New upstream version 1.67.1+dfsg1

[rustc.git] / compiler / rustc_type_ir / src / ty_info.rs

diff --git a/compiler/rustc_type_ir/src/ty_info.rs b/compiler/rustc_type_ir/src/ty_info.rs
new file mode 100644 (file)
index 0000000..4e5d424
--- /dev/null
+++ b/compiler/rustc_type_ir/src/ty_info.rs
@@ -0,0 +1,122 @@
+use std::{
+    cmp::Ordering,
+    hash::{Hash, Hasher},
+    ops::Deref,
+};
+
+use rustc_data_structures::{
+    fingerprint::Fingerprint,
+    stable_hasher::{HashStable, StableHasher},
+};
+
+use crate::{DebruijnIndex, TypeFlags};
+
+/// A helper type that you can wrap round your own type in order to automatically
+/// cache the stable hash, type flags and debruijn index on creation and
+/// not recompute it whenever the information is needed.
+/// This is only done in incremental mode. You can also opt out of caching by using
+/// StableHash::ZERO for the hash, in which case the hash gets computed each time.
+/// This is useful if you have values that you intern but never (can?) use for stable
+/// hashing.
+#[derive(Copy, Clone)]
+pub struct WithCachedTypeInfo<T> {
+    pub internee: T,
+    pub stable_hash: Fingerprint,
+
+    /// This field provides fast access to information that is also contained
+    /// in `kind`.
+    ///
+    /// This field shouldn't be used directly and may be removed in the future.
+    /// Use `Ty::flags()` instead.
+    pub flags: TypeFlags,
+
+    /// This field provides fast access to information that is also contained
+    /// in `kind`.
+    ///
+    /// This is a kind of confusing thing: it stores the smallest
+    /// binder such that
+    ///
+    /// (a) the binder itself captures nothing but
+    /// (b) all the late-bound things within the type are captured
+    ///     by some sub-binder.
+    ///
+    /// So, for a type without any late-bound things, like `u32`, this
+    /// will be *innermost*, because that is the innermost binder that
+    /// captures nothing. But for a type `&'D u32`, where `'D` is a
+    /// late-bound region with De Bruijn index `D`, this would be `D + 1`
+    /// -- the binder itself does not capture `D`, but `D` is captured
+    /// by an inner binder.
+    ///
+    /// We call this concept an "exclusive" binder `D` because all
+    /// De Bruijn indices within the type are contained within `0..D`
+    /// (exclusive).
+    pub outer_exclusive_binder: DebruijnIndex,
+}
+
+impl<T: PartialEq> PartialEq for WithCachedTypeInfo<T> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.internee.eq(&other.internee)
+    }
+}
+
+impl<T: Eq> Eq for WithCachedTypeInfo<T> {}
+
+impl<T: Ord> PartialOrd for WithCachedTypeInfo<T> {
+    fn partial_cmp(&self, other: &WithCachedTypeInfo<T>) -> Option<Ordering> {
+        Some(self.internee.cmp(&other.internee))
+    }
+}
+
+impl<T: Ord> Ord for WithCachedTypeInfo<T> {
+    fn cmp(&self, other: &WithCachedTypeInfo<T>) -> Ordering {
+        self.internee.cmp(&other.internee)
+    }
+}
+
+impl<T> Deref for WithCachedTypeInfo<T> {
+    type Target = T;
+
+    #[inline]
+    fn deref(&self) -> &T {
+        &self.internee
+    }
+}
+
+impl<T: Hash> Hash for WithCachedTypeInfo<T> {
+    #[inline]
+    fn hash<H: Hasher>(&self, s: &mut H) {
+        if self.stable_hash != Fingerprint::ZERO {
+            self.stable_hash.hash(s)
+        } else {
+            self.internee.hash(s)
+        }
+    }
+}
+
+impl<T: HashStable<CTX>, CTX> HashStable<CTX> for WithCachedTypeInfo<T> {
+    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) {
+        if self.stable_hash == Fingerprint::ZERO || cfg!(debug_assertions) {
+            // No cached hash available. This can only mean that incremental is disabled.
+            // We don't cache stable hashes in non-incremental mode, because they are used
+            // so rarely that the performance actually suffers.
+
+            // We need to build the hash as if we cached it and then hash that hash, as
+            // otherwise the hashes will differ between cached and non-cached mode.
+            let stable_hash: Fingerprint = {
+                let mut hasher = StableHasher::new();
+                self.internee.hash_stable(hcx, &mut hasher);
+                hasher.finish()
+            };
+            if cfg!(debug_assertions) && self.stable_hash != Fingerprint::ZERO {
+                assert_eq!(
+                    stable_hash, self.stable_hash,
+                    "cached stable hash does not match freshly computed stable hash"
+                );
+            }
+            stable_hash.hash_stable(hcx, hasher);
+        } else {
+            self.stable_hash.hash_stable(hcx, hasher);
+        }
+    }
+}