Auto merge of #110083 - saethlin:encode-hashes-as-bytes, r=cjgillot

Encode hashes as bytes, not varint

In a few places, we store hashes as `u64` or `u128` and then apply `derive(Decodable, Encodable)` to the enclosing struct/enum. It is more efficient to encode hashes directly than try to apply some varint encoding. This PR adds two new types `Hash64` and `Hash128` which are produced by `StableHasher` and replace every use of storing a `u64` or `u128` that represents a hash.

Distribution of the byte lengths of leb128 encodings, from `x build --stage 2` with `incremental = true`

Before:
```
(  1) 373418203 (53.7%, 53.7%): 1
(  2) 196240113 (28.2%, 81.9%): 3
(  3) 108157958 (15.6%, 97.5%): 2
(  4)  17213120 ( 2.5%, 99.9%): 4
(  5)    223614 ( 0.0%,100.0%): 9
(  6)    216262 ( 0.0%,100.0%): 10
(  7)     15447 ( 0.0%,100.0%): 5
(  8)      3633 ( 0.0%,100.0%): 19
(  9)      3030 ( 0.0%,100.0%): 8
( 10)      1167 ( 0.0%,100.0%): 18
( 11)      1032 ( 0.0%,100.0%): 7
( 12)      1003 ( 0.0%,100.0%): 6
( 13)        10 ( 0.0%,100.0%): 16
( 14)        10 ( 0.0%,100.0%): 17
( 15)         5 ( 0.0%,100.0%): 12
( 16)         4 ( 0.0%,100.0%): 14
```

After:
```
(  1) 372939136 (53.7%, 53.7%): 1
(  2) 196240140 (28.3%, 82.0%): 3
(  3) 108014969 (15.6%, 97.5%): 2
(  4)  17192375 ( 2.5%,100.0%): 4
(  5)       435 ( 0.0%,100.0%): 5
(  6)        83 ( 0.0%,100.0%): 18
(  7)        79 ( 0.0%,100.0%): 10
(  8)        50 ( 0.0%,100.0%): 9
(  9)         6 ( 0.0%,100.0%): 19
```

The remaining 9 or 10 and 18 or 19 are `u64` and `u128` respectively that have the high bits set. As far as I can tell these are coming primarily from `SwitchTargets`.

compiler/rustc_abi/src/layout.rs

@@ -79,7 +79,8 @@ pub trait LayoutCalculator {
                 {
                     // `ReprOptions.layout_seed` is a deterministic seed that we can use to
                     // randomize field ordering with
-                    let mut rng = Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed);
+                    let mut rng =
+                        Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed.as_u64());
 
                     // Shuffle the ordering of the fields
                     optimizing.shuffle(&mut rng);

compiler/rustc_abi/src/lib.rs

@@ -9,6 +9,7 @@ use std::str::FromStr;
 
 use bitflags::bitflags;
 use rustc_data_structures::intern::Interned;
+use rustc_data_structures::stable_hasher::Hash64;
 #[cfg(feature = "nightly")]
 use rustc_data_structures::stable_hasher::StableOrd;
 use rustc_index::vec::{IndexSlice, IndexVec};
@@ -77,12 +78,12 @@ pub struct ReprOptions {
     pub flags: ReprFlags,
     /// The seed to be used for randomizing a type's layout
     ///
-    /// Note: This could technically be a `[u8; 16]` (a `u128`) which would
+    /// Note: This could technically be a `Hash128` which would
     /// be the "most accurate" hash as it'd encompass the item and crate
     /// hash without loss, but it does pay the price of being larger.
-    /// Everything's a tradeoff, a `u64` seed should be sufficient for our
+    /// Everything's a tradeoff, a 64-bit seed should be sufficient for our
     /// purposes (primarily `-Z randomize-layout`)
-    pub field_shuffle_seed: u64,
+    pub field_shuffle_seed: Hash64,
 }
 
 impl ReprOptions {

compiler/rustc_codegen_llvm/src/common.rs

@@ -10,7 +10,7 @@ use crate::value::Value;
 use rustc_ast::Mutability;
 use rustc_codegen_ssa::mir::place::PlaceRef;
 use rustc_codegen_ssa::traits::*;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash128, HashStable, StableHasher};
 use rustc_hir::def_id::DefId;
 use rustc_middle::bug;
 use rustc_middle::mir::interpret::{ConstAllocation, GlobalAlloc, Scalar};
@@ -261,7 +261,7 @@ impl<'ll, 'tcx> ConstMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                             let hash = self.tcx.with_stable_hashing_context(|mut hcx| {
                                 let mut hasher = StableHasher::new();
                                 alloc.hash_stable(&mut hcx, &mut hasher);
-                                hasher.finish::<u128>()
+                                hasher.finish::<Hash128>()
                             });
                             llvm::set_value_name(value, format!("alloc_{hash:032x}").as_bytes());
                         }

compiler/rustc_codegen_llvm/src/debuginfo/mod.rs

@@ -21,6 +21,7 @@ use rustc_codegen_ssa::debuginfo::type_names;
 use rustc_codegen_ssa::mir::debuginfo::{DebugScope, FunctionDebugContext, VariableKind};
 use rustc_codegen_ssa::traits::*;
 use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::stable_hasher::Hash128;
 use rustc_data_structures::sync::Lrc;
 use rustc_hir::def_id::{DefId, DefIdMap};
 use rustc_index::vec::IndexVec;
@@ -61,7 +62,7 @@ pub struct CodegenUnitDebugContext<'ll, 'tcx> {
     llcontext: &'ll llvm::Context,
     llmod: &'ll llvm::Module,
     builder: &'ll mut DIBuilder<'ll>,
-    created_files: RefCell<FxHashMap<Option<(u128, SourceFileHash)>, &'ll DIFile>>,
+    created_files: RefCell<FxHashMap<Option<(Hash128, SourceFileHash)>, &'ll DIFile>>,
 
     type_map: metadata::TypeMap<'ll, 'tcx>,
     namespace_map: RefCell<DefIdMap<&'ll DIScope>>,

compiler/rustc_codegen_ssa/src/debuginfo/type_names.rs

@@ -12,7 +12,7 @@
 // * `"` is treated as the start of a string.
 
 use rustc_data_structures::fx::FxHashSet;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_hir::def_id::DefId;
 use rustc_hir::definitions::{DefPathData, DefPathDataName, DisambiguatedDefPathData};
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind, Mutability};
@@ -675,8 +675,7 @@ fn push_const_param<'tcx>(tcx: TyCtxt<'tcx>, ct: ty::Const<'tcx>, output: &mut S
                     hcx.while_hashing_spans(false, |hcx| {
                         ct.to_valtree().hash_stable(hcx, &mut hasher)
                     });
-                    let hash: u64 = hasher.finish();
+                    hasher.finish::<Hash64>()
-                    hash
                 });
 
                 if cpp_like_debuginfo(tcx) {

compiler/rustc_const_eval/src/interpret/intrinsics.rs

@@ -75,7 +75,7 @@ pub(crate) fn eval_nullary_intrinsic<'tcx>(
         }
         sym::type_id => {
             ensure_monomorphic_enough(tcx, tp_ty)?;
-            ConstValue::from_u64(tcx.type_id_hash(tp_ty))
+            ConstValue::from_u64(tcx.type_id_hash(tp_ty).as_u64())
         }
         sym::variant_count => match tp_ty.kind() {
             // Correctly handles non-monomorphic calls, so there is no need for ensure_monomorphic_enough.

compiler/rustc_data_structures/src/fingerprint.rs

@@ -1,4 +1,4 @@
-use crate::stable_hasher;
+use crate::stable_hasher::{Hash64, StableHasher, StableHasherResult};
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
 use std::hash::{Hash, Hasher};
 
@@ -9,32 +9,49 @@ mod tests;
 #[repr(C)]
 pub struct Fingerprint(u64, u64);
 
+pub trait FingerprintComponent {
+    fn as_u64(&self) -> u64;
+}
+
+impl FingerprintComponent for Hash64 {
+    #[inline]
+    fn as_u64(&self) -> u64 {
+        Hash64::as_u64(*self)
+    }
+}
+
+impl FingerprintComponent for u64 {
+    #[inline]
+    fn as_u64(&self) -> u64 {
+        *self
+    }
+}
+
 impl Fingerprint {
     pub const ZERO: Fingerprint = Fingerprint(0, 0);
 
     #[inline]
-    pub fn new(_0: u64, _1: u64) -> Fingerprint {
+    pub fn new<A, B>(_0: A, _1: B) -> Fingerprint
-        Fingerprint(_0, _1)
+    where
+        A: FingerprintComponent,
+        B: FingerprintComponent,
+    {
+        Fingerprint(_0.as_u64(), _1.as_u64())
     }
 
     #[inline]
-    pub fn from_smaller_hash(hash: u64) -> Fingerprint {
+    pub fn to_smaller_hash(&self) -> Hash64 {
-        Fingerprint(hash, hash)
-    }
-
-    #[inline]
-    pub fn to_smaller_hash(&self) -> u64 {
         // Even though both halves of the fingerprint are expected to be good
         // quality hash values, let's still combine the two values because the
         // Fingerprints in DefPathHash have the StableCrateId portion which is
         // the same for all DefPathHashes from the same crate. Combining the
         // two halves makes sure we get a good quality hash in such cases too.
-        self.0.wrapping_mul(3).wrapping_add(self.1)
+        Hash64::new(self.0.wrapping_mul(3).wrapping_add(self.1))
     }
 
     #[inline]
-    pub fn as_value(&self) -> (u64, u64) {
+    pub fn split(&self) -> (Hash64, Hash64) {
-        (self.0, self.1)
+        (Hash64::new(self.0), Hash64::new(self.1))
     }
 
     #[inline]
@@ -131,9 +148,9 @@ impl FingerprintHasher for crate::unhash::Unhasher {
     }
 }
 
-impl stable_hasher::StableHasherResult for Fingerprint {
+impl StableHasherResult for Fingerprint {
     #[inline]
-    fn finish(hasher: stable_hasher::StableHasher) -> Self {
+    fn finish(hasher: StableHasher) -> Self {
         let (_0, _1) = hasher.finalize();
         Fingerprint(_0, _1)
     }

compiler/rustc_data_structures/src/fingerprint/tests.rs

@@ -1,11 +1,12 @@
 use super::*;
+use crate::stable_hasher::Hash64;
 
 // Check that `combine_commutative` is order independent.
 #[test]
 fn combine_commutative_is_order_independent() {
-    let a = Fingerprint::new(0xf6622fb349898b06, 0x70be9377b2f9c610);
+    let a = Fingerprint::new(Hash64::new(0xf6622fb349898b06), Hash64::new(0x70be9377b2f9c610));
-    let b = Fingerprint::new(0xa9562bf5a2a5303c, 0x67d9b6c82034f13d);
+    let b = Fingerprint::new(Hash64::new(0xa9562bf5a2a5303c), Hash64::new(0x67d9b6c82034f13d));
-    let c = Fingerprint::new(0x0d013a27811dbbc3, 0x9a3f7b3d9142ec43);
+    let c = Fingerprint::new(Hash64::new(0x0d013a27811dbbc3), Hash64::new(0x9a3f7b3d9142ec43));
     let permutations = [(a, b, c), (a, c, b), (b, a, c), (b, c, a), (c, a, b), (c, b, a)];
     let f = a.combine_commutative(b).combine_commutative(c);
     for p in &permutations {

compiler/rustc_data_structures/src/hashes.rs

@@ -0,0 +1,132 @@
+//! rustc encodes a lot of hashes. If hashes are stored as `u64` or `u128`, a `derive(Encodable)`
+//! will apply varint encoding to the hashes, which is less efficient than directly encoding the 8
+//! or 16 bytes of the hash.
+//!
+//! The types in this module represent 64-bit or 128-bit hashes produced by a `StableHasher`.
+//! `Hash64` and `Hash128` expose some utilty functions to encourage users to not extract the inner
+//! hash value as an integer type and accidentally apply varint encoding to it.
+//!
+//! In contrast with `Fingerprint`, users of these types cannot and should not attempt to construct
+//! and decompose these types into constitutent pieces. The point of these types is only to
+//! connect the fact that they can only be produced by a `StableHasher` to their
+//! `Encode`/`Decode` impls.
+
+use crate::stable_hasher::{StableHasher, StableHasherResult};
+use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use std::fmt;
+use std::ops::BitXorAssign;
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
+pub struct Hash64 {
+    inner: u64,
+}
+
+impl Hash64 {
+    pub const ZERO: Hash64 = Hash64 { inner: 0 };
+
+    #[inline]
+    pub(crate) fn new(n: u64) -> Self {
+        Self { inner: n }
+    }
+
+    #[inline]
+    pub fn as_u64(self) -> u64 {
+        self.inner
+    }
+}
+
+impl BitXorAssign<u64> for Hash64 {
+    #[inline]
+    fn bitxor_assign(&mut self, rhs: u64) {
+        self.inner ^= rhs;
+    }
+}
+
+impl<S: Encoder> Encodable<S> for Hash64 {
+    #[inline]
+    fn encode(&self, s: &mut S) {
+        s.emit_raw_bytes(&self.inner.to_le_bytes());
+    }
+}
+
+impl<D: Decoder> Decodable<D> for Hash64 {
+    #[inline]
+    fn decode(d: &mut D) -> Self {
+        Self { inner: u64::from_le_bytes(d.read_raw_bytes(8).try_into().unwrap()) }
+    }
+}
+
+impl StableHasherResult for Hash64 {
+    #[inline]
+    fn finish(hasher: StableHasher) -> Self {
+        Self { inner: hasher.finalize().0 }
+    }
+}
+
+impl fmt::Debug for Hash64 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::LowerHex for Hash64 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.inner, f)
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord, Default)]
+pub struct Hash128 {
+    inner: u128,
+}
+
+impl Hash128 {
+    #[inline]
+    pub fn truncate(self) -> Hash64 {
+        Hash64 { inner: self.inner as u64 }
+    }
+
+    #[inline]
+    pub fn wrapping_add(self, other: Self) -> Self {
+        Self { inner: self.inner.wrapping_add(other.inner) }
+    }
+
+    #[inline]
+    pub fn as_u128(self) -> u128 {
+        self.inner
+    }
+}
+
+impl<S: Encoder> Encodable<S> for Hash128 {
+    #[inline]
+    fn encode(&self, s: &mut S) {
+        s.emit_raw_bytes(&self.inner.to_le_bytes());
+    }
+}
+
+impl<D: Decoder> Decodable<D> for Hash128 {
+    #[inline]
+    fn decode(d: &mut D) -> Self {
+        Self { inner: u128::from_le_bytes(d.read_raw_bytes(16).try_into().unwrap()) }
+    }
+}
+
+impl StableHasherResult for Hash128 {
+    #[inline]
+    fn finish(hasher: StableHasher) -> Self {
+        let (_0, _1) = hasher.finalize();
+        Self { inner: u128::from(_0) | (u128::from(_1) << 64) }
+    }
+}
+
+impl fmt::Debug for Hash128 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.inner.fmt(f)
+    }
+}
+
+impl fmt::LowerHex for Hash128 {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.inner, f)
+    }
+}

compiler/rustc_data_structures/src/lib.rs

@@ -86,6 +86,7 @@ pub mod work_queue;
 pub use atomic_ref::AtomicRef;
 pub mod aligned;
 pub mod frozen;
+mod hashes;
 pub mod owned_slice;
 pub mod sso;
 pub mod steal;

compiler/rustc_data_structures/src/stable_hasher.rs

@@ -2,6 +2,7 @@ use crate::sip128::SipHasher128;
 use rustc_index::bit_set;
 use rustc_index::vec;
 use smallvec::SmallVec;
+use std::fmt;
 use std::hash::{BuildHasher, Hash, Hasher};
 use std::marker::PhantomData;
 use std::mem;
@@ -9,6 +10,8 @@ use std::mem;
 #[cfg(test)]
 mod tests;
 
+pub use crate::hashes::{Hash128, Hash64};
+
 /// When hashing something that ends up affecting properties like symbol names,
 /// we want these symbol names to be calculated independently of other factors
 /// like what architecture you're compiling *from*.
@@ -20,8 +23,8 @@ pub struct StableHasher {
     state: SipHasher128,
 }
 
-impl ::std::fmt::Debug for StableHasher {
+impl fmt::Debug for StableHasher {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{:?}", self.state)
     }
 }
@@ -42,21 +45,6 @@ impl StableHasher {
     }
 }
 
-impl StableHasherResult for u128 {
-    #[inline]
-    fn finish(hasher: StableHasher) -> Self {
-        let (_0, _1) = hasher.finalize();
-        u128::from(_0) | (u128::from(_1) << 64)
-    }
-}
-
-impl StableHasherResult for u64 {
-    #[inline]
-    fn finish(hasher: StableHasher) -> Self {
-        hasher.finalize().0
-    }
-}
-
 impl StableHasher {
     #[inline]
     pub fn finalize(self) -> (u64, u64) {
@@ -287,6 +275,9 @@ impl_stable_traits_for_trivial_type!(i128);
 impl_stable_traits_for_trivial_type!(char);
 impl_stable_traits_for_trivial_type!(());
 
+impl_stable_traits_for_trivial_type!(Hash64);
+impl_stable_traits_for_trivial_type!(Hash128);
+
 impl<CTX> HashStable<CTX> for ! {
     fn hash_stable(&self, _ctx: &mut CTX, _hasher: &mut StableHasher) {
         unreachable!()
@@ -669,7 +660,7 @@ fn stable_hash_reduce<HCX, I, C, F>(
                 .map(|value| {
                     let mut hasher = StableHasher::new();
                     hash_function(&mut hasher, hcx, value);
-                    hasher.finish::<u128>()
+                    hasher.finish::<Hash128>()
                 })
                 .reduce(|accum, value| accum.wrapping_add(value));
             hash.hash_stable(hcx, hasher);

compiler/rustc_data_structures/src/stable_hasher/tests.rs

@@ -72,7 +72,7 @@ fn test_hash_isize() {
     assert_eq!(h.finalize(), expected);
 }
 
-fn hash<T: HashStable<()>>(t: &T) -> u128 {
+fn hash<T: HashStable<()>>(t: &T) -> Hash128 {
     let mut h = StableHasher::new();
     let ctx = &mut ();
     t.hash_stable(ctx, &mut h);

compiler/rustc_data_structures/src/svh.rs

@@ -24,7 +24,7 @@ impl Svh {
     }
 
     pub fn as_u64(&self) -> u64 {
-        self.hash.to_smaller_hash()
+        self.hash.to_smaller_hash().as_u64()
     }
 
     pub fn to_string(&self) -> String {

compiler/rustc_errors/src/lib.rs

@@ -31,7 +31,7 @@ use Level::*;
 use emitter::{is_case_difference, Emitter, EmitterWriter};
 use registry::Registry;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
-use rustc_data_structures::stable_hasher::StableHasher;
+use rustc_data_structures::stable_hasher::{Hash128, StableHasher};
 use rustc_data_structures::sync::{self, Lock, Lrc};
 use rustc_data_structures::AtomicRef;
 pub use rustc_error_messages::{
@@ -427,7 +427,7 @@ struct HandlerInner {
     /// This set contains a hash of every diagnostic that has been emitted by
     /// this handler. These hashes is used to avoid emitting the same error
     /// twice.
-    emitted_diagnostics: FxHashSet<u128>,
+    emitted_diagnostics: FxHashSet<Hash128>,
 
     /// Stashed diagnostics emitted in one stage of the compiler that may be
     /// stolen by other stages (e.g. to improve them and add more information).

compiler/rustc_hir/src/definitions.rs

@@ -9,7 +9,7 @@ use crate::def_id::{CrateNum, DefIndex, LocalDefId, StableCrateId, CRATE_DEF_IND
 use crate::def_path_hash_map::DefPathHashMap;
 
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::stable_hasher::StableHasher;
+use rustc_data_structures::stable_hasher::{Hash64, StableHasher};
 use rustc_index::vec::IndexVec;
 use rustc_span::symbol::{kw, sym, Symbol};
 
@@ -130,7 +130,7 @@ impl DefKey {
 
         disambiguator.hash(&mut hasher);
 
-        let local_hash: u64 = hasher.finish();
+        let local_hash = hasher.finish();
 
         // Construct the new DefPathHash, making sure that the `crate_id`
         // portion of the hash is properly copied from the parent. This way the
@@ -325,7 +325,7 @@ impl Definitions {
             },
         };
 
-        let parent_hash = DefPathHash::new(stable_crate_id, 0);
+        let parent_hash = DefPathHash::new(stable_crate_id, Hash64::ZERO);
         let def_path_hash = key.compute_stable_hash(parent_hash);
 
         // Create the root definition.

compiler/rustc_hir/src/tests.rs

@@ -1,4 +1,5 @@
 use crate::definitions::{DefKey, DefPathData, DisambiguatedDefPathData};
+use rustc_data_structures::stable_hasher::Hash64;
 use rustc_span::def_id::{DefPathHash, StableCrateId};
 use rustc_span::edition::Edition;
 use rustc_span::{create_session_if_not_set_then, Symbol};
@@ -24,7 +25,7 @@ fn def_path_hash_depends_on_crate_id() {
         assert_ne!(h0.local_hash(), h1.local_hash());
 
         fn mk_test_hash(stable_crate_id: StableCrateId) -> DefPathHash {
-            let parent_hash = DefPathHash::new(stable_crate_id, 0);
+            let parent_hash = DefPathHash::new(stable_crate_id, Hash64::ZERO);
 
             let key = DefKey {
                 parent: None,

compiler/rustc_incremental/src/persist/fs.rs

@@ -601,7 +601,7 @@ fn string_to_timestamp(s: &str) -> Result<SystemTime, ()> {
 fn crate_path(sess: &Session, crate_name: Symbol, stable_crate_id: StableCrateId) -> PathBuf {
     let incr_dir = sess.opts.incremental.as_ref().unwrap().clone();
 
-    let stable_crate_id = base_n::encode(stable_crate_id.to_u64() as u128, INT_ENCODE_BASE);
+    let stable_crate_id = base_n::encode(stable_crate_id.as_u64() as u128, INT_ENCODE_BASE);
 
     let crate_name = format!("{}-{}", crate_name, stable_crate_id);
     incr_dir.join(crate_name)

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -7,7 +7,7 @@ use rustc_ast::Attribute;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::memmap::{Mmap, MmapMut};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash128, HashStable, StableHasher};
 use rustc_data_structures::sync::{join, par_iter, Lrc, ParallelIterator};
 use rustc_data_structures::temp_dir::MaybeTempDir;
 use rustc_hir as hir;
@@ -531,7 +531,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
                         adapted.name_hash = {
                             let mut hasher: StableHasher = StableHasher::new();
                             adapted.name.hash(&mut hasher);
-                            hasher.finish::<u128>()
+                            hasher.finish::<Hash128>()
                         };
                         Lrc::new(adapted)
                     } else {

compiler/rustc_middle/src/dep_graph/dep_node.rs

@@ -357,7 +357,7 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
         Fingerprint::new(
             // `owner` is local, so is completely defined by the local hash
             def_path_hash.local_hash(),
-            local_id.as_u32().into(),
+            local_id.as_u32() as u64,
         )
     }
 
@@ -370,7 +370,7 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
     #[inline(always)]
     fn recover(tcx: TyCtxt<'tcx>, dep_node: &DepNode) -> Option<Self> {
         if tcx.fingerprint_style(dep_node.kind) == FingerprintStyle::HirId {
-            let (local_hash, local_id) = Fingerprint::from(dep_node.hash).as_value();
+            let (local_hash, local_id) = Fingerprint::from(dep_node.hash).split();
             let def_path_hash = DefPathHash::new(tcx.sess.local_stable_crate_id(), local_hash);
             let def_id = tcx
                 .def_path_hash_to_def_id(def_path_hash, &mut || {
@@ -378,6 +378,7 @@ impl<'tcx> DepNodeParams<TyCtxt<'tcx>> for HirId {
                 })
                 .expect_local();
             let local_id = local_id
+                .as_u64()
                 .try_into()
                 .unwrap_or_else(|_| panic!("local id should be u32, found {:?}", local_id));
             Some(HirId { owner: OwnerId { def_id }, local_id: ItemLocalId::from_u32(local_id) })

compiler/rustc_middle/src/middle/exported_symbols.rs

@@ -72,6 +72,6 @@ pub fn metadata_symbol_name(tcx: TyCtxt<'_>) -> String {
     format!(
         "rust_metadata_{}_{:08x}",
         tcx.crate_name(LOCAL_CRATE),
-        tcx.sess.local_stable_crate_id().to_u64(),
+        tcx.sess.local_stable_crate_id(),
     )
 }

compiler/rustc_middle/src/mir/mono.rs

@@ -4,7 +4,7 @@ use rustc_attr::InlineAttr;
 use rustc_data_structures::base_n;
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash128, HashStable, StableHasher};
 use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc_hir::ItemId;
 use rustc_index::vec::Idx;
@@ -313,8 +313,8 @@ impl<'tcx> CodegenUnit<'tcx> {
         // avoid collisions and is still reasonably short for filenames.
         let mut hasher = StableHasher::new();
         human_readable_name.hash(&mut hasher);
-        let hash: u128 = hasher.finish();
+        let hash: Hash128 = hasher.finish();
-        let hash = hash & ((1u128 << 80) - 1);
+        let hash = hash.as_u128() & ((1u128 << 80) - 1);
         base_n::encode(hash, base_n::CASE_INSENSITIVE)
     }
 
@@ -505,22 +505,13 @@ impl<'tcx> CodegenUnitNameBuilder<'tcx> {
             // instantiating stuff for upstream crates.
             let local_crate_id = if cnum != LOCAL_CRATE {
                 let local_stable_crate_id = tcx.sess.local_stable_crate_id();
-                format!(
+                format!("-in-{}.{:08x}", tcx.crate_name(LOCAL_CRATE), local_stable_crate_id)
-                    "-in-{}.{:08x}",
-                    tcx.crate_name(LOCAL_CRATE),
-                    local_stable_crate_id.to_u64() as u32,
-                )
             } else {
                 String::new()
             };
 
             let stable_crate_id = tcx.sess.local_stable_crate_id();
-            format!(
+            format!("{}.{:08x}{}", tcx.crate_name(cnum), stable_crate_id, local_crate_id)
-                "{}.{:08x}{}",
-                tcx.crate_name(cnum),
-                stable_crate_id.to_u64() as u32,
-                local_crate_id,
-            )
         });
 
         write!(cgu_name, "{}", crate_prefix).unwrap();

compiler/rustc_middle/src/ty/consts/int.rs

@@ -141,14 +141,18 @@ impl<CTX> crate::ty::HashStable<CTX> for ScalarInt {
 
 impl<S: Encoder> Encodable<S> for ScalarInt {
     fn encode(&self, s: &mut S) {
-        s.emit_u128(self.data);
+        let size = self.size.get();
-        s.emit_u8(self.size.get());
+        s.emit_u8(size);
+        s.emit_raw_bytes(&self.data.to_le_bytes()[..size as usize]);
     }
 }
 
 impl<D: Decoder> Decodable<D> for ScalarInt {
     fn decode(d: &mut D) -> ScalarInt {
-        ScalarInt { data: d.read_u128(), size: NonZeroU8::new(d.read_u8()).unwrap() }
+        let mut data = [0u8; 16];
+        let size = d.read_u8();
+        data[..size as usize].copy_from_slice(d.read_raw_bytes(size as usize));
+        ScalarInt { data: u128::from_le_bytes(data), size: NonZeroU8::new(size).unwrap() }
     }
 }
 

compiler/rustc_middle/src/ty/context.rs

@@ -925,7 +925,7 @@ impl<'tcx> TyCtxt<'tcx> {
             crate_name,
             // Don't print the whole stable crate id. That's just
             // annoying in debug output.
-            stable_crate_id.to_u64() >> (8 * 6),
+            stable_crate_id.as_u64() >> (8 * 6),
             self.def_path(def_id).to_string_no_crate_verbose()
         )
     }

compiler/rustc_middle/src/ty/util.rs

@@ -11,7 +11,7 @@ use crate::ty::{
 use crate::ty::{GenericArgKind, SubstsRef};
 use rustc_apfloat::Float as _;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
@@ -124,7 +124,7 @@ impl IntTypeExt for IntegerType {
 impl<'tcx> TyCtxt<'tcx> {
     /// Creates a hash of the type `Ty` which will be the same no matter what crate
     /// context it's calculated within. This is used by the `type_id` intrinsic.
-    pub fn type_id_hash(self, ty: Ty<'tcx>) -> u64 {
+    pub fn type_id_hash(self, ty: Ty<'tcx>) -> Hash64 {
         // We want the type_id be independent of the types free regions, so we
         // erase them. The erase_regions() call will also anonymize bound
         // regions, which is desirable too.

compiler/rustc_mir_transform/src/coverage/mod.rs

@@ -577,5 +577,10 @@ fn get_body_span<'tcx>(
 fn hash_mir_source<'tcx>(tcx: TyCtxt<'tcx>, hir_body: &'tcx rustc_hir::Body<'tcx>) -> u64 {
     // FIXME(cjgillot) Stop hashing HIR manually here.
     let owner = hir_body.id().hir_id.owner;
-    tcx.hir_owner_nodes(owner).unwrap().opt_hash_including_bodies.unwrap().to_smaller_hash()
+    tcx.hir_owner_nodes(owner)
+        .unwrap()
+        .opt_hash_including_bodies
+        .unwrap()
+        .to_smaller_hash()
+        .as_u64()
 }

compiler/rustc_query_impl/src/on_disk_cache.rs

@@ -1,6 +1,7 @@
 use crate::QueryCtxt;
 use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::memmap::Mmap;
+use rustc_data_structures::stable_hasher::Hash64;
 use rustc_data_structures::sync::{HashMapExt, Lock, Lrc, RwLock};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_data_structures::unord::UnordSet;
@@ -138,7 +139,7 @@ impl AbsoluteBytePos {
 /// is the only thing available when decoding the cache's [Footer].
 #[derive(Encodable, Decodable, Clone, Debug)]
 struct EncodedSourceFileId {
-    file_name_hash: u64,
+    file_name_hash: Hash64,
     stable_crate_id: StableCrateId,
 }
 
@@ -667,7 +668,7 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for ExpnId {
             #[cfg(debug_assertions)]
             {
                 use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
-                let local_hash: u64 = decoder.tcx.with_stable_hashing_context(|mut hcx| {
+                let local_hash = decoder.tcx.with_stable_hashing_context(|mut hcx| {
                     let mut hasher = StableHasher::new();
                     expn_id.expn_data().hash_stable(&mut hcx, &mut hasher);
                     hasher.finish()

compiler/rustc_query_impl/src/plumbing.rs

@@ -5,7 +5,7 @@
 use crate::on_disk_cache::{CacheDecoder, CacheEncoder, EncodedDepNodeIndex};
 use crate::profiling_support::QueryKeyStringCache;
 use crate::{on_disk_cache, Queries};
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_data_structures::sync::{AtomicU64, Lock};
 use rustc_errors::{Diagnostic, Handler};
 use rustc_middle::dep_graph::{
@@ -342,7 +342,7 @@ pub(crate) fn create_query_frame<
             let mut hasher = StableHasher::new();
             std::mem::discriminant(&kind).hash_stable(&mut hcx, &mut hasher);
             key.hash_stable(&mut hcx, &mut hasher);
-            hasher.finish::<u64>()
+            hasher.finish::<Hash64>()
         })
     };
     let ty_adt_id = key.ty_adt_id();

compiler/rustc_query_system/src/query/mod.rs

@@ -16,6 +16,7 @@ pub use self::config::{HashResult, QueryConfig, TryLoadFromDisk};
 
 use crate::dep_graph::DepKind;
 use crate::dep_graph::{DepNodeIndex, HasDepContext, SerializedDepNodeIndex};
+use rustc_data_structures::stable_hasher::Hash64;
 use rustc_data_structures::sync::Lock;
 use rustc_errors::Diagnostic;
 use rustc_hir::def::DefKind;
@@ -37,7 +38,7 @@ pub struct QueryStackFrame<D: DepKind> {
     /// This hash is used to deterministically pick
     /// a query to remove cycles in the parallel compiler.
     #[cfg(parallel_compiler)]
-    hash: u64,
+    hash: Hash64,
 }
 
 impl<D: DepKind> QueryStackFrame<D> {
@@ -49,7 +50,7 @@ impl<D: DepKind> QueryStackFrame<D> {
         def_kind: Option<DefKind>,
         dep_kind: D,
         ty_adt_id: Option<DefId>,
-        _hash: impl FnOnce() -> u64,
+        _hash: impl FnOnce() -> Hash64,
     ) -> Self {
         Self {
             description,

compiler/rustc_query_system/src/query/plumbing.rs

@@ -573,7 +573,7 @@ where
             // from disk. Re-hashing results is fairly expensive, so we can't
             // currently afford to verify every hash. This subset should still
             // give us some coverage of potential bugs though.
-            let try_verify = prev_fingerprint.as_value().1 % 32 == 0;
+            let try_verify = prev_fingerprint.split().1.as_u64() % 32 == 0;
             if std::intrinsics::unlikely(
                 try_verify || qcx.dep_context().sess().opts.unstable_opts.incremental_verify_ich,
             ) {

compiler/rustc_session/src/session.rs

@@ -811,7 +811,7 @@ impl Session {
     }
 
     pub fn generate_proc_macro_decls_symbol(&self, stable_crate_id: StableCrateId) -> String {
-        format!("__rustc_proc_macro_decls_{:08x}__", stable_crate_id.to_u64())
+        format!("__rustc_proc_macro_decls_{:08x}__", stable_crate_id.as_u64())
     }
 
     pub fn target_filesearch(&self, kind: PathKind) -> filesearch::FileSearch<'_> {

compiler/rustc_span/src/def_id.rs

@@ -1,12 +1,11 @@
 use crate::{HashStableContext, Symbol};
 use rustc_data_structures::fingerprint::Fingerprint;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher, ToStableHashKey};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher, ToStableHashKey};
 use rustc_data_structures::unhash::Unhasher;
 use rustc_data_structures::AtomicRef;
 use rustc_index::vec::Idx;
 use rustc_macros::HashStable_Generic;
 use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
-use std::borrow::Borrow;
 use std::fmt;
 use std::hash::{BuildHasherDefault, Hash, Hasher};
 
@@ -105,20 +104,20 @@ impl DefPathHash {
     /// originates from.
     #[inline]
     pub fn stable_crate_id(&self) -> StableCrateId {
-        StableCrateId(self.0.as_value().0)
+        StableCrateId(self.0.split().0)
     }
 
     /// Returns the crate-local part of the [DefPathHash].
     ///
     /// Used for tests.
     #[inline]
-    pub fn local_hash(&self) -> u64 {
+    pub fn local_hash(&self) -> Hash64 {
-        self.0.as_value().1
+        self.0.split().1
     }
 
     /// Builds a new [DefPathHash] with the given [StableCrateId] and
     /// `local_hash`, where `local_hash` must be unique within its crate.
-    pub fn new(stable_crate_id: StableCrateId, local_hash: u64) -> DefPathHash {
+    pub fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> DefPathHash {
         DefPathHash(Fingerprint::new(stable_crate_id.0, local_hash))
     }
 }
@@ -129,13 +128,6 @@ impl Default for DefPathHash {
     }
 }
 
-impl Borrow<Fingerprint> for DefPathHash {
-    #[inline]
-    fn borrow(&self) -> &Fingerprint {
-        &self.0
-    }
-}
-
 /// A [`StableCrateId`] is a 64-bit hash of a crate name, together with all
 /// `-Cmetadata` arguments, and some other data. It is to [`CrateNum`] what [`DefPathHash`] is to
 /// [`DefId`]. It is stable across compilation sessions.
@@ -147,15 +139,11 @@ impl Borrow<Fingerprint> for DefPathHash {
 ///
 /// For more information on the possibility of hash collisions in rustc,
 /// see the discussion in [`DefId`].
-#[derive(Copy, Clone, Hash, PartialEq, Eq, PartialOrd, Ord, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
-#[derive(HashStable_Generic, Encodable, Decodable)]
+#[derive(Hash, HashStable_Generic, Encodable, Decodable)]
-pub struct StableCrateId(pub(crate) u64);
+pub struct StableCrateId(pub(crate) Hash64);
 
 impl StableCrateId {
-    pub fn to_u64(self) -> u64 {
-        self.0
-    }
-
     /// Computes the stable ID for a crate with the given name and
     /// `-Cmetadata` arguments.
     pub fn new(crate_name: Symbol, is_exe: bool, mut metadata: Vec<String>) -> StableCrateId {
@@ -197,6 +185,17 @@ impl StableCrateId {
 
         StableCrateId(hasher.finish())
     }
+
+    #[inline]
+    pub fn as_u64(self) -> u64 {
+        self.0.as_u64()
+    }
+}
+
+impl fmt::LowerHex for StableCrateId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::LowerHex::fmt(&self.0, f)
+    }
 }
 
 rustc_index::newtype_index! {

compiler/rustc_span/src/hygiene.rs

@@ -33,7 +33,7 @@ use crate::def_id::{CrateNum, DefId, StableCrateId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_data_structures::fingerprint::Fingerprint;
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_data_structures::stable_hasher::HashingControls;
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_data_structures::sync::{Lock, Lrc};
 use rustc_data_structures::unhash::UnhashMap;
 use rustc_index::vec::IndexVec;
@@ -123,15 +123,15 @@ impl ExpnHash {
     /// originates from.
     #[inline]
     pub fn stable_crate_id(self) -> StableCrateId {
-        StableCrateId(self.0.as_value().0)
+        StableCrateId(self.0.split().0)
     }
 
     /// Returns the crate-local part of the [ExpnHash].
     ///
     /// Used for tests.
     #[inline]
-    pub fn local_hash(self) -> u64 {
+    pub fn local_hash(self) -> Hash64 {
-        self.0.as_value().1
+        self.0.split().1
     }
 
     #[inline]
@@ -141,7 +141,7 @@ impl ExpnHash {
 
     /// Builds a new [ExpnHash] with the given [StableCrateId] and
     /// `local_hash`, where `local_hash` must be unique within its crate.
-    fn new(stable_crate_id: StableCrateId, local_hash: u64) -> ExpnHash {
+    fn new(stable_crate_id: StableCrateId, local_hash: Hash64) -> ExpnHash {
         ExpnHash(Fingerprint::new(stable_crate_id.0, local_hash))
     }
 }
@@ -350,7 +350,7 @@ pub struct HygieneData {
     /// would have collisions without a disambiguator.
     /// The keys of this map are always computed with `ExpnData.disambiguator`
     /// set to 0.
-    expn_data_disambiguators: FxHashMap<u64, u32>,
+    expn_data_disambiguators: FxHashMap<Hash64, u32>,
 }
 
 impl HygieneData {
@@ -1040,7 +1040,7 @@ impl ExpnData {
     }
 
     #[inline]
-    fn hash_expn(&self, ctx: &mut impl HashStableContext) -> u64 {
+    fn hash_expn(&self, ctx: &mut impl HashStableContext) -> Hash64 {
         let mut hasher = StableHasher::new();
         self.hash_stable(ctx, &mut hasher);
         hasher.finish()

compiler/rustc_span/src/lib.rs

@@ -59,7 +59,7 @@ pub mod fatal_error;
 
 pub mod profiling;
 
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash128, Hash64, HashStable, StableHasher};
 use rustc_data_structures::sync::{Lock, Lrc};
 
 use std::borrow::Cow;
@@ -282,22 +282,22 @@ impl RealFileName {
 pub enum FileName {
     Real(RealFileName),
     /// Call to `quote!`.
-    QuoteExpansion(u64),
+    QuoteExpansion(Hash64),
     /// Command line.
-    Anon(u64),
+    Anon(Hash64),
     /// Hack in `src/librustc_ast/parse.rs`.
     // FIXME(jseyfried)
-    MacroExpansion(u64),
+    MacroExpansion(Hash64),
-    ProcMacroSourceCode(u64),
+    ProcMacroSourceCode(Hash64),
     /// Strings provided as `--cfg [cfgspec]` stored in a `crate_cfg`.
-    CfgSpec(u64),
+    CfgSpec(Hash64),
     /// Strings provided as crate attributes in the CLI.
-    CliCrateAttr(u64),
+    CliCrateAttr(Hash64),
     /// Custom sources for explicit parser calls from plugins and drivers.
     Custom(String),
     DocTest(PathBuf, isize),
     /// Post-substitution inline assembly from LLVM.
-    InlineAsm(u64),
+    InlineAsm(Hash64),
 }
 
 impl From<PathBuf> for FileName {
@@ -1343,7 +1343,7 @@ pub struct SourceFile {
     /// Locations of characters removed during normalization.
     pub normalized_pos: Vec<NormalizedPos>,
     /// A hash of the filename, used for speeding up hashing in incremental compilation.
-    pub name_hash: u128,
+    pub name_hash: Hash128,
     /// Indicates which crate this `SourceFile` was imported from.
     pub cnum: CrateNum,
 }
@@ -1472,7 +1472,7 @@ impl<D: Decoder> Decodable<D> for SourceFile {
         };
         let multibyte_chars: Vec<MultiByteChar> = Decodable::decode(d);
         let non_narrow_chars: Vec<NonNarrowChar> = Decodable::decode(d);
-        let name_hash: u128 = Decodable::decode(d);
+        let name_hash = Decodable::decode(d);
         let normalized_pos: Vec<NormalizedPos> = Decodable::decode(d);
         let cnum: CrateNum = Decodable::decode(d);
         SourceFile {
@@ -1514,7 +1514,7 @@ impl SourceFile {
         let name_hash = {
             let mut hasher: StableHasher = StableHasher::new();
             name.hash(&mut hasher);
-            hasher.finish::<u128>()
+            hasher.finish()
         };
         let end_pos = start_pos.to_usize() + src.len();
         assert!(end_pos <= u32::MAX as usize);

compiler/rustc_span/src/source_map.rs

@@ -13,7 +13,7 @@ pub use crate::hygiene::{ExpnData, ExpnKind};
 pub use crate::*;
 
 use rustc_data_structures::fx::FxHashMap;
-use rustc_data_structures::stable_hasher::StableHasher;
+use rustc_data_structures::stable_hasher::{Hash128, Hash64, StableHasher};
 use rustc_data_structures::sync::{AtomicU32, Lrc, MappedReadGuard, ReadGuard, RwLock};
 use std::cmp;
 use std::hash::Hash;
@@ -138,7 +138,7 @@ impl FileLoader for RealFileLoader {
 pub struct StableSourceFileId {
     /// A hash of the source file's [`FileName`]. This is hash so that it's size
     /// is more predictable than if we included the actual [`FileName`] value.
-    pub file_name_hash: u64,
+    pub file_name_hash: Hash64,
 
     /// The [`CrateNum`] of the crate this source file was originally parsed for.
     /// We cannot include this information in the hash because at the time
@@ -331,7 +331,7 @@ impl SourceMap {
         &self,
         filename: FileName,
         src_hash: SourceFileHash,
-        name_hash: u128,
+        name_hash: Hash128,
         source_len: usize,
         cnum: CrateNum,
         file_local_lines: Lock<SourceFileLines>,

compiler/rustc_span/src/tests.rs

@@ -3,8 +3,12 @@ use super::*;
 #[test]
 fn test_lookup_line() {
     let source = "abcdefghijklm\nabcdefghij\n...".to_owned();
-    let sf =
+    let sf = SourceFile::new(
-        SourceFile::new(FileName::Anon(0), source, BytePos(3), SourceFileHashAlgorithm::Sha256);
+        FileName::Anon(Hash64::ZERO),
+        source,
+        BytePos(3),
+        SourceFileHashAlgorithm::Sha256,
+    );
     sf.lines(|lines| assert_eq!(lines, &[BytePos(3), BytePos(17), BytePos(28)]));
 
     assert_eq!(sf.lookup_line(BytePos(0)), None);

compiler/rustc_symbol_mangling/src/legacy.rs

@@ -1,4 +1,4 @@
-use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
+use rustc_data_structures::stable_hasher::{Hash64, HashStable, StableHasher};
 use rustc_hir::def_id::CrateNum;
 use rustc_hir::definitions::{DefPathData, DisambiguatedDefPathData};
 use rustc_middle::ty::print::{PrettyPrinter, Print, Printer};
@@ -93,7 +93,7 @@ fn get_symbol_hash<'tcx>(
     item_type: Ty<'tcx>,
 
     instantiating_crate: Option<CrateNum>,
-) -> u64 {
+) -> Hash64 {
     let def_id = instance.def_id();
     let substs = instance.substs;
     debug!("get_symbol_hash(def_id={:?}, parameters={:?})", def_id, substs);
@@ -138,7 +138,7 @@ fn get_symbol_hash<'tcx>(
         });
 
         // 64 bits should be enough to avoid collisions.
-        hasher.finish::<u64>()
+        hasher.finish::<Hash64>()
     })
 }
 
@@ -176,7 +176,7 @@ impl SymbolPath {
         }
     }
 
-    fn finish(mut self, hash: u64) -> String {
+    fn finish(mut self, hash: Hash64) -> String {
         self.finalize_pending_component();
         // E = end name-sequence
         let _ = write!(self.result, "17h{hash:016x}E");

compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -406,7 +406,7 @@ fn encode_ty_name(tcx: TyCtxt<'_>, def_id: DefId) -> String {
 
     // Crate disambiguator and name
     s.push('C');
-    s.push_str(&to_disambiguator(tcx.stable_crate_id(def_path.krate).to_u64()));
+    s.push_str(&to_disambiguator(tcx.stable_crate_id(def_path.krate).as_u64()));
     let crate_name = tcx.crate_name(def_path.krate).to_string();
     let _ = write!(s, "{}{}", crate_name.len(), &crate_name);
 

compiler/rustc_symbol_mangling/src/v0.rs

@@ -731,7 +731,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
     fn path_crate(self, cnum: CrateNum) -> Result<Self::Path, Self::Error> {
         self.push("C");
         let stable_crate_id = self.tcx.def_path_hash(cnum.as_def_id()).stable_crate_id();
-        self.push_disambiguator(stable_crate_id.to_u64());
+        self.push_disambiguator(stable_crate_id.as_u64());
         let name = self.tcx.crate_name(cnum);
         self.push_ident(name.as_str());
         Ok(self)