From 86b4658c569d59452863b3161acd78aaa30abb86 Mon Sep 17 00:00:00 2001 From: Dan Gohman Date: Thu, 3 Mar 2022 14:41:10 -0800 Subject: [PATCH] Generalize `get_nullable_type` to allow types where null is all-ones. Generalize get_nullable_type to accept types that have an all-ones bit pattern as their sentry "null" value. This will allow [`OwnedFd`], [`BorrowedFd`], [`OwnedSocket`], and [`BorrowedSocket`] to be marked with `#[rustc_nonnull_optimization_guaranteed]`, which will allow `Option`, `Option`, `Option`, and `Option` to be used in FFI declarations, as described in the [I/O safety RFC]. For example, it will allow a function like `open` on Unix and `WSASocketW` on Windows to be declared using `Option` and `Option` return types, respectively. The actual change to add `#[rustc_nonnull_optimization_guaranteed]` to the abovementioned types will be a separate PR, as it'll depend on having this patch in the stage0 compiler. Also, update the diagnostics to mention that "niche optimizations" are used in libstd as well as libcore, as `rustc_layout_scalar_valid_range_start` and `rustc_layout_scalar_valid_range_end` are already in use in libstd. [`OwnedFd`]: https://github.com/rust-lang/rust/blob/c9dc44be24c58ff13ce46416c4b97ab5c1bd8429/library/std/src/os/fd/owned.rs#L49 [`BorrowedFd`]: https://github.com/rust-lang/rust/blob/c9dc44be24c58ff13ce46416c4b97ab5c1bd8429/library/std/src/os/fd/owned.rs#L29 [`OwnedSocket`]: https://github.com/rust-lang/rust/blob/c9dc44be24c58ff13ce46416c4b97ab5c1bd8429/library/std/src/os/windows/io/socket.rs#L51 [`BorrowedSocket`]: https://github.com/rust-lang/rust/blob/c9dc44be24c58ff13ce46416c4b97ab5c1bd8429/library/std/src/os/windows/io/socket.rs#L29 [I/O safety RFC]: https://github.com/rust-lang/rfcs/blob/master/text/3128-io-safety.md#ownedfd-and-borrowedfdfd-1 --- compiler/rustc_feature/src/builtin_attrs.rs | 6 +++--- compiler/rustc_lint/src/types.rs | 4 +++- src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs | 2 +- src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr | 2 +- 4 files changed, 8 insertions(+), 6 deletions(-) diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs index 4b9cf784495..bb51f880099 100644 --- a/compiler/rustc_feature/src/builtin_attrs.rs +++ b/compiler/rustc_feature/src/builtin_attrs.rs @@ -606,17 +606,17 @@ pub const BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[ rustc_attr!( rustc_layout_scalar_valid_range_start, Normal, template!(List: "value"), ErrorFollowing, "the `#[rustc_layout_scalar_valid_range_start]` attribute is just used to enable \ - niche optimizations in libcore and will never be stable", + niche optimizations in libcore and libstd and will never be stable", ), rustc_attr!( rustc_layout_scalar_valid_range_end, Normal, template!(List: "value"), ErrorFollowing, "the `#[rustc_layout_scalar_valid_range_end]` attribute is just used to enable \ - niche optimizations in libcore and will never be stable", + niche optimizations in libcore and libstd and will never be stable", ), rustc_attr!( rustc_nonnull_optimization_guaranteed, Normal, template!(Word), WarnFollowing, "the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable \ - niche optimizations in libcore and will never be stable", + niche optimizations in libcore and libstd and will never be stable", ), // ========================================================================== diff --git a/compiler/rustc_lint/src/types.rs b/compiler/rustc_lint/src/types.rs index c0bf64387ff..cb26f91f0e8 100644 --- a/compiler/rustc_lint/src/types.rs +++ b/compiler/rustc_lint/src/types.rs @@ -795,7 +795,9 @@ crate fn repr_nullable_ptr<'tcx>( let field_ty_abi = &cx.layout_of(field_ty).unwrap().abi; if let Abi::Scalar(field_ty_scalar) = field_ty_abi { match (field_ty_scalar.valid_range.start, field_ty_scalar.valid_range.end) { - (0, _) => unreachable!("Non-null optimisation extended to a non-zero value."), + (0, x) if x == field_ty_scalar.value.size(&cx.tcx).unsigned_int_max() - 1 => { + return Some(get_nullable_type(cx, field_ty).unwrap()); + } (1, _) => { return Some(get_nullable_type(cx, field_ty).unwrap()); } diff --git a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs index 04f816ea501..667bc9f8ddf 100644 --- a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs +++ b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.rs @@ -2,6 +2,6 @@ #[rustc_variance] //~ ERROR the `#[rustc_variance]` attribute is just used for rustc unit tests and will never be stable #[rustc_error] //~ ERROR the `#[rustc_error]` attribute is just used for rustc unit tests and will never be stable -#[rustc_nonnull_optimization_guaranteed] //~ ERROR the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and will never be stable +#[rustc_nonnull_optimization_guaranteed] //~ ERROR the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and libstd and will never be stable fn main() {} diff --git a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr index 822368a5946..45a095903d2 100644 --- a/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr +++ b/src/test/ui/feature-gates/feature-gate-rustc-attrs-1.stderr @@ -14,7 +14,7 @@ LL | #[rustc_error] | = help: add `#![feature(rustc_attrs)]` to the crate attributes to enable -error[E0658]: the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and will never be stable +error[E0658]: the `#[rustc_nonnull_optimization_guaranteed]` attribute is just used to enable niche optimizations in libcore and libstd and will never be stable --> $DIR/feature-gate-rustc-attrs-1.rs:5:1 | LL | #[rustc_nonnull_optimization_guaranteed]