instructions_arm.h

// Copyright (c) 2013, 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.
// Classes that describe assembly patterns as used by inline caches.

#ifndef RUNTIME_VM_INSTRUCTIONS_ARM_H_
#define RUNTIME_VM_INSTRUCTIONS_ARM_H_

#ifndef RUNTIME_VM_INSTRUCTIONS_H_
#error Do not include instructions_arm.h directly; use instructions.h instead.
#endif

#include "vm/allocation.h"
#include "vm/constants.h"
#include "vm/native_function.h"
#include "vm/tagged_pointer.h"

#if !defined(DART_PRECOMPILED_RUNTIME)
#include "vm/compiler/assembler/assembler.h"
#endif  // !defined(DART_PRECOMPILED_RUNTIME)

namespace dart {

class ICData;
class Code;
class Object;
class ObjectPool;
class UntaggedCode;

class InstructionPattern : public AllStatic {
 public:
  // Decodes a load sequence ending at 'end' (the last instruction of the
  // load sequence is the instruction before the one at end).  Returns the
  // address of the first instruction in the sequence.  Returns the register
  // being loaded and the loaded immediate value in the output parameters
  // 'reg' and 'value' respectively.
  static uword DecodeLoadWordImmediate(uword end,
                                       Register* reg,
                                       intptr_t* value);

  // Encodes a load immediate sequence ending at 'end' (the last instruction of
  // the load sequence is the instruction before the one at end).
  //
  // Supports only a subset of [DecodeLoadWordImmediate], namely:
  //   movw r, #lower16
  //   movt r, #upper16
  static void EncodeLoadWordImmediate(uword end, Register reg, intptr_t value);

  // Decodes a load sequence ending at 'end' (the last instruction of the
  // load sequence is the instruction before the one at end).  Returns the
  // address of the first instruction in the sequence.  Returns the register
  // being loaded and the index in the pool being read from in the output
  // parameters 'reg' and 'index' respectively.
  // IMPORTANT: When generating code loading values from pool on ARM use
  // LoadWordFromPool macro instruction instead of emitting direct load.
  // The macro instruction takes care of pool offsets that can't be
  // encoded as immediates.
  static uword DecodeLoadWordFromPool(uword end,
                                      Register* reg,
                                      intptr_t* index);
};

class CallPattern : public ValueObject {
 public:
  CallPattern(uword pc, const Code& code);

  CodePtr TargetCode() const;
  void SetTargetCode(const Code& code) const;

 private:
  const ObjectPool& object_pool_;

  intptr_t target_code_pool_index_;

  DISALLOW_COPY_AND_ASSIGN(CallPattern);
};

class ICCallPattern : public ValueObject {
 public:
  ICCallPattern(uword pc, const Code& code);

  ObjectPtr Data() const;
  void SetData(const Object& data) const;

  CodePtr TargetCode() const;
  void SetTargetCode(const Code& code) const;

 private:
  const ObjectPool& object_pool_;

  intptr_t target_pool_index_;
  intptr_t data_pool_index_;

  DISALLOW_COPY_AND_ASSIGN(ICCallPattern);
};

class NativeCallPattern : public ValueObject {
 public:
  NativeCallPattern(uword pc, const Code& code);

  CodePtr target() const;
  void set_target(const Code& target) const;

  NativeFunction native_function() const;
  void set_native_function(NativeFunction target) const;

 private:
  const ObjectPool& object_pool_;

  uword end_;
  intptr_t native_function_pool_index_;
  intptr_t target_code_pool_index_;

  DISALLOW_COPY_AND_ASSIGN(NativeCallPattern);
};

// Instance call that can switch between a direct monomorphic call, an IC call,
// and a megamorphic call.
//   load guarded cid            load ICData             load MegamorphicCache
//   load monomorphic target <-> load ICLookup stub  ->  load MMLookup stub
//   call target.entry           call stub.entry         call stub.entry
class SwitchableCallPatternBase : public ValueObject {
 public:
  explicit SwitchableCallPatternBase(const ObjectPool& object_pool);

  ObjectPtr data() const;
  void SetData(const Object& data) const;

 protected:
  const ObjectPool& object_pool_;
  intptr_t data_pool_index_;
  intptr_t target_pool_index_;

 private:
  DISALLOW_COPY_AND_ASSIGN(SwitchableCallPatternBase);
};

// See [SwitchableCallBase] for a switchable calls in general.
//
// The target slot is always a [Code] object: Either the code of the
// monomorphic function or a stub code.
class SwitchableCallPattern : public SwitchableCallPatternBase {
 public:
  SwitchableCallPattern(uword pc, const Code& code);

  uword target_entry() const;
  void SetTarget(const Code& target) const;

 private:
  DISALLOW_COPY_AND_ASSIGN(SwitchableCallPattern);
};

// See [SwitchableCallBase] for a switchable calls in general.
//
// The target slot is always a direct entrypoint address: Either the entry point
// of the monomorphic function or a stub entry point.
class BareSwitchableCallPattern : public SwitchableCallPatternBase {
 public:
  explicit BareSwitchableCallPattern(uword pc);

  uword target_entry() const;
  void SetTarget(const Code& target) const;

 private:
  DISALLOW_COPY_AND_ASSIGN(BareSwitchableCallPattern);
};

class ReturnPattern : public ValueObject {
 public:
  explicit ReturnPattern(uword pc);

  // bx_lr = 1.
  static constexpr int kLengthInBytes = 1 * Instr::kInstrSize;

  int pattern_length_in_bytes() const { return kLengthInBytes; }

  bool IsValid() const;

 private:
  const uword pc_;
};

class PcRelativeCallPatternBase : public ValueObject {
 public:
  // 24 bit signed integer which will get multiplied by 4.
  static constexpr intptr_t kLowerCallingRange =
      -(1 << 25) + Instr::kPCReadOffset;
  static constexpr intptr_t kUpperCallingRange =
      (1 << 25) - Instr::kInstrSize + Instr::kPCReadOffset;

  explicit PcRelativeCallPatternBase(uword pc) : pc_(pc) {}

  static constexpr int kLengthInBytes = 1 * Instr::kInstrSize;

  int32_t distance() {
#if !defined(DART_PRECOMPILED_RUNTIME)
    return compiler::Assembler::DecodeBranchOffset(
        *reinterpret_cast<int32_t*>(pc_));
#else
    UNREACHABLE();
    return 0;
#endif
  }

  void set_distance(int32_t distance) {
#if !defined(DART_PRECOMPILED_RUNTIME)
    int32_t* word = reinterpret_cast<int32_t*>(pc_);
    *word = compiler::Assembler::EncodeBranchOffset(distance, *word);
#else
    UNREACHABLE();
#endif
  }

 protected:
  uword pc_;
};

class PcRelativeCallPattern : public PcRelativeCallPatternBase {
 public:
  explicit PcRelativeCallPattern(uword pc) : PcRelativeCallPatternBase(pc) {}

  bool IsValid() const;
};

class PcRelativeTailCallPattern : public PcRelativeCallPatternBase {
 public:
  explicit PcRelativeTailCallPattern(uword pc)
      : PcRelativeCallPatternBase(pc) {}

  bool IsValid() const;
};

// Instruction pattern for a tail call to a signed 32-bit PC-relative offset
//
// The AOT compiler can emit PC-relative calls. If the destination of such a
// call is not in range for the "bl.<cond> <offset>" instruction, the AOT
// compiler will emit a trampoline which is in range. That trampoline will
// then tail-call to the final destination (also via PC-relative offset, but it
// supports a full signed 32-bit offset).
//
// The pattern of the trampoline looks like:
//
//     movw TMP, #lower16
//     movt TMP, #upper16
//     add  PC, PC, TMP lsl #0
//
class PcRelativeTrampolineJumpPattern : public ValueObject {
 public:
  explicit PcRelativeTrampolineJumpPattern(uword pattern_start)
      : pattern_start_(pattern_start) {
    USE(pattern_start_);
  }

  static constexpr int kLengthInBytes = 3 * Instr::kInstrSize;

  void Initialize();

  int32_t distance();
  void set_distance(int32_t distance);
  bool IsValid() const;

 private:
  // This offset must be applied to account for the fact that
  //   a) the actual "branch" is only in the 3rd instruction
  //   b) when reading the PC it reports current instruction + 8
  static constexpr intptr_t kDistanceOffset = -4 * Instr::kInstrSize;

  // add  PC, PC, TMP lsl #0
  static constexpr uint32_t kAddPcEncoding =
      (ADD << kOpcodeShift) | (AL << kConditionShift) | (PC << kRnShift) |
      (PC << kRdShift) | (TMP << kRmShift);

  uword pattern_start_;
};

}  // namespace dart

#endif  // RUNTIME_VM_INSTRUCTIONS_ARM_H_