Update should_unify to use the enum

compiler/noirc_evaluator/src/ssa/opt/mem2reg/alias_set.rs

@@ -46,6 +46,10 @@ impl AliasSet {
         matches!(self, AliasSet::Unknown)
     }
 
+    pub(super) fn is_empty(&self) -> bool {
+        matches!(self, AliasSet::Empty)
+    }
+
     /// Return the single known alias if there is exactly one.
     /// Otherwise, return None.
     pub(super) fn single_alias(&self) -> Option<ValueId> {
@@ -94,12 +98,21 @@ impl AliasSet {
     /// This is an optimization to avoid having to look up an entry ready to be modified in the [Block](crate::ssa::opt::mem2reg::block::Block),
     /// because doing so would involve calling `Arc::make_mut` which clones the entry, ready for modification.
     pub(super) fn should_unify(&self, other: &Self) -> bool {
-        if let (Some(self_aliases), Some(other_aliases)) = (&self.aliases, &other.aliases) {
-            // `unify` would extend `self_aliases` with `other_aliases`, so if `other_aliases` is a subset, then nothing would happen.
-            !other_aliases.is_subset(self_aliases)
-        } else {
-            // `unify` would set `aliases` to `None`, so if it's not `Some`, then nothing would happen.
-            self.aliases.is_some()
+        match self {
+            AliasSet::Unknown => false,
+            AliasSet::Empty => !other.is_empty(),
+            AliasSet::Known(id) => match other {
+                AliasSet::Unknown => !self.is_unknown(),
+                AliasSet::Empty => false,
+                AliasSet::Known(other_id) => id != other_id,
+                AliasSet::KnownMultiple(_) => true,
+            },
+            AliasSet::KnownMultiple(values) => match other {
+                AliasSet::Unknown => !self.is_unknown(),
+                AliasSet::Empty => false,
+                AliasSet::Known(other_id) => values.contains(other_id),
+                AliasSet::KnownMultiple(other_values) => !other_values.is_subset(values),
+            },
         }
     }