[Interpreter] Preserve source positions in peephole optimizer.

src/interpreter/bytecode-peephole-optimizer.cc

Index: src/interpreter/bytecode-peephole-optimizer.cc
diff --git a/src/interpreter/bytecode-peephole-optimizer.cc b/src/interpreter/bytecode-peephole-optimizer.cc
index 803fc23089927faf47fe893deb178dd479265d6f..fa5916aabe2caa6a943d5ac6f0fed39e8ce9bbdc 100644
--- a/src/interpreter/bytecode-peephole-optimizer.cc
+++ b/src/interpreter/bytecode-peephole-optimizer.cc
@@ -164,10 +164,11 @@ BytecodeNode* BytecodePeepholeOptimizer::Optimize(BytecodeNode* current) {
     } 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;