[RFC] Adding target-specific overrides for Indirect Call Promotion (ICP)

Hi,
We see improved performance on the PowerPC platform by increasing the aggressiveness of Indirect Call Promotion (ICP).
In particular, lowering the promotion threshold and increasing the maximum number of promotions helps.
The following command line options (default values shown) control some of the ICP parameters:
-icp-max-annotations=3
-icp-max-prom=3
-icp-remaining-percent-threshold=30
We would like to change their defaults to a target specific value.

The above are defaults - what values are you finding are best on PowerPC? I’d be interested in trying the values you found to be optimal there again on e.g. x86 to evaluate their effectiveness. We’ve done various experiments and tuning of these values, but curious to try.

I have few questions:

  1. Is anyone else interested in having target specific default values for the above options?

It if makes sense from an architectural standpoint - i.e. are indirect calls much more expensive in PowerPC than say x86?

Teresa

Hi Teresa,

-icp-max-annotations=7
-icp-max-prom=7
-icp-remaining-percent-threshold=10
are the values that shown improvement on Power9. Please see my reply to Hal Finkel in this thread for more details.

Wael

-----Teresa Johnson <tejohnson@google.com> wrote: -----

Ok, thanks. For some odd reason I got two copies of the original email, so I missed Hal and your responses. Let’s continue on that thread. Teresa