On Jun 20, 2011, at 12:17 PM, Tom Rodriguez wrote: > On Jun 18, 2011, at 5:15 AM, Rémi Forax wrote: > >> On 06/18/2011 03:15 AM, Tom Rodriguez wrote: >>> On Jun 17, 2011, at 5:00 PM, John Rose wrote: >>> >>>> On Jun 17, 2011, at 10:21 AM, Tom Rodriguez wrote: >>>> >>>>>> Sorry, I was thinking recording which branch of the GWT is taken and >>>>>> storing them in the GWT. >>>>>> Two GWTs should not share the same metadata. >>>>> This is the major problem with GWT/selectAlternative. Previously when >>>>> GWT was bytecodes we at least had a chance to get some profile >>>>> information on which way the branch was likely to go but with the >>>>> ricochet frame version we have no knowledge so each side of the if has >>>>> equal probability. The were no guarantees that the GWT would always be >>>>> used as a fast/slow idiom but in practice it was so we used to get good >>>>> data. We'll have to find someway to capture profiles for this if we can >>>>> to treat fast/slow in a more aggressive way. >>>> selectAlternative has a branch profile. As long as GWT is being used as >>>> expected (for fast/slow splits), selectAlternative will have a fast/slow >>>> profile, just like the original GWT invokers. >>>> >>>> The PROB_FAIR in CallGenerator::for_method_handle_inline could be made >>>> "smarter", by feeding from the control inputs of the Phi; that would be a >>>> good start. >>> Well duh on me. When I wrote that my brain was thinking cmove instruction, >>> not a real If diamond with probability. I don't think fixing this will >>> improve the inlining in the fast case but it should reduce useless inlining >>> in the slow path. I've got part of this working. >>> >>> tom >> >> But all GWT share the same selectAlternative, so the probability >> of the inputs of the Phi is the propability of all GWTs. >> I think it's better to artificially mark the fallback as never been >> called instead of relying >> on a global shared profile.
One way to do this on the cheap is to intrinsify selectAlternative in MHW, so that MHW-compiled GWT graphs automatically get fresh profilable copies of the if/then/else. This doesn't scale to other kinds of MH graphs, of course, but GWT is arguably a fundamental building block that deserves special case to be rendered as if/then/else bytecodes. -- John _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
