compiler: Avoid CSE across Reserved keywords

Author: FabioLuporini

devito/passes/clusters/cse.py

@@ -12,7 +12,7 @@
 
 from devito.finite_differences.differentiable import IndexDerivative
 from devito.ir import Cluster, Scope, cluster_pass
-from devito.symbolics import estimate_cost, q_leaf, q_terminal
+from devito.symbolics import Reserved, estimate_cost, q_leaf, q_terminal
 from devito.symbolics.search import search
 from devito.symbolics.manipulation import _uxreplace
 from devito.tools import DAG, as_list, as_tuple, frozendict, extract_dtype
@@ -401,6 +401,7 @@ def _(expr):
 
 @_catch.register(Indexed)
 @_catch.register(Symbol)
+@_catch.register(Reserved)
 def _(expr):
     """
     Handler for objects preventing CSE to propagate through their arguments.

devito/symbolics/extended_sympy.py

@@ -18,12 +18,12 @@
 from devito.types.basic import Basic
 
 __all__ = ['CondEq', 'CondNe', 'BitwiseNot', 'BitwiseXor', 'BitwiseAnd',  # noqa
-           'LeftShift', 'RightShift', 'IntDiv', 'CallFromPointer',
+           'LeftShift', 'RightShift', 'IntDiv',  'CallFromPointer',
            'CallFromComposite', 'FieldFromPointer', 'FieldFromComposite',
            'ListInitializer', 'Byref', 'IndexedPointer', 'Cast', 'DefFunction',
-           'MathFunction', 'InlineIf', 'ReservedWord', 'Keyword', 'String',
-           'Macro', 'Class', 'MacroArgument', 'Deref', 'Namespace', 'Rvalue',
-           'Null', 'SizeOf', 'rfunc', 'BasicWrapperMixin', 'ValueLimit',
+           'MathFunction', 'InlineIf', 'Reserved', 'ReservedWord', 'Keyword',
+           'String', 'Macro', 'Class', 'MacroArgument', 'Deref', 'Namespace',
+           'Rvalue', 'Null', 'SizeOf', 'rfunc', 'BasicWrapperMixin', 'ValueLimit',
            'VectorAccess']
 
 
@@ -537,7 +537,21 @@ def __str__(self):
     __reduce_ex__ = Pickable.__reduce_ex__
 
 
-class ReservedWord(sympy.Atom, Pickable):
+class Reserved(Pickable):
+
+    """
+    A base class for all reserved words used throughout the lowering process,
+    including the final stage of code generation itself.
+
+    Reserved objects have the following properties:
+
+        * `estimate_cost(o) = 0`, where `o` is an instance of Reserved
+    """
+
+    pass
+
+
+class ReservedWord(sympy.Atom, Reserved):
 
     """
     A `ReservedWord` carries a value that has special meaning in the

devito/symbolics/inspection.py

@@ -10,8 +10,9 @@
 from devito.finite_differences.differentiable import IndexDerivative
 from devito.logger import warning
 from devito.symbolics.extended_dtypes import INT
-from devito.symbolics.extended_sympy import (CallFromPointer, Cast,
-                                             DefFunction, ReservedWord)
+from devito.symbolics.extended_sympy import (
+    CallFromPointer, Cast, DefFunction, Reserved
+)
 from devito.symbolics.queries import q_routine
 from devito.tools import as_tuple, prod, is_integer
 from devito.tools.dtypes_lowering import infer_dtype
@@ -175,7 +176,7 @@ def _(expr, estimate, seen):
 
 @_estimate_cost.register(ImaginaryUnit)
 @_estimate_cost.register(Number)
-@_estimate_cost.register(ReservedWord)
+@_estimate_cost.register(Reserved)
 def _(expr, estimate, seen):
     return 0, False