Method Process

source/opt/loop_fission.cpp:455–519

}

Pass::Status LoopFissionPass::Process() {
  bool changed = false;

  for (Function& f : *context()->module()) {
    // We collect all the inner most loops in the function and run the loop
    // splitting util on each. The reason we do this is to allow us to iterate
    // over each, as creating new loops will invalidate the loop iterator.
    std::vector<Loop*> inner_most_loops{};
    LoopDescriptor& loop_descriptor = *context()->GetLoopDescriptor(&f);
    for (Loop& loop : loop_descriptor) {
      if (!loop.HasChildren() && ShouldSplitLoop(loop, context())) {
        inner_most_loops.push_back(&loop);
      }
    }

    // List of new loops which meet the criteria to be split again.
    std::vector<Loop*> new_loops_to_split{};

    while (!inner_most_loops.empty()) {
      for (Loop* loop : inner_most_loops) {
        LoopFissionImpl impl{context(), loop};

        // Group the instructions in the loop into two different sets of related
        // instructions. If we can't group the instructions into the two sets
        // then we can't split the loop any further.
        if (!impl.GroupInstructionsByUseDef()) {
          continue;
        }

        if (impl.CanPerformSplit()) {
          Loop* second_loop = impl.SplitLoop();
          if (!second_loop) {
            return Status::Failure;
          }
          changed = true;
          context()->InvalidateAnalysesExceptFor(
              IRContext::kAnalysisLoopAnalysis);

          // If the newly created loop meets the criteria to be split, split it
          // again.
          if (ShouldSplitLoop(*second_loop, context()))
            new_loops_to_split.push_back(second_loop);

          // If the original loop (now split) still meets the criteria to be
          // split, split it again.
          if (ShouldSplitLoop(*loop, context()))
            new_loops_to_split.push_back(loop);
        }
      }

      // If the split multiple times flag has been set add the new loops which
      // meet the splitting criteria into the list of loops to be split on the
      // next iteration.
      if (split_multiple_times_) {
        inner_most_loops = std::move(new_loops_to_split);
        new_loops_to_split = {};
      } else {
        break;