chromium/v8/src/compiler/decompression-optimizer.h

// Copyright 2019 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.

#ifndef V8_COMPILER_DECOMPRESSION_OPTIMIZER_H_
#define V8_COMPILER_DECOMPRESSION_OPTIMIZER_H_

#include "src/compiler/common-operator.h"
#include "src/compiler/machine-operator.h"
#include "src/compiler/node-marker.h"

namespace v8 {
namespace internal {
namespace compiler {

// Forward declare.
class Graph;

// DecompressionOptimizer purpose is to hide the distinction between 32 bit and
// 64 bit tagged values, while being able to use the compressed version of nodes
// whenever possible. Its scope is narrowed down to loads of TaggedPointer and
// AnyTagged (since TaggedSigned avoids full decompression always), and
// HeapConstants.

// DecompressionOptimizer will run only when pointer compression is enabled.

// The phase needs to be run when Machine are present in the graph, i.e
// at the very end of the pipeline. Also, since this phase may change
// the load's MachineRepresentation from Tagged to Compressed, it's best
// to run it as late as possible in order to keep the phases that know
// about Compressed MachineRepresentation to a minimum.

// As an example, if we Load a Tagged value only to Store it back again (i.e
// Load -> Store nodes, with the Load's value being the Store's value) we don't
// need to fully decompress it since the Store will ignore the top bits.
class V8_EXPORT_PRIVATE DecompressionOptimizer final { … };

}  // namespace compiler
}  // namespace internal
}  // namespace v8

#endif  // V8_COMPILER_DECOMPRESSION_OPTIMIZER_H_