compiler: Add LocalType._C_tag

Author: FabioLuporini

devito/ir/iet/visitors.py

@@ -321,6 +321,9 @@ def _gen_value(self, obj, mode=1, masked=()):
         qualifiers = [v for k, v in self._qualifiers_mapper.items()
                       if getattr(obj.function, k, False) and v not in masked]
 
+        if obj.is_LocalObject and mode == 2:
+            qualifiers.extend(as_tuple(obj._C_tag))
+
         if (obj._mem_stack or obj._mem_constant) and mode == 1:
             strtype = self.ccode(obj._C_typedata)
             strshape = ''.join(f'[{self.ccode(i)}]' for i in obj.symbolic_shape)

devito/types/basic.py

@@ -1937,8 +1937,17 @@ def _mem_internal_lazy(self):
         return self._liveness == 'lazy'
 
     """
-    A modifier added to the subclass C declaration when it appears
-    in a function signature. For example, a subclass might define `_C_modifier = '&'`
+    A modifier added to the declaration of the LocalType when it appears in a
+    function signature. For example, a subclass might define `_C_modifier = '&'`
     to impose pass-by-reference semantics.
     """
     _C_modifier = None
+
+    """
+    One or more optional keywords added to the declaration of the LocalType
+    in between the type and the variable name when it appears in a function
+    signature. For example, some languages support these to modify the way
+    the compiler generates code for passing the parameter and how the
+    runtime accesses it.
+    """
+    _C_tag = None