[Interpreter] Preserve source positions in peephole optimizer.

src/interpreter/bytecode-peephole-optimizer.cc

 // Copyright 2015 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/bytecode-peephole-optimizer.h"
 
 #include "src/interpreter/constant-array-builder.h"
 #include "src/objects-inl.h"
 #include "src/objects.h"
 
@@ skipping 146 matching lines @@
 
 BytecodeNode* BytecodePeepholeOptimizer::Optimize(BytecodeNode* current) {
   UpdateCurrentBytecode(current);
 
   if (CanElideCurrent(current)) {
     if (current->source_info().is_valid()) {
       current->set_bytecode(Bytecode::kNop);
     } else {
       current = nullptr;
     }
-  } else if (CanElideLast(current)) {
-    if (last_.source_info().is_valid()) {
-      current->source_info().Update(last_.source_info());
-    }
+  } else if (CanElideLast(current) &&
+             ((last_.source_info().is_valid() !=
+               current->source_info().is_valid()) ||
+              (last_.source_info() == current->source_info()))) {

[rmcilroy, 2016/05/20 16:31:13]

nit - could we just move the source position checking into CanElideLast?

[oth, 2016/05/21 12:40:10]

Done.

+    current->source_info().Update(last_.source_info());
     InvalidateLast();
   }
   return current;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8