diff options
| -rw-r--r-- | compiler/optimizing/code_generator_arm.cc | 475 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_arm64.cc | 484 | ||||
| -rw-r--r-- | compiler/optimizing/code_generator_arm_vixl.cc | 472 |
3 files changed, 1012 insertions, 419 deletions
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc index 710ca7ad45..2560c9fedd 100644 --- a/compiler/optimizing/code_generator_arm.cc +++ b/compiler/optimizing/code_generator_arm.cc @@ -636,10 +636,75 @@ class ArraySetSlowPathARM : public SlowPathCodeARM { DISALLOW_COPY_AND_ASSIGN(ArraySetSlowPathARM); }; +// Abstract base class for read barrier slow paths marking a reference +// `ref`. +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class ReadBarrierMarkSlowPathBaseARM : public SlowPathCodeARM { + protected: + ReadBarrierMarkSlowPathBaseARM(HInstruction* instruction, Location ref, Location entrypoint) + : SlowPathCodeARM(instruction), ref_(ref), entrypoint_(entrypoint) { + DCHECK(kEmitCompilerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARM"; } + + // Generate assembly code calling the read barrier marking runtime + // entry point (ReadBarrierMarkRegX). + void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) { + Register ref_reg = ref_.AsRegister<Register>(); + + // No need to save live registers; it's taken care of by the + // entrypoint. Also, there is no need to update the stack mask, + // as this runtime call will not trigger a garbage collection. + CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen); + DCHECK_NE(ref_reg, SP); + DCHECK_NE(ref_reg, LR); + DCHECK_NE(ref_reg, PC); + // IP is used internally by the ReadBarrierMarkRegX entry point + // as a temporary, it cannot be the entry point's input/output. + DCHECK_NE(ref_reg, IP); + DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg; + // "Compact" slow path, saving two moves. + // + // Instead of using the standard runtime calling convention (input + // and output in R0): + // + // R0 <- ref + // R0 <- ReadBarrierMark(R0) + // ref <- R0 + // + // we just use rX (the register containing `ref`) as input and output + // of a dedicated entrypoint: + // + // rX <- ReadBarrierMarkRegX(rX) + // + if (entrypoint_.IsValid()) { + arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); + __ blx(entrypoint_.AsRegister<Register>()); + } else { + // Entrypoint is not already loaded, load from the thread. + int32_t entry_point_offset = + CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg); + // This runtime call does not require a stack map. + arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); + } + } + + // The location (register) of the marked object reference. + const Location ref_; + + // The location of the entrypoint if it is already loaded. + const Location entrypoint_; + + private: + DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARM); +}; + // Slow path marking an object reference `ref` during a read // barrier. The field `obj.field` in the object `obj` holding this -// reference does not get updated by this slow path after marking (see -// ReadBarrierMarkAndUpdateFieldSlowPathARM below for that). +// reference does not get updated by this slow path after marking. // // This means that after the execution of this slow path, `ref` will // always be up-to-date, but `obj.field` may not; i.e., after the @@ -651,12 +716,12 @@ class ArraySetSlowPathARM : public SlowPathCodeARM { // If `entrypoint` is a valid location it is assumed to already be // holding the entrypoint. The case where the entrypoint is passed in // is when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM { +class ReadBarrierMarkSlowPathARM : public ReadBarrierMarkSlowPathBaseARM { public: ReadBarrierMarkSlowPathARM(HInstruction* instruction, Location ref, Location entrypoint = Location::NoLocation()) - : SlowPathCodeARM(instruction), ref_(ref), entrypoint_(entrypoint) { + : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint) { DCHECK(kEmitCompilerReadBarrier); } @@ -664,15 +729,77 @@ class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM { void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { LocationSummary* locations = instruction_->GetLocations(); + DCHECK(locations->CanCall()); + if (kIsDebugBuild) { + Register ref_reg = ref_.AsRegister<Register>(); + DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg; + } + DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString()) + << "Unexpected instruction in read barrier marking slow path: " + << instruction_->DebugName(); + + __ Bind(GetEntryLabel()); + GenerateReadBarrierMarkRuntimeCall(codegen); + __ b(GetExitLabel()); + } + + private: + DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM); +}; + +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). The field `obj.field` in the object `obj` holding +// this reference does not get updated by this slow path after marking +// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM +// below for that). +// +// This means that after the execution of this slow path, `ref` will +// always be up-to-date, but `obj.field` may not; i.e., after the +// flip, `ref` will be a to-space reference, but `obj.field` will +// probably still be a from-space reference (unless it gets updated by +// another thread, or if another thread installed another object +// reference (different from `ref`) in `obj.field`). +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierSlowPathARM : public ReadBarrierMarkSlowPathBaseARM { + public: + LoadReferenceWithBakerReadBarrierSlowPathARM(HInstruction* instruction, + Location ref, + Register obj, + uint32_t offset, + Location index, + ScaleFactor scale_factor, + bool needs_null_check, + Register temp, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint), + obj_(obj), + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), + temp_(temp) { + DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { + return "LoadReferenceWithBakerReadBarrierSlowPathARM"; + } + + void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { + LocationSummary* locations = instruction_->GetLocations(); Register ref_reg = ref_.AsRegister<Register>(); DCHECK(locations->CanCall()); DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg; + DCHECK_NE(ref_reg, temp_); DCHECK(instruction_->IsInstanceFieldGet() || instruction_->IsStaticFieldGet() || instruction_->IsArrayGet() || instruction_->IsArraySet() || - instruction_->IsLoadClass() || - instruction_->IsLoadString() || instruction_->IsInstanceOf() || instruction_->IsCheckCast() || (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) || @@ -686,158 +813,202 @@ class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM { instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress())); __ Bind(GetEntryLabel()); - // No need to save live registers; it's taken care of by the - // entrypoint. Also, there is no need to update the stack mask, - // as this runtime call will not trigger a garbage collection. - CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen); - DCHECK_NE(ref_reg, SP); - DCHECK_NE(ref_reg, LR); - DCHECK_NE(ref_reg, PC); - // IP is used internally by the ReadBarrierMarkRegX entry point - // as a temporary, it cannot be the entry point's input/output. - DCHECK_NE(ref_reg, IP); - DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg; - // "Compact" slow path, saving two moves. - // - // Instead of using the standard runtime calling convention (input - // and output in R0): + + // When using MaybeGenerateReadBarrierSlow, the read barrier call is + // inserted after the original load. However, in fast path based + // Baker's read barriers, we need to perform the load of + // mirror::Object::monitor_ *before* the original reference load. + // This load-load ordering is required by the read barrier. + // The fast path/slow path (for Baker's algorithm) should look like: // - // R0 <- ref - // R0 <- ReadBarrierMark(R0) - // ref <- R0 + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = entrypoint(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } // - // we just use rX (the register containing `ref`) as input and output - // of a dedicated entrypoint: + // Note: the original implementation in ReadBarrier::Barrier is + // slightly more complex as it performs additional checks that we do + // not do here for performance reasons. + + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + __ LoadFromOffset(kLoadWord, temp_, obj_, monitor_offset); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including the rb_state, + // which shall prevent load-load reordering without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp`. + __ add(obj_, obj_, ShifterOperand(temp_, LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen); + arm_codegen->GenerateRawReferenceLoad( + instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false); + + // Mark the object `ref` when `obj` is gray. // - // rX <- ReadBarrierMarkRegX(rX) + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); // - if (entrypoint_.IsValid()) { - arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); - __ blx(entrypoint_.AsRegister<Register>()); - } else { - // Entrypoint is not already loaded, load from the thread. - int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg); - // This runtime call does not require a stack map. - arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); - } + // Given the numeric representation, it's enough to check the low bit of the + // rb_state. We do that by shifting the bit out of the lock word with LSRS + // which can be a 16-bit instruction unlike the TST immediate. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Lsrs(temp_, temp_, LockWord::kReadBarrierStateShift + 1); + __ b(GetExitLabel(), CC); // Carry flag is the last bit shifted out by LSRS. + GenerateReadBarrierMarkRuntimeCall(codegen); + __ b(GetExitLabel()); } private: - // The location (register) of the marked object reference. - const Location ref_; - - // The location of the entrypoint if already loaded. - const Location entrypoint_; - - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM); + // The register containing the object holding the marked object reference field. + Register obj_; + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + ScaleFactor scale_factor_; + // Is a null check required? + bool needs_null_check_; + // A temporary register used to hold the lock word of `obj_`. + Register temp_; + + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARM); }; -// Slow path marking an object reference `ref` during a read barrier, -// and if needed, atomically updating the field `obj.field` in the -// object `obj` holding this reference after marking (contrary to -// ReadBarrierMarkSlowPathARM above, which never tries to update -// `obj.field`). +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). If needed, this slow path also atomically updates +// the field `obj.field` in the object `obj` holding this reference +// after marking (contrary to +// LoadReferenceWithBakerReadBarrierSlowPathARM above, which never +// tries to update `obj.field`). // // This means that after the execution of this slow path, both `ref` // and `obj.field` will be up-to-date; i.e., after the flip, both will // hold the same to-space reference (unless another thread installed // another object reference (different from `ref`) in `obj.field`). // -// If `entrypoint` is a valid location it is assumed to already be -// holding the entrypoint. The case where the entrypoint is passed in -// is when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkAndUpdateFieldSlowPathARM : public SlowPathCodeARM { +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM + : public ReadBarrierMarkSlowPathBaseARM { public: - ReadBarrierMarkAndUpdateFieldSlowPathARM(HInstruction* instruction, - Location ref, - Register obj, - Location field_offset, - Register temp1, - Register temp2, - Location entrypoint = Location::NoLocation()) - : SlowPathCodeARM(instruction), - ref_(ref), + LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM(HInstruction* instruction, + Location ref, + Register obj, + uint32_t offset, + Location index, + ScaleFactor scale_factor, + bool needs_null_check, + Register temp1, + Register temp2, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARM(instruction, ref, entrypoint), obj_(obj), - field_offset_(field_offset), + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), temp1_(temp1), - temp2_(temp2), - entrypoint_(entrypoint) { + temp2_(temp2) { DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); } - const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkAndUpdateFieldSlowPathARM"; } + const char* GetDescription() const OVERRIDE { + return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM"; + } void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { LocationSummary* locations = instruction_->GetLocations(); Register ref_reg = ref_.AsRegister<Register>(); DCHECK(locations->CanCall()); DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg)) << ref_reg; - // This slow path is only used by the UnsafeCASObject intrinsic. + DCHECK_NE(ref_reg, temp1_); + + // This slow path is only used by the UnsafeCASObject intrinsic at the moment. DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified())) << "Unexpected instruction in read barrier marking and field updating slow path: " << instruction_->DebugName(); DCHECK(instruction_->GetLocations()->Intrinsified()); DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject); - DCHECK(field_offset_.IsRegisterPair()) << field_offset_; + DCHECK_EQ(offset_, 0u); + DCHECK_EQ(scale_factor_, ScaleFactor::TIMES_1); + // The location of the offset of the marked reference field within `obj_`. + Location field_offset = index_; + DCHECK(field_offset.IsRegisterPair()) << field_offset; __ Bind(GetEntryLabel()); - // Save the old reference. + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + __ LoadFromOffset(kLoadWord, temp1_, obj_, monitor_offset); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including the rb_state, + // which shall prevent load-load reordering without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp1`. + __ add(obj_, obj_, ShifterOperand(temp1_, LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen); + arm_codegen->GenerateRawReferenceLoad( + instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false); + + // Mark the object `ref` when `obj` is gray. + // + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); + // + // Given the numeric representation, it's enough to check the low bit of the + // rb_state. We do that by shifting the bit out of the lock word with LSRS + // which can be a 16-bit instruction unlike the TST immediate. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Lsrs(temp1_, temp1_, LockWord::kReadBarrierStateShift + 1); + __ b(GetExitLabel(), CC); // Carry flag is the last bit shifted out by LSRS. + + // Save the old value of the reference before marking it. // Note that we cannot use IP to save the old reference, as IP is // used internally by the ReadBarrierMarkRegX entry point, and we // need the old reference after the call to that entry point. DCHECK_NE(temp1_, IP); __ Mov(temp1_, ref_reg); - // No need to save live registers; it's taken care of by the - // entrypoint. Also, there is no need to update the stack mask, - // as this runtime call will not trigger a garbage collection. - CodeGeneratorARM* arm_codegen = down_cast<CodeGeneratorARM*>(codegen); - DCHECK_NE(ref_reg, SP); - DCHECK_NE(ref_reg, LR); - DCHECK_NE(ref_reg, PC); - // IP is used internally by the ReadBarrierMarkRegX entry point - // as a temporary, it cannot be the entry point's input/output. - DCHECK_NE(ref_reg, IP); - DCHECK(0 <= ref_reg && ref_reg < kNumberOfCoreRegisters) << ref_reg; - // "Compact" slow path, saving two moves. - // - // Instead of using the standard runtime calling convention (input - // and output in R0): - // - // R0 <- ref - // R0 <- ReadBarrierMark(R0) - // ref <- R0 - // - // we just use rX (the register containing `ref`) as input and output - // of a dedicated entrypoint: - // - // rX <- ReadBarrierMarkRegX(rX) - // - if (entrypoint_.IsValid()) { - arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); - __ blx(entrypoint_.AsRegister<Register>()); - } else { - // Entrypoint is not already loaded, load from the thread. - int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg); - // This runtime call does not require a stack map. - arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); - } + GenerateReadBarrierMarkRuntimeCall(codegen); // If the new reference is different from the old reference, - // update the field in the holder (`*(obj_ + field_offset_)`). + // update the field in the holder (`*(obj_ + field_offset)`). // // Note that this field could also hold a different object, if // another thread had concurrently changed it. In that case, the // LDREX/SUBS/ITNE sequence of instructions in the compare-and-set // (CAS) operation below would abort the CAS, leaving the field // as-is. - Label done; __ cmp(temp1_, ShifterOperand(ref_reg)); - __ b(&done, EQ); + __ b(GetExitLabel(), EQ); // Update the the holder's field atomically. This may fail if // mutator updates before us, but it's OK. This is achieved @@ -850,7 +1021,7 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARM : public SlowPathCodeARM { // The UnsafeCASObject intrinsic uses a register pair as field // offset ("long offset"), of which only the low part contains // data. - Register offset = field_offset_.AsRegisterPairLow<Register>(); + Register offset = field_offset.AsRegisterPairLow<Register>(); Register expected = temp1_; Register value = ref_reg; Register tmp_ptr = IP; // Pointer to actual memory. @@ -900,25 +1071,27 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARM : public SlowPathCodeARM { } } - __ Bind(&done); __ b(GetExitLabel()); } private: - // The location (register) of the marked object reference. - const Location ref_; // The register containing the object holding the marked object reference field. const Register obj_; - // The location of the offset of the marked reference field within `obj_`. - Location field_offset_; - + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + ScaleFactor scale_factor_; + // Is a null check required? + bool needs_null_check_; + // A temporary register used to hold the lock word of `obj_`; and + // also to hold the original reference value, when the reference is + // marked. const Register temp1_; + // A temporary register used in the implementation of the CAS, to + // update the object's reference field. const Register temp2_; - // The location of the entrypoint if already loaded. - const Location entrypoint_; - - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARM); + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM); }; // Slow path generating a read barrier for a heap reference. @@ -7310,13 +7483,11 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i DCHECK(kEmitCompilerReadBarrier); DCHECK(kUseBakerReadBarrier); - // After loading the reference from `obj.field` into `ref`, query - // `art::Thread::Current()->GetIsGcMarking()` to decide whether we - // need to enter the slow path to mark the reference. This - // optimistic strategy (we expect the GC to not be marking most of - // the time) does not check `obj`'s lock word (to see if it is a - // gray object or not), so may sometimes mark an already marked - // object. + // Query `art::Thread::Current()->GetIsGcMarking()` to decide + // whether we need to enter the slow path to mark the reference. + // Then, in the slow path, check the gray bit in the lock word of + // the reference's holder (`obj`) to decide whether to mark `ref` or + // not. // // Note that we do not actually check the value of `GetIsGcMarking()`; // instead, we load into `temp3` the read barrier mark entry point @@ -7324,14 +7495,19 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i // that `GetIsGcMarking()` is false, and vice versa. // // temp3 = Thread::Current()->pReadBarrierMarkReg ## root.reg() - // HeapReference<mirror::Object> ref = *src; // Original reference load. // if (temp3 != nullptr) { // <=> Thread::Current()->GetIsGcMarking() // // Slow path. - // ref = temp3(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = temp3(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } + // } else { + // HeapReference<mirror::Object> ref = *src; // Original reference load. // } - // TODO: This temp register is only necessary when - // `always_update_field` is true; make it optional (like `temp2`). Register temp_reg = temp.AsRegister<Register>(); // Slow path marking the object `ref` when the GC is marking. The @@ -7340,18 +7516,37 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i SlowPathCodeARM* slow_path; if (always_update_field) { DCHECK(temp2 != nullptr); - // ReadBarrierMarkAndUpdateFieldSlowPathARM only supports address - // of the form `obj + field_offset`, where `obj` is a register and - // `field_offset` is a register pair (of which only the lower half - // is used). Thus `offset` and `scale_factor` above are expected - // to be null in this code path. + // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM only + // supports address of the form `obj + field_offset`, where `obj` + // is a register and `field_offset` is a register pair (of which + // only the lower half is used). Thus `offset` and `scale_factor` + // above are expected to be null in this code path. DCHECK_EQ(offset, 0u); DCHECK_EQ(scale_factor, ScaleFactor::TIMES_1); - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARM( - instruction, ref, obj, /* field_offset */ index, temp_reg, *temp2, /* entrypoint */ temp3); + Location field_offset = index; + slow_path = + new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM( + instruction, + ref, + obj, + offset, + /* index */ field_offset, + scale_factor, + needs_null_check, + temp_reg, + *temp2, + /* entrypoint */ temp3); } else { - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM( - instruction, ref, /* entrypoint */ temp3); + slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARM( + instruction, + ref, + obj, + offset, + index, + scale_factor, + needs_null_check, + temp_reg, + /* entrypoint */ temp3); } AddSlowPath(slow_path); @@ -7361,11 +7556,11 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i // Loading the entrypoint does not require a load acquire since it is only changed when // threads are suspended or running a checkpoint. __ LoadFromOffset(kLoadWord, temp3.AsRegister<Register>(), TR, entry_point_offset); - // The reference load. - GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check); // The entrypoint is null when the GC is not marking, this prevents one load compared to // checking GetIsGcMarking. __ CompareAndBranchIfNonZero(temp3.AsRegister<Register>(), slow_path->GetEntryLabel()); + // Fast path: just load the reference. + GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check); __ Bind(slow_path->GetExitLabel()); } diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc index 5bdaac2e4a..7b6c97cd23 100644 --- a/compiler/optimizing/code_generator_arm64.cc +++ b/compiler/optimizing/code_generator_arm64.cc @@ -633,10 +633,73 @@ void JumpTableARM64::EmitTable(CodeGeneratorARM64* codegen) { } } +// Abstract base class for read barrier slow paths marking a reference +// `ref`. +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class ReadBarrierMarkSlowPathBaseARM64 : public SlowPathCodeARM64 { + protected: + ReadBarrierMarkSlowPathBaseARM64(HInstruction* instruction, Location ref, Location entrypoint) + : SlowPathCodeARM64(instruction), ref_(ref), entrypoint_(entrypoint) { + DCHECK(kEmitCompilerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARM64"; } + + // Generate assembly code calling the read barrier marking runtime + // entry point (ReadBarrierMarkRegX). + void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) { + // No need to save live registers; it's taken care of by the + // entrypoint. Also, there is no need to update the stack mask, + // as this runtime call will not trigger a garbage collection. + CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen); + DCHECK_NE(ref_.reg(), LR); + DCHECK_NE(ref_.reg(), WSP); + DCHECK_NE(ref_.reg(), WZR); + // IP0 is used internally by the ReadBarrierMarkRegX entry point + // as a temporary, it cannot be the entry point's input/output. + DCHECK_NE(ref_.reg(), IP0); + DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg(); + // "Compact" slow path, saving two moves. + // + // Instead of using the standard runtime calling convention (input + // and output in W0): + // + // W0 <- ref + // W0 <- ReadBarrierMark(W0) + // ref <- W0 + // + // we just use rX (the register containing `ref`) as input and output + // of a dedicated entrypoint: + // + // rX <- ReadBarrierMarkRegX(rX) + // + if (entrypoint_.IsValid()) { + arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); + __ Blr(XRegisterFrom(entrypoint_)); + } else { + // Entrypoint is not already loaded, load from the thread. + int32_t entry_point_offset = + CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg()); + // This runtime call does not require a stack map. + arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); + } + } + + // The location (register) of the marked object reference. + const Location ref_; + + // The location of the entrypoint if it is already loaded. + const Location entrypoint_; + + private: + DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARM64); +}; + // Slow path marking an object reference `ref` during a read // barrier. The field `obj.field` in the object `obj` holding this -// reference does not get updated by this slow path after marking (see -// ReadBarrierMarkAndUpdateFieldSlowPathARM64 below for that). +// reference does not get updated by this slow path after marking. // // This means that after the execution of this slow path, `ref` will // always be up-to-date, but `obj.field` may not; i.e., after the @@ -648,14 +711,12 @@ void JumpTableARM64::EmitTable(CodeGeneratorARM64* codegen) { // If `entrypoint` is a valid location it is assumed to already be // holding the entrypoint. The case where the entrypoint is passed in // is when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkSlowPathARM64 : public SlowPathCodeARM64 { +class ReadBarrierMarkSlowPathARM64 : public ReadBarrierMarkSlowPathBaseARM64 { public: ReadBarrierMarkSlowPathARM64(HInstruction* instruction, Location ref, Location entrypoint = Location::NoLocation()) - : SlowPathCodeARM64(instruction), - ref_(ref), - entrypoint_(entrypoint) { + : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint) { DCHECK(kEmitCompilerReadBarrier); } @@ -666,12 +727,75 @@ class ReadBarrierMarkSlowPathARM64 : public SlowPathCodeARM64 { DCHECK(locations->CanCall()); DCHECK(ref_.IsRegister()) << ref_; DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg(); + DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString()) + << "Unexpected instruction in read barrier marking slow path: " + << instruction_->DebugName(); + + __ Bind(GetEntryLabel()); + GenerateReadBarrierMarkRuntimeCall(codegen); + __ B(GetExitLabel()); + } + + private: + DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM64); +}; + +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). The field `obj.field` in the object `obj` holding +// this reference does not get updated by this slow path after marking +// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64 +// below for that). +// +// This means that after the execution of this slow path, `ref` will +// always be up-to-date, but `obj.field` may not; i.e., after the +// flip, `ref` will be a to-space reference, but `obj.field` will +// probably still be a from-space reference (unless it gets updated by +// another thread, or if another thread installed another object +// reference (different from `ref`) in `obj.field`). +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierSlowPathARM64 : public ReadBarrierMarkSlowPathBaseARM64 { + public: + LoadReferenceWithBakerReadBarrierSlowPathARM64(HInstruction* instruction, + Location ref, + Register obj, + uint32_t offset, + Location index, + size_t scale_factor, + bool needs_null_check, + bool use_load_acquire, + Register temp, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint), + obj_(obj), + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), + use_load_acquire_(use_load_acquire), + temp_(temp) { + DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { + return "LoadReferenceWithBakerReadBarrierSlowPathARM64"; + } + + void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { + LocationSummary* locations = instruction_->GetLocations(); + DCHECK(locations->CanCall()); + DCHECK(ref_.IsRegister()) << ref_; + DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg(); + DCHECK(obj_.IsW()); + DCHECK_NE(ref_.reg(), LocationFrom(temp_).reg()); DCHECK(instruction_->IsInstanceFieldGet() || instruction_->IsStaticFieldGet() || instruction_->IsArrayGet() || instruction_->IsArraySet() || - instruction_->IsLoadClass() || - instruction_->IsLoadString() || instruction_->IsInstanceOf() || instruction_->IsCheckCast() || (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) || @@ -685,87 +809,129 @@ class ReadBarrierMarkSlowPathARM64 : public SlowPathCodeARM64 { instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress())); __ Bind(GetEntryLabel()); - // No need to save live registers; it's taken care of by the - // entrypoint. Also, there is no need to update the stack mask, - // as this runtime call will not trigger a garbage collection. - CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen); - DCHECK_NE(ref_.reg(), LR); - DCHECK_NE(ref_.reg(), WSP); - DCHECK_NE(ref_.reg(), WZR); - // IP0 is used internally by the ReadBarrierMarkRegX entry point - // as a temporary, it cannot be the entry point's input/output. - DCHECK_NE(ref_.reg(), IP0); - DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg(); - // "Compact" slow path, saving two moves. - // - // Instead of using the standard runtime calling convention (input - // and output in W0): + + // When using MaybeGenerateReadBarrierSlow, the read barrier call is + // inserted after the original load. However, in fast path based + // Baker's read barriers, we need to perform the load of + // mirror::Object::monitor_ *before* the original reference load. + // This load-load ordering is required by the read barrier. + // The fast path/slow path (for Baker's algorithm) should look like: // - // W0 <- ref - // W0 <- ReadBarrierMark(W0) - // ref <- W0 + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = entrypoint(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } // - // we just use rX (the register containing `ref`) as input and output - // of a dedicated entrypoint: + // Note: the original implementation in ReadBarrier::Barrier is + // slightly more complex as it performs additional checks that we do + // not do here for performance reasons. + + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + __ Ldr(temp_, HeapOperand(obj_, monitor_offset)); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including rb_state, + // to prevent load-load reordering, and without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp`. + __ Add(obj_.X(), obj_.X(), Operand(temp_.X(), LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen); + arm64_codegen->GenerateRawReferenceLoad(instruction_, + ref_, + obj_, + offset_, + index_, + scale_factor_, + /* needs_null_check */ false, + use_load_acquire_); + + // Mark the object `ref` when `obj` is gray. // - // rX <- ReadBarrierMarkRegX(rX) + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); // - if (entrypoint_.IsValid()) { - arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); - __ Blr(XRegisterFrom(entrypoint_)); - } else { - // Entrypoint is not already loaded, load from the thread. - int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg()); - // This runtime call does not require a stack map. - arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); - } + // Given the numeric representation, it's enough to check the low bit of the rb_state. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Tbz(temp_, LockWord::kReadBarrierStateShift, GetExitLabel()); + GenerateReadBarrierMarkRuntimeCall(codegen); + __ B(GetExitLabel()); } private: - // The location (register) of the marked object reference. - const Location ref_; - - // The location of the entrypoint if it is already loaded. - const Location entrypoint_; - - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARM64); + // The register containing the object holding the marked object reference field. + Register obj_; + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + size_t scale_factor_; + // Is a null check required? + bool needs_null_check_; + // Should this reference load use Load-Acquire semantics? + bool use_load_acquire_; + // A temporary register used to hold the lock word of `obj_`. + Register temp_; + + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARM64); }; -// Slow path marking an object reference `ref` during a read barrier, -// and if needed, atomically updating the field `obj.field` in the -// object `obj` holding this reference after marking (contrary to -// ReadBarrierMarkSlowPathARM64 above, which never tries to update -// `obj.field`). +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). If needed, this slow path also atomically updates +// the field `obj.field` in the object `obj` holding this reference +// after marking (contrary to +// LoadReferenceWithBakerReadBarrierSlowPathARM64 above, which never +// tries to update `obj.field`). // // This means that after the execution of this slow path, both `ref` // and `obj.field` will be up-to-date; i.e., after the flip, both will // hold the same to-space reference (unless another thread installed // another object reference (different from `ref`) in `obj.field`). // -// If `entrypoint` is a valid location it is assumed to already be -// holding the entrypoint. The case where the entrypoint is passed in -// is when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkAndUpdateFieldSlowPathARM64 : public SlowPathCodeARM64 { +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64 + : public ReadBarrierMarkSlowPathBaseARM64 { public: - ReadBarrierMarkAndUpdateFieldSlowPathARM64(HInstruction* instruction, - Location ref, - Register obj, - Location field_offset, - Register temp, - Location entrypoint = Location::NoLocation()) - : SlowPathCodeARM64(instruction), - ref_(ref), + LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64(HInstruction* instruction, + Location ref, + Register obj, + uint32_t offset, + Location index, + size_t scale_factor, + bool needs_null_check, + bool use_load_acquire, + Register temp, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARM64(instruction, ref, entrypoint), obj_(obj), - field_offset_(field_offset), - temp_(temp), - entrypoint_(entrypoint) { + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), + use_load_acquire_(use_load_acquire), + temp_(temp) { DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); } const char* GetDescription() const OVERRIDE { - return "ReadBarrierMarkAndUpdateFieldSlowPathARM64"; + return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64"; } void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { @@ -774,70 +940,82 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARM64 : public SlowPathCodeARM64 { DCHECK(locations->CanCall()); DCHECK(ref_.IsRegister()) << ref_; DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg(); - // This slow path is only used by the UnsafeCASObject intrinsic. + DCHECK(obj_.IsW()); + DCHECK_NE(ref_.reg(), LocationFrom(temp_).reg()); + + // This slow path is only used by the UnsafeCASObject intrinsic at the moment. DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified())) << "Unexpected instruction in read barrier marking and field updating slow path: " << instruction_->DebugName(); DCHECK(instruction_->GetLocations()->Intrinsified()); DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject); - DCHECK(field_offset_.IsRegister()) << field_offset_; + DCHECK_EQ(offset_, 0u); + DCHECK_EQ(scale_factor_, 0u); + DCHECK_EQ(use_load_acquire_, false); + // The location of the offset of the marked reference field within `obj_`. + Location field_offset = index_; + DCHECK(field_offset.IsRegister()) << field_offset; __ Bind(GetEntryLabel()); - // Save the old reference. + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + __ Ldr(temp_, HeapOperand(obj_, monitor_offset)); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including rb_state, + // to prevent load-load reordering, and without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp`. + __ Add(obj_.X(), obj_.X(), Operand(temp_.X(), LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen); + arm64_codegen->GenerateRawReferenceLoad(instruction_, + ref_, + obj_, + offset_, + index_, + scale_factor_, + /* needs_null_check */ false, + use_load_acquire_); + + // Mark the object `ref` when `obj` is gray. + // + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); + // + // Given the numeric representation, it's enough to check the low bit of the rb_state. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Tbz(temp_, LockWord::kReadBarrierStateShift, GetExitLabel()); + + // Save the old value of the reference before marking it. // Note that we cannot use IP to save the old reference, as IP is // used internally by the ReadBarrierMarkRegX entry point, and we // need the old reference after the call to that entry point. DCHECK_NE(LocationFrom(temp_).reg(), IP0); __ Mov(temp_.W(), ref_reg); - // No need to save live registers; it's taken care of by the - // entrypoint. Also, there is no need to update the stack mask, - // as this runtime call will not trigger a garbage collection. - CodeGeneratorARM64* arm64_codegen = down_cast<CodeGeneratorARM64*>(codegen); - DCHECK_NE(ref_.reg(), LR); - DCHECK_NE(ref_.reg(), WSP); - DCHECK_NE(ref_.reg(), WZR); - // IP0 is used internally by the ReadBarrierMarkRegX entry point - // as a temporary, it cannot be the entry point's input/output. - DCHECK_NE(ref_.reg(), IP0); - DCHECK(0 <= ref_.reg() && ref_.reg() < kNumberOfWRegisters) << ref_.reg(); - // "Compact" slow path, saving two moves. - // - // Instead of using the standard runtime calling convention (input - // and output in W0): - // - // W0 <- ref - // W0 <- ReadBarrierMark(W0) - // ref <- W0 - // - // we just use rX (the register containing `ref`) as input and output - // of a dedicated entrypoint: - // - // rX <- ReadBarrierMarkRegX(rX) - // - if (entrypoint_.IsValid()) { - arm64_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); - __ Blr(XRegisterFrom(entrypoint_)); - } else { - // Entrypoint is not already loaded, load from the thread. - int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArm64PointerSize>(ref_.reg()); - // This runtime call does not require a stack map. - arm64_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); - } + GenerateReadBarrierMarkRuntimeCall(codegen); // If the new reference is different from the old reference, - // update the field in the holder (`*(obj_ + field_offset_)`). + // update the field in the holder (`*(obj_ + field_offset)`). // // Note that this field could also hold a different object, if // another thread had concurrently changed it. In that case, the // LDXR/CMP/BNE sequence of instructions in the compare-and-set // (CAS) operation below would abort the CAS, leaving the field // as-is. - vixl::aarch64::Label done; __ Cmp(temp_.W(), ref_reg); - __ B(eq, &done); + __ B(eq, GetExitLabel()); // Update the the holder's field atomically. This may fail if // mutator updates before us, but it's OK. This is achieved @@ -850,7 +1028,7 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARM64 : public SlowPathCodeARM64 { // Convenience aliases. Register base = obj_.W(); - Register offset = XRegisterFrom(field_offset_); + Register offset = XRegisterFrom(field_offset); Register expected = temp_.W(); Register value = ref_reg; Register tmp_ptr = temps.AcquireX(); // Pointer to actual memory. @@ -894,24 +1072,26 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARM64 : public SlowPathCodeARM64 { } } - __ Bind(&done); __ B(GetExitLabel()); } private: - // The location (register) of the marked object reference. - const Location ref_; // The register containing the object holding the marked object reference field. const Register obj_; - // The location of the offset of the marked reference field within `obj_`. - Location field_offset_; - + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + size_t scale_factor_; + // Is a null check required? + bool needs_null_check_; + // Should this reference load use Load-Acquire semantics? + bool use_load_acquire_; + // A temporary register used to hold the lock word of `obj_`; and + // also to hold the original reference value, when the reference is + // marked. const Register temp_; - // The location of the entrypoint if it is already loaded. - const Location entrypoint_; - - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARM64); + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64); }; // Slow path generating a read barrier for a heap reference. @@ -5773,13 +5953,11 @@ void CodeGeneratorARM64::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* // `instruction->IsArrayGet()` => `!use_load_acquire`. DCHECK(!instruction->IsArrayGet() || !use_load_acquire); - // After loading the reference from `obj.field` into `ref`, query - // `art::Thread::Current()->GetIsGcMarking()` to decide whether we - // need to enter the slow path to mark the reference. This - // optimistic strategy (we expect the GC to not be marking most of - // the time) does not check `obj`'s lock word (to see if it is a - // gray object or not), so may sometimes mark an already marked - // object. + // Query `art::Thread::Current()->GetIsGcMarking()` to decide + // whether we need to enter the slow path to mark the reference. + // Then, in the slow path, check the gray bit in the lock word of + // the reference's holder (`obj`) to decide whether to mark `ref` or + // not. // // Note that we do not actually check the value of `GetIsGcMarking()`; // instead, we load into `temp2` the read barrier mark entry point @@ -5787,10 +5965,17 @@ void CodeGeneratorARM64::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* // that `GetIsGcMarking()` is false, and vice versa. // // temp2 = Thread::Current()->pReadBarrierMarkReg ## root.reg() - // HeapReference<mirror::Object> ref = *src; // Original reference load. // if (temp2 != nullptr) { // <=> Thread::Current()->GetIsGcMarking() // // Slow path. - // ref = temp2(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = temp2(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } + // } else { + // HeapReference<mirror::Object> ref = *src; // Original reference load. // } // Slow path marking the object `ref` when the GC is marking. The @@ -5799,17 +5984,38 @@ void CodeGeneratorARM64::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* Location temp2_loc = LocationFrom(temp2); SlowPathCodeARM64* slow_path; if (always_update_field) { - // ReadBarrierMarkAndUpdateFieldSlowPathARM64 only supports - // address of the form `obj + field_offset`, where `obj` is a - // register and `field_offset` is a register. Thus `offset` and - // `scale_factor` above are expected to be null in this code path. + // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64 + // only supports address of the form `obj + field_offset`, where + // `obj` is a register and `field_offset` is a register. Thus + // `offset` and `scale_factor` above are expected to be null in + // this code path. DCHECK_EQ(offset, 0u); DCHECK_EQ(scale_factor, 0u); /* "times 1" */ - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARM64( - instruction, ref, obj, /* field_offset */ index, temp, /* entrypoint */ temp2_loc); + Location field_offset = index; + slow_path = + new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM64( + instruction, + ref, + obj, + offset, + /* index */ field_offset, + scale_factor, + needs_null_check, + use_load_acquire, + temp, + /* entrypoint */ temp2_loc); } else { - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM64( - instruction, ref, /* entrypoint */ temp2_loc); + slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARM64( + instruction, + ref, + obj, + offset, + index, + scale_factor, + needs_null_check, + use_load_acquire, + temp, + /* entrypoint */ temp2_loc); } AddSlowPath(slow_path); @@ -5819,12 +6025,12 @@ void CodeGeneratorARM64::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* // Loading the entrypoint does not require a load acquire since it is only changed when // threads are suspended or running a checkpoint. __ Ldr(temp2, MemOperand(tr, entry_point_offset)); - // The reference load. - GenerateRawReferenceLoad( - instruction, ref, obj, offset, index, scale_factor, needs_null_check, use_load_acquire); // The entrypoint is null when the GC is not marking, this prevents one load compared to // checking GetIsGcMarking. __ Cbnz(temp2, slow_path->GetEntryLabel()); + // Fast path: just load the reference. + GenerateRawReferenceLoad( + instruction, ref, obj, offset, index, scale_factor, needs_null_check, use_load_acquire); __ Bind(slow_path->GetExitLabel()); } diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc index c92a056f32..0239ac9c45 100644 --- a/compiler/optimizing/code_generator_arm_vixl.cc +++ b/compiler/optimizing/code_generator_arm_vixl.cc @@ -657,56 +657,25 @@ class ArraySetSlowPathARMVIXL : public SlowPathCodeARMVIXL { DISALLOW_COPY_AND_ASSIGN(ArraySetSlowPathARMVIXL); }; -// Slow path marking an object reference `ref` during a read -// barrier. The field `obj.field` in the object `obj` holding this -// reference does not get updated by this slow path after marking (see -// ReadBarrierMarkAndUpdateFieldSlowPathARM below for that). -// -// This means that after the execution of this slow path, `ref` will -// always be up-to-date, but `obj.field` may not; i.e., after the -// flip, `ref` will be a to-space reference, but `obj.field` will -// probably still be a from-space reference (unless it gets updated by -// another thread, or if another thread installed another object -// reference (different from `ref`) in `obj.field`). +// Abstract base class for read barrier slow paths marking a reference +// `ref`. // -// If `entrypoint` is a valid location it is assumed to already be -// holding the entrypoint. The case where the entrypoint is passed in -// when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkSlowPathARMVIXL : public SlowPathCodeARMVIXL { - public: - ReadBarrierMarkSlowPathARMVIXL(HInstruction* instruction, - Location ref, - Location entrypoint = Location::NoLocation()) +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class ReadBarrierMarkSlowPathBaseARMVIXL : public SlowPathCodeARMVIXL { + protected: + ReadBarrierMarkSlowPathBaseARMVIXL(HInstruction* instruction, Location ref, Location entrypoint) : SlowPathCodeARMVIXL(instruction), ref_(ref), entrypoint_(entrypoint) { DCHECK(kEmitCompilerReadBarrier); } - const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathARMVIXL"; } + const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathBaseARMVIXL"; } - void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { - LocationSummary* locations = instruction_->GetLocations(); + // Generate assembly code calling the read barrier marking runtime + // entry point (ReadBarrierMarkRegX). + void GenerateReadBarrierMarkRuntimeCall(CodeGenerator* codegen) { vixl32::Register ref_reg = RegisterFrom(ref_); - DCHECK(locations->CanCall()); - DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg.GetCode())) << ref_reg; - DCHECK(instruction_->IsInstanceFieldGet() || - instruction_->IsStaticFieldGet() || - instruction_->IsArrayGet() || - instruction_->IsArraySet() || - instruction_->IsLoadClass() || - instruction_->IsLoadString() || - instruction_->IsInstanceOf() || - instruction_->IsCheckCast() || - (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) || - (instruction_->IsInvokeStaticOrDirect() && instruction_->GetLocations()->Intrinsified())) - << "Unexpected instruction in read barrier marking slow path: " - << instruction_->DebugName(); - // The read barrier instrumentation of object ArrayGet - // instructions does not support the HIntermediateAddress - // instruction. - DCHECK(!(instruction_->IsArrayGet() && - instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress())); - __ Bind(GetEntryLabel()); // No need to save live registers; it's taken care of by the // entrypoint. Also, there is no need to update the stack mask, // as this runtime call will not trigger a garbage collection. @@ -742,54 +711,246 @@ class ReadBarrierMarkSlowPathARMVIXL : public SlowPathCodeARMVIXL { // This runtime call does not require a stack map. arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); } - __ B(GetExitLabel()); } - private: // The location (register) of the marked object reference. const Location ref_; // The location of the entrypoint if already loaded. const Location entrypoint_; + private: + DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathBaseARMVIXL); +}; + +// Slow path marking an object reference `ref` during a read +// barrier. The field `obj.field` in the object `obj` holding this +// reference does not get updated by this slow path after marking. +// +// This means that after the execution of this slow path, `ref` will +// always be up-to-date, but `obj.field` may not; i.e., after the +// flip, `ref` will be a to-space reference, but `obj.field` will +// probably still be a from-space reference (unless it gets updated by +// another thread, or if another thread installed another object +// reference (different from `ref`) in `obj.field`). +// +// If `entrypoint` is a valid location it is assumed to already be +// holding the entrypoint. The case where the entrypoint is passed in +// is when the decision to mark is based on whether the GC is marking. +class ReadBarrierMarkSlowPathARMVIXL : public ReadBarrierMarkSlowPathBaseARMVIXL { + public: + ReadBarrierMarkSlowPathARMVIXL(HInstruction* instruction, + Location ref, + Location entrypoint = Location::NoLocation()) + : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint) { + DCHECK(kEmitCompilerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { return "ReadBarrierMarkSlowPathARMVIXL"; } + + void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { + LocationSummary* locations = instruction_->GetLocations(); + DCHECK(locations->CanCall()); + DCHECK(ref_.IsRegister()) << ref_; + DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_.reg())) << ref_.reg(); + DCHECK(instruction_->IsLoadClass() || instruction_->IsLoadString()) + << "Unexpected instruction in read barrier marking slow path: " + << instruction_->DebugName(); + + __ Bind(GetEntryLabel()); + GenerateReadBarrierMarkRuntimeCall(codegen); + __ B(GetExitLabel()); + } + + private: DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkSlowPathARMVIXL); }; -// Slow path marking an object reference `ref` during a read barrier, -// and if needed, atomically updating the field `obj.field` in the -// object `obj` holding this reference after marking (contrary to -// ReadBarrierMarkSlowPathARM above, which never tries to update -// `obj.field`). +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). The field `obj.field` in the object `obj` holding +// this reference does not get updated by this slow path after marking +// (see LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL +// below for that). +// +// This means that after the execution of this slow path, `ref` will +// always be up-to-date, but `obj.field` may not; i.e., after the +// flip, `ref` will be a to-space reference, but `obj.field` will +// probably still be a from-space reference (unless it gets updated by +// another thread, or if another thread installed another object +// reference (different from `ref`) in `obj.field`). +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierSlowPathARMVIXL : public ReadBarrierMarkSlowPathBaseARMVIXL { + public: + LoadReferenceWithBakerReadBarrierSlowPathARMVIXL(HInstruction* instruction, + Location ref, + vixl32::Register obj, + uint32_t offset, + Location index, + ScaleFactor scale_factor, + bool needs_null_check, + vixl32::Register temp, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint), + obj_(obj), + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), + temp_(temp) { + DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); + } + + const char* GetDescription() const OVERRIDE { + return "LoadReferenceWithBakerReadBarrierSlowPathARMVIXL"; + } + + void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { + LocationSummary* locations = instruction_->GetLocations(); + vixl32::Register ref_reg = RegisterFrom(ref_); + DCHECK(locations->CanCall()); + DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg.GetCode())) << ref_reg; + DCHECK(instruction_->IsInstanceFieldGet() || + instruction_->IsStaticFieldGet() || + instruction_->IsArrayGet() || + instruction_->IsArraySet() || + instruction_->IsInstanceOf() || + instruction_->IsCheckCast() || + (instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified()) || + (instruction_->IsInvokeStaticOrDirect() && instruction_->GetLocations()->Intrinsified())) + << "Unexpected instruction in read barrier marking slow path: " + << instruction_->DebugName(); + // The read barrier instrumentation of object ArrayGet + // instructions does not support the HIntermediateAddress + // instruction. + DCHECK(!(instruction_->IsArrayGet() && + instruction_->AsArrayGet()->GetArray()->IsIntermediateAddress())); + + __ Bind(GetEntryLabel()); + + // When using MaybeGenerateReadBarrierSlow, the read barrier call is + // inserted after the original load. However, in fast path based + // Baker's read barriers, we need to perform the load of + // mirror::Object::monitor_ *before* the original reference load. + // This load-load ordering is required by the read barrier. + // The fast path/slow path (for Baker's algorithm) should look like: + // + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = entrypoint(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } + // + // Note: the original implementation in ReadBarrier::Barrier is + // slightly more complex as it performs additional checks that we do + // not do here for performance reasons. + + CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen); + + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + arm_codegen->GetAssembler()->LoadFromOffset(kLoadWord, temp_, obj_, monitor_offset); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including the rb_state, + // which shall prevent load-load reordering without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp`. + __ Add(obj_, obj_, Operand(temp_, ShiftType::LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + arm_codegen->GenerateRawReferenceLoad( + instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false); + + // Mark the object `ref` when `obj` is gray. + // + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); + // + // Given the numeric representation, it's enough to check the low bit of the + // rb_state. We do that by shifting the bit out of the lock word with LSRS + // which can be a 16-bit instruction unlike the TST immediate. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Lsrs(temp_, temp_, LockWord::kReadBarrierStateShift + 1); + __ B(cc, GetExitLabel()); // Carry flag is the last bit shifted out by LSRS. + GenerateReadBarrierMarkRuntimeCall(codegen); + + __ B(GetExitLabel()); + } + + private: + // The register containing the object holding the marked object reference field. + vixl32::Register obj_; + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + ScaleFactor scale_factor_; + // Is a null check required? + bool needs_null_check_; + // A temporary register used to hold the lock word of `obj_`. + vixl32::Register temp_; + + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierSlowPathARMVIXL); +}; + +// Slow path loading `obj`'s lock word, loading a reference from +// object `*(obj + offset + (index << scale_factor))` into `ref`, and +// marking `ref` if `obj` is gray according to the lock word (Baker +// read barrier). If needed, this slow path also atomically updates +// the field `obj.field` in the object `obj` holding this reference +// after marking (contrary to +// LoadReferenceWithBakerReadBarrierSlowPathARMVIXL above, which never +// tries to update `obj.field`). // // This means that after the execution of this slow path, both `ref` // and `obj.field` will be up-to-date; i.e., after the flip, both will // hold the same to-space reference (unless another thread installed // another object reference (different from `ref`) in `obj.field`). // -// If `entrypoint` is a valid location it is assumed to already be -// holding the entrypoint. The case where the entrypoint is passed in -// when the decision to mark is based on whether the GC is marking. -class ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL : public SlowPathCodeARMVIXL { +// +// Argument `entrypoint` must be a register location holding the read +// barrier marking runtime entry point to be invoked. +class LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL + : public ReadBarrierMarkSlowPathBaseARMVIXL { public: - ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL(HInstruction* instruction, - Location ref, - vixl32::Register obj, - Location field_offset, - vixl32::Register temp1, - vixl32::Register temp2, - Location entrypoint = Location::NoLocation()) - : SlowPathCodeARMVIXL(instruction), - ref_(ref), + LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL(HInstruction* instruction, + Location ref, + vixl32::Register obj, + uint32_t offset, + Location index, + ScaleFactor scale_factor, + bool needs_null_check, + vixl32::Register temp1, + vixl32::Register temp2, + Location entrypoint) + : ReadBarrierMarkSlowPathBaseARMVIXL(instruction, ref, entrypoint), obj_(obj), - field_offset_(field_offset), + offset_(offset), + index_(index), + scale_factor_(scale_factor), + needs_null_check_(needs_null_check), temp1_(temp1), - temp2_(temp2), - entrypoint_(entrypoint) { + temp2_(temp2) { DCHECK(kEmitCompilerReadBarrier); + DCHECK(kUseBakerReadBarrier); } const char* GetDescription() const OVERRIDE { - return "ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL"; + return "LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL"; } void EmitNativeCode(CodeGenerator* codegen) OVERRIDE { @@ -797,70 +958,77 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL : public SlowPathCodeARMVIXL vixl32::Register ref_reg = RegisterFrom(ref_); DCHECK(locations->CanCall()); DCHECK(!locations->GetLiveRegisters()->ContainsCoreRegister(ref_reg.GetCode())) << ref_reg; - // This slow path is only used by the UnsafeCASObject intrinsic. + DCHECK_NE(ref_.reg(), LocationFrom(temp1_).reg()); + + // This slow path is only used by the UnsafeCASObject intrinsic at the moment. DCHECK((instruction_->IsInvokeVirtual() && instruction_->GetLocations()->Intrinsified())) << "Unexpected instruction in read barrier marking and field updating slow path: " << instruction_->DebugName(); DCHECK(instruction_->GetLocations()->Intrinsified()); DCHECK_EQ(instruction_->AsInvoke()->GetIntrinsic(), Intrinsics::kUnsafeCASObject); - DCHECK(field_offset_.IsRegisterPair()) << field_offset_; + DCHECK_EQ(offset_, 0u); + DCHECK_EQ(scale_factor_, ScaleFactor::TIMES_1); + Location field_offset = index_; + DCHECK(field_offset.IsRegisterPair()) << field_offset; __ Bind(GetEntryLabel()); - // Save the old reference. + CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen); + + // /* int32_t */ monitor = obj->monitor_ + uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); + arm_codegen->GetAssembler()->LoadFromOffset(kLoadWord, temp1_, obj_, monitor_offset); + if (needs_null_check_) { + codegen->MaybeRecordImplicitNullCheck(instruction_); + } + // /* LockWord */ lock_word = LockWord(monitor) + static_assert(sizeof(LockWord) == sizeof(int32_t), + "art::LockWord and int32_t have different sizes."); + + // Introduce a dependency on the lock_word including the rb_state, + // which shall prevent load-load reordering without using + // a memory barrier (which would be more expensive). + // `obj` is unchanged by this operation, but its value now depends + // on `temp`. + __ Add(obj_, obj_, Operand(temp1_, ShiftType::LSR, 32)); + + // The actual reference load. + // A possible implicit null check has already been handled above. + arm_codegen->GenerateRawReferenceLoad( + instruction_, ref_, obj_, offset_, index_, scale_factor_, /* needs_null_check */ false); + + // Mark the object `ref` when `obj` is gray. + // + // if (rb_state == ReadBarrier::GrayState()) + // ref = ReadBarrier::Mark(ref); + // + // Given the numeric representation, it's enough to check the low bit of the + // rb_state. We do that by shifting the bit out of the lock word with LSRS + // which can be a 16-bit instruction unlike the TST immediate. + static_assert(ReadBarrier::WhiteState() == 0, "Expecting white to have value 0"); + static_assert(ReadBarrier::GrayState() == 1, "Expecting gray to have value 1"); + __ Lsrs(temp1_, temp1_, LockWord::kReadBarrierStateShift + 1); + __ B(cc, GetExitLabel()); // Carry flag is the last bit shifted out by LSRS. + + // Save the old value of the reference before marking it. // Note that we cannot use IP to save the old reference, as IP is // used internally by the ReadBarrierMarkRegX entry point, and we // need the old reference after the call to that entry point. DCHECK(!temp1_.Is(ip)); __ Mov(temp1_, ref_reg); - // No need to save live registers; it's taken care of by the - // entrypoint. Also, there is no need to update the stack mask, - // as this runtime call will not trigger a garbage collection. - CodeGeneratorARMVIXL* arm_codegen = down_cast<CodeGeneratorARMVIXL*>(codegen); - DCHECK(!ref_reg.Is(sp)); - DCHECK(!ref_reg.Is(lr)); - DCHECK(!ref_reg.Is(pc)); - // IP is used internally by the ReadBarrierMarkRegX entry point - // as a temporary, it cannot be the entry point's input/output. - DCHECK(!ref_reg.Is(ip)); - DCHECK(ref_reg.IsRegister()) << ref_reg; - // "Compact" slow path, saving two moves. - // - // Instead of using the standard runtime calling convention (input - // and output in R0): - // - // R0 <- ref - // R0 <- ReadBarrierMark(R0) - // ref <- R0 - // - // we just use rX (the register containing `ref`) as input and output - // of a dedicated entrypoint: - // - // rX <- ReadBarrierMarkRegX(rX) - // - if (entrypoint_.IsValid()) { - arm_codegen->ValidateInvokeRuntimeWithoutRecordingPcInfo(instruction_, this); - __ Blx(RegisterFrom(entrypoint_)); - } else { - // Entrypoint is not already loaded, load from the thread. - int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref_reg.GetCode()); - // This runtime call does not require a stack map. - arm_codegen->InvokeRuntimeWithoutRecordingPcInfo(entry_point_offset, instruction_, this); - } + GenerateReadBarrierMarkRuntimeCall(codegen); // If the new reference is different from the old reference, - // update the field in the holder (`*(obj_ + field_offset_)`). + // update the field in the holder (`*(obj_ + field_offset)`). // // Note that this field could also hold a different object, if // another thread had concurrently changed it. In that case, the // LDREX/SUBS/ITNE sequence of instructions in the compare-and-set // (CAS) operation below would abort the CAS, leaving the field // as-is. - vixl32::Label done; __ Cmp(temp1_, ref_reg); - __ B(eq, &done, /* far_target */ false); + __ B(eq, GetExitLabel()); // Update the the holder's field atomically. This may fail if // mutator updates before us, but it's OK. This is achieved @@ -874,7 +1042,7 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL : public SlowPathCodeARMVIXL // The UnsafeCASObject intrinsic uses a register pair as field // offset ("long offset"), of which only the low part contains // data. - vixl32::Register offset = LowRegisterFrom(field_offset_); + vixl32::Register offset = LowRegisterFrom(field_offset); vixl32::Register expected = temp1_; vixl32::Register value = ref_reg; vixl32::Register tmp_ptr = temps.Acquire(); // Pointer to actual memory. @@ -930,25 +1098,27 @@ class ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL : public SlowPathCodeARMVIXL } } - __ Bind(&done); __ B(GetExitLabel()); } private: - // The location (register) of the marked object reference. - const Location ref_; // The register containing the object holding the marked object reference field. const vixl32::Register obj_; - // The location of the offset of the marked reference field within `obj_`. - Location field_offset_; - + // The offset, index and scale factor to access the reference in `obj_`. + uint32_t offset_; + Location index_; + ScaleFactor scale_factor_; + // Is a null check required? + bool needs_null_check_; + // A temporary register used to hold the lock word of `obj_`; and + // also to hold the original reference value, when the reference is + // marked. const vixl32::Register temp1_; + // A temporary register used in the implementation of the CAS, to + // update the object's reference field. const vixl32::Register temp2_; - // The location of the entrypoint if already loaded. - const Location entrypoint_; - - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL); + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL); }; // Slow path generating a read barrier for a heap reference. @@ -7392,13 +7562,11 @@ void CodeGeneratorARMVIXL::GenerateReferenceLoadWithBakerReadBarrier(HInstructio DCHECK(kEmitCompilerReadBarrier); DCHECK(kUseBakerReadBarrier); - // After loading the reference from `obj.field` into `ref`, query - // `art::Thread::Current()->GetIsGcMarking()` to decide whether we - // need to enter the slow path to mark the reference. This - // optimistic strategy (we expect the GC to not be marking most of - // the time) does not check `obj`'s lock word (to see if it is a - // gray object or not), so may sometimes mark an already marked - // object. + // Query `art::Thread::Current()->GetIsGcMarking()` to decide + // whether we need to enter the slow path to mark the reference. + // Then, in the slow path, check the gray bit in the lock word of + // the reference's holder (`obj`) to decide whether to mark `ref` or + // not. // // Note that we do not actually check the value of `GetIsGcMarking()`; // instead, we load into `temp3` the read barrier mark entry point @@ -7406,14 +7574,19 @@ void CodeGeneratorARMVIXL::GenerateReferenceLoadWithBakerReadBarrier(HInstructio // that `GetIsGcMarking()` is false, and vice versa. // // temp3 = Thread::Current()->pReadBarrierMarkReg ## root.reg() - // HeapReference<mirror::Object> ref = *src; // Original reference load. // if (temp3 != nullptr) { // <=> Thread::Current()->GetIsGcMarking() // // Slow path. - // ref = temp3(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); + // lfence; // Load fence or artificial data dependency to prevent load-load reordering + // HeapReference<mirror::Object> ref = *src; // Original reference load. + // bool is_gray = (rb_state == ReadBarrier::GrayState()); + // if (is_gray) { + // ref = temp3(ref); // ref = ReadBarrier::Mark(ref); // Runtime entry point call. + // } + // } else { + // HeapReference<mirror::Object> ref = *src; // Original reference load. // } - // TODO: This temp register is only necessary when - // `always_update_field` is true; make it optional (like `temp2`). vixl32::Register temp_reg = RegisterFrom(temp); // Slow path marking the object `ref` when the GC is marking. The @@ -7422,18 +7595,37 @@ void CodeGeneratorARMVIXL::GenerateReferenceLoadWithBakerReadBarrier(HInstructio SlowPathCodeARMVIXL* slow_path; if (always_update_field) { DCHECK(temp2 != nullptr); - // ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL only supports address - // of the form `obj + field_offset`, where `obj` is a register and - // `field_offset` is a register pair (of which only the lower half - // is used). Thus `offset` and `scale_factor` above are expected - // to be null in this code path. + // LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL + // only supports address of the form `obj + field_offset`, where + // `obj` is a register and `field_offset` is a register pair (of + // which only the lower half is used). Thus `offset` and + // `scale_factor` above are expected to be null in this code path. DCHECK_EQ(offset, 0u); DCHECK_EQ(scale_factor, ScaleFactor::TIMES_1); - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkAndUpdateFieldSlowPathARMVIXL( - instruction, ref, obj, /* field_offset */ index, temp_reg, *temp2, /* entrypoint */ temp3); + Location field_offset = index; + slow_path = + new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARMVIXL( + instruction, + ref, + obj, + offset, + /* index */ field_offset, + scale_factor, + needs_null_check, + temp_reg, + *temp2, + /* entrypoint */ temp3); } else { - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARMVIXL( - instruction, ref, /* entrypoint */ temp3); + slow_path = new (GetGraph()->GetArena()) LoadReferenceWithBakerReadBarrierSlowPathARMVIXL( + instruction, + ref, + obj, + offset, + index, + scale_factor, + needs_null_check, + temp_reg, + /* entrypoint */ temp3); } AddSlowPath(slow_path); @@ -7443,11 +7635,11 @@ void CodeGeneratorARMVIXL::GenerateReferenceLoadWithBakerReadBarrier(HInstructio // Loading the entrypoint does not require a load acquire since it is only changed when // threads are suspended or running a checkpoint. GetAssembler()->LoadFromOffset(kLoadWord, RegisterFrom(temp3), tr, entry_point_offset); - // The reference load. - GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check); // The entrypoint is null when the GC is not marking, this prevents one load compared to // checking GetIsGcMarking. __ CompareAndBranchIfNonZero(RegisterFrom(temp3), slow_path->GetEntryLabel()); + // Fast path: just load the reference. + GenerateRawReferenceLoad(instruction, ref, obj, offset, index, scale_factor, needs_null_check); __ Bind(slow_path->GetExitLabel()); } |