1 files changed, 185 insertions, 0 deletions
diff --git a/compiler/rustc_data_structures/src/tagged_ptr/copy.rs b/compiler/rustc_data_structures/src/tagged_ptr/copy.rs
new file mode 100644
index 000000000..e1d3e0bd3
--- /dev/null
+++ b/compiler/rustc_data_structures/src/tagged_ptr/copy.rs
@@ -0,0 +1,185 @@
+use super::{Pointer, Tag};
+use crate::stable_hasher::{HashStable, StableHasher};
+use std::fmt;
+use std::marker::PhantomData;
+use std::num::NonZeroUsize;
+
+/// A `Copy` TaggedPtr.
+///
+/// You should use this instead of the `TaggedPtr` type in all cases where
+/// `P: Copy`.
+///
+/// If `COMPARE_PACKED` is true, then the pointers will be compared and hashed without
+/// unpacking. Otherwise we don't implement PartialEq/Eq/Hash; if you want that,
+/// wrap the TaggedPtr.
+pub struct CopyTaggedPtr<P, T, const COMPARE_PACKED: bool>
+where
+    P: Pointer,
+    T: Tag,
+{
+    packed: NonZeroUsize,
+    data: PhantomData<(P, T)>,
+}
+
+impl<P, T, const COMPARE_PACKED: bool> Copy for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer,
+    T: Tag,
+    P: Copy,
+{
+}
+
+impl<P, T, const COMPARE_PACKED: bool> Clone for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer,
+    T: Tag,
+    P: Copy,
+{
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+// We pack the tag into the *upper* bits of the pointer to ease retrieval of the
+// value; a left shift is a multiplication and those are embeddable in
+// instruction encoding.
+impl<P, T, const COMPARE_PACKED: bool> CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer,
+    T: Tag,
+{
+    const TAG_BIT_SHIFT: usize = usize::BITS as usize - T::BITS;
+    const ASSERTION: () = {
+        assert!(T::BITS <= P::BITS);
+        // Used for the transmute_copy's below
+        assert!(std::mem::size_of::<&P::Target>() == std::mem::size_of::<usize>());
+    };
+
+    pub fn new(pointer: P, tag: T) -> Self {
+        // Trigger assert!
+        let () = Self::ASSERTION;
+        let packed_tag = tag.into_usize() << Self::TAG_BIT_SHIFT;
+
+        Self {
+            // SAFETY: We know that the pointer is non-null, as it must be
+            // dereferenceable per `Pointer` safety contract.
+            packed: unsafe {
+                NonZeroUsize::new_unchecked((P::into_usize(pointer) >> T::BITS) | packed_tag)
+            },
+            data: PhantomData,
+        }
+    }
+
+    pub(super) fn pointer_raw(&self) -> usize {
+        self.packed.get() << T::BITS
+    }
+    pub fn pointer(self) -> P
+    where
+        P: Copy,
+    {
+        // SAFETY: pointer_raw returns the original pointer
+        //
+        // Note that this isn't going to double-drop or anything because we have
+        // P: Copy
+        unsafe { P::from_usize(self.pointer_raw()) }
+    }
+    pub fn pointer_ref(&self) -> &P::Target {
+        // SAFETY: pointer_raw returns the original pointer
+        unsafe { std::mem::transmute_copy(&self.pointer_raw()) }
+    }
+    pub fn pointer_mut(&mut self) -> &mut P::Target
+    where
+        P: std::ops::DerefMut,
+    {
+        // SAFETY: pointer_raw returns the original pointer
+        unsafe { std::mem::transmute_copy(&self.pointer_raw()) }
+    }
+    #[inline]
+    pub fn tag(&self) -> T {
+        unsafe { T::from_usize(self.packed.get() >> Self::TAG_BIT_SHIFT) }
+    }
+    #[inline]
+    pub fn set_tag(&mut self, tag: T) {
+        let mut packed = self.packed.get();
+        let new_tag = T::into_usize(tag) << Self::TAG_BIT_SHIFT;
+        let tag_mask = (1 << T::BITS) - 1;
+        packed &= !(tag_mask << Self::TAG_BIT_SHIFT);
+        packed |= new_tag;
+        self.packed = unsafe { NonZeroUsize::new_unchecked(packed) };
+    }
+}
+
+impl<P, T, const COMPARE_PACKED: bool> std::ops::Deref for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer,
+    T: Tag,
+{
+    type Target = P::Target;
+    fn deref(&self) -> &Self::Target {
+        self.pointer_ref()
+    }
+}
+
+impl<P, T, const COMPARE_PACKED: bool> std::ops::DerefMut for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer + std::ops::DerefMut,
+    T: Tag,
+{
+    fn deref_mut(&mut self) -> &mut Self::Target {
+        self.pointer_mut()
+    }
+}
+
+impl<P, T, const COMPARE_PACKED: bool> fmt::Debug for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer,
+    P::Target: fmt::Debug,
+    T: Tag + fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("CopyTaggedPtr")
+            .field("pointer", &self.pointer_ref())
+            .field("tag", &self.tag())
+            .finish()
+    }
+}
+
+impl<P, T> PartialEq for CopyTaggedPtr<P, T, true>
+where
+    P: Pointer,
+    T: Tag,
+{
+    fn eq(&self, other: &Self) -> bool {
+        self.packed == other.packed
+    }
+}
+
+impl<P, T> Eq for CopyTaggedPtr<P, T, true>
+where
+    P: Pointer,
+    T: Tag,
+{
+}
+
+impl<P, T> std::hash::Hash for CopyTaggedPtr<P, T, true>
+where
+    P: Pointer,
+    T: Tag,
+{
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.packed.hash(state);
+    }
+}
+
+impl<P, T, HCX, const COMPARE_PACKED: bool> HashStable<HCX> for CopyTaggedPtr<P, T, COMPARE_PACKED>
+where
+    P: Pointer + HashStable<HCX>,
+    T: Tag + HashStable<HCX>,
+{
+    fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
+        unsafe {
+            Pointer::with_ref(self.pointer_raw(), |p: &P| p.hash_stable(hcx, hasher));
+        }
+        self.tag().hash_stable(hcx, hasher);
+    }
+}