[interpreter, debugger] implement bytecode break location iterator.

src/interpreter/source-position-table.cc

 // 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/interpreter/source-position-table.h"
 
 #include "src/assembler.h"
 #include "src/objects-inl.h"
 #include "src/objects.h"
 
 namespace v8 {
 namespace internal {
 namespace interpreter {
 
 class IsStatementField : public BitField<bool, 0, 1> {};
 class SourcePositionField : public BitField<int, 1, 30> {};
 
 void SourcePositionTableBuilder::AddStatementPosition(size_t bytecode_offset,
                                                       int source_position) {
   int offset = static_cast<int>(bytecode_offset);
-  AssertMonotonic(offset);
+  // If a position has already been assigned to this bytecode offset,
+  // do not reassign a new statement position.
+  if (CodeOffsetHasPosition(offset)) return;
   uint32_t encoded = IsStatementField::encode(true) |
                      SourcePositionField::encode(source_position);
   entries_.push_back({offset, encoded});
 }
 
 void SourcePositionTableBuilder::AddExpressionPosition(size_t bytecode_offset,
                                                        int source_position) {
   int offset = static_cast<int>(bytecode_offset);
-  AssertMonotonic(offset);
+  // If a position has already been assigned to this bytecode offset,
+  // do not reassign a new statement position.
+  if (CodeOffsetHasPosition(offset)) return;
   uint32_t encoded = IsStatementField::encode(false) |
                      SourcePositionField::encode(source_position);
   entries_.push_back({offset, encoded});
 }
 
 void SourcePositionTableBuilder::RevertPosition(size_t bytecode_offset) {
   int offset = static_cast<int>(bytecode_offset);
   // If we already added a source position table entry, but the bytecode array
   // builder ended up not outputting a bytecode for the corresponding bytecode
   // offset, we have to remove that entry.
-  if (entries_.size() > 0 && entries_.back().bytecode_offset == offset) {
-    entries_.pop_back();
-  }
+  if (CodeOffsetHasPosition(offset)) entries_.pop_back();
 }
 
 Handle<FixedArray> SourcePositionTableBuilder::ToFixedArray() {
   int length = static_cast<int>(entries_.size());
   Handle<FixedArray> table =
       isolate_->factory()->NewFixedArray(length * 2, TENURED);
   for (int i = 0; i < length; i++) {
     table->set(i * 2, Smi::FromInt(entries_[i].bytecode_offset));
     table->set(i * 2 + 1, Smi::FromInt(entries_[i].source_position_and_type));
   }
@@ skipping 19 matching lines @@
         static_cast<uint32_t>(Smi::cast(table_->get(index_ + 1))->value());
     is_statement_ = IsStatementField::decode(source_position_and_type);
     source_position_ = SourcePositionField::decode(source_position_and_type);
   }
   index_ += 2;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8