| // Copyright (c) 2020 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/fuzz/transformation_flatten_conditional_branch.h" |
| |
| #include "source/fuzz/fuzzer_util.h" |
| #include "source/fuzz/instruction_descriptor.h" |
| |
| namespace spvtools { |
| namespace fuzz { |
| |
| TransformationFlattenConditionalBranch::TransformationFlattenConditionalBranch( |
| const protobufs::TransformationFlattenConditionalBranch& message) |
| : message_(message) {} |
| |
| TransformationFlattenConditionalBranch::TransformationFlattenConditionalBranch( |
| uint32_t header_block_id, bool true_branch_first, |
| uint32_t fresh_id_for_bvec2_selector, uint32_t fresh_id_for_bvec3_selector, |
| uint32_t fresh_id_for_bvec4_selector, |
| const std::vector<protobufs::SideEffectWrapperInfo>& |
| side_effect_wrappers_info) { |
| message_.set_header_block_id(header_block_id); |
| message_.set_true_branch_first(true_branch_first); |
| message_.set_fresh_id_for_bvec2_selector(fresh_id_for_bvec2_selector); |
| message_.set_fresh_id_for_bvec3_selector(fresh_id_for_bvec3_selector); |
| message_.set_fresh_id_for_bvec4_selector(fresh_id_for_bvec4_selector); |
| for (auto const& side_effect_wrapper_info : side_effect_wrappers_info) { |
| *message_.add_side_effect_wrapper_info() = side_effect_wrapper_info; |
| } |
| } |
| |
| bool TransformationFlattenConditionalBranch::IsApplicable( |
| opt::IRContext* ir_context, |
| const TransformationContext& transformation_context) const { |
| auto header_block = |
| fuzzerutil::MaybeFindBlock(ir_context, message_.header_block_id()); |
| |
| // The block must have been found and it must be a selection header. |
| if (!header_block || !header_block->GetMergeInst() || |
| header_block->GetMergeInst()->opcode() != SpvOpSelectionMerge) { |
| return false; |
| } |
| |
| // The header block must end with an OpBranchConditional instruction. |
| if (header_block->terminator()->opcode() != SpvOpBranchConditional) { |
| return false; |
| } |
| |
| // The branch condition cannot be irrelevant: we will make reference to it |
| // multiple times and we need to be guaranteed that these references will |
| // yield the same result; if they are replaced by other ids that will not |
| // work. |
| if (transformation_context.GetFactManager()->IdIsIrrelevant( |
| header_block->terminator()->GetSingleWordInOperand(0))) { |
| return false; |
| } |
| |
| std::set<uint32_t> used_fresh_ids; |
| |
| // If ids have been provided to be used as vector guards for OpSelect |
| // instructions then they must be fresh. |
| for (uint32_t fresh_id_for_bvec_selector : |
| {message_.fresh_id_for_bvec2_selector(), |
| message_.fresh_id_for_bvec3_selector(), |
| message_.fresh_id_for_bvec4_selector()}) { |
| if (fresh_id_for_bvec_selector != 0) { |
| if (!CheckIdIsFreshAndNotUsedByThisTransformation( |
| fresh_id_for_bvec_selector, ir_context, &used_fresh_ids)) { |
| return false; |
| } |
| } |
| } |
| |
| if (OpSelectArgumentsAreRestricted(ir_context)) { |
| // OpPhi instructions at the convergence block for the selection are handled |
| // by turning them into OpSelect instructions. As the SPIR-V version in use |
| // has restrictions on the arguments that OpSelect can take, we must check |
| // that any OpPhi instructions are compatible with these restrictions. |
| uint32_t convergence_block_id = |
| FindConvergenceBlock(ir_context, *header_block); |
| // Consider every OpPhi instruction at the convergence block. |
| if (!ir_context->cfg() |
| ->block(convergence_block_id) |
| ->WhileEachPhiInst([this, |
| ir_context](opt::Instruction* inst) -> bool { |
| // Decide whether the OpPhi can be handled based on its result |
| // type. |
| opt::Instruction* phi_result_type = |
| ir_context->get_def_use_mgr()->GetDef(inst->type_id()); |
| switch (phi_result_type->opcode()) { |
| case SpvOpTypeBool: |
| case SpvOpTypeInt: |
| case SpvOpTypeFloat: |
| case SpvOpTypePointer: |
| // Fine: OpSelect can work directly on scalar and pointer |
| // types. |
| return true; |
| case SpvOpTypeVector: { |
| // In its restricted form, OpSelect can only select between |
| // vectors if the condition of the select is a boolean |
| // boolean vector. We thus require the appropriate boolean |
| // vector type to be present. |
| uint32_t bool_type_id = |
| fuzzerutil::MaybeGetBoolType(ir_context); |
| uint32_t dimension = |
| phi_result_type->GetSingleWordInOperand(1); |
| if (fuzzerutil::MaybeGetVectorType(ir_context, bool_type_id, |
| dimension) == 0) { |
| // The required boolean vector type is not present. |
| return false; |
| } |
| // The transformation needs to be equipped with a fresh id |
| // in which to store the vectorized version of the selection |
| // construct's condition. |
| switch (dimension) { |
| case 2: |
| return message_.fresh_id_for_bvec2_selector() != 0; |
| case 3: |
| return message_.fresh_id_for_bvec3_selector() != 0; |
| default: |
| assert(dimension == 4 && "Invalid vector dimension."); |
| return message_.fresh_id_for_bvec4_selector() != 0; |
| } |
| } |
| default: |
| return false; |
| } |
| })) { |
| return false; |
| } |
| } |
| |
| // Use a set to keep track of the instructions that require fresh ids. |
| std::set<opt::Instruction*> instructions_that_need_ids; |
| |
| // Check that, if there are enough ids, the conditional can be flattened and, |
| // if so, add all the problematic instructions that need to be enclosed inside |
| // conditionals to |instructions_that_need_ids|. |
| if (!GetProblematicInstructionsIfConditionalCanBeFlattened( |
| ir_context, header_block, &instructions_that_need_ids)) { |
| return false; |
| } |
| |
| // Get the mapping from instructions to the fresh ids needed to enclose them |
| // inside conditionals. |
| auto insts_to_wrapper_info = GetInstructionsToWrapperInfo(ir_context); |
| |
| { |
| // Check the ids in the map. |
| for (const auto& inst_to_info : insts_to_wrapper_info) { |
| // Check the fresh ids needed for all of the instructions that need to be |
| // enclosed inside a conditional. |
| for (uint32_t id : {inst_to_info.second.merge_block_id(), |
| inst_to_info.second.execute_block_id()}) { |
| if (!id || !CheckIdIsFreshAndNotUsedByThisTransformation( |
| id, ir_context, &used_fresh_ids)) { |
| return false; |
| } |
| } |
| |
| // Check the other ids needed, if the instruction needs a placeholder. |
| if (InstructionNeedsPlaceholder(ir_context, *inst_to_info.first)) { |
| // Check the fresh ids. |
| for (uint32_t id : {inst_to_info.second.actual_result_id(), |
| inst_to_info.second.alternative_block_id(), |
| inst_to_info.second.placeholder_result_id()}) { |
| if (!id || !CheckIdIsFreshAndNotUsedByThisTransformation( |
| id, ir_context, &used_fresh_ids)) { |
| return false; |
| } |
| } |
| |
| // Check that the placeholder value id exists, has the right type and is |
| // available to use at this point. |
| auto value_def = ir_context->get_def_use_mgr()->GetDef( |
| inst_to_info.second.value_to_copy_id()); |
| if (!value_def || |
| value_def->type_id() != inst_to_info.first->type_id() || |
| !fuzzerutil::IdIsAvailableBeforeInstruction( |
| ir_context, inst_to_info.first, |
| inst_to_info.second.value_to_copy_id())) { |
| return false; |
| } |
| } |
| } |
| } |
| |
| // If some instructions that require ids are not in the map, the |
| // transformation needs overflow ids to be applicable. |
| for (auto instruction : instructions_that_need_ids) { |
| if (insts_to_wrapper_info.count(instruction) == 0 && |
| !transformation_context.GetOverflowIdSource()->HasOverflowIds()) { |
| return false; |
| } |
| } |
| |
| // All checks were passed. |
| return true; |
| } |
| |
| void TransformationFlattenConditionalBranch::Apply( |
| opt::IRContext* ir_context, |
| TransformationContext* transformation_context) const { |
| // branch = 1 corresponds to the true branch, branch = 2 corresponds to the |
| // false branch. If the true branch is to be laid out first, we need to visit |
| // the false branch first, because each branch is moved to right after the |
| // header while it is visited. |
| std::vector<uint32_t> branches = {2, 1}; |
| if (!message_.true_branch_first()) { |
| // Similarly, we need to visit the true branch first, if we want it to be |
| // laid out after the false branch. |
| branches = {1, 2}; |
| } |
| |
| auto header_block = ir_context->cfg()->block(message_.header_block_id()); |
| |
| // Get the ids of the starting blocks of the first and last branches to be |
| // laid out. The first branch is the true branch iff |
| // |message_.true_branch_first| is true. |
| auto branch_instruction = header_block->terminator(); |
| uint32_t first_block_first_branch_id = |
| branch_instruction->GetSingleWordInOperand(branches[1]); |
| uint32_t first_block_last_branch_id = |
| branch_instruction->GetSingleWordInOperand(branches[0]); |
| |
| uint32_t convergence_block_id = |
| FindConvergenceBlock(ir_context, *header_block); |
| |
| // If the OpBranchConditional instruction in the header branches to the same |
| // block for both values of the condition, this is the convergence block (the |
| // flow does not actually diverge) and the OpPhi instructions in it are still |
| // valid, so we do not need to make any changes. |
| if (first_block_first_branch_id != first_block_last_branch_id) { |
| RewriteOpPhiInstructionsAtConvergenceBlock( |
| *header_block, convergence_block_id, ir_context); |
| } |
| |
| // Get the mapping from instructions to fresh ids. |
| auto insts_to_info = GetInstructionsToWrapperInfo(ir_context); |
| |
| // Get a reference to the last block in the first branch that will be laid out |
| // (this depends on |message_.true_branch_first|). The last block is the block |
| // in the branch just before flow converges (it might not exist). |
| opt::BasicBlock* last_block_first_branch = nullptr; |
| |
| // Keep track of blocks and ids for which we should later add dead block and |
| // irrelevant id facts. We wait until we have finished applying the |
| // transformation before adding these facts, so that the fact manager has |
| // access to the fully up-to-date module. |
| std::vector<uint32_t> dead_blocks; |
| std::vector<uint32_t> irrelevant_ids; |
| |
| // Adjust the conditional branches by enclosing problematic instructions |
| // within conditionals and get references to the last block in each branch. |
| for (uint32_t branch : branches) { |
| auto current_block = header_block; |
| // Get the id of the first block in this branch. |
| uint32_t next_block_id = branch_instruction->GetSingleWordInOperand(branch); |
| |
| // Consider all blocks in the branch until the convergence block is reached. |
| while (next_block_id != convergence_block_id) { |
| // Move the next block to right after the current one. |
| current_block->GetParent()->MoveBasicBlockToAfter(next_block_id, |
| current_block); |
| |
| // Move forward in the branch. |
| current_block = ir_context->cfg()->block(next_block_id); |
| |
| // Find all the instructions in the current block which need to be |
| // enclosed inside conditionals. |
| std::vector<opt::Instruction*> problematic_instructions; |
| |
| current_block->ForEachInst( |
| [&problematic_instructions](opt::Instruction* instruction) { |
| if (instruction->opcode() != SpvOpLabel && |
| instruction->opcode() != SpvOpBranch && |
| !fuzzerutil::InstructionHasNoSideEffects(*instruction)) { |
| problematic_instructions.push_back(instruction); |
| } |
| }); |
| |
| uint32_t condition_id = |
| header_block->terminator()->GetSingleWordInOperand(0); |
| |
| // Enclose all of the problematic instructions in conditionals, with the |
| // same condition as the selection construct being flattened. |
| for (auto instruction : problematic_instructions) { |
| // Get the info needed by this instruction to wrap it inside a |
| // conditional. |
| protobufs::SideEffectWrapperInfo wrapper_info; |
| |
| if (insts_to_info.count(instruction) != 0) { |
| // Get the fresh ids from the map, if present. |
| wrapper_info = insts_to_info[instruction]; |
| } else { |
| // If we could not get it from the map, use overflow ids. We don't |
| // need to set |wrapper_info.instruction|, as it will not be used. |
| wrapper_info.set_merge_block_id( |
| transformation_context->GetOverflowIdSource() |
| ->GetNextOverflowId()); |
| wrapper_info.set_execute_block_id( |
| transformation_context->GetOverflowIdSource() |
| ->GetNextOverflowId()); |
| |
| if (InstructionNeedsPlaceholder(ir_context, *instruction)) { |
| // Ge the fresh ids from the overflow ids. |
| wrapper_info.set_actual_result_id( |
| transformation_context->GetOverflowIdSource() |
| ->GetNextOverflowId()); |
| wrapper_info.set_alternative_block_id( |
| transformation_context->GetOverflowIdSource() |
| ->GetNextOverflowId()); |
| wrapper_info.set_placeholder_result_id( |
| transformation_context->GetOverflowIdSource() |
| ->GetNextOverflowId()); |
| |
| // Try to find a zero constant. It does not matter whether it is |
| // relevant or irrelevant. |
| for (bool is_irrelevant : {true, false}) { |
| wrapper_info.set_value_to_copy_id( |
| fuzzerutil::MaybeGetZeroConstant( |
| ir_context, *transformation_context, |
| instruction->type_id(), is_irrelevant)); |
| if (wrapper_info.value_to_copy_id()) { |
| break; |
| } |
| } |
| } |
| } |
| |
| // Enclose the instruction in a conditional and get the merge block |
| // generated by this operation (this is where all the following |
| // instructions will be). |
| current_block = EncloseInstructionInConditional( |
| ir_context, *transformation_context, current_block, instruction, |
| wrapper_info, condition_id, branch == 1, &dead_blocks, |
| &irrelevant_ids); |
| } |
| |
| next_block_id = current_block->terminator()->GetSingleWordInOperand(0); |
| |
| // If the next block is the convergence block and this the branch that |
| // will be laid out right after the header, record this as the last block |
| // in the first branch. |
| if (next_block_id == convergence_block_id && branch == branches[1]) { |
| last_block_first_branch = current_block; |
| } |
| } |
| } |
| |
| // The current header should unconditionally branch to the starting block in |
| // the first branch to be laid out, if such a branch exists (i.e. the header |
| // does not branch directly to the convergence block), and to the starting |
| // block in the last branch to be laid out otherwise. |
| uint32_t after_header = first_block_first_branch_id != convergence_block_id |
| ? first_block_first_branch_id |
| : first_block_last_branch_id; |
| |
| // Kill the merge instruction and the branch instruction in the current |
| // header. |
| auto merge_inst = header_block->GetMergeInst(); |
| ir_context->KillInst(branch_instruction); |
| ir_context->KillInst(merge_inst); |
| |
| // Add a new, unconditional, branch instruction from the current header to |
| // |after_header|. |
| header_block->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpBranch, 0, 0, |
| opt::Instruction::OperandList{{SPV_OPERAND_TYPE_ID, {after_header}}})); |
| |
| // If the first branch to be laid out exists, change the branch instruction so |
| // that the last block in such branch unconditionally branches to the first |
| // block in the other branch (or the convergence block if there is no other |
| // branch) and change the OpPhi instructions in the last branch accordingly |
| // (the predecessor changed). |
| if (last_block_first_branch) { |
| last_block_first_branch->terminator()->SetInOperand( |
| 0, {first_block_last_branch_id}); |
| |
| // Change the OpPhi instructions of the last branch (if there is another |
| // branch) so that the predecessor is now the last block of the first |
| // branch. The block must have a single predecessor, so the operand |
| // specifying the predecessor is always in the same position. |
| if (first_block_last_branch_id != convergence_block_id) { |
| ir_context->get_instr_block(first_block_last_branch_id) |
| ->ForEachPhiInst( |
| [&last_block_first_branch](opt::Instruction* phi_inst) { |
| // The operand specifying the predecessor is the second input |
| // operand. |
| phi_inst->SetInOperand(1, {last_block_first_branch->id()}); |
| }); |
| } |
| } |
| |
| // Invalidate all analyses |
| ir_context->InvalidateAnalysesExceptFor(opt::IRContext::kAnalysisNone); |
| |
| // Now that we have finished adding blocks and ids to the module and |
| // invalidated existing analyses, update the fact manager regarding dead |
| // blocks and irrelevant ids. |
| for (auto dead_block : dead_blocks) { |
| transformation_context->GetFactManager()->AddFactBlockIsDead(dead_block); |
| } |
| for (auto irrelevant_id : irrelevant_ids) { |
| transformation_context->GetFactManager()->AddFactIdIsIrrelevant( |
| irrelevant_id); |
| } |
| } |
| |
| protobufs::Transformation TransformationFlattenConditionalBranch::ToMessage() |
| const { |
| protobufs::Transformation result; |
| *result.mutable_flatten_conditional_branch() = message_; |
| return result; |
| } |
| |
| bool TransformationFlattenConditionalBranch:: |
| GetProblematicInstructionsIfConditionalCanBeFlattened( |
| opt::IRContext* ir_context, opt::BasicBlock* header, |
| std::set<opt::Instruction*>* instructions_that_need_ids) { |
| uint32_t merge_block_id = header->MergeBlockIdIfAny(); |
| assert(merge_block_id && |
| header->GetMergeInst()->opcode() == SpvOpSelectionMerge && |
| header->terminator()->opcode() == SpvOpBranchConditional && |
| "|header| must be the header of a conditional."); |
| |
| auto enclosing_function = header->GetParent(); |
| auto dominator_analysis = |
| ir_context->GetDominatorAnalysis(enclosing_function); |
| auto postdominator_analysis = |
| ir_context->GetPostDominatorAnalysis(enclosing_function); |
| |
| // Check that the header and the merge block describe a single-entry, |
| // single-exit region. |
| if (!dominator_analysis->Dominates(header->id(), merge_block_id) || |
| !postdominator_analysis->Dominates(merge_block_id, header->id())) { |
| return false; |
| } |
| |
| // Traverse the CFG starting from the header and check that, for all the |
| // blocks that can be reached by the header before the flow converges: |
| // - they don't contain merge, barrier or OpSampledImage instructions |
| // - they branch unconditionally to another block |
| // Add any side-effecting instruction, requiring fresh ids, to |
| // |instructions_that_need_ids| |
| std::list<uint32_t> to_check; |
| header->ForEachSuccessorLabel( |
| [&to_check](uint32_t label) { to_check.push_back(label); }); |
| |
| while (!to_check.empty()) { |
| uint32_t block_id = to_check.front(); |
| to_check.pop_front(); |
| |
| // If the block post-dominates the header, this is where flow converges, and |
| // we don't need to check this branch any further, because the |
| // transformation will only change the part of the graph where flow is |
| // divergent. |
| if (postdominator_analysis->Dominates(block_id, header->id())) { |
| continue; |
| } |
| |
| auto block = ir_context->cfg()->block(block_id); |
| |
| // The block must not have a merge instruction, because inner constructs are |
| // not allowed. |
| if (block->GetMergeInst()) { |
| return false; |
| } |
| |
| // The terminator instruction for the block must be OpBranch. |
| if (block->terminator()->opcode() != SpvOpBranch) { |
| return false; |
| } |
| |
| // Check all of the instructions in the block. |
| bool all_instructions_compatible = |
| block->WhileEachInst([ir_context, instructions_that_need_ids]( |
| opt::Instruction* instruction) { |
| // We can ignore OpLabel instructions. |
| if (instruction->opcode() == SpvOpLabel) { |
| return true; |
| } |
| |
| // If the instruction is a branch, it must be an unconditional branch. |
| if (instruction->IsBranch()) { |
| return instruction->opcode() == SpvOpBranch; |
| } |
| |
| // We cannot go ahead if we encounter an instruction that cannot be |
| // handled. |
| if (!InstructionCanBeHandled(ir_context, *instruction)) { |
| return false; |
| } |
| |
| // If the instruction has side effects, add it to the |
| // |instructions_that_need_ids| set. |
| if (!fuzzerutil::InstructionHasNoSideEffects(*instruction)) { |
| instructions_that_need_ids->emplace(instruction); |
| } |
| |
| return true; |
| }); |
| |
| if (!all_instructions_compatible) { |
| return false; |
| } |
| |
| // Add the successor of this block to the list of blocks that need to be |
| // checked. |
| to_check.push_back(block->terminator()->GetSingleWordInOperand(0)); |
| } |
| |
| // All the blocks are compatible with the transformation and this is indeed a |
| // single-entry, single-exit region. |
| return true; |
| } |
| |
| bool TransformationFlattenConditionalBranch::InstructionNeedsPlaceholder( |
| opt::IRContext* ir_context, const opt::Instruction& instruction) { |
| assert(!fuzzerutil::InstructionHasNoSideEffects(instruction) && |
| InstructionCanBeHandled(ir_context, instruction) && |
| "The instruction must have side effects and it must be possible to " |
| "enclose it inside a conditional."); |
| |
| if (instruction.HasResultId()) { |
| // We need a placeholder iff the type is not Void. |
| auto type = ir_context->get_type_mgr()->GetType(instruction.type_id()); |
| return type && !type->AsVoid(); |
| } |
| |
| return false; |
| } |
| |
| std::unordered_map<opt::Instruction*, protobufs::SideEffectWrapperInfo> |
| TransformationFlattenConditionalBranch::GetInstructionsToWrapperInfo( |
| opt::IRContext* ir_context) const { |
| std::unordered_map<opt::Instruction*, protobufs::SideEffectWrapperInfo> |
| instructions_to_ids; |
| for (const auto& wrapper_info : message_.side_effect_wrapper_info()) { |
| auto instruction = FindInstruction(wrapper_info.instruction(), ir_context); |
| if (instruction) { |
| instructions_to_ids.emplace(instruction, wrapper_info); |
| } |
| } |
| |
| return instructions_to_ids; |
| } |
| |
| opt::BasicBlock* |
| TransformationFlattenConditionalBranch::EncloseInstructionInConditional( |
| opt::IRContext* ir_context, |
| const TransformationContext& transformation_context, opt::BasicBlock* block, |
| opt::Instruction* instruction, |
| const protobufs::SideEffectWrapperInfo& wrapper_info, uint32_t condition_id, |
| bool exec_if_cond_true, std::vector<uint32_t>* dead_blocks, |
| std::vector<uint32_t>* irrelevant_ids) const { |
| // Get the next instruction (it will be useful for splitting). |
| auto next_instruction = instruction->NextNode(); |
| |
| // Update the module id bound. |
| for (uint32_t id : |
| {wrapper_info.merge_block_id(), wrapper_info.execute_block_id()}) { |
| fuzzerutil::UpdateModuleIdBound(ir_context, id); |
| } |
| |
| // Create the block where the instruction is executed by splitting the |
| // original block. |
| auto execute_block = block->SplitBasicBlock( |
| ir_context, wrapper_info.execute_block_id(), |
| fuzzerutil::GetIteratorForInstruction(block, instruction)); |
| |
| // Create the merge block for the conditional that we are about to create by |
| // splitting execute_block (this will leave |instruction| as the only |
| // instruction in |execute_block|). |
| auto merge_block = execute_block->SplitBasicBlock( |
| ir_context, wrapper_info.merge_block_id(), |
| fuzzerutil::GetIteratorForInstruction(execute_block, next_instruction)); |
| |
| // Propagate the fact that the block is dead to the newly-created blocks. |
| if (transformation_context.GetFactManager()->BlockIsDead(block->id())) { |
| dead_blocks->emplace_back(execute_block->id()); |
| dead_blocks->emplace_back(merge_block->id()); |
| } |
| |
| // Initially, consider the merge block as the alternative block to branch to |
| // if the instruction should not be executed. |
| auto alternative_block = merge_block; |
| |
| // Add an unconditional branch from |execute_block| to |merge_block|. |
| execute_block->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpBranch, 0, 0, |
| opt::Instruction::OperandList{ |
| {SPV_OPERAND_TYPE_ID, {merge_block->id()}}})); |
| |
| // If the instruction requires a placeholder, it means that it has a result id |
| // and its result needs to be able to be used later on, and we need to: |
| // - add an additional block |ids.alternative_block_id| where a placeholder |
| // result id (using fresh id |ids.placeholder_result_id|) is obtained either |
| // by using OpCopyObject and copying |ids.value_to_copy_id| or, if such id |
| // was not given and a suitable constant was not found, by using OpUndef. |
| // - mark |ids.placeholder_result_id| as irrelevant |
| // - change the result id of the instruction to a fresh id |
| // (|ids.actual_result_id|). |
| // - add an OpPhi instruction, which will have the original result id of the |
| // instruction, in the merge block. |
| if (InstructionNeedsPlaceholder(ir_context, *instruction)) { |
| // Update the module id bound with the additional ids. |
| for (uint32_t id : |
| {wrapper_info.actual_result_id(), wrapper_info.alternative_block_id(), |
| wrapper_info.placeholder_result_id()}) { |
| fuzzerutil::UpdateModuleIdBound(ir_context, id); |
| } |
| |
| // Create a new block using |fresh_ids.alternative_block_id| for its label. |
| auto alternative_block_temp = |
| MakeUnique<opt::BasicBlock>(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpLabel, 0, wrapper_info.alternative_block_id(), |
| opt::Instruction::OperandList{})); |
| |
| // Keep the original result id of the instruction in a variable. |
| uint32_t original_result_id = instruction->result_id(); |
| |
| // Set the result id of the instruction to be |ids.actual_result_id|. |
| instruction->SetResultId(wrapper_info.actual_result_id()); |
| |
| // Add a placeholder instruction, with the same type as the original |
| // instruction and id |ids.placeholder_result_id|, to the new block. |
| if (wrapper_info.value_to_copy_id()) { |
| // If there is an available id to copy from, the placeholder instruction |
| // will be %placeholder_result_id = OpCopyObject %type %value_to_copy_id |
| alternative_block_temp->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpCopyObject, instruction->type_id(), |
| wrapper_info.placeholder_result_id(), |
| opt::Instruction::OperandList{ |
| {SPV_OPERAND_TYPE_ID, {wrapper_info.value_to_copy_id()}}})); |
| } else { |
| // If there is no such id, use an OpUndef instruction. |
| alternative_block_temp->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpUndef, instruction->type_id(), |
| wrapper_info.placeholder_result_id(), |
| opt::Instruction::OperandList{})); |
| } |
| |
| // Mark |ids.placeholder_result_id| as irrelevant. |
| irrelevant_ids->emplace_back(wrapper_info.placeholder_result_id()); |
| |
| // Add an unconditional branch from the new block to the merge block. |
| alternative_block_temp->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpBranch, 0, 0, |
| opt::Instruction::OperandList{ |
| {SPV_OPERAND_TYPE_ID, {merge_block->id()}}})); |
| |
| // Insert the block before the merge block. |
| alternative_block = block->GetParent()->InsertBasicBlockBefore( |
| std::move(alternative_block_temp), merge_block); |
| |
| // Using the original instruction result id, add an OpPhi instruction to the |
| // merge block, which will either take the value of the result of the |
| // instruction or the placeholder value defined in the alternative block. |
| merge_block->begin().InsertBefore(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpPhi, instruction->type_id(), original_result_id, |
| opt::Instruction::OperandList{ |
| {SPV_OPERAND_TYPE_ID, {instruction->result_id()}}, |
| {SPV_OPERAND_TYPE_ID, {execute_block->id()}}, |
| {SPV_OPERAND_TYPE_ID, {wrapper_info.placeholder_result_id()}}, |
| {SPV_OPERAND_TYPE_ID, {alternative_block->id()}}})); |
| |
| // Propagate the fact that the block is dead to the new block. |
| if (transformation_context.GetFactManager()->BlockIsDead(block->id())) { |
| dead_blocks->emplace_back(alternative_block->id()); |
| } |
| } |
| |
| // Depending on whether the instruction should be executed in the if branch or |
| // in the else branch, get the corresponding ids. |
| auto if_block_id = (exec_if_cond_true ? execute_block : alternative_block) |
| ->GetLabel() |
| ->result_id(); |
| auto else_block_id = (exec_if_cond_true ? alternative_block : execute_block) |
| ->GetLabel() |
| ->result_id(); |
| |
| // Add an OpSelectionMerge instruction to the block. |
| block->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpSelectionMerge, 0, 0, |
| opt::Instruction::OperandList{{SPV_OPERAND_TYPE_ID, {merge_block->id()}}, |
| {SPV_OPERAND_TYPE_SELECTION_CONTROL, |
| {SpvSelectionControlMaskNone}}})); |
| |
| // Add an OpBranchConditional, to the block, using |condition_id| as the |
| // condition and branching to |if_block_id| if the condition is true and to |
| // |else_block_id| if the condition is false. |
| block->AddInstruction(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpBranchConditional, 0, 0, |
| opt::Instruction::OperandList{{SPV_OPERAND_TYPE_ID, {condition_id}}, |
| {SPV_OPERAND_TYPE_ID, {if_block_id}}, |
| {SPV_OPERAND_TYPE_ID, {else_block_id}}})); |
| |
| return merge_block; |
| } |
| |
| bool TransformationFlattenConditionalBranch::InstructionCanBeHandled( |
| opt::IRContext* ir_context, const opt::Instruction& instruction) { |
| // We can handle all instructions with no side effects. |
| if (fuzzerutil::InstructionHasNoSideEffects(instruction)) { |
| return true; |
| } |
| |
| // We cannot handle barrier instructions, while we should be able to handle |
| // all other instructions by enclosing them inside a conditional. |
| if (instruction.opcode() == SpvOpControlBarrier || |
| instruction.opcode() == SpvOpMemoryBarrier || |
| instruction.opcode() == SpvOpNamedBarrierInitialize || |
| instruction.opcode() == SpvOpMemoryNamedBarrier || |
| instruction.opcode() == SpvOpTypeNamedBarrier) { |
| return false; |
| } |
| |
| // We cannot handle OpSampledImage instructions, as they need to be in the |
| // same block as their use. |
| if (instruction.opcode() == SpvOpSampledImage) { |
| return false; |
| } |
| |
| // We cannot handle a sampled image load, because we re-work loads using |
| // conditional branches and OpPhi instructions, and the result type of OpPhi |
| // cannot be OpTypeSampledImage. |
| if (instruction.opcode() == SpvOpLoad && |
| ir_context->get_def_use_mgr()->GetDef(instruction.type_id())->opcode() == |
| SpvOpTypeSampledImage) { |
| return false; |
| } |
| |
| // We cannot handle instructions with an id which return a void type, if the |
| // result id is used in the module (e.g. a function call to a function that |
| // returns nothing). |
| if (instruction.HasResultId()) { |
| auto type = ir_context->get_type_mgr()->GetType(instruction.type_id()); |
| assert(type && "The type should be found in the module"); |
| |
| if (type->AsVoid() && |
| !ir_context->get_def_use_mgr()->WhileEachUse( |
| instruction.result_id(), |
| [](opt::Instruction* use_inst, uint32_t use_index) { |
| // Return false if the id is used as an input operand. |
| return use_index < |
| use_inst->NumOperands() - use_inst->NumInOperands(); |
| })) { |
| return false; |
| } |
| } |
| |
| return true; |
| } |
| |
| std::unordered_set<uint32_t> |
| TransformationFlattenConditionalBranch::GetFreshIds() const { |
| std::unordered_set<uint32_t> result = { |
| message_.fresh_id_for_bvec2_selector(), |
| message_.fresh_id_for_bvec3_selector(), |
| message_.fresh_id_for_bvec4_selector()}; |
| for (auto& side_effect_wrapper_info : message_.side_effect_wrapper_info()) { |
| result.insert(side_effect_wrapper_info.merge_block_id()); |
| result.insert(side_effect_wrapper_info.execute_block_id()); |
| result.insert(side_effect_wrapper_info.actual_result_id()); |
| result.insert(side_effect_wrapper_info.alternative_block_id()); |
| result.insert(side_effect_wrapper_info.placeholder_result_id()); |
| } |
| return result; |
| } |
| |
| uint32_t TransformationFlattenConditionalBranch::FindConvergenceBlock( |
| opt::IRContext* ir_context, const opt::BasicBlock& header_block) { |
| uint32_t result = header_block.terminator()->GetSingleWordInOperand(1); |
| auto postdominator_analysis = |
| ir_context->GetPostDominatorAnalysis(header_block.GetParent()); |
| while (!postdominator_analysis->Dominates(result, header_block.id())) { |
| auto current_block = ir_context->get_instr_block(result); |
| // If the transformation is applicable, the terminator is OpBranch. |
| result = current_block->terminator()->GetSingleWordInOperand(0); |
| } |
| return result; |
| } |
| |
| bool TransformationFlattenConditionalBranch::OpSelectArgumentsAreRestricted( |
| opt::IRContext* ir_context) { |
| switch (ir_context->grammar().target_env()) { |
| case SPV_ENV_UNIVERSAL_1_0: |
| case SPV_ENV_UNIVERSAL_1_1: |
| case SPV_ENV_UNIVERSAL_1_2: |
| case SPV_ENV_UNIVERSAL_1_3: { |
| return true; |
| } |
| default: |
| return false; |
| } |
| } |
| |
| void TransformationFlattenConditionalBranch::AddBooleanVectorConstructorToBlock( |
| uint32_t fresh_id, uint32_t dimension, |
| const opt::Operand& branch_condition_operand, opt::IRContext* ir_context, |
| opt::BasicBlock* block) const { |
| opt::Instruction::OperandList in_operands; |
| for (uint32_t i = 0; i < dimension; i++) { |
| in_operands.emplace_back(branch_condition_operand); |
| } |
| block->begin()->InsertBefore(MakeUnique<opt::Instruction>( |
| ir_context, SpvOpCompositeConstruct, |
| fuzzerutil::MaybeGetVectorType( |
| ir_context, fuzzerutil::MaybeGetBoolType(ir_context), dimension), |
| fresh_id, in_operands)); |
| fuzzerutil::UpdateModuleIdBound(ir_context, fresh_id); |
| } |
| |
| void TransformationFlattenConditionalBranch:: |
| RewriteOpPhiInstructionsAtConvergenceBlock( |
| const opt::BasicBlock& header_block, uint32_t convergence_block_id, |
| opt::IRContext* ir_context) const { |
| const opt::Instruction& branch_instruction = *header_block.terminator(); |
| |
| const opt::Operand& branch_condition_operand = |
| branch_instruction.GetInOperand(0); |
| |
| // If we encounter OpPhi instructions on vector types then we may need to |
| // introduce vector versions of the selection construct's condition to use |
| // in corresponding OpSelect instructions. These booleans track whether we |
| // need to introduce such boolean vectors. |
| bool require_2d_boolean_vector = false; |
| bool require_3d_boolean_vector = false; |
| bool require_4d_boolean_vector = false; |
| |
| // Consider every OpPhi instruction at the convergence block. |
| opt::BasicBlock* convergence_block = |
| ir_context->get_instr_block(convergence_block_id); |
| convergence_block->ForEachPhiInst( |
| [this, &branch_condition_operand, branch_instruction, &header_block, |
| ir_context, &require_2d_boolean_vector, &require_3d_boolean_vector, |
| &require_4d_boolean_vector](opt::Instruction* phi_inst) { |
| assert(phi_inst->NumInOperands() == 4 && |
| "We are going to replace an OpPhi with an OpSelect. This " |
| "only makes sense if the block has two distinct " |
| "predecessors."); |
| // We are going to replace the OpPhi with an OpSelect. By default, |
| // the condition for the OpSelect will be the branch condition's |
| // operand. However, if the OpPhi has vector result type we may need |
| // to use a boolean vector as the condition instead. |
| opt::Operand selector_operand = branch_condition_operand; |
| opt::Instruction* type_inst = |
| ir_context->get_def_use_mgr()->GetDef(phi_inst->type_id()); |
| if (type_inst->opcode() == SpvOpTypeVector) { |
| uint32_t dimension = type_inst->GetSingleWordInOperand(1); |
| switch (dimension) { |
| case 2: |
| // The OpPhi's result type is a 2D vector. If a fresh id for a |
| // bvec2 selector was provided then we should use it as the |
| // OpSelect's condition, and note the fact that we will need to |
| // add an instruction to bring this bvec2 into existence. |
| if (message_.fresh_id_for_bvec2_selector() != 0) { |
| selector_operand = {SPV_OPERAND_TYPE_TYPE_ID, |
| {message_.fresh_id_for_bvec2_selector()}}; |
| require_2d_boolean_vector = true; |
| } |
| break; |
| case 3: |
| // Similar to the 2D case. |
| if (message_.fresh_id_for_bvec3_selector() != 0) { |
| selector_operand = {SPV_OPERAND_TYPE_TYPE_ID, |
| {message_.fresh_id_for_bvec3_selector()}}; |
| require_3d_boolean_vector = true; |
| } |
| break; |
| default: |
| assert(dimension == 4 && "Invalid vector dimension."); |
| // Similar to the 2D case. |
| if (message_.fresh_id_for_bvec4_selector() != 0) { |
| selector_operand = {SPV_OPERAND_TYPE_TYPE_ID, |
| {message_.fresh_id_for_bvec4_selector()}}; |
| require_4d_boolean_vector = true; |
| } |
| break; |
| } |
| } |
| std::vector<opt::Operand> operands; |
| operands.emplace_back(selector_operand); |
| |
| uint32_t branch_instruction_true_block_id = |
| branch_instruction.GetSingleWordInOperand(1); |
| |
| // The OpPhi takes values from two distinct predecessors. One |
| // predecessor is associated with the "true" path of the conditional |
| // we are flattening, the other with the "false" path, but these |
| // predecessors can appear in either order as operands to the OpPhi |
| // instruction. We determine in which order the OpPhi inputs should |
| // appear as OpSelect arguments by checking dominance of the true and |
| // false immediate successors of the header block. |
| if (ir_context->GetDominatorAnalysis(header_block.GetParent()) |
| ->Dominates(branch_instruction_true_block_id, |
| phi_inst->GetSingleWordInOperand(1))) { |
| // The "true" branch is handled first in the OpPhi's operands; we |
| // thus provide operands to OpSelect in the same order that they |
| // appear in the OpPhi. |
| operands.emplace_back(phi_inst->GetInOperand(0)); |
| operands.emplace_back(phi_inst->GetInOperand(2)); |
| } else { |
| // The "false" branch is handled first in the OpPhi's operands; we |
| // thus provide operands to OpSelect in reverse of the order that |
| // they appear in the OpPhi. |
| operands.emplace_back(phi_inst->GetInOperand(2)); |
| operands.emplace_back(phi_inst->GetInOperand(0)); |
| } |
| phi_inst->SetOpcode(SpvOpSelect); |
| phi_inst->SetInOperands(std::move(operands)); |
| }); |
| |
| // Add boolean vector instructions to the start of the block as required. |
| if (require_2d_boolean_vector) { |
| AddBooleanVectorConstructorToBlock(message_.fresh_id_for_bvec2_selector(), |
| 2, branch_condition_operand, ir_context, |
| convergence_block); |
| } |
| if (require_3d_boolean_vector) { |
| AddBooleanVectorConstructorToBlock(message_.fresh_id_for_bvec3_selector(), |
| 3, branch_condition_operand, ir_context, |
| convergence_block); |
| } |
| if (require_4d_boolean_vector) { |
| AddBooleanVectorConstructorToBlock(message_.fresh_id_for_bvec4_selector(), |
| 4, branch_condition_operand, ir_context, |
| convergence_block); |
| } |
| } |
| |
| } // namespace fuzz |
| } // namespace spvtools |
