Memoize class sorting

cppwg/input/module_info.py

@@ -85,6 +85,46 @@ def sort_classes(self) -> None:
         """
         Sort the class info collection in order of dependence.
         """
+        cache = dict()
+
+        def compare(a: CppClassInfo, b: CppClassInfo) -> int:
+            """
+            Compare two class info objects for dependence order.
+
+            Parameters
+            ----------
+            a : CppClassInfo
+            b : CppClassInfo
+
+            Returns
+            -------
+            int
+                -1 if a comes before b (b depends on a)
+                 0 if there is no dependence
+                 1 if a comes after b (a depends on b)
+            """
+            order = cache.get((a, b), None)
+            if order is not None:
+                return order
+
+            a_req_b = a.requires(b)
+            b_req_a = b.requires(a)
+            if a.is_child_of(b) or (a_req_b and not b_req_a):
+                # a comes after b (ignore cyclic dependencies)
+                cache[(a, b)] = 1
+                cache[(b, a)] = -1
+                return 1
+            elif b.is_child_of(a) or (b_req_a and not a_req_b):
+                # a comes before b (ignore cyclic dependencies)
+                cache[(a, b)] = -1
+                cache[(b, a)] = 1
+                return -1
+
+            # Order doesn't matter
+            cache[(a, b)] = 0
+            cache[(b, a)] = 0
+            return 0
+
         self.class_info_collection.sort(key=lambda x: x.name)
 
         i = 0
@@ -96,13 +136,11 @@ def sort_classes(self) -> None:
 
             for j in range(i + 1, n):
                 cls_j = self.class_info_collection[j]
-                i_req_j = cls_i.requires(cls_j)
-                j_req_i = cls_j.requires(cls_i)
-                if cls_i.is_child_of(cls_j) or (i_req_j and not j_req_i):
-                    # Position cls_i after all classes it depends on,
-                    # ignoring forward declaration cycles
+                order = compare(cls_i, cls_j)
+                if order == 1:
+                    # Position cls_i after all classes it depends on
                     ii = j
-                elif cls_j.is_child_of(cls_i) or (j_req_i and not i_req_j):
+                elif order == -1:
                     # Collect positions of cls_i's dependents
                     j_pos.append(j)