perf: cache visited exprs at `CheckAssignmentQuick`

src/Lean/Meta/ExprDefEq.lean

diff --git a/src/Lean/Meta/ExprDefEq.lean b/src/Lean/Meta/ExprDefEq.lean
index 0750964..12f2447 100644
--- a/src/Lean/Meta/ExprDefEq.lean
+++ b/src/Lean/Meta/ExprDefEq.lean
@@ -895,23 +895,27 @@
 
 namespace CheckAssignmentQuick
 
-partial def check
+unsafe def checkImpl
     (hasCtxLocals : Bool)
     (mctx : MetavarContext) (lctx : LocalContext) (mvarDecl : MetavarDecl) (mvarId : MVarId) (fvars : Array Expr) (e : Expr) : Bool :=
-  let rec visit (e : Expr) : Bool := Id.run do
+  let rec visit (e : Expr) : StateM (PtrSet Expr) Bool := do
     if !e.hasExprMVar && !e.hasFVar then
       return true
+    if (← get).contains e then
+      return true
+    modify fun visited => visited.insert e
     match e with
     | .mdata _ b       => visit b
     | .proj _ _ s      => visit s
-    | .app f a         => visit f && visit a
-    | .lam _ d b _     => visit d && visit b
-    | .forallE _ d b _ => visit d && visit b
-    | .letE _ t v b _  => visit t && visit v && visit b
+    | .app f a         => visit f <&&> visit a
+    | .lam _ d b _     => visit d <&&> visit b
+    | .forallE _ d b _ => visit d <&&> visit b
+    | .letE _ t v b _  => visit t <&&> visit v <&&> visit b
     | .bvar .. | .sort .. | .const ..
     | .lit .. => return true
     | .fvar fvarId ..  =>
-      if mvarDecl.lctx.contains fvarId then return true
+      if mvarDecl.lctx.contains fvarId then
+        return true
       if let some (LocalDecl.ldecl ..) := lctx.find? fvarId then
         return false -- need expensive CheckAssignment.check
       if fvars.any fun x => x.fvarId! == fvarId then
@@ -925,7 +929,13 @@
       if !mvarDecl'.lctx.isSubPrefixOf mvarDecl.lctx fvars then return false -- use CheckAssignment.check
       let none := mctx.getDelayedMVarAssignmentCore? mvarId' | return false -- use CheckAssignment.check
       return true
-  visit e
+  if !e.hasExprMVar && !e.hasFVar then
+    true
+  else
+    visit e |>.run' mkPtrSet
+
+def check (hasCtxLocals : Bool) (mctx : MetavarContext) (lctx : LocalContext) (mvarDecl : MetavarDecl) (mvarId : MVarId) (fvars : Array Expr) (e : Expr) : Bool :=
+  unsafe checkImpl hasCtxLocals mctx lctx mvarDecl mvarId fvars e
 
 end CheckAssignmentQuick