diff options
Diffstat (limited to 'compiler/rustc_data_structures')
4 files changed, 204 insertions, 6 deletions
diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs index 426d2c4034b..004017ec5f3 100644 --- a/compiler/rustc_data_structures/src/lib.rs +++ b/compiler/rustc_data_structures/src/lib.rs @@ -31,6 +31,7 @@ #![feature(unwrap_infallible)] #![feature(strict_provenance)] #![feature(ptr_alignment_type)] +#![feature(macro_metavar_expr)] #![allow(rustc::default_hash_types)] #![allow(rustc::potential_query_instability)] #![deny(rustc::untranslatable_diagnostic)] diff --git a/compiler/rustc_data_structures/src/tagged_ptr.rs b/compiler/rustc_data_structures/src/tagged_ptr.rs index 8568aac67c0..2914eece679 100644 --- a/compiler/rustc_data_structures/src/tagged_ptr.rs +++ b/compiler/rustc_data_structures/src/tagged_ptr.rs @@ -24,6 +24,7 @@ use crate::aligned::Aligned; mod copy; mod drop; +mod impl_tag; pub use copy::CopyTaggedPtr; pub use drop::TaggedPtr; @@ -141,6 +142,30 @@ pub unsafe trait Tag: Copy { unsafe fn from_usize(tag: usize) -> Self; } +/// Returns the number of bits available for use for tags in a pointer to `T` +/// (this is based on `T`'s alignment). +pub const fn bits_for<T: ?Sized + Aligned>() -> u32 { + crate::aligned::align_of::<T>().as_nonzero().trailing_zeros() +} + +/// Returns the correct [`Tag::BITS`] constant for a set of tag values. +pub const fn bits_for_tags(mut tags: &[usize]) -> u32 { + let mut bits = 0; + + while let &[tag, ref rest @ ..] = tags { + tags = rest; + + // bits required to represent `tag`, + // position of the most significant 1 + let b = usize::BITS - tag.leading_zeros(); + if b > bits { + bits = b; + } + } + + bits +} + unsafe impl<T: ?Sized + Aligned> Pointer for Box<T> { const BITS: u32 = bits_for::<Self::Target>(); @@ -221,12 +246,6 @@ unsafe impl<'a, T: 'a + ?Sized + Aligned> Pointer for &'a mut T { } } -/// Returns the number of bits available for use for tags in a pointer to `T` -/// (this is based on `T`'s alignment). -pub const fn bits_for<T: ?Sized + Aligned>() -> u32 { - crate::aligned::align_of::<T>().as_nonzero().trailing_zeros() -} - /// A tag type used in [`CopyTaggedPtr`] and [`TaggedPtr`] tests. #[derive(Copy, Clone, Debug, PartialEq, Eq)] #[cfg(test)] diff --git a/compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs new file mode 100644 index 00000000000..cb7f7d318dc --- /dev/null +++ b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs @@ -0,0 +1,144 @@ +/// Implements [`Tag`] for a given type. +/// +/// You can use `impl_tag` on structs and enums. +/// You need to specify the type and all its possible values, +/// which can only be paths with optional fields. +/// +/// [`Tag`]: crate::tagged_ptr::Tag +/// +/// # Examples +/// +/// Basic usage: +/// +/// ``` +/// #![feature(macro_metavar_expr)] +/// use rustc_data_structures::{impl_tag, tagged_ptr::Tag}; +/// +/// #[derive(Copy, Clone, PartialEq, Debug)] +/// enum SomeTag { +/// A, +/// B, +/// X { v: bool }, +/// Y(bool, bool), +/// } +/// +/// impl_tag! { +/// // The type for which the `Tag` will be implemented +/// impl Tag for SomeTag; +/// // You need to specify all possible tag values: +/// SomeTag::A, // 0 +/// SomeTag::B, // 1 +/// // For variants with fields, you need to specify the fields: +/// SomeTag::X { v: true }, // 2 +/// SomeTag::X { v: false }, // 3 +/// // For tuple variants use named syntax: +/// SomeTag::Y { 0: true, 1: true }, // 4 +/// SomeTag::Y { 0: false, 1: true }, // 5 +/// SomeTag::Y { 0: true, 1: false }, // 6 +/// SomeTag::Y { 0: false, 1: false }, // 7 +/// } +/// +/// // Tag values are assigned in order: +/// assert_eq!(SomeTag::A.into_usize(), 0); +/// assert_eq!(SomeTag::X { v: false }.into_usize(), 3); +/// assert_eq!(SomeTag::Y(false, true).into_usize(), 5); +/// +/// assert_eq!(unsafe { SomeTag::from_usize(1) }, SomeTag::B); +/// assert_eq!(unsafe { SomeTag::from_usize(2) }, SomeTag::X { v: true }); +/// assert_eq!(unsafe { SomeTag::from_usize(7) }, SomeTag::Y(false, false)); +/// ``` +/// +/// Structs are supported: +/// +/// ``` +/// #![feature(macro_metavar_expr)] +/// # use rustc_data_structures::impl_tag; +/// #[derive(Copy, Clone)] +/// struct Flags { a: bool, b: bool } +/// +/// impl_tag! { +/// impl Tag for Flags; +/// Flags { a: true, b: true }, +/// Flags { a: false, b: true }, +/// Flags { a: true, b: false }, +/// Flags { a: false, b: false }, +/// } +/// ``` +/// +/// Not specifying all values results in a compile error: +/// +/// ```compile_fail,E0004 +/// #![feature(macro_metavar_expr)] +/// # use rustc_data_structures::impl_tag; +/// #[derive(Copy, Clone)] +/// enum E { +/// A, +/// B, +/// } +/// +/// impl_tag! { +/// impl Tag for E; +/// E::A, +/// } +/// ``` +#[macro_export] +macro_rules! impl_tag { + ( + impl Tag for $Self:ty; + $( + $($path:ident)::* $( { $( $fields:tt )* })?, + )* + ) => { + // Safety: + // `bits_for_tags` is called on the same `${index()}`-es as + // `into_usize` returns, thus `BITS` constant is correct. + unsafe impl $crate::tagged_ptr::Tag for $Self { + const BITS: u32 = $crate::tagged_ptr::bits_for_tags(&[ + $( + ${index()}, + $( ${ignore(path)} )* + )* + ]); + + #[inline] + fn into_usize(self) -> usize { + // This forbids use of repeating patterns (`Enum::V`&`Enum::V`, etc) + // (or at least it should, see <https://github.com/rust-lang/rust/issues/110613>) + #[forbid(unreachable_patterns)] + match self { + // `match` is doing heavy lifting here, by requiring exhaustiveness + $( + $($path)::* $( { $( $fields )* } )? => ${index()}, + )* + } + } + + #[inline] + unsafe fn from_usize(tag: usize) -> Self { + match tag { + $( + ${index()} => $($path)::* $( { $( $fields )* } )?, + )* + + // Safety: + // `into_usize` only returns `${index()}` of the same + // repetition as we are filtering above, thus if this is + // reached, the safety contract of this function was + // already breached. + _ => unsafe { + debug_assert!( + false, + "invalid tag: {tag}\ + (this is a bug in the caller of `from_usize`)" + ); + std::hint::unreachable_unchecked() + }, + } + } + + } + }; +} + +#[cfg(test)] +mod tests; diff --git a/compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs new file mode 100644 index 00000000000..62c926153e1 --- /dev/null +++ b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs @@ -0,0 +1,34 @@ +#[test] +fn bits_constant() { + use crate::tagged_ptr::Tag; + + #[derive(Copy, Clone)] + struct Unit; + impl_tag! { impl Tag for Unit; Unit, } + assert_eq!(Unit::BITS, 0); + + #[derive(Copy, Clone)] + enum Enum3 { + A, + B, + C, + } + impl_tag! { impl Tag for Enum3; Enum3::A, Enum3::B, Enum3::C, } + assert_eq!(Enum3::BITS, 2); + + #[derive(Copy, Clone)] + struct Eight(bool, bool, bool); + impl_tag! { + impl Tag for Eight; + Eight { 0: true, 1: true, 2: true }, + Eight { 0: true, 1: true, 2: false }, + Eight { 0: true, 1: false, 2: true }, + Eight { 0: true, 1: false, 2: false }, + Eight { 0: false, 1: true, 2: true }, + Eight { 0: false, 1: true, 2: false }, + Eight { 0: false, 1: false, 2: true }, + Eight { 0: false, 1: false, 2: false }, + } + + assert_eq!(Eight::BITS, 3); +} |