compiler: Start work on hook for operator lookup

Author: EdCaunt

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_opt(cls, expressions, **kwargs):
+        return
+
     @classmethod
     def _build(cls, expressions, **kwargs):
         # Python- (i.e., compile-) and C-level (i.e., run-time) performance