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Josh Triplett 1b23b64be4 Add -Z hint-mostly-unused to tell rustc that most of a crate will go unused
This hint allows the compiler to optimize its operation based on this
assumption, in order to compile faster. This is a hint, and does not
guarantee any particular behavior.

This option can substantially speed up compilation if applied to a large
dependency where the majority of the dependency does not get used. This flag
may slow down compilation in other cases.

Currently, this option makes the compiler defer as much code generation as
possible from functions in the crate, until later crates invoke those
functions. Functions that never get invoked will never have code generated for
them. For instance, if a crate provides thousands of functions, but only a few
of them will get called, this flag will result in the compiler only doing code
generation for the called functions. (This uses the same mechanisms as
cross-crate inlining of functions.) This does not affect `extern` functions, or
functions marked as `#[inline(never)]`.

Some performance numbers, based on a crate with many dependencies having
just *one* large dependency set to `-Z hint-mostly-unused` (using
Cargo's `profile-rustflags` option):

A release build went from 4m07s to 2m04s.

A non-release build went from 2m26s to 1m28s.
2025-06-06 19:12:00 -07:00
.github ci: use arm to calculate job matrix 2025-05-30 15:11:30 +02:00
compiler Add -Z hint-mostly-unused to tell rustc that most of a crate will go unused 2025-06-06 19:12:00 -07:00
library Rollup merge of #142091 - thaliaarchi:aix-getenv, r=workingjubilee 2025-06-06 00:58:48 +02:00
LICENSES Synchronize Unicode license text from unicode.org 2024-11-20 00:54:12 -08:00
src Add -Z hint-mostly-unused to tell rustc that most of a crate will go unused 2025-06-06 19:12:00 -07:00
tests Auto merge of #141681 - compiler-errors:fast-path-stalled, r=lcnr 2025-06-06 15:20:21 +00:00
.clang-format Add .clang-format 2024-06-26 05:56:00 +08:00
.editorconfig Don't apply editorconfig to llvm 2025-02-09 16:21:14 -05:00
.git-blame-ignore-revs git: ignore 60600a6fa4 for blame purposes 2025-04-17 11:50:24 +08:00
.gitattributes Mark .pp files as Rust 2025-03-29 12:39:06 +01:00
.gitignore change config.toml to bootstrap.toml for bootstrap module 2025-03-17 12:56:41 +05:30
.gitmodules Lowercase git url for rust-lang/enzyme.git 2025-05-15 21:37:49 +00:00
.ignore change config.toml to bootstrap.toml for bootstrap module 2025-03-17 12:56:41 +05:30
.mailmap tshepang has a new email 2025-06-02 12:13:08 +02:00
bootstrap.example.toml add rust.debug-assertions-tools option 2025-04-29 11:05:06 +02:00
Cargo.lock rustdoc-json-type: Depend on serde and serde_derive seperately 2025-06-03 21:17:33 +00:00
Cargo.toml move test-float-parse tool into src/tools dir 2025-06-03 11:05:51 +03:00
CODE_OF_CONDUCT.md Remove the code of conduct; instead link https://www.rust-lang.org/conduct.html 2019-10-05 22:55:19 +02:00
configure Ensure ./configure works when configure.py path contains spaces 2024-02-16 18:57:22 +00:00
CONTRIBUTING.md Improve CONTRIBUTING.md grammar and clarity 2025-05-23 23:03:06 +02:00
COPYRIGHT dist: Re-work how we describe the licence of Rust in our distributions 2024-12-09 10:18:55 +00:00
INSTALL.md mention about x.py setup in INSTALL.md 2025-04-24 09:15:53 +03:00
LICENSE-APACHE Remove appendix from LICENCE-APACHE 2019-12-30 14:25:53 +00:00
license-metadata.json Update license metadata 2025-02-15 16:48:37 +01:00
LICENSE-MIT dist: Re-work how we describe the licence of Rust in our distributions 2024-12-09 10:18:55 +00:00
README.md Update Rust Foundation links in Readme 2025-03-16 19:03:40 -07:00
RELEASES.md Rollup merge of #140879 - pthariensflame:patch-1, r=pietroalbini 2025-05-10 16:26:04 +02:00
REUSE.toml change config.toml to bootstrap.toml for bootstrap module 2025-03-17 12:56:41 +05:30
rust-bors.toml Increase timeout for new bors try builds 2025-05-30 15:59:14 +02:00
rustfmt.toml Do not run rustfmt on the compiler-builtins subtree 2025-05-18 15:42:35 +00:00
triagebot.toml Rollup merge of #142084 - jdonszelmann:add-review-rotation, r=BoxyUwU 2025-06-06 00:58:48 +02:00
x Look for python3 first on MacOS, not py 2025-02-13 10:24:54 -05:00
x.ps1 use & instead of start-process in x.ps1 2023-12-09 09:46:16 -05:00
x.py Reformat Python code with ruff 2024-12-04 23:03:44 +01:00

This is the main source code repository for Rust. It contains the compiler, standard library, and documentation.

Why Rust?

  • Performance: Fast and memory-efficient, suitable for critical services, embedded devices, and easily integrated with other languages.

  • Reliability: Our rich type system and ownership model ensure memory and thread safety, reducing bugs at compile-time.

  • Productivity: Comprehensive documentation, a compiler committed to providing great diagnostics, and advanced tooling including package manager and build tool (Cargo), auto-formatter (rustfmt), linter (Clippy) and editor support (rust-analyzer).

Quick Start

Read "Installation" from The Book.

Installing from Source

If you really want to install from source (though this is not recommended), see INSTALL.md.

Getting Help

See https://www.rust-lang.org/community for a list of chat platforms and forums.

Contributing

See CONTRIBUTING.md.

License

Rust is primarily distributed under the terms of both the MIT license and the Apache License (Version 2.0), with portions covered by various BSD-like licenses.

See LICENSE-APACHE, LICENSE-MIT, and COPYRIGHT for details.

Trademark

The Rust Foundation owns and protects the Rust and Cargo trademarks and logos (the "Rust Trademarks").

If you want to use these names or brands, please read the Rust language trademark policy.

Third-party logos may be subject to third-party copyrights and trademarks. See Licenses for details.