diff options
Diffstat (limited to 'compiler/optimizing/ssa_builder.cc')
| -rw-r--r-- | compiler/optimizing/ssa_builder.cc | 381 |
1 files changed, 97 insertions, 284 deletions
diff --git a/compiler/optimizing/ssa_builder.cc b/compiler/optimizing/ssa_builder.cc index 4565590bc3..20a8bdb016 100644 --- a/compiler/optimizing/ssa_builder.cc +++ b/compiler/optimizing/ssa_builder.cc @@ -22,204 +22,18 @@ namespace art { -/** - * A debuggable application may require to reviving phis, to ensure their - * associated DEX register is available to a debugger. This class implements - * the logic for statement (c) of the SsaBuilder (see ssa_builder.h). It - * also makes sure that phis with incompatible input types are not revived - * (statement (b) of the SsaBuilder). - * - * This phase must be run after detecting dead phis through the - * DeadPhiElimination phase, and before deleting the dead phis. - */ -class DeadPhiHandling : public ValueObject { - public: - explicit DeadPhiHandling(HGraph* graph) - : graph_(graph), worklist_(graph->GetArena()->Adapter(kArenaAllocSsaBuilder)) { - worklist_.reserve(kDefaultWorklistSize); - } - - void Run(); - - private: - void VisitBasicBlock(HBasicBlock* block); - void ProcessWorklist(); - void AddToWorklist(HPhi* phi); - void AddDependentInstructionsToWorklist(HPhi* phi); - bool UpdateType(HPhi* phi); - - HGraph* const graph_; - ArenaVector<HPhi*> worklist_; - - static constexpr size_t kDefaultWorklistSize = 8; - - DISALLOW_COPY_AND_ASSIGN(DeadPhiHandling); -}; - -static bool HasConflictingEquivalent(HPhi* phi) { - if (phi->GetNext() == nullptr) { - return false; - } - HPhi* next = phi->GetNext()->AsPhi(); - if (next->GetRegNumber() == phi->GetRegNumber()) { - if (next->GetType() == Primitive::kPrimVoid) { - // We only get a void type for an equivalent phi we processed and found out - // it was conflicting. - return true; - } else { - // Go to the next phi, in case it is also an equivalent. - return HasConflictingEquivalent(next); - } - } - return false; -} - -bool DeadPhiHandling::UpdateType(HPhi* phi) { - if (phi->IsDead()) { - // Phi was rendered dead while waiting in the worklist because it was replaced - // with an equivalent. - return false; - } - - Primitive::Type existing = phi->GetType(); - - bool conflict = false; - Primitive::Type new_type = existing; - for (size_t i = 0, e = phi->InputCount(); i < e; ++i) { - HInstruction* input = phi->InputAt(i); - if (input->IsPhi() && input->AsPhi()->IsDead()) { - // We are doing a reverse post order visit of the graph, reviving - // phis that have environment uses and updating their types. If an - // input is a phi, and it is dead (because its input types are - // conflicting), this phi must be marked dead as well. - conflict = true; - break; - } - Primitive::Type input_type = HPhi::ToPhiType(input->GetType()); - - // The only acceptable transitions are: - // - From void to typed: first time we update the type of this phi. - // - From int to reference (or reference to int): the phi has to change - // to reference type. If the integer input cannot be converted to a - // reference input, the phi will remain dead. - if (new_type == Primitive::kPrimVoid) { - new_type = input_type; - } else if (new_type == Primitive::kPrimNot && input_type == Primitive::kPrimInt) { - if (input->IsPhi() && HasConflictingEquivalent(input->AsPhi())) { - // If we already asked for an equivalent of the input phi, but that equivalent - // ended up conflicting, make this phi conflicting too. - conflict = true; - break; - } - HInstruction* equivalent = SsaBuilder::GetReferenceTypeEquivalent(input); - if (equivalent == nullptr) { - conflict = true; - break; - } - phi->ReplaceInput(equivalent, i); - if (equivalent->IsPhi()) { - DCHECK_EQ(equivalent->GetType(), Primitive::kPrimNot); - // We created a new phi, but that phi has the same inputs as the old phi. We - // add it to the worklist to ensure its inputs can also be converted to reference. - // If not, it will remain dead, and the algorithm will make the current phi dead - // as well. - equivalent->AsPhi()->SetLive(); - AddToWorklist(equivalent->AsPhi()); - } - } else if (new_type == Primitive::kPrimInt && input_type == Primitive::kPrimNot) { - new_type = Primitive::kPrimNot; - // Start over, we may request reference equivalents for the inputs of the phi. - i = -1; - } else if (new_type != input_type) { - conflict = true; - break; - } - } - - if (conflict) { - phi->SetType(Primitive::kPrimVoid); - phi->SetDead(); - return true; - } else if (existing == new_type) { - return false; - } - - DCHECK(phi->IsLive()); - phi->SetType(new_type); - - // There might exist a `new_type` equivalent of `phi` already. In that case, - // we replace the equivalent with the, now live, `phi`. - HPhi* equivalent = phi->GetNextEquivalentPhiWithSameType(); - if (equivalent != nullptr) { - // There cannot be more than two equivalents with the same type. - DCHECK(equivalent->GetNextEquivalentPhiWithSameType() == nullptr); - // If doing fix-point iteration, the equivalent might be in `worklist_`. - // Setting it dead will make UpdateType skip it. - equivalent->SetDead(); - equivalent->ReplaceWith(phi); - } - - return true; -} - -void DeadPhiHandling::VisitBasicBlock(HBasicBlock* block) { - for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) { - HPhi* phi = it.Current()->AsPhi(); - if (phi->IsDead() && phi->HasEnvironmentUses()) { - phi->SetLive(); - if (block->IsLoopHeader()) { - // Give a type to the loop phi to guarantee convergence of the algorithm. - // Note that the dead phi may already have a type if it is an equivalent - // generated for a typed LoadLocal. In that case we do not change the - // type because it could lead to an unsupported PrimNot/Float/Double -> - // PrimInt/Long transition and create same type equivalents. - if (phi->GetType() == Primitive::kPrimVoid) { - phi->SetType(phi->InputAt(0)->GetType()); - } - AddToWorklist(phi); - } else { - // Because we are doing a reverse post order visit, all inputs of - // this phi have been visited and therefore had their (initial) type set. - UpdateType(phi); +void SsaBuilder::SetLoopPhiInputs() { + for (HBasicBlock* block : loop_headers_) { + for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) { + HPhi* phi = it.Current()->AsPhi(); + for (HBasicBlock* predecessor : block->GetPredecessors()) { + HInstruction* input = ValueOfLocal(predecessor, phi->GetRegNumber()); + phi->AddInput(input); } } } } -void DeadPhiHandling::ProcessWorklist() { - while (!worklist_.empty()) { - HPhi* instruction = worklist_.back(); - worklist_.pop_back(); - // Note that the same equivalent phi can be added multiple times in the work list, if - // used by multiple phis. The first call to `UpdateType` will know whether the phi is - // dead or live. - if (instruction->IsLive() && UpdateType(instruction)) { - AddDependentInstructionsToWorklist(instruction); - } - } -} - -void DeadPhiHandling::AddToWorklist(HPhi* instruction) { - DCHECK(instruction->IsLive()); - worklist_.push_back(instruction); -} - -void DeadPhiHandling::AddDependentInstructionsToWorklist(HPhi* instruction) { - for (HUseIterator<HInstruction*> it(instruction->GetUses()); !it.Done(); it.Advance()) { - HPhi* phi = it.Current()->GetUser()->AsPhi(); - if (phi != nullptr && !phi->IsDead()) { - AddToWorklist(phi); - } - } -} - -void DeadPhiHandling::Run() { - for (HReversePostOrderIterator it(*graph_); !it.Done(); it.Advance()) { - VisitBasicBlock(it.Current()); - } - ProcessWorklist(); -} - void SsaBuilder::FixNullConstantType() { // The order doesn't matter here. for (HReversePostOrderIterator itb(*GetGraph()); !itb.Done(); itb.Advance()) { @@ -259,10 +73,11 @@ void SsaBuilder::EquivalentPhisCleanup() { HPhi* phi = it.Current()->AsPhi(); HPhi* next = phi->GetNextEquivalentPhiWithSameType(); if (next != nullptr) { - // Make sure we do not replace a live phi with a dead phi. A live phi has been - // handled by the type propagation phase, unlike a dead phi. + // Make sure we do not replace a live phi with a dead phi. A live phi + // has been handled by the type propagation phase, unlike a dead phi. if (next->IsLive()) { phi->ReplaceWith(next); + phi->SetDead(); } else { next->ReplaceWith(phi); } @@ -274,6 +89,29 @@ void SsaBuilder::EquivalentPhisCleanup() { } } +void SsaBuilder::FixEnvironmentPhis() { + for (HReversePostOrderIterator it(*GetGraph()); !it.Done(); it.Advance()) { + HBasicBlock* block = it.Current(); + for (HInstructionIterator it_phis(block->GetPhis()); !it_phis.Done(); it_phis.Advance()) { + HPhi* phi = it_phis.Current()->AsPhi(); + // If the phi is not dead, or has no environment uses, there is nothing to do. + if (!phi->IsDead() || !phi->HasEnvironmentUses()) continue; + HInstruction* next = phi->GetNext(); + if (!phi->IsVRegEquivalentOf(next)) continue; + if (next->AsPhi()->IsDead()) { + // If the phi equivalent is dead, check if there is another one. + next = next->GetNext(); + if (!phi->IsVRegEquivalentOf(next)) continue; + // There can be at most two phi equivalents. + DCHECK(!phi->IsVRegEquivalentOf(next->GetNext())); + if (next->AsPhi()->IsDead()) continue; + } + // We found a live phi equivalent. Update the environment uses of `phi` with it. + phi->ReplaceWith(next); + } + } +} + void SsaBuilder::BuildSsa() { // 1) Visit in reverse post order. We need to have all predecessors of a block visited // (with the exception of loops) in order to create the right environment for that @@ -283,101 +121,57 @@ void SsaBuilder::BuildSsa() { } // 2) Set inputs of loop phis. - for (HBasicBlock* block : loop_headers_) { - for (HInstructionIterator it(block->GetPhis()); !it.Done(); it.Advance()) { - HPhi* phi = it.Current()->AsPhi(); - for (HBasicBlock* predecessor : block->GetPredecessors()) { - HInstruction* input = ValueOfLocal(predecessor, phi->GetRegNumber()); - phi->AddInput(input); - } - } - } + SetLoopPhiInputs(); + + // 3) Propagate types of phis. At this point, phis are typed void in the general + // case, or float/double/reference if we created an equivalent phi. So we need + // to propagate the types across phis to give them a correct type. If a type + // conflict is detected in this stage, the phi is marked dead. + PrimitiveTypePropagation(GetGraph()).Run(); - // 3) Mark dead phis. This will mark phis that are only used by environments: - // at the DEX level, the type of these phis does not need to be consistent, but - // our code generator will complain if the inputs of a phi do not have the same - // type. The marking allows the type propagation to know which phis it needs - // to handle. We mark but do not eliminate: the elimination will be done in - // step 9). - SsaDeadPhiElimination dead_phis_for_type_propagation(GetGraph()); - dead_phis_for_type_propagation.MarkDeadPhis(); - - // 4) Propagate types of phis. At this point, phis are typed void in the general - // case, or float/double/reference when we created an equivalent phi. So we - // need to propagate the types across phis to give them a correct type. - PrimitiveTypePropagation type_propagation(GetGraph()); - type_propagation.Run(); - - // 5) When creating equivalent phis we copy the inputs of the original phi which + // 4) When creating equivalent phis we copy the inputs of the original phi which // may be improperly typed. This was fixed during the type propagation in 4) but // as a result we may end up with two equivalent phis with the same type for // the same dex register. This pass cleans them up. EquivalentPhisCleanup(); - // 6) Mark dead phis again. Step 4) may have introduced new phis. - // Step 5) might enable the death of new phis. + // 5) Mark dead phis. This will mark phis which are not used by instructions or + // other live phis. If compiling as debuggable code, phis will also be kept live + // if they have an environment use. SsaDeadPhiElimination dead_phis(GetGraph()); dead_phis.MarkDeadPhis(); - // 7) Now that the graph is correctly typed, we can get rid of redundant phis. + // 6) Make sure environments use the right phi equivalent: a phi marked dead + // can have a phi equivalent that is not dead. In that case we have to replace + // it with the live equivalent because deoptimization and try/catch rely on + // environments containing values of all live vregs at that point. Note that + // there can be multiple phis for the same Dex register that are live + // (for example when merging constants), in which case it is okay for the + // environments to just reference one. + FixEnvironmentPhis(); + + // 7) Now that the right phis are used for the environments, we can eliminate + // phis we do not need. Regardless of the debuggable status, this phase is + /// necessary for statement (b) of the SsaBuilder (see ssa_builder.h), as well + // as for the code generation, which does not deal with phis of conflicting + // input types. + dead_phis.EliminateDeadPhis(); + + // 8) Now that the graph is correctly typed, we can get rid of redundant phis. // Note that we cannot do this phase before type propagation, otherwise // we could get rid of phi equivalents, whose presence is a requirement for the // type propagation phase. Note that this is to satisfy statement (a) of the // SsaBuilder (see ssa_builder.h). - SsaRedundantPhiElimination redundant_phi(GetGraph()); - redundant_phi.Run(); + SsaRedundantPhiElimination(GetGraph()).Run(); - // 8) Fix the type for null constants which are part of an equality comparison. + // 9) Fix the type for null constants which are part of an equality comparison. // We need to do this after redundant phi elimination, to ensure the only cases // that we can see are reference comparison against 0. The redundant phi // elimination ensures we do not see a phi taking two 0 constants in a HEqual // or HNotEqual. FixNullConstantType(); - // 9) Make sure environments use the right phi "equivalent": a phi marked dead - // can have a phi equivalent that is not dead. We must therefore update - // all environment uses of the dead phi to use its equivalent. Note that there - // can be multiple phis for the same Dex register that are live (for example - // when merging constants), in which case it is OK for the environments - // to just reference one. - for (HReversePostOrderIterator it(*GetGraph()); !it.Done(); it.Advance()) { - HBasicBlock* block = it.Current(); - for (HInstructionIterator it_phis(block->GetPhis()); !it_phis.Done(); it_phis.Advance()) { - HPhi* phi = it_phis.Current()->AsPhi(); - // If the phi is not dead, or has no environment uses, there is nothing to do. - if (!phi->IsDead() || !phi->HasEnvironmentUses()) continue; - HInstruction* next = phi->GetNext(); - if (!phi->IsVRegEquivalentOf(next)) continue; - if (next->AsPhi()->IsDead()) { - // If the phi equivalent is dead, check if there is another one. - next = next->GetNext(); - if (!phi->IsVRegEquivalentOf(next)) continue; - // There can be at most two phi equivalents. - DCHECK(!phi->IsVRegEquivalentOf(next->GetNext())); - if (next->AsPhi()->IsDead()) continue; - } - // We found a live phi equivalent. Update the environment uses of `phi` with it. - phi->ReplaceWith(next); - } - } - - // 10) Deal with phis to guarantee liveness of phis in case of a debuggable - // application. This is for satisfying statement (c) of the SsaBuilder - // (see ssa_builder.h). - if (GetGraph()->IsDebuggable()) { - DeadPhiHandling dead_phi_handler(GetGraph()); - dead_phi_handler.Run(); - } - - // 11) Now that the right phis are used for the environments, and we - // have potentially revive dead phis in case of a debuggable application, - // we can eliminate phis we do not need. Regardless of the debuggable status, - // this phase is necessary for statement (b) of the SsaBuilder (see ssa_builder.h), - // as well as for the code generation, which does not deal with phis of conflicting - // input types. - dead_phis.EliminateDeadPhis(); - - // 12) Clear locals. + // 10) Clear locals. for (HInstructionIterator it(GetGraph()->GetEntryBlock()->GetInstructions()); !it.Done(); it.Advance()) { @@ -561,6 +355,8 @@ HDoubleConstant* SsaBuilder::GetDoubleEquivalent(HLongConstant* constant) { * phi with a floating point / reference type. */ HPhi* SsaBuilder::GetFloatDoubleOrReferenceEquivalentOfPhi(HPhi* phi, Primitive::Type type) { + DCHECK(phi->IsLive()) << "Cannot get equivalent of a dead phi since it would create a live one."; + // We place the floating point /reference phi next to this phi. HInstruction* next = phi->GetNext(); if (next != nullptr @@ -576,15 +372,18 @@ HPhi* SsaBuilder::GetFloatDoubleOrReferenceEquivalentOfPhi(HPhi* phi, Primitive: ArenaAllocator* allocator = phi->GetBlock()->GetGraph()->GetArena(); HPhi* new_phi = new (allocator) HPhi(allocator, phi->GetRegNumber(), phi->InputCount(), type); for (size_t i = 0, e = phi->InputCount(); i < e; ++i) { - // Copy the inputs. Note that the graph may not be correctly typed by doing this copy, - // but the type propagation phase will fix it. + // Copy the inputs. Note that the graph may not be correctly typed + // by doing this copy, but the type propagation phase will fix it. new_phi->SetRawInputAt(i, phi->InputAt(i)); } phi->GetBlock()->InsertPhiAfter(new_phi, phi); + DCHECK(new_phi->IsLive()); return new_phi; } else { DCHECK_EQ(next->GetType(), type); - return next->AsPhi(); + // An existing equivalent was found. If it is dead, conflict was previously + // identified and we return nullptr instead. + return next->AsPhi()->IsLive() ? next->AsPhi() : nullptr; } } @@ -592,11 +391,15 @@ HInstruction* SsaBuilder::GetFloatOrDoubleEquivalent(HInstruction* user, HInstruction* value, Primitive::Type type) { if (value->IsArrayGet()) { - // The verifier has checked that values in arrays cannot be used for both - // floating point and non-floating point operations. It is therefore safe to just - // change the type of the operation. - value->AsArrayGet()->SetType(type); - return value; + HArrayGet* aget = value->AsArrayGet(); + if (aget->GetType() != type && aget->IsTypeFixed()) { + // Requested a float/double equivalent of ArrayGet with int/long uses. + // Must be a phi with type conflict. + DCHECK(user->IsPhi()); + return nullptr; + } + aget->SetType(type); + return aget; } else if (value->IsLongConstant()) { return GetDoubleEquivalent(value->AsLongConstant()); } else if (value->IsIntConstant()) { @@ -604,12 +407,7 @@ HInstruction* SsaBuilder::GetFloatOrDoubleEquivalent(HInstruction* user, } else if (value->IsPhi()) { return GetFloatDoubleOrReferenceEquivalentOfPhi(value->AsPhi(), type); } else { - // For other instructions, we assume the verifier has checked that the dex format is correctly - // typed and the value in a dex register will not be used for both floating point and - // non-floating point operations. So the only reason an instruction would want a floating - // point equivalent is for an unused phi that will be removed by the dead phi elimination phase. - DCHECK(user->IsPhi()) << "is actually " << user->DebugName() << " (" << user->GetId() << ")"; - return value; + return nullptr; } } @@ -633,6 +431,21 @@ void SsaBuilder::VisitLoadLocal(HLoadLocal* load) { value = GetReferenceTypeEquivalent(value); } } + + // If value is HArrayGet, check if uses of the HLoadLocal disambiguate its + // type between int/long and float/double. + if (value->IsArrayGet() && !value->AsArrayGet()->IsTypeFixed()) { + for (HUseIterator<HInstruction*> use_it(load->GetUses()); !use_it.Done(); use_it.Advance()) { + HInstruction* user = use_it.Current()->GetUser(); + if (!user->IsStoreLocal() && + !user->IsPhi() && + (!user->IsArraySet() || user->AsArraySet()->GetIndex() == value)) { + value->AsArrayGet()->FixType(); + break; + } + } + } + load->ReplaceWith(value); load->GetBlock()->RemoveInstruction(load); } |