging, and this uncovers SSA splits which is more
// important. In practice, the original loads will almost always be fully
// split and removed eventually, and the splits will be merged by any
// trivial CSE, including instcombine.
if (LI->hasOneUse()) {
assert(*LI->user_begin() == SI && "Single use isn't this store!");
DeadInsts.insert(LI);
}
DeadInsts.insert(SI);
Offsets.S->kill();
}
// Remove the killed slices that have ben pre-split.
AS.erase(std::remove_if(AS.begin(), AS.end(), [](const Slice &S) {
return S.isDead();
}), AS.end());
// Insert our new slices. This will sort and merge them into the sorted
// sequence.
AS.insert(NewSlices);
DEBUG(dbgs() << " Pre-split slices:\n");
#ifndef NDEBUG
for (auto I = AS.begin(), E = AS.end(); I != E; ++I)
DEBUG(AS.print(dbgs(), I, " "));
#endif
// Finally, don't try to promote any allocas that new require re-splitting.
// They have already been added to the worklist above.
PromotableAllocas.erase(
std::remove_if(
PromotableAllocas.begin(), PromotableAllocas.end(),
[&](AllocaInst *AI) { return ResplitPromotableAllocas.count(AI); }),
PromotableAllocas.end());
return true;
}
/// \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.
AllocaInst *SROA::rewritePartition(AllocaInst &AI, AllocaSlices &AS,
AllocaSlices::Partition &P) {
// 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 = nullptr;
const DataLayout &DL = AI.getModule()->getDataLayout();
if (Type *CommonUseTy = findCommonType(P.begin(), P.end(), P.endOffset()))
if (DL.getTypeAllocSize(CommonUseTy) >= P.size())
SliceTy = CommonUseTy;
if (!SliceTy)
if (Type *TypePartitionTy = getTypePartition(DL, AI.getAllocatedType(),
P.beginOffset(), P.size()))
SliceTy = TypePartitionTy;
if ((!SliceTy || (SliceTy->isArrayTy() &&
SliceTy->getArrayElementType()->isIntegerTy())) &&
DL.isLegalInteger(P.size() * 8))
SliceTy = Type::getIntNTy(*C, P.size() * 8);
if (!SliceTy)
SliceTy = ArrayType::get(Type::getInt8Ty(*C), P.size());
assert(DL.getTypeAllocSize(SliceTy) >= P.size());
bool IsIntegerPromotable = isIntegerWideningViable(P, SliceTy, DL);
VectorType *VecTy =
IsIntegerPromotable ? nullptr : isVectorPromotionViable(P, DL);
if (VecTy)
SliceTy = VecTy;
// 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(P.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.
// FIXME: return nullptr;
} 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, P.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, nullptr, Alignment,
AI.getName() + ".sroa." + Twine(P.begin() - AS.begin()), &AI);
++NumNewAllocas;
}
DEBUG(dbgs() << "Rewriting alloca partition "
<< "[" << P.beginOffset() << "," << P.endOffset()
<< ") to: " << *NewAI << "\n");
// Track the high watermark on the worklist as it is 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 NumUses = 0;
SmallPtrSet<PHINode *, 8> PHIUsers;
SmallPtrSet<SelectInst *, 8> SelectUsers;
AllocaSliceRewriter Rewriter(DL, AS, *this, AI, *NewAI, P.beginOffset(),
P.endOffset(), IsIntegerPromotable, VecTy,
PHIUsers, SelectUsers);
bool Promotable = true;
for (Slice *S : P.splitSliceTails()) {
Promotable &= Rewriter.visit(S);
++NumUses;
}
for (Slice &S : P) {
Promotable &= Rewriter.visit(&S);
++NumUses;
}
NumAllocaPartitionUses += NumUses;
MaxUsesPerAllocaPartition =
std::max<unsigned>(NumUses, MaxUsesPerAllocaPartition);
// Now that we've processed all the slices in the new partition, check if any
// PHIs or Selects would block promotion.
for (SmallPtrSetImpl<PHINode *>::iterator I = PHIUsers.begin(),
E = PHIUsers.end();
I != E; ++I)
if (!isSafePHIToSpeculate(**I)) {
Promotable = false;
PHIUsers.clear();
SelectUsers.clear();
break;
}
for (SmallPtrSetImpl<SelectInst *>::iterator I = SelectUsers.begin(),
E = SelectUsers.end();
I != E; ++I)
if (!isSafeSelectToSpeculate(**I)) {
Promotable = false;
PHIUsers.clear();
SelectUsers.clear();
break;
}
if (Promotable) {
if (PHIUsers.empty() && SelectUsers.empty()) {
// Promote the alloca.
PromotableAllocas.push_back(NewAI);
} else {
// If we have either PHIs or Selects to speculate, add them to those
// worklists and re-queue the new alloca so that we promote in on the
// next iteration.
for (PHINode *PHIUser : PHIUsers)
SpeculatablePHIs.insert(PHIUser);
for (SelectInst *SelectUser : SelectUsers)
SpeculatableSelects.insert(SelectUser);
Worklist.insert(NewAI);
}
} else {
// 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.
if (NewAI != &AI)
Worklist.insert(NewAI);
// Drop any post-promotion work items if promotion didn't happen.
while (PostPromotionWorklist.size() > PPWOldSize)
PostPromotionWorklist.pop_back();
}
return NewAI;
}
/// \brief Walks the slices of an alloca and form partitions based on them,
/// rewriting each of their uses.
bool SROA::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
if (AS.begin() == AS.end())
return false;
unsigned NumPartitions = 0;
bool Changed = false;
const DataLayout &DL = AI.getModule()->getDataLayout();
// First try to pre-split loads and stores.
Changed |= presplitLoadsAndStores(AI, AS);
// Now that we have identified any pre-splitting opportunities, mark any
// splittable (non-whole-alloca) loads and stores as unsplittable. If we fail
// to split these during pre-splitting, we want to force them to be
// rewritten into a partition.
bool IsSorted = true;
for (Slice &S : AS) {
if (!S.isSplittable())
continue;
// FIXME: We currently leave whole-alloca splittable loads and stores. This
// used to be the only splittable loads and stores and we need to be
// confident that the above handling of splittable loads and stores is
// completely sufficient before we forcibly disable the remaining handling.
if (S.beginOffset() == 0 &&
S.endOffset() >= DL.getTypeAllocSize(AI.getAllocatedType()))
continue;
if (isa<LoadInst>(S.getUse()->getUser()) ||
isa<StoreInst>(S.getUse()->getUser())) {
S.makeUnsplittable();
IsSorted = false;
}
}
if (!IsSorted)
std::sort(AS.begin(), AS.end());
/// \brief Describes the allocas introduced by rewritePartition
/// in order to migrate the debug info.
struct Piece {
AllocaInst *Alloca;
uint64_t Offset;
uint64_t Size;
Piece(AllocaInst *AI, uint64_t O, uint64_t S)
: Alloca(AI), Offset(O), Size(S) {}
};
SmallVector<Piece, 4> Pieces;
// Rewrite each partition.
for (auto &P : AS.partitions()) {
if (AllocaInst *NewAI = rewritePartition(AI, AS, P)) {
Changed = true;
if (NewAI != &AI) {
uint64_t SizeOfByte = 8;
uint64_t AllocaSize = DL.getTypeSizeInBits(NewAI->getAllocatedType());
// Don't include any padding.
uint64_t Size = std::min(AllocaSize, P.size() * SizeOfByte);
Pieces.push_back(Piece(NewAI, P.beginOffset() * SizeOfByte, Size));
}
}
++NumPartitions;
}
NumAllocaPartitions += NumPartitions;
MaxPartitionsPerAlloca =
std::max<unsigned>(NumPartitions, MaxPartitionsPerAlloca);
// Migrate debug information from the old alloca to the new alloca(s)
// and the individial partitions.
if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(&AI)) {
auto *Var = DbgDecl->getVariable();
auto *Expr = DbgDecl->getExpression();
DIBuilder DIB(*AI.getParent()->getParent()->getParent(),
/*AllowUnresolved*/ false);
bool IsSplit = Pieces.size() > 1;
for (auto Piece : Pieces) {
// Create a piece expression describing the new partition or reuse AI's
// expression if there is only one partition.
auto *PieceExpr = Expr;
if (IsSplit || Expr->isBitPiece()) {
// If this alloca is already a scalar replacement of a larger aggregate,
// Piece.Offset describes the offset inside the scalar.
uint64_t Offset = Expr->isBitPiece() ? Expr->getBitPieceOffset() : 0;
uint64_t Start = Offset + Piece.Offset;
uint64_t Size = Piece.Size;
if (Expr->isBitPiece()) {
uint64_t AbsEnd = Expr->getBitPieceOffset() + Expr->getBitPieceSize();
if (Start >= AbsEnd)
// No need to describe a SROAed padding.
continue;
Size = std::min(Size, AbsEnd - Start);
}
PieceExpr = DIB.createBitPieceExpression(Start, Size);
}
// Remove any existing dbg.declare intrinsic describing the same alloca.
if (DbgDeclareInst *OldDDI = FindAllocaDbgDeclare(Piece.Alloca))
OldDDI->eraseFromParent();
DIB.insertDeclare(Piece.Alloca, Var, PieceExpr, DbgDecl->getDebugLoc(),
&AI);
}
}
return Changed;
}
/// \brief Clobber a use with undef, deleting the used value if it becomes dead.
void SROA::clobberUse(Use &U) {
Value *OldV = U;
// Replace the use with an undef value.
U = UndefValue::get(OldV->getType());
// Check for this making an instruction dead. We have to garbage collect
// all the dead instructions to ensure the uses of any alloca end up being
// minimal.
if (Instruction *OldI = dyn_cast<Instruction>(OldV))
if (isInstructionTriviallyDead(OldI)) {
DeadInsts.insert(OldI);
}
}
/// \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;
}
const DataLayout &DL = AI.getModule()->getDataLayout();
// 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 AS(DL, AI);
DEBUG(AS.print(dbgs()));
if (AS.isEscaped())
return Changed;
// Delete all the dead users of this alloca before splitting and rewriting it.
for (Instruction *DeadUser : AS.getDeadUsers()) {
// Free up everything used by this instruction.
for (Use &DeadOp : DeadUser->operands())
clobberUse(DeadOp);
// Now replace the uses of this instruction.
DeadUser->replaceAllUsesWith(UndefValue::get(DeadUser->getType()));
// And mark it for deletion.
DeadInsts.insert(DeadUser);
Changed = true;
}
for (Use *DeadOp : AS.getDeadOperands()) {
clobberUse(*DeadOp);
Changed = true;
}
// No slices to split. Leave the dead alloca for a later pass to clean up.
if (AS.begin() == AS.end())
return Changed;
Changed |= splitAlloca(AI, AS);
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(
SmallPtrSetImpl<AllocaInst *> &DeletedAllocas) {
while (!DeadInsts.empty()) {
Instruction *I = DeadInsts.pop_back_val();
DEBUG(dbgs() << "Deleting dead instruction: " << *I << "\n");
I->replaceAllUsesWith(UndefValue::get(I->getType()));
for (Use &Operand : I->operands())
if (Instruction *U = dyn_cast<Instruction>(Operand)) {
// Zero out the operand and see if it becomes trivially dead.
Operand = nullptr;
if (isInstructionTriviallyDead(U))
DeadInsts.insert(U);
}
if (AllocaInst *AI = dyn_cast<AllocaInst>(I)) {
DeletedAllocas.insert(AI);
if (DbgDeclareInst *DbgDecl = FindAllocaDbgDeclare(AI))
DbgDecl->eraseFromParent();
}
++NumDeleted;
I->eraseFromParent();
}
}
static void enqueueUsersInWorklist(Instruction &I,
SmallVectorImpl<Instruction *> &Worklist,
SmallPtrSetImpl<Instruction *> &Visited) {
for (User *U : I.users())
if (Visited.insert(cast<Instruction>(U)).second)
Worklist.push_back(cast<Instruction>(U));
}
/// \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, nullptr, AC);
PromotableAllocas.clear();
return true;
}
DEBUG(dbgs() << "Promoting allocas with SSAUpdater...\n");
SSAUpdater SSA;
DIBuilder DIB(*F.getParent(), /*AllowUnresolved*/ false);
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;
}
bool SROA::runOnFunction(Function &F) {
if (skipOptnoneFunction(F))
return false;
DEBUG(dbgs() << "SROA function: " << F.getName() << "\n");
C = &F.getContext();
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DT = DTWP ? &DTWP->getDomTree() : nullptr;
AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
BasicBlock &EntryBB = F.getEntryBlock();
for (BasicBlock::iterator I = EntryBB.begin(), E = std::prev(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()) {
auto IsInSet = [&](AllocaInst *AI) { return DeletedAllocas.count(AI); };
Worklist.remove_if(IsInSet);
PostPromotionWorklist.remove_if(IsInSet);
PromotableAllocas.erase(std::remove_if(PromotableAllocas.begin(),
PromotableAllocas.end(),
IsInSet),
PromotableAllocas.end());
DeletedAllocas.clear();
}
}
Changed |= promoteAllocas(F);
Worklist = PostPromotionWorklist;
PostPromotionWorklist.clear();
} while (!Worklist.empty());
return Changed;
}
void SROA::getAnalysisUsage(AnalysisUsage &AU) const {
AU.addRequired<AssumptionCacheTracker>();
if (RequiresDomTree)
AU.addRequired<DominatorTreeWrapperPass>();
AU.setPreservesCFG();
}
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