February 7 project call

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Agenda

Opening, welcome and roll call
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3. Please help take notes.
4. Thanks!
Announcements
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Other agenda items
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2. avanhatt: ISLE rule verification update/open questions (Alexa, Fraser, Monica).

avanhatt presented ISLE SMT rule verification prototype, currently type and term variants for IR-to-IR verification.

avanhatt: open question, what should the syntax be? LHS, extractor, is more complex.
cfallin: Feels like global type inference. Annotations on prelude or standard library, keep them out of lowering rules.
avanhatt: Agreed, that it would be good to not have to specify downstream rules.
cfallin: Recursion could be a problem.
uweigand: Not sure I understand the big picture. How do we define formal semantics of backend ISAs?
avanhatt: Current research and tools are available for x86 and Arm.
cfallin: We don't even have a good prose descriptions of CLIF operations yet.
avanhatt: The Alive project managed without formal semantics.
uweigand: Will look to see if there's anything for S390.
uweigand: Could the semantics annotations be used to generate the isel code?
cfallin: Would depend whether it could produce efficient code, would be good for asserts though.
avanhatt: Yes, we could use it for asserts to strengthen fuzzing.
FB: Could be used for equivalence checks on rust code too.

sparker-arm: Sizeless vector RFC updated, atomics isle porting.
uweigand: Branches and traps lowering changes merged. Implemented atomics, which was complicated for narrow types, involved emitting loops. - sparker-arm: Would the SMT verifier be capable of handling loops?
uweigand: Still not sure to do about call lowering, as calls can return more than two values. - cfallin: Should we do it? - uweigand: S390 ABI wants extended values and isle could be useful for this. - cfallin: Separate call instruction from arg/return setup..?
uweigand: Reorganising ABICaller(Callee?) to simplify the communication between the backend.
uweigand: Next moving onto SIMD.
abrown: ISLE select lowering for x64, seems like more flag handling infrastructure needs to be added. Now looking at sightglass for instantiation metrics.
jlbirch: Worked on a patch for sightglass to automatically trigger benchmarking when a patch is committed. Would like to know why this isn't a good idea for github actions. - cfallin: Need to trust that a PR isn't malicious.
bnjbvr: Has been working on ittapi for cross-platform Vtune support. - abrown: Thanks so much for this.
cfallin: Will be thinking about isle rule precedence.