text: // Copyright 2016 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/backend/arm/unwinding-info-writer-arm.h"
  #include "src/compiler/backend/instruction.h"
  
  namespace v8 {
  namespace internal {
  namespace compiler {
  
  void UnwindingInfoWriter::BeginInstructionBlock(int pc_offset,
                                                  const InstructionBlock* block) {
    if (!enabled()) return;
  
    block_will_exit_ = false;
  
    DCHECK_LT(block->rpo_number().ToInt(),
              static_cast<int>(block_initial_states_.size()));
    const BlockInitialState* initial_state =
        block_initial_states_[block->rpo_number().ToInt()];
    if (!initial_state) return;
    if (initial_state->saved_lr_ != saved_lr_) {
      eh_frame_writer_.AdvanceLocation(pc_offset);
      if (initial_state->saved_lr_) {
        eh_frame_writer_.RecordRegisterSavedToStack(lr, kSystemPointerSize);
      } else {
        eh_frame_writer_.RecordRegisterFollowsInitialRule(lr);
      }
      saved_lr_ = initial_state->saved_lr_;
    }
  }
  
  void UnwindingInfoWriter::EndInstructionBlock(const InstructionBlock* block) {
    if (!enabled() || block_will_exit_) return;
  
    for (const RpoNumber& successor : block->successors()) {
      int successor_index = successor.ToInt();
      DCHECK_LT(successor_index, static_cast<int>(block_initial_states_.size()));
      const BlockInitialState* existing_state =
          block_initial_states_[successor_index];
  
      // If we already had an entry for this BB, check that the values are the
      // same we are trying to insert.
      if (existing_state) {
        DCHECK_EQ(existing_state->saved_lr_, saved_lr_);
      } else {
        block_initial_states_[successor_index] =
            zone_->New<BlockInitialState>(saved_lr_);
      }
    }
  }
  
  void UnwindingInfoWriter::MarkFrameConstructed(int at_pc) {
    if (!enabled()) return;
  
    // Regardless of the type of frame constructed, the relevant part of the
    // layout is always the one in the diagram:
    //
    // |   ....   |         higher addresses
    // +----------+               ^
    // |    LR    |               |            |
    // +----------+               |            |
    // | saved FP |               |            |
    // +----------+ <-- FP                     v
    // |   ....   |                       stack growth
    //
    // The LR is pushed on the stack, and we can record this fact at the end of
    // the construction, since the LR itself is not modified in the process.
    eh_frame_writer_.AdvanceLocation(at_pc);
    eh_frame_writer_.RecordRegisterSavedToStack(lr, kSystemPointerSize);
    saved_lr_ = true;
  }
  
  void UnwindingInfoWriter::MarkFrameDeconstructed(int at_pc) {
    if (!enabled()) return;
  
    // The lr is restored by the last operation in LeaveFrame().
    eh_frame_writer_.AdvanceLocation(at_pc);
    eh_frame_writer_.RecordRegisterFollowsInitialRule(lr);
    saved_lr_ = false;
  }
  
  void UnwindingInfoWriter::MarkLinkRegisterOnTopOfStack(int pc_offset) {
    if (!enabled()) return;
  
    eh_frame_writer_.AdvanceLocation(pc_offset);
    eh_frame_writer_.SetBaseAddressRegisterAndOffset(sp, 0);
    eh_frame_writer_.RecordRegisterSavedToStack(lr, 0);
  }
  
  void UnwindingInfoWriter::MarkPopLinkRegisterFromTopOfStack(int pc_offset) {
    if (!enabled()) return;
  
    eh_frame_writer_.AdvanceLocation(pc_offset);
    eh_frame_writer_.SetBaseAddressRegisterAndOffset(fp, 0);
    eh_frame_writer_.RecordRegisterFollowsInitialRule(lr);
  }
  
  }  // namespace compiler
  }  // namespace internal
  }  // namespace v8
  