[interpreter] Bytecode register optimizer.

test/cctest/interpreter/bytecode_expectations/CreateArguments.golden

Index: test/cctest/interpreter/bytecode_expectations/CreateArguments.golden
diff --git a/test/cctest/interpreter/bytecode_expectations/CreateArguments.golden b/test/cctest/interpreter/bytecode_expectations/CreateArguments.golden
index 6788a7c8f1b2feaaf5493021ef4c82cc08d0528c..99f5c5d4a9f3dad94cc3a4a2dbd2769e986482a0 100644
--- a/test/cctest/interpreter/bytecode_expectations/CreateArguments.golden
+++ b/test/cctest/interpreter/bytecode_expectations/CreateArguments.golden
@@ -33,17 +33,15 @@ snippet: "
   function f() { return arguments[0]; }
   f();
 "
-frame size: 2
+frame size: 1
 parameter count: 1
-bytecode array length: 13
+bytecode array length: 9
 bytecodes: [
                 B(CreateMappedArguments),
                 B(Star), R(0),
   /*   10 E> */ B(StackCheck),
-  /*   15 S> */ B(Ldar), R(0),
-                B(Star), R(1),
-  /*   31 E> */ B(LdaZero),
-                B(KeyedLoadIC), R(1), U8(1),
+  /*   15 S> */ B(LdaZero),
+                B(KeyedLoadIC), R(0), U8(1),

[Yang, 2016/05/20 08:00:55]

The expression position disappeared. If the load throws, we will have a
diffferent stack trace. It would be nicer to preserve the expression position at
the load.

[oth, 2016/05/20 09:01:04]

Ack. Need to fix this. For the debugging experience, perhaps we emit a nop here
with the statement and ensure we keep the expression on the load.

   /*   36 S> */ B(Return),
 ]
 constant pool: [
@@ -76,9 +74,9 @@ snippet: "
   function f(a) { return arguments[0]; }
   f();
 "
-frame size: 3
+frame size: 2
 parameter count: 2
-bytecode array length: 25
+bytecode array length: 21
 bytecodes: [
                 B(CallRuntime), U16(Runtime::kNewFunctionContext), R(closure), U8(1),
                 B(PushContext), R(1),
@@ -87,10 +85,8 @@ bytecodes: [
                 B(CreateMappedArguments),
                 B(Star), R(0),
   /*   10 E> */ B(StackCheck),
-  /*   16 S> */ B(Ldar), R(0),
-                B(Star), R(2),
-  /*   32 E> */ B(LdaZero),
-                B(KeyedLoadIC), R(2), U8(1),
+  /*   16 S> */ B(LdaZero),
+                B(KeyedLoadIC), R(0), U8(1),

[Yang, 2016/05/20 08:00:55]

Ditto.

   /*   37 S> */ B(Return),
 ]
 constant pool: [