Auto merge of #110367 - saethlin:no-truncations, r=oli-obk

Remove some suspicious cast truncations

These truncations were added a long time ago, and as best I can tell without a perf justification. And with rust-lang/rust#110410 it has become perf-neutral to not truncate anymore. We worked hard for all these bits, let's use them.

compiler/rustc_data_structures/src/svh.rs

@@ -5,40 +5,30 @@
 //! mismatches where we have two versions of the same crate that were
 //! compiled from distinct sources.
 
-use rustc_serialize::{Decodable, Decoder, Encodable, Encoder};
+use crate::fingerprint::Fingerprint;
 use std::fmt;
-use std::hash::{Hash, Hasher};
 
 use crate::stable_hasher;
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Encodable, Decodable, Hash)]
 pub struct Svh {
-    hash: u64,
+    hash: Fingerprint,
 }
 
 impl Svh {
     /// Creates a new `Svh` given the hash. If you actually want to
     /// compute the SVH from some HIR, you want the `calculate_svh`
     /// function found in `rustc_incremental`.
-    pub fn new(hash: u64) -> Svh {
+    pub fn new(hash: Fingerprint) -> Svh {
         Svh { hash }
     }
 
     pub fn as_u64(&self) -> u64 {
-        self.hash
+        self.hash.to_smaller_hash()
     }
 
     pub fn to_string(&self) -> String {
-        format!("{:016x}", self.hash)
-    }
-}
-
-impl Hash for Svh {
-    fn hash<H>(&self, state: &mut H)
-    where
-        H: Hasher,
-    {
-        self.hash.to_le().hash(state);
+        format!("{:016x}", self.hash.to_smaller_hash())
     }
 }
 
@@ -48,18 +38,6 @@ impl fmt::Display for Svh {
     }
 }
 
-impl<S: Encoder> Encodable<S> for Svh {
-    fn encode(&self, s: &mut S) {
-        s.emit_u64(self.as_u64().to_le());
-    }
-}
-
-impl<D: Decoder> Decodable<D> for Svh {
-    fn decode(d: &mut D) -> Svh {
-        Svh::new(u64::from_le(d.read_u64()))
-    }
-}
-
 impl<T> stable_hasher::HashStable<T> for Svh {
     #[inline]
     fn hash_stable(&self, ctx: &mut T, hasher: &mut stable_hasher::StableHasher) {