[interpreter] Bytecode register optimizer.

test/cctest/interpreter/bytecode_expectations/OuterContextVariables.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: mixed
 execute: yes
 wrap: no
 test function name: f
 
 ---
 snippet: "
   function Outer() {
     var outerVar = 1;
     function Inner(innerArg) {
       this.innerFunc = function() { return outerVar * innerArg; }
     }
     this.getInnerFunc = function() { return new Inner(1).innerFunc; }
   }
   var f = new Outer().getInnerFunc();
   f();
 "
 frame size: 2
 parameter count: 1
-bytecode array length: 19
+bytecode array length: 15
 bytecodes: [
   /*   97 E> */ B(StackCheck),
-  /*  102 S> */ B(Ldar), R(context),
-                B(Star), R(0),
-                B(LdrContextSlot), R(0), U8(1), R(0),
+  /*  102 S> */ B(LdrContextSlot), R(context), U8(1), R(0),
                 B(LdrContextSlot), R(0), U8(4), R(1),
   /*  120 E> */ B(LdaContextSlot), R(context), U8(4),
                 B(Mul), R(1),
   /*  130 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   function Outer() {
     var outerVar = 1;
     function Inner(innerArg) {
       this.innerFunc = function() { outerVar = innerArg; }
     }
     this.getInnerFunc = function() { return new Inner(1).innerFunc; }
   }
   var f = new Outer().getInnerFunc();
   f();
 "
 frame size: 2
 parameter count: 1
-bytecode array length: 20
+bytecode array length: 17
 bytecodes: [
   /*   97 E> */ B(StackCheck),
-  /*  102 S> */ B(LdrContextSlot), R(context), U8(4), R(0),
-                B(Ldar), R(context),
-                B(Star), R(1),
-                B(LdrContextSlot), R(1), U8(1), R(1),
+  /*  102 S> */ B(LdaContextSlot), R(context), U8(4),
+  /*  111 E> */ B(Star), R(0),
+                B(LdrContextSlot), R(context), U8(1), R(1),
                 B(Ldar), R(0),
                 B(StaContextSlot), R(1), U8(4),
                 B(LdaUndefined),
   /*  123 S> */ B(Return),
 ]
 constant pool: [
 ]
 handlers: [
 ]