Clock reconvergence pessimism removal (CRPR) 2

CRPR: is to remove the unnecessary pessimism for the common clock path for the launching and receiving registers.

The removal portion or the credit is the difference between max delay and min delay of the common portion.

There is a command called : report_crpr which could give the exact crp value. Calculate crpr is quite expensive, so report_timing won't give you the exact cpr value. The value given by the report_timing is the exact value +/- the range of "timing_crpr_threshold_ps".  That is the reason that you could see different crp value between report_crpr and report_timing.

To deal with the above issue, synopsys create another variable "timing_crpr_enable_adaptive_engine" to handle, when this variable is set to true, only the path with violation will be recalculate cpr, so the cpr will be accurate.