vm_exec.c: reduced repeated same calls

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@62648 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_exec.c

@@ -143,7 +143,7 @@ static VALUE
 vm_exec_core(rb_execution_context_t *ec, VALUE initial)
 {
     register rb_control_frame_t *reg_cfp = ec->cfp;
-    rb_thread_t *th = rb_ec_thread_ptr(ec);
+    rb_thread_t *th;
 
     while (1) {
 	reg_cfp = ((rb_insn_func_t) (*GET_PC()))(ec, reg_cfp);
@@ -153,9 +153,9 @@ vm_exec_core(rb_execution_context_t *ec, VALUE initial)
 	}
     }
 
-    if (rb_ec_thread_ptr(ec)->retval != Qundef) {
+    if ((th = rb_ec_thread_ptr(ec))->retval != Qundef) {
 	VALUE ret = th->retval;
-	rb_ec_thread_ptr(ec)->retval = Qundef;
+	th->retval = Qundef;
 	return ret;
     }
     else {