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      1 // Copyright 2016 the V8 project authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 
      5 #include "src/interpreter/bytecode-dead-code-optimizer.h"
      6 
      7 namespace v8 {
      8 namespace internal {
      9 namespace interpreter {
     10 
     11 BytecodeDeadCodeOptimizer::BytecodeDeadCodeOptimizer(
     12     BytecodePipelineStage* next_stage)
     13     : next_stage_(next_stage), exit_seen_in_block_(false) {}
     14 
     15 // override
     16 Handle<BytecodeArray> BytecodeDeadCodeOptimizer::ToBytecodeArray(
     17     Isolate* isolate, int register_count, int parameter_count,
     18     Handle<FixedArray> handler_table) {
     19   return next_stage_->ToBytecodeArray(isolate, register_count, parameter_count,
     20                                       handler_table);
     21 }
     22 
     23 // override
     24 void BytecodeDeadCodeOptimizer::Write(BytecodeNode* node) {
     25   // Don't emit dead code.
     26   if (exit_seen_in_block_) return;
     27 
     28   switch (node->bytecode()) {
     29     case Bytecode::kReturn:
     30     case Bytecode::kThrow:
     31     case Bytecode::kReThrow:
     32       exit_seen_in_block_ = true;
     33       break;
     34     default:
     35       break;
     36   }
     37 
     38   next_stage_->Write(node);
     39 }
     40 
     41 // override
     42 void BytecodeDeadCodeOptimizer::WriteJump(BytecodeNode* node,
     43                                           BytecodeLabel* label) {
     44   // Don't emit dead code.
     45   // TODO(rmcilroy): For forward jumps we could mark the label as dead, thereby
     46   // avoiding emitting dead code when we bind the label.
     47   if (exit_seen_in_block_) return;
     48 
     49   switch (node->bytecode()) {
     50     case Bytecode::kJump:
     51     case Bytecode::kJumpConstant:
     52       exit_seen_in_block_ = true;
     53       break;
     54     default:
     55       break;
     56   }
     57 
     58   next_stage_->WriteJump(node, label);
     59 }
     60 
     61 // override
     62 void BytecodeDeadCodeOptimizer::BindLabel(BytecodeLabel* label) {
     63   next_stage_->BindLabel(label);
     64   exit_seen_in_block_ = false;
     65 }
     66 
     67 // override
     68 void BytecodeDeadCodeOptimizer::BindLabel(const BytecodeLabel& target,
     69                                           BytecodeLabel* label) {
     70   next_stage_->BindLabel(target, label);
     71   // exit_seen_in_block_ was reset when target was bound, so shouldn't be
     72   // changed here.
     73 }
     74 
     75 }  // namespace interpreter
     76 }  // namespace internal
     77 }  // namespace v8
     78