diff options
Diffstat (limited to 'compiler/optimizing/nodes.h')
| -rw-r--r-- | compiler/optimizing/nodes.h | 153 |
1 files changed, 151 insertions, 2 deletions
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 { |