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| author | bors <bors@rust-lang.org> | 2024-03-05 00:13:01 +0000 |
|---|---|---|
| committer | bors <bors@rust-lang.org> | 2024-03-05 00:13:01 +0000 |
| commit | 2eeff462b762ed00f9d557d8c6ad7a3d562f692a (patch) | |
| tree | d5e2442dec8294e89a12d0680109e0ef3fd8d7cf /src/doc | |
| parent | 50e77f133f8eb1f745e05681163a0143d6c4dd7d (diff) | |
| parent | c04f0caaff5b09a2202bb220579ef45722e74ed2 (diff) | |
Auto merge of #120675 - oli-obk:intrinsics3.0, r=pnkfelix
Add a scheme for moving away from `extern "rust-intrinsic"` entirely All `rust-intrinsic`s can become free functions now, either with a fallback body, or with a dummy body and an attribute, requiring backends to actually implement the intrinsic. This PR demonstrates the dummy-body scheme with the `vtable_size` intrinsic. cc https://github.com/rust-lang/rust/issues/63585 follow-up to #120500 MCP at https://github.com/rust-lang/compiler-team/issues/720
Diffstat (limited to 'src/doc')
| -rw-r--r-- | src/doc/unstable-book/src/language-features/intrinsics.md | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/src/doc/unstable-book/src/language-features/intrinsics.md b/src/doc/unstable-book/src/language-features/intrinsics.md index 1a8c1c0b36a..02a009d56d3 100644 --- a/src/doc/unstable-book/src/language-features/intrinsics.md +++ b/src/doc/unstable-book/src/language-features/intrinsics.md @@ -52,12 +52,23 @@ with any regular function. Various intrinsics have native MIR operations that they correspond to. Instead of requiring backends to implement both the intrinsic and the MIR operation, the `lower_intrinsics` pass will convert the calls to the MIR operation. Backends do not need to know about these intrinsics -at all. +at all. These intrinsics only make sense without a body, and can either be declared as a "rust-intrinsic" +or as a `#[rustc_intrinsic]`. The body is never used, as calls to the intrinsic do not exist +anymore after MIR analyses. ## Intrinsics without fallback logic These must be implemented by all backends. +### `#[rustc_intrinsic]` declarations + +These are written like intrinsics with fallback bodies, but the body is irrelevant. +Use `loop {}` for the body or call the intrinsic recursively and add +`#[rustc_intrinsic_must_be_overridden]` to the function to ensure that backends don't +invoke the body. + +### Legacy extern ABI based intrinsics + These are imported as if they were FFI functions, with the special `rust-intrinsic` ABI. For example, if one was in a freestanding context, but wished to be able to `transmute` between types, and |