dispatch_table.h

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// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
 
#ifndef RUNTIME_VM_DISPATCH_TABLE_H_
#define RUNTIME_VM_DISPATCH_TABLE_H_
 
#include <memory>
 
#include "vm/globals.h"
 
namespace dart {
 
class DispatchTable {
 public:
  explicit DispatchTable(intptr_t length)
      : length_(length), array_(new uword[length]()) {}
 
  intptr_t length() const { return length_; }
 
  // The element of the dispatch table array to which the dispatch table
  // register points.
#if defined(TARGET_ARCH_X64)
  // Max negative byte offset / 8
  static constexpr intptr_t kOriginElement = 16;
#elif defined(TARGET_ARCH_ARM)
  // Max negative load offset / 4
  static constexpr intptr_t kOriginElement = 1023;
#elif defined(TARGET_ARCH_ARM64)
  // Max consecutive sub immediate value
  static constexpr intptr_t kOriginElement = 4096;
#elif defined(TARGET_ARCH_RISCV32)
  // Max consecutive sub immediate value
  static constexpr intptr_t kOriginElement = 2048 / 4;
#elif defined(TARGET_ARCH_RISCV64)
  // Max consecutive sub immediate value
  static constexpr intptr_t kOriginElement = 2048 / 8;
#else
  static constexpr intptr_t kOriginElement = 0;
#endif
 
#if defined(TARGET_ARCH_X64)
  // Origin + Max positive byte offset / 8
  static constexpr intptr_t kLargestSmallOffset = 31;
#elif defined(TARGET_ARCH_ARM)
  // Origin + Max positive load offset / 4
  static constexpr intptr_t kLargestSmallOffset = 2046;
#elif defined(TARGET_ARCH_ARM64)
  // Origin + Max consecutive add immediate value
  static constexpr intptr_t kLargestSmallOffset = 8192;
#elif defined(TARGET_ARCH_RISCV32)
  // Origin + Max consecutive add immediate value
  static constexpr intptr_t kLargestSmallOffset = 4096 / 4;
#elif defined(TARGET_ARCH_RISCV64)
  // Origin + Max consecutive add immediate value
  static constexpr intptr_t kLargestSmallOffset = 4096 / 8;
#else
  // No AOT on IA32
  static constexpr intptr_t kLargestSmallOffset = 0;
#endif
 
  // Dispatch table array pointer to put into the dispatch table register.
  const uword* ArrayOrigin() const;
 
 private:
  uword* array() { return array_.get(); }
 
  intptr_t length_;
  std::unique_ptr<uword[]> array_;
 
  friend class Deserializer;  // For non-const array().
  DISALLOW_COPY_AND_ASSIGN(DispatchTable);
};
 
}  // namespace dart
 
#endif  // RUNTIME_VM_DISPATCH_TABLE_H_