1. A computer system for maintaining liveness information for executing programs, the system comprising: processor configured to communicate with a main storage, the processor comprising an instruction fetcher, an instruction optimizer and one or more execution units for executing optimized instructions, the processor configured to perform a method comprising: maintaining, by a processor, current operand state information, the current operand state information for indicating whether corresponding current operands are any one of enabled or disabled for use by a first program module, the first program module comprising machine instructions of an instruction set architecture (ISA), the first program module currently being executed by the processor; accessing a current operand, by a machine instruction of said first program module, the accessing comprising using the current operand state information to determine whether a previously stored current operand value is accessible by the first program module.