| // Copyright (c) 2019 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_add_dead_break.h" |
| |
| #include "source/fuzz/fuzzer_util.h" |
| #include "source/fuzz/transformation_context.h" |
| #include "source/opt/basic_block.h" |
| #include "source/opt/ir_context.h" |
| #include "source/opt/struct_cfg_analysis.h" |
| |
| namespace spvtools { |
| namespace fuzz { |
| |
| TransformationAddDeadBreak::TransformationAddDeadBreak( |
| protobufs::TransformationAddDeadBreak message) |
| : message_(std::move(message)) {} |
| |
| TransformationAddDeadBreak::TransformationAddDeadBreak( |
| uint32_t from_block, uint32_t to_block, bool break_condition_value, |
| std::vector<uint32_t> phi_id) { |
| message_.set_from_block(from_block); |
| message_.set_to_block(to_block); |
| message_.set_break_condition_value(break_condition_value); |
| for (auto id : phi_id) { |
| message_.add_phi_id(id); |
| } |
| } |
| |
| bool TransformationAddDeadBreak::AddingBreakRespectsStructuredControlFlow( |
| opt::IRContext* ir_context, opt::BasicBlock* bb_from) const { |
| // Look at the structured control flow associated with |from_block| and |
| // check whether it is contained in an appropriate construct with merge id |
| // |to_block| such that a break from |from_block| to |to_block| is legal. |
| |
| // There are three legal cases to consider: |
| // (1) |from_block| is a loop header and |to_block| is its merge |
| // (2) |from_block| is a non-header node of a construct, and |to_block| |
| // is the merge for that construct |
| // (3) |from_block| is a non-header node of a selection construct, and |
| // |to_block| is the merge for the innermost loop containing |
| // |from_block| |
| // |
| // TODO(https://github.com/KhronosGroup/SPIRV-Tools/issues/2653) It may be |
| // possible to be more aggressive in breaking from switch constructs. |
| // |
| // The reason we need to distinguish between cases (1) and (2) is that the |
| // structured CFG analysis does not deem a header to be part of the construct |
| // that it heads. |
| |
| // Consider case (1) |
| if (bb_from->IsLoopHeader()) { |
| // Case (1) holds if |to_block| is the merge block for the loop; |
| // otherwise no case holds |
| return bb_from->MergeBlockId() == message_.to_block(); |
| } |
| |
| // Both cases (2) and (3) require that |from_block| is inside some |
| // structured control flow construct. |
| |
| auto containing_construct = |
| ir_context->GetStructuredCFGAnalysis()->ContainingConstruct( |
| message_.from_block()); |
| if (!containing_construct) { |
| // |from_block| is not in a construct from which we can break. |
| return false; |
| } |
| |
| // Consider case (2) |
| if (message_.to_block() == |
| ir_context->cfg()->block(containing_construct)->MergeBlockId()) { |
| // This looks like an instance of case (2). |
| // However, the structured CFG analysis regards the continue construct of a |
| // loop as part of the loop, but it is not legal to jump from a loop's |
| // continue construct to the loop's merge (except from the back-edge block), |
| // so we need to check for this case. |
| return !fuzzerutil::BlockIsInLoopContinueConstruct( |
| ir_context, message_.from_block(), containing_construct) || |
| fuzzerutil::BlockIsBackEdge(ir_context, message_.from_block(), |
| containing_construct); |
| } |
| |
| // Case (3) holds if and only if |to_block| is the merge block for this |
| // innermost loop that contains |from_block| |
| auto containing_loop_header = |
| ir_context->GetStructuredCFGAnalysis()->ContainingLoop( |
| message_.from_block()); |
| if (containing_loop_header && |
| message_.to_block() == |
| ir_context->cfg()->block(containing_loop_header)->MergeBlockId()) { |
| return !fuzzerutil::BlockIsInLoopContinueConstruct( |
| ir_context, message_.from_block(), containing_loop_header) || |
| fuzzerutil::BlockIsBackEdge(ir_context, message_.from_block(), |
| containing_loop_header); |
| } |
| return false; |
| } |
| |
| bool TransformationAddDeadBreak::IsApplicable( |
| opt::IRContext* ir_context, |
| const TransformationContext& transformation_context) const { |
| // First, we check that a constant with the same value as |
| // |message_.break_condition_value| is present. |
| const auto bool_id = |
| fuzzerutil::MaybeGetBoolConstant(ir_context, transformation_context, |
| message_.break_condition_value(), false); |
| if (!bool_id) { |
| // The required constant is not present, so the transformation cannot be |
| // applied. |
| return false; |
| } |
| |
| // Check that |message_.from_block| and |message_.to_block| really are block |
| // ids |
| opt::BasicBlock* bb_from = |
| fuzzerutil::MaybeFindBlock(ir_context, message_.from_block()); |
| if (bb_from == nullptr) { |
| return false; |
| } |
| opt::BasicBlock* bb_to = |
| fuzzerutil::MaybeFindBlock(ir_context, message_.to_block()); |
| if (bb_to == nullptr) { |
| return false; |
| } |
| |
| if (!ir_context->IsReachable(*bb_to)) { |
| // If the target of the break is unreachable, we conservatively do not |
| // allow adding a dead break, to avoid the compilations that arise due to |
| // the lack of sensible dominance information for unreachable blocks. |
| return false; |
| } |
| |
| // Check that |message_.from_block| ends with an unconditional branch. |
| if (bb_from->terminator()->opcode() != spv::Op::OpBranch) { |
| // The block associated with the id does not end with an unconditional |
| // branch. |
| return false; |
| } |
| |
| assert(bb_from != nullptr && |
| "We should have found a block if this line of code is reached."); |
| assert( |
| bb_from->id() == message_.from_block() && |
| "The id of the block we found should match the source id for the break."); |
| assert(bb_to != nullptr && |
| "We should have found a block if this line of code is reached."); |
| assert( |
| bb_to->id() == message_.to_block() && |
| "The id of the block we found should match the target id for the break."); |
| |
| // Check whether the data passed to extend OpPhi instructions is appropriate. |
| if (!fuzzerutil::PhiIdsOkForNewEdge(ir_context, bb_from, bb_to, |
| message_.phi_id())) { |
| return false; |
| } |
| |
| // Check that adding the break would respect the rules of structured |
| // control flow. |
| if (!AddingBreakRespectsStructuredControlFlow(ir_context, bb_from)) { |
| return false; |
| } |
| |
| // Adding the dead break is only valid if SPIR-V rules related to dominance |
| // hold. |
| return fuzzerutil::NewTerminatorPreservesDominationRules( |
| ir_context, message_.from_block(), |
| fuzzerutil::CreateUnreachableEdgeInstruction( |
| ir_context, message_.from_block(), message_.to_block(), bool_id)); |
| } |
| |
| void TransformationAddDeadBreak::Apply( |
| opt::IRContext* ir_context, |
| TransformationContext* transformation_context) const { |
| fuzzerutil::AddUnreachableEdgeAndUpdateOpPhis( |
| ir_context, ir_context->cfg()->block(message_.from_block()), |
| ir_context->cfg()->block(message_.to_block()), |
| fuzzerutil::MaybeGetBoolConstant(ir_context, *transformation_context, |
| message_.break_condition_value(), false), |
| message_.phi_id()); |
| |
| // Invalidate all analyses |
| ir_context->InvalidateAnalysesExceptFor( |
| opt::IRContext::Analysis::kAnalysisNone); |
| } |
| |
| protobufs::Transformation TransformationAddDeadBreak::ToMessage() const { |
| protobufs::Transformation result; |
| *result.mutable_add_dead_break() = message_; |
| return result; |
| } |
| |
| std::unordered_set<uint32_t> TransformationAddDeadBreak::GetFreshIds() const { |
| return std::unordered_set<uint32_t>(); |
| } |
| |
| } // namespace fuzz |
| } // namespace spvtools |