Method GroupInstructionsByUseDef

source/opt/loop_fission.cpp:188–267

}

bool LoopFissionImpl::GroupInstructionsByUseDef() {
  std::vector<std::set<Instruction*>> sets{};

  // We want to ignore all the instructions stemming from the loop condition
  // instruction.
  BasicBlock* condition_block = loop_->FindConditionBlock();

  if (!condition_block) return false;
  Instruction* condition = &*condition_block->tail();

  // We iterate over the blocks via iterating over all the blocks in the
  // function, we do this so we are iterating in the same order which the blocks
  // appear in the binary.
  Function& function = *loop_->GetHeaderBlock()->GetParent();

  // Create a temporary set to ignore certain groups of instructions within the
  // loop. We don't want any instructions related to control flow to be removed
  // from either loop only instructions within the control flow bodies.
  std::set<Instruction*> instructions_to_ignore{};
  TraverseUseDef(condition, &instructions_to_ignore, true, true);

  // Traverse control flow instructions to ensure they are added to the
  // seen_instructions_ set and will be ignored when it it called with actual
  // sets.
  for (BasicBlock& block : function) {
    if (!loop_->IsInsideLoop(block.id())) continue;

    for (Instruction& inst : block) {
      // Ignore all instructions related to control flow.
      if (inst.opcode() == spv::Op::OpSelectionMerge || inst.IsBranch()) {
        TraverseUseDef(&inst, &instructions_to_ignore, true, true);
      }
    }
  }

  // Traverse the instructions and generate the sets, automatically ignoring any
  // instructions in instructions_to_ignore.
  for (BasicBlock& block : function) {
    if (!loop_->IsInsideLoop(block.id()) ||
        loop_->GetHeaderBlock()->id() == block.id())
      continue;

    for (Instruction& inst : block) {
      // Record the order that each load/store is seen.
      if (inst.opcode() == spv::Op::OpLoad ||
          inst.opcode() == spv::Op::OpStore) {
        instruction_order_[&inst] = instruction_order_.size();
      }

      // Ignore instructions already seen in a traversal.
      if (seen_instructions_.count(&inst) != 0) {
        continue;
      }

      // Build the set.
      std::set<Instruction*> inst_set{};
      TraverseUseDef(&inst, &inst_set);
      if (!inst_set.empty()) sets.push_back(std::move(inst_set));