source/fuzz/fuzzer_pass_outline_functions.cpp

   1 // Copyright (c) 2019 Google LLC
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //     http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 #include "source/fuzz/fuzzer_pass_outline_functions.h"
  16
  17 #include <vector>
  18
  19 #include "source/fuzz/fuzzer_util.h"
  20 #include "source/fuzz/instruction_descriptor.h"
  21 #include "source/fuzz/transformation_outline_function.h"
  22 #include "source/fuzz/transformation_split_block.h"
  23
  24 namespace spvtools {
  25 namespace fuzz {
  26
  27 FuzzerPassOutlineFunctions::FuzzerPassOutlineFunctions(
  28     opt::IRContext* ir_context, TransformationContext* transformation_context,
  29     FuzzerContext* fuzzer_context,
  30     protobufs::TransformationSequence* transformations,
  31     bool ignore_inapplicable_transformations)
  32     : FuzzerPass(ir_context, transformation_context, fuzzer_context,
  33                  transformations, ignore_inapplicable_transformations) {}
  34
  35 void FuzzerPassOutlineFunctions::Apply() {
  36   std::vector<opt::Function*> original_functions;
  37   for (auto& function : *GetIRContext()->module()) {
  38     original_functions.push_back(&function);
  39   }
  40   for (auto& function : original_functions) {
  41     if (!GetFuzzerContext()->ChoosePercentage(
  42             GetFuzzerContext()->GetChanceOfOutliningFunction())) {
  43       continue;
  44     }
  45     std::vector<opt::BasicBlock*> blocks;
  46     for (auto& block : *function) {
  47       blocks.push_back(&block);
  48     }
  49     auto entry_block = MaybeGetEntryBlockSuitableForOutlining(
  50         blocks[GetFuzzerContext()->RandomIndex(blocks)]);
  51
  52     if (!entry_block) {
  53       // The chosen block is not suitable to be the entry block of a region that
  54       // will be outlined.
  55       continue;
  56     }
  57
  58     auto dominator_analysis = GetIRContext()->GetDominatorAnalysis(function);
  59     auto postdominator_analysis =
  60         GetIRContext()->GetPostDominatorAnalysis(function);
  61     std::vector<opt::BasicBlock*> candidate_exit_blocks;
  62     for (auto postdominates_entry_block = entry_block;
  63          postdominates_entry_block != nullptr;
  64          postdominates_entry_block = postdominator_analysis->ImmediateDominator(
  65              postdominates_entry_block)) {
  66       // Consider the block if it is dominated by the entry block, ignore it if
  67       // it is a continue target.
  68       if (dominator_analysis->Dominates(entry_block,
  69                                         postdominates_entry_block) &&
  70           !GetIRContext()->GetStructuredCFGAnalysis()->IsContinueBlock(
  71               postdominates_entry_block->id())) {
  72         candidate_exit_blocks.push_back(postdominates_entry_block);
  73       }
  74     }
  75     if (candidate_exit_blocks.empty()) {
  76       continue;
  77     }
  78     auto exit_block = MaybeGetExitBlockSuitableForOutlining(
  79         candidate_exit_blocks[GetFuzzerContext()->RandomIndex(
  80             candidate_exit_blocks)]);
  81
  82     if (!exit_block) {
  83       // The block chosen is not suitable
  84       continue;
  85     }
  86
  87     auto region_blocks = TransformationOutlineFunction::GetRegionBlocks(
  88         GetIRContext(), entry_block, exit_block);
  89     std::map<uint32_t, uint32_t> input_id_to_fresh_id;
  90     for (auto id : TransformationOutlineFunction::GetRegionInputIds(
  91              GetIRContext(), region_blocks, exit_block)) {
  92       input_id_to_fresh_id[id] = GetFuzzerContext()->GetFreshId();
  93     }
  94     std::map<uint32_t, uint32_t> output_id_to_fresh_id;
  95     for (auto id : TransformationOutlineFunction::GetRegionOutputIds(
  96              GetIRContext(), region_blocks, exit_block)) {
  97       output_id_to_fresh_id[id] = GetFuzzerContext()->GetFreshId();
  98     }
  99     TransformationOutlineFunction transformation(
 100         entry_block->id(), exit_block->id(),
 101         /*new_function_struct_return_type_id*/
 102         GetFuzzerContext()->GetFreshId(),
 103         /*new_function_type_id*/ GetFuzzerContext()->GetFreshId(),
 104         /*new_function_id*/ GetFuzzerContext()->GetFreshId(),
 105         /*new_function_region_entry_block*/
 106         GetFuzzerContext()->GetFreshId(),
 107         /*new_caller_result_id*/ GetFuzzerContext()->GetFreshId(),
 108         /*new_callee_result_id*/ GetFuzzerContext()->GetFreshId(),
 109         /*input_id_to_fresh_id*/ input_id_to_fresh_id,
 110         /*output_id_to_fresh_id*/ output_id_to_fresh_id);
 111     MaybeApplyTransformation(transformation);
 112   }
 113 }
 114
 115 opt::BasicBlock*
 116 FuzzerPassOutlineFunctions::MaybeGetEntryBlockSuitableForOutlining(
 117     opt::BasicBlock* entry_block) {
 118   // If the entry block is a loop header, we need to get or create its
 119   // preheader and make it the entry block, if possible.
 120   if (entry_block->IsLoopHeader()) {
 121     auto predecessors =
 122         GetIRContext()->cfg()->preds(entry_block->GetLabel()->result_id());
 123
 124     if (predecessors.size() < 2) {
 125       // The header only has one predecessor (the back-edge block) and thus
 126       // it is unreachable. The block cannot be adjusted to be suitable for
 127       // outlining.
 128       return nullptr;
 129     }
 130
 131     // Get or create a suitable preheader and make it become the entry block.
 132     entry_block =
 133         GetOrCreateSimpleLoopPreheader(entry_block->GetLabel()->result_id());
 134   }
 135
 136   assert(!entry_block->IsLoopHeader() &&
 137          "The entry block cannot be a loop header at this point.");
 138
 139   // If the entry block starts with OpPhi or OpVariable, try to split it.
 140   if (entry_block->begin()->opcode() == spv::Op::OpPhi ||
 141       entry_block->begin()->opcode() == spv::Op::OpVariable) {
 142     // Find the first non-OpPhi and non-OpVariable instruction.
 143     auto non_phi_or_var_inst = &*entry_block->begin();
 144     while (non_phi_or_var_inst->opcode() == spv::Op::OpPhi ||
 145            non_phi_or_var_inst->opcode() == spv::Op::OpVariable) {
 146       non_phi_or_var_inst = non_phi_or_var_inst->NextNode();
 147     }
 148
 149     // Split the block.
 150     uint32_t new_block_id = GetFuzzerContext()->GetFreshId();
 151     ApplyTransformation(TransformationSplitBlock(
 152         MakeInstructionDescriptor(GetIRContext(), non_phi_or_var_inst),
 153         new_block_id));
 154
 155     // The new entry block is the newly-created block.
 156     entry_block = &*entry_block->GetParent()->FindBlock(new_block_id);
 157   }
 158
 159   return entry_block;
 160 }
 161
 162 opt::BasicBlock*
 163 FuzzerPassOutlineFunctions::MaybeGetExitBlockSuitableForOutlining(
 164     opt::BasicBlock* exit_block) {
 165   // The exit block must not be a continue target.
 166   assert(!GetIRContext()->GetStructuredCFGAnalysis()->IsContinueBlock(
 167              exit_block->id()) &&
 168          "A candidate exit block cannot be a continue target.");
 169
 170   // If the exit block is a merge block, try to split it and return the second
 171   // block in the pair as the exit block.
 172   if (GetIRContext()->GetStructuredCFGAnalysis()->IsMergeBlock(
 173           exit_block->id())) {
 174     uint32_t new_block_id = GetFuzzerContext()->GetFreshId();
 175
 176     // Find the first non-OpPhi instruction, after which to split.
 177     auto split_before = &*exit_block->begin();
 178     while (split_before->opcode() == spv::Op::OpPhi) {
 179       split_before = split_before->NextNode();
 180     }
 181
 182     if (!MaybeApplyTransformation(TransformationSplitBlock(
 183             MakeInstructionDescriptor(GetIRContext(), split_before),
 184             new_block_id))) {
 185       return nullptr;
 186     }
 187
 188     return &*exit_block->GetParent()->FindBlock(new_block_id);
 189   }
 190
 191   return exit_block;
 192 }
 193
 194 }  // namespace fuzz
 195 }  // namespace spvtools