[interpreter] Bytecode register optimizer.

test/cctest/interpreter/bytecode_expectations/LetVariable.golden

Index: test/cctest/interpreter/bytecode_expectations/LetVariable.golden
diff --git a/test/cctest/interpreter/bytecode_expectations/LetVariable.golden b/test/cctest/interpreter/bytecode_expectations/LetVariable.golden
index 3ac793ab012ef4bcd26ab64da5c61f57a368bb39..a6866ceb6a105bed1f6277711007e262219f2b55 100644
--- a/test/cctest/interpreter/bytecode_expectations/LetVariable.golden
+++ b/test/cctest/interpreter/bytecode_expectations/LetVariable.golden
@@ -59,7 +59,7 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 27
+bytecode array length: 28
 bytecodes: [
                 B(LdaTheHole),
                 B(Star), R(0),
@@ -71,9 +71,9 @@ bytecodes: [
                 B(LdaConstant), U8(0),
                 B(Star), R(2),
                 B(CallRuntime), U16(Runtime::kThrowReferenceError), R(2), U8(1),
-                B(Ldar), R(1),
-                B(Star), R(0),
-  /*   45 E> */ B(LdaUndefined),
+                B(Mov), R(1), R(0),
+  /*   45 E> */ B(Ldar), R(0),
+                B(LdaUndefined),
   /*   52 S> */ B(Return),
 ]
 constant pool: [
@@ -88,7 +88,7 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 31
+bytecode array length: 30
 bytecodes: [
                 B(LdaTheHole),
                 B(Star), R(0),
@@ -102,8 +102,7 @@ bytecodes: [
                 B(LdaConstant), U8(0),
                 B(Star), R(2),
                 B(CallRuntime), U16(Runtime::kThrowReferenceError), R(2), U8(1),
-                B(Ldar), R(1),
-                B(Star), R(0),
+                B(Mov), R(1), R(0),
                 B(LdaUndefined),
   /*   54 S> */ B(Return),
 ]