SPIRV-Tools/source/fuzz/transformation_replace_id_with_synonym.cpp

// 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_replace_id_with_synonym.h"

#include <algorithm>

#include "source/fuzz/data_descriptor.h"
#include "source/fuzz/fuzzer_util.h"
#include "source/fuzz/id_use_descriptor.h"
#include "source/opt/types.h"
#include "source/util/make_unique.h"

namespace spvtools {
namespace fuzz {

TransformationReplaceIdWithSynonym::TransformationReplaceIdWithSynonym(
    const spvtools::fuzz::protobufs::TransformationReplaceIdWithSynonym&
        message)
    : message_(message) {}

TransformationReplaceIdWithSynonym::TransformationReplaceIdWithSynonym(
    protobufs::IdUseDescriptor id_use_descriptor,
    protobufs::DataDescriptor data_descriptor,
    uint32_t fresh_id_for_temporary) {
  assert((fresh_id_for_temporary == 0) == (data_descriptor.index().empty()));
  *message_.mutable_id_use_descriptor() = std::move(id_use_descriptor);
  *message_.mutable_data_descriptor() = std::move(data_descriptor);
  message_.set_fresh_id_for_temporary(fresh_id_for_temporary);
}

bool TransformationReplaceIdWithSynonym::IsApplicable(
    spvtools::opt::IRContext* context,
    const spvtools::fuzz::FactManager& fact_manager) const {
  auto id_of_interest = message_.id_use_descriptor().id_of_interest();

  // Does the fact manager know about the synonym?
  if (fact_manager.GetIdsForWhichSynonymsAreKnown().count(id_of_interest) ==
      0) {
    return false;
  }

  auto available_synonyms = fact_manager.GetSynonymsForId(id_of_interest);
  if (std::find_if(available_synonyms.begin(), available_synonyms.end(),
                   [this](protobufs::DataDescriptor dd) -> bool {
                     return DataDescriptorEquals()(&dd,
                                                   &message_.data_descriptor());
                   }) == available_synonyms.end()) {
    return false;
  }

  // Does the id use descriptor in the transformation identify an instruction?
  auto use_instruction =
      transformation::FindInstruction(message_.id_use_descriptor(), context);
  if (!use_instruction) {
    return false;
  }

  // Is it legitimate to replace the use identified by the id use descriptor
  // with a synonym?
  if (!ReplacingUseWithSynonymIsOk(
          context, use_instruction,
          message_.id_use_descriptor().in_operand_index(),
          message_.data_descriptor())) {
    return false;
  }

  if (message_.fresh_id_for_temporary() == 0) {
    if (!message_.data_descriptor().index().empty()) {
      // If we have no id to use as a temporary variable, we should not have any
      // indices to extract from.
      return false;
    }
  } else {
    if (!fuzzerutil::IsFreshId(context, message_.fresh_id_for_temporary())) {
      // The id to be used as a temporary needs to be fresh.
      return false;
    }
    if (message_.data_descriptor().index_size() != 1) {
      // At present we support just a single index to allow extracting directly
      // from a composite.
      return false;
    }
  }

  return true;
}

void TransformationReplaceIdWithSynonym::Apply(
    spvtools::opt::IRContext* context,
    spvtools::fuzz::FactManager* /*unused*/) const {
  auto instruction_to_change =
      transformation::FindInstruction(message_.id_use_descriptor(), context);

  // Ultimately we are going to replace the id use identified in the
  // transformation with |replacement_id|, which will either be the synonym's
  // id, or the id of a temporary used to extract the synonym from a composite.
  uint32_t replacement_id;

  if (message_.fresh_id_for_temporary()) {
    // The transformation having a temporary variable means that we need to
    // extract the synonym from a composite.

    uint32_t type_id_of_id_to_be_replaced =
        context->get_def_use_mgr()
            ->GetDef(message_.id_use_descriptor().id_of_interest())
            ->type_id();
    opt::analysis::Type* type_of_id_to_be_replaced =
        context->get_type_mgr()->GetType(type_id_of_id_to_be_replaced);
    opt::analysis::Type* type_of_composite = context->get_type_mgr()->GetType(
        context->get_def_use_mgr()
            ->GetDef(message_.data_descriptor().object())
            ->type_id());

    // Intuitively we want to make an OpCompositeExtract instruction, to get the
    // synonym out of the composite. But in the case of a vector, the synonym
    // might involve multiple vector indices; e.g. the y and z components of a
    // vec4 might be synonymous with a vec2, and in that case OpCompositeExtract
    // doesn't give us what we want; we need to use OpVectorShuffle instead.
    std::unique_ptr<opt::Instruction> new_instruction;
    if (type_of_composite->AsVector() &&
        type_of_composite->AsVector()->element_type() !=
            type_of_id_to_be_replaced) {
      // We need to extract a vector from inside a vector, so we will need to
      // use OpVectorShuffle.

      assert(type_of_id_to_be_replaced->AsVector());
      assert(type_of_id_to_be_replaced->AsVector()->element_type() ==
             type_of_composite->AsVector()->element_type());
      opt::Instruction::OperandList shuffle_operands = {
          {SPV_OPERAND_TYPE_ID, {message_.data_descriptor().object()}},
          {SPV_OPERAND_TYPE_ID, {message_.data_descriptor().object()}}};
      for (uint32_t i = 0;
           i < type_of_id_to_be_replaced->AsVector()->element_count(); i++) {
        shuffle_operands.push_back({SPV_OPERAND_TYPE_LITERAL_INTEGER,
                                    {message_.data_descriptor().index(0) + i}});
      }
      new_instruction = MakeUnique<opt::Instruction>(
          context, SpvOpVectorShuffle, type_id_of_id_to_be_replaced,
          message_.fresh_id_for_temporary(), shuffle_operands);
    } else {
      // We are either extracting from a non-vector, or extracting a scalar from
      // a vector, so we can use OpCompositeExtract.
      opt::Instruction::OperandList extract_operands = {
          {SPV_OPERAND_TYPE_ID, {message_.data_descriptor().object()}},
          {SPV_OPERAND_TYPE_LITERAL_INTEGER,
           {message_.data_descriptor().index(0)}}};
      new_instruction = MakeUnique<opt::Instruction>(
          context, SpvOpCompositeExtract, type_id_of_id_to_be_replaced,
          message_.fresh_id_for_temporary(), extract_operands);
    }
    instruction_to_change->InsertBefore(std::move(new_instruction));

    // The replacement id is the temporary variable we used to extract the
    // synonym from a composite.
    replacement_id = message_.fresh_id_for_temporary();
    fuzzerutil::UpdateModuleIdBound(context, replacement_id);
  } else {
    // The replacement id is the synonym's id.
    replacement_id = message_.data_descriptor().object();
  }

  instruction_to_change->SetInOperand(
      message_.id_use_descriptor().in_operand_index(), {replacement_id});
  context->InvalidateAnalysesExceptFor(opt::IRContext::Analysis::kAnalysisNone);
}

protobufs::Transformation TransformationReplaceIdWithSynonym::ToMessage()
    const {
  protobufs::Transformation result;
  *result.mutable_replace_id_with_synonym() = message_;
  return result;
}

bool TransformationReplaceIdWithSynonym::ReplacingUseWithSynonymIsOk(
    opt::IRContext* context, opt::Instruction* use_instruction,
    uint32_t use_in_operand_index, const protobufs::DataDescriptor& synonym) {
  auto defining_instruction =
      context->get_def_use_mgr()->GetDef(synonym.object());

  if (use_instruction == defining_instruction) {
    // If we have an instruction:
    //   %a = OpCopyObject %t %b
    // then we know %a and %b are synonymous, but we do *not* want to turn
    // this into:
    //   %a = OpCopyObject %t %a
    // We require this special case because an instruction dominates itself.
    return false;
  }

  if (use_instruction->opcode() == SpvOpAccessChain &&
      use_in_operand_index > 0) {
    // This is an access chain index.  If the (sub-)object being accessed by the
    // given index has struct type then we cannot replace the use with a
    // synonym, as the use needs to be an OpConstant.

    // Get the top-level composite type that is being accessed.
    auto object_being_accessed = context->get_def_use_mgr()->GetDef(
        use_instruction->GetSingleWordInOperand(0));
    auto pointer_type =
        context->get_type_mgr()->GetType(object_being_accessed->type_id());
    assert(pointer_type->AsPointer());
    auto composite_type_being_accessed =
        pointer_type->AsPointer()->pointee_type();

    // Now walk the access chain, tracking the type of each sub-object of the
    // composite that is traversed, until the index of interest is reached.
    for (uint32_t index_in_operand = 1; index_in_operand < use_in_operand_index;
         index_in_operand++) {
      // For vectors, matrices and arrays, getting the type of the sub-object is
      // trivial. For the struct case, the sub-object type is field-sensitive,
      // and depends on the constant index that is used.
      if (composite_type_being_accessed->AsVector()) {
        composite_type_being_accessed =
            composite_type_being_accessed->AsVector()->element_type();
      } else if (composite_type_being_accessed->AsMatrix()) {
        composite_type_being_accessed =
            composite_type_being_accessed->AsMatrix()->element_type();
      } else if (composite_type_being_accessed->AsArray()) {
        composite_type_being_accessed =
            composite_type_being_accessed->AsArray()->element_type();
      } else {
        assert(composite_type_being_accessed->AsStruct());
        auto constant_index_instruction = context->get_def_use_mgr()->GetDef(
            use_instruction->GetSingleWordInOperand(index_in_operand));
        assert(constant_index_instruction->opcode() == SpvOpConstant);
        uint32_t member_index =
            constant_index_instruction->GetSingleWordInOperand(0);
        composite_type_being_accessed =
            composite_type_being_accessed->AsStruct()
                ->element_types()[member_index];
      }
    }

    // We have found the composite type being accessed by the index we are
    // considering replacing. If it is a struct, then we cannot do the
    // replacement as struct indices must be constants.
    if (composite_type_being_accessed->AsStruct()) {
      return false;
    }
  }

  if (use_instruction->opcode() == SpvOpFunctionCall &&
      use_in_operand_index > 0) {
    // This is a function call argument.  It is not allowed to have pointer
    // type.

    // Get the definition of the function being called.
    auto function = context->get_def_use_mgr()->GetDef(
        use_instruction->GetSingleWordInOperand(0));
    // From the function definition, get the function type.
    auto function_type =
        context->get_def_use_mgr()->GetDef(function->GetSingleWordInOperand(1));
    // OpTypeFunction's 0-th input operand is the function return type, and the
    // function argument types follow. Because the arguments to OpFunctionCall
    // start from input operand 1, we can use |use_in_operand_index| to get the
    // type associated with this function argument.
    auto parameter_type = context->get_type_mgr()->GetType(
        function_type->GetSingleWordInOperand(use_in_operand_index));
    if (parameter_type->AsPointer()) {
      return false;
    }
  }

  // We now need to check that replacing the use with the synonym will respect
  // dominance rules - i.e. the synonym needs to dominate the use.
  auto dominator_analysis = context->GetDominatorAnalysis(
      context->get_instr_block(use_instruction)->GetParent());
  if (use_instruction->opcode() == SpvOpPhi) {
    // In the case where the use is an operand to OpPhi, it is actually the
    // *parent* block associated with the operand that must be dominated by the
    // synonym.
    auto parent_block =
        use_instruction->GetSingleWordInOperand(use_in_operand_index + 1);
    if (!dominator_analysis->Dominates(
            context->get_instr_block(defining_instruction)->id(),
            parent_block)) {
      return false;
    }
  } else if (!dominator_analysis->Dominates(defining_instruction,
                                            use_instruction)) {
    return false;
  }
  return true;
}

}  // namespace fuzz
}  // namespace spvtools