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Define UB in float-to-int casts to saturate #71269

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merged 4 commits into from
May 6, 2020

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Mark-Simulacrum
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This closes #10184 by defining the behavior there to saturate infinities and values exceeding the integral range (on the lower or upper end). NaN is sent to zero.

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r? @nikomatsakis

(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 Apr 18, 2020
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Mark-Simulacrum commented Apr 18, 2020

I've also done some research and summarized the state AIUI (though I would be happy for folks to update this comment if there's details I missed):

This was briefly discussed in the last language team meeting, and we agreed that it seems time to write up a comment about the current state and the plan to (finally!) close this soundness hole.

The current state is:

  • The support for the unchecked casts via unsafe methods from floats to integers of all sizes was stabilized during this cycle, and will hit stable June 4th.
  • -Zsaturating-float-casts currently implements the following semantics, quoting from the code:

Semantically, the mathematical value of the input is rounded towards zero to the next mathematical integer, and then the result is clamped into the range of the destination integer type. Positive and negative infinity are mapped to the maximum and minimum value of the destination integer type. NaN is mapped to 0.

We gathered benchmark results as to the performance of the saturating code, and those resulted in the following:

  • Most use cases have essentially no impact
  • Notably, bench_rgb from the image crate has a 22% slowdown;
    • There is a scattering of similar regressions elsewhere.

There has been some commentary throughout this thread that the current routine implemented in the compiler is not as optimized as possible, but AFAICT, exploiting most of the wins requires platform-specific code, likely written in inline assembly due to insufficient support on LLVM's side.

Some background on what other languages do:

  • Julia defines the following functions:
  • Java (look for "narrowing conversion of a floating-point number"):
    • NaN is converted to 0
    • Finite floating point numbers are rounded to integer (toward zero), either i64 or i32, and then truncated into the final type (essentially, in pseudo-Rust syntax, I think this would be f64 as i64 as iN).
    • Infinities are sent to iN::{MIN, MAX}.
    • Floating point values that cannot be represented in a iN are also saturated to iN::{MIN, MAX}.
    • Note that Java does not have unsigned integer primitives.
  • C++ (stripped down presuming Rust supports only IEEE arithmetic, but see the link for full details):
    • if the value can be represented exactly by the target type, it is unchanged
    • if the value can be represented, but cannot be represented exactly, the result is the nearest value. It is unspecified whether FE_INEXACT is raised in this case.
    • if the value cannot be represented, FE_INVALID is raised and the result value is unspecified.
  • WASM
    • Has two opcode sets (for the matrix of {i,u}N by f{32,64})
      • saturating which implement:
        • infinities go to MAX/MIN, NaN goes to 0
      • trapping which trap on the infinities and NaNs.
  • Go (look for "Conversions between numeric types")
    • Truncates toward zero if representable,
    • Non-representable: result is implementation-dependent (I have not tested)
  • C#
    • Checked context:
      • NaN or infinity, throw exception
      • Rounded towards zero
        • If cannot be represented, throw exception
    • Unchecked context:
      • Exceptions are instead unspecified values

Hard to pull out anything completely conclusive from this, seems to be a mix of options. But seems like overall rounding to zero and saturation is the common case. It's also what -Zsaturating-float-casts does today in Rust.

It seems clear that the saturating (and NaN → 0) behavior isn't a bad option, and given that it's at least shared by some other languages and already implemented in Rust, I'm inclined to recommend that it's the behavior we stabilize for Rust itself.

In particular, we would define f{32,64} as {u,i}N to behave as follows, defining the undefined behavior:

  • Round to zero, and representable values cast directly.
  • NaN goes to 0
  • Values beyond the limits of the type are saturated to the "nearest value" (essentially rounding to zero, in some sense) in the integral type, so e.g. f32::INFINITY would go to {u,i}N::MAX.

To my knowledge, there has not been opposition to this definition, beyond perhaps wanting to leave it even more open (e.g. stating that the values are unspecified rather than defined to be these). I think in practice we try to avoid that sort of lack of specificity, and beyond potential for performance wins on some targets for other behavior, there doesn't seem to be much point — in most cases the unchecked cast functions should be sufficient, or we can provide intrinsics in the future which are "fast but less nice."

We know that this behavior is a fairly sizable performance regression for some crates, in which case where possible the recommendation is to switch to the unchecked casts. Obviously, that implies that the code never encounters NaN or otherwise non-representable values, but AFAICT, that's true of the cases we know of.

We can separately work on improving the performance of the saturating casts, but I don't think that would be a blocker for stabilization.

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@Mark-Simulacrum Mark-Simulacrum force-pushed the sat-float-casts branch 2 times, most recently from fbc6d36 to 7db1919 Compare April 19, 2020 00:26
@scottmcm scottmcm added the T-lang Relevant to the language team, which will review and decide on the PR/issue. label Apr 20, 2020
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Please read @Mark-Simulacrum's excellent summary: #71269 (comment)

@rfcbot fcp merge

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rfcbot commented Apr 20, 2020

Team member @scottmcm has proposed to merge this. The next step is review by the rest of the tagged team members:

No concerns currently listed.

Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up!

See this document for info about what commands tagged team members can give me.

@rfcbot rfcbot added proposed-final-comment-period Proposed to merge/close by relevant subteam, see T-<team> label. Will enter FCP once signed off. disposition-merge This issue / PR is in PFCP or FCP with a disposition to merge it. labels Apr 20, 2020
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@rfcbot reviewed

My only concern is timing -- I do want to be sure that we ping the authors of known crates which are affected and/or give them a window of time as needed. I remember we talked about doing this in the meeting.

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@Mark-Simulacrum wrote:

We know that this behavior is a fairly sizable performance regression for some crates, in which case where possible the recommendation is to switch to the unchecked casts.

The unchecked casts being approx_unchecked_to?

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RalfJung commented Apr 20, 2020

@joshtriplett pretty sure, yes. But it has since been renamed to to_int_unchecked.

That method behaves exactly like as casts behave today.

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bors commented Apr 20, 2020

☔ The latest upstream changes (presumably #70729) made this pull request unmergeable. Please resolve the merge conflicts.

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@rfcbot reviewed

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estebank commented Apr 21, 2020

@Mark-Simulacrum could you also change this warning as part of this PR?

err.warn(
"if the rounded value cannot be represented by the target \
integer type, including `Inf` and `NaN`, casting will cause \
undefined behavior \
(see issue #10184 <https://github.com/rust-lang/rust/issues/10184> \
for more information)",
);

@nikomatsakis nikomatsakis added S-waiting-on-team Status: Awaiting decision from the relevant subteam (see the T-<team> label). and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 21, 2020
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Mark-Simulacrum commented Apr 21, 2020

Removed the warning, though it was never emitted (can_cast is always false today).

Unless you want to update it to note the lossy parts of the conversion? Not sure.

@rfcbot rfcbot added the final-comment-period In the final comment period and will be merged soon unless new substantive objections are raised. label Apr 22, 2020
@bors bors merged commit 14d608f into rust-lang:master May 6, 2020
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ehuss commented May 6, 2020

@Mark-Simulacrum (or anyone else), would you be willing to make a PR to the reference to update the documentation for this? I think the relevant section is the "note" here: https://github.com/rust-lang/reference/blob/master/src/expressions/operator-expr.md#semantics

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Yes, I can do so. Thanks for the reminder!

@Mark-Simulacrum Mark-Simulacrum deleted the sat-float-casts branch May 6, 2020 21:06
Mark-Simulacrum added a commit to Mark-Simulacrum/reference that referenced this pull request May 12, 2020
Mark-Simulacrum added a commit to Mark-Simulacrum/reference that referenced this pull request May 13, 2020
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jun 8, 2020
Pkgsrc changes:
 * Remove a couple diffs which are now integrated upstream.
 * Adjust cargo checksums after upstream upgrades.
 * Belatedly bump the curl dependency
 * Unset DESTDIR during the build phase, to work around a mysterious
   build bug deep in the bowels of llvm.
 * Bump nearly all bootstraps to 1.43.1.

Upstream changes:

Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind`, to have zero-cost unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]

Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is less than 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  +-- ammonia v3.0.0
  |   +-- html5ever v0.24.0
  |   |   +-- log v0.4.8
  |   |   |   +-- cfg-if v0.1.9
  |   |   +-- mac v0.1.1
  |   |   +-- markup5ever v0.9.0
  |   |       +-- log v0.4.8 (*)
  |   |       +-- phf v0.7.24
  |   |       |   +-- phf_shared v0.7.24
  |   |       |       +-- siphasher v0.2.3
  |   |       |       +-- unicase v1.4.2
  |   |       |           [build-dependencies]
  |   |       |           +-- version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was
  previously undefined behaviour, you can use the `{f64, f32}::to_int_unchecked`
  methods to continue using the current behaviour which may desirable in rare
  performance sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jun 9, 2020
Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind` to have zero-cost, unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]


Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is at most 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  ├── ammonia v3.0.0
  │   ├── html5ever v0.24.0
  │   │   ├── log v0.4.8
  │   │   │   └── cfg-if v0.1.9
  │   │   ├── mac v0.1.1
  │   │   └── markup5ever v0.9.0
  │   │       ├── log v0.4.8 (*)
  │   │       ├── phf v0.7.24
  │   │       │   └── phf_shared v0.7.24
  │   │       │       ├── siphasher v0.2.3
  │   │       │       └── unicase v1.4.2
  │   │       │           [build-dependencies]
  │   │       │           └── version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point to a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was previously
  undefined behaviour, but you can use the `{f64, f32}::to_int_unchecked` methods to
  continue using the current behaviour, which may be desirable in rare performance
  sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Jul 6, 2020
Pkgsrc changes:
 * Remove the clutter caused by the cross-compile setup from Makefile
   (Now consigned to my own private cross.mk file.)
 * Remove a couple of patches which are now integrated upstream.
 * Minor adjustments to a couple of other patches.
 * Adjust cargo checksums after upstream upgrades.
 * Belatedly bump the curl dependency
 * If doing a "dist" build, unset DESTDIR during the build phase,
   to work around a mysterious build bug deep in the bowels of llvm,
   causing llvm tools to be installed to a directory unexpecetd by
   the rest of the rust build, ref.
   rust-lang/rust#73132
   A "dist" build is not expected to be followed by an "install".
 * Bump nearly all bootstraps to 1.43.1; NetBSD earmv7hf bootstrap
   bumped to 1.44.0, as that one now finally builds and works.

Upstream changes:

Version 1.44.0 (2020-06-04)
==========================

Language
--------
- [You can now use `async/.await` with `#[no_std]` enabled.][69033]
- [Added the `unused_braces` lint.][70081]

**Syntax-only changes**

- [Expansion-driven outline module parsing][69838]
```rust
#[cfg(FALSE)]
mod foo {
    mod bar {
        mod baz; // `foo/bar/baz.rs` doesn't exist, but no error!
    }
}
```

These are still rejected semantically, so you will likely receive an error but
these changes can be seen and parsed by macros and conditional compilation.

Compiler
--------
- [Rustc now respects the `-C codegen-units` flag in incremental mode.][70156]
  Additionally when in incremental mode rustc defaults to 256 codegen units.
- [Refactored `catch_unwind`, to have zero-cost unless unwinding is enabled and
  a panic is thrown.][67502]
- [Added tier 3\* support for the `aarch64-unknown-none` and
  `aarch64-unknown-none-softfloat` targets.][68334]
- [Added tier 3 support for `arm64-apple-tvos` and
  `x86_64-apple-tvos` targets.][68191]

Libraries
---------
- [Special cased `vec![]` to map directly to `Vec::new()`.][70632] This allows
  `vec![]` to be able to be used in `const` contexts.
- [`convert::Infallible` now implements `Hash`.][70281]
- [`OsString` now implements `DerefMut` and `IndexMut` returning
  a `&mut OsStr`.][70048]
- [Unicode 13 is now supported.][69929]
- [`String` now implements `From<&mut str>`.][69661]
- [`IoSlice` now implements `Copy`.][69403]
- [`Vec<T>` now implements `From<[T; N]>`.][68692] Where `N` is less than 32.
- [`proc_macro::LexError` now implements `fmt::Display` and `Error`.][68899]
- [`from_le_bytes`, `to_le_bytes`, `from_be_bytes`, `to_be_bytes`,
  `from_ne_bytes`, and `to_ne_bytes` methods are now `const` for all
  integer types.][69373]

Stabilized APIs
---------------
- [`PathBuf::with_capacity`]
- [`PathBuf::capacity`]
- [`PathBuf::clear`]
- [`PathBuf::reserve`]
- [`PathBuf::reserve_exact`]
- [`PathBuf::shrink_to_fit`]
- [`f32::to_int_unchecked`]
- [`f64::to_int_unchecked`]
- [`Layout::align_to`]
- [`Layout::pad_to_align`]
- [`Layout::array`]
- [`Layout::extend`]

Cargo
-----
- [Added the `cargo tree` command which will print a tree graph of
  your dependencies.][cargo/8062] E.g.
  ```
    mdbook v0.3.2 (/Users/src/rust/mdbook)
  +-- ammonia v3.0.0
  |   +-- html5ever v0.24.0
  |   |   +-- log v0.4.8
  |   |   |   +-- cfg-if v0.1.9
  |   |   +-- mac v0.1.1
  |   |   +-- markup5ever v0.9.0
  |   |       +-- log v0.4.8 (*)
  |   |       +-- phf v0.7.24
  |   |       |   +-- phf_shared v0.7.24
  |   |       |       +-- siphasher v0.2.3
  |   |       |       +-- unicase v1.4.2
  |   |       |           [build-dependencies]
  |   |       |           +-- version_check v0.1.5
  ...
  ```
  You can also display dependencies on multiple versions of the same crate with
  `cargo tree -d` (short for `cargo tree --duplicates`).

Misc
----
- [Rustdoc now allows you to specify `--crate-version` to have rustdoc include
  the version in the sidebar.][69494]

Compatibility Notes
-------------------
- [Rustc now correctly generates static libraries on Windows GNU targets with
  the `.a` extension, rather than the previous `.lib`.][70937]
- [Removed the `-C no_integrated_as` flag from rustc.][70345]
- [The `file_name` property in JSON output of macro errors now points the actual
  source file rather than the previous format of `<NAME macros>`.][70969]
  **Note:** this may not point a file that actually exists on the user's system.
- [The minimum required external LLVM version has been bumped to LLVM 8.][71147]
- [`mem::{zeroed, uninitialised}` will now panic when used with types that do
  not allow zero initialization such as `NonZeroU8`.][66059] This was
  previously a warning.
- [In 1.45.0 (the next release) converting a `f64` to `u32` using the `as`
  operator has been defined as a saturating operation.][71269] This was
  previously undefined behaviour, you can use the `{f64, f32}::to_int_unchecked`
  methods to continue using the current behaviour which may desirable in rare
  performance sensitive situations.

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of rustc and
related tools.

- [dep_graph Avoid allocating a set on when the number reads are small.][69778]
- [Replace big JS dict with JSON parsing.][71250]

[69373]: rust-lang/rust#69373
[66059]: rust-lang/rust#66059
[68191]: rust-lang/rust#68191
[68899]: rust-lang/rust#68899
[71147]: rust-lang/rust#71147
[71250]: rust-lang/rust#71250
[70937]: rust-lang/rust#70937
[70969]: rust-lang/rust#70969
[70632]: rust-lang/rust#70632
[70281]: rust-lang/rust#70281
[70345]: rust-lang/rust#70345
[70048]: rust-lang/rust#70048
[70081]: rust-lang/rust#70081
[70156]: rust-lang/rust#70156
[71269]: rust-lang/rust#71269
[69838]: rust-lang/rust#69838
[69929]: rust-lang/rust#69929
[69661]: rust-lang/rust#69661
[69778]: rust-lang/rust#69778
[69494]: rust-lang/rust#69494
[69403]: rust-lang/rust#69403
[69033]: rust-lang/rust#69033
[68692]: rust-lang/rust#68692
[68334]: rust-lang/rust#68334
[67502]: rust-lang/rust#67502
[cargo/8062]: rust-lang/cargo#8062
[`PathBuf::with_capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.with_capacity
[`PathBuf::capacity`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.capacity
[`PathBuf::clear`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.clear
[`PathBuf::reserve`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve
[`PathBuf::reserve_exact`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.reserve_exact
[`PathBuf::shrink_to_fit`]: https://doc.rust-lang.org/std/path/struct.PathBuf.html#method.shrink_to_fit
[`f32::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f32.html#method.to_int_unchecked
[`f64::to_int_unchecked`]: https://doc.rust-lang.org/std/primitive.f64.html#method.to_int_unchecked
[`Layout::align_to`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.align_to
[`Layout::pad_to_align`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.pad_to_align
[`Layout::array`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.array
[`Layout::extend`]: https://doc.rust-lang.org/std/alloc/struct.Layout.html#method.extend
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request Aug 6, 2020
While here clean up all pkglint warnings.  Changes since 1.44.1:

Version 1.45.2 (2020-08-03)
==========================

* [Fix bindings in tuple struct patterns][74954]
* [Fix track_caller integration with trait objects][74784]

[74954]: rust-lang/rust#74954
[74784]: rust-lang/rust#74784

Version 1.45.1 (2020-07-30)
==========================

* [Fix const propagation with references.][73613]
* [rustfmt accepts rustfmt_skip in cfg_attr again.][73078]
* [Avoid spurious implicit region bound.][74509]
* [Install clippy on x.py install][74457]

[73613]: rust-lang/rust#73613
[73078]: rust-lang/rust#73078
[74509]: rust-lang/rust#74509
[74457]: rust-lang/rust#74457

Version 1.45.0 (2020-07-16)
==========================

Language
--------
- [Out of range float to int conversions using `as` has been defined as a saturating
  conversion.][71269] This was previously undefined behaviour, but you can use the
   `{f64, f32}::to_int_unchecked` methods to continue using the current behaviour, which
   may be desirable in rare performance sensitive situations.
- [`mem::Discriminant<T>` now uses `T`'s discriminant type instead of always
  using `u64`.][70705]
- [Function like procedural macros can now be used in expression, pattern, and  statement
  positions.][68717] This means you can now use a function-like procedural macro
  anywhere you can use a declarative (`macro_rules!`) macro.

Compiler
--------
- [You can now override individual target features through the `target-feature`
  flag.][72094] E.g. `-C target-feature=+avx2 -C target-feature=+fma` is now
  equivalent to `-C target-feature=+avx2,+fma`.
- [Added the `force-unwind-tables` flag.][69984] This option allows
  rustc to always generate unwind tables regardless of panic strategy.
- [Added the `embed-bitcode` flag.][71716] This codegen flag allows rustc
  to include LLVM bitcode into generated `rlib`s (this is on by default).
- [Added the `tiny` value to the `code-model` codegen flag.][72397]
- [Added tier 3 support\* for the `mipsel-sony-psp` target.][72062]
- [Added tier 3 support for the `thumbv7a-uwp-windows-msvc` target.][72133]

\* Refer to Rust's [platform support page][forge-platform-support] for more
information on Rust's tiered platform support.


Libraries
---------
- [`net::{SocketAddr, SocketAddrV4, SocketAddrV6}` now implements `PartialOrd`
  and `Ord`.][72239]
- [`proc_macro::TokenStream` now implements `Default`.][72234]
- [You can now use `char` with
  `ops::{Range, RangeFrom, RangeFull, RangeInclusive, RangeTo}` to iterate over
  a range of codepoints.][72413] E.g.
  you can now write the following;
  ```rust
  for ch in 'a'..='z' {
      print!("{}", ch);
  }
  println!();
  // Prints "abcdefghijklmnopqrstuvwxyz"
  ```
- [`OsString` now implements `FromStr`.][71662]
- [The `saturating_neg` method as been added to all signed integer primitive
  types, and the `saturating_abs` method has been added for all integer
  primitive types.][71886]
- [`Arc<T>`, `Rc<T>` now implement  `From<Cow<'_, T>>`, and `Box` now
  implements `From<Cow>` when `T` is `[T: Copy]`, `str`, `CStr`, `OsStr`,
  or `Path`.][71447]
- [`Box<[T]>` now implements `From<[T; N]>`.][71095]
- [`BitOr` and `BitOrAssign` are implemented for all `NonZero`
  integer types.][69813]
- [The `fetch_min`, and `fetch_max` methods have been added to all atomic
  integer types.][72324]
- [The `fetch_update` method has been added to all atomic integer types.][71843]

Stabilized APIs
---------------
- [`Arc::as_ptr`]
- [`BTreeMap::remove_entry`]
- [`Rc::as_ptr`]
- [`rc::Weak::as_ptr`]
- [`rc::Weak::from_raw`]
- [`rc::Weak::into_raw`]
- [`str::strip_prefix`]
- [`str::strip_suffix`]
- [`sync::Weak::as_ptr`]
- [`sync::Weak::from_raw`]
- [`sync::Weak::into_raw`]
- [`char::UNICODE_VERSION`]
- [`Span::resolved_at`]
- [`Span::located_at`]
- [`Span::mixed_site`]
- [`unix::process::CommandExt::arg0`]

Cargo
-----

Misc
----
- [Rustdoc now supports strikethrough text in Markdown.][71928] E.g.
  `~~outdated information~~` becomes "~~outdated information~~".
- [Added an emoji to Rustdoc's deprecated API message.][72014]

Compatibility Notes
-------------------
- [Trying to self initialize a static value (that is creating a value using
  itself) is unsound and now causes a compile error.][71140]
- [`{f32, f64}::powi` now returns a slightly different value on Windows.][73420]
  This is due to changes in LLVM's intrinsics which `{f32, f64}::powi` uses.
- [Rustdoc's CLI's extra error exit codes have been removed.][71900] These were
  previously undocumented and not intended for public use. Rustdoc still provides
  a non-zero exit code on errors.

Internals Only
--------------
- [Make clippy a git subtree instead of a git submodule][70655]
- [Unify the undo log of all snapshot types][69464]

[73420]: rust-lang/rust#73420
[72324]: rust-lang/rust#72324
[71843]: rust-lang/rust#71843
[71886]: rust-lang/rust#71886
[72234]: rust-lang/rust#72234
[72239]: rust-lang/rust#72239
[72397]: rust-lang/rust#72397
[72413]: rust-lang/rust#72413
[72014]: rust-lang/rust#72014
[72062]: rust-lang/rust#72062
[72094]: rust-lang/rust#72094
[72133]: rust-lang/rust#72133
[71900]: rust-lang/rust#71900
[71928]: rust-lang/rust#71928
[71662]: rust-lang/rust#71662
[71716]: rust-lang/rust#71716
[71447]: rust-lang/rust#71447
[71269]: rust-lang/rust#71269
[71095]: rust-lang/rust#71095
[71140]: rust-lang/rust#71140
[70655]: rust-lang/rust#70655
[70705]: rust-lang/rust#70705
[69984]: rust-lang/rust#69984
[69813]: rust-lang/rust#69813
[69464]: rust-lang/rust#69464
[68717]: rust-lang/rust#68717
[`Arc::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.as_ptr
[`BTreeMap::remove_entry`]: https://doc.rust-lang.org/stable/std/collections/struct.BTreeMap.html#method.remove_entry
[`Rc::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Rc.html#method.as_ptr
[`rc::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.as_ptr
[`rc::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.from_raw
[`rc::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/rc/struct.Weak.html#method.into_raw
[`sync::Weak::as_ptr`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.as_ptr
[`sync::Weak::from_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.from_raw
[`sync::Weak::into_raw`]: https://doc.rust-lang.org/stable/std/sync/struct.Weak.html#method.into_raw
[`str::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_prefix
[`str::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.str.html#method.strip_suffix
[`char::UNICODE_VERSION`]: https://doc.rust-lang.org/stable/std/char/constant.UNICODE_VERSION.html
[`Span::resolved_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.resolved_at
[`Span::located_at`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.located_at
[`Span::mixed_site`]: https://doc.rust-lang.org/stable/proc_macro/struct.Span.html#method.mixed_site
[`unix::process::CommandExt::arg0`]: https://doc.rust-lang.org/std/os/unix/process/trait.CommandExt.html#tymethod.arg0
Havvy pushed a commit to Havvy/reference that referenced this pull request Aug 25, 2020
mlodato517 pushed a commit to deepgram-devs/bevy-deepgram that referenced this pull request May 6, 2022
**This Commit**
Just fixes two small `clippy` lints.

**Note**
When handling one of the `clippy` lints (unnecessary `return`) I took a
look at `f32_to_i16` and it looked to me like this was doing a
saturating cast. If that's the case then, after [doing some
research][0], it looks like `as` [already does saturating casts][1]!

[0]: rust-lang/rust#71269
[1]: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=1348ce2173e812ff4199446a4fed5a99
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floating point to integer casts can cause undefined behaviour