diff options
Diffstat (limited to 'compiler/optimizing/code_generator_arm.cc')
| -rw-r--r-- | compiler/optimizing/code_generator_arm.cc | 590 |
1 files changed, 405 insertions, 185 deletions
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc index 511bd9b7ef..2b0ab3e20e 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 @@ -650,13 +715,13 @@ 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 for the GcRoot read barrier. -class ReadBarrierMarkSlowPathARM : public SlowPathCodeARM { +// is when the decision to mark is based on whether the GC is marking. +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()) || @@ -686,145 +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. + + // 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: // - // Instead of using the standard runtime calling convention (input - // and output in 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. + // } // - // R0 <- ref - // R0 <- ReadBarrierMark(R0) - // ref <- R0 - // - // 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 { - 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`). -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) - : 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) { 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) - // - 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 @@ -837,7 +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. @@ -887,22 +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_; - DISALLOW_COPY_AND_ASSIGN(ReadBarrierMarkAndUpdateFieldSlowPathARM); + DISALLOW_COPY_AND_ASSIGN(LoadReferenceWithBakerReadBarrierAndUpdateFieldSlowPathARM); }; // Slow path generating a read barrier for a heap reference. @@ -7183,14 +7372,35 @@ void InstructionCodeGeneratorARM::GenerateGcRootFieldLoad(HInstruction* instruct DCHECK(kEmitCompilerReadBarrier); if (kUseBakerReadBarrier) { // Fast path implementation of art::ReadBarrier::BarrierForRoot when - // Baker's read barrier are used: + // Baker's read barrier are used. + // + // Note that we do not actually check the value of + // `GetIsGcMarking()` to decide whether to mark the loaded GC + // root or not. Instead, we load into `temp` the read barrier + // mark entry point corresponding to register `root`. If `temp` + // is null, it means that `GetIsGcMarking()` is false, and vice + // versa. // - // root = obj.field; // temp = Thread::Current()->pReadBarrierMarkReg ## root.reg() - // if (temp != null) { - // root = temp(root) + // GcRoot<mirror::Object> root = *(obj+offset); // Original reference load. + // if (temp != nullptr) { // <=> Thread::Current()->GetIsGcMarking() + // // Slow path. + // root = temp(root); // root = ReadBarrier::Mark(root); // Runtime entry point call. // } + // Slow path marking the GC root `root`. The entrypoint will already be loaded in `temp`. + Location temp = Location::RegisterLocation(LR); + SlowPathCodeARM* slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM( + instruction, root, /* entrypoint */ temp); + codegen_->AddSlowPath(slow_path); + + // temp = Thread::Current()->pReadBarrierMarkReg ## root.reg() + const int32_t entry_point_offset = + CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(root.reg()); + // Loading the entrypoint does not require a load acquire since it is only changed when + // threads are suspended or running a checkpoint. + __ LoadFromOffset(kLoadWord, temp.AsRegister<Register>(), TR, entry_point_offset); + // /* GcRoot<mirror::Object> */ root = *(obj + offset) __ LoadFromOffset(kLoadWord, root_reg, obj, offset); static_assert( @@ -7201,21 +7411,6 @@ void InstructionCodeGeneratorARM::GenerateGcRootFieldLoad(HInstruction* instruct "art::mirror::CompressedReference<mirror::Object> and int32_t " "have different sizes."); - // Slow path marking the GC root `root`. - Location temp = Location::RegisterLocation(LR); - SlowPathCodeARM* slow_path = - new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM( - instruction, - root, - /*entrypoint*/ temp); - codegen_->AddSlowPath(slow_path); - - // temp = Thread::Current()->pReadBarrierMarkReg ## root.reg() - const int32_t entry_point_offset = - CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(root.reg()); - // Loading the entrypoint does not require a load acquire since it is only changed when - // threads are suspended or running a checkpoint. - __ LoadFromOffset(kLoadWord, temp.AsRegister<Register>(), TR, entry_point_offset); // The entrypoint is null when the GC is not marking, this prevents one load compared to // checking GetIsGcMarking. __ CompareAndBranchIfNonZero(temp.AsRegister<Register>(), slow_path->GetEntryLabel()); @@ -7286,51 +7481,101 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i DCHECK(kEmitCompilerReadBarrier); DCHECK(kUseBakerReadBarrier); - // In slow path based read barriers, 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: + // 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. // - // uint32_t rb_state = Lockword(obj->monitor_).ReadBarrierState(); - // lfence; // Load fence or artificial data dependency to prevent load-load reordering - // HeapReference<Object> ref = *src; // Original reference load. - // bool is_gray = (rb_state == ReadBarrier::GrayState()); - // if (is_gray) { - // ref = ReadBarrier::Mark(ref); // Performed by runtime entrypoint slow path. - // } + // Note that we do not actually check the value of `GetIsGcMarking()`; + // instead, we load into `temp3` the read barrier mark entry point + // corresponding to register `ref`. If `temp3` is null, it means + // that `GetIsGcMarking()` is false, and vice versa. // - // 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. + // temp3 = Thread::Current()->pReadBarrierMarkReg ## root.reg() + // if (temp3 != nullptr) { // <=> Thread::Current()->GetIsGcMarking() + // // Slow path. + // 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. + // } - Register ref_reg = ref.AsRegister<Register>(); Register temp_reg = temp.AsRegister<Register>(); - uint32_t monitor_offset = mirror::Object::MonitorOffset().Int32Value(); - // /* int32_t */ monitor = obj->monitor_ - __ LoadFromOffset(kLoadWord, temp_reg, obj, monitor_offset); - if (needs_null_check) { - MaybeRecordImplicitNullCheck(instruction); + // Slow path marking the object `ref` when the GC is marking. The + // entrypoint will already be loaded in `temp3`. + Location temp3 = Location::RegisterLocation(LR); + SlowPathCodeARM* slow_path; + if (always_update_field) { + DCHECK(temp2 != nullptr); + // 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); + 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()) LoadReferenceWithBakerReadBarrierSlowPathARM( + instruction, + ref, + obj, + offset, + index, + scale_factor, + needs_null_check, + temp_reg, + /* entrypoint */ temp3); } - // /* LockWord */ lock_word = LockWord(monitor) - static_assert(sizeof(LockWord) == sizeof(int32_t), - "art::LockWord and int32_t have different sizes."); + AddSlowPath(slow_path); - // 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_reg`. - __ add(obj, obj, ShifterOperand(temp_reg, LSR, 32)); + // temp3 = Thread::Current()->pReadBarrierMarkReg ## ref.reg() + const int32_t entry_point_offset = + CodeGenerator::GetReadBarrierMarkEntryPointsOffset<kArmPointerSize>(ref.reg()); + // 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 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()); +} + +void CodeGeneratorARM::GenerateRawReferenceLoad(HInstruction* instruction, + Location ref, + Register obj, + uint32_t offset, + Location index, + ScaleFactor scale_factor, + bool needs_null_check) { + Register ref_reg = ref.AsRegister<Register>(); - // The actual reference load. if (index.IsValid()) { // Load types involving an "index": ArrayGet, // UnsafeGetObject/UnsafeGetObjectVolatile and UnsafeCASObject // intrinsics. - // /* HeapReference<Object> */ ref = *(obj + offset + (index << scale_factor)) + // /* HeapReference<mirror::Object> */ ref = *(obj + offset + (index << scale_factor)) if (index.IsConstant()) { size_t computed_offset = (index.GetConstant()->AsIntConstant()->GetValue() << scale_factor) + offset; @@ -7347,41 +7592,16 @@ void CodeGeneratorARM::GenerateReferenceLoadWithBakerReadBarrier(HInstruction* i __ LoadFromOffset(kLoadWord, ref_reg, IP, offset); } } else { - // /* HeapReference<Object> */ ref = *(obj + offset) + // /* HeapReference<mirror::Object> */ ref = *(obj + offset) __ LoadFromOffset(kLoadWord, ref_reg, obj, offset); } - // Object* ref = ref_addr->AsMirrorPtr() - __ MaybeUnpoisonHeapReference(ref_reg); - - // Slow path marking the object `ref` when it is gray. - 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. - 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); - } else { - slow_path = new (GetGraph()->GetArena()) ReadBarrierMarkSlowPathARM(instruction, ref); + if (needs_null_check) { + MaybeRecordImplicitNullCheck(instruction); } - AddSlowPath(slow_path); - // 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_reg, temp_reg, LockWord::kReadBarrierStateShift + 1); - __ b(slow_path->GetEntryLabel(), CS); // Carry flag is the last bit shifted out by LSRS. - __ Bind(slow_path->GetExitLabel()); + // Object* ref = ref_addr->AsMirrorPtr() + __ MaybeUnpoisonHeapReference(ref_reg); } void CodeGeneratorARM::GenerateReadBarrierSlow(HInstruction* instruction, |