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Clarify ArenaAllocatable's second parameter.

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It's simply a binary thing to allow different behaviour for `Copy` vs
`!Copy` types. The new code makes this much clearer; I was scratching my
head over the old code for some time.
This commit is contained in:
Nicholas Nethercote 2022-01-26 10:46:40 +11:00
parent 9065c7ced6
commit 6035487715
1 changed files with 10 additions and 5 deletions
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15
compiler/rustc_arena/src/lib.rs
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@ -546,7 +546,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
$($name: $crate::TypedArena<$ty>,)* $($name: $crate::TypedArena<$ty>,)*
} }
pub trait ArenaAllocatable<'tcx, T = Self>: Sized { pub trait ArenaAllocatable<'tcx, C = rustc_arena::IsNotCopy>: Sized {
fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self; fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self;
fn allocate_from_iter<'a>( fn allocate_from_iter<'a>(
arena: &'a Arena<'tcx>, arena: &'a Arena<'tcx>,
@ -555,7 +555,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
} }
// Any type that impls `Copy` can be arena-allocated in the `DroplessArena`. // Any type that impls `Copy` can be arena-allocated in the `DroplessArena`.
impl<'tcx, T: Copy> ArenaAllocatable<'tcx, ()> for T { impl<'tcx, T: Copy> ArenaAllocatable<'tcx, rustc_arena::IsCopy> for T {
#[inline] #[inline]
fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self { fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
arena.dropless.alloc(self) arena.dropless.alloc(self)
@ -569,7 +569,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
} }
} }
$( $(
impl<'tcx> ArenaAllocatable<'tcx, $ty> for $ty { impl<'tcx> ArenaAllocatable<'tcx, rustc_arena::IsNotCopy> for $ty {
#[inline] #[inline]
fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self { fn allocate_on<'a>(self, arena: &'a Arena<'tcx>) -> &'a mut Self {
if !::std::mem::needs_drop::<Self>() { if !::std::mem::needs_drop::<Self>() {
@ -595,7 +595,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
impl<'tcx> Arena<'tcx> { impl<'tcx> Arena<'tcx> {
#[inline] #[inline]
pub fn alloc<T: ArenaAllocatable<'tcx, U>, U>(&self, value: T) -> &mut T { pub fn alloc<T: ArenaAllocatable<'tcx, C>, C>(&self, value: T) -> &mut T {
value.allocate_on(self) value.allocate_on(self)
} }
@ -608,7 +608,7 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
self.dropless.alloc_slice(value) self.dropless.alloc_slice(value)
} }
pub fn alloc_from_iter<'a, T: ArenaAllocatable<'tcx, U>, U>( pub fn alloc_from_iter<'a, T: ArenaAllocatable<'tcx, C>, C>(
&'a self, &'a self,
iter: impl ::std::iter::IntoIterator<Item = T>, iter: impl ::std::iter::IntoIterator<Item = T>,
) -> &'a mut [T] { ) -> &'a mut [T] {
@ -617,5 +617,10 @@ pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
} }
} }
// Marker types that let us give different behaviour for arenas allocating
// `Copy` types vs `!Copy` types.
pub struct IsCopy;
pub struct IsNotCopy;
#[cfg(test)] #[cfg(test)]
mod tests; mod tests;