itsscb/rust
1
0
Fork 0
mirror of https://github.com/rust-lang/rust.git synced 2025-10-06 04:06:31 +00:00
Code Issues Packages Projects Releases Wiki Activity
rust/library/stdarch/crates/std_detect
History
Alex Crichton 770964adac
Update and revamp wasm32 SIMD intrinsics (#874) 
Lots of time and lots of things have happened since the simd128 support
was first added to this crate. Things are starting to settle down now so
this commit syncs the Rust intrinsic definitions with the current
specification (https://github.com/WebAssembly/simd). Unfortuantely not
everything can be enabled just yet but everything is in the pipeline for
getting enabled soon.

This commit also applies a major revamp to how intrinsics are tested.
The intention is that the setup should be much more lightweight and/or
easy to work with after this commit.

At a high-level, the changes here are:

* Testing with node.js and `#[wasm_bindgen]` has been removed. Instead
  intrinsics are tested with Wasmtime which has a nearly complete
  implementation of the SIMD spec (and soon fully complete!)

* Testing is switched to `wasm32-wasi` to make idiomatic Rust bits a bit
  easier to work with (e.g. `panic!)`

* Testing of this crate's simd128 feature for wasm is re-enabled. This
  will run on CI and both compile and execute intrinsics. This should
  bring wasm intrinsics to the same level of parity as x86 intrinsics,
  for example.

* New wasm intrinsics have been added:
  * `iNNxMM_loadAxA_{s,u}`
  * `vNNxMM_load_splat`
  * `v8x16_swizzle`
  * `v128_andnot`
  * `iNNxMM_abs`
  * `iNNxMM_narrow_*_{u,s}`
  * `iNNxMM_bitmask` - commented out until LLVM is updated to LLVM 11
  * `iNNxMM_widen_*_{u,s}` - commented out until
    bytecodealliance/wasmtime#1994 lands
  * `iNNxMM_{max,min}_{u,s}`
  * `iNNxMM_avgr_u`

* Some wasm intrinsics have been removed:
  * `i64x2_trunc_*`
  * `f64x2_convert_*`
  * `i8x16_mul`

* The `v8x16.shuffle` instruction is exposed. This is done through a
  `macro` (not `macro_rules!`, but `macro`). This is intended to be
  somewhat experimental and unstable until we decide otherwise. This
  instruction has 16 immediate-mode expressions and is as a result
  unsuited to the existing `constify_*` logic of this crate. I'm hoping
  that we can game out over time what a macro might look like and/or
  look for better solutions. For now, though, what's implemented is the
  first of its kind in this crate (an architecture-specific macro), so
  some extra scrutiny looking at it would be appreciated.

* Lots of `assert_instr` annotations have been fixed for wasm.

* All wasm simd128 tests are uncommented and passing now.

This is still missing tests for new intrinsics and it's also missing
tests for various corner cases. I hope to get to those later as the
upstream spec itself gets closer to stabilization.

In the meantime, however, I went ahead and updated the `hex.rs` example
with a wasm implementation using intrinsics. With it I got some very
impressive speedups using Wasmtime:

    test benches::large_default  ... bench:     213,961 ns/iter (+/- 5,108) = 4900 MB/s
    test benches::large_fallback ... bench:   3,108,434 ns/iter (+/- 75,730) = 337 MB/s
    test benches::small_default  ... bench:          52 ns/iter (+/- 0) = 2250 MB/s
    test benches::small_fallback ... bench:         358 ns/iter (+/- 0) = 326 MB/s

or otherwise using Wasmtime hex encoding using SIMD is 15x faster on 1MB
chunks or 7x faster on small <128byte chunks.

All of these intrinsics are still unstable and will continue to be so
presumably until the simd proposal in wasm itself progresses to a later
stage. Additionaly we'll still want to sync with clang on intrinsic
names (or decide not to) at some point in the future.

* wasm: Unconditionally expose SIMD functions

This commit unconditionally exposes SIMD functions from the `wasm32`
module. This is done in such a way that the standard library does not
need to be recompiled to access SIMD intrinsics and use them. This,
hopefully, is the long-term story for SIMD in WebAssembly in Rust.

It's unlikely that all WebAssembly runtimes will end up implementing
SIMD so the standard library is unlikely to use SIMD any time soon, but
we want to make sure it's easily available to folks! This commit enables
all this by ensuring that SIMD is available to the standard library,
regardless of compilation flags.

This'll come with the same caveats as x86 support, where it doesn't make
sense to call these functions unless you're enabling simd support one
way or another locally. Additionally, as with x86, if you don't call
these functions then the instructions won't show up in your binary.

While I was here I went ahead and expanded the WebAssembly-specific
documentation for the wasm32 module as well, ensuring that the current
state of SIMD/Atomics are documented.
2020-07-18 13:32:52 +01:00
..
src
Update and revamp wasm32 SIMD intrinsics (#874)
2020-07-18 13:32:52 +01:00
tests
Implementation for Aarch64 TME intrinsics
2020-05-29 19:05:48 +01:00
Cargo.toml
Remove need for #[macro_use] with cfg-if
2019-10-10 12:43:27 +02:00
LICENSE-APACHE
Readme from std_detect
2019-01-22 18:49:24 +01:00
LICENSE-MIT
Readme from std_detect
2019-01-22 18:49:24 +01:00
README.md
Remove azure pipelines badges
2019-10-10 12:42:41 +02:00

README.md

std::detect - Rust's standard library run-time CPU feature detection

std_detect_crate_badge std_detect_docs_badge

The private std::detect module implements run-time feature detection in Rust's standard library. This allows detecting whether the CPU the binary runs on supports certain features, like SIMD instructions.

Usage

std::detect APIs are available as part of libstd. Prefer using it via the standard library than through this crate. Unstable features of std::detect are available on nightly Rust behind the feature(stdsimd) feature-gate.

If you need run-time feature detection in #[no_std] environments, Rust core library cannot help you. By design, Rust core is platform independent, but performing run-time feature detection requires a certain level of cooperation from the platform.

You can then manually include std_detect as a dependency to get similar run-time feature detection support than the one offered by Rust's standard library. We intend to make std_detect more flexible and configurable in this regard to better serve the needs of #[no_std] targets.

Features

  • std_detect_dlsym_getauxval (enabled by default, requires libc): Enable to use libc::dlsym to query whether getauxval is linked into the binary. When this is not the case, this feature allows other fallback methods to perform run-time feature detection. When this feature is disabled, std_detect assumes that getauxval is linked to the binary. If that is not the case the behavior is undefined.

  • std_detect_file_io (enabled by default, requires std): Enable to perform run-time feature detection using file APIs (e.g. /proc/cpuinfo, etc.) if other more performant methods fail. This feature requires libstd as a dependency, preventing the crate from working on applications in which std is not available.

Platform support

  • All x86/x86_64 targets are supported on all platforms by querying the cpuid instruction directly for the features supported by the hardware and the operating system. std_detect assumes that the binary is an user-space application. If you need raw support for querying cpuid, consider using the cupid crate.

  • Linux:

    • arm{32, 64}, mips{32,64}{,el}, powerpc{32,64}{,le}: std_detect supports these on Linux by querying ELF auxiliary vectors (using getauxval when available), and if that fails, by querying /proc/cpuinfo.
    • arm64: partial support for doing run-time feature detection by directly querying mrs is implemented for Linux >= 4.11, but not enabled by default.

  • FreeBSD:

    • arm64: run-time feature detection is implemented by directly querying mrs.

License

This project is licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in std_detect by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.