Add 2021-10-18 Cranelift meeting notes (#3458)

* Add 2021-10-18 Cranelift meeting notes

* Update cranelift-10-18.md

meetings/cranelift/2021/cranelift-10-18.md

@@ -18,4 +18,90 @@
 
 ### Attendees
 
+- cfallin
+- fitzgen
+- acrichto
+- uweigand
+- bjorn3
+- sparker
+- jlbirch
+- bbouvier
+
 ### Notes
+
+#### ISLE
+
+- fitzgen: first few rules working and integrated into Cranelift with tests
+  passing, (few == 3, iconst, bconst, and catch-all for add). Glue isn't too bad
+  and now plan to work on complicated lowerings next. If there are ideas of
+  things to prove out the DSL let me know. Next is add with sinking loads, add
+  with an immediate, popcnt lowering, compare-and-branch, etc. Hope to have
+  final yay/nay in 2 weeks. Personally have enjoyed ISLE so far and it was
+  super-easy to add case to 0-immediates are xor reg/reg. Didn't involve fitting
+  into match tree and was nice to write as a standalone rule.
+- cfallin: gist?
+- fitzgen: not PR ready but sure!
+- cfallin: this is definitely something I would have wanted last year, but take
+  that with a grain of salt. Need to evaluate whether it's worth the complexity.
+  Any questions/comments?
+- cfallin: no vote today at all, just a progress update, but after two weeks
+  hopefully will find consensus one way or another to move forward. Hope to make
+  a decision soon though so this doesn't continue indefinitely.
+- fitzgen: plan to have enough by next mtg for sure, yeah.
+- jlbirch: which aspect is this supplementing or replacing? [the files posted]
+- fitzgen: the handwritten match statements in lowering code going from clif to
+  machinst.
+- jlbirch: these looks like comments for types and not instructions?
+- cfallin: oh there's inst.isle and lower.isle
+
+...
+discussion of
+https://github.com/fitzgen/wasmtime/blob/isle/cranelift/codegen/src/isa/x64/lower.isle
+...
+
+...
+discussion of
+https://github.com/fitzgen/wasmtime/blob/isle/cranelift/codegen/src/isa/x64/inst.isle
+...
+
+- sparker: looks quite good for addressing modes on memory operations
+- fitzgen: next goal for me!
+- bjorn3: looks like a lot of new dependencies?
+- fitzgen: uses miette - current branch unconditionally rebuilds isle crate,
+  but shouldn't have to rebuild any of this unless you're changing various data
+  types. Most don't touch this, so dependencies should only matter if you're
+  actively hacking on these areas.
+- cfallin: eventually we may not have the meta step or might check in more of
+  the code. Would improve build times by a lot, but this is a separate
+  discussion with different pros/cons. If build time is a concern there are
+  avenues to take.
+
+#### Status
+
+- cfallin: not much, working on non-cranelift things. RA2 progressing a bit,
+  jseward planning on finishing review for regalloc.rs adapter. Should be able
+  to release to crates.io after that and license bits sorted.
+- fitzgen: no other updates than from above.
+- bbouvier: no update
+- acrichto: no update
+- jlbirch: starting to look at some fuzz bugs
+- uweigand: working on atomics, everything is cas loops, tedious. Seems like
+  clif supports a lot of atomic ops which are easy on x86 as a single
+  instruction but not as easy on other platforms. Should we remove bits from
+  clif ir?
+- cfallin: github issues to remove things and can discuss there?
+- uweigand: building wasi binaries from Rust needs a linker which isn't
+  available on s390x.
+- sparker: looking at flexible vectors, gonna try to put into cranelift somehow.
+  Hoping to use ISLE to convert between flexible vectors and neon.
+- cfallin: new clif instructions?
+- sparker: using existing instructions but getting size of vector into system
+  and have backends never see it later ideally.
+- cfallin: feel free to post an issue and we can discuss there too
+- jlbirch: based on flexible vector proposal?
+- sparker: yes
+- jlbirch: I would be interested! Would be great to have shared infrastructure.
+- sparker: hoping to separate into 3 tiers, first being current simd. Want to
+  have shared infrastructure to map to existing targets first.
+- bjorn3: cleaning up after old x86 backend removal
+- cfallin: great to see so much deleted!