From c0acb066b4503a407ee13f7b99a3a7111bcdfc82 Mon Sep 17 00:00:00 2001
From: Markus Westerlind <marwes91@gmail.com>
Date: Sat, 26 Jan 2019 21:50:35 +0100
Subject: [PATCH] perf: Avoid recursing more in occurs check

---
 base/src/types/mod.rs     | 25 +++++++++++++++++++++----
 check/src/substitution.rs | 20 ++++++++------------
 2 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/base/src/types/mod.rs b/base/src/types/mod.rs
index a2403ecd3b..329d5c499e 100644
--- a/base/src/types/mod.rs
+++ b/base/src/types/mod.rs
@@ -2527,7 +2527,6 @@ where
     I: 'a,
 {
     match **typ {
-        Type::Forall(_, ref typ) => f.walk(typ),
         Type::Function(_, ref arg, ref ret) => {
             f.walk(arg);
             f.walk(ret);
@@ -2538,7 +2537,10 @@ where
                 f.walk(a);
             }
         }
-        Type::Record(ref row) | Type::Variant(ref row) | Type::Effect(ref row) => f.walk(row),
+        Type::Forall(_, ref typ)
+        | Type::Record(ref typ)
+        | Type::Variant(ref typ)
+        | Type::Effect(ref typ) => f.walk(typ),
         Type::ExtendRow {
             ref types,
             ref fields,
@@ -3442,9 +3444,24 @@ where
     }
 }
 
-impl<'a, I, T, F: ?Sized> Walker<'a, T> for F
+pub struct FlagsVisitor<F: ?Sized>(pub Flags, pub F);
+
+impl<'a, T, F> Walker<'a, T> for FlagsVisitor<F>
+where
+    F: ?Sized + FnMut(&'a T),
+    T: TypeExt + 'a,
+{
+    fn walk(&mut self, typ: &'a T) {
+        if self.0.intersects(typ.flags()) {
+            (self.1)(typ);
+            walk_type_(typ, self);
+        }
+    }
+}
+
+impl<'a, I, T, F> Walker<'a, T> for F
 where
-    F: FnMut(&'a T),
+    F: ?Sized + FnMut(&'a T),
     T: Deref<Target = Type<I, T>> + 'a,
     I: 'a,
 {
diff --git a/check/src/substitution.rs b/check/src/substitution.rs
index aa23dbc9de..5563e29979 100644
--- a/check/src/substitution.rs
+++ b/check/src/substitution.rs
@@ -158,7 +158,7 @@ where
         T: Substitutable,
     {
         fn walk(&mut self, typ: &'t T) {
-            if self.occurs {
+            if !typ.contains_variables() || self.occurs {
                 return;
             }
             let typ = self.subs.real(typ);
@@ -174,17 +174,13 @@ where
         }
     }
 
-    if typ.contains_variables() {
-        let mut occurs = Occurs {
-            occurs: false,
-            var: var,
-            subs: subs,
-        };
-        occurs.walk(typ);
-        occurs.occurs
-    } else {
-        false
-    }
+    let mut occurs = Occurs {
+        occurs: false,
+        var: var,
+        subs: subs,
+    };
+    occurs.walk(typ);
+    occurs.occurs
 }
 
 /// Specialized union implementation which makes sure that variables with a higher level always