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Stuart Cook b618119fa9
Rollup merge of #145974 - pmur:murp/stabilize-zno-jump-tables, r=wesleywiser 
Stabilize -Zno-jump-tables into -Cjump-tables=bool

I propose stabilizing the -Zno-jump-tables option into -Cjump-tables=<bool>.

# `-Zno-jump-tables` stabilization report
## What is the RFC for this feature and what changes have occurred to the user-facing design since the RFC was finalized?
No RFC was created for this option. This was a narrowly scoped option introduced in rust-lang/rust#105812 to support code generation requirements of the x86-64 linux kernel, and eventually other targets as Rust For Linux grows.

The tracking is rust-lang/rust#116592.

##  What behavior are we committing to that has been controversial? Summarize the major arguments pro/con.

The behavior of this flag is well defined, and mimics the existing `-fno-jump-tables` option currently available with LLVM and GCC with some caveats:

* Unlike clang or gcc, this option may be ignored by the code generation backend. Rust can support multiple code-generation backends. For stabilization, only the LLVM backend honors this option.
* The usage of this option will not guarantee a library or binary is free of jump tables. To ensure a jump-table free binary, all crates in the build graph must be compiled with this option. This includes implicitly linked crates such as std or core.
* This option only enforces the crate being compiled is free of jump tables.
* No verification is done to ensure other crates are compiled with this option. Enforcing code generation options are applied across the crate graph is out of scope for this option.

What should the flag name be?
* As introduced, this option was named `-Zno-jump-tables`. However, other major toolchains allow both positive and negative variants of this option to toggle this feature. Renaming the option to `-Cjump-tables=<bool>` makes this option consistent, and if for some reason, expandable to other arguments in the future. Notably, many LLVM targets have a configurable and different thresholds for when to lower into a jump table.

## Are there extensions to this feature that remain unstable? How do we know that we are not accidentally committing to those.
No. This option is used exclusively to gate a very specific class of optimization.

## Summarize the major parts of the implementation and provide links into the code (or to PRs)
* The original PR rust-lang/rust#105812 by ```@ojeda```
* The stabilized CLI option is parsed as a bool:
68bfda9025/compiler/rustc_session/src/options.rs (L2025-L2026)
* This options adds an attribute to each llvm function via:
68bfda9025/compiler/rustc_codegen_llvm/src/attributes.rs (L210-L215)
* Finally, the rustc book is updated with the new option:
68bfda9025/src/doc/rustc/src/codegen-options/index.md (L212-L223)

## Has a call-for-testing period been conducted? If so, what feedback was received?
No. The option has originally created is being used by Rust For Linux to build the x86-64 kernel without issue.

## What outstanding bugs in the issue tracker involve this feature? Are they stabilization-blocking?
There are no outstanding issues.

## Summarize contributors to the feature by name for recognition and assuredness that people involved in the feature agree with stabilization

* ```@ojeda``` implemented this feature in rust-lang/rust#105815 as  `-Zno-jump-tables`.
* ```@tgross35``` created and maintained the tracking issue rust-lang/rust#116592, and provided feedback about the naming of the cli option.

## What FIXMEs are still in the code for that feature and why is it ok to leave them there?
There are none.

## What static checks are done that are needed to prevent undefined behavior?
This option cannot cause undefined behavior. It is a boolean option with well defined behavior in both cases.

## In what way does this feature interact with the reference/specification, and are those edits prepared?
This adds a new cli option to `rustc`. The documentation is updated, and the unstable documentation cleaned up in this PR.

## Does this feature introduce new expressions and can they produce temporaries? What are the lifetimes of those temporaries?
No.

## What other unstable features may be exposed by this feature?
None.

## What is tooling support like for this feature, w.r.t rustdoc, clippy, rust-analzyer, rustfmt, etc.?
No support is required from other rust tooling.

## Open Items

- [x] Are there objections renaming `-Zno-jump-tables` to `-Cjump-tables=<bool>`? The consensus is no.
- [x] Is it desirable to keep `-Zno-jump-tables` for a period of time? The consensus is no.

---

Closes rust-lang/rust#116592
2025-11-04 13:44:48 +11:00
.github Generalize branch references to HEAD 2025-11-02 11:15:55 +01:00
compiler Rollup merge of #145974 - pmur:murp/stabilize-zno-jump-tables, r=wesleywiser 2025-11-04 13:44:48 +11:00
library Rollup merge of #145915 - coolreader18:stabilize-fmt_from_fn, r=dtolnay 2025-11-04 13:44:47 +11:00
LICENSES Synchronize Unicode license text from unicode.org 2024-11-20 00:54:12 -08:00
src Rollup merge of #145974 - pmur:murp/stabilize-zno-jump-tables, r=wesleywiser 2025-11-04 13:44:48 +11:00
tests Rollup merge of #145974 - pmur:murp/stabilize-zno-jump-tables, r=wesleywiser 2025-11-04 13:44:48 +11:00
.clang-format Add .clang-format 2024-06-26 05:56:00 +08:00
.editorconfig editorconfig: don't use nonexistant syntax 2025-08-24 10:37:19 -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 Ignore test-dashboard related files 2025-10-17 13:40:27 +02:00
.gitmodules Update to LLVM 21 2025-08-01 10:17:04 +02:00
.ignore change config.toml to bootstrap.toml for bootstrap module 2025-03-17 12:56:41 +05:30
.mailmap add a mailmap entry 2025-10-26 22:54:41 +01:00
bootstrap.example.toml Allow manually opting in and out of Linux linker overrides 2025-10-06 10:30:46 +02:00
Cargo.lock Rollup merge of #148340 - flip1995:clippy-subtree-update, r=Manishearth 2025-11-01 08:25:48 +01:00
Cargo.toml Bump Clippy version -> 0.1.93 2025-10-31 18:58:42 +01:00
CODE_OF_CONDUCT.md Update link to the Code of Conduct 2025-10-17 20:03:29 +05:00
configure Ensure ./configure works when configure.py path contains spaces 2024-02-16 18:57:22 +00:00
CONTRIBUTING.md chore: remove dead links 2025-09-22 10:15:50 +01:00
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
package-lock.json Update browser-ui-test version to 0.22.2 2025-09-09 17:19:36 +02:00
package.json Update browser-ui-test version to 0.22.2 2025-09-09 17:19:36 +02:00
README.md Update Rust Foundation links in Readme 2025-03-16 19:03:40 -07:00
RELEASES.md Link to i32 for strict_div/rem methods 2025-10-27 09:45:28 -07:00
REUSE.toml REUSE.toml: add new package.json and package-lock.json 2025-07-19 14:44:16 -05:00
rust-bors.toml Add t- prefix to S-waiting-on-{team} labels 2025-10-07 18:15:02 +02:00
rustfmt.toml Rename tests/codegen into tests/codegen-llvm 2025-07-22 14:28:48 +02:00
triagebot.toml Enable regression labeling aliases 2025-10-30 16:52:31 +01:00
typos.toml chore: Update typos to 1.38.1 2025-10-20 12:20:15 -06:00
x fix ./x readdir logic when CDPATH is set 2025-09-19 16:48:05 +02:00
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

README.md

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

Why Rust?

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Read "Installation" from The Book.

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