[Custom Descriptors] Optimize descriptors in AbstractTypeRefining (#7738)

Now that we no longer change subtype relationships in
AbstractTypeRefining, it is straightforward to optimize descriptor and
described types.

Author: tlively

src/passes/AbstractTypeRefining.cpp

@@ -112,15 +112,12 @@ struct AbstractTypeRefining : public Pass {
     //       module, given closed world, but we'd also need to make sure that
     //       we don't need to make any changes to public types that refer to
     //       them.
-    // Similarly, treat all descriptor and described types as allocated because
-    // we cannot yet optimize them correctly.
     auto heapTypes = ModuleUtils::collectHeapTypeInfo(
       *module,
       ModuleUtils::TypeInclusion::AllTypes,
       ModuleUtils::VisibilityHandling::FindVisibility);
     for (auto& [type, info] : heapTypes) {
-      if (info.visibility == ModuleUtils::Visibility::Public ||
-          type.getDescribedType() || type.getDescriptorType()) {
+      if (info.visibility == ModuleUtils::Visibility::Public) {
         createdTypes.insert(type);
       }
     }

test/lit/passes/abstract-type-refining-desc.wast

@@ -38,3 +38,37 @@
     )
   )
 )
+
+(module
+  ;; Same as above, but now we should see references to $A.desc and $B.desc
+  ;; optimized to nullref because they are not instantiated. Similarly, $A is
+  ;; optimized to $B with TNH.
+  (rec
+    ;; YESTNH:      (rec
+    ;; YESTNH-NEXT:  (type $A (sub (descriptor $A.desc (struct (field (ref null $B)) (field (ref null $B))))))
+    ;; NO_TNH:      (rec
+    ;; NO_TNH-NEXT:  (type $A (sub (descriptor $A.desc (struct (field (ref null $A)) (field (ref null $B))))))
+    (type $A (sub (descriptor $A.desc (struct (field (ref null $A) (ref null $B))))))
+    ;; YESTNH:       (type $A.desc (sub (describes $A (struct (field nullref) (field nullref)))))
+    ;; NO_TNH:       (type $A.desc (sub (describes $A (struct (field nullref) (field nullref)))))
+    (type $A.desc (sub (describes $A (struct (field (ref null $A.desc) (ref null $B.desc))))))
+    ;; YESTNH:       (type $B (sub $A (descriptor $B.desc (struct (field (ref null $B)) (field (ref null $B))))))
+    ;; NO_TNH:       (type $B (sub $A (descriptor $B.desc (struct (field (ref null $A)) (field (ref null $B))))))
+    (type $B (sub $A (descriptor $B.desc (struct (field (ref null $A) (ref null $B))))))
+    ;; YESTNH:       (type $B.desc (sub $A.desc (describes $B (struct (field nullref) (field nullref)))))
+    ;; NO_TNH:       (type $B.desc (sub $A.desc (describes $B (struct (field nullref) (field nullref)))))
+    (type $B.desc (sub $A.desc (describes $B (struct (field (ref null $A.desc) (ref null $B.desc))))))
+  )
+
+  ;; YESTNH:      (global $g (ref (exact $B)) (struct.new_default $B
+  ;; YESTNH-NEXT:  (ref.null none)
+  ;; YESTNH-NEXT: ))
+  ;; NO_TNH:      (global $g (ref (exact $B)) (struct.new_default $B
+  ;; NO_TNH-NEXT:  (ref.null none)
+  ;; NO_TNH-NEXT: ))
+  (global $g (ref (exact $B))
+    (struct.new_default $B
+      (ref.null none)
+    )
+  )
+)