Method DuplicateAndConnectLoop

source/opt/loop_peeling.cpp:48–160

size_t LoopPeelingPass::code_grow_threshold_ = 1000;

bool LoopPeeling::DuplicateAndConnectLoop(
    LoopUtils::LoopCloningResult* clone_results) {
  CFG& cfg = *context_->cfg();
  analysis::DefUseManager* def_use_mgr = context_->get_def_use_mgr();

  assert(CanPeelLoop() && "Cannot peel loop!");

  std::vector<BasicBlock*> ordered_loop_blocks;
  BasicBlock* pre_header = loop_->GetOrCreatePreHeaderBlock();
  if (!pre_header) {
    return false;
  }

  loop_->ComputeLoopStructuredOrder(&ordered_loop_blocks);

  cloned_loop_ = loop_utils_.CloneLoop(clone_results, ordered_loop_blocks);
  if (!cloned_loop_) {
    return false;
  }

  // Add the basic block to the function.
  Function::iterator it =
      loop_utils_.GetFunction()->FindBlock(pre_header->id());
  assert(it != loop_utils_.GetFunction()->end() &&
         "Pre-header not found in the function.");
  loop_utils_.GetFunction()->AddBasicBlocks(
      clone_results->cloned_bb_.begin(), clone_results->cloned_bb_.end(), ++it);

  // Make the |loop_|'s preheader the |cloned_loop_| one.
  BasicBlock* cloned_header = cloned_loop_->GetHeaderBlock();
  pre_header->ForEachSuccessorLabel(
      [cloned_header](uint32_t* succ) { *succ = cloned_header->id(); });

  // Update cfg.
  cfg.RemoveEdge(pre_header->id(), loop_->GetHeaderBlock()->id());
  cloned_loop_->SetPreHeaderBlock(pre_header);
  loop_->SetPreHeaderBlock(nullptr);

  // When cloning the loop, we didn't cloned the merge block, so currently
  // |cloned_loop_| shares the same block as |loop_|.
  // We mutate all branches from |cloned_loop_| block to |loop_|'s merge into a
  // branch to |loop_|'s header (so header will also be the merge of
  // |cloned_loop_|).
  uint32_t cloned_loop_exit = 0;
  for (uint32_t pred_id : cfg.preds(loop_->GetMergeBlock()->id())) {
    if (loop_->IsInsideLoop(pred_id)) continue;
    BasicBlock* bb = cfg.block(pred_id);
    assert(cloned_loop_exit == 0 && "The loop has multiple exits.");
    cloned_loop_exit = bb->id();
    bb->ForEachSuccessorLabel([this](uint32_t* succ) {
      if (*succ == loop_->GetMergeBlock()->id())
        *succ = loop_->GetHeaderBlock()->id();
    });
  }

  // Update cfg.
  cfg.RemoveNonExistingEdges(loop_->GetMergeBlock()->id());
  cfg.AddEdge(cloned_loop_exit, loop_->GetHeaderBlock()->id());