Go compiler and runtime meeting notes

[jeremyfaller]

Google's Go compiler and runtime team meets periodically (roughly weekly) to discuss ongoing development of the compiler and runtime. While not open to the public, there's been desire by the community to learn what the compiler and runtime team is working on. While we learn what is a good format, and what works and doesn't, we will start publishing meeting minutes here.

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

This meta-issue records minutes of Google's Go compiler and runtime meetings as issue comments, so that they can be cross-linked easily with the relevant issues. This meta-issue is for minutes only; comments that are not meeting minutes will be deleted.

[jeremyfaller]

2021-01-19

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We continued a discussion about increasing the bootstrap version of Go from 1.4 to 1.16 after the 1.17 release. We wanted to make sure it wasn't hard for people to build from scratch, but we would like to use features that have been added over time. Consensus was that this would be okay to submit as a formal proposal.
• We discussed Austin's benchmark unit proposal. Consensus was hopeful that it would be accepted.
• We discussed the weak maps proposal. A number of corner cases, gotchas, and subtleties were discussed. Consensus was that the discussion on the issue was up to date.
• After falling off the prior week's agenda, we began a discussion about releasing the compiler and runtime meeting notes. We all felt communication with the community was important, and we would start with an internal publication of meeting notes. No dates were set for a final decision.

[jeremyfaller]

2021-01-26

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We continued discussing whether or not there were any concerns with publishing compiler and runtime meeting notes. No issues were raised, so it's likely I will go ahead and start publishing the notes.
• We discussed the redirecting crash output proposal. No major concerns were raised, but consensus was that a call would be best approach (against environment variables, etc).
• We discussed the pain merging the development branches (master -> dev.regabi -> dev.typeparams). The consensus was that without acceptance of the generics proposal, we need to keep living with the pain.
• We briefly discussed using the type checker in dev.typeparams as the default type checker. Using that type checker is blocked on either acceptance of generics proposal or a separate proposal to move to a new type checker.

[jeremyfaller]

2021-02-02
These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We continued our discussion of moving to the new default typechecker on dev.typeparams. Engineering effort continues at a break-neck pace, and we're hopeful we'll be able to have this early.
• We discussed the issue with spinning M's, and have seen large improvements for unique workloads within Google. Consensus was that this was an excellent find.
• We had a brief discussion of integer constant resolution.
• We briefly discussed merging the dev.regabi branch back to master when the tree opens. Consensus was that it would be safe to merge when the tree opened.
• We discussed some recent additions to dev.typeparams, that added support for generic functions and types. It's possible the backend work will happen on the branch's compiler soon.

[jeremyfaller]

2021-02-08

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We briefly discussed the status of 1.16.
• We discussed the tree reopening, and landing of the dev.regabi branch, and the dev.typeparms branches on master. Current plans are to merge dev.regabi during the first week. If both proposals (1, 2) are accepted, dev.typeparams will also be merged during that week.
• We discussed the new pacer proposal, and its benefits.
• We also discussed the status of the register abi. While functionality is gated behind a flag, we don't want to go into code-freeze, enabling the ABI that late. We discussed the amount of soak time we think we will need.

[jeremyfaller]

2021-02-16

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We had a small celebration about the acceptance of the Generics Proposal.
• We discussed merging the dev.typeparams branch to master. There are public API typechecking changes on that branch that aren't stable. As a result, we will likely hide the APIs using buildtags.
• We continued a long-running discussion on making types2 the default typechecker. We still don't need to make a decision here, so back into the oven it goes.
• We discussed revising the syntax for typelists in generics. An internally floated proposal is similar to public proposals. More to come.
• We discussed adding attendance to entries in this document. As no one objected to having their name added, I will start doing that. I won't start by CC-ing people, just linking to their github profile for now.

Attendees:
Carlos Amedee
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Than McIntosh
Martin Möhrmann
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-02-23

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We celebrated the reopening of tree for 1.17 development.
• We discussed some of the features we want to land for 1.17, including the register ABI, foundational work for generics, the new gc pacer, improvements to the scheduler, escape analysis improvements, and possibly some phase changes to the compiler. We also had a more in-depth discussion of subtle points in types2.
• We discussed the work on register ABI. A hello world is working (in review, not fully committed). More work for return values has also started, and we're having some success there.
• A new ABI with G in R14 and a zeroed X15 has shown reasonable promise to offer good runtime performance improvements. Work is ongoing to confirm results, and clean up some poorly understood overhead in wrappers. Also, not all of the places where we use G in assembly have been converted over. More data to come.
• We discussed an issue that turning on stack poisoning seems to bork the openbsd-amd64-68 trybot.
• We discussed a proposal to add zeroing for cryptographic functions. Consensus was that this is non-trivial.

Attendees:
Carlos Amedee
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Than McIntosh
Martin Möhrmann
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-03-02

These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• We discussed the current status of our 1.17 and 1.18 goals, including the register ABI, and generics.
• We discussed a small issue on sum types. Likely more external communication to come.
• We discussed how best to handle the meeting notes (this issue), and questions and feedback. We decided it would be best to move queries to the mailing list(s) for now.
• We discussed moving GOEXPERIMENT, and how important it would be to help the registerABI work to land.
• We discussed a subtle issue in the register ABI to simplify the internal representation and requirements for go & defer. Specifically, having the compiler rewrite defer f(x) ⇒ x' := x; defer func() { f(x') }().

Attendees:
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Than McIntosh
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Cherry Zhang

[jeremyfaller]

2021-03-09
These compiler and runtime meeting minutes are under development. We welcome feedback on content, format, level of detail, timeliness, and so on. If the minutes are helpful, please let us know. If they are less than helpful, we welcome constructive comments on how to improve them.

Notes on agenda items that address Google specific needs are elided.

• Again, we discussed the status of our 1.17 and 1.18 goals.
• We hope that move GOEXPERIMENT knob is accepted, as the current plan with the register ABI is to use it for turnup.
• We discussed the progress on type lists. An internal proposal likely addresses all concerns, and an external document will be available.

Attendees:
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Than McIntosh
Martin Möhrmann
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-03-16

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• We discussed typelists again.
• We discussed possibly updating MIPS to MIPS32r2. The thinking is that R2's been around for a long time (10years?), and there is significant performance to be gained in the crypto libraries if we adopt it. Previous attempts have failed because of Loongson users. Discussion will likely continue.
• We discussed how to address amd64 per-architecture optimizations. Haswell specific optimizations have shown large improvements in certain workloads, and it might be worth providing for these wins. Discussion will likely continue.

Attendees:
The notetaker would like to apologize for leaving off Michael Knyszek from previous attendance. I don't have a good system yet, and it's quite manual.
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Michael Knyszek
Than McIntosh
Martin Möhrmann
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-03-23

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Most of the meeting was a discussion about 1.18.
• We discussed changes to the standard library for generics in 1.18
• We discussed followon work for the register ABI (beyond amd64).
• We discussed measuring PGO and other GC (Immix) ideas.

Attendees:
I was absent from the meeting, and unable to grab the screenshot.

[jeremyfaller]

2021-03-30

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• We discussed the remaining outstanding work, now that we're 1 month from the code freeze.
• Windows/ARM: completed, status of cgo is unknown
• RegisterABI: most of the rest of the changes are in review, will be able to start debugging in earnest.
• GC Pacer: Not complicated, but currently unscheduled. Register ABI is taking precedence, and if we get a chance, it'll get in.
• Scheduler Improvements: Most CLs are ready for review, need to do more testing for metrics.
• Improving Escape Analysis: Most CLs are ready for review
• Haswell Improvements: Needs a proposal first.
• Compiler phase changes: (interleaving front-end and SSA) mostly delayed.
• We discussed using GOEXPERIMENT as a one true feature gating system. Register ABI work has found this to be helpful

Attendees:
Lost to the sands of time. I forgot to take a screenshot.

[jeremyfaller]

2021-04-06

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• We discussed turning up the register abi. Our current plan is to turn the five flags that control it one-by-one, and watching the builders/trybots. The date for this turn up is TBD.
• We discussed branching again (during the freeze) for register abi and generics. Our current plan is to use a single branch for both.
• We discussed how debug information for generics was going to work. We talked about how other compilers (gcc, swift) do it. Some issues might be brought up in a future meeting with the delve folks.

Attendees:
David Chase
Austin Clements
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Michael Knyszek
Patrik Nyblom
Michael Pratt
Keith Randall
Dmitri Shuralyov
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-04-20

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• We discussed regabi which has been completely enabled in master. Please let us know if there are any instabilities. Performance (while still changing) is showing ≥ 5% wins, and smaller binaries by 2%, with 10% smaller .TEXT sections.
• We discussed the status of types2. It's not in yet, but we intend to get it in before release.

Attendees:
David Chase
Matthew Dempsky
Jeremy Faller
Robert Griesemer
Michael Knyszek
Than McIntosh
Martin Möhrmann
Patrik Nyblom
Michael Pratt
Keith Randall
Dan Scales
Ian Lance Taylor
Cherry Zhang

[jeremyfaller]

2021-05-11
These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

I'm a little behind updating these notes. I'll consolidate the last couple of meetings into this one.

• The freeze is on. Generics and the register ABI work will continue on a the dev.typeparams branch.
• The register ABI is holding true on the ~5% performance improvement, and smaller binaries. There are some regressions in some benchmarks, likely related to live variables over loops with register pressure, but we might not feel comfortable fixing these for 1.17.
• On May 11, we discussed the Uber blog post. We think it's being adequately discussed on the proposal.
• On May 4, we discussed Ian's slices proposal.
• We continue to track the 1.17 release milestone. So far, it looks like we're on track for the 1.17 beta.

[changkun]

Ping. Is the meeting stopped since May? :)

[thanm]

2023-10-24

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Go Team Summit (Google-internal) took place last week; lots of good information exchange
• we are now <1 month before freeze (freeze begins Nov. 21)
• Likely accepted proposal: spec: add range over int, range over func spec: add range over int, range over func #61405
  • Specifically, range-over-int for 1.22, and range-over-func behind GOEXPERIMENT=rangefunc for 1.22.
• proposal: testing: add Keep, to force evaluation in benchmarks proposal: testing: add Keep, to force evaluation in benchmarks #61179
  • On hold pending a prototype implementation in the compiler.
  • Keith: Anyone working on the prototype?
  • MichaelK: it is on hold anyway so probably too late for 1.22. We have plenty of time for 1.23.
  • Keith: it is possible to just add testing.Keep without any compiler changes. Downside is people may add testing.Keep in too many places.
  • MichaelK: should it be two proposals? One for adding testing.Keep, one for auto-Keep. ?
  • Keith(AI): post on the issue to clarify.
• Discussion of google-internal applications
• MichaelK: still working on tracer.
  • Close to production ready, one issue with cgo.
  • goal is to land in 1.22 behind a GOEXPERIMENT, maybe on by default.
  • Already test against Sweet, works well.
• Do we want to look over “os: make use of pidfd for linux os: make use of pidfd for linux #62654”
  • Michael Pratt will review CLs.
  • There is a new Linux API to query the process status without race. The CLs are going to use that.
• Range-over-func tasks
  • Change GOEXPERIMENT name to “rangefunc”
  • Yield checking
  • Named result details
    • Matthew: when a return statement updates named result values. There is a straightforward solution and we should do that.
  • David: is Russ doing this, or is Russ busy?
  • Cherry: how much of this needs to be in for 1.22?
  • Matthew: I will handle the named result details.
• Q: range-over-int fully implemented?
  • Matthew: believe it is done, will double check. go/types support is also done. Maybe go/ssa needs support.
  • Matthew: currently behind GOEXPERIMENT=range. Will make it on by default.
• Keith: I have a CL to change GC work buffers from gray to white. Work buffer will mean "to be marked and scanned". The benefit will be save a lookup.
  • David: will this cause more things in the work buffer?
  • Keith: yes
  • MichaelK: Austin tried something like this a while back and it is somewhat a wash?

Attendees:

Cherry Mui
David Chase
Eli Bendersky
Matthew Dempsky
Michael Knyszek
Michael Pratt
Than McIntosh

[thanm]

2023-10-31

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Happy Halloween
• FYI
  • Likely accepted proposal: unique: new package with unique.Handle unique: new package with unique.Handle #62483
  • Likely accepted proposal: all: add GORISCV64 environment variable all: add GORISCV64 environment variable #61476
    • add GORISCV64=rva20u64,rva22u64,rva23u64, not emitting C instructions until dust settles
• Range-over-int and range-over-func
  • proposal accepted
  • Change GOEXPERIMENT name to “rangefunc”, bring range-over-int out of experiment (Cherry to look into this)
  • Yield checking for range-over-func (David to look into this)
  • Spec change of range-over-int (Robert to look into this)
• Status
  • PGO
    • Michael Pratt: Prototype for function value devirt. Have it implemented, will send it out. Delayed by LUCI work but going fairly well.
    • Scalable builds: CL from Uber that adds a new command to do preprocessing for ingestion by the go command. Might not get around to landing integration of that for Go 1.22.
    • Method devirt CLs are already in, got 0.5% of performance gain.
    • No numbers yet for function value devirt. The prototype has a bunch of limitations.
  • Loop scoping
    • David: Talked to Tim King, working on getting the SSA semantics right in the downstream ssa package. Should that happen before the freeze?
    • Cherry: Maybe doesn't need to be, but pending proposals for go/types and the new go/versions package.
    • Robert: go/types proposal expected to be accepted soon. Needs prose in the spec, I'll work on it.
  • Inlining
    • Than McIntosh: Working on tuning the score adjustments to try and improve performance numbers.
    • Ran compilebench over the weekend with the new inliner. The compile time has gotten a good deal worse from new heuristics. Slowdown due to heavy use of ir.StaticValue in new heuristics. Looking at a more efficient replacement.
    • Cherry Mui: What does ir.StaticValue do?
    • Than McIntosh: detects cases where you assign a local variable "x := 1", then never re-assign "x". In such cases if the RHS is invariant, you can then substitute in the RHS where you see uses of the var.
    • Keith: There's probably a flag on variables on whether it has been reassigned. That might help to avoid recomputation.
    • Than McIntosh: concern for the flag is that it could get stale
    • Matthew: Main complexity we've had is that if we insert new IR concepts during inlining, we make changes that could affect StaticValue. So we do a failsafe that checks all the conditions again to make sure everything makes sense. It should be possible to track that more strictly to avoid the checks.
    • Any risk for finishing new inliner before Go 1.22? Are you considering downscoping?
    • Than McIntosh: Doesn't make sense to enable experiment in current state. Still needs work. Compile times are too high and the runtime improvement is too low. 1-2% improvement. Compile time is up 8-9%. For the compiler's SSA package it's 23% slower. The slowdown is mostly not due to additional inlines, but heuristic computation. Pessimistic that we'll ship anything for Go 1.22.
  • Matthew Dempsky: If hypothetically StaticValue didn't have any overhead, would we be good to ship? We should be able to speed it up. If that's what's keeping us from landing a 1-2% improvement then maybe we can just fix it.
  • Than McIntosh: We'll have to check.
  • Matthew Dempsky: Working on inliner scheduling; should have CLs soon. Don't know what the performance impact of this will be. Filippo seems to believe it'll have a high impact.
• Tracer work
  • Michael Knyszek: in good shape, last corner case is cgo callbacks. Getting Michael Pratt's review. Blocked on cmd/trace update, Felix from DataDog is working on cmd/trace integration. Michael Knyszek as a backup. On track for on by default in 1.22.
• Allocation headers CLs
  • Michael Knyszek: support arenas now, behind a GOEXPERIMENT. Cherry Mui and Keith Randall are reviewing. A concern is that as the header is at the beginning of the allocation, shifting the allocated pointer by 8 bytes. So now allocation is not 16-byte aligned; unsure whether that is a concern or to what degree.

Attendees:

Carlos Amedee
Cherry Mui
David Chase
Eli Bendersky
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2023-11-07

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Discussion of Keith's demo on faster type switches and asserts
  • Keith considering about doing some version of the talk for Gophercon
  • Than: did you use any other benchmarks?
  • Keith: no. Other benchmarks don't use much type switches.
• FYI
  • Likely accepted proposal: cmd/compile: create GOARCH=wasm32 cmd/compile: create GOARCH=wasm32 #63131
    • this is adding a new GOARCH, not changing the current GOARCH=wasm
    • there is a 64-bit wasm VM, probably not widely used
    • this is proposed by the WASI folks
    • Matthew: sandboxing 32-bit programs may be easier
  • Likely accepted proposal: sync/atomic: add Uint64Pair sync/atomic: add Uint64Pair #61236
    • MichaelK: is this 16-byte aligned? e.g.
      "the compiler and toolchain will provide the necessary alignment automatically"
    • Matthew: pad the type size to at least 32 bytes?
    • MichaelK: the allocation headers will break it (16-byte aligned for object >= 32 bytes), unless it is noscan
    • Matthew: need type checker support. As we do more and more aligned types, it may be a good idea to revisit how we do alignments
    • Cherry: SGTM. also as we may do SIMD in the future
    • Keith: the stack is not aligned, so need to escape to the heap
    • MichaelK: we should consider to do the AlignedTo types, soon. Or user would do "_ [0]atomic.Uint64Pair". If there is already a way, may give user a better way to specify it.
    • Cherry: for only atomics, it may not matter much for stack locals, as long as the instruction doesn't fault
• 1.22 stuff
  • Robert: a fun CL 539299, math/big: implement Rat.FloatPrec
    not urgent but want to get in for 1.22
    • Cherry will review
  • execution tracer work:
    • MichaelK: everything put up for review is pretty close to landing
    • new tracer will land pretty soon, but enabling by default is blocked by cmd/trace support. cmd/trace code has no abstraction. Working on it. Need review.
    • What about a release exception, just in case? The freeze exception would include enabling new tracer by default.
    • MichaelP: happy to review cmd/trace CLs. Release exception sounds fine, but should be done soon.
    • MichaelK: Felix has a working implementation but not all features. Will have a good chance done by freeze.
    • Matthew: freeze exception is up to the release team. My impression is that they've been increasingly strict about this.
    • Matthew: could the cmd/trace development be done in a branch or a separate repo, so power users could pull it in?
    • MichaelK: if new tracer is not on by default, it will be a hurdle for people to use it.
  • Inliner work
    • Than: CL reviews are a little stalled but will get them reviewed in the next two weeks
    • Matthew will review

Attendees:

Carlos Amedee
Cherry Mui
David Chase
Eli Bendersky
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2023-11-14

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• One week before the release freeze(!)
• FYI
  • Likely accepted proposal: go/types: API changes to support explicit Alias nodes go/types: API changes to support explicit Alias nodes #63223
    • go/types Alias API → alias with type parameter → iterators
    • [Robert]: code is already checked in
  • Likely accepted proposal: runtime: software floating point for GOARM=6, 7 (not only GOARM=5) runtime: software floating point for GOARM=6, 7 (not only GOARM=5) #61588
  • Accepted proposal: cmd/go: add support for dealing with flaky tests cmd/go: add support for dealing with flaky tests #62244
• 1.22 status
  • new inliner: should we enable GOEXPERIMENT=newinliner by default to turn on the new inlining heuristics in 1.22?
    • [Than] on positive side, provides some modest performance improvements, with acceptable compiler speed overhead, and google-internal testing runs have been clean, so risk appears low.
    • [Than]: inlining diagnostics messages change, needs to be communicated
    • [Than]: leaning towards enabling by default, with a more "toned down" announcement to moderate user expectations
    • [Matthew]: go ahead and ship it if there is an overall performance improvement. turn it on in RC. if there are many bugs we can turn it back off
    • [David]: need to decide how to handle any changes for the LSP JSON logging users. The plan is to keep the old words in the old version, enable the new words in new version
    • [Matthew]: what sort of stability guarantees are we promising for LSP users?
    • [David]: we are not supposed to surprise users. If we change something, we change the version number
    • [Matthew]: what exactly does "surprise" mean here
    • [David]: we intend to not change the words
    • [Cherry]: version number is specified by the tool?
    • [David]: yes. if/when we let them know and they can change version
    • [MichaelP]: how we keep the old words? "can inline" means inline everywhere, but that will not be true
    • [David/Than]: this is happening already for large functions (ex: for callee of size 79 we'll advertise is as inlinable but then not inline it in a big func) * [David] sounds like concensus is to leave JSON as is
    • [Eli]: TGP status for Matthew's CLs?
    • [Matthew]: not yet
  • range over function check
    • [David]: once it gets reviewed it can go in. overhead is high in some cases, very small with very cheap iterators. Plan to have a thorough check, no optimization, but have a compiler debug flag to turn the checks off. Performance is generally not bad.
    • CLs are under review
    • semantics for named results
      • [Matthew]: fine for now for experiment, will clarify when turning it on by default
      • [Matthew]: will find test cases
      • [Cherry]: documenting the caveat
  • allocation headers
    • [MichaelK]: allocation header is in and enabled. google-internal testing is clean. issue tracker is clean. not yet released into google-internal prod
    • [MichaelK]: tracer: a lot is in, may not need freeze exception

Attendees:

Carlos Amedee
Cherry Mui
David Chase
Eli Bendersky
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2023-11-21

• Go 1.22 freeze today!
• performance comparison Go 1.20 vs tip+PGO
  • -4.59% geomean on Sweet
  • BiogoKrishna +20% regression
  • [Matthew]: does Sweet run old/new configs interleaved
  • [Michael]: yes, interleaved (but not randomized)
  • [Michael]: BiogoKrishna is not a representative benchmarks. built with some nonpreemptible loops, a lot of bit arithmetics and table lookups. The reason we keep it is it is a good preemption benchmarks. It can be sensitive to code layout.
  • [Michael]: cool debug trick on the dashboard
• Please write release notes doc: write release notes for Go 1.22 #61422
• Go 1.22 issues
• 2024 topics
  • KSLO cost reduction
  • Go on future platforms (RAM efficiency. NUMA?)
  • (maybe) Go-Python interop for AI-powered applications
  • [David]: is it a good idea to use cgo for Go-Python interop?
  • [Michael]: no. better with pipe or RPC (EDIT: I'm wrong about this. A conversation after the meeting clarified a misunderstanding I had about Go->Python calls specifically. Both Go->Python and Python->Go with cgo may very well be preferable to pipe/RPC in many circumstances. :))
  • [Michael]: excited with RAM efficiency work. Not sure if NUMA is the right target. Austin's analysis shows memory bandwidth is going to be an issue.
    User survey: impact vs effort mapping graph of the potential optimizations?
  • [Michael]: intended to do another session with Alice with user survey for 2024 priority. Austin has a good start for RAM efficiency things
  • [discussions about project prioritization]
  • [Michael]: go.dev/fast is under RAM efficiency?
  • [Eli] documentation work is its own thing. Sounds important, but don't spend too much time. New tracing work is also in this direction.

[thanm]

2023-11-28

• Go 1.22 RC1 is scheduled on Dec 12 (2 weeks from now)
• Please write release notes doc: write release notes for Go 1.22 #61422
  • [Keith] there was some discussion previously about revising and/or improving the process for putting together release notes -- has anything happened on this front?
  • sounds like not for this cycle on the new process front
  • Loop scoping (David or Russ to write relnotes)
  • Range-over-int (David to write relnotes)
  • Range-over-func under GOEXPERIMENT (David and/or Russ to write relnotes)
  • go/types new APIs (Alias, FileVersion) (Robert Griesemer to write relnotes)
  • New tracer (Michael Knyszek to write relnotes)
  • Bump bootstrap to 1.20 (MichaelK)
  • PGO devirtualization changes (Michael Pratt to write relnotes)
  • Allocation headers (Michael Knyszek to write notes)
  • CL 544195 runtime: profile contended lock calls (Michael Pratt or Rhys)
  • CL 534161 runtime/metrics: add STW stopping and total time metrics (Michael Pratt)
  • CL 537515 runtime/pprof: include labels for caller of goroutine profile (Michael Knyszek or Michael Pratt)
  • CL 511475 cmd/link: allow deriving GNU build ID from Go build ID ID (Cherry Mui)
  • CL 493136 cmd/link: rationalize -s and -w flags (Cherry Mui)
• Port specific changes that might require release notes
  • CL 461697 default to PIE on darwin/amd64 (Cherry Mui)
  • CL 514907 GOARM=softfloat/hardfloat (Keith Randall)
  • CL 521790 enable register ABI on Loong64 (David Chase or Loong64 owners)
  • CL 521778 enable plugin on Loong64
  • [Than] Windows SEH stack unwind runtime: support SEH stack unwinding on Windows #57302? need to ping CL/issue
• Robert Griesemer: writing release notes is time consuming because the format is tedious
  • Cherry Mui: there was some discussion about moving to markdown
  • Michael Knyszek: this is actively being worked on
  • Carlos Amedee: good to give feedback to Jonathan
  • Matthew Dempsky: similar to api/next, we can do relnotes/next
  • Carlos Amedee: this is the direction
• Go 1.22 issues
• Status
  • discussion of range-over-func efficiency
  • David Chase: Russ's CL is related
  • Michael Knyszek: do need freeze exception for anything here?
  • David Chase: iter package needs a separate GOEXPERIMENT
  • Keith Randall: iter package should land in x/exp?
  • Matthew Dempsky: need some coroutine stuff from runtime

Attendees:

Carlos Amedee
Cherry Mui
David Chase
Eli Bendersky
Joedian Reid
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2023-12-12

• Schedule
  • go team fixit week (this week)
  • go team "quiet" week (next week)
• Go 1.22 RC1 is rescheduled to next Tuesday, December 19
  • Thank you for writing the release notes!
• topic: //go:linkname
  • Than: do we need to start making a more concrete plan for disallowing “pull” style go:linknames of runtime/stdlib symbols?
  • Than: there are a lot linknames in opensource code. If we plan to change this, maybe we start communicating.
  • MichaelP: it is still unclear if we can and should change it. If we don't provide an alternative, I don't think we can just turn it off. If we delete entirely, users may resort to assembly.
  • Matthew: assembly code is a good point, user can still call it from assembly code. Balancing that we want to stop user poke into runtime, while provide things they want to do
  • Cherry: we can stop assembly code call them in the linker
  • Keith: we can find the top users of it and try to fix it somehow. The problem is if we change the name of popular things, we can help them
  • Than: if we leave things entirely unchanged, it would block future projects (e.g. renaming runtime to internal/runtime)
  • Cherry: for the rename, we could provide forwarding linknames
  • MichaelK: we can treat the list of existing linknames as a priority list and provide workarounds
    • rand (handled in 1.22)
    • nanotime
    • memhash
  • MichaelK: fine to break programs that linkname to stoptheworld
  • Matthew: maybe a good starting point is to start implement the logic in the linker and a vulncheck-style tool for why they might fail the build, to communicate with users, and get feedback from users which linknames are needed
  • MichaelP: discourage linknames by providing a compiler flag to turn it back on. That will strongly discourage uses in libraries
  • Robert: we should have a better idea for why users use them
  • survey from Matthew, MichaelP shows 700 linknames for packages with 10+ imports
• Status
  • compiler error URLs
    • Robert: Russ thinks we should be doing this with mnemonics, not numbers. Robert Griesemer will look into the mnemonics. Also need to write the documents. Russ vetoed autogenerated docs. The docs could be more explanatory. Carried over to 2024.
  • Heap analysis improvements -- viewcore
    • MichaelK: want to work on it this week for fixit, for viewcode.
  • PGO devirt
    • MichaelP: done, with minor issues, not clear we want to address them soon
  • Traceback iterator: simplify defer
    • Matthew Dempsky: done. will check with Austin.

Attendees:

Carlos Amedee
Cherry Mui
David Chase
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2023-12-19

No meeting today (Go team "quiet" week)

[thanm]

2024-01-02

• Allocation headers results
  • still evaluating impact of GOEXPERIMENT=allocheaders change on google-internal applications. It is generally positive, but not clear to what degree.
• Go developer survey
  • “The top requests for improving toolchain warnings and errors were to make the messages more comprehensible and actionable”
  • Some of this is also about runtime errors
  • mild surprises (at least to attendees):
    • 5% targeting wasm
    • 56% “use” ARM64 (!)
      • “However, Apple hardware isn’t the only factor driving ARM64 adoption: among respondents who don’t develop on macOS at all, 29% still say they develop for ARM64.”
      • rumor has it that ARM just laid off their whole Go team in China
  • “improved expressivity [“creature comforts”] (12%), improved error handling (12%), and improved type safety or reliability (9%). Respondents had a variety of ideas for improving expressivity, with the general trend of this feedback being “Here’s a specific thing I write frequently, and I wish it were easier to express this in Go”. The issues with error handling continue to be complaints about the verbosity of this code today, while feedback about type safety most commonly touched on sum types.”
  • [MichaelP]: 50% said they use protobufs (mostly via gRPC)
• 2024 plans
  • Finishing in flight (done by end of Q1)
    • LUCI migration
    • Inlining: enable new heuristics
    • Inlining: scheduler
    • PGO: scalable builds
    • Runtime trace overhaul: cleanup (delete old tracer, old cmd/trace, moving old trace parser behind new API)
    • Runtime trace overhaul: reader API
    • go build -json
• 1.23
  • Range-over-func GA
  • /e/ URLs?
  • Type parameters for type aliases?
    • [Eli]: I think this is very far along. Ask Robert next week.
  • sync/atomic And/Or
  • sync/atomic Uint64Pair?
  • Cost reduction (RAM efficiency)
  • Performance analysis
  • [MichaelK]: CockroachDB is excited about contributing benchmarks to our suite.
• administrivia
  • more of the work formerly done by the release team is being transferred over to the core (C+R) team

Attendees:

Austin Clements
David Chase
Dmitri Shuraylov
Eli Bendersky
Michael Knyszek
Michael Pratt
Than McIntosh

[randall77]

2024-01-23

• Tree open! 🎉
• Upcoming 2024 plans
  •  MichaelK: Is the iter package going to land in 1.23?
  • Cherry Mui: My tooling for cold path escapes could probably also be used to estimate up-stack escape analysis (by excluding returned values)
  • Single bit reference counting
    • Matthew Dempsky: https://mdempsky.notion.site/Dynamic-escape-analysis-76bbeecd3ac4440c88d0cb2f722aaf75
    • Michael Knyszek: Unique pointer optimization and freegc
    • We should brainstorm about this.
• People are grumpy we dropped Windows 7 support (also without a good error message)
  • Dmitri Shuralyov: We dropped support in a major release and updated our installer check
  • The minor release change may have been that we now get a dynamic linking error instead of something nice.
  • Michael Pratt: This seems to have come from a security fix.
  • Michael Pratt: Considering a proposal for Windows 7 as a secondary port. Seems like a reasonable path.
  • Dmitri Shuralyov: We’ve never done that before. This is WAI and went through the proposal process. Adding back support would have to be a new proposal.

Attendees:

Austin Clements
Cherry Mui
David Chase
Dmitri Shuraylov
Joedian Reid
Keith Randall
Michael Knyszek
Michael Pratt
Robert Griesemer

[thanm]

No C&R meeting today (this is a Google Core "no meetings" quiet week).

[thanm]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-02-27

• Amazing out-of-tree SwissTable results from Peter Mattis (CockroachDB’s CTO)
  • TL;DR: Iteration is ~60% faster, gets are ~20% faster (though there are some odd slowdowns with gets of non-existent elements on large maps), puts are ~30–45% faster (~20% faster if they grow the map), deletes are a mixed bag
  • Austin’s benchmark analysis, benchstat, benchplots
  • Uses extendible hashing to avoid resize latency of earlier implementation
  • Missing some optimizations that would be fairly easy to do in a runtime implementation. Mostly because it’s using Go generics so can’t do the type specialization we do.
  • Doesn’t currently even use SIMD, though again in the runtime it wouldn’t be hard to add that.
  • The implementation is complex, but looks really clean.
  • Peter is supportive of getting it into the runtime; it seems clear that we (Go C&R team) should work to make this happen.
  • Keith Randall and Michael Pratt to work on bringing this in.
  • Michael Pratt: Expecting a long tail of weird performance regressions for google-internal tests and such. Probably needs to be behind a GOEXPERIMENT.
• misc wasm discussions
• misc meeting-scheduling discussions

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Dmitri Shuralyov
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2024-03-12

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Lengthy discussion on iter.Pull and LockOSThread semantics
  • Case: Both goroutines call LockOSThread
    • 1. G1 is on a locked OS thread
    • 2. G1 calls next, which switches to G2
    • 3. G2 locks its OS thread
    • 4. G2 calls yield
    • Option 1: Step 2 does a thread switch
    • Option 2: Step 2 “donates” the OS thread. Step 3 moves G2 to a new thread
    • Option 3: Step 3 panics
  • Case: yield crosses goroutines
    • 1. G1 is on a locked OS thread
    • 2. G1 calls next, which switches to G2
    • 3. G2 passes yield to another goroutine, G3, and continues executing
    • 4. G3 calls yield, which switches to G1
    • If step 2 does a coroutine switch, then it has to “donate” the locked thread to G2. But then in step 4, you have both G1 and G2 that have to run on the same locked thread.
    • Option 1: Step 2 does a thread switch
    • Option 2: Step 4 interrupts G2 (which may take arbitrarily long) in order to run G1
    • Option 3: Step 4 panics because yield was called on another goroutine. (just iter.Pull or iter.Pull and range-over-func).
    • David Chase: G3 can do a lock OS thread, too.
      • Austin Clements: I’m not sure that matters for this case.
      • Michael Pratt: That could be a problem with the first case, where G2 calls lock OS thread, but G1 does not.
  • Case: next crosses goroutines
  • Michael Knyszek: Cgo callbacks are a pain because that thread is always locked.
  • Matthew Dempsky: Deprecate LockOSThread and add RunOnLockedOSThread(f func())
    • Michael Knyszek: Maybe that’s what we should have done in the first place. A lot of UI libraries have a “take this function and run it on the main thread”.
    • Cherry Mui: go.dev/issue/64777
    • Ian Lance Taylor: go.dev/issue/64755
    • Austin Clements: Even if we deprecate LockOSThread, we have to deal with it forever (though the performance may be less of a concern).
    • Michael Pratt: Passing yield to a RunOnLockedOSThread goroutine, same trouble
  • Ian Lance Taylor: What’s the downside of making the switch do a full goroutine switch if the thread is locked?
    • Austin Clements: Semantically that works out. Performance is an issue. You don’t necessarily control whether you’re locked, like in the cgo callback case.
    • Ian Lance Taylor: iter.Pull is not going to be that common
    • David Chase: I agree. We have a mechanism that works: goroutines. It’s unfortunate that many of these iterators could easily give you a pull, but we’re not exposing that.
    • Keith Randall: The issue I see is that you may use some code that uses iter.Pull internally. It feels like an abstraction break between the OS thread locking (maybe from a cgo callback) and the iter.Pull.
• Struct packing/reordering
  • David Chase: Struct packing/reordering is a mechanical thing humans shouldn’t be doing. If we had been doing this with protobufs, we’d have huge savings. 3% RAM footprint, ~20% GC cache traffic. We may end up doing GopherPen and being able to reorder struct fields eliminates a lot of the RAM footprint expense.
  • David Chase: I was figuring this would work for all structs, but Russ Cox said it should depend on the module language version. But you can do var x *pkgA.T; (*pkgB.U)(x), if T and U have the same underlying type, and if we laid out T and U differently, it’s not clear how we could implement this cast. If this is rare, maybe we can just break it.
    • Matthew Dempsky: A “fragile conversion” is a conversion form *T to *U where T and U’s underlying type literals appeared in source files from different Go modules.
  • David Chase: Ran fragilecast ecosystem analysis, only 27 instances in the 21305 10-or-more imports projects. Classification of conversions.
    • David Chase: I’ve been trying to make it module-aware to reduce false positives, but having trouble. Presumably in this case there’s shared ownership, and a single go.mod language version.
  • Ian Lance Taylor: What about the case of passing the address of a struct to C code?
    • David Chase: I don’t pick that up. I’m working on a proposal for a signal type that says “follow the platform rules.” Cgo would automatically add this.
  • Robert Griesemer: What about per-file versions?
    • David Chase: I think this would ignore those and just use the module version.
  • What does “work” mean? Is there a language change here?
    • Austin Clements: Old code keeps working, even if it has unsafe assumptions about struct layout.
    • David Chase: There is a small language change here if we disallow “fragile” casts.
  • Matthew Dempsky: The language spec only has “conversion”, not “cast”.
  • Matthew Dempsky: Type aliases have a disadvantage for documentation. E.g., if you alias an internal type, the exported type won’t necessarily have documentation.
    • Austin Clements: Russ and I have talked about fixing that in go doc.
  • Robert Griesemer: Is reordering based on the structure of the type? Or profile-based? Could it be done in a way that results in the same reordering for the same underlying types?
    • David Chase: I can imagine someone would want to try profiling, but my assumption is that we would use a stable algorithm that worked the same way for structurally identical types. Partly because there’s unsafe code out there.
  • Michael Knyszek: How are type aliases represented in documentation today? Should it copy not just the documentation but the definition?
    • Austin Clements: I think you would want to copy the definition (though don’t hide that it’s an alias).
  • Matthew Dempsky: So two struct types that are identical would be reordered in the same way
  • Keith Randall: Fighting concerns. We don’t want to break everyone’s unsafe code all at once, but we don’t want to disallow cross-module conversions.
  • Austin Clements: That’s why David did the ecosystem analysis. These conversions are very rare.
  • Keith Randall: What about plain struct conversions? Memcpy now, but across language versions, a reorder.
    • David Chase: My analysis doesn’t look for these right now.
    • Cherry Mui: There’s at least a way to compile this. The pointer case just can’t be fixed.

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Ian Lance Taylor
Joedian Reid
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2024-03-19

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• FYI
  • cmd/compile: add go:wasmexport directive cmd/compile: add go:wasmexport directive #65199 accepted
  • proposal: runtime/debug: add SetCrashHeader function proposal: runtime/debug: add SetCrashHeader function #64590 declined
  • proposal: spec: support int(bool) conversions proposal: spec: support int(bool) conversions #64825 declined
  • runtime: CL 561635 changes relative PCs printed in tracebacks runtime: CL 561635 changes relative PCs printed in tracebacks #65761
    • Still an open question. If we’re going to do structured tracebacks, it should probably be tied to the new debug.SetCrashOutput API, so we need to at least decide on the API this release.
• discussion about ways to automate Go best practices
  • Matthew Dempsky: Tangential to that, Austin and I were discussing doing team screencasts. I can feel stuck with my development workflow from 20 years ago and being familiar with workflows other people are using could make us more productive and realize where things could still be improved.
• brainstorming ideas for AI-powered apps useful for Go team itself
  • Solving our own problems through AI, to get us more familiar with AI applications.
  • OSS project use cases
  • Build-time use cases
• Austin is working on a Go GC efficiency downselection doc

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Dmitri Shuralyov
Ian Lance Taylor
Joedian Reid
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2024-03-26

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• upcoming inliner heuristics review during this Thursday’s Go breakout
• Project status updates
  • Range-over-func iter.Pull and LockOSThread
    • David: We could always use goroutines.
    • Austin: Russ did have an inbetween version that used goroutines and channels, but with fused channel operations.
    • Michael Knyszek: That might be an easier fallback path and general channels.
    • Cherry: Did Russ’ fused channel operations work with locked OS threads?
    • Austin: I’m not sure.
    • Cherry: It might still be easier to implement the fallback for that with locked OS threads.
  • Joedian: Are there things we’re worried about for 1.23?
    • Range-over-func has a lot of open tasks
      • David: Checking semantics will be fine. Worried about defer with named results. Performance probably okay. Worried about weird things for debugger integration because it’s not clear we can do exactly what they want.
    • Cleaning up old tracer
      • Austin: Does this have to happen in 1.23?
      • Michael Knyszek: It will break with things like iter.Pull, which aren’t supported in the old tracer.
    • Structured go build -json doesn’t have to happen for 1.23
    • SwissTables doesn’t have to happen for 1.23, but it would be good for hitting our 5% target.
      • Michael Pratt: I’m hoping to start this after returning from vacation.

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Dmitri Shuralyov
Ian Lance Taylor
Joedian Reid
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Robert Griesemer
Than McIntosh

[thanm]

2024-03-28

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• On Thursday 3/28 we held a design review looking at the new inlining heuristics framework being developed as part of the inlining overhaul effort (this was a separate session from the usual C&R meeting)
  • Slides from the talk: https://docs.google.com/presentation/d/1Lf3WoRyCNicS1K3NCuVl_VnJFhvew_6nAQF_Wx--F54/edit#slide=id.p
• Notes from questions/discussion during the talk
  • Litmus tests
    • Inline sort.Search with a (small) function literal
    • Fast path/slow path inlines the fast path
    • Singleton calls to non-exported functions
    • Or specifically closures. Comes up as a way to do “function literals”, and also to give more control over defers (though that will prevent inlining).
    • Russ gave some examples on the bug
    • A call site weight of 57 makes no sense. We should be able to significantly lower that.
  • Parameter heuristics: constant feeds if/switch
    • Michael Pratt: If you could analyze the effect of propagating a constant, you could potentially significantly reduce the size. It would be nice to capture that in the score.
    • Than: We don’t currently look at the value of these constants. Tracking that could significantly bloat the export data.
  • Sweet benchmark results
    • The GoBuild (non-Link) benchmarks are measuring the impact of doing more work on compile time, so it’s not directly comparable with other benchmarks. That’s fine, but means the overall geomean isn’t meaningful.
  • Difficulties/obstacles
    • Michael Pratt: With PGO, we’ve noticed that about half of the performance effect comes from optimizing the runtime, in particular the garbage collector. We’ve never checked closely if that’s from making the GC faster or the application doing less allocation.
  • Robert: Why don’t we let users say “inline this”?
    • Ian: GCC shows that people often get this wrong.
    • Russ: Overfitting to “right now”
    • Ian: OTOH, GCC experience shows that people usually use “don’t inline” correctly.
  • Keith: To some extent we train our users to write code for the inliner. Like manual hot/cold splits today. It’s better if users don’t have to jump through hoops to get “the right thing.”
  • Robert: If people write lots of small functions, you might get the large function in the end. If people write large functions, we can’t do anything. Maybe we should tell people to write smaller functions.
  • Tim: Do we know how well these heuristics correlate with places of user angst?
    • Russ: Perhaps replace angst with “places where inlining actually helps”
    • Than: I think that happens with passing concrete values to interface arguments. People get grumpy when they have to contort their code around that.
  • Ian: Heuristic that specifically targets removing escapes?
    • Than: Passing a concrete value to an interface helps, but that’s just one example.
    • Ian: Also feeds into type switch or type assertion. Maybe “likely” interface type at call site? Also unused parameters, though that helps more with interface method calls (e.g., caller does some work to compute a parameter that isn’t used).
• Notes from questions/discussion after the talk
  • Austin: I would expect the common case to be a constructor function that returns a pointer, but the result doesn’t escape past the call site.
  • Than: That’s hard to capture in a heuristic that’s not doing full escape analysis.
  • Austin: Long ago, we talked about doing the data flow before inlining, then using that information to drive inlining, then producing final escape summaries.
  • Than: That would definitely require an escape analysis expert.
  • Russ: Seems like the strategy is to think about heuristics and try them and see what happens, which doesn’t feel very directed. Maybe, turn the inliner up really high, see what that gives you, and then figure out why. Hash bisection may be able to tell you this: write a function that says “is etcd still > 10% faster?” and run hash bisection to get the set of places where it really matters. Then ask what patterns get you those. Then worry about false positives that come with those.
  • Than and others: idea from Russ sounds good
    • probably need to finish stack slot merging before we do this, or the costs of inlining may be too dominant to seek out the wins.
    • Than: bisection could be made more difficut due to noisy benchmarks
    • Than: For escape effects, we could measure the allocation count, which should be pretty stable.
  • Tim: Range-over-funcs don’t exist in any code, but do you have a sense of how that will interact with these when that does start to exist?
    • David: It resolves things down to flat code pretty often right now. Though if something prevents inlining, the whole house of cards falls apart.
  • Austin: “Calls cost 57” is a clear red flag. A call isn’t expensive. Right now this is our backstop against making lots of bad decisions, but it also prevents us from making a lot of good decisions.
  • Austin: “Don’t inline here” heuristics, if they’re working right, should have almost no effect on performance, just reduce binary size. Should check binary size effects of those.

[thanm]

2024-04-02

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• Discussion about how to help automate / and ease the introduction/rollout for Go "best" practices" that we use in the Go core team
  • Ensure users are getting the benefit of the core team’s work. (For example, IDE integration is great for build-time things, but we don’t have great answers for deploy/run-time.)
    • PGO example: How do developers consume profiles today? Can we integrate with those? (Vendors like DataDog?)
    • How do people coordinate production builds today?
      • “GitOps”: CICD & triggers, Github Actions
    • should we partner more closely with other teams? If we did, what could we do better?
    • If we did partner, then what happens? A single integration only does so much, while building a partner relationship keeps on giving.
  • Keith: It would be great if this problem didn’t exist. A lot of our performance optimizations just happen when you upgrade. Hopefully the places where we couldn’t just make it automatic are a minority of places.
  • Matthew: Go could be missing more of an “application level framework.” Right now if you want to build applications with Go, you have to use a lot of external packages. Unless you’re writing a 1970’s CLI. (Ian Lance Taylor: Gophers on Rails.) Opinionated Go way.
    • Michael Knyszek: Service weaver?
    • Carlos: go-kit
    • Austin: I don’t know what’s stopping us.
    • Matthew: What’s stopping me is that I’ve never built an application in Go and it seems scary and keeps changing. Go simplicity for building applications that work nicely over time.
  • Michael Knyszek: I think there’s room for improving, e.g., net/http/pprof. Gophers Slack was discussing how everyone exposes basic debugging endpoints. Everyone does it differently because net/http/pprof is a security hazard. Where we did try to provide convenience, we’re now, today, doing a bad job. Pprof should just be there, and secure, and working by default. That impedes PGO integration. Could we integrate into the new “hot thing”, OpenTelemetry?
• strings.Compare optimization
  • Keith: Used for sorting. We have an old “Less” implementation, and strings.Compare builds a 3-way compare on two “Less”es. We’ve pushed back on optimizing strings.Compare, but now it’s the thing to use for sorting because “you should be using the built-in comparisons.”
    • Ian: Seen “if strings.Compare(a, b) < 0” many times because people don’t realize you can just directly compare strings.
  • Compare the strings once instead of twice, using internal/bytealg
  • CL 532195
  • Austin: Can we do the same for cmp.Compare?
    • Ian: No because we can’t specialize it for string. (We could type switch on string, but not ~string. And it’s not clear if the compiler would specialize in that case anyway)
    • Austin: We could teach the compiler about this special case.
  • Keith: The other option was to look for the three-way comparison code pattern and compile that specially. That would catch both strings.Compare and cmp.Compare. But it’s a tricky optimization.
    • Austin: It could be pretty specific to the pattern in strings.Compare and cmp.Compare.
  • Way forward: just land this CL. We can undo it if we ever do the general optimization.
• Austin: LLVM MLIR uses “basic block arguments” instead of “phi functions” and it sounds like that makes it easier to do block graph manipulations. Have we considered doing that sort of thing?
  • Matthew: That’s what I was suggesting with reorganizing the compiler around basic blocks that do tail calls instead of functions. This seems to be the popular SSA-like representation these days.
  • Austin: It seems like we could do an 80/20 thing where we don’t have to restructure the whole compiler toward a sea of basic blocks. We could still have regular functions, and just make it easier to manipulate the BB graph.
  • Austin: What’s the implication for, say, BB1 dominates BB2 but isn’t a direct predecessor, and BB2 uses a variable introduced in BB1. Does that mean that variable has to be threaded through the arguments to the intermediate BBs?
  • Matthew: Example: Thorin IR (see Figure 4 on page 4 for syntax/semantics/typing). BB arguments directly correspond to phi functions and you’re allowed to do “implicit capture”. Results in a very concise semantics.

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Dmitri Shuralyov
Ian Lance Taylor
Joedian Reid
Keith Randall
Matthew Dempsky
Michael Knyszek
Michael Pratt
Than McIntosh

[cherrymui]

2024-08-06

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

• FYI
  • hash/maphash: add func Comparable #54670 re-likely accepted
• Resume public meeting minutes at #43930
• Went over H2 plan
  • Bump bootstrap to 1.22
  • Bump minimum Linux to 3.17
  • Switch built-in maps to SwissTables
  • Range-over-func
    • Range-over-func: Fix addrtaken with inlining [DONE]
    • Range-over-func: Fix iter.Pull performance under cgo
  • PGO: Discriminator support
  • Type params on aliases
    • Export data support
    • Enable GOEXPERIMENT=aliastypeparams by default
  • Structured all.bash: go build -json
  • GC efficiency
  • WASM
    • Implement go:wasmexport
    • Integrate structs.HostLayout into go:wasmexport and wasm32

Attendees:

Austin Clements
Carlos Amedee
Cherry Mui
David Chase
Dmitri Shuralyov
Eli Bendersky
Ian Lance Taylor
Michael Knyszek
Michael Pratt
Robert Griesemer
Tim King

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-08-13

• Go 1.23.0 is released today 🎉
• #68658 cmd/go: breaking change in 1.23rc2 with version constraints in GOPATH mode
  • Decided not to include CL 603895 in 1.23.0
  • Discussions on CL 603895
  • Robert Griesemer: if the file local version is not correct (e.g. go1.21.4 is invalid), it is silently ignored, which may be surprising to user
    • #64127
    • Tim King: vet has a "likely match" build tag check that should catch this
    • Cherry Mui: is the file not being built by go command at all?
    • David Chase: is it syntactically invalid? What about //go:build !go1.21.4 ?
    • Michael Knyszek: is there a recorded talk about version upgrading/downgrading
      • Russ Cox has a blog post (and this)
  • Continue discussion on the issue
• 1.24 cross-team features
  • parameterized type alias, with tools team. Robert Griesemer and Tim King are already talking with them.
    • Tim King: would be very nice to get it in before the next x/tools version bump, which is September
    • It is not yet on by default. Tim King has a checklist exportdata: support type parameterized aliases #68778
    • Keith Randall: the flip is prerequisite for x/tools change?
      • Tim King: yes, but need tools's export data in first before flipping
  • Keith Randall: bump the bootstrap version. There is already a CL that wants to use 1.22 feature in the compiler
    • Dmitri Shuralyov: will get in this or next week

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-08-20

• Status
  • Bootstrap bump
    • Dmitri Shuralyov: LUCI builders are all updated, done a minimal fix for legacy builders, just submitted first CL that requires new version at tip.
  • Linux bump
    • Ian Lance Taylor: The actual version we’ll be requiring has not been finalized yet. Brad pointed out that 3.17 is a problem because there are a lot of old Synology boxes out there. It’ll probably be 3.2.
  • SwissTables
    • Michael Pratt: I have a full working implementation with extendible hashing. A bunch of benchmarks are slower vs the existing maps. We’ll almost certainly need special paths like fast32/64. Mostly really small benchmarks, like small maps looking up the same key over and over.
    • Could we make the new map actually generic?
      • We don’t have anything that makes up instantiations like these in the compiler.
      • Problem: runtime.a isn’t always available today (we could fix that)
      • Problem: what types do we instantiate? Do we pre-instantiate common types in the runtime package?
        • Michael Pratt: We may want the “GC shape” of these to be defined somewhat differently than the usual.
    • Turning the equality call from an indirect call into a direct equality check would be much faster.
  • Type parameters on type aliases
    • Tim King: Most of the hard bits are out for review. Need to turn on more builders. Need to copy various bits into x/tools.
    • Austin Clements: Could we ever fully decouple these?
      • Tim King: It would be wasteful. You could still have the compiler do type checking, but then call out to something that would write the data for vet.
      • Cherry Mui: The compiler export data has a lot more than what tools need and does a lot of non-type-checking work. If my cache is empty and I run go vet, it does a lot of unnecessary work recompiling everything.
      • Robert Griesemer: There is a source importer that’s existed for years. The API checker does more or less what Cherry said, but doesn’t cache the results. I don’t know how much x/tools depends on caching repeated work. There’s a lot of work in the unified importer to only import what you need. Not impossible, but quite a lot of work.
      • Cherry Mui: I’ve heard gopls has its own export data format (not positive). Presumably gopls is quite latency sensitive, so if they can do it, vet probably can, too.
      • David Chase: Do the tools get the same view of the module import graph as the compiler? (This came up because I’m looking at making go doc look at other packages.)
      • Tim King: I believe it all comes from “go list”, but it might depend on the tool.
      • Tim King: We also run vet from “go test”, so spawning a duplicate process to write duplicate type information seems wasteful, but it would definitely simplify everything for the two sides to use their own views of export data.
  • WASM
    • Cherry Mui: wasmexport is pretty much done. WASIp1 is in. WASM JS is out for review. May want to add more tests.
• David Chase: Found loop alignment anomaly on ARM64. Goes different ways on M2/M3.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-08-27

• cmd/go: breaking change in 1.23rc2 with version constraints in GOPATH mode #68658
  • Michael Matloob proposed solution: max(1.21, fileVersion) independent of -lang (moduleVersion)
  • We'll probably do this in 1.24 and 1.23.1
    • Robert Griesemer: 1.23.1 is scheduled next Wednesday, and Monday is U.S. Labor Day. If we want to do it in 1.23.1, it needs to be in soon.
    • Currently there is no backport issue.
    • Dmitri Shuralyov: Is it okay to be 1.23.2?
    • Cherry Mui: I think it's okay. It's not new in 1.23.0.
• Proposal: testing/synctest: new package for testing concurrent code #67434
  • Michael Knyszek and Michael Pratt will review
• Elimination of core types from spec #63940
  • Robert Griesemer: I have implemented 60-70%. Will see how it goes. Will need a proposal and get accepted. There will not be a huge change to users.
  • Cherry Mui: Is the concept of Core type just in the spec and internal to the compiler? Is there any public API about core type?
  • Robert Griesemer: will sync with the tools team
• Range-func/iterators performance
  • David Chase: at least for a particular small loop, if the body includes a 4K boundary, it will run 2x fast on Apple M3, but 2x slow on Apple M2, no difference on GCP ARM64 VM
  • David Chase: we are mostly happy with the performance (on sensible machines) after deadlocals. There is a case that the inliner could do better.
    • The inline budget calculation about OCLOSURE
    • Keith Randall: you want the cost to be proportional to the size of the code to create the closure object

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-09-03

• Status
  • Range-over-func: Inliner improvement on handling closures
    • David Chase: https://go.dev/cl/609095 reduces call site penalty if callee is param. Seems to reduce binary size, helps some iter benchmarks, there is one regression in gonum, looking at that. Another approach decoupling OCLOSURE size from cost of containing function would help, but was not done correctly, so, not yet.
    • Keith Randall: this really only helps if the callee is a known function
  • Parameterized type alias
    • Alan has a proposal to support only 2 recent versions or export data in x/tools #68898
    • Tim King: there is a backlog of go/types users that are not yet go 1.22. They should update to 1.23 or 1.24 to use parameterized type aliases. We should probably figure out a good way to advertise this to tool authors.
      • golang-dev, Slack, tools team may have some channels
  • HostLayout
    • Keith Randall: Is it coming to 1.24?
    • David Chase: structs.HostLayout landed in 1.23. Working on adding it to syscall and cgo. Ian thinks we probably need to do something with unkeyed struct literals. Vet didn't flag them, as they are "local".
    • Cherry Mui: another possibility is to have the compiler special-case cgo structs without adding the field.
    • Ian's proposal is to rewrite it in-place in the cgo tool.
  • Bump bootstrap to 1.22
  • SwissTables maps
  • Wasmexport
  • Diagnostics

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-09-10

• FYI
  • Likely accepted proposal: runtime: add AddCleanup and deprecate SetFinalizer #67535
  • Likely accepted proposal: weak: new package providing weak pointers #67552
• [From Austin] Make wasmimport/wasmexport accept pointers to HostLayout structs?
  • proposal: cmd/compile: relax wasm32 function import signature type constraints #66984 includes this but is pretty complex. Do we want to do this whole thing or just start with allowing pointers to HostLayout structs?
  • Worried about letting the horse out of the barn with a wasmexport that only supports unsafe.Pointer.
  • Cherry Mui: The proposal is in a good direction. GOARCH=wasm32 is still going and uncertain. What do we do with GOARCH=wasm? We could allow structs with HostLayout and only non-pointer fields?
• Michael Knyszek: Should we backport https://go.dev/cl/610738?
  • Summary: unique.Make intends to clone almost all strings before storing them in the central map, but erroneously stores the original string as the map key.
  • Pros:
    • Users of unique.Make don't need to defensively clone strings.
  • Cons:
    • It's not really documented anywhere (yet) that we clone these strings. Ian suggested doing so a while ago and I never got around to it. So, this isn't going to break anybody, and there is a workaround.
  • Ian Lance Taylor: I think we should backport. Eli Bendersky agrees.
• Discussed about runtime/compiler office hours and contributors sync.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-09-17

• FYI
  • Accepted proposal: runtime: add AddCleanup and deprecate SetFinalizer #67535
  • Accepted proposal: weak: new package providing weak pointers #67552
    • Michael Knyszek: Getting it landed is trivial, just renaming the package and a method. Strongly feel getting both land is better. AddCleanup is the only thing that will take work, but not a lot.
    • Carlos Amedee will work on AddCleanup.
  • Likely accepted proposal: cmd/compile: relax wasm/wasm32 function import signature type constraints #66984
  • Likely accepted proposal: crypto/subtle: add WithDataIndependentTiming #66450
• Michael Knyszek: From Slack: can we make unique.Make(string(byteSlice)) not allocate?
  • The byte slice will be cloned as a string if we store it, so semantically, it's safe to do this. But I don't know how difficult it would be to make this work in the compiler.
  • Austin Clements: Is there a general inter-procedural optimization here? (cmd/compile: consider to add move-like optimization for some string<->[]byte operations #50846)
    • Cherry Mui: Maybe related to David Chase's work about pure / read-only functions
    • Keith Randall: For F(string(slice)), can we use the escape information to know the string doesn't outlast the call? Have to make sure it also doesn’t escape to the result.
    • Keith Randall: Worried about synchronization.
      • Example: Goroutine 2 modifies slice then sends on a channel, F reads from the channel, then uses its string argument. Before this optimization, we’d copy at the call site and see the old data (racy), but after this optimization, we’d copy after the modification and see the new data.
    • Keith Randall: Bigger problem: F could have a reference to slice and modify it.
    • Austin Clements: Needs some guarantee of the uniqueness of that slice.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-10-08

No meeting due to Go quiet week.

2024-10-15

No meeting due to internal team summit.

2024-10-22

• FYI
  • Go 1.24 Release Freeze is in a month (Nov. 21)
  • Handy reference to which wasm proposals are in what state and where they’re supported
    • Michael Knyszek: Austin proposed to use a similar mechanism to track GODEBUG. What values are set for each release.
• testing.B.Loop auto-Keep semantics
  • testing: add testing.B.Loop for iteration #61515 (comment) mentioned "we would implicitly apply Keep to every function argument and result in the closure passed directly to Loop."
  • Michael Pratt: We don't want to keep too many or too few things alive unexpectedly.
  • Cherry Mui: Would like to have a mechanism that covers a large portion (80%?) and not keep alive too much. One can always manually keep things alive, but hard to undo.
  • Junyang Shao: Current implementation keeps the result of the last assignment or function call alive.
  • Michael Knyszek: Would it be fine to try something? I don't think it is so critical to get it perfectly right. One can always use b.N loop as a workaround, if they don't like the semantics. I realize there's some pressure to get it right the first time, though. Maybe we could do some ecosystem analysis?
  • Cherry Mui: I'm thinking about doing some analysis, keep everything alive and see if it deoptimizes things unexpectedly.
  • Michael Pratt: Would be nice to get it right when we release the feature. There are also some complexity in matching just the loop body. It may be simpler to keep everything alive in the function. Things outside of the loop are not important.
  • Michael Pratt: We could also apply to b.N loop as well. May cause surprise in people's benchmarks. May slow things down, or fix bugs.
  • Junyang Shao: Austin’s semantics of keep everything alive are pretty straightforward and clear to users.
  • Michael Pratt: In favor of clear semantics.
  • Sounds like we can try keeping all function args and results live and see.
  • Junyang Shao: Can change the implementation to match b.N loop and see if it slows down anything.
• Junyang Shao: Do we plan to add interprocedural SSA passes? There is some issue about propagating discriminators for PGO basic block layout.
  • Keith Randall: We don't have plan for interprocedural SSA for now. We have ideas, like code size for inlining, register clobber sets.
  • David Chase: Is the problem with the PGO basic block CL is that we need to profile twice? One for regular PGO (inlining+devirt) and another round for basic block.
  • Cherry Mui: We should use line number (and perhaps column number) first, and only use discriminators if the line/column numbers are the same.
  • Michael Pratt: Normal PGO workflow (PGO on prod) would work because it is profiling PGO binaries. It is confusing that they get the optimal result on the second run.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-10-29

• FYI
  • Public office hour is scheduled on Nov. 4, 1pm PT/4pm ET
• Michael Pratt: Enable swissmaps by default?
  • Michael Pratt: Plan to submit all CLs today or tomorrow, implementation is solid.
  • Michael Pratt: Sweet geomean is 1-1.5% faster. Some microbenchmarks may be slower, e.g. mapaccess with 9-256 elements. Unclear how this maps to production use case. Very small maps have a special code path. After 256 it gets a lot better.
• 1.24 status
  • range-over-func cgo performance
    • Probably not going to do this for 1.24.
  • Type parameter for type alias
    • Done
  • PGO discriminator support
    • Michael Pratt: We could submit the discriminator support, but less important to evaluating the actual uses.
    • David Chase: Hard to use.
    • Junyang Shao: The propagation of discriminators is lossy.
    • Cherry Mui: Using basic block ID seems not the right approach.
    • Michael Pratt: Some issues for column numbers: multiple blocks have the same column number, like some Values are moved to another block.
    • Keith Randall: Line and column numbers are meant for the debugger, not for optimization. The compiler keeps track and propagate them for the debugger.
    • David Chase: We could use the initial basic block ID when constructing SSA.
  • Struct reordering
    • David Chase: Discussed with Tim King and Ian Lance Taylor, but there are concerns about gating this on module Go version. New plan is to change how we treat anon fields, will do an ecosystem analysis. Vet check not for 1.24.
    • David Chase: I will try a GOEXPERIMENT for Go 1.24.
  • range-over-func general performance
    • David Chase: Some CLs went in that help. Related to closure inlining. Good enough for 1.24. I will keep looking for improvements, but I don't expect to find anything more.
  • Eliminating core types
    • Robert Griesemer: Working on a proposal. I don't expect it to happen for 1.24.
  • runtime.AddCleanup
    • Carlos Amedee: Working local version. Working on Stop. Need to get a CL going.
  • maphash.Comparable
    • Keith Randall: It's done.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-11-05

• GoLab is next week in Florence.
• Swissmaps is enabled by default 🎉
  • Michael Pratt: There will be followup optimizations. Make use of compiler intrinsics.
• 1.24 status (cont.)
  • testing.B.Loop
    • Junyang Shao: Implemented as noinlining in the b.Loop body. https://go.dev/cl/612043
  • PGO discriminators
    • Junyang Shao: Using column number as discriminator seems to work pretty well. Plumbing is easier. Will split out and make it submittable.
  • Diagnostics
  • Flight recorder
    • Michael Knyszek: Updated proposal.
  • GC efficiency: Microarchitectural optimizations

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-11-12

• Unable to integrate with the latest race.syso from LLVM tip #70283
  • Bug in LLVM, fixed in LLVM already.
• Junyang Shao: Update on PGO block layout: simple algorithm improves 0.8% for CockroachDB, 0.2% for others. Gopher-lua is 2% regression.
  • Keith Randall: Is it putting hot blocks together?
  • Junyang Shao: Use edge frequency, put the hot successor next.
• 1.24 issues
  • Please work on them, or bump to the next milestone
• sync/atomic: TestNilDeref flaky failure on windows-386 with runtime fatal error #70288
  • Start failing yesterday, causing frequent trybot failures
  • Michael Knyszek: We haven't touched Windows builders in a year. Given that it seems to die without saying anything, maybe it is bad dereference during a signal?
  • Russ fixed it.

[cherrymui]

These compiler and runtime meeting minutes are a snapshot of what was discussed in an internal Google meeting. Notes on agenda items that address Google specific needs are elided. Any comments on this issue will be removed, and discussion about topics raised should be taken to the appropriate mailing list. Additionally, any feedback or suggestions for additions to the notes should be handled there as well.

2024-11-19

• FYI
  • Go 1.24 freeze is this week (Nov 21 at 11:59 PM Eastern; docs)
  • Likely accepted proposal: testing/synctest: experimental package for testing concurrent code #69687
    • This is adding testing/synctest behind a GOEXPERIMENT
    • Damien has CLs out, Michael +2'd, working on fixing nosplit overflow on OpenBSD
    • Michael Knyszek: Should we prioritize fixing the stack check?
    • Cherry Mui: Yes. Will file an issue about it.
  • Austin landed CLs for go build -json
    • Followup work on the LUCI side to make use of it.
    • Dmitri Shuralyov: Need a small change (#70435). Currently the structured build failure is behind a GODEBUG and not yet enabled on our builders.
• Updated perf dashboard
  • Michael Knyszek: Added geomean to the main page. This is comparing with Go 1.23.
  • Numbers are good, -3% on 16-core amd64, -4% on 88-core amd64, -2% on arm64
  • Michael Pratt: Showing comparison with older Go releases would be good
  • Michael Knyszek: Have limited machine resources.
  • Cherry Mui: Numbers should be composable?
  • Michael Knyszek: Probably fine. We try to not compose numbers after the fact, as machine changes from time to time.
• Junyang Shao: Is it possible to merge PGO block layout?
  • Michael Knyszek: There were some inconsistencies in the CockroachDB metrics reporting. Fixed by now. Looks like your result is using the updated metrics. The inconsistencies are worth looking into, but the numbers are probably still meaningful.
  • Michael Pratt: The other thing we need to take into account is that we need to add column numbers to the binary. It increases the binary size by 8%, 5% in pclntab and 3% in DWARF.
  • Michael Pratt: One idea is to add column numbers only in hot functions. Another idea is to add them only when multiple blocks have the same line.
  • Junyang Shao: DWARF line table is delta encoded, can we do the same thing?
  • Michael Pratt: Pclntab is similar. Also, it may not help much for column numbers.
  • Time feels tight for getting it in for this cycle.
• Carlos Amedee: AddCleanup proposal included deprecating SetFinalizer. Ian Lance Taylor mentioned that there is no 1-1 mapping from SetFinalizer to AddCleanup. So we break up deprecating SetFinalizer to a separate issue, aiming for 1.25.
  • Michael Pratt: Document that we prefer AddCleanup when possible
  • Cherry Mui: Changing finalizer uses in the standard library to Cleanup?
  • Carlos Amedee: Yes. Working on the os package.
  • Michael Knyszek: That would help shake out bugs.
  • Ian Lance Taylor: 42 calls of SetFinalizer in the standard library.
• Tim King: Moving issues on milestones. Some times manually, sometimes by gopherbot.
  • Gopherbot push issues to the next milestone when the final release goes out.
  • Dmitri Shuralyov: Would still be helpful to manually update
• runtime: improve scaling of lock2 #68578 by Rhys
  • Michael Knyszek: For contended mutexes, many threads spin and hammer on it. Another issue is integrating runtime.mutex to mutex profile incorrectly. Rhys fixed it by allowing 1 thread to take ownership and spin on it. Has a high impact on microbenchmarks. Performance neutral for most of our benchmarks. Trust the implementation as Rhys model checked it. Enabled by default, with a GOEXPERIMENT for easily turning off.