[ignition, debugger] correctly set position for return with elided bytecode.

src/interpreter/source-position-table.h

 // 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.
 
 #ifndef V8_INTERPRETER_SOURCE_POSITION_TABLE_H_
 #define V8_INTERPRETER_SOURCE_POSITION_TABLE_H_
 
 #include "src/assert-scope.h"
 #include "src/checks.h"
 #include "src/handles.h"
@@ skipping 18 matching lines @@
         source_position(source),
         is_statement(statement) {}
 
   int bytecode_offset;
   int source_position;
   bool is_statement;
 };
 
 class SourcePositionTableBuilder : public PositionsRecorder {
  public:
+  enum OnDuplicateCodeOffset {
+    DISCARD_DUPLICATE,
+    OVERWRITE_DUPLICATE,
+  };
+
   explicit SourcePositionTableBuilder(Isolate* isolate, Zone* zone)
       : isolate_(isolate),
         bytes_(zone),
 #ifdef ENABLE_SLOW_DCHECKS
         raw_entries_(zone),
 #endif
-        previous_() {
+        candidate_(kUninitializedCandidateOffset, 0, false) {
   }
 
-  void AddStatementPosition(size_t bytecode_offset, int source_position);
+  void AddStatementPosition(
+      size_t bytecode_offset, int source_position,
+      OnDuplicateCodeOffset on_duplicate = DISCARD_DUPLICATE);
   void AddExpressionPosition(size_t bytecode_offset, int source_position);
   Handle<ByteArray> ToSourcePositionTable();
 
  private:
-  void AddEntry(const PositionTableEntry& entry);
+  static const int kUninitializedCandidateOffset = -1;
+
+  void AddEntry(const PositionTableEntry& entry,
+                OnDuplicateCodeOffset on_duplicate = DISCARD_DUPLICATE);
+  void CommitEntry();
 
   Isolate* isolate_;
   ZoneVector<byte> bytes_;
 #ifdef ENABLE_SLOW_DCHECKS
   ZoneVector<PositionTableEntry> raw_entries_;
 #endif
-  PositionTableEntry previous_;
+  PositionTableEntry candidate_;  // Next entry to be written, if initialized.
+  PositionTableEntry previous_;   // Previously written entry, to compute delta.
 };
 
 class SourcePositionTableIterator {
  public:
   explicit SourcePositionTableIterator(ByteArray* byte_array);
 
   void Advance();
 
   int bytecode_offset() const {
     DCHECK(!done());
@@ skipping 16 matching lines @@
   int index_;
   PositionTableEntry current_;
   DisallowHeapAllocation no_gc;
 };
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_INTERPRETER_SOURCE_POSITION_TABLE_H_