Decoding instructions that are modified by one or more other instructions

摘要

Methods and apparatus are provided for decoding instructions in a computer program wherein the instructions include one or more base instructions that are subject to modification by one or more other instructions. A decoder determines whether a first received instruction was arrived at by a non-incremental change to a program counter (i.e. a jump in the program). If the first instruction was arrived at by a non-incremental change to the program counter the decoder decodes the immediately preceding instruction to determine if the original instruction is a base instruction subject to modification by one or more other instructions. If the preceding instruction indicates that the original instruction is a base instruction an error has occurred and exception handling code is invoked.