Sync portable-simd to remove autosplats

[workingjubilee]

This PR syncs portable-simd in up to rust-lang/portable-simd@a838552 in order to address the type inference breakages documented on nightly in #90904 by removing the vector + scalar binary operations (called "autosplats", "broadcasting", or "rank promotion", depending on who you ask) that allow {scalar} + &'_ {scalar} to fail in some cases, because it becomes possible the programmer may have meant {scalar} + &'_ {vector}.

A few quality-of-life improvements make their way in as well:

• Lane counts can now go to 64, as LLVM seems to have fixed their miscompilation for those.
• {i,u}8x64 to __m512i is now available.
• a bunch of #[must_use] notes appear throughout the module.
• Some implementations, mostly instances of impl core::ops::{Op}<Simd> for Simd that aren't {vector} + {vector} (e.g. {vector} + &'_ {vector}), leverage some generics and where bounds now to make them easier to understand by reducing a dozen implementations into one (and make it possible for people to open the docs on less burly devices).
• And some internal-only improvements.

None of these changes should affect a beta backport, only actual users of core::simd (and most aren't even visible in the programmatic sense), though I can extract an even more minimal changeset for beta if necessary. It seemed simpler to just keep moving forward.

[rust-highfive]

r? @Mark-Simulacrum

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[workingjubilee]

All of the minimized examples documented so far as of 2021-12-02 can be compiled by rustc with these changes to core.

[Mark-Simulacrum]

@bors r+ rollup=never

I'll leave beta-accepted to T-compiler (?) discussion, but I suspect it probably makes sense to just backport this wholesale, or do a targeted backport that cfg's out the submodule entirely -- those two strategies feel like the best options to me at this point.

[bors]

📌 Commit eef4371 has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit eef4371 with merge 11fb21f...

[bors]

☀️ Test successful - checks-actions
Approved by: Mark-Simulacrum
Pushing 11fb21f to master...

[petrochenkov]

I get these errors after this PR (most likely):

   Compiling core v0.0.0 (C:\msys64\home\we\rust\library\core)
error[E0425]: cannot find function `simd_select_bitmask` in module `crate::intrinsics`
   --> library\core\src\..\..\portable-simd\crates\core_simd\src\masks\bitmask.rs:108:32
    |
108 |             crate::intrinsics::simd_select_bitmask(
    |                                ^^^^^^^^^^^^^^^^^^^ not found in `crate::intrinsics`
    |
help: consider importing this function
    |
2   | use crate::simd::intrinsics::simd_select_bitmask;
    |

error[E0425]: cannot find function `simd_bitmask` in module `crate::intrinsics`
   --> library\core\src\..\..\portable-simd\crates\core_simd\src\masks\bitmask.rs:119:42
    |
119 |         unsafe { Self(crate::intrinsics::simd_bitmask(value), PhantomData) }
    |                                          ^^^^^^^^^^^^ not found in `crate::intrinsics`
    |
help: consider importing this function
    |
2   | use crate::simd::intrinsics::simd_bitmask;
    |

For more information about this error, try `rustc --explain E0425`.
error: could not compile `core` due to 2 previous errors

I didn't investigate further yet.

[apiraino]

Discussed today in T-compiler meeting on Zulip.

Beta backport is deferred after investigation of this comment and the best strategy to adopt for backport (as laid out in this comment)

[workingjubilee]

Huh, that's... weird. What were you trying to build? Surely not just std?

[petrochenkov]

@workingjubilee

Huh, that's... weird. What were you trying to build? Surely not just std?

A regular rustc build - ./x.py test --bless src/test/ui --test-args something.
I'm building with incremental = true, so I'd blame that if the error wasn't from name resolution when incremental compilation is not in effect yet.
I'm also using -Ctarget-cpu=native, so some cfg-related issues like #91315 are also possible.

I'll be able to investigate further later today or tomorrow, if it's something incremental then it should go away after just a fresh rebuild.

[workingjubilee]

That explains it. Yes, I think this is triggered by your target having AVX512 and apparently the paths not being quite right on our end, now that I look at it... somehow missed in the million other things I had to adjust or reflag to make them work in the compiler, ugh.

[pnkfelix]

Discussed in T-compiler triage meeting.

1. We believe Sync portable-simd to remove autosplats #91484 is a T-libs issue, not T-compiler one,
2. Nonetheless, we do think some backport is justified here. We as a team recommend just removing the module entirely in a targeted backport.

[m-ou-se]

We as a team recommend just removing the module entirely in a targeted backport.

Discussed it in the libs-api meeting. Backporting either this PR or a complete removal both seems fine. Marked as accepted. The backporter can decide whatever is easiest for them.