diff options
Diffstat (limited to 'compiler/optimizing')
| -rw-r--r-- | compiler/optimizing/code_generator_arm.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_arm64.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_arm_vixl.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_mips.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_mips64.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_x86.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_x86_64.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/graph_checker.cc | 7 | ||||
| -rw-r--r-- | compiler/optimizing/inliner.cc | 9 | ||||
| -rw-r--r-- | compiler/optimizing/instruction_builder.cc | 27 | ||||
| -rw-r--r-- | compiler/optimizing/instruction_builder.h | 6 | ||||
| -rw-r--r-- | compiler/optimizing/load_store_elimination.cc | 10 | ||||
| -rw-r--r-- | compiler/optimizing/nodes.cc | 84 | ||||
| -rw-r--r-- | compiler/optimizing/nodes.h | 153 | ||||
| -rw-r--r-- | compiler/optimizing/prepare_for_register_allocation.cc | 7 | ||||
| -rw-r--r-- | compiler/optimizing/prepare_for_register_allocation.h | 1 |
16 files changed, 358 insertions, 9 deletions
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc index d7cc577580..ebd578c5cd 100644 --- a/compiler/optimizing/code_generator_arm.cc +++ b/compiler/optimizing/code_generator_arm.cc @@ -3067,6 +3067,15 @@ void InstructionCodeGeneratorARM::VisitDoubleConstant(HDoubleConstant* constant // Will be generated at use site. } +void LocationsBuilderARM::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorARM::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + codegen_->GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderARM::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc index eee832a732..78b627ad90 100644 --- a/compiler/optimizing/code_generator_arm64.cc +++ b/compiler/optimizing/code_generator_arm64.cc @@ -5479,6 +5479,15 @@ void InstructionCodeGeneratorARM64::VisitRem(HRem* rem) { } } +void LocationsBuilderARM64::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorARM64::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + codegen_->GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderARM64::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc index b6678b03ef..8744cc8210 100644 --- a/compiler/optimizing/code_generator_arm_vixl.cc +++ b/compiler/optimizing/code_generator_arm_vixl.cc @@ -3103,6 +3103,15 @@ void InstructionCodeGeneratorARMVIXL::VisitDoubleConstant( // Will be generated at use site. } +void LocationsBuilderARMVIXL::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorARMVIXL::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + codegen_->GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderARMVIXL::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_mips.cc b/compiler/optimizing/code_generator_mips.cc index aa030b279c..9736626b70 100644 --- a/compiler/optimizing/code_generator_mips.cc +++ b/compiler/optimizing/code_generator_mips.cc @@ -7766,6 +7766,15 @@ void InstructionCodeGeneratorMIPS::VisitRem(HRem* instruction) { } } +void LocationsBuilderMIPS::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorMIPS::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderMIPS::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_mips64.cc b/compiler/optimizing/code_generator_mips64.cc index 19250c64e3..6f37ed44c4 100644 --- a/compiler/optimizing/code_generator_mips64.cc +++ b/compiler/optimizing/code_generator_mips64.cc @@ -5653,6 +5653,15 @@ void InstructionCodeGeneratorMIPS64::VisitRem(HRem* instruction) { } } +void LocationsBuilderMIPS64::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorMIPS64::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderMIPS64::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc index 08a752f1d2..1e867dde51 100644 --- a/compiler/optimizing/code_generator_x86.cc +++ b/compiler/optimizing/code_generator_x86.cc @@ -2057,6 +2057,15 @@ void InstructionCodeGeneratorX86::VisitDoubleConstant(HDoubleConstant* constant // Will be generated at use site. } +void LocationsBuilderX86::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorX86::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + codegen_->GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderX86::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/code_generator_x86_64.cc b/compiler/optimizing/code_generator_x86_64.cc index ff6e099d12..f413739a68 100644 --- a/compiler/optimizing/code_generator_x86_64.cc +++ b/compiler/optimizing/code_generator_x86_64.cc @@ -2165,6 +2165,15 @@ void InstructionCodeGeneratorX86_64::VisitDoubleConstant( // Will be generated at use site. } +void LocationsBuilderX86_64::VisitConstructorFence(HConstructorFence* constructor_fence) { + constructor_fence->SetLocations(nullptr); +} + +void InstructionCodeGeneratorX86_64::VisitConstructorFence( + HConstructorFence* constructor_fence ATTRIBUTE_UNUSED) { + codegen_->GenerateMemoryBarrier(MemBarrierKind::kStoreStore); +} + void LocationsBuilderX86_64::VisitMemoryBarrier(HMemoryBarrier* memory_barrier) { memory_barrier->SetLocations(nullptr); } diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc index 12340b416d..6a140458a6 100644 --- a/compiler/optimizing/graph_checker.cc +++ b/compiler/optimizing/graph_checker.cc @@ -341,7 +341,12 @@ void GraphChecker::VisitInstruction(HInstruction* instruction) { const HInstructionList& list = input->IsPhi() ? input->GetBlock()->GetPhis() : input->GetBlock()->GetInstructions(); - if (!list.Contains(input)) { + if (input->GetBlock() == nullptr) { + AddError(StringPrintf("Input %d of instruction %d is not in any " + "basic block of the control-flow graph.", + input->GetId(), + instruction->GetId())); + } else if (!list.Contains(input)) { AddError(StringPrintf("Input %d of instruction %d is not defined " "in a basic block of the control-flow graph.", input->GetId(), diff --git a/compiler/optimizing/inliner.cc b/compiler/optimizing/inliner.cc index 1f8a58cdaa..d71d7863ce 100644 --- a/compiler/optimizing/inliner.cc +++ b/compiler/optimizing/inliner.cc @@ -1462,8 +1462,13 @@ bool HInliner::TryPatternSubstitution(HInvoke* invoke_instruction, } } if (needs_constructor_barrier) { - HMemoryBarrier* barrier = new (graph_->GetArena()) HMemoryBarrier(kStoreStore, kNoDexPc); - invoke_instruction->GetBlock()->InsertInstructionBefore(barrier, invoke_instruction); + // See CompilerDriver::RequiresConstructorBarrier for more details. + DCHECK(obj != nullptr) << "only non-static methods can have a constructor fence"; + + HConstructorFence* constructor_fence = + new (graph_->GetArena()) HConstructorFence(obj, kNoDexPc, graph_->GetArena()); + invoke_instruction->GetBlock()->InsertInstructionBefore(constructor_fence, + invoke_instruction); } *return_replacement = nullptr; break; diff --git a/compiler/optimizing/instruction_builder.cc b/compiler/optimizing/instruction_builder.cc index 978c6a2d71..8b79da8c73 100644 --- a/compiler/optimizing/instruction_builder.cc +++ b/compiler/optimizing/instruction_builder.cc @@ -451,10 +451,13 @@ void HInstructionBuilder::InitializeParameters() { referrer_method_id.class_idx_, parameter_index++, Primitive::kPrimNot, - true); + /* is_this */ true); AppendInstruction(parameter); UpdateLocal(locals_index++, parameter); number_of_parameters--; + current_this_parameter_ = parameter; + } else { + DCHECK(current_this_parameter_ == nullptr); } const DexFile::ProtoId& proto = dex_file_->GetMethodPrototype(referrer_method_id); @@ -465,7 +468,7 @@ void HInstructionBuilder::InitializeParameters() { arg_types->GetTypeItem(shorty_pos - 1).type_idx_, parameter_index++, Primitive::GetType(shorty[shorty_pos]), - false); + /* is_this */ false); ++shorty_pos; AppendInstruction(parameter); // Store the parameter value in the local that the dex code will use @@ -588,6 +591,8 @@ void HInstructionBuilder::Binop_22b(const Instruction& instruction, bool reverse UpdateLocal(instruction.VRegA(), current_block_->GetLastInstruction()); } +// Does the method being compiled need any constructor barriers being inserted? +// (Always 'false' for methods that aren't <init>.) static bool RequiresConstructorBarrier(const DexCompilationUnit* cu, CompilerDriver* driver) { // Can be null in unit tests only. if (UNLIKELY(cu == nullptr)) { @@ -596,6 +601,11 @@ static bool RequiresConstructorBarrier(const DexCompilationUnit* cu, CompilerDri Thread* self = Thread::Current(); return cu->IsConstructor() + && !cu->IsStatic() + // RequiresConstructorBarrier must only be queried for <init> methods; + // it's effectively "false" for every other method. + // + // See CompilerDriver::RequiresConstructBarrier for more explanation. && driver->RequiresConstructorBarrier(self, cu->GetDexFile(), cu->GetClassDefIndex()); } @@ -639,13 +649,24 @@ void HInstructionBuilder::BuildReturn(const Instruction& instruction, Primitive::Type type, uint32_t dex_pc) { if (type == Primitive::kPrimVoid) { + // Only <init> (which is a return-void) could possibly have a constructor fence. // This may insert additional redundant constructor fences from the super constructors. // TODO: remove redundant constructor fences (b/36656456). if (RequiresConstructorBarrier(dex_compilation_unit_, compiler_driver_)) { - AppendInstruction(new (arena_) HMemoryBarrier(kStoreStore, dex_pc)); + // Compiling instance constructor. + if (kIsDebugBuild) { + std::string method_name = graph_->GetMethodName(); + CHECK_EQ(std::string("<init>"), method_name); + } + + HInstruction* fence_target = current_this_parameter_; + DCHECK(fence_target != nullptr); + + AppendInstruction(new (arena_) HConstructorFence(fence_target, dex_pc, arena_)); } AppendInstruction(new (arena_) HReturnVoid(dex_pc)); } else { + DCHECK(!RequiresConstructorBarrier(dex_compilation_unit_, compiler_driver_)); HInstruction* value = LoadLocal(instruction.VRegA(), type); AppendInstruction(new (arena_) HReturn(value, dex_pc)); } diff --git a/compiler/optimizing/instruction_builder.h b/compiler/optimizing/instruction_builder.h index 7fdc1883ca..2fb5c7b94d 100644 --- a/compiler/optimizing/instruction_builder.h +++ b/compiler/optimizing/instruction_builder.h @@ -62,6 +62,7 @@ class HInstructionBuilder : public ValueObject { current_block_(nullptr), current_locals_(nullptr), latest_result_(nullptr), + current_this_parameter_(nullptr), compiler_driver_(driver), code_generator_(code_generator), dex_compilation_unit_(dex_compilation_unit), @@ -325,6 +326,11 @@ class HInstructionBuilder : public ValueObject { HBasicBlock* current_block_; ArenaVector<HInstruction*>* current_locals_; HInstruction* latest_result_; + // Current "this" parameter. + // Valid only after InitializeParameters() finishes. + // * Null for static methods. + // * Non-null for instance methods. + HParameterValue* current_this_parameter_; CompilerDriver* const compiler_driver_; diff --git a/compiler/optimizing/load_store_elimination.cc b/compiler/optimizing/load_store_elimination.cc index 48699b33ae..8d8cc93b9b 100644 --- a/compiler/optimizing/load_store_elimination.cc +++ b/compiler/optimizing/load_store_elimination.cc @@ -566,14 +566,22 @@ class LSEVisitor : public HGraphVisitor { store->GetBlock()->RemoveInstruction(store); } - // Eliminate allocations that are not used. + // Eliminate singleton-classified instructions: + // * - Constructor fences (they never escape this thread). + // * - Allocations (if they are unused). for (HInstruction* new_instance : singleton_new_instances_) { + HConstructorFence::RemoveConstructorFences(new_instance); + if (!new_instance->HasNonEnvironmentUses()) { new_instance->RemoveEnvironmentUsers(); new_instance->GetBlock()->RemoveInstruction(new_instance); } } for (HInstruction* new_array : singleton_new_arrays_) { + // TODO: Delete constructor fences for new-array + // In the future HNewArray instructions will have HConstructorFence's for them. + // HConstructorFence::RemoveConstructorFences(new_array); + if (!new_array->HasNonEnvironmentUses()) { new_array->RemoveEnvironmentUsers(); new_array->GetBlock()->RemoveInstruction(new_array); diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc index ca953a1a7e..f250c1a10b 100644 --- a/compiler/optimizing/nodes.cc +++ b/compiler/optimizing/nodes.cc @@ -528,6 +528,15 @@ HCurrentMethod* HGraph::GetCurrentMethod() { return cached_current_method_; } +const char* HGraph::GetMethodName() const { + const DexFile::MethodId& method_id = dex_file_.GetMethodId(method_idx_); + return dex_file_.GetMethodName(method_id); +} + +std::string HGraph::PrettyMethod(bool with_signature) const { + return dex_file_.PrettyMethod(method_idx_, with_signature); +} + HConstant* HGraph::GetConstant(Primitive::Type type, int64_t value, uint32_t dex_pc) { switch (type) { case Primitive::Type::kPrimBoolean: @@ -1150,6 +1159,81 @@ void HVariableInputSizeInstruction::RemoveInputAt(size_t index) { } } +void HVariableInputSizeInstruction::RemoveAllInputs() { + RemoveAsUserOfAllInputs(); + DCHECK(!HasNonEnvironmentUses()); + + inputs_.clear(); + DCHECK_EQ(0u, InputCount()); +} + +void HConstructorFence::RemoveConstructorFences(HInstruction* instruction) { + DCHECK(instruction->GetBlock() != nullptr); + // Removing constructor fences only makes sense for instructions with an object return type. + DCHECK_EQ(Primitive::kPrimNot, instruction->GetType()); + + // Efficient implementation that simultaneously (in one pass): + // * Scans the uses list for all constructor fences. + // * Deletes that constructor fence from the uses list of `instruction`. + // * Deletes `instruction` from the constructor fence's inputs. + // * Deletes the constructor fence if it now has 0 inputs. + + const HUseList<HInstruction*>& uses = instruction->GetUses(); + // Warning: Although this is "const", we might mutate the list when calling RemoveInputAt. + for (auto it = uses.begin(), end = uses.end(); it != end; ) { + const HUseListNode<HInstruction*>& use_node = *it; + HInstruction* const use_instruction = use_node.GetUser(); + + // Advance the iterator immediately once we fetch the use_node. + // Warning: If the input is removed, the current iterator becomes invalid. + ++it; + + if (use_instruction->IsConstructorFence()) { + HConstructorFence* ctor_fence = use_instruction->AsConstructorFence(); + size_t input_index = use_node.GetIndex(); + + // Process the candidate instruction for removal + // from the graph. + + // Constructor fence instructions are never + // used by other instructions. + // + // If we wanted to make this more generic, it + // could be a runtime if statement. + DCHECK(!ctor_fence->HasUses()); + + // A constructor fence's return type is "kPrimVoid" + // and therefore it can't have any environment uses. + DCHECK(!ctor_fence->HasEnvironmentUses()); + + // Remove the inputs first, otherwise removing the instruction + // will try to remove its uses while we are already removing uses + // and this operation will fail. + DCHECK_EQ(instruction, ctor_fence->InputAt(input_index)); + + // Removing the input will also remove the `use_node`. + // (Do not look at `use_node` after this, it will be a dangling reference). + ctor_fence->RemoveInputAt(input_index); + + // Once all inputs are removed, the fence is considered dead and + // is removed. + if (ctor_fence->InputCount() == 0u) { + ctor_fence->GetBlock()->RemoveInstruction(ctor_fence); + } + } + } + + if (kIsDebugBuild) { + // Post-condition checks: + // * None of the uses of `instruction` are a constructor fence. + // * The `instruction` itself did not get removed from a block. + for (const HUseListNode<HInstruction*>& use_node : instruction->GetUses()) { + CHECK(!use_node.GetUser()->IsConstructorFence()); + } + CHECK(instruction->GetBlock() != nullptr); + } +} + #define DEFINE_ACCEPT(name, super) \ void H##name::Accept(HGraphVisitor* visitor) { \ visitor->Visit##name(this); \ diff --git a/compiler/optimizing/nodes.h b/compiler/optimizing/nodes.h index 36c7df70ce..e40361eb5d 100644 --- a/compiler/optimizing/nodes.h +++ b/compiler/optimizing/nodes.h @@ -46,6 +46,7 @@ namespace art { class GraphChecker; class HBasicBlock; +class HConstructorFence; class HCurrentMethod; class HDoubleConstant; class HEnvironment; @@ -57,6 +58,7 @@ class HIntConstant; class HInvoke; class HLongConstant; class HNullConstant; +class HParameterValue; class HPhi; class HSuspendCheck; class HTryBoundary; @@ -537,6 +539,12 @@ class HGraph : public ArenaObject<kArenaAllocGraph> { return method_idx_; } + // Get the method name (without the signature), e.g. "<init>" + const char* GetMethodName() const; + + // Get the pretty method name (class + name + optionally signature). + std::string PrettyMethod(bool with_signature = true) const; + InvokeType GetInvokeType() const { return invoke_type_; } @@ -1297,6 +1305,7 @@ class HLoopInformationOutwardIterator : public ValueObject { M(ClearException, Instruction) \ M(ClinitCheck, Instruction) \ M(Compare, BinaryOperation) \ + M(ConstructorFence, Instruction) \ M(CurrentMethod, Instruction) \ M(ShouldDeoptimizeFlag, Instruction) \ M(Deoptimize, Instruction) \ @@ -1476,8 +1485,11 @@ FOR_EACH_INSTRUCTION(FORWARD_DECLARATION) template <typename T> class HUseListNode : public ArenaObject<kArenaAllocUseListNode> { public: + // Get the instruction which has this use as one of the inputs. T GetUser() const { return user_; } + // Get the position of the input record that this use corresponds to. size_t GetIndex() const { return index_; } + // Set the position of the input record that this use corresponds to. void SetIndex(size_t index) { index_ = index; } // Hook for the IntrusiveForwardList<>. @@ -2037,7 +2049,8 @@ class HInstruction : public ArenaObject<kArenaAllocInstruction> { !IsNativeDebugInfo() && !IsParameterValue() && // If we added an explicit barrier then we should keep it. - !IsMemoryBarrier(); + !IsMemoryBarrier() && + !IsConstructorFence(); } bool IsDeadAndRemovable() const { @@ -2431,6 +2444,11 @@ class HVariableInputSizeInstruction : public HInstruction { void InsertInputAt(size_t index, HInstruction* input); void RemoveInputAt(size_t index); + // Removes all the inputs. + // Also removes this instructions from each input's use list + // (for non-environment uses only). + void RemoveAllInputs(); + protected: HVariableInputSizeInstruction(SideEffects side_effects, uint32_t dex_pc, @@ -5069,7 +5087,7 @@ class HParameterValue FINAL : public HExpression<0> { const DexFile& GetDexFile() const { return dex_file_; } dex::TypeIndex GetTypeIndex() const { return type_index_; } uint8_t GetIndex() const { return index_; } - bool IsThis() const ATTRIBUTE_UNUSED { return GetPackedFlag<kFlagIsThis>(); } + bool IsThis() const { return GetPackedFlag<kFlagIsThis>(); } bool CanBeNull() const OVERRIDE { return GetPackedFlag<kFlagCanBeNull>(); } void SetCanBeNull(bool can_be_null) { SetPackedFlag<kFlagCanBeNull>(can_be_null); } @@ -6507,6 +6525,137 @@ class HMemoryBarrier FINAL : public HTemplateInstruction<0> { DISALLOW_COPY_AND_ASSIGN(HMemoryBarrier); }; +// A constructor fence orders all prior stores to fields that could be accessed via a final field of +// the specified object(s), with respect to any subsequent store that might "publish" +// (i.e. make visible) the specified object to another thread. +// +// JLS 17.5.1 "Semantics of final fields" states that a freeze action happens +// for all final fields (that were set) at the end of the invoked constructor. +// +// The constructor fence models the freeze actions for the final fields of an object +// being constructed (semantically at the end of the constructor). Constructor fences +// have a per-object affinity; two separate objects being constructed get two separate +// constructor fences. +// +// (Note: that if calling a super-constructor or forwarding to another constructor, +// the freezes would happen at the end of *that* constructor being invoked). +// +// The memory model guarantees that when the object being constructed is "published" after +// constructor completion (i.e. escapes the current thread via a store), then any final field +// writes must be observable on other threads (once they observe that publication). +// +// Further, anything written before the freeze, and read by dereferencing through the final field, +// must also be visible (so final object field could itself have an object with non-final fields; +// yet the freeze must also extend to them). +// +// Constructor example: +// +// class HasFinal { +// final int field; Optimizing IR for <init>()V: +// HasFinal() { +// field = 123; HInstanceFieldSet(this, HasFinal.field, 123) +// // freeze(this.field); HConstructorFence(this) +// } HReturn +// } +// +// HConstructorFence can serve double duty as a fence for new-instance/new-array allocations of +// already-initialized classes; in that case the allocation must act as a "default-initializer" +// of the object which effectively writes the class pointer "final field". +// +// For example, we can model default-initialiation as roughly the equivalent of the following: +// +// class Object { +// private final Class header; +// } +// +// Java code: Optimizing IR: +// +// T new_instance<T>() { +// Object obj = allocate_memory(T.class.size); obj = HInvoke(art_quick_alloc_object, T) +// obj.header = T.class; // header write is done by above call. +// // freeze(obj.header) HConstructorFence(obj) +// return (T)obj; +// } +// +// See also: +// * CompilerDriver::RequiresConstructorBarrier +// * QuasiAtomic::ThreadFenceForConstructor +// +class HConstructorFence FINAL : public HVariableInputSizeInstruction { + // A fence has variable inputs because the inputs can be removed + // after prepare_for_register_allocation phase. + // (TODO: In the future a fence could freeze multiple objects + // after merging two fences together.) + public: + // `fence_object` is the reference that needs to be protected for correct publication. + // + // It makes sense in the following situations: + // * <init> constructors, it's the "this" parameter (i.e. HParameterValue, s.t. IsThis() == true). + // * new-instance-like instructions, it's the return value (i.e. HNewInstance). + // + // After construction the `fence_object` becomes the 0th input. + // This is not an input in a real sense, but just a convenient place to stash the information + // about the associated object. + HConstructorFence(HInstruction* fence_object, + uint32_t dex_pc, + ArenaAllocator* arena) + // We strongly suspect there is not a more accurate way to describe the fine-grained reordering + // constraints described in the class header. We claim that these SideEffects constraints + // enforce a superset of the real constraints. + // + // The ordering described above is conservatively modeled with SideEffects as follows: + // + // * To prevent reordering of the publication stores: + // ----> "Reads of objects" is the initial SideEffect. + // * For every primitive final field store in the constructor: + // ----> Union that field's type as a read (e.g. "Read of T") into the SideEffect. + // * If there are any stores to reference final fields in the constructor: + // ----> Use a more conservative "AllReads" SideEffect because any stores to any references + // that are reachable from `fence_object` also need to be prevented for reordering + // (and we do not want to do alias analysis to figure out what those stores are). + // + // In the implementation, this initially starts out as an "all reads" side effect; this is an + // even more conservative approach than the one described above, and prevents all of the + // above reordering without analyzing any of the instructions in the constructor. + // + // If in a later phase we discover that there are no writes to reference final fields, + // we can refine the side effect to a smaller set of type reads (see above constraints). + : HVariableInputSizeInstruction(SideEffects::AllReads(), + dex_pc, + arena, + /* number_of_inputs */ 1, + kArenaAllocConstructorFenceInputs) { + DCHECK(fence_object != nullptr); + SetRawInputAt(0, fence_object); + } + + // The object associated with this constructor fence. + // + // (Note: This will be null after the prepare_for_register_allocation phase, + // as all constructor fence inputs are removed there). + HInstruction* GetFenceObject() const { + return InputAt(0); + } + + // Find all the HConstructorFence uses (`fence_use`) for `this` and: + // - Delete `fence_use` from `this`'s use list. + // - Delete `this` from `fence_use`'s inputs list. + // - If the `fence_use` is dead, remove it from the graph. + // + // A fence is considered dead once it no longer has any uses + // and all of the inputs are dead. + // + // This must *not* be called during/after prepare_for_register_allocation, + // because that removes all the inputs to the fences but the fence is actually + // still considered live. + static void RemoveConstructorFences(HInstruction* instruction); + + DECLARE_INSTRUCTION(ConstructorFence); + + private: + DISALLOW_COPY_AND_ASSIGN(HConstructorFence); +}; + class HMonitorOperation FINAL : public HTemplateInstruction<1> { public: enum class OperationKind { diff --git a/compiler/optimizing/prepare_for_register_allocation.cc b/compiler/optimizing/prepare_for_register_allocation.cc index 66bfea9860..c3c141bff7 100644 --- a/compiler/optimizing/prepare_for_register_allocation.cc +++ b/compiler/optimizing/prepare_for_register_allocation.cc @@ -167,6 +167,13 @@ void PrepareForRegisterAllocation::VisitCondition(HCondition* condition) { } } +void PrepareForRegisterAllocation::VisitConstructorFence(HConstructorFence* constructor_fence) { + // Delete all the inputs to the constructor fence; + // they aren't used by the InstructionCodeGenerator and this lets us avoid creating a + // LocationSummary in the LocationsBuilder. + constructor_fence->RemoveAllInputs(); +} + void PrepareForRegisterAllocation::VisitInvokeStaticOrDirect(HInvokeStaticOrDirect* invoke) { if (invoke->IsStaticWithExplicitClinitCheck()) { HLoadClass* last_input = invoke->GetInputs().back()->AsLoadClass(); diff --git a/compiler/optimizing/prepare_for_register_allocation.h b/compiler/optimizing/prepare_for_register_allocation.h index 7ffbe44ef6..395d4ba2ee 100644 --- a/compiler/optimizing/prepare_for_register_allocation.h +++ b/compiler/optimizing/prepare_for_register_allocation.h @@ -43,6 +43,7 @@ class PrepareForRegisterAllocation : public HGraphDelegateVisitor { void VisitArraySet(HArraySet* instruction) OVERRIDE; void VisitClinitCheck(HClinitCheck* check) OVERRIDE; void VisitCondition(HCondition* condition) OVERRIDE; + void VisitConstructorFence(HConstructorFence* constructor_fence) OVERRIDE; void VisitInvokeStaticOrDirect(HInvokeStaticOrDirect* invoke) OVERRIDE; void VisitDeoptimize(HDeoptimize* deoptimize) OVERRIDE; |