Method Fuse

source/opt/loop_fusion.cpp:533–730

}

void LoopFusion::Fuse() {
  assert(AreCompatible() && "Can't fuse, loops aren't compatible");
  assert(IsLegal() && "Can't fuse, illegal");

  // Save the pointers/ids, won't be found in the middle of doing modifications.
  auto header_1 = loop_1_->GetHeaderBlock()->id();
  auto condition_1 = loop_1_->FindConditionBlock()->id();
  auto continue_1 = loop_1_->GetContinueBlock()->id();
  auto continue_0 = loop_0_->GetContinueBlock()->id();
  auto condition_block_of_0 = loop_0_->FindConditionBlock();

  // Find the blocks whose branches need updating.
  auto first_block_of_1 = &*(++containing_function_->FindBlock(condition_1));
  auto last_block_of_1 = &*(--containing_function_->FindBlock(continue_1));
  auto last_block_of_0 = &*(--containing_function_->FindBlock(continue_0));

  // Update the branch for |last_block_of_loop_0| to go to |first_block_of_1|.
  last_block_of_0->ForEachSuccessorLabel(
      [first_block_of_1](uint32_t* succ) { *succ = first_block_of_1->id(); });

  // Update the branch for the |last_block_of_loop_1| to go to the continue
  // block of |loop_0_|.
  last_block_of_1->ForEachSuccessorLabel(
      [this](uint32_t* succ) { *succ = loop_0_->GetContinueBlock()->id(); });

  // Update merge block id in the header of |loop_0_| to the merge block of
  // |loop_1_|.
  loop_0_->GetHeaderBlock()->ForEachInst([this](Instruction* inst) {
    if (inst->opcode() == spv::Op::OpLoopMerge) {
      inst->SetInOperand(0, {loop_1_->GetMergeBlock()->id()});
    }
  });

  // Update condition branch target in |loop_0_| to the merge block of
  // |loop_1_|.
  condition_block_of_0->ForEachInst([this](Instruction* inst) {
    if (inst->opcode() == spv::Op::OpBranchConditional) {
      auto loop_0_merge_block_id = loop_0_->GetMergeBlock()->id();

      if (inst->GetSingleWordInOperand(1) == loop_0_merge_block_id) {
        inst->SetInOperand(1, {loop_1_->GetMergeBlock()->id()});
      } else {
        inst->SetInOperand(2, {loop_1_->GetMergeBlock()->id()});
      }
    }
  });

  // Move OpPhi instructions not corresponding to the induction variable from
  // the header of |loop_1_| to the header of |loop_0_|.
  std::vector<Instruction*> instructions_to_move{};
  for (auto& instruction : *loop_1_->GetHeaderBlock()) {
    if (instruction.opcode() == spv::Op::OpPhi &&
        &instruction != induction_1_) {
      instructions_to_move.push_back(&instruction);
    }
  }

  for (auto& it : instructions_to_move) {