Method and system for detecting a flush of an instruction without a flush indicator

A data processing system for monitoring instructions in an instruction pipeline of a processor, the data processing system comprising:

• first selecting means for selecting an instruction as a sampled instruction;
• loading means for loading, in response to selecting the sampled instruction, a countdown register with a value equal to or greater than the maximum number of active instructions in the instruction pipeline;
• monitoring means for monitoring progress of the sampled instruction through the instruction pipeline;
• decrementing means for decrementing, in response to an indication of progress of an instruction through a completion stage of the instruction pipeline, a value in the countdown register;
• detecting means for detecting that the sampled instruction has been flushed from the instruction pipeline by monitoring the countdown register for a value of zero;
• and
• generating means for generating, in response to the value of the countdown register equaling zero, an indication that the sampled instruction has been flushed.

A computer program product in a computer-readable medium for use in a data processing system for monitoring instructions in an instruction pipeline of a processor, the computer program product comprising:

• first instructions for selecting an instruction as a sampled instruction;
• second instructions for loading, in response to selecting the sampled instruction, a countdown register with a value equal to or greater than the maximum number of active instructions in the instruction pipeline;
• third instructions for monitoring progress of the sampled instruction through the instruction pipeline;
• fourth instructions for decrementing, in response to an indication of progress of an instruction through a completion stage of the instruction pipeline, a value in the countdown register;
• fifth instructions for detecting that the sampled instruction has been flushed from the instruction pipeline by monitoring the countdown register for a value of zero;
• and
• sixth instructions for generating, in response to the value of the countdown register equaling zero, an indication that the sampled instruction has been flushed.