Files
rust/tests/codegen-llvm
Jonathan Brouwer 27d6b3c9b7 Rollup merge of #151576 - tgross35:stabilize-cold-path, r=jhpratt
Stabilize `core::hint::cold_path`

`cold_path` has been around unstably for a while and is a rather useful tool to have. It does what it is supposed to and there are no known remaining issues, so stabilize it here (including const).

Newly stable API:

```rust
// in core::hint
pub const fn cold_path();
```

I have opted to exclude `likely` and `unlikely` for now since they have had some concerns about ease of use that `cold_path` doesn't suffer from. `cold_path` is also significantly more flexible; in addition to working with boolean `if` conditions, it can be used in `match` arms, `if let`, closures, and other control flow blocks. `likely` and `unlikely` are also possible to implement in user code via `cold_path`, if desired.

Closes: https://github.com/rust-lang/rust/issues/136873 (tracking issue)

---

There has been some design and implementation work for making `#[cold]` function in more places, such as `if` arms, `match` arms, and closure bodies. Considering a stable `cold_path` will cover all of these usecases, it does not seem worth pursuing a more powerful `#[cold]` as an alternative way to do the same thing. If the lang team agrees, then:

Closes: https://github.com/rust-lang/rust/issues/26179
Closes: https://github.com/rust-lang/rust/pull/120193
2026-02-07 13:06:35 +01:00
..
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The files here use the LLVM FileCheck framework, documented at https://llvm.org/docs/CommandGuide/FileCheck.html.

One extension worth noting is the use of revisions as custom prefixes for FileCheck. If your codegen test has different behavior based on the chosen target or different compiler flags that you want to exercise, you can use a revisions annotation, like so:

// revisions: aaa bbb
// [bbb] compile-flags: --flags-for-bbb

After specifying those variations, you can write different expected, or explicitly unexpected output by using <prefix>-SAME: and <prefix>-NOT:, like so:

// CHECK: expected code
// aaa-SAME: emitted-only-for-aaa
// aaa-NOT:                        emitted-only-for-bbb
// bbb-NOT:  emitted-only-for-aaa
// bbb-SAME:                       emitted-only-for-bbb