1. A method for measuring processor performance during speculative execution, comprising: executing instructions in a normal-execution mode; entering a speculative-execution episode wherein instructions are speculatively executed without being committed to an architectural state of the processor; wherein entering the speculative-execution episode involves enabling a speculative execution monitor which monitors instructions only during the speculative-execution episode and records data values relating only to the speculative-execution episode; upon determining that the speculative-execution episode is complete, disabling the speculative execution monitor and returning to normal-execution mode; and reporting the data values recorded by the speculative execution monitor during the speculative-execution episode only after returning to normal-execution mode, wherein the data values recorded by the speculative execution monitor facilitate measuring processor performance during speculative execution.