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 during the speculative-execution episode and records data values relating to the speculative-execution episode; disabling the speculative execution monitor upon returning to normal-execution mode; and wherein the data values recorded by the speculative execution monitor facilitate measuring processor performance during speculative execution.