Method TraverseUseDef

source/opt/loop_fission.cpp:119–186

}

void LoopFissionImpl::TraverseUseDef(Instruction* inst,
                                     std::set<Instruction*>* returned_set,
                                     bool ignore_phi_users, bool report_loads) {
  assert(returned_set && "Set to be returned cannot be null.");

  analysis::DefUseManager* def_use = context_->get_def_use_mgr();
  std::set<Instruction*>& inst_set = *returned_set;

  // We create this functor to traverse the use def chain to build the
  // grouping of related instructions. The lambda captures the std::function
  // to allow it to recurse.
  std::function<void(Instruction*)> traverser_functor;
  traverser_functor = [this, def_use, &inst_set, &traverser_functor,
                       ignore_phi_users, report_loads](Instruction* user) {
    // If we've seen the instruction before or it is not inside the loop end the
    // traversal.
    if (!user || seen_instructions_.count(user) != 0 ||
        !context_->get_instr_block(user) ||
        !loop_->IsInsideLoop(context_->get_instr_block(user))) {
      return;
    }

    // Don't include labels or loop merge instructions in the instruction sets.
    // Including them would mean we group instructions related only by using the
    // same labels (i.e phis). We already preempt the inclusion of
    // OpSelectionMerge by adding related instructions to the seen_instructions_
    // set.
    if (user->opcode() == spv::Op::OpLoopMerge ||
        user->opcode() == spv::Op::OpLabel)
      return;

    // If the |report_loads| flag is set, set the class field
    // load_used_in_condition_ to false. This is used to check that none of the
    // condition checks in the loop rely on loads.
    if (user->opcode() == spv::Op::OpLoad && report_loads) {
      load_used_in_condition_ = true;
    }

    // Add the instruction to the set of instructions already seen, this breaks
    // recursion and allows us to ignore certain instructions.
    seen_instructions_.insert(user);

    inst_set.insert(user);

    // Wrapper functor to traverse the operands of each instruction.
    auto traverse_operand = [&traverser_functor, def_use](const uint32_t* id) {
      traverser_functor(def_use->GetDef(*id));
    };
    user->ForEachInOperand(traverse_operand);

    // For the first traversal we want to ignore the users of the phi.
    if (ignore_phi_users && user->opcode() == spv::Op::OpPhi) return;

    // Traverse each user with this lambda.
    def_use->ForEachUser(user, traverser_functor);

    // Wrapper functor for the use traversal.
    auto traverse_use = [&traverser_functor](Instruction* use, uint32_t) {