peepmatic: Make the results of match operations a smaller and more cache friendly

cranelift/peepmatic/crates/runtime/src/integer_interner.rs

@@ -7,11 +7,11 @@
 
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
-use std::convert::TryInto;
+use std::num::NonZeroU32;
 
 /// An identifier for an interned integer.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
-pub struct IntegerId(#[doc(hidden)] pub u32);
+pub struct IntegerId(#[doc(hidden)] pub NonZeroU32);
 
 /// An interner for integer values.
 #[derive(Debug, Default, Serialize, Deserialize)]
@@ -40,7 +40,8 @@ impl IntegerInterner {
             return *id;
         }
 
-        let id = IntegerId(self.values.len().try_into().unwrap());
+        assert!((self.values.len() as u64) < (std::u32::MAX as u64));
+        let id = IntegerId(unsafe { NonZeroU32::new_unchecked(self.values.len() as u32 + 1) });
 
         self.values.push(value);
         self.map.insert(value, id);
@@ -59,13 +60,21 @@ impl IntegerInterner {
     /// Lookup a previously interned integer by id.
     #[inline]
     pub fn lookup(&self, id: IntegerId) -> u64 {
-        self.values[id.0 as usize]
+        let index = id.0.get() as usize - 1;
+        self.values[index]
     }
 }
 
 impl From<IntegerId> for u32 {
     #[inline]
     fn from(id: IntegerId) -> u32 {
+        id.0.get()
+    }
+}
+
+impl From<IntegerId> for NonZeroU32 {
+    #[inline]
+    fn from(id: IntegerId) -> NonZeroU32 {
         id.0
     }
 }