compiler: Introduce Terminal mixin for SymPy subclasses

Author: FabioLuporini

devito/symbolics/extended_sympy.py

@@ -19,7 +19,7 @@
 from devito.types.basic import Basic
 
 __all__ = ['CondEq', 'CondNe', 'BitwiseNot', 'BitwiseXor', 'BitwiseAnd',  # noqa
-           'LeftShift', 'RightShift', 'IntDiv',  'CallFromPointer',
+           'LeftShift', 'RightShift', 'IntDiv', 'Terminal', 'CallFromPointer',
            'CallFromComposite', 'FieldFromPointer', 'FieldFromComposite',
            'ListInitializer', 'Byref', 'IndexedPointer', 'Cast', 'DefFunction',
            'MathFunction', 'InlineIf', 'Reserved', 'ReservedWord', 'Keyword',
@@ -148,6 +148,17 @@ def __mul__(self, other):
         return super().__mul__(other)
 
 
+class Terminal:
+
+    """
+    Abstract base class for all terminal objects, that is, those objects
+    collected by `retrieve_terminals` in addition to all other SymPy atoms
+    such as `Symbol`, `Number`, etc.
+    """
+
+    pass
+
+
 class BasicWrapperMixin:
 
     """
@@ -189,7 +200,7 @@ def _sympystr(self, printer):
         return str(self)
 
 
-class CallFromPointer(sympy.Expr, Pickable, BasicWrapperMixin):
+class CallFromPointer(Expr, Pickable, BasicWrapperMixin, Terminal):
 
     """
     Symbolic representation of the C notation ``pointer->call(params)``.
@@ -257,7 +268,7 @@ def free_symbols(self):
     __reduce_ex__ = Pickable.__reduce_ex__
 
 
-class CallFromComposite(CallFromPointer, Pickable):
+class CallFromComposite(CallFromPointer):
 
     """
     Symbolic representation of the C notation ``composite.call(params)``.
@@ -270,7 +281,7 @@ def __str__(self):
     __repr__ = __str__
 
 
-class FieldFromPointer(CallFromPointer, Pickable):
+class FieldFromPointer(CallFromPointer):
 
     """
     Symbolic representation of the C notation ``pointer->field``.
@@ -291,7 +302,7 @@ def field(self):
     __repr__ = __str__
 
 
-class FieldFromComposite(CallFromPointer, Pickable):
+class FieldFromComposite(CallFromPointer):
 
     """
     Symbolic representation of the C notation ``composite.field``,
@@ -353,7 +364,7 @@ def is_numeric(self):
     __reduce_ex__ = Pickable.__reduce_ex__
 
 
-class UnaryOp(sympy.Expr, Pickable, BasicWrapperMixin):
+class UnaryOp(Expr, Pickable, BasicWrapperMixin):
 
     """
     Symbolic representation of a unary C operator.
@@ -486,7 +497,7 @@ def __str__(self):
         return f"{self._op}{self.base}"
 
 
-class IndexedPointer(sympy.Expr, Pickable, BasicWrapperMixin):
+class IndexedPointer(Expr, Pickable, BasicWrapperMixin, Terminal):
 
     """
     Symbolic representation of the C notation ``symbol[...]``

devito/symbolics/queries.py

@@ -1,8 +1,6 @@
 from sympy import Eq, IndexedBase, Mod, S, diff, nan
 
-from devito.symbolics.extended_sympy import (
-    FieldFromComposite, FieldFromPointer, IndexedPointer, IntDiv
-)
+from devito.symbolics.extended_sympy import IntDiv, Terminal
 from devito.tools import as_tuple, is_integer
 from devito.types.array import ComponentAccess
 from devito.types.basic import AbstractFunction
@@ -32,13 +30,9 @@
 ]
 
 
-# The following SymPy objects are considered tree leaves:
-#
-# * Number
-# * Symbol
-# * Indexed
-extra_leaves = (FieldFromPointer, FieldFromComposite, IndexedBase, AbstractObject,
-                IndexedPointer)
+# The following SymPy objects are considered tree leaves in addition to the classic
+# SymPy atoms such as Number, Symbol, Indexed, etc
+extra_leaves = (IndexedBase, AbstractObject, Terminal)
 
 
 def q_symbol(expr):