From 77c83c09653f5c4437717e2e8aa7f10c1ff94fe4 Mon Sep 17 00:00:00 2001 From: Maybe Waffle Date: Thu, 20 Apr 2023 16:23:13 +0000 Subject: [PATCH] Add `impl_tag!` macro to implement `Tag` for tagged pointer easily --- .../rustc_data_structures/src/tagged_ptr.rs | 41 ++++- .../src/tagged_ptr/impl_tag.rs | 170 ++++++++++++++++++ .../src/tagged_ptr/impl_tag/tests.rs | 33 ++++ compiler/rustc_middle/src/ty/mod.rs | 29 +-- 4 files changed, 244 insertions(+), 29 deletions(-) create mode 100644 compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs create mode 100644 compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs diff --git a/compiler/rustc_data_structures/src/tagged_ptr.rs b/compiler/rustc_data_structures/src/tagged_ptr.rs index 8568aac67c08c..a25046986cc59 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 +142,40 @@ 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() -> u32 { + crate::aligned::align_of::().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; + + let b = bits_for_tag(tag); + if b > bits { + bits = b; + } + } + + bits +} + +/// Returns `(size_of::() * 8) - tag.leading_zeros()` +const fn bits_for_tag(mut tag: usize) -> u32 { + let mut bits = 0; + + while tag > 0 { + bits += 1; + tag >>= 1; + } + + bits +} + unsafe impl Pointer for Box { const BITS: u32 = bits_for::(); @@ -221,12 +256,6 @@ 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() -> u32 { - crate::aligned::align_of::().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 0000000000000..deaaee4cc1728 --- /dev/null +++ b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag.rs @@ -0,0 +1,170 @@ +/// 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: +/// +/// ``` +/// 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 +/// for SomeTag; +/// // You need to specify the `{value_of_the_type} <=> {tag}` relationship +/// 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, +/// } +/// +/// 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: +/// +/// ``` +/// # use rustc_data_structures::impl_tag; +/// #[derive(Copy, Clone)] +/// struct Flags { a: bool, b: bool } +/// +/// impl_tag! { +/// for Flags; +/// Flags { a: true, b: true } <=> 3, +/// Flags { a: false, b: true } <=> 2, +/// Flags { a: true, b: false } <=> 1, +/// Flags { a: false, b: false } <=> 0, +/// } +/// ``` +/// +// This is supposed to produce a compile error, but does not, +// see for more information. +// +// Using the same pattern twice results in a compile error: +// +// ```compile_fail +// # use rustc_data_structures::impl_tag; +// #[derive(Copy, Clone)] +// struct Unit; +// +// impl_tag! { +// for Unit; +// Unit <=> 0, +// Unit <=> 1, +// } +// ``` +// +// Using the same tag twice results in a compile error: +// +// ```compile_fail +// # use rustc_data_structures::impl_tag; +// #[derive(Copy, Clone)] +// enum E { A, B }; +// +// impl_tag! { +// for E; +// E::A <=> 0, +// E::B <=> 0, +// } +// ``` +// +/// Not specifying all values results in a compile error: +/// +/// ```compile_fail,E0004 +/// # use rustc_data_structures::impl_tag; +/// #[derive(Copy, Clone)] +/// enum E { +/// A, +/// B, +/// } +/// +/// impl_tag! { +/// for E; +/// E::A <=> 0, +/// } +/// ``` +#[macro_export] +macro_rules! impl_tag { + ( + for $Self:ty; + $( + $($path:ident)::* $( { $( $fields:tt )* })? <=> $tag:literal, + )* + ) => { + // Safety: + // `into_usize` only returns one of `$tag`s, + // `bits_for_tags` is called on all `$tag`s, + // thus `BITS` constant is correct. + unsafe impl $crate::tagged_ptr::Tag for $Self { + const BITS: u32 = $crate::tagged_ptr::bits_for_tags(&[ + $( $tag, )* + ]); + + fn into_usize(self) -> usize { + // This forbids use of repeating patterns (`Enum::V`&`Enum::V`, etc) + // (or at least it should, see ) + #[forbid(unreachable_patterns)] + match self { + // `match` is doing heavy lifting here, by requiring exhaustiveness + $( + $($path)::* $( { $( $fields )* } )? => $tag, + )* + } + } + + unsafe fn from_usize(tag: usize) -> Self { + // Similarly to the above, this forbids repeating tags + // (or at least it should, see ) + #[forbid(unreachable_patterns)] + match tag { + $( + $tag => $($path)::* $( { $( $fields )* } )?, + )* + + // Safety: + // `into_usize` only returns one of `$tag`s, + // all `$tag`s are filtered up 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 0000000000000..26d1cf3b45422 --- /dev/null +++ b/compiler/rustc_data_structures/src/tagged_ptr/impl_tag/tests.rs @@ -0,0 +1,33 @@ +#[test] +fn bits_constant() { + use crate::tagged_ptr::Tag; + + #[derive(Copy, Clone)] + struct Unit; + impl_tag! { for Unit; Unit <=> 0, } + assert_eq!(Unit::BITS, 0); + + #[derive(Copy, Clone)] + struct Unit1; + impl_tag! { for Unit1; Unit1 <=> 1, } + assert_eq!(Unit1::BITS, 1); + + #[derive(Copy, Clone)] + struct Unit2; + impl_tag! { for Unit2; Unit2 <=> 0b10, } + assert_eq!(Unit2::BITS, 2); + + #[derive(Copy, Clone)] + struct Unit3; + impl_tag! { for Unit3; Unit3 <=> 0b100, } + assert_eq!(Unit3::BITS, 3); + + #[derive(Copy, Clone)] + enum Enum { + A, + B, + C, + } + impl_tag! { for Enum; Enum::A <=> 0b1, Enum::B <=> 0b1000, Enum::C <=> 0b10, } + assert_eq!(Enum::BITS, 4); +} diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs index 1061c32079305..f520faa6a6154 100644 --- a/compiler/rustc_middle/src/ty/mod.rs +++ b/compiler/rustc_middle/src/ty/mod.rs @@ -1626,29 +1626,12 @@ struct ParamTag { constness: hir::Constness, } -unsafe impl rustc_data_structures::tagged_ptr::Tag for ParamTag { - const BITS: u32 = 2; - - #[inline] - fn into_usize(self) -> usize { - match self { - Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst } => 0, - Self { reveal: traits::Reveal::All, constness: hir::Constness::NotConst } => 1, - Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const } => 2, - Self { reveal: traits::Reveal::All, constness: hir::Constness::Const } => 3, - } - } - - #[inline] - unsafe fn from_usize(ptr: usize) -> Self { - match ptr { - 0 => Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst }, - 1 => Self { reveal: traits::Reveal::All, constness: hir::Constness::NotConst }, - 2 => Self { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const }, - 3 => Self { reveal: traits::Reveal::All, constness: hir::Constness::Const }, - _ => std::hint::unreachable_unchecked(), - } - } +impl_tag! { + for ParamTag; + ParamTag { reveal: traits::Reveal::UserFacing, constness: hir::Constness::NotConst } <=> 0, + ParamTag { reveal: traits::Reveal::All, constness: hir::Constness::NotConst } <=> 1, + ParamTag { reveal: traits::Reveal::UserFacing, constness: hir::Constness::Const } <=> 2, + ParamTag { reveal: traits::Reveal::All, constness: hir::Constness::Const } <=> 3, } impl<'tcx> fmt::Debug for ParamEnv<'tcx> {