[interpreter] Ensure optimizations preserve source positions.

src/interpreter/bytecodes.cc

Index: src/interpreter/bytecodes.cc
diff --git a/src/interpreter/bytecodes.cc b/src/interpreter/bytecodes.cc
index 46134b7f1d418c52dbecbfe82775ad20586f08cf..b3ec6a6162408edd4f18f042afbde13ec98ad943 100644
--- a/src/interpreter/bytecodes.cc
+++ b/src/interpreter/bytecodes.cc
@@ -492,8 +492,9 @@ bool Bytecodes::IsWithoutExternalSideEffects(Bytecode bytecode) {
   // These bytecodes only manipulate interpreter frame state and will
   // never throw.
   return (IsAccumulatorLoadWithoutEffects(bytecode) || IsLdarOrStar(bytecode) ||
-          bytecode == Bytecode::kMov || bytecode == Bytecode::kNop ||
-          IsJump(bytecode));
+          bytecode == Bytecode::kLdrUndefined || bytecode == Bytecode::kMov ||

[rmcilroy, 2016/06/07 09:46:11]

nit - Could we add IsRegisterLoadWithoutEffects, for kLdrUndefined, kStar and
kMov (avoiding the need for IsLdarOrStar and giving somewhere to put any more
Ldr bytecodes we might add).

[oth, 2016/06/07 13:46:17]

Done.

The thought had occurred whether we should annotate bytecodes with this
information so each is explicitly classified. This would be less error prone
should bytecodes change. I don't propose doing it here, but something we might
consider.

+          bytecode == Bytecode::kNop ||
+          (IsJump(bytecode) && !IsJumpIfToBoolean(bytecode)));

[rmcilroy, 2016/06/07 09:46:11]

nit - could we add IsJumpWithoutExternalEffect() for clarity.

[oth, 2016/06/07 13:46:17]

Done.

 }
 
 // static