[interpreter] source positions should not be emitted for dead code.

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(int bytecode_offset,
+void SourcePositionTableBuilder::AddStatementPosition(size_t bytecode_offset,
                                                       int source_position) {
-  AssertMonotonic(bytecode_offset);
+  int offset = static_cast<int>(bytecode_offset);
+  AssertMonotonic(offset);
   uint32_t encoded = IsStatementField::encode(true) |
                      SourcePositionField::encode(source_position);
-  entries_.push_back({bytecode_offset, encoded});
+  entries_.push_back({offset, encoded});
 }
 
-void SourcePositionTableBuilder::AddExpressionPosition(int bytecode_offset,
+void SourcePositionTableBuilder::AddExpressionPosition(size_t bytecode_offset,
                                                        int source_position) {
-  AssertMonotonic(bytecode_offset);
+  int offset = static_cast<int>(bytecode_offset);
+  AssertMonotonic(offset);
   uint32_t encoded = IsStatementField::encode(false) |
                      SourcePositionField::encode(source_position);
-  entries_.push_back({bytecode_offset, encoded});
+  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();
+  }
 }
 
 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 30 matching lines @@
        !iterator.done() && iterator.bytecode_offset() <= bytecode_offset;
        iterator.Advance()) {
     last_position = iterator.source_position();
   }
   return last_position;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8