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// Copyright (c) 2016, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#if !defined(DART_PRECOMPILED_RUNTIME)
#include "vm/compiler/backend/redundancy_elimination.h"
#include "vm/bit_vector.h"
#include "vm/compiler/backend/flow_graph.h"
#include "vm/compiler/backend/il.h"
#include "vm/compiler/backend/il_printer.h"
#include "vm/hash_map.h"
#include "vm/stack_frame.h"
namespace dart {
DEFINE_FLAG(bool, dead_store_elimination, true, "Eliminate dead stores");
DEFINE_FLAG(bool, load_cse, true, "Use redundant load elimination.");
DEFINE_FLAG(bool,
trace_load_optimization,
false,
"Print live sets for load optimization pass.");
// Quick access to the current zone.
#define Z (zone())
class CSEInstructionMap : public ValueObject {
public:
CSEInstructionMap() : map_() {}
explicit CSEInstructionMap(const CSEInstructionMap& other)
: ValueObject(), map_(other.map_) {}
Instruction* Lookup(Instruction* other) const {
ASSERT(other->AllowsCSE());
return map_.LookupValue(other);
}
void Insert(Instruction* instr) {
ASSERT(instr->AllowsCSE());
return map_.Insert(instr);
}
private:
typedef DirectChainedHashMap<PointerKeyValueTrait<Instruction> > Map;
Map map_;
};
// Place describes an abstract location (e.g. field) that IR can load
// from or store to.
//
// Places are also used to describe wild-card locations also known as aliases,
// that essentially represent sets of places that alias each other. Places A
// and B are said to alias each other if store into A can affect load from B.
//
// We distinguish the following aliases:
//
// - for fields
// - *.f, *.@offs - field inside some object;
// - X.f, X.@offs - field inside an allocated object X;
// - for indexed accesses
// - *[*] - non-constant index inside some object;
// - *[C] - constant index inside some object;
// - X[*] - non-constant index inside an allocated object X;
// - X[C] - constant index inside an allocated object X.
//
// Constant indexed places are divided into two subcategories:
//
// - Access to homogeneous array-like objects: Array, ImmutableArray,
// OneByteString, TwoByteString. These objects can only be accessed
// on element by element basis with all elements having the same size.
// This means X[C] aliases X[K] if and only if C === K.
// - TypedData accesses. TypedData allow to read one of the primitive
// data types at the given byte offset. When TypedData is accessed through
// index operator on a typed array or a typed array view it is guaranteed
// that the byte offset is always aligned by the element size. We write
// these accesses as X[C|S], where C is constant byte offset and S is size
// of the data type. Obviously X[C|S] and X[K|U] alias if and only if either
// C = RoundDown(K, S) or K = RoundDown(C, U).
// Note that not all accesses to typed data are aligned: e.g. ByteData
// allows unanaligned access through it's get*/set* methods.
// Check in Place::SetIndex ensures that we never create a place X[C|S]
// such that C is not aligned by S.
//
// Separating allocations from other objects improves precision of the
// load forwarding pass because of the following two properties:
//
// - if X can be proven to have no aliases itself (i.e. there is no other SSA
// variable that points to X) then no place inside X can be aliased with any
// wildcard dependent place (*.f, *.@offs, *[*], *[C]);
// - given allocations X and Y no place inside X can be aliased with any place
// inside Y even if any of them or both escape.
//
// It important to realize that single place can belong to multiple aliases.
// For example place X.f with aliased allocation X belongs both to X.f and *.f
// aliases. Likewise X[C] with non-aliased allocation X belongs to X[C] and X[*]
// aliases.
//
class Place : public ValueObject {
public:
enum Kind {
kNone,
// Field location. For instance fields is represented as a pair of a Field
// object and an instance (SSA definition) that is being accessed.
// For static fields instance is NULL.
kField,
// VMField location. Represented as a pair of an instance (SSA definition)
// being accessed and offset to the field.
kVMField,
// Indexed location with a non-constant index.
kIndexed,
// Indexed location with a constant index.
kConstantIndexed,
};
// Size of the element accessed by constant index. Size is only important
// for TypedData because those accesses can alias even when constant indexes
// are not the same: X[0|4] aliases X[0|2] and X[2|2].
enum ElementSize {
// If indexed access is not a TypedData access then element size is not
// important because there is only a single possible access size depending
// on the receiver - X[C] aliases X[K] if and only if C == K.
// This is the size set for Array, ImmutableArray, OneByteString and
// TwoByteString accesses.
kNoSize,
// 1 byte (Int8List, Uint8List, Uint8ClampedList).
kInt8,
// 2 bytes (Int16List, Uint16List).
kInt16,
// 4 bytes (Int32List, Uint32List, Float32List).
kInt32,
// 8 bytes (Int64List, Uint64List, Float64List).
kInt64,
// 16 bytes (Int32x4List, Float32x4List, Float64x2List).
kInt128,
kLargestElementSize = kInt128,
};
Place(const Place& other)
: ValueObject(),
flags_(other.flags_),
instance_(other.instance_),
raw_selector_(other.raw_selector_),
id_(other.id_) {}
// Construct a place from instruction if instruction accesses any place.
// Otherwise constructs kNone place.
Place(Instruction* instr, bool* is_load, bool* is_store)
: flags_(0), instance_(NULL), raw_selector_(0), id_(0) {
switch (instr->tag()) {
case Instruction::kLoadField: {
LoadFieldInstr* load_field = instr->AsLoadField();
set_representation(load_field->representation());
instance_ = load_field->instance()->definition()->OriginalDefinition();
if (load_field->field() != NULL) {
set_kind(kField);
field_ = load_field->field();
} else {
set_kind(kVMField);
offset_in_bytes_ = load_field->offset_in_bytes();
}
*is_load = true;
break;
}
case Instruction::kStoreInstanceField: {
StoreInstanceFieldInstr* store = instr->AsStoreInstanceField();
set_representation(store->RequiredInputRepresentation(
StoreInstanceFieldInstr::kValuePos));
instance_ = store->instance()->definition()->OriginalDefinition();
if (!store->field().IsNull()) {
set_kind(kField);
field_ = &store->field();
} else {
set_kind(kVMField);
offset_in_bytes_ = store->offset_in_bytes();
}
*is_store = true;
break;
}
case Instruction::kLoadStaticField:
set_kind(kField);
set_representation(instr->AsLoadStaticField()->representation());
field_ = &instr->AsLoadStaticField()->StaticField();
*is_load = true;
break;
case Instruction::kStoreStaticField:
set_kind(kField);
set_representation(
instr->AsStoreStaticField()->RequiredInputRepresentation(
StoreStaticFieldInstr::kValuePos));
field_ = &instr->AsStoreStaticField()->field();
*is_store = true;
break;
case Instruction::kLoadIndexed: {
LoadIndexedInstr* load_indexed = instr->AsLoadIndexed();
set_representation(load_indexed->representation());
instance_ = load_indexed->array()->definition()->OriginalDefinition();
SetIndex(load_indexed->index()->definition(),
load_indexed->index_scale(), load_indexed->class_id());
*is_load = true;
break;
}
case Instruction::kStoreIndexed: {
StoreIndexedInstr* store_indexed = instr->AsStoreIndexed();
set_representation(store_indexed->RequiredInputRepresentation(
StoreIndexedInstr::kValuePos));
instance_ = store_indexed->array()->definition()->OriginalDefinition();
SetIndex(store_indexed->index()->definition(),
store_indexed->index_scale(), store_indexed->class_id());
*is_store = true;
break;
}
default:
break;
}
}
// Create object representing *[*] alias.
static Place* CreateAnyInstanceAnyIndexAlias(Zone* zone, intptr_t id) {
return Wrap(
zone, Place(EncodeFlags(kIndexed, kNoRepresentation, kNoSize), NULL, 0),
id);
}
// Return least generic alias for this place. Given that aliases are
// essentially sets of places we define least generic alias as a smallest
// alias that contains this place.
//
// We obtain such alias by a simple transformation:
//
// - for places that depend on an instance X.f, X.@offs, X[i], X[C]
// we drop X if X is not an allocation because in this case X does not
// possess an identity obtaining aliases *.f, *.@offs, *[i] and *[C]
// respectively;
// - for non-constant indexed places X[i] we drop information about the
// index obtaining alias X[*].
// - we drop information about representation, but keep element size
// if any.
//
Place ToAlias() const {
return Place(
RepresentationBits::update(kNoRepresentation, flags_),
(DependsOnInstance() && IsAllocation(instance())) ? instance() : NULL,
(kind() == kIndexed) ? 0 : raw_selector_);
}
bool DependsOnInstance() const {
switch (kind()) {
case kField:
case kVMField:
case kIndexed:
case kConstantIndexed:
return true;
case kNone:
return false;
}
UNREACHABLE();
return false;
}
// Given instance dependent alias X.f, X.@offs, X[C], X[*] return
// wild-card dependent alias *.f, *.@offs, *[C] or *[*] respectively.
Place CopyWithoutInstance() const {
ASSERT(DependsOnInstance());
return Place(flags_, NULL, raw_selector_);
}
// Given alias X[C] or *[C] return X[*] and *[*] respectively.
Place CopyWithoutIndex() const {
ASSERT(kind() == kConstantIndexed);
return Place(EncodeFlags(kIndexed, kNoRepresentation, kNoSize), instance_,
0);
}
// Given alias X[ByteOffs|S] and a larger element size S', return
// alias X[RoundDown(ByteOffs, S')|S'] - this is the byte offset of a larger
// typed array element that contains this typed array element.
// In other words this method computes the only possible place with the given
// size that can alias this place (due to alignment restrictions).
// For example for X[9|kInt8] and target size kInt32 we would return
// X[8|kInt32].
Place ToLargerElement(ElementSize to) const {
ASSERT(kind() == kConstantIndexed);
ASSERT(element_size() != kNoSize);
ASSERT(element_size() < to);
return Place(ElementSizeBits::update(to, flags_), instance_,
RoundByteOffset(to, index_constant_));
}
intptr_t id() const { return id_; }
Kind kind() const { return KindBits::decode(flags_); }
Representation representation() const {
return RepresentationBits::decode(flags_);
}
Definition* instance() const {
ASSERT(DependsOnInstance());
return instance_;
}
void set_instance(Definition* def) {
ASSERT(DependsOnInstance());
instance_ = def->OriginalDefinition();
}
const Field& field() const {
ASSERT(kind() == kField);
return *field_;
}
intptr_t offset_in_bytes() const {
ASSERT(kind() == kVMField);
return offset_in_bytes_;
}
Definition* index() const {
ASSERT(kind() == kIndexed);
return index_;
}
ElementSize element_size() const { return ElementSizeBits::decode(flags_); }
intptr_t index_constant() const {
ASSERT(kind() == kConstantIndexed);
return index_constant_;
}
static const char* DefinitionName(Definition* def) {
if (def == NULL) {
return "*";
} else {
return Thread::Current()->zone()->PrintToString("v%" Pd,
def->ssa_temp_index());
}
}
const char* ToCString() const {
switch (kind()) {
case kNone:
return "<none>";
case kField: {
const char* field_name = String::Handle(field().name()).ToCString();
if (field().is_static()) {
return Thread::Current()->zone()->PrintToString("<%s>", field_name);
} else {
return Thread::Current()->zone()->PrintToString(
"<%s.%s>", DefinitionName(instance()), field_name);
}
}
case kVMField:
return Thread::Current()->zone()->PrintToString(
"<%s.@%" Pd ">", DefinitionName(instance()), offset_in_bytes());
case kIndexed:
return Thread::Current()->zone()->PrintToString(
"<%s[%s]>", DefinitionName(instance()), DefinitionName(index()));
case kConstantIndexed:
if (element_size() == kNoSize) {
return Thread::Current()->zone()->PrintToString(
"<%s[%" Pd "]>", DefinitionName(instance()), index_constant());
} else {
return Thread::Current()->zone()->PrintToString(
"<%s[%" Pd "|%" Pd "]>", DefinitionName(instance()),
index_constant(), ElementSizeMultiplier(element_size()));
}
}
UNREACHABLE();
return "<?>";
}
// Fields that are considered immutable by load optimization.
// Handle static finals as non-final with precompilation because
// they may be reset to uninitialized after compilation.
bool IsImmutableField() const {
return (kind() == kField) && field().is_final() &&
(!field().is_static() || !FLAG_fields_may_be_reset);
}
intptr_t Hashcode() const {
return (flags_ * 63 + reinterpret_cast<intptr_t>(instance_)) * 31 +
FieldHashcode();
}
bool Equals(const Place* other) const {
return (flags_ == other->flags_) && (instance_ == other->instance_) &&
SameField(other);
}
// Create a zone allocated copy of this place and assign given id to it.
static Place* Wrap(Zone* zone, const Place& place, intptr_t id);
static bool IsAllocation(Definition* defn) {
return (defn != NULL) &&
(defn->IsAllocateObject() || defn->IsCreateArray() ||
defn->IsAllocateUninitializedContext() ||
(defn->IsStaticCall() &&
defn->AsStaticCall()->IsRecognizedFactory()));
}
private:
Place(uword flags, Definition* instance, intptr_t selector)
: flags_(flags), instance_(instance), raw_selector_(selector), id_(0) {}
bool SameField(const Place* other) const {
return (kind() == kField)
? (field().Original() == other->field().Original())
: (offset_in_bytes_ == other->offset_in_bytes_);
}
intptr_t FieldHashcode() const {
return (kind() == kField) ? reinterpret_cast<intptr_t>(field().Original())
: offset_in_bytes_;
}
void set_representation(Representation rep) {
flags_ = RepresentationBits::update(rep, flags_);
}
void set_kind(Kind kind) { flags_ = KindBits::update(kind, flags_); }
void set_element_size(ElementSize scale) {
flags_ = ElementSizeBits::update(scale, flags_);
}
void SetIndex(Definition* index, intptr_t scale, intptr_t class_id) {
ConstantInstr* index_constant = index->AsConstant();
if ((index_constant != NULL) && index_constant->value().IsSmi()) {
const intptr_t index_value = Smi::Cast(index_constant->value()).Value();
const ElementSize size = ElementSizeFor(class_id);
const bool is_typed_data = (size != kNoSize);
// If we are writing into the typed data scale the index to
// get byte offset. Otherwise ignore the scale.
if (!is_typed_data) {
scale = 1;
}
// Guard against potential multiplication overflow and negative indices.
if ((0 <= index_value) && (index_value < (kMaxInt32 / scale))) {
const intptr_t scaled_index = index_value * scale;
// Guard against unaligned byte offsets.
if (!is_typed_data ||
Utils::IsAligned(scaled_index, ElementSizeMultiplier(size))) {
set_kind(kConstantIndexed);
set_element_size(size);
index_constant_ = scaled_index;
return;
}
}
// Fallthrough: create generic _[*] place.
}
set_kind(kIndexed);
index_ = index;
}
static uword EncodeFlags(Kind kind, Representation rep, ElementSize scale) {
ASSERT((kind == kConstantIndexed) || (scale == kNoSize));
return KindBits::encode(kind) | RepresentationBits::encode(rep) |
ElementSizeBits::encode(scale);
}
static ElementSize ElementSizeFor(intptr_t class_id) {
switch (class_id) {
case kArrayCid:
case kImmutableArrayCid:
case kOneByteStringCid:
case kTwoByteStringCid:
case kExternalOneByteStringCid:
case kExternalTwoByteStringCid:
// Object arrays and strings do not allow accessing them through
// different types. No need to attach scale.
return kNoSize;
case kTypedDataInt8ArrayCid:
case kTypedDataUint8ArrayCid:
case kTypedDataUint8ClampedArrayCid:
case kExternalTypedDataUint8ArrayCid:
case kExternalTypedDataUint8ClampedArrayCid:
return kInt8;
case kTypedDataInt16ArrayCid:
case kTypedDataUint16ArrayCid:
return kInt16;
case kTypedDataInt32ArrayCid:
case kTypedDataUint32ArrayCid:
case kTypedDataFloat32ArrayCid:
return kInt32;
case kTypedDataInt64ArrayCid:
case kTypedDataUint64ArrayCid:
case kTypedDataFloat64ArrayCid:
return kInt64;
case kTypedDataInt32x4ArrayCid:
case kTypedDataFloat32x4ArrayCid:
case kTypedDataFloat64x2ArrayCid:
return kInt128;
default:
UNREACHABLE();
return kNoSize;
}
}
static intptr_t ElementSizeMultiplier(ElementSize size) {
return 1 << (static_cast<intptr_t>(size) - static_cast<intptr_t>(kInt8));
}
static intptr_t RoundByteOffset(ElementSize size, intptr_t offset) {
return offset & ~(ElementSizeMultiplier(size) - 1);
}
class KindBits : public BitField<uword, Kind, 0, 3> {};
class RepresentationBits
: public BitField<uword, Representation, KindBits::kNextBit, 11> {};
class ElementSizeBits
: public BitField<uword, ElementSize, RepresentationBits::kNextBit, 3> {};
uword flags_;
Definition* instance_;
union {
intptr_t raw_selector_;
const Field* field_;
intptr_t offset_in_bytes_;
intptr_t index_constant_;
Definition* index_;
};
intptr_t id_;
};
class ZonePlace : public ZoneAllocated {
public:
explicit ZonePlace(const Place& place) : place_(place) {}
Place* place() { return &place_; }
private:
Place place_;
};
Place* Place::Wrap(Zone* zone, const Place& place, intptr_t id) {
Place* wrapped = (new (zone) ZonePlace(place))->place();
wrapped->id_ = id;
return wrapped;
}
// Correspondence between places connected through outgoing phi moves on the
// edge that targets join.
class PhiPlaceMoves : public ZoneAllocated {
public:
// Record a move from the place with id |from| to the place with id |to| at
// the given block.
void CreateOutgoingMove(Zone* zone,
BlockEntryInstr* block,
intptr_t from,
intptr_t to) {
const intptr_t block_num = block->preorder_number();
while (moves_.length() <= block_num) {
moves_.Add(NULL);
}
if (moves_[block_num] == NULL) {
moves_[block_num] = new (zone) ZoneGrowableArray<Move>(5);
}
moves_[block_num]->Add(Move(from, to));
}
class Move {
public:
Move(intptr_t from, intptr_t to) : from_(from), to_(to) {}
intptr_t from() const { return from_; }
intptr_t to() const { return to_; }
private:
intptr_t from_;
intptr_t to_;
};
typedef const ZoneGrowableArray<Move>* MovesList;
MovesList GetOutgoingMoves(BlockEntryInstr* block) const {
const intptr_t block_num = block->preorder_number();
return (block_num < moves_.length()) ? moves_[block_num] : NULL;
}
private:
GrowableArray<ZoneGrowableArray<Move>*> moves_;
};
// A map from aliases to a set of places sharing the alias. Additionally
// carries a set of places that can be aliased by side-effects, essentially
// those that are affected by calls.
class AliasedSet : public ZoneAllocated {
public:
AliasedSet(Zone* zone,
DirectChainedHashMap<PointerKeyValueTrait<Place> >* places_map,
ZoneGrowableArray<Place*>* places,
PhiPlaceMoves* phi_moves)
: zone_(zone),
places_map_(places_map),
places_(*places),
phi_moves_(phi_moves),
aliases_(5),
aliases_map_(),
typed_data_access_sizes_(),
representatives_(),
killed_(),
aliased_by_effects_(new (zone) BitVector(zone, places->length())) {
InsertAlias(Place::CreateAnyInstanceAnyIndexAlias(
zone_, kAnyInstanceAnyIndexAlias));
for (intptr_t i = 0; i < places_.length(); i++) {
AddRepresentative(places_[i]);
}
ComputeKillSets();
}
intptr_t LookupAliasId(const Place& alias) {
const Place* result = aliases_map_.LookupValue(&alias);
return (result != NULL) ? result->id() : static_cast<intptr_t>(kNoAlias);
}
BitVector* GetKilledSet(intptr_t alias) {
return (alias < killed_.length()) ? killed_[alias] : NULL;
}
intptr_t max_place_id() const { return places().length(); }
bool IsEmpty() const { return max_place_id() == 0; }
BitVector* aliased_by_effects() const { return aliased_by_effects_; }
const ZoneGrowableArray<Place*>& places() const { return places_; }
Place* LookupCanonical(Place* place) const {
return places_map_->LookupValue(place);
}
void PrintSet(BitVector* set) {
bool comma = false;
for (BitVector::Iterator it(set); !it.Done(); it.Advance()) {
if (comma) {
THR_Print(", ");
}
THR_Print("%s", places_[it.Current()]->ToCString());
comma = true;
}
}
const PhiPlaceMoves* phi_moves() const { return phi_moves_; }
void RollbackAliasedIdentites() {
for (intptr_t i = 0; i < identity_rollback_.length(); ++i) {
identity_rollback_[i]->SetIdentity(AliasIdentity::Unknown());
}
}
// Returns false if the result of an allocation instruction can't be aliased
// by another SSA variable and true otherwise.
bool CanBeAliased(Definition* alloc) {
if (!Place::IsAllocation(alloc)) {
return true;
}
if (alloc->Identity().IsUnknown()) {
ComputeAliasing(alloc);
}
return !alloc->Identity().IsNotAliased();
}
enum { kNoAlias = 0 };
private:
enum {
// Artificial alias that is used to collect all representatives of the
// *[C], X[C] aliases for arbitrary C.
kAnyConstantIndexedAlias = 1,
// Artificial alias that is used to collect all representatives of
// *[C] alias for arbitrary C.
kUnknownInstanceConstantIndexedAlias = 2,
// Artificial alias that is used to collect all representatives of
// X[*] alias for all X.
kAnyAllocationIndexedAlias = 3,
// *[*] alias.
kAnyInstanceAnyIndexAlias = 4
};
// Compute least generic alias for the place and assign alias id to it.
void AddRepresentative(Place* place) {
if (!place->IsImmutableField()) {
const Place* alias = CanonicalizeAlias(place->ToAlias());
EnsureSet(&representatives_, alias->id())->Add(place->id());
// Update cumulative representative sets that are used during
// killed sets computation.
if (alias->kind() == Place::kConstantIndexed) {
if (CanBeAliased(alias->instance())) {
EnsureSet(&representatives_, kAnyConstantIndexedAlias)
->Add(place->id());
}
if (alias->instance() == NULL) {
EnsureSet(&representatives_, kUnknownInstanceConstantIndexedAlias)
->Add(place->id());
}
// Collect all element sizes used to access TypedData arrays in
// the function. This is used to skip sizes without representatives
// when computing kill sets.
if (alias->element_size() != Place::kNoSize) {
typed_data_access_sizes_.Add(alias->element_size());
}
} else if ((alias->kind() == Place::kIndexed) &&
CanBeAliased(place->instance())) {
EnsureSet(&representatives_, kAnyAllocationIndexedAlias)
->Add(place->id());
}
if (!IsIndependentFromEffects(place)) {
aliased_by_effects_->Add(place->id());
}
}
}
void ComputeKillSets() {
for (intptr_t i = 0; i < aliases_.length(); ++i) {
const Place* alias = aliases_[i];
// Add all representatives to the kill set.
AddAllRepresentatives(alias->id(), alias->id());
ComputeKillSet(alias);
}
if (FLAG_trace_load_optimization) {
THR_Print("Aliases KILL sets:\n");
for (intptr_t i = 0; i < aliases_.length(); ++i) {
const Place* alias = aliases_[i];
BitVector* kill = GetKilledSet(alias->id());
THR_Print("%s: ", alias->ToCString());
if (kill != NULL) {
PrintSet(kill);
}
THR_Print("\n");
}
}
}
void InsertAlias(const Place* alias) {
aliases_map_.Insert(alias);
aliases_.Add(alias);
}
const Place* CanonicalizeAlias(const Place& alias) {
const Place* canonical = aliases_map_.LookupValue(&alias);
if (canonical == NULL) {
canonical = Place::Wrap(zone_, alias,
kAnyInstanceAnyIndexAlias + aliases_.length());
InsertAlias(canonical);
}
ASSERT(aliases_map_.LookupValue(&alias) == canonical);
return canonical;
}
BitVector* GetRepresentativesSet(intptr_t alias) {
return (alias < representatives_.length()) ? representatives_[alias] : NULL;
}
BitVector* EnsureSet(GrowableArray<BitVector*>* sets, intptr_t alias) {
while (sets->length() <= alias) {
sets->Add(NULL);
}
BitVector* set = (*sets)[alias];
if (set == NULL) {
(*sets)[alias] = set = new (zone_) BitVector(zone_, max_place_id());
}
return set;
}
void AddAllRepresentatives(const Place* to, intptr_t from) {
AddAllRepresentatives(to->id(), from);
}
void AddAllRepresentatives(intptr_t to, intptr_t from) {
BitVector* from_set = GetRepresentativesSet(from);
if (from_set != NULL) {
EnsureSet(&killed_, to)->AddAll(from_set);
}
}
void CrossAlias(const Place* to, const Place& from) {
const intptr_t from_id = LookupAliasId(from);
if (from_id == kNoAlias) {
return;
}
CrossAlias(to, from_id);
}
void CrossAlias(const Place* to, intptr_t from) {
AddAllRepresentatives(to->id(), from);
AddAllRepresentatives(from, to->id());
}
// When computing kill sets we let less generic alias insert its
// representatives into more generic alias'es kill set. For example
// when visiting alias X[*] instead of searching for all aliases X[C]
// and inserting their representatives into kill set for X[*] we update
// kill set for X[*] each time we visit new X[C] for some C.
// There is an exception however: if both aliases are parametric like *[C]
// and X[*] which cross alias when X is an aliased allocation then we use
// artificial aliases that contain all possible representatives for the given
// alias for any value of the parameter to compute resulting kill set.
void ComputeKillSet(const Place* alias) {
switch (alias->kind()) {
case Place::kIndexed: // Either *[*] or X[*] alias.
if (alias->instance() == NULL) {
// *[*] aliases with X[*], X[C], *[C].
AddAllRepresentatives(alias, kAnyConstantIndexedAlias);
AddAllRepresentatives(alias, kAnyAllocationIndexedAlias);
} else if (CanBeAliased(alias->instance())) {
// X[*] aliases with X[C].
// If X can be aliased then X[*] also aliases with *[C], *[*].
CrossAlias(alias, kAnyInstanceAnyIndexAlias);
AddAllRepresentatives(alias, kUnknownInstanceConstantIndexedAlias);
}
break;
case Place::kConstantIndexed: // Either X[C] or *[C] alias.
if (alias->element_size() != Place::kNoSize) {
const bool has_aliased_instance =
(alias->instance() != NULL) && CanBeAliased(alias->instance());
// If this is a TypedData access then X[C|S] aliases larger elements
// covering this one X[RoundDown(C, S')|S'] for all S' > S and
// all smaller elements being covered by this one X[C'|S'] for
// some S' < S and all C' such that C = RoundDown(C', S).
// In the loop below it's enough to only propagate aliasing to
// larger aliases because propagation is symmetric: smaller aliases
// (if there are any) would update kill set for this alias when they
// are visited.
for (intptr_t i = static_cast<intptr_t>(alias->element_size()) + 1;
i <= Place::kLargestElementSize; i++) {
// Skip element sizes that a guaranteed to have no representatives.
if (!typed_data_access_sizes_.Contains(alias->element_size())) {
continue;
}
// X[C|S] aliases with X[RoundDown(C, S')|S'] and likewise
// *[C|S] aliases with *[RoundDown(C, S')|S'].
const Place larger_alias =
alias->ToLargerElement(static_cast<Place::ElementSize>(i));
CrossAlias(alias, larger_alias);
if (has_aliased_instance) {
// If X is an aliased instance then X[C|S] aliases
// with *[RoundDown(C, S')|S'].
CrossAlias(alias, larger_alias.CopyWithoutInstance());
}
}
}
if (alias->instance() == NULL) {
// *[C] aliases with X[C], X[*], *[*].
AddAllRepresentatives(alias, kAnyAllocationIndexedAlias);
CrossAlias(alias, kAnyInstanceAnyIndexAlias);
} else {
// X[C] aliases with X[*].
// If X can be aliased then X[C] also aliases with *[C], *[*].
CrossAlias(alias, alias->CopyWithoutIndex());
if (CanBeAliased(alias->instance())) {
CrossAlias(alias, alias->CopyWithoutInstance());
CrossAlias(alias, kAnyInstanceAnyIndexAlias);
}
}
break;
case Place::kField:
case Place::kVMField:
if (CanBeAliased(alias->instance())) {
// X.f or X.@offs alias with *.f and *.@offs respectively.
CrossAlias(alias, alias->CopyWithoutInstance());
}
break;
case Place::kNone:
UNREACHABLE();
}
}
// Returns true if the given load is unaffected by external side-effects.
// This essentially means that no stores to the same location can
// occur in other functions.
bool IsIndependentFromEffects(Place* place) {
if (place->IsImmutableField()) {
// Note that we can't use LoadField's is_immutable attribute here because
// some VM-fields (those that have no corresponding Field object and
// accessed through offset alone) can share offset but have different
// immutability properties.
// One example is the length property of growable and fixed size list. If
// loads of these two properties occur in the same function for the same
// receiver then they will get the same expression number. However
// immutability of the length of fixed size list does not mean that
// growable list also has immutable property. Thus we will make a
// conservative assumption for the VM-properties.
// TODO(vegorov): disambiguate immutable and non-immutable VM-fields with
// the same offset e.g. through recognized kind.
return true;
}
return ((place->kind() == Place::kField) ||
(place->kind() == Place::kVMField)) &&
!CanBeAliased(place->instance());
}
// Returns true if there are direct loads from the given place.
bool HasLoadsFromPlace(Definition* defn, const Place* place) {
ASSERT((place->kind() == Place::kField) ||
(place->kind() == Place::kVMField));
for (Value* use = defn->input_use_list(); use != NULL;
use = use->next_use()) {
Instruction* instr = use->instruction();
if ((instr->IsRedefinition() || instr->IsAssertAssignable()) &&
HasLoadsFromPlace(instr->AsDefinition(), place)) {
return true;
}
bool is_load = false, is_store;
Place load_place(instr, &is_load, &is_store);
if (is_load && load_place.Equals(place)) {
return true;
}
}
return false;
}
// Check if any use of the definition can create an alias.
// Can add more objects into aliasing_worklist_.
bool AnyUseCreatesAlias(Definition* defn) {
for (Value* use = defn->input_use_list(); use != NULL;
use = use->next_use()) {
Instruction* instr = use->instruction();
if (instr->IsPushArgument() || instr->IsCheckedSmiOp() ||
instr->IsCheckedSmiComparison() ||
(instr->IsStoreIndexed() &&
(use->use_index() == StoreIndexedInstr::kValuePos)) ||
instr->IsStoreStaticField() || instr->IsPhi()) {
return true;
} else if ((instr->IsAssertAssignable() || instr->IsRedefinition()) &&
AnyUseCreatesAlias(instr->AsDefinition())) {
return true;
} else if ((instr->IsStoreInstanceField() &&
(use->use_index() !=
StoreInstanceFieldInstr::kInstancePos))) {
ASSERT(use->use_index() == StoreInstanceFieldInstr::kValuePos);
// If we store this value into an object that is not aliased itself
// and we never load again then the store does not create an alias.
StoreInstanceFieldInstr* store = instr->AsStoreInstanceField();
Definition* instance =
store->instance()->definition()->OriginalDefinition();
if (Place::IsAllocation(instance) &&
!instance->Identity().IsAliased()) {
bool is_load, is_store;
Place store_place(instr, &is_load, &is_store);
if (!HasLoadsFromPlace(instance, &store_place)) {
// No loads found that match this store. If it is yet unknown if
// the object is not aliased then optimistically assume this but
// add it to the worklist to check its uses transitively.
if (instance->Identity().IsUnknown()) {
instance->SetIdentity(AliasIdentity::NotAliased());
aliasing_worklist_.Add(instance);
}
continue;
}
}
return true;
}
}
return false;
}
// Mark any value stored into the given object as potentially aliased.
void MarkStoredValuesEscaping(Definition* defn) {
// Find all stores into this object.
for (Value* use = defn->input_use_list(); use != NULL;
use = use->next_use()) {
if (use->instruction()->IsRedefinition() ||
use->instruction()->IsAssertAssignable()) {
MarkStoredValuesEscaping(use->instruction()->AsDefinition());
continue;
}
if ((use->use_index() == StoreInstanceFieldInstr::kInstancePos) &&
use->instruction()->IsStoreInstanceField()) {
StoreInstanceFieldInstr* store =
use->instruction()->AsStoreInstanceField();
Definition* value = store->value()->definition()->OriginalDefinition();
if (value->Identity().IsNotAliased()) {
value->SetIdentity(AliasIdentity::Aliased());
identity_rollback_.Add(value);
// Add to worklist to propagate the mark transitively.
aliasing_worklist_.Add(value);
}
}
}
}
// Determine if the given definition can't be aliased.
void ComputeAliasing(Definition* alloc) {
ASSERT(Place::IsAllocation(alloc));
ASSERT(alloc->Identity().IsUnknown());
ASSERT(aliasing_worklist_.is_empty());
alloc->SetIdentity(AliasIdentity::NotAliased());
aliasing_worklist_.Add(alloc);
while (!aliasing_worklist_.is_empty()) {
Definition* defn = aliasing_worklist_.RemoveLast();
ASSERT(Place::IsAllocation(defn));
// If the definition in the worklist was optimistically marked as
// not-aliased check that optimistic assumption still holds: check if
// any of its uses can create an alias.
if (!defn->Identity().IsAliased() && AnyUseCreatesAlias(defn)) {
defn->SetIdentity(AliasIdentity::Aliased());
identity_rollback_.Add(defn);
}
// If the allocation site is marked as aliased conservatively mark
// any values stored into the object aliased too.
if (defn->Identity().IsAliased()) {
MarkStoredValuesEscaping(defn);
}
}
}
Zone* zone_;
DirectChainedHashMap<PointerKeyValueTrait<Place> >* places_map_;
const ZoneGrowableArray<Place*>& places_;
const PhiPlaceMoves* phi_moves_;
// A list of all seen aliases and a map that allows looking up canonical
// alias object.
GrowableArray<const Place*> aliases_;
DirectChainedHashMap<PointerKeyValueTrait<const Place> > aliases_map_;
SmallSet<Place::ElementSize> typed_data_access_sizes_;
// Maps alias id to set of ids of places representing the alias.
// Place represents an alias if this alias is least generic alias for
// the place.
// (see ToAlias for the definition of least generic alias).
GrowableArray<BitVector*> representatives_;
// Maps alias id to set of ids of places aliased.
GrowableArray<BitVector*> killed_;
// Set of ids of places that can be affected by side-effects other than
// explicit stores (i.e. through calls).
BitVector* aliased_by_effects_;
// Worklist used during alias analysis.
GrowableArray<Definition*> aliasing_worklist_;
// List of definitions that had their identity set to Aliased. At the end
// of load optimization their identity will be rolled back to Unknown to
// avoid treating them as Aliased at later stages without checking first
// as optimizations can potentially eliminate instructions leading to
// aliasing.
GrowableArray<Definition*> identity_rollback_;
};
static Definition* GetStoredValue(Instruction* instr) {
if (instr->IsStoreIndexed()) {
return instr->AsStoreIndexed()->value()->definition();
}
StoreInstanceFieldInstr* store_instance_field = instr->AsStoreInstanceField();
if (store_instance_field != NULL) {
return store_instance_field->value()->definition();
}
StoreStaticFieldInstr* store_static_field = instr->AsStoreStaticField();
if (store_static_field != NULL) {
return store_static_field->value()->definition();
}
UNREACHABLE(); // Should only be called for supported store instructions.
return NULL;
}
static bool IsPhiDependentPlace(Place* place) {
return ((place->kind() == Place::kField) ||
(place->kind() == Place::kVMField)) &&
(place->instance() != NULL) && place->instance()->IsPhi();
}
// For each place that depends on a phi ensure that equivalent places
// corresponding to phi input are numbered and record outgoing phi moves
// for each block which establish correspondence between phi dependent place
// and phi input's place that is flowing in.
static PhiPlaceMoves* ComputePhiMoves(
DirectChainedHashMap<PointerKeyValueTrait<Place> >* map,
ZoneGrowableArray<Place*>* places) {
Thread* thread = Thread::Current();
Zone* zone = thread->zone();
PhiPlaceMoves* phi_moves = new (zone) PhiPlaceMoves();
for (intptr_t i = 0; i < places->length(); i++) {
Place* place = (*places)[i];
if (IsPhiDependentPlace(place)) {
PhiInstr* phi = place->instance()->AsPhi();
BlockEntryInstr* block = phi->GetBlock();
if (FLAG_trace_optimization) {
THR_Print("phi dependent place %s\n", place->ToCString());
}
Place input_place(*place);
for (intptr_t j = 0; j < phi->InputCount(); j++) {
input_place.set_instance(phi->InputAt(j)->definition());
Place* result = map->LookupValue(&input_place);
if (result == NULL) {
result = Place::Wrap(zone, input_place, places->length());
map->Insert(result);
places->Add(result);
if (FLAG_trace_optimization) {
THR_Print(" adding place %s as %" Pd "\n", result->ToCString(),
result->id());
}
}
phi_moves->CreateOutgoingMove(zone, block->PredecessorAt(j),
result->id(), place->id());
}
}
}
return phi_moves;
}
enum CSEMode { kOptimizeLoads, kOptimizeStores };
static AliasedSet* NumberPlaces(
FlowGraph* graph,
DirectChainedHashMap<PointerKeyValueTrait<Place> >* map,
CSEMode mode) {
// Loads representing different expression ids will be collected and
// used to build per offset kill sets.
Zone* zone = graph->zone();
ZoneGrowableArray<Place*>* places = new (zone) ZoneGrowableArray<Place*>(10);
bool has_loads = false;
bool has_stores = false;
for (BlockIterator it = graph->reverse_postorder_iterator(); !it.Done();
it.Advance()) {
BlockEntryInstr* block = it.Current();
for (ForwardInstructionIterator instr_it(block); !instr_it.Done();
instr_it.Advance()) {
Instruction* instr = instr_it.Current();
Place place(instr, &has_loads, &has_stores);
if (place.kind() == Place::kNone) {
continue;
}
Place* result = map->LookupValue(&place);
if (result == NULL) {
result = Place::Wrap(zone, place, places->length());
map->Insert(result);
places->Add(result);
if (FLAG_trace_optimization) {
THR_Print("numbering %s as %" Pd "\n", result->ToCString(),
result->id());
}
}
instr->set_place_id(result->id());
}
}
if ((mode == kOptimizeLoads) && !has_loads) {
return NULL;
}
if ((mode == kOptimizeStores) && !has_stores) {
return NULL;
}
PhiPlaceMoves* phi_moves = ComputePhiMoves(map, places);
// Build aliasing sets mapping aliases to loads.
return new (zone) AliasedSet(zone, map, places, phi_moves);
}
// Load instructions handled by load elimination.
static bool IsLoadEliminationCandidate(Instruction* instr) {
return instr->IsLoadField() || instr->IsLoadIndexed() ||
instr->IsLoadStaticField();
}
static bool IsLoopInvariantLoad(ZoneGrowableArray<BitVector*>* sets,
intptr_t loop_header_index,
Instruction* instr) {
return IsLoadEliminationCandidate(instr) && (sets != NULL) &&
instr->HasPlaceId() && ((*sets)[loop_header_index] != NULL) &&
(*sets)[loop_header_index]->Contains(instr->place_id());
}
LICM::LICM(FlowGraph* flow_graph) : flow_graph_(flow_graph) {
ASSERT(flow_graph->is_licm_allowed());
}
void LICM::Hoist(ForwardInstructionIterator* it,
BlockEntryInstr* pre_header,
Instruction* current) {
if (current->IsCheckClass()) {
current->AsCheckClass()->set_licm_hoisted(true);
} else if (current->IsCheckSmi()) {
current->AsCheckSmi()->set_licm_hoisted(true);
} else if (current->IsCheckEitherNonSmi()) {
current->AsCheckEitherNonSmi()->set_licm_hoisted(true);
} else if (current->IsCheckArrayBound()) {
current->AsCheckArrayBound()->set_licm_hoisted(true);
} else if (current->IsTestCids()) {
current->AsTestCids()->set_licm_hoisted(true);
}
if (FLAG_trace_optimization) {
THR_Print("Hoisting instruction %s:%" Pd " from B%" Pd " to B%" Pd "\n",
current->DebugName(), current->GetDeoptId(),
current->GetBlock()->block_id(), pre_header->block_id());
}
// Move the instruction out of the loop.
current->RemoveEnvironment();
if (it != NULL) {
it->RemoveCurrentFromGraph();
} else {
current->RemoveFromGraph();
}
GotoInstr* last = pre_header->last_instruction()->AsGoto();
// Using kind kEffect will not assign a fresh ssa temporary index.
flow_graph()->InsertBefore(last, current, last->env(), FlowGraph::kEffect);
current->CopyDeoptIdFrom(*last);
}
void LICM::TrySpecializeSmiPhi(PhiInstr* phi,
BlockEntryInstr* header,
BlockEntryInstr* pre_header) {
if (phi->Type()->ToCid() == kSmiCid) {
return;
}
// Check if there is only a single kDynamicCid input to the phi that
// comes from the pre-header.
const intptr_t kNotFound = -1;
intptr_t non_smi_input = kNotFound;
for (intptr_t i = 0; i < phi->InputCount(); ++i) {
Value* input = phi->InputAt(i);
if (input->Type()->ToCid() != kSmiCid) {
if ((non_smi_input != kNotFound) ||
(input->Type()->ToCid() != kDynamicCid)) {
// There are multiple kDynamicCid inputs or there is an input that is
// known to be non-smi.
return;
} else {
non_smi_input = i;
}
}
}
if ((non_smi_input == kNotFound) ||
(phi->block()->PredecessorAt(non_smi_input) != pre_header)) {
return;
}
CheckSmiInstr* check = NULL;
for (Value* use = phi->input_use_list(); (use != NULL) && (check == NULL);
use = use->next_use()) {
check = use->instruction()->AsCheckSmi();
}
if (check == NULL) {
return;
}
// Host CheckSmi instruction and make this phi smi one.
Hoist(NULL, pre_header, check);
// Replace value we are checking with phi's input.
check->value()->BindTo(phi->InputAt(non_smi_input)->definition());
check->value()->SetReachingType(phi->InputAt(non_smi_input)->Type());
phi->UpdateType(CompileType::FromCid(kSmiCid));
}
void LICM::OptimisticallySpecializeSmiPhis() {
if (flow_graph()->function().ProhibitsHoistingCheckClass() ||
FLAG_precompiled_mode) {
// Do not hoist any: Either deoptimized on a hoisted check,
// or compiling precompiled code where we can't do optimistic
// hoisting of checks.
return;
}
const ZoneGrowableArray<BlockEntryInstr*>& loop_headers =
flow_graph()->LoopHeaders();
for (intptr_t i = 0; i < loop_headers.length(); ++i) {
JoinEntryInstr* header = loop_headers[i]->AsJoinEntry();
// Skip loop that don't have a pre-header block.
BlockEntryInstr* pre_header = header->ImmediateDominator();
if (pre_header == NULL) continue;
for (PhiIterator it(header); !it.Done(); it.Advance()) {
TrySpecializeSmiPhi(it.Current(), header, pre_header);
}
}
}
void LICM::Optimize() {
if (flow_graph()->function().ProhibitsHoistingCheckClass()) {
// Do not hoist any.
return;
}
const ZoneGrowableArray<BlockEntryInstr*>& loop_headers =
flow_graph()->LoopHeaders();
ZoneGrowableArray<BitVector*>* loop_invariant_loads =
flow_graph()->loop_invariant_loads();
for (intptr_t i = 0; i < loop_headers.length(); ++i) {
BlockEntryInstr* header = loop_headers[i];
// Skip loop that don't have a pre-header block.
BlockEntryInstr* pre_header = header->ImmediateDominator();
if (pre_header == NULL) continue;
for (BitVector::Iterator loop_it(header->loop_info()); !loop_it.Done();
loop_it.Advance()) {
BlockEntryInstr* block = flow_graph()->preorder()[loop_it.Current()];
for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
Instruction* current = it.Current();
// Treat loads of static final fields specially: we can CSE them but
// we should not move them around unless the field is initialized.
// Otherwise we might move load past the initialization.
if (LoadStaticFieldInstr* load = current->AsLoadStaticField()) {
if (load->AllowsCSE() && !load->IsFieldInitialized()) {
continue;
}
}
if ((current->AllowsCSE() ||
IsLoopInvariantLoad(loop_invariant_loads, i, current)) &&
!current->MayThrow()) {
bool inputs_loop_invariant = true;
for (int i = 0; i < current->InputCount(); ++i) {
Definition* input_def = current->InputAt(i)->definition();
if (!input_def->GetBlock()->Dominates(pre_header)) {
inputs_loop_invariant = false;
break;
}
}
if (inputs_loop_invariant) {
Hoist(&it, pre_header, current);
}
}
}
}
}
}
class LoadOptimizer : public ValueObject {
public:
LoadOptimizer(FlowGraph* graph, AliasedSet* aliased_set)
: graph_(graph),
aliased_set_(aliased_set),
in_(graph_->preorder().length()),
out_(graph_->preorder().length()),
gen_(graph_->preorder().length()),
kill_(graph_->preorder().length()),
exposed_values_(graph_->preorder().length()),
out_values_(graph_->preorder().length()),
phis_(5),
worklist_(5),
congruency_worklist_(6),
in_worklist_(NULL),
forwarded_(false) {
const intptr_t num_blocks = graph_->preorder().length();
for (intptr_t i = 0; i < num_blocks; i++) {
out_.Add(NULL);
gen_.Add(new (Z) BitVector(Z, aliased_set_->max_place_id()));
kill_.Add(new (Z) BitVector(Z, aliased_set_->max_place_id()));
in_.Add(new (Z) BitVector(Z, aliased_set_->max_place_id()));
exposed_values_.Add(NULL);
out_values_.Add(NULL);
}
}
~LoadOptimizer() { aliased_set_->RollbackAliasedIdentites(); }
Isolate* isolate() const { return graph_->isolate(); }
Zone* zone() const { return graph_->zone(); }
static bool OptimizeGraph(FlowGraph* graph) {
ASSERT(FLAG_load_cse);
// For now, bail out for large functions to avoid OOM situations.
// TODO(fschneider): Fix the memory consumption issue.
intptr_t function_length = graph->function().end_token_pos().Pos() -
graph->function().token_pos().Pos();
if (function_length >= FLAG_huge_method_cutoff_in_tokens) {
return false;
}
DirectChainedHashMap<PointerKeyValueTrait<Place> > map;
AliasedSet* aliased_set = NumberPlaces(graph, &map, kOptimizeLoads);
if ((aliased_set != NULL) && !aliased_set->IsEmpty()) {
// If any loads were forwarded return true from Optimize to run load
// forwarding again. This will allow to forward chains of loads.
// This is especially important for context variables as they are built
// as loads from loaded context.
// TODO(vegorov): renumber newly discovered congruences during the
// forwarding to forward chains without running whole pass twice.
LoadOptimizer load_optimizer(graph, aliased_set);
return load_optimizer.Optimize();
}
return false;
}
private:
bool Optimize() {
ComputeInitialSets();
ComputeOutSets();
ComputeOutValues();
if (graph_->is_licm_allowed()) {
MarkLoopInvariantLoads();
}
ForwardLoads();
EmitPhis();
return forwarded_;
}
// Compute sets of loads generated and killed by each block.
// Additionally compute upwards exposed and generated loads for each block.
// Exposed loads are those that can be replaced if a corresponding
// reaching load will be found.
// Loads that are locally redundant will be replaced as we go through
// instructions.
void ComputeInitialSets() {
for (BlockIterator block_it = graph_->reverse_postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
const intptr_t preorder_number = block->preorder_number();
BitVector* kill = kill_[preorder_number];
BitVector* gen = gen_[preorder_number];
ZoneGrowableArray<Definition*>* exposed_values = NULL;
ZoneGrowableArray<Definition*>* out_values = NULL;
for (ForwardInstructionIterator instr_it(block); !instr_it.Done();
instr_it.Advance()) {
Instruction* instr = instr_it.Current();
bool is_load = false, is_store = false;
Place place(instr, &is_load, &is_store);
BitVector* killed = NULL;
if (is_store) {
const intptr_t alias_id =
aliased_set_->LookupAliasId(place.ToAlias());
if (alias_id != AliasedSet::kNoAlias) {
killed = aliased_set_->GetKilledSet(alias_id);
} else if (!place.IsImmutableField()) {
// We encountered unknown alias: this means intrablock load
// forwarding refined parameter of this store, for example
//
// o <- alloc()
// a.f <- o
// u <- a.f
// u.x <- null ;; this store alias is *.x
//
// after intrablock load forwarding
//
// o <- alloc()
// a.f <- o
// o.x <- null ;; this store alias is o.x
//
// In this case we fallback to using place id recorded in the
// instruction that still points to the old place with a more
// generic alias.
const intptr_t old_alias_id = aliased_set_->LookupAliasId(
aliased_set_->places()[instr->place_id()]->ToAlias());
killed = aliased_set_->GetKilledSet(old_alias_id);
}
if (killed != NULL) {
kill->AddAll(killed);
// There is no need to clear out_values when clearing GEN set
// because only those values that are in the GEN set
// will ever be used.
gen->RemoveAll(killed);
}
// Only forward stores to normal arrays, float64, and simd arrays
// to loads because other array stores (intXX/uintXX/float32)
// may implicitly convert the value stored.
StoreIndexedInstr* array_store = instr->AsStoreIndexed();
if ((array_store == NULL) || (array_store->class_id() == kArrayCid) ||
(array_store->class_id() == kTypedDataFloat64ArrayCid) ||
(array_store->class_id() == kTypedDataFloat32ArrayCid) ||
(array_store->class_id() == kTypedDataFloat32x4ArrayCid)) {
Place* canonical_place = aliased_set_->LookupCanonical(&place);
if (canonical_place != NULL) {
// Store has a corresponding numbered place that might have a
// load. Try forwarding stored value to it.
gen->Add(canonical_place->id());
if (out_values == NULL) out_values = CreateBlockOutValues();
(*out_values)[canonical_place->id()] = GetStoredValue(instr);
}
}
ASSERT(!instr->IsDefinition() ||
!IsLoadEliminationCandidate(instr->AsDefinition()));
continue;
} else if (is_load) {
// Check if this load needs renumbering because of the intrablock
// load forwarding.
const Place* canonical = aliased_set_->LookupCanonical(&place);
if ((canonical != NULL) &&
(canonical->id() != instr->AsDefinition()->place_id())) {
instr->AsDefinition()->set_place_id(canonical->id());
}
}
// If instruction has effects then kill all loads affected.
if (instr->HasUnknownSideEffects()) {
kill->AddAll(aliased_set_->aliased_by_effects());
// There is no need to clear out_values when removing values from GEN
// set because only those values that are in the GEN set
// will ever be used.
gen->RemoveAll(aliased_set_->aliased_by_effects());
continue;
}
Definition* defn = instr->AsDefinition();
if (defn == NULL) {
continue;
}
// For object allocation forward initial values of the fields to
// subsequent loads. For skip final fields. Final fields are
// initialized in constructor that potentially can be not inlined into
// the function that we are currently optimizing. However at the same
// time we assume that values of the final fields can be forwarded
// across side-effects. If we add 'null' as known values for these
// fields here we will incorrectly propagate this null across
// constructor invocation.
AllocateObjectInstr* alloc = instr->AsAllocateObject();
if ((alloc != NULL)) {
for (Value* use = alloc->input_use_list(); use != NULL;
use = use->next_use()) {
// Look for all immediate loads from this object.
if (use->use_index() != 0) {
continue;
}
LoadFieldInstr* load = use->instruction()->AsLoadField();
if (load != NULL) {
// Found a load. Initialize current value of the field to null for
// normal fields, or with type arguments.
// Forward for all fields for non-escaping objects and only
// non-final fields and type arguments for escaping ones.
if (aliased_set_->CanBeAliased(alloc) &&
(load->field() != NULL) && load->field()->is_final()) {
continue;
}
Definition* forward_def = graph_->constant_null();
if (alloc->ArgumentCount() > 0) {
ASSERT(alloc->ArgumentCount() == 1);
intptr_t type_args_offset =
alloc->cls().type_arguments_field_offset();
if (load->offset_in_bytes() == type_args_offset) {
forward_def = alloc->PushArgumentAt(0)->value()->definition();
}
}
gen->Add(load->place_id());
if (out_values == NULL) out_values = CreateBlockOutValues();
(*out_values)[load->place_id()] = forward_def;
}
}
continue;
}
if (!IsLoadEliminationCandidate(defn)) {
continue;
}
const intptr_t place_id = defn->place_id();
if (gen->Contains(place_id)) {
// This is a locally redundant load.
ASSERT((out_values != NULL) && ((*out_values)[place_id] != NULL));
Definition* replacement = (*out_values)[place_id];
graph_->EnsureSSATempIndex(defn, replacement);
if (FLAG_trace_optimization) {
THR_Print("Replacing load v%" Pd " with v%" Pd "\n",
defn->ssa_temp_index(), replacement->ssa_temp_index());
}
defn->ReplaceUsesWith(replacement);
instr_it.RemoveCurrentFromGraph();
forwarded_ = true;
continue;
} else if (!kill->Contains(place_id)) {
// This is an exposed load: it is the first representative of a
// given expression id and it is not killed on the path from
// the block entry.
if (exposed_values == NULL) {
static const intptr_t kMaxExposedValuesInitialSize = 5;
exposed_values = new (Z) ZoneGrowableArray<Definition*>(
Utils::Minimum(kMaxExposedValuesInitialSize,
aliased_set_->max_place_id()));
}
exposed_values->Add(defn);
}
gen->Add(place_id);
if (out_values == NULL) out_values = CreateBlockOutValues();
(*out_values)[place_id] = defn;
}
exposed_values_[preorder_number] = exposed_values;
out_values_[preorder_number] = out_values;
}
}
static void PerformPhiMoves(PhiPlaceMoves::MovesList phi_moves,
BitVector* out,
BitVector* forwarded_loads) {
forwarded_loads->Clear();
for (intptr_t i = 0; i < phi_moves->length(); i++) {
const intptr_t from = (*phi_moves)[i].from();
const intptr_t to = (*phi_moves)[i].to();
if (from == to) continue;
if (out->Contains(from)) {
forwarded_loads->Add(to);
}
}
for (intptr_t i = 0; i < phi_moves->length(); i++) {
const intptr_t from = (*phi_moves)[i].from();
const intptr_t to = (*phi_moves)[i].to();
if (from == to) continue;
out->Remove(to);
}
out->AddAll(forwarded_loads);
}
// Compute OUT sets by propagating them iteratively until fix point
// is reached.
void ComputeOutSets() {
BitVector* temp = new (Z) BitVector(Z, aliased_set_->max_place_id());
BitVector* forwarded_loads =
new (Z) BitVector(Z, aliased_set_->max_place_id());
BitVector* temp_out = new (Z) BitVector(Z, aliased_set_->max_place_id());
bool changed = true;
while (changed) {
changed = false;
for (BlockIterator block_it = graph_->reverse_postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
const intptr_t preorder_number = block->preorder_number();
BitVector* block_in = in_[preorder_number];
BitVector* block_out = out_[preorder_number];
BitVector* block_kill = kill_[preorder_number];
BitVector* block_gen = gen_[preorder_number];
// Compute block_in as the intersection of all out(p) where p
// is a predecessor of the current block.
if (block->IsGraphEntry()) {
temp->Clear();
} else {
temp->SetAll();
ASSERT(block->PredecessorCount() > 0);
for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
BlockEntryInstr* pred = block->PredecessorAt(i);
BitVector* pred_out = out_[pred->preorder_number()];
if (pred_out == NULL) continue;
PhiPlaceMoves::MovesList phi_moves =
aliased_set_->phi_moves()->GetOutgoingMoves(pred);
if (phi_moves != NULL) {
// If there are phi moves, perform intersection with
// a copy of pred_out where the phi moves are applied.
temp_out->CopyFrom(pred_out);
PerformPhiMoves(phi_moves, temp_out, forwarded_loads);
pred_out = temp_out;
}
temp->Intersect(pred_out);
}
}
if (!temp->Equals(*block_in) || (block_out == NULL)) {
// If IN set has changed propagate the change to OUT set.
block_in->CopyFrom(temp);
temp->RemoveAll(block_kill);
temp->AddAll(block_gen);
if ((block_out == NULL) || !block_out->Equals(*temp)) {
if (block_out == NULL) {
block_out = out_[preorder_number] =
new (Z) BitVector(Z, aliased_set_->max_place_id());
}
block_out->CopyFrom(temp);
changed = true;
}
}
}
}
}
// Compute out_values mappings by propagating them in reverse postorder once
// through the graph. Generate phis on back edges where eager merge is
// impossible.
// No replacement is done at this point and thus any out_value[place_id] is
// changed at most once: from NULL to an actual value.
// When merging incoming loads we might need to create a phi.
// These phis are not inserted at the graph immediately because some of them
// might become redundant after load forwarding is done.
void ComputeOutValues() {
GrowableArray<PhiInstr*> pending_phis(5);
ZoneGrowableArray<Definition*>* temp_forwarded_values = NULL;
for (BlockIterator block_it = graph_->reverse_postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
const bool can_merge_eagerly = CanMergeEagerly(block);
const intptr_t preorder_number = block->preorder_number();
ZoneGrowableArray<Definition*>* block_out_values =
out_values_[preorder_number];
// If OUT set has changed then we have new values available out of
// the block. Compute these values creating phi where necessary.
for (BitVector::Iterator it(out_[preorder_number]); !it.Done();
it.Advance()) {
const intptr_t place_id = it.Current();
if (block_out_values == NULL) {
out_values_[preorder_number] = block_out_values =
CreateBlockOutValues();
}
if ((*block_out_values)[place_id] == NULL) {
ASSERT(block->PredecessorCount() > 0);
Definition* in_value =
can_merge_eagerly ? MergeIncomingValues(block, place_id) : NULL;
if ((in_value == NULL) &&
(in_[preorder_number]->Contains(place_id))) {
PhiInstr* phi = new (Z)
PhiInstr(block->AsJoinEntry(), block->PredecessorCount());
phi->set_place_id(place_id);
pending_phis.Add(phi);
in_value = phi;
}
(*block_out_values)[place_id] = in_value;
}
}
// If the block has outgoing phi moves perform them. Use temporary list
// of values to ensure that cyclic moves are performed correctly.
PhiPlaceMoves::MovesList phi_moves =
aliased_set_->phi_moves()->GetOutgoingMoves(block);
if ((phi_moves != NULL) && (block_out_values != NULL)) {
if (temp_forwarded_values == NULL) {
temp_forwarded_values = CreateBlockOutValues();
}
for (intptr_t i = 0; i < phi_moves->length(); i++) {
const intptr_t from = (*phi_moves)[i].from();
const intptr_t to = (*phi_moves)[i].to();
if (from == to) continue;
(*temp_forwarded_values)[to] = (*block_out_values)[from];
}
for (intptr_t i = 0; i < phi_moves->length(); i++) {
const intptr_t from = (*phi_moves)[i].from();
const intptr_t to = (*phi_moves)[i].to();
if (from == to) continue;
(*block_out_values)[to] = (*temp_forwarded_values)[to];
}
}
if (FLAG_trace_load_optimization) {
THR_Print("B%" Pd "\n", block->block_id());
THR_Print(" IN: ");
aliased_set_->PrintSet(in_[preorder_number]);
THR_Print("\n");
THR_Print(" KILL: ");
aliased_set_->PrintSet(kill_[preorder_number]);
THR_Print("\n");
THR_Print(" OUT: ");
aliased_set_->PrintSet(out_[preorder_number]);
THR_Print("\n");
}
}
// All blocks were visited. Fill pending phis with inputs
// that flow on back edges.
for (intptr_t i = 0; i < pending_phis.length(); i++) {
FillPhiInputs(pending_phis[i]);
}
}
bool CanMergeEagerly(BlockEntryInstr* block) {
for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
BlockEntryInstr* pred = block->PredecessorAt(i);
if (pred->postorder_number() < block->postorder_number()) {
return false;
}
}
return true;
}
void MarkLoopInvariantLoads() {
const ZoneGrowableArray<BlockEntryInstr*>& loop_headers =
graph_->LoopHeaders();
ZoneGrowableArray<BitVector*>* invariant_loads =
new (Z) ZoneGrowableArray<BitVector*>(loop_headers.length());
for (intptr_t i = 0; i < loop_headers.length(); i++) {
BlockEntryInstr* header = loop_headers[i];
BlockEntryInstr* pre_header = header->ImmediateDominator();
if (pre_header == NULL) {
invariant_loads->Add(NULL);
continue;
}
BitVector* loop_gen = new (Z) BitVector(Z, aliased_set_->max_place_id());
for (BitVector::Iterator loop_it(header->loop_info()); !loop_it.Done();
loop_it.Advance()) {
const intptr_t preorder_number = loop_it.Current();
loop_gen->AddAll(gen_[preorder_number]);
}
for (BitVector::Iterator loop_it(header->loop_info()); !loop_it.Done();
loop_it.Advance()) {
const intptr_t preorder_number = loop_it.Current();
loop_gen->RemoveAll(kill_[preorder_number]);
}
if (FLAG_trace_optimization) {
for (BitVector::Iterator it(loop_gen); !it.Done(); it.Advance()) {
THR_Print("place %s is loop invariant for B%" Pd "\n",
aliased_set_->places()[it.Current()]->ToCString(),
header->block_id());
}
}
invariant_loads->Add(loop_gen);
}
graph_->set_loop_invariant_loads(invariant_loads);
}
// Compute incoming value for the given expression id.
// Will create a phi if different values are incoming from multiple
// predecessors.
Definition* MergeIncomingValues(BlockEntryInstr* block, intptr_t place_id) {
// First check if the same value is coming in from all predecessors.
static Definition* const kDifferentValuesMarker =
reinterpret_cast<Definition*>(-1);
Definition* incoming = NULL;
for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
BlockEntryInstr* pred = block->PredecessorAt(i);
ZoneGrowableArray<Definition*>* pred_out_values =
out_values_[pred->preorder_number()];
if ((pred_out_values == NULL) || ((*pred_out_values)[place_id] == NULL)) {
return NULL;
} else if (incoming == NULL) {
incoming = (*pred_out_values)[place_id];
} else if (incoming != (*pred_out_values)[place_id]) {
incoming = kDifferentValuesMarker;
}
}
if (incoming != kDifferentValuesMarker) {
ASSERT(incoming != NULL);
return incoming;
}
// Incoming values are different. Phi is required to merge.
PhiInstr* phi =
new (Z) PhiInstr(block->AsJoinEntry(), block->PredecessorCount());
phi->set_place_id(place_id);
FillPhiInputs(phi);
return phi;
}
void FillPhiInputs(PhiInstr* phi) {
BlockEntryInstr* block = phi->GetBlock();
const intptr_t place_id = phi->place_id();
for (intptr_t i = 0; i < block->PredecessorCount(); i++) {
BlockEntryInstr* pred = block->PredecessorAt(i);
ZoneGrowableArray<Definition*>* pred_out_values =
out_values_[pred->preorder_number()];
ASSERT((*pred_out_values)[place_id] != NULL);
// Sets of outgoing values are not linked into use lists so
// they might contain values that were replaced and removed
// from the graph by this iteration.
// To prevent using them we additionally mark definitions themselves
// as replaced and store a pointer to the replacement.
Definition* replacement = (*pred_out_values)[place_id]->Replacement();
Value* input = new (Z) Value(replacement);
phi->SetInputAt(i, input);
replacement->AddInputUse(input);
}
graph_->AllocateSSAIndexes(phi);
phis_.Add(phi); // Postpone phi insertion until after load forwarding.
if (FLAG_support_il_printer && FLAG_trace_load_optimization) {
THR_Print("created pending phi %s for %s at B%" Pd "\n", phi->ToCString(),
aliased_set_->places()[place_id]->ToCString(),
block->block_id());
}
}
// Iterate over basic blocks and replace exposed loads with incoming
// values.
void ForwardLoads() {
for (BlockIterator block_it = graph_->reverse_postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
ZoneGrowableArray<Definition*>* loads =
exposed_values_[block->preorder_number()];
if (loads == NULL) continue; // No exposed loads.
BitVector* in = in_[block->preorder_number()];
for (intptr_t i = 0; i < loads->length(); i++) {
Definition* load = (*loads)[i];
if (!in->Contains(load->place_id())) continue; // No incoming value.
Definition* replacement = MergeIncomingValues(block, load->place_id());
ASSERT(replacement != NULL);
// Sets of outgoing values are not linked into use lists so
// they might contain values that were replace and removed
// from the graph by this iteration.
// To prevent using them we additionally mark definitions themselves
// as replaced and store a pointer to the replacement.
replacement = replacement->Replacement();
if (load != replacement) {
graph_->EnsureSSATempIndex(load, replacement);
if (FLAG_trace_optimization) {
THR_Print("Replacing load v%" Pd " with v%" Pd "\n",
load->ssa_temp_index(), replacement->ssa_temp_index());
}
load->ReplaceUsesWith(replacement);
load->RemoveFromGraph();
load->SetReplacement(replacement);
forwarded_ = true;
}
}
}
}
// Check if the given phi take the same value on all code paths.
// Eliminate it as redundant if this is the case.
// When analyzing phi operands assumes that only generated during
// this load phase can be redundant. They can be distinguished because
// they are not marked alive.
// TODO(vegorov): move this into a separate phase over all phis.
bool EliminateRedundantPhi(PhiInstr* phi) {
Definition* value = NULL; // Possible value of this phi.
worklist_.Clear();
if (in_worklist_ == NULL) {
in_worklist_ = new (Z) BitVector(Z, graph_->current_ssa_temp_index());
} else {
in_worklist_->Clear();
}
worklist_.Add(phi);
in_worklist_->Add(phi->ssa_temp_index());
for (intptr_t i = 0; i < worklist_.length(); i++) {
PhiInstr* phi = worklist_[i];
for (intptr_t i = 0; i < phi->InputCount(); i++) {
Definition* input = phi->InputAt(i)->definition();
if (input == phi) continue;
PhiInstr* phi_input = input->AsPhi();
if ((phi_input != NULL) && !phi_input->is_alive()) {
if (!in_worklist_->Contains(phi_input->ssa_temp_index())) {
worklist_.Add(phi_input);
in_worklist_->Add(phi_input->ssa_temp_index());
}
continue;
}
if (value == NULL) {
value = input;
} else if (value != input) {
return false; // This phi is not redundant.
}
}
}
// All phis in the worklist are redundant and have the same computed
// value on all code paths.
ASSERT(value != NULL);
for (intptr_t i = 0; i < worklist_.length(); i++) {
worklist_[i]->ReplaceUsesWith(value);
}
return true;
}
// Returns true if definitions are congruent assuming their inputs
// are congruent.
bool CanBeCongruent(Definition* a, Definition* b) {
return (a->tag() == b->tag()) &&
((a->IsPhi() && (a->GetBlock() == b->GetBlock())) ||
(a->AllowsCSE() && a->AttributesEqual(b)));
}
// Given two definitions check if they are congruent under assumption that
// their inputs will be proven congruent. If they are - add them to the
// worklist to check their inputs' congruency.
// Returns true if pair was added to the worklist or is already in the
// worklist and false if a and b are not congruent.
bool AddPairToCongruencyWorklist(Definition* a, Definition* b) {
if (!CanBeCongruent(a, b)) {
return false;
}
// If a is already in the worklist check if it is being compared to b.
// Give up if it is not.
if (in_worklist_->Contains(a->ssa_temp_index())) {
for (intptr_t i = 0; i < congruency_worklist_.length(); i += 2) {
if (a == congruency_worklist_[i]) {
return (b == congruency_worklist_[i + 1]);
}
}
UNREACHABLE();
} else if (in_worklist_->Contains(b->ssa_temp_index())) {
return AddPairToCongruencyWorklist(b, a);
}
congruency_worklist_.Add(a);
congruency_worklist_.Add(b);
in_worklist_->Add(a->ssa_temp_index());
return true;
}
bool AreInputsCongruent(Definition* a, Definition* b) {
ASSERT(a->tag() == b->tag());
ASSERT(a->InputCount() == b->InputCount());
for (intptr_t j = 0; j < a->InputCount(); j++) {
Definition* inputA = a->InputAt(j)->definition();
Definition* inputB = b->InputAt(j)->definition();
if (inputA != inputB) {
if (!AddPairToCongruencyWorklist(inputA, inputB)) {
return false;
}
}
}
return true;
}
// Returns true if instruction dom dominates instruction other.
static bool Dominates(Instruction* dom, Instruction* other) {
BlockEntryInstr* dom_block = dom->GetBlock();
BlockEntryInstr* other_block = other->GetBlock();
if (dom_block == other_block) {
for (Instruction* current = dom->next(); current != NULL;
current = current->next()) {
if (current == other) {
return true;
}
}
return false;
}
return dom_block->Dominates(other_block);
}
// Replace the given phi with another if they are congruent.
// Returns true if succeeds.
bool ReplacePhiWith(PhiInstr* phi, PhiInstr* replacement) {
ASSERT(phi->InputCount() == replacement->InputCount());
ASSERT(phi->block() == replacement->block());
congruency_worklist_.Clear();
if (in_worklist_ == NULL) {
in_worklist_ = new (Z) BitVector(Z, graph_->current_ssa_temp_index());
} else {
in_worklist_->Clear();
}
// During the comparison worklist contains pairs of definitions to be
// compared.
if (!AddPairToCongruencyWorklist(phi, replacement)) {
return false;
}
// Process the worklist. It might grow during each comparison step.
for (intptr_t i = 0; i < congruency_worklist_.length(); i += 2) {
if (!AreInputsCongruent(congruency_worklist_[i],
congruency_worklist_[i + 1])) {
return false;
}
}
// At this point worklist contains pairs of congruent definitions.
// Replace the one member of the pair with another maintaining proper
// domination relation between definitions and uses.
for (intptr_t i = 0; i < congruency_worklist_.length(); i += 2) {
Definition* a = congruency_worklist_[i];
Definition* b = congruency_worklist_[i + 1];
// If these definitions are not phis then we need to pick up one
// that dominates another as the replacement: if a dominates b swap them.
// Note: both a and b are used as a phi input at the same block B which
// means a dominates B and b dominates B, which guarantees that either
// a dominates b or b dominates a.
if (!a->IsPhi()) {
if (Dominates(a, b)) {
Definition* t = a;
a = b;
b = t;
}
ASSERT(Dominates(b, a));
}
if (FLAG_support_il_printer && FLAG_trace_load_optimization) {
THR_Print("Replacing %s with congruent %s\n", a->ToCString(),
b->ToCString());
}
a->ReplaceUsesWith(b);
if (a->IsPhi()) {
// We might be replacing a phi introduced by the load forwarding
// that is not inserted in the graph yet.
ASSERT(b->IsPhi());
PhiInstr* phi_a = a->AsPhi();
if (phi_a->is_alive()) {
phi_a->mark_dead();
phi_a->block()->RemovePhi(phi_a);
phi_a->UnuseAllInputs();
}
} else {
a->RemoveFromGraph();
}
}
return true;
}
// Insert the given phi into the graph. Attempt to find an equal one in the
// target block first.
// Returns true if the phi was inserted and false if it was replaced.
bool EmitPhi(PhiInstr* phi) {
for (PhiIterator it(phi->block()); !it.Done(); it.Advance()) {
if (ReplacePhiWith(phi, it.Current())) {
return false;
}
}
phi->mark_alive();
phi->block()->InsertPhi(phi);
return true;
}
// Phis have not yet been inserted into the graph but they have uses of
// their inputs. Insert the non-redundant ones and clear the input uses
// of the redundant ones.
void EmitPhis() {
// First eliminate all redundant phis.
for (intptr_t i = 0; i < phis_.length(); i++) {
PhiInstr* phi = phis_[i];
if (!phi->HasUses() || EliminateRedundantPhi(phi)) {
phi->UnuseAllInputs();
phis_[i] = NULL;
}
}
// Now emit phis or replace them with equal phis already present in the
// graph.
for (intptr_t i = 0; i < phis_.length(); i++) {
PhiInstr* phi = phis_[i];
if ((phi != NULL) && (!phi->HasUses() || !EmitPhi(phi))) {
phi->UnuseAllInputs();
}
}
}
ZoneGrowableArray<Definition*>* CreateBlockOutValues() {
ZoneGrowableArray<Definition*>* out =
new (Z) ZoneGrowableArray<Definition*>(aliased_set_->max_place_id());
for (intptr_t i = 0; i < aliased_set_->max_place_id(); i++) {
out->Add(NULL);
}
return out;
}
FlowGraph* graph_;
DirectChainedHashMap<PointerKeyValueTrait<Place> >* map_;
// Mapping between field offsets in words and expression ids of loads from
// that offset.
AliasedSet* aliased_set_;
// Per block sets of expression ids for loads that are: incoming (available
// on the entry), outgoing (available on the exit), generated and killed.
GrowableArray<BitVector*> in_;
GrowableArray<BitVector*> out_;
GrowableArray<BitVector*> gen_;
GrowableArray<BitVector*> kill_;
// Per block list of upwards exposed loads.
GrowableArray<ZoneGrowableArray<Definition*>*> exposed_values_;
// Per block mappings between expression ids and outgoing definitions that
// represent those ids.
GrowableArray<ZoneGrowableArray<Definition*>*> out_values_;
// List of phis generated during ComputeOutValues and ForwardLoads.
// Some of these phis might be redundant and thus a separate pass is
// needed to emit only non-redundant ones.
GrowableArray<PhiInstr*> phis_;
// Auxiliary worklist used by redundant phi elimination.
GrowableArray<PhiInstr*> worklist_;
GrowableArray<Definition*> congruency_worklist_;
BitVector* in_worklist_;
// True if any load was eliminated.
bool forwarded_;
DISALLOW_COPY_AND_ASSIGN(LoadOptimizer);
};
bool DominatorBasedCSE::Optimize(FlowGraph* graph) {
bool changed = false;
if (FLAG_load_cse) {
changed = LoadOptimizer::OptimizeGraph(graph) || changed;
}
CSEInstructionMap map;
changed = OptimizeRecursive(graph, graph->graph_entry(), &map) || changed;
return changed;
}
bool DominatorBasedCSE::OptimizeRecursive(FlowGraph* graph,
BlockEntryInstr* block,
CSEInstructionMap* map) {
bool changed = false;
for (ForwardInstructionIterator it(block); !it.Done(); it.Advance()) {
Instruction* current = it.Current();
if (current->AllowsCSE()) {
Instruction* replacement = map->Lookup(current);
if (replacement != NULL) {
// Replace current with lookup result.
ASSERT(replacement->AllowsCSE());
graph->ReplaceCurrentInstruction(&it, current, replacement);
changed = true;
continue;
}
map->Insert(current);
}
}
// Process children in the dominator tree recursively.
intptr_t num_children = block->dominated_blocks().length();
if (num_children != 0) {
graph->thread()->CheckForSafepoint();
}
for (intptr_t i = 0; i < num_children; ++i) {
BlockEntryInstr* child = block->dominated_blocks()[i];
if (i < num_children - 1) {
// Copy map.
CSEInstructionMap child_map(*map);
changed = OptimizeRecursive(graph, child, &child_map) || changed;
} else {
// Reuse map for the last child.
changed = OptimizeRecursive(graph, child, map) || changed;
}
}
return changed;
}
class StoreOptimizer : public LivenessAnalysis {
public:
StoreOptimizer(FlowGraph* graph,
AliasedSet* aliased_set,
DirectChainedHashMap<PointerKeyValueTrait<Place> >* map)
: LivenessAnalysis(aliased_set->max_place_id(), graph->postorder()),
graph_(graph),
map_(map),
aliased_set_(aliased_set),
exposed_stores_(graph_->postorder().length()) {
const intptr_t num_blocks = graph_->postorder().length();
for (intptr_t i = 0; i < num_blocks; i++) {
exposed_stores_.Add(NULL);
}
}
static void OptimizeGraph(FlowGraph* graph) {
ASSERT(FLAG_load_cse);
// For now, bail out for large functions to avoid OOM situations.
// TODO(fschneider): Fix the memory consumption issue.
intptr_t function_length = graph->function().end_token_pos().Pos() -
graph->function().token_pos().Pos();
if (function_length >= FLAG_huge_method_cutoff_in_tokens) {
return;
}
DirectChainedHashMap<PointerKeyValueTrait<Place> > map;
AliasedSet* aliased_set = NumberPlaces(graph, &map, kOptimizeStores);
if ((aliased_set != NULL) && !aliased_set->IsEmpty()) {
StoreOptimizer store_optimizer(graph, aliased_set, &map);
store_optimizer.Optimize();
}
}
private:
void Optimize() {
Analyze();
if (FLAG_trace_load_optimization) {
Dump();
}
EliminateDeadStores();
}
bool CanEliminateStore(Instruction* instr) {
switch (instr->tag()) {
case Instruction::kStoreInstanceField: {
StoreInstanceFieldInstr* store_instance = instr->AsStoreInstanceField();
// Can't eliminate stores that initialize fields.
return !store_instance->is_initialization();
}
case Instruction::kStoreIndexed:
case Instruction::kStoreStaticField:
return true;
default:
UNREACHABLE();
return false;
}
}
virtual void ComputeInitialSets() {
Zone* zone = graph_->zone();
BitVector* all_places =
new (zone) BitVector(zone, aliased_set_->max_place_id());
all_places->SetAll();
for (BlockIterator block_it = graph_->postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
const intptr_t postorder_number = block->postorder_number();
BitVector* kill = kill_[postorder_number];
BitVector* live_in = live_in_[postorder_number];
BitVector* live_out = live_out_[postorder_number];
ZoneGrowableArray<Instruction*>* exposed_stores = NULL;
// Iterate backwards starting at the last instruction.
for (BackwardInstructionIterator instr_it(block); !instr_it.Done();
instr_it.Advance()) {
Instruction* instr = instr_it.Current();
bool is_load = false;
bool is_store = false;
Place place(instr, &is_load, &is_store);
if (place.IsImmutableField()) {
// Loads/stores of final fields do not participate.
continue;
}
// Handle stores.
if (is_store) {
if (kill->Contains(instr->place_id())) {
if (!live_in->Contains(instr->place_id()) &&
CanEliminateStore(instr)) {
if (FLAG_trace_optimization) {
THR_Print("Removing dead store to place %" Pd " in block B%" Pd
"\n",
instr->place_id(), block->block_id());
}
instr_it.RemoveCurrentFromGraph();
}
} else if (!live_in->Contains(instr->place_id())) {
// Mark this store as down-ward exposed: They are the only
// candidates for the global store elimination.
if (exposed_stores == NULL) {
const intptr_t kMaxExposedStoresInitialSize = 5;
exposed_stores = new (zone) ZoneGrowableArray<Instruction*>(
Utils::Minimum(kMaxExposedStoresInitialSize,
aliased_set_->max_place_id()));
}
exposed_stores->Add(instr);
}
// Interfering stores kill only loads from the same place.
kill->Add(instr->place_id());
live_in->Remove(instr->place_id());
continue;
}
// Handle side effects, deoptimization and function return.
if (instr->HasUnknownSideEffects() || instr->CanDeoptimize() ||
instr->MayThrow() || instr->IsReturn()) {
// Instructions that return from the function, instructions with side
// effects and instructions that can deoptimize are considered as
// loads from all places.
live_in->CopyFrom(all_places);
if (instr->IsThrow() || instr->IsReThrow() || instr->IsReturn()) {
// Initialize live-out for exit blocks since it won't be computed
// otherwise during the fixed point iteration.
live_out->CopyFrom(all_places);
}
continue;
}
// Handle loads.
Definition* defn = instr->AsDefinition();
if ((defn != NULL) && IsLoadEliminationCandidate(defn)) {
const intptr_t alias = aliased_set_->LookupAliasId(place.ToAlias());
live_in->AddAll(aliased_set_->GetKilledSet(alias));
continue;
}
}
exposed_stores_[postorder_number] = exposed_stores;
}
if (FLAG_trace_load_optimization) {
Dump();
THR_Print("---\n");
}
}
void EliminateDeadStores() {
// Iteration order does not matter here.
for (BlockIterator block_it = graph_->postorder_iterator();
!block_it.Done(); block_it.Advance()) {
BlockEntryInstr* block = block_it.Current();
const intptr_t postorder_number = block->postorder_number();
BitVector* live_out = live_out_[postorder_number];
ZoneGrowableArray<Instruction*>* exposed_stores =
exposed_stores_[postorder_number];
if (exposed_stores == NULL) continue; // No exposed stores.
// Iterate over candidate stores.
for (intptr_t i = 0; i < exposed_stores->length(); ++i) {
Instruction* instr = (*exposed_stores)[i];
bool is_load = false;
bool is_store = false;
Place place(instr, &is_load, &is_store);
ASSERT(!is_load && is_store);
if (place.IsImmutableField()) {
// Final field do not participate in dead store elimination.
continue;
}
// Eliminate a downward exposed store if the corresponding place is not
// in live-out.
if (!live_out->Contains(instr->place_id()) &&
CanEliminateStore(instr)) {
if (FLAG_trace_optimization) {
THR_Print("Removing dead store to place %" Pd " block B%" Pd "\n",
instr->place_id(), block->block_id());
}
instr->RemoveFromGraph(/* ignored */ false);
}
}
}
}
FlowGraph* graph_;
DirectChainedHashMap<PointerKeyValueTrait<Place> >* map_;
// Mapping between field offsets in words and expression ids of loads from
// that offset.
AliasedSet* aliased_set_;
// Per block list of downward exposed stores.
GrowableArray<ZoneGrowableArray<Instruction*>*> exposed_stores_;
DISALLOW_COPY_AND_ASSIGN(StoreOptimizer);
};
void DeadStoreElimination::Optimize(FlowGraph* graph) {
if (FLAG_dead_store_elimination) {
StoreOptimizer::OptimizeGraph(graph);
}
}
enum SafeUseCheck { kOptimisticCheck, kStrictCheck };