compiler: Introduce operator lookup hook

devito/operator/operator.py

@@ -182,6 +182,12 @@ def __new__(cls, expressions, **kwargs):
         cls._check_kwargs(**kwargs)
         expressions = cls._sanitize_exprs(expressions, **kwargs)
 
+        # Hook for retrieval of preexisting operators
+        # TODO: should this emit timing info if an operator is retrieved
+        maybe_op = cls._retrieve_op(expressions, **kwargs)
+        if maybe_op:
+            return maybe_op
+
         # Lower to a JIT-compilable object
         with timed_region('op-compile') as r:
             op = cls._build(expressions, **kwargs)
@@ -211,6 +217,10 @@ def _sanitize_exprs(cls, expressions, **kwargs):
 
         return expressions
 
+    @classmethod
+    def _retrieve_op(cls, expressions, **kwargs):
+        return
+
     @classmethod
     def _build(cls, expressions, **kwargs):
         # Python- (i.e., compile-) and C-level (i.e., run-time) performance

devito/types/equation.py

@@ -183,6 +183,9 @@ def xreplace(self, rules):
         return self.func(self.lhs.xreplace(rules), self.rhs.xreplace(rules))
 
     def __str__(self):
+        if self._subdomain is not None:
+            return (f"{self.__class__.__name__}({self.lhs}, {self.rhs},"
+                    f" subdomain={self._subdomain})")
         return f"{self.__class__.__name__}({self.lhs}, {self.rhs})"
 
     __repr__ = __str__