[interpreter] Ensure optimizations preserve source positions.

src/interpreter/bytecodes.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/bytecodes.h"
 
 #include <iomanip>
 
 #include "src/frames.h"
 #include "src/interpreter/bytecode-traits.h"
@@ skipping 474 matching lines @@
     default:
       return false;
   }
 }
 
 // static
 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
 bool Bytecodes::IsJumpOrReturn(Bytecode bytecode) {
   return bytecode == Bytecode::kReturn || IsJump(bytecode);
 }
 
 // static
 bool Bytecodes::IsMaybeRegisterOperandType(OperandType operand_type) {
   return operand_type == OperandType::kMaybeReg;
@@ skipping 465 matching lines @@
   } else {
     std::ostringstream s;
     s << "r" << index();
     return s.str();
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8