On 3/9/23 3:42 PM, Deepti Gandluri wrote:
Quick note that I realized my title was accidentally cropped, it
should be:
"Intent to Implement and Ship: WebAssembly Relaxed SIMD".
On Wed, Mar 8, 2023 at 4:11 PM Deepti Gandluri <[email protected]>
wrote:
Contact emails
[email protected], [email protected], [email protected]
Explainer
https://github.com/WebAssembly/relaxed-simd/blob/main/proposals/relaxed-simd/Overview.md
Specification
https://github.com/WebAssembly/relaxed-simd/tree/main/document
Summary
Relaxed SIMD extends the existing SIMD proposal to
introduce vector instructions that relax the strict
determinism constraints of portable SIMD to take better
advantage of the underlying hardware. The operations
introduced in this proposal take advantage of widely
available instruction sets to accelerate compute workloads.
Blink component
Blink>JavaScript>WebAssembly
<https://bugs.chromium.org/p/chromium/issues/list?q=component:Blink%3EJavaScript%3EWebAssembly>
TAG review
Not required as per:
https://v8.dev/docs/feature-launch-process. This
introduces an additional set of vector operations to
WebAssembly, and makes no API changes.
Risks
Interoperability and Compatibility
/Gecko/: In development, enabled in nightly
/WebKit/: No signal as per request for position:
mail-archive.com/[email protected]/msg30574.html
<http://mail-archive.com/[email protected]/msg30574.html>
This should be updated to neutral, with concerns around potential compat
issues (it was manually moved to the new standards-position repo:
https://github.com/WebKit/standards-positions/issues/4#issuecomment-1170364495).
/Web developers/: Strongly positive, Proposal in Phase 3
in the WebAssembly CG the proposal was incubated to
address some of the developer/user requests from the
previous SIMD proposal.
/Other signals/: Proposal voted to a provisional phase 4
as per meeting notes in the February 14th CG meeting
(notes:
https://github.com/WebAssembly/meetings/blob/main/main/2023/CG-02-14.md).
The feature has consensus in the CG, but the vote is
provisional till the formal spec is up to date (Tracking
issue:
https://github.com/WebAssembly/relaxed-simd/issues/134,
PRs also in flight).
WebView application risks
Does this intent deprecate or change behavior of existing
APIs, such that it has potentially high risk for Android
WebView-based applications? No
Debuggability
Supported instructions are enabled in Liftoff, and are
visible to DevTools for debuggability.
Will this feature be supported on all six Blink platforms
(Windows, Mac, Linux, Chrome OS, Android, and Android
WebView)?
Yes
Is this feature fully tested by web-platform-tests
<https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md>?
Not applicable, tested by WebAssembly spec tests
Flag name
V8: --wasm-relaxed-simd
Chrome: Features::kWebAssemblyRelaxedSimd
Requires code in //chrome?
False
Tracking bug
https://bugs.chromium.org/p/v8/issues/detail?id=12284
Estimated milestones
114
Anticipated spec changes
No anticipated spec changes, but some potential for compat
issues based on hardware, more details in this Entropy.md
<https://github.com/WebAssembly/relaxed-simd/blob/main/proposals/relaxed-simd/Entropy.md>,
and the linked issues.
Thanks for the Entropy.md doc - it's incredibly helpful.
For most of the exposed entropy, we already expose this via the
User-Agent string, or the Arch UA Client Hint. Can you say more about
"Differences between hardware that has native FMA support, and hardware
that does not." and "whether the Dot product extension is supported in
the most optimal codegen" - any idea what the distributions would look
there there?
As to compat, "code compiled for one browser works differently on a
different browser" - this sounds a little bit scary! Do we have any
ideas on how to minimize (I assume preventing isn't a reality) this outcome?
Link to entry on the Chrome Platform Status
https://chromestatus.com/feature/5082417973952512
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