simplify-tf-loops.cc

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// Copyright 2022 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include "src/compiler/turboshaft/simplify-tf-loops.h"
 
#include "src/base/small-vector.h"
#include "src/compiler/machine-graph.h"
#include "src/compiler/node-properties.h"
 
namespace v8::internal::compiler {
 
Reduction SimplifyTFLoops::Reduce(Node* node) {
  if (node->opcode() != IrOpcode::kLoop) return NoChange();
  if (node->InputCount() <= 2) return NoChange();
 
  Node* new_loop = mcgraph_->graph()->NewNode(mcgraph_->common()->Loop(2),
                                              node->InputAt(0), node);
  node->RemoveInput(0);
  NodeProperties::ChangeOp(node, mcgraph_->common()->Merge(node->InputCount()));
 
  base::SmallVector<Edge, 4> control_uses;
 
  for (Edge edge : node->use_edges()) {
    Node* use = edge.from();
    if (!NodeProperties::IsPhi(use)) {
      control_uses.emplace_back(edge);
      continue;
    }
    Node* dominating_input = use->InputAt(0);
    use->RemoveInput(0);
    NodeProperties::ChangeOp(
        use, use->opcode() == IrOpcode::kPhi
                 ? mcgraph_->common()->Phi(PhiRepresentationOf(use->op()),
                                           use->InputCount() - 1)
                 : mcgraph_->common()->EffectPhi(use->InputCount() - 1));
 
    Node* new_phi = mcgraph_->graph()->NewNode(
        use->opcode() == IrOpcode::kPhi
            ? mcgraph_->common()->Phi(PhiRepresentationOf(use->op()), 2)
            : mcgraph_->common()->EffectPhi(2),
        dominating_input, use, new_loop);
 
    ReplaceWithValue(use, new_phi, new_phi, new_phi);
    // Restore the use <- new_phi edge we just broke.
    new_phi->ReplaceInput(1, use);
  }
 
  for (Edge edge : control_uses) {
    if (edge.from() != new_loop) {
      edge.from()->ReplaceInput(edge.index(), new_loop);
    }
  }
 
  return NoChange();
}
 
}  // namespace v8::internal::compiler