assembler.cc.svn-base

Google浏览器V8内核代码

// Copyright (c) 1994-2006 Sun Microsystems Inc.
// All Rights Reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// - Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
//
// - Redistribution in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// - Neither the name of Sun Microsystems or the names of contributors may
// be used to endorse or promote products derived from this software without
// specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
// IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
// THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
// EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
// LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
// NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

// The original source code covered by the above license above has been
// modified significantly by Google Inc.
// Copyright 2006-2008 the V8 project authors. All rights reserved.

#include "v8.h"

#include "arguments.h"
#include "execution.h"
#include "ic-inl.h"
#include "factory.h"
#include "runtime.h"
#include "serialize.h"
#include "stub-cache.h"

namespace v8 { namespace internal {


// -----------------------------------------------------------------------------
// Implementation of Label

int Label::pos() const {
  if (pos_ < 0) return -pos_ - 1;
  if (pos_ > 0) return  pos_ - 1;
  UNREACHABLE();
  return 0;
}


// -----------------------------------------------------------------------------
// Implementation of RelocInfoWriter and RelocIterator
//
// Encoding
//
// The most common modes are given single-byte encodings.  Also, it is
// easy to identify the type of reloc info and skip unwanted modes in
// an iteration.
//
// The encoding relies on the fact that there are less than 14
// different relocation modes.
//
// embedded_object:    [6 bits pc delta] 00
//
// code_taget:         [6 bits pc delta] 01
//
// position:           [6 bits pc delta] 10,
//                     [7 bits signed data delta] 0
//
// statement_position: [6 bits pc delta] 10,
//                     [7 bits signed data delta] 1
//
// any nondata mode:   00 [4 bits rmode] 11,  // rmode: 0..13 only
//                     00 [6 bits pc delta]
//
// pc-jump:            00 1111 11,
//                     00 [6 bits pc delta]
//
// pc-jump:            01 1111 11,
// (variable length)   7 - 26 bit pc delta, written in chunks of 7
//                     bits, the lowest 7 bits written first.
//
// data-jump + pos:    00 1110 11,
//                     signed int, lowest byte written first
//
// data-jump + st.pos: 01 1110 11,
//                     signed int, lowest byte written first
//
// data-jump + comm.:  10 1110 11,
//                     signed int, lowest byte written first
//
const int kMaxRelocModes = 14;

const int kTagBits = 2;
const int kTagMask = (1 << kTagBits) - 1;
const int kExtraTagBits = 4;
const int kPositionTypeTagBits = 1;
const int kSmallDataBits = kBitsPerByte - kPositionTypeTagBits;

const int kEmbeddedObjectTag = 0;
const int kCodeTargetTag = 1;
const int kPositionTag = 2;
const int kDefaultTag = 3;

const int kPCJumpTag = (1 << kExtraTagBits) - 1;

const int kSmallPCDeltaBits = kBitsPerByte - kTagBits;
const int kSmallPCDeltaMask = (1 << kSmallPCDeltaBits) - 1;

const int kVariableLengthPCJumpTopTag = 1;
const int kChunkBits = 7;
const int kChunkMask = (1 << kChunkBits) - 1;
const int kLastChunkTagBits = 1;
const int kLastChunkTagMask = 1;
const int kLastChunkTag = 1;


const int kDataJumpTag = kPCJumpTag - 1;

const int kNonstatementPositionTag = 0;
const int kStatementPositionTag = 1;
const int kCommentTag = 2;


uint32_t RelocInfoWriter::WriteVariableLengthPCJump(uint32_t pc_delta) {
  // Return if the pc_delta can fit in kSmallPCDeltaBits bits.
  // Otherwise write a variable length PC jump for the bits that do
  // not fit in the kSmallPCDeltaBits bits.
  if (is_uintn(pc_delta, kSmallPCDeltaBits)) return pc_delta;
  WriteExtraTag(kPCJumpTag, kVariableLengthPCJumpTopTag);
  uint32_t pc_jump = pc_delta >> kSmallPCDeltaBits;
  ASSERT(pc_jump > 0);
  // Write kChunkBits size chunks of the pc_jump.
  for (; pc_jump > 0; pc_jump = pc_jump >> kChunkBits) {
    byte b = pc_jump & kChunkMask;
    *--pos_ = b << kLastChunkTagBits;
  }
  // Tag the last chunk so it can be identified.
  *pos_ = *pos_ | kLastChunkTag;
  // Return the remaining kSmallPCDeltaBits of the pc_delta.
  return pc_delta & kSmallPCDeltaMask;
}


void RelocInfoWriter::WriteTaggedPC(uint32_t pc_delta, int tag) {
  // Write a byte of tagged pc-delta, possibly preceded by var. length pc-jump.
  pc_delta = WriteVariableLengthPCJump(pc_delta);
  *--pos_ = pc_delta << kTagBits | tag;
}


void RelocInfoWriter::WriteTaggedData(int32_t data_delta, int tag) {
  *--pos_ = data_delta << kPositionTypeTagBits | tag;
}


void RelocInfoWriter::WriteExtraTag(int extra_tag, int top_tag) {
  *--pos_ = top_tag << (kTagBits + kExtraTagBits) |
            extra_tag << kTagBits |
            kDefaultTag;
}


void RelocInfoWriter::WriteExtraTaggedPC(uint32_t pc_delta, int extra_tag) {
  // Write two-byte tagged pc-delta, possibly preceded by var. length pc-jump.
  pc_delta = WriteVariableLengthPCJump(pc_delta);
  WriteExtraTag(extra_tag, 0);
  *--pos_ = pc_delta;
}


void RelocInfoWriter::WriteExtraTaggedData(int32_t data_delta, int top_tag) {
  WriteExtraTag(kDataJumpTag, top_tag);
  for (int i = 0; i < kIntSize; i++) {
    *--pos_ = data_delta;
    data_delta = ArithmeticShiftRight(data_delta, kBitsPerByte);
  }
}


void RelocInfoWriter::Write(const RelocInfo* rinfo) {
#ifdef DEBUG
  byte* begin_pos = pos_;
#endif
  Counters::reloc_info_count.Increment();
  ASSERT(rinfo->pc() - last_pc_ >= 0);
  ASSERT(RelocInfo::NUMBER_OF_MODES < kMaxRelocModes);
  // Use unsigned delta-encoding for pc.
  uint32_t pc_delta = rinfo->pc() - last_pc_;
  RelocInfo::Mode rmode = rinfo->rmode();

  // The two most common modes are given small tags, and usually fit in a byte.
  if (rmode == RelocInfo::EMBEDDED_OBJECT) {
    WriteTaggedPC(pc_delta, kEmbeddedObjectTag);
  } else if (rmode == RelocInfo::CODE_TARGET) {
    WriteTaggedPC(pc_delta, kCodeTargetTag);
  } else if (RelocInfo::IsPosition(rmode)) {
    // Use signed delta-encoding for data.
    int32_t data_delta = rinfo->data() - last_data_;
    int pos_type_tag = rmode == RelocInfo::POSITION ? kNonstatementPositionTag
                                                    : kStatementPositionTag;
    // Check if data is small enough to fit in a tagged byte.
    if (is_intn(data_delta, kSmallDataBits)) {
      WriteTaggedPC(pc_delta, kPositionTag);
      WriteTaggedData(data_delta, pos_type_tag);
      last_data_ = rinfo->data();
    } else {
      // Otherwise, use costly encoding.
      WriteExtraTaggedPC(pc_delta, kPCJumpTag);
      WriteExtraTaggedData(data_delta, pos_type_tag);
      last_data_ = rinfo->data();
    }
  } else if (RelocInfo::IsComment(rmode)) {
    // Comments are normally not generated, so we use the costly encoding.
    WriteExtraTaggedPC(pc_delta, kPCJumpTag);
    WriteExtraTaggedData(rinfo->data() - last_data_, kCommentTag);
    last_data_ = rinfo->data();
  } else {
    // For all other modes we simply use the mode as the extra tag.
    // None of these modes need a data component.
    ASSERT(rmode < kPCJumpTag && rmode < kDataJumpTag);
    WriteExtraTaggedPC(pc_delta, rmode);
  }
  last_pc_ = rinfo->pc();
#ifdef DEBUG
  ASSERT(begin_pos - pos_ <= kMaxSize);
#endif
}


inline int RelocIterator::AdvanceGetTag() {
  return *--pos_ & kTagMask;
}


inline int RelocIterator::GetExtraTag() {
  return (*pos_ >> kTagBits) & ((1 << kExtraTagBits) - 1);
}


inline int RelocIterator::GetTopTag() {
  return *pos_ >> (kTagBits + kExtraTagBits);
}


inline void RelocIterator::ReadTaggedPC() {
  rinfo_.pc_ += *pos_ >> kTagBits;
}


inline void RelocIterator::AdvanceReadPC() {
  rinfo_.pc_ += *--pos_;
}


void RelocIterator::AdvanceReadData() {
  int32_t x = 0;
  for (int i = 0; i < kIntSize; i++) {
    x |= *--pos_ << i * kBitsPerByte;
  }
  rinfo_.data_ += x;
}


void RelocIterator::AdvanceReadVariableLengthPCJump() {
  // Read the 32-kSmallPCDeltaBits most significant bits of the
  // pc jump in kChunkBits bit chunks and shift them into place.
  // Stop when the last chunk is encountered.
  uint32_t pc_jump = 0;
  for (int i = 0; i < kIntSize; i++) {
    byte pc_jump_part = *--pos_;
    pc_jump |= (pc_jump_part >> kLastChunkTagBits) << i * kChunkBits;
    if ((pc_jump_part & kLastChunkTagMask) == 1) break;
  }
  // The least significant kSmallPCDeltaBits bits will be added
  // later.
  rinfo_.pc_ += pc_jump << kSmallPCDeltaBits;
}


inline int RelocIterator::GetPositionTypeTag() {