Auto merge of #25070 - dotdash:inline_hash, r=alexcrichton

Since the hashmap and its hasher are implemented in different crates, we
currently can't benefit from inlining, which means that especially for
small, fixed size keys, there is a huge overhead in hash calculations,
because the compiler can't apply optimizations that only apply for these
keys.

Fixes the brainfuck benchmark in #24014.

src/libcore/hash/sip.rs

@@ -111,6 +111,7 @@ impl SipHasher {
         state
     }
 
+    #[inline]
     fn reset(&mut self) {
         self.length = 0;
         self.v0 = self.k0 ^ 0x736f6d6570736575;
@@ -120,6 +121,7 @@ impl SipHasher {
         self.ntail = 0;
     }
 
+    #[inline]
     fn write(&mut self, msg: &[u8]) {
         let length = msg.len();
         self.length += length;
@@ -173,6 +175,7 @@ impl Hasher for SipHasher {
         self.write(msg)
     }
 
+    #[inline]
     fn finish(&self) -> u64 {
         let mut v0 = self.v0;
         let mut v1 = self.v1;

src/libstd/collections/hash/map.rs

@@ -1600,6 +1600,7 @@ impl RandomState {
            reason = "hashing an hash maps may be altered")]
 impl HashState for RandomState {
     type Hasher = SipHasher;
+    #[inline]
     fn hasher(&self) -> SipHasher {
         SipHasher::new_with_keys(self.k0, self.k1)
     }