1. A method of facilitating processing in a computing environment, said method comprising: optimizing, by an optimizer executing in a processor, an application by generating modified code of the application, wherein the application comprises unmodified code and modified code; wherein the optimizing further comprises setting one or more controls to selectively enable exclusive use, by the application at a first instruction set level, of extended mode features, the extended mode features comprising one or more features at a second instruction set level, wherein the second instruction set level exceeds the first instruction set level and is available to the application in conjunction with optimization, based on the setting one or more controls to selectively enable exclusive use in the optimizing, but is otherwise unknown or unavailable to the application, wherein the first instruction set level and the second instruction set level are determined to be used by an instruction state context, and wherein the one or more controls comprise a first control located in an entry of an address translation structure associated with the application to indicate use of extended mode features is enabled, and one or more second controls in a control register to indicate one or more specific extended mode features available to the application.