| // Copyright (c) 2018 Google LLC |
| // |
| // Licensed under the Apache License, Version 2.0 (the "License"); |
| // you may not use this file except in compliance with the License. |
| // You may obtain a copy of the License at |
| // |
| // http://www.apache.org/licenses/LICENSE-2.0 |
| // |
| // Unless required by applicable law or agreed to in writing, software |
| // distributed under the License is distributed on an "AS IS" BASIS, |
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| // See the License for the specific language governing permissions and |
| // limitations under the License. |
| |
| #include "source/opt/if_conversion.h" |
| |
| #include <memory> |
| #include <vector> |
| |
| #include "source/opt/value_number_table.h" |
| |
| namespace spvtools { |
| namespace opt { |
| |
| Pass::Status IfConversion::Process() { |
| if (!context()->get_feature_mgr()->HasCapability(SpvCapabilityShader)) { |
| return Status::SuccessWithoutChange; |
| } |
| |
| const ValueNumberTable& vn_table = *context()->GetValueNumberTable(); |
| bool modified = false; |
| std::vector<Instruction*> to_kill; |
| for (auto& func : *get_module()) { |
| DominatorAnalysis* dominators = context()->GetDominatorAnalysis(&func); |
| for (auto& block : func) { |
| // Check if it is possible for |block| to have phis that can be |
| // transformed. |
| BasicBlock* common = nullptr; |
| if (!CheckBlock(&block, dominators, &common)) continue; |
| |
| // Get an insertion point. |
| auto iter = block.begin(); |
| while (iter != block.end() && iter->opcode() == SpvOpPhi) { |
| ++iter; |
| } |
| |
| InstructionBuilder builder( |
| context(), &*iter, |
| IRContext::kAnalysisDefUse | IRContext::kAnalysisInstrToBlockMapping); |
| block.ForEachPhiInst([this, &builder, &modified, &common, &to_kill, |
| dominators, &block, &vn_table](Instruction* phi) { |
| // This phi is not compatible, but subsequent phis might be. |
| if (!CheckType(phi->type_id())) return; |
| |
| // We cannot transform cases where the phi is used by another phi in the |
| // same block due to instruction ordering restrictions. |
| // TODO(alan-baker): If all inappropriate uses could also be |
| // transformed, we could still remove this phi. |
| if (!CheckPhiUsers(phi, &block)) return; |
| |
| // Identify the incoming values associated with the true and false |
| // branches. If |then_block| dominates |inc0| or if the true edge |
| // branches straight to this block and |common| is |inc0|, then |inc0| |
| // is on the true branch. Otherwise the |inc1| is on the true branch. |
| BasicBlock* inc0 = GetIncomingBlock(phi, 0u); |
| Instruction* branch = common->terminator(); |
| uint32_t condition = branch->GetSingleWordInOperand(0u); |
| BasicBlock* then_block = GetBlock(branch->GetSingleWordInOperand(1u)); |
| Instruction* true_value = nullptr; |
| Instruction* false_value = nullptr; |
| if ((then_block == &block && inc0 == common) || |
| dominators->Dominates(then_block, inc0)) { |
| true_value = GetIncomingValue(phi, 0u); |
| false_value = GetIncomingValue(phi, 1u); |
| } else { |
| true_value = GetIncomingValue(phi, 1u); |
| false_value = GetIncomingValue(phi, 0u); |
| } |
| |
| BasicBlock* true_def_block = context()->get_instr_block(true_value); |
| BasicBlock* false_def_block = context()->get_instr_block(false_value); |
| |
| uint32_t true_vn = vn_table.GetValueNumber(true_value); |
| uint32_t false_vn = vn_table.GetValueNumber(false_value); |
| if (true_vn != 0 && true_vn == false_vn) { |
| Instruction* inst_to_use = nullptr; |
| |
| // Try to pick an instruction that is not in a side node. If we can't |
| // pick either the true for false branch as long as they can be |
| // legally moved. |
| if (!true_def_block || |
| dominators->Dominates(true_def_block, &block)) { |
| inst_to_use = true_value; |
| } else if (!false_def_block || |
| dominators->Dominates(false_def_block, &block)) { |
| inst_to_use = false_value; |
| } else if (CanHoistInstruction(true_value, common, dominators)) { |
| inst_to_use = true_value; |
| } else if (CanHoistInstruction(false_value, common, dominators)) { |
| inst_to_use = false_value; |
| } |
| |
| if (inst_to_use != nullptr) { |
| modified = true; |
| HoistInstruction(inst_to_use, common, dominators); |
| context()->KillNamesAndDecorates(phi); |
| context()->ReplaceAllUsesWith(phi->result_id(), |
| inst_to_use->result_id()); |
| } |
| return; |
| } |
| |
| // If either incoming value is defined in a block that does not dominate |
| // this phi, then we cannot eliminate the phi with a select. |
| // TODO(alan-baker): Perform code motion where it makes sense to enable |
| // the transform in this case. |
| if (true_def_block && !dominators->Dominates(true_def_block, &block)) |
| return; |
| |
| if (false_def_block && !dominators->Dominates(false_def_block, &block)) |
| return; |
| |
| analysis::Type* data_ty = |
| context()->get_type_mgr()->GetType(true_value->type_id()); |
| if (analysis::Vector* vec_data_ty = data_ty->AsVector()) { |
| condition = SplatCondition(vec_data_ty, condition, &builder); |
| } |
| |
| Instruction* select = builder.AddSelect(phi->type_id(), condition, |
| true_value->result_id(), |
| false_value->result_id()); |
| context()->ReplaceAllUsesWith(phi->result_id(), select->result_id()); |
| to_kill.push_back(phi); |
| modified = true; |
| |
| return; |
| }); |
| } |
| } |
| |
| for (auto inst : to_kill) { |
| context()->KillInst(inst); |
| } |
| |
| return modified ? Status::SuccessWithChange : Status::SuccessWithoutChange; |
| } |
| |
| bool IfConversion::CheckBlock(BasicBlock* block, DominatorAnalysis* dominators, |
| BasicBlock** common) { |
| const std::vector<uint32_t>& preds = cfg()->preds(block->id()); |
| |
| // TODO(alan-baker): Extend to more than two predecessors |
| if (preds.size() != 2) return false; |
| |
| BasicBlock* inc0 = context()->get_instr_block(preds[0]); |
| if (dominators->Dominates(block, inc0)) return false; |
| |
| BasicBlock* inc1 = context()->get_instr_block(preds[1]); |
| if (dominators->Dominates(block, inc1)) return false; |
| |
| // All phis will have the same common dominator, so cache the result |
| // for this block. If there is no common dominator, then we cannot transform |
| // any phi in this basic block. |
| *common = dominators->CommonDominator(inc0, inc1); |
| if (!*common || cfg()->IsPseudoEntryBlock(*common)) return false; |
| Instruction* branch = (*common)->terminator(); |
| if (branch->opcode() != SpvOpBranchConditional) return false; |
| auto merge = (*common)->GetMergeInst(); |
| if (!merge || merge->opcode() != SpvOpSelectionMerge) return false; |
| if ((*common)->MergeBlockIdIfAny() != block->id()) return false; |
| |
| return true; |
| } |
| |
| bool IfConversion::CheckPhiUsers(Instruction* phi, BasicBlock* block) { |
| return get_def_use_mgr()->WhileEachUser(phi, [block, |
| this](Instruction* user) { |
| if (user->opcode() == SpvOpPhi && context()->get_instr_block(user) == block) |
| return false; |
| return true; |
| }); |
| } |
| |
| uint32_t IfConversion::SplatCondition(analysis::Vector* vec_data_ty, |
| uint32_t cond, |
| InstructionBuilder* builder) { |
| // If the data inputs to OpSelect are vectors, the condition for |
| // OpSelect must be a boolean vector with the same number of |
| // components. So splat the condition for the branch into a vector |
| // type. |
| analysis::Bool bool_ty; |
| analysis::Vector bool_vec_ty(&bool_ty, vec_data_ty->element_count()); |
| uint32_t bool_vec_id = |
| context()->get_type_mgr()->GetTypeInstruction(&bool_vec_ty); |
| std::vector<uint32_t> ids(vec_data_ty->element_count(), cond); |
| return builder->AddCompositeConstruct(bool_vec_id, ids)->result_id(); |
| } |
| |
| bool IfConversion::CheckType(uint32_t id) { |
| Instruction* type = get_def_use_mgr()->GetDef(id); |
| SpvOp op = type->opcode(); |
| if (spvOpcodeIsScalarType(op) || op == SpvOpTypePointer || |
| op == SpvOpTypeVector) |
| return true; |
| return false; |
| } |
| |
| BasicBlock* IfConversion::GetBlock(uint32_t id) { |
| return context()->get_instr_block(get_def_use_mgr()->GetDef(id)); |
| } |
| |
| BasicBlock* IfConversion::GetIncomingBlock(Instruction* phi, |
| uint32_t predecessor) { |
| uint32_t in_index = 2 * predecessor + 1; |
| return GetBlock(phi->GetSingleWordInOperand(in_index)); |
| } |
| |
| Instruction* IfConversion::GetIncomingValue(Instruction* phi, |
| uint32_t predecessor) { |
| uint32_t in_index = 2 * predecessor; |
| return get_def_use_mgr()->GetDef(phi->GetSingleWordInOperand(in_index)); |
| } |
| |
| void IfConversion::HoistInstruction(Instruction* inst, BasicBlock* target_block, |
| DominatorAnalysis* dominators) { |
| BasicBlock* inst_block = context()->get_instr_block(inst); |
| if (!inst_block) { |
| // This is in the header, and dominates everything. |
| return; |
| } |
| |
| if (dominators->Dominates(inst_block, target_block)) { |
| // Already in position. No work to do. |
| return; |
| } |
| |
| assert(inst->IsOpcodeCodeMotionSafe() && |
| "Trying to move an instruction that is not safe to move."); |
| |
| // First hoist all instructions it depends on. |
| analysis::DefUseManager* def_use_mgr = context()->get_def_use_mgr(); |
| inst->ForEachInId( |
| [this, target_block, def_use_mgr, dominators](uint32_t* id) { |
| Instruction* operand_inst = def_use_mgr->GetDef(*id); |
| HoistInstruction(operand_inst, target_block, dominators); |
| }); |
| |
| Instruction* insertion_pos = target_block->terminator(); |
| if ((insertion_pos)->PreviousNode()->opcode() == SpvOpSelectionMerge) { |
| insertion_pos = insertion_pos->PreviousNode(); |
| } |
| inst->RemoveFromList(); |
| insertion_pos->InsertBefore(std::unique_ptr<Instruction>(inst)); |
| context()->set_instr_block(inst, target_block); |
| } |
| |
| bool IfConversion::CanHoistInstruction(Instruction* inst, |
| BasicBlock* target_block, |
| DominatorAnalysis* dominators) { |
| BasicBlock* inst_block = context()->get_instr_block(inst); |
| if (!inst_block) { |
| // This is in the header, and dominates everything. |
| return true; |
| } |
| |
| if (dominators->Dominates(inst_block, target_block)) { |
| // Already in position. No work to do. |
| return true; |
| } |
| |
| if (!inst->IsOpcodeCodeMotionSafe()) { |
| return false; |
| } |
| |
| // Check all instruction |inst| depends on. |
| analysis::DefUseManager* def_use_mgr = context()->get_def_use_mgr(); |
| return inst->WhileEachInId( |
| [this, target_block, def_use_mgr, dominators](uint32_t* id) { |
| Instruction* operand_inst = def_use_mgr->GetDef(*id); |
| return CanHoistInstruction(operand_inst, target_block, dominators); |
| }); |
| } |
| |
| } // namespace opt |
| } // namespace spvtools |
