[interpreter] Bytecode register optimizer.

test/cctest/interpreter/bytecode_expectations/CreateArguments.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: string
 execute: yes
 wrap: no
 test function name: f
 
@@ skipping 15 matching lines @@
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 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: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   function f() { 'use strict'; return arguments; }
@@ skipping 12 matching lines @@
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 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),
                 B(Ldar), R(arg0),
                 B(StaContextSlot), R(context), U8(4),
                 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: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   function f(a, b, c) { return arguments; }
@@ skipping 35 matching lines @@
                 B(Star), R(0),
   /*   10 E> */ B(StackCheck),
   /*   36 S> */ B(Ldar), R(0),
   /*   54 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]