Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Use niche-filling optimization even when multiple variants have data. #94075

Merged
merged 2 commits into from
Sep 8, 2022

Conversation

mikebenfield
Copy link
Contributor

Fixes #46213

@rust-highfive
Copy link
Collaborator

Some changes occured to the CTFE / Miri engine

cc @rust-lang/miri

@rustbot rustbot added the T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. label Feb 17, 2022
@rust-highfive
Copy link
Collaborator

r? @michaelwoerister

(rust-highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 17, 2022
@mikebenfield
Copy link
Contributor Author

Several static size checks needed the size lowered. I'm unsure how to handle this since they'll fail with a bootstrapped compiler, so I've just commented them out for now.

@rust-log-analyzer

This comment has been minimized.

@rust-log-analyzer

This comment has been minimized.

Copy link
Contributor

@oli-obk oli-obk left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This is amazing! Will review in detail later, but starting a perf run now

compiler/rustc_ast/src/ast.rs Outdated Show resolved Hide resolved
@oli-obk
Copy link
Contributor

oli-obk commented Feb 17, 2022

@bors try @rust-timer queue

@rust-timer
Copy link
Collaborator

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Feb 17, 2022
@bors
Copy link
Contributor

bors commented Feb 17, 2022

⌛ Trying commit 31b86437df15d7b335697d3f971721104335d04e with merge dbc0f1b7dd1014d9c7e56714953a0daf1b4f4c35...

@michaelwoerister
Copy link
Member

r? @eddyb -- reviewing this is out of my league ;)

Before merging something like this, we need to make sure that debuginfo generation handles this correctly (especially the cpp-like encoding). cc @wesleywiser

@rust-log-analyzer

This comment has been minimized.

@RalfJung
Copy link
Member

Wow that's cool. :D

It would probably be good to also have a ui test ensuring specific cases are handled (like some of the examples from the issue). I imagine there would be an existing ui test that can be extended, but I am not sure.

@mikebenfield
Copy link
Contributor Author

I added a simple test case.

not(bootstrap) doesn't seem to do the trick; I still get assertion failures with that.

@mikebenfield
Copy link
Contributor Author

Nevermind; not(bootstrap) works fine.

@rust-log-analyzer

This comment has been minimized.

@@ -0,0 +1,14 @@
fn main() {
cfg!(target_has_atomic_load_store = "8");
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This test case seems to have crept in from another PR...?

@joshtriplett
Copy link
Member

This is incredible work! I've wanted to see this level of niche optimization for a long time. I think this makes niche optimization work more like people often expect it'll work.

celinval added a commit to model-checking/kani that referenced this pull request Oct 3, 2022
Fixes #1615

Relevant changes to rustc:
  - rust-lang/rust#101483: Change to intrinsics.
  - rust-lang/rust#94075: Change to niche opt.
  - rust-lang/rust#101101: Method rename.

Co-authored-by: Adrian Palacios <[email protected]>
nnethercote added a commit to nnethercote/rust that referenced this pull request Oct 17, 2022
This shrinks the size of `Option<Span>` and similar types, which shrinks
several AST and HIR nodes. The most important of these are `hir::Expr`
and `ast::Ty`.

This change was first attempted in rust-lang#93747 where it had little effect.
But the improved niche-filling implemented by rust-lang#94075 means this change
now has a much bigger effect.

Co-authored-by: Camille Gillot <[email protected]>
@jdahlstrom
Copy link

jdahlstrom commented Nov 1, 2022

Hmm, should the following enum be eligible for niche optimization now (courtesy u/gitpy on Reddit)?

enum Data {
    A(f64),
    B(Buf),
}

struct Buf(*const u8, i16);

fn main() {
    println!("{}", std::mem::size_of::<Buf>());  // 16
    println!("{}", std::mem::size_of::<Data>()); // 24 even on nightly
}

@cuviper
Copy link
Member

cuviper commented Nov 1, 2022

Padding is not used as a niche -- it could contain anything, including the value that you would want to indicate the other variant.

@jdahlstrom
Copy link

jdahlstrom commented Nov 1, 2022

@cuviper Ah, right. Amusingly you can now offer the compiler a place that works as a niche, though =)

enum Data {
    A(f64),
    B(Buf),
}
struct Buf(*const u8, i16, bool);
//                       ++++++

println!("{}", std::mem::size_of::<Buf>());  // 16
println!("{}", std::mem::size_of::<Data>()); // 16 on nightly!

@cuviper
Copy link
Member

cuviper commented Nov 1, 2022

Yep! And if you want even more niche, you can use a univariant enum, with a repr to keep it from being a ZST:

#[repr(u8)] // or bigger!
enum Pad { Empty }

wip-sync pushed a commit to NetBSD/pkgsrc-wip that referenced this pull request Nov 27, 2022
Pkgsrc changes:
 * We now manage to build for mipsel-unknown-netbsd, but despite the
   target spec saying cpu = "mips3", the compiler manages to emit 64-bit
   instructions which cause "illegal instruction" error.  Will need more
   work.  The mipsel-unknown-netbsd entry is commentd out since there
   is no 1.64.0 bootstrap.
 * Managed to retain the build of aarch64_be, llvm needed a patch to
   avoid use of neon instructions in the BE case (llvm doesn't support
   use of neon in BE mode).  Ref. patch to
   src/llvm-project/llvm/lib/Support/BLAKE3/blake3_impl.h.
 * The minimum gcc version is now 7.x, and that includes the cross-compiler
   for the targets.  For i386 this also needs to /usr/include/gcc-7 include
   files in the target root, because immintrin.h from gcc 5 is not
   compatible with gcc 7.x.  This applies for the targets where we build
   against a root from netbsd-8 (sparc64, powerpc, i386), and files/gcc-wrap
   gets a hack for this.
 * Pick up tweak for -latomic inclusion from
   rust-lang/rust#104220
   and
   rust-lang/rust#104572
 * Retain ability to do 32-bit NetBSD, by changing from 64 to 32 bit
   types in library/std/src/sys/unix/thread_parker/netbsd.rs.
 * I've struggled a bit to get the "openssl-src" build with -latomic
   where it's needed.  I introduce "NetBSD-generic32" system type and
   use it for the NetBSD mipsel target.  There is another attempt to
   do the same in the patch to vendor/openssl-sys/build/main.rs.
 * Bump bootstraps to 1.64.0, checksum updates.

Upstream changes:

Version 1.65.0 (2022-11-03)
==========================

Language
--------
- [Error on `as` casts of enums with `#[non_exhaustive]` variants]
  (rust-lang/rust#92744)
- [Stabilize `let else`](rust-lang/rust#93628)
- [Stabilize generic associated types (GATs)]
  (rust-lang/rust#96709)
- [Add lints `let_underscore_drop`, `let_underscore_lock`, and
  `let_underscore_must_use` from Clippy]
  (rust-lang/rust#97739)
- [Stabilize `break`ing from arbitrary labeled blocks ("label-break-value")]
  (rust-lang/rust#99332)
- [Uninitialized integers, floats, and raw pointers are now considered
  immediate UB](rust-lang/rust#98919).
  Usage of `MaybeUninit` is the correct way to work with uninitialized
  memory.
- [Stabilize raw-dylib for Windows x86_64, aarch64, and thumbv7a]
  (rust-lang/rust#99916)
- [Do not allow `Drop` impl on foreign ADTs]
  (rust-lang/rust#99576)

Compiler
--------
- [Stabilize -Csplit-debuginfo on Linux]
  (rust-lang/rust#98051)
- [Use niche-filling optimization even when multiple variants have
  data] (rust-lang/rust#94075)
- [Associated type projections are now verified to be well-formed
  prior to resolving the underlying type]
  (rust-lang/rust#99217)
- [Stringify non-shorthand visibility correctly]
  (rust-lang/rust#100350)
- [Normalize struct field types when unsizing]
  (rust-lang/rust#101831)
- [Update to LLVM 15](rust-lang/rust#99464)
- [Fix aarch64 call abi to correctly zeroext when needed]
  (rust-lang/rust#97800)
- [debuginfo: Generalize C++-like encoding for enums]
  (rust-lang/rust#98393)
- [Add `special_module_name` lint]
  (rust-lang/rust#94467)
- [Add support for generating unique profraw files by default when
  using `-C instrument-coverage`]
  (rust-lang/rust#100384)
- [Allow dynamic linking for iOS/tvOS targets]
  (rust-lang/rust#100636)

New targets:
- [Add armv4t-none-eabi as a tier 3 target]
  (rust-lang/rust#100244)
- [Add powerpc64-unknown-openbsd and riscv64-unknown-openbsd as tier 3 targets]
  (rust-lang/rust#101025)
- Refer to Rust's [platform support page][platform-support-doc] for more
  information on Rust's tiered platform support.

Libraries
---------
- [Don't generate `PartialEq::ne` in derive(PartialEq)]
  (rust-lang/rust#98655)
- [Windows RNG: Use `BCRYPT_RNG_ALG_HANDLE` by default]
  (rust-lang/rust#101325)
- [Forbid mixing `System` with direct system allocator calls]
  (rust-lang/rust#101394)
- [Document no support for writing to non-blocking stdio/stderr]
  (rust-lang/rust#101416)
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`](rust-lang/rust#95295)
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.

Stabilized APIs
---------------
- [`std::backtrace::Backtrace`]
  (https://doc.rust-lang.org/stable/std/backtrace/struct.Backtrace.html)
- [`Bound::as_ref`]
  (https://doc.rust-lang.org/stable/std/ops/enum.Bound.html#method.as_ref)
- [`std::io::read_to_string`]
  (https://doc.rust-lang.org/stable/std/io/fn.read_to_string.html)
- [`<*const T>::cast_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_mut)
- [`<*mut T>::cast_const`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_const)

These APIs are now stable in const contexts:
- [`<*const T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)
- [`<*mut T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)

Cargo
-----
- [Apply GitHub fast path even for partial hashes]
  (rust-lang/cargo#10807)
- [Do not add home bin path to PATH if it's already there]
  (rust-lang/cargo#11023)
- [Take priority into account within the pending queue]
  (rust-lang/cargo#11032).
  This slightly optimizes job scheduling by Cargo, with typically
  small improvements on larger crate graph builds.

Compatibility Notes
-------------------
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`] (rust-lang/rust#95295).
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.
- [`PollFn` now only implements `Unpin` if the closure is `Unpin`]
  (rust-lang/rust#102737).
  This is a possible breaking change if users were relying on the
  blanket unpin implementation.  See discussion on the PR for
  details of why this change was made.
- [Drop ExactSizeIterator impl from std::char::EscapeAscii]
  (rust-lang/rust#99880)
  This is a backwards-incompatible change to the standard library's
  surface area, but is unlikely to affect real world usage.
- [Do not consider a single repeated lifetime eligible for elision
  in the return type] (rust-lang/rust#103450)
  This behavior was unintentionally changed in 1.64.0, and this
  release reverts that change by making this an error again.
- [Reenable disabled early syntax gates as future-incompatibility
  lints] (rust-lang/rust#99935)
- [Update the minimum external LLVM to 13]
  (rust-lang/rust#100460)
- [Don't duplicate file descriptors into stdio fds]
  (rust-lang/rust#101426)
- [Sunset RLS](rust-lang/rust#100863)
- [Deny usage of `#![cfg_attr(..., crate_type = ...)]` to set the
  crate type] (rust-lang/rust#99784)
  This strengthens the forward compatibility lint
  deprecated_cfg_attr_crate_type_name to deny.
- [`llvm-has-rust-patches` allows setting the build system to treat
  the LLVM as having Rust-specific patches]
  (rust-lang/rust#101072)
  This option may need to be set for distributions that are building
  Rust with a patched LLVM via `llvm-config`, not the built-in
  LLVM.

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Add `x.sh` and `x.ps1` shell scripts]
  (rust-lang/rust#99992)
- [compiletest: use target cfg instead of hard-coded tables]
  (rust-lang/rust#100260)
- [Use object instead of LLVM for reading bitcode from rlibs]
  (rust-lang/rust#98100)
- [Enable MIR inlining for optimized compilations]
  (rust-lang/rust#91743)
  This provides a 3-10% improvement in compiletimes for real world
  crates. See [perf results]
  (https://perf.rust-lang.org/compare.html?start=aedf78e56b2279cc869962feac5153b6ba7001ed&end=0075bb4fad68e64b6d1be06bf2db366c30bc75e1&stat=instructions:u).
@tjni tjni mentioned this pull request Dec 6, 2022
13 tasks
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jan 23, 2023
Pkgsrc changes:
 * pkglint cleanups, bump bootstrap kits to 1.65.0.
 * New target: mipsel-unknown-netbsd, for cpu=mips32 with soft-float.
 * Managed to retain the build of aarch64_be, llvm needed a patch to
   avoid use of neon instructions in the BE case (llvm doesn't support
   use of neon in BE mode).  Ref. patch to
   src/llvm-project/llvm/lib/Support/BLAKE3/blake3_impl.h.
   Also submitted upstream of LLVM to the BLAKE3 maintainers.
 * The minimum gcc version is now 7.x, and that includes the
   cross-compiler for the targets.  For i386 this also needs to
   /usr/include/gcc-7 include files in the target root, because
   immintrin.h from gcc 5 is not compatible with gcc 7.x.  This
   applies for the targets where we build against a root from netbsd-8
   (sparc64, powerpc, i386), and files/gcc-wrap gets a hack for this.
 * Pick up tweak for -latomic inclusion from
   rust-lang/rust#104220
   and
   rust-lang/rust#104572
 * Retain ability to do 32-bit NetBSD, by changing from 64 to 32 bit
   types in library/std/src/sys/unix/thread_parker/netbsd.rs.
 * I've tried to get the "openssl-src" build with -latomic where it's
   needed.  I've introduced the "NetBSD-generic32" system type and use
   it for the NetBSD mipsel target.  There is another attempt to do
   the same in the patch to vendor/openssl-sys/build/main.rs.


Upstream changes:

Version 1.66.1 (2023-01-10)
===========================

- Added validation of SSH host keys for git URLs in Cargo
  ([CVE-2022-46176](https://www.cve.org/CVERecord?id=CVE-2022-46176))


Version 1.66.0 (2022-12-15)
===========================

Language
--------
- [Permit specifying explicit discriminants on all `repr(Int)`
  enums](rust-lang/rust#95710)
  ```rust
  #[repr(u8)]
  enum Foo {
      A(u8) = 0,
      B(i8) = 1,
      C(bool) = 42,
  }
  ```
- [Allow transmutes between the same type differing only in
  lifetimes](rust-lang/rust#101520)
- [Change constant evaluation errors from a deny-by-default lint to a
  hard error](rust-lang/rust#102091)
- [Trigger `must_use` on `impl Trait` for
  supertraits](rust-lang/rust#102287) This
  makes `impl ExactSizeIterator` respect the existing `#[must_use]`
  annotation on `Iterator`.
- [Allow `..X` and `..=X` in
  patterns](rust-lang/rust#102275)
- [Uplift `clippy::for_loops_over_fallibles` lint into
  rustc](rust-lang/rust#99696)
- [Stabilize `sym` operands in inline
  assembly](rust-lang/rust#103168)
- [Update to Unicode 15](rust-lang/rust#101912)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474) This is a
  soundness fix which may break code that was erroneously relying on this
  behavior.

Compiler
--------
- [Add armv5te-none-eabi and thumbv5te-none-eabi tier 3
  targets](rust-lang/rust#101329)
  - Refer to Rust's [platform support page][platform-support-doc] for
    more information on Rust's tiered platform support.
- [Add support for linking against macOS universal
  libraries](rust-lang/rust#98736)

Libraries
---------
- [Fix `#[derive(Default)]` on a generic `#[default]` enum adding
  unnecessary `Default`
  bounds](rust-lang/rust#101040)
- [Update to Unicode 15](rust-lang/rust#101821)

Stabilized APIs
---------------
- [`proc_macro::Span::source_text`](https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.source_text)
- [`uX::{checked_add_signed, overflowing_add_signed,
  saturating_add_signed,
  wrapping_add_signed}`](https://doc.rust-lang.org/stable/std/primitive.u8.html#method.checked_add_signed)
- [`iX::{checked_add_unsigned, overflowing_add_unsigned,
  saturating_add_unsigned,
  wrapping_add_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_add_unsigned)
- [`iX::{checked_sub_unsigned, overflowing_sub_unsigned,
  saturating_sub_unsigned,
  wrapping_sub_unsigned}`](https://doc.rust-lang.org/stable/std/primitive.i8.html#method.checked_sub_unsigned)
- [`BTreeSet::{first, last, pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeSet.html#method.first)
- [`BTreeMap::{first_key_value, last_key_value, first_entry, last_entry,
  pop_first,
  pop_last}`](https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.first_key_value)
- [Add `AsFd` implementations for stdio lock types on
  WASI.](rust-lang/rust#101768)
- [`impl TryFrom<Vec<T>> for Box<[T;
  N]>`](https://doc.rust-lang.org/stable/std/boxed/struct.Box.html#impl-TryFrom%3CVec%3CT%2C%20Global%3E%3E-for-Box%3C%5BT%3B%20N%5D%2C%20Global%3E)
- [`core::hint::black_box`](https://doc.rust-lang.org/stable/std/hint/fn.black_box.html)
- [`Duration::try_from_secs_{f32,f64}`](https://doc.rust-lang.org/stable/std/time/struct.Duration.html#method.try_from_secs_f32)
- [`Option::unzip`](https://doc.rust-lang.org/stable/std/option/enum.Option.html#method.unzip)
- [`std::os::fd`](https://doc.rust-lang.org/stable/std/os/fd/index.html)

Rustdoc
-------
- [Add Rustdoc warning for invalid HTML tags in the
  documentation](rust-lang/rust#101720)

Cargo
-----
- [Added `cargo remove` to remove dependencies from
  Cargo.toml](https://doc.rust-lang.org/nightly/cargo/commands/cargo-remove.html)
- [`cargo publish` now waits for the new version to be downloadable
  before exiting](rust-lang/cargo#11062)

See [detailed release notes](https://github.com/rust-lang/cargo/blob/master/CHANGELOG.md#cargo-166-2022-12-15) for more.

Compatibility Notes
-------------------
- [Only apply `ProceduralMasquerade` hack to older versions of
  `rental`](rust-lang/rust#94063)
- [Don't export `__heap_base` and `__data_end` on
  wasm32-wasi.](rust-lang/rust#102385)
- [Don't export `__wasm_init_memory` on
  WebAssembly.](rust-lang/rust#102426)
- [Only export `__tls_*` on
  wasm32-unknown-unknown.](rust-lang/rust#102440)
- [Don't link to `libresolv` in libstd on
  Darwin](rust-lang/rust#102766)
- [Update libstd's libc to 0.2.135 (to make `libstd` no longer pull in
  `libiconv.dylib` on
  Darwin)](rust-lang/rust#103277)
- [Opaque types no longer imply lifetime
  bounds](rust-lang/rust#95474)
  This is a soundness fix which may break code that was erroneously
  relying on this behavior.
- [Make `order_dependent_trait_objects` show up in future-breakage
  reports](rust-lang/rust#102635)
- [Change std::process::Command spawning to default to inheriting the
  parent's signal mask](rust-lang/rust#101077)

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they
represent significant improvements to the performance or internals of
rustc and related tools.

- [Enable BOLT for LLVM
  compilation](rust-lang/rust#94381)
- [Enable LTO for
  rustc_driver.so](rust-lang/rust#101403)


Version 1.65.0 (2022-11-03)
==========================

Language
--------
- [Error on `as` casts of enums with `#[non_exhaustive]` variants]
  (rust-lang/rust#92744)
- [Stabilize `let else`](rust-lang/rust#93628)
- [Stabilize generic associated types (GATs)]
  (rust-lang/rust#96709)
- [Add lints `let_underscore_drop`, `let_underscore_lock`, and
  `let_underscore_must_use` from Clippy]
  (rust-lang/rust#97739)
- [Stabilize `break`ing from arbitrary labeled blocks ("label-break-value")]
  (rust-lang/rust#99332)
- [Uninitialized integers, floats, and raw pointers are now considered
  immediate UB](rust-lang/rust#98919).
  Usage of `MaybeUninit` is the correct way to work with uninitialized
  memory.
- [Stabilize raw-dylib for Windows x86_64, aarch64, and thumbv7a]
  (rust-lang/rust#99916)
- [Do not allow `Drop` impl on foreign ADTs]
  (rust-lang/rust#99576)

Compiler
--------
- [Stabilize -Csplit-debuginfo on Linux]
  (rust-lang/rust#98051)
- [Use niche-filling optimization even when multiple variants have
  data] (rust-lang/rust#94075)
- [Associated type projections are now verified to be well-formed
  prior to resolving the underlying type]
  (rust-lang/rust#99217)
- [Stringify non-shorthand visibility correctly]
  (rust-lang/rust#100350)
- [Normalize struct field types when unsizing]
  (rust-lang/rust#101831)
- [Update to LLVM 15](rust-lang/rust#99464)
- [Fix aarch64 call abi to correctly zeroext when needed]
  (rust-lang/rust#97800)
- [debuginfo: Generalize C++-like encoding for enums]
  (rust-lang/rust#98393)
- [Add `special_module_name` lint]
  (rust-lang/rust#94467)
- [Add support for generating unique profraw files by default when
  using `-C instrument-coverage`]
  (rust-lang/rust#100384)
- [Allow dynamic linking for iOS/tvOS targets]
  (rust-lang/rust#100636)

New targets:
- [Add armv4t-none-eabi as a tier 3 target]
  (rust-lang/rust#100244)
- [Add powerpc64-unknown-openbsd and riscv64-unknown-openbsd as tier 3 targets]
  (rust-lang/rust#101025)
- Refer to Rust's [platform support page][platform-support-doc] for more
  information on Rust's tiered platform support.

Libraries
---------
- [Don't generate `PartialEq::ne` in derive(PartialEq)]
  (rust-lang/rust#98655)
- [Windows RNG: Use `BCRYPT_RNG_ALG_HANDLE` by default]
  (rust-lang/rust#101325)
- [Forbid mixing `System` with direct system allocator calls]
  (rust-lang/rust#101394)
- [Document no support for writing to non-blocking stdio/stderr]
  (rust-lang/rust#101416)
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`](rust-lang/rust#95295)
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.

Stabilized APIs
---------------
- [`std::backtrace::Backtrace`]
  (https://doc.rust-lang.org/stable/std/backtrace/struct.Backtrace.html)
- [`Bound::as_ref`]
  (https://doc.rust-lang.org/stable/std/ops/enum.Bound.html#method.as_ref)
- [`std::io::read_to_string`]
  (https://doc.rust-lang.org/stable/std/io/fn.read_to_string.html)
- [`<*const T>::cast_mut`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_mut)
- [`<*mut T>::cast_const`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.cast_const)

These APIs are now stable in const contexts:
- [`<*const T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)
- [`<*mut T>::offset_from`]
  (https://doc.rust-lang.org/stable/std/primitive.pointer.html#method.offset_from)

Cargo
-----
- [Apply GitHub fast path even for partial hashes]
  (rust-lang/cargo#10807)
- [Do not add home bin path to PATH if it's already there]
  (rust-lang/cargo#11023)
- [Take priority into account within the pending queue]
  (rust-lang/cargo#11032).
  This slightly optimizes job scheduling by Cargo, with typically
  small improvements on larger crate graph builds.

Compatibility Notes
-------------------
- [`std::layout::Layout` size must not overflow `isize::MAX` when
  rounded up to `align`] (rust-lang/rust#95295).
  This also changes the safety conditions on
  `Layout::from_size_align_unchecked`.
- [`PollFn` now only implements `Unpin` if the closure is `Unpin`]
  (rust-lang/rust#102737).
  This is a possible breaking change if users were relying on the
  blanket unpin implementation.  See discussion on the PR for
  details of why this change was made.
- [Drop ExactSizeIterator impl from std::char::EscapeAscii]
  (rust-lang/rust#99880)
  This is a backwards-incompatible change to the standard library's
  surface area, but is unlikely to affect real world usage.
- [Do not consider a single repeated lifetime eligible for elision
  in the return type] (rust-lang/rust#103450)
  This behavior was unintentionally changed in 1.64.0, and this
  release reverts that change by making this an error again.
- [Reenable disabled early syntax gates as future-incompatibility
  lints] (rust-lang/rust#99935)
- [Update the minimum external LLVM to 13]
  (rust-lang/rust#100460)
- [Don't duplicate file descriptors into stdio fds]
  (rust-lang/rust#101426)
- [Sunset RLS](rust-lang/rust#100863)
- [Deny usage of `#![cfg_attr(..., crate_type = ...)]` to set the
  crate type] (rust-lang/rust#99784)
  This strengthens the forward compatibility lint
  deprecated_cfg_attr_crate_type_name to deny.
- [`llvm-has-rust-patches` allows setting the build system to treat
  the LLVM as having Rust-specific patches]
  (rust-lang/rust#101072)
  This option may need to be set for distributions that are building
  Rust with a patched LLVM via `llvm-config`, not the built-in
  LLVM.

Internal Changes
----------------

These changes do not affect any public interfaces of Rust, but they represent
significant improvements to the performance or internals of rustc and related
tools.

- [Add `x.sh` and `x.ps1` shell scripts]
  (rust-lang/rust#99992)
- [compiletest: use target cfg instead of hard-coded tables]
  (rust-lang/rust#100260)
- [Use object instead of LLVM for reading bitcode from rlibs]
  (rust-lang/rust#98100)
- [Enable MIR inlining for optimized compilations]
  (rust-lang/rust#91743)
  This provides a 3-10% improvement in compiletimes for real world
  crates. See [perf results]
  (https://perf.rust-lang.org/compare.html?start=aedf78e56b2279cc869962feac5153b6ba7001ed&end=0075bb4fad68e64b6d1be06bf2db366c30bc75e1&stat=instructions:u).
relrelb added a commit to relrelb/ruffle that referenced this pull request Mar 25, 2023
`static_assertions` seems unmaintained, and anyway `assert!()` is
usable in `const` contexts since Rust 1.57.0:
https://blog.rust-lang.org/2021/12/02/Rust-1.57.0.html#panic-in-const-contexts
So simply use the suggested method instead.

Also the `rustversion` dependency is no longer needed because
rust-lang/rust#94075 already landed in stable.
relrelb added a commit to ruffle-rs/ruffle that referenced this pull request Mar 25, 2023
`static_assertions` seems unmaintained, and anyway `assert!()` is
usable in `const` contexts since Rust 1.57.0:
https://blog.rust-lang.org/2021/12/02/Rust-1.57.0.html#panic-in-const-contexts
So simply use the suggested method instead.

Also the `rustversion` dependency is no longer needed because
rust-lang/rust#94075 already landed in stable.
thaliaarchi added a commit to thaliaarchi/nebula2 that referenced this pull request Jun 9, 2023
Niche-filling optimization was improved in rust-lang/rust#94075, which
allows PrefixEntry to use the niche in Vec, but not SmallVec.
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
merged-by-bors This PR was explicitly merged by bors. perf-regression Performance regression. relnotes Marks issues that should be documented in the release notes of the next release. S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
Projects
None yet
Development

Successfully merging this pull request may close these issues.

Optimize enums by niche-filling even when the smaller variants also have data.