Valhalla EG 20200422

[David Simms]

Attendees: Remi, Simms, Brian, John, Fred, DanS, Tobi, DanH

  - Brian: So there is Fred's proposal for translation strategy for cast 
(using the whole envelop and treat Q sig as not-null)
  - DanH: yeah we need to look at how legacy would work
  - Brian: So Q types didn't exist before, old files assume L
  - John: A little concern about "L-type" envelopes appearing there 
too...need to read the full email...
  - Remi: why was this a probably ?
  - Brian: because `checkcast` with `null` on TOS will let it pass for 
Q-types, it won't look any for further if `null`
  - John: think of if as null-check gate for Q-type sig
  - DanH: so does that mean we need to pre-load at its appearance ?
  - John: not necessarily
  - Brian: pretty sure Fred left that blank on purpose
      - Read through, look at impl, debate on list
  - Fred: Summary for `checkcast`:
      - ("Hey `null`") "are you are part of the value set of this type ?"
  - Simms: so the "preload" question, is that for list debate ?
  - Fred: well we don't preload for `ldc` etc so...
  - Debate follows whereby the "note taker" was far too interested in 
talking
      - There is an argument to say we have limited "pre-loading" for 
specific feature enablement...
      - ...if `checkcast` hitting `null` TOS and throwing `CCE` is not 
preformant anyway, extra load won't matter...not common
      - if `checkcast` not `null` TOS, type needs resolving anyway
  - ...
  - John: do we need to be explicit about this in the spec
  - DanH: we want to be explicit
  - Remi: agreed
  - Debate Summary: All operations naming Q-type, must load, so 
`instanceof` and `checkcast`
  - Simms: so the design space is narrowing, I owe an email listing 
remaining items, will appreciate if anything is missing, or if there are 
concerns to name them...
      - ...would prefer to move on to longer GS design discussion
      - also inline types seem close, and still "simple to use" (further 
features would be hard to motivate)
  - Brian: also owe an email on specialization