compiler: Ensure Weights always get printed before any other expr

devito/finite_differences/differentiable.py

@@ -749,6 +749,12 @@ def __init_finalize__(self, *args, **kwargs):
 
         super().__init_finalize__(*args, **kwargs)
 
+    @classmethod
+    def class_key(cls):
+        # Ensure Weights appear before any other AbstractFunction
+        p, v, _ = Array.class_key()
+        return p, v - 1, cls.__name__
+
     def __eq__(self, other):
         return (isinstance(other, Weights) and
                 self.name == other.name and

devito/types/array.py

@@ -2,7 +2,7 @@
 from functools import cached_property
 
 import numpy as np
-from sympy import Expr
+from sympy import Expr, cacheit
 
 from devito.tools import (Reconstructable, as_tuple, c_restrict_void_p,
                           dtype_to_ctype, dtypes_vector_mapper, is_integer)
@@ -556,6 +556,10 @@ def indices(self):
     def dtype(self):
         return self.function.dtype
 
+    @cacheit
+    def sort_key(self, order=None):
+        return self.base.sort_key(order=order)
+
     # Default assumptions correspond to those of the `base`
     for i in ('is_real', 'is_imaginary', 'is_commutative'):
         locals()[i] = property(lambda self, v=i: getattr(self.base, v))

devito/types/basic.py

@@ -1527,6 +1527,12 @@ def __new__(cls, label, shape, function=None):
 
     func = Pickable._rebuild
 
+    @sympy.cacheit
+    def sort_key(self, order=None):
+        class_key, args, exp, coeff = super().sort_key(order=order)
+        args = (self.function.class_key(), *args)
+        return class_key, args, exp, coeff
+
     def __getitem__(self, indices, **kwargs):
         """Produce a types.Indexed, rather than a sympy.Indexed."""
         return Indexed(self, *as_tuple(indices))

tests/test_symbolics.py

@@ -8,7 +8,7 @@
 from devito import (Constant, Dimension, Grid, Function, solve, TimeFunction, Eq,  # noqa
                     Operator, SubDimension, norm, Le, Ge, Gt, Lt, Abs, sin, cos,
                     Min, Max)
-from devito.finite_differences.differentiable import SafeInv
+from devito.finite_differences.differentiable import SafeInv, Weights
 from devito.ir import Expression, FindNodes
 from devito.symbolics import (retrieve_functions, retrieve_indexed, evalrel,  # noqa
                               CallFromPointer, Cast, DefFunction, FieldFromPointer,
@@ -17,7 +17,7 @@
                               retrieve_derivatives)
 from devito.tools import as_tuple
 from devito.types import (Array, Bundle, FIndexed, LocalObject, Object,
-                          Symbol as dSymbol)
+                          ComponentAccess, StencilDimension, Symbol as dSymbol)
 from devito.types.basic import AbstractSymbol
 
 
@@ -448,6 +448,26 @@ def test_findexed():
     assert new_fi.strides_map == strides_map
 
 
+def test_canonical_ordering_of_weights():
+    grid = Grid(shape=(3, 3, 3))
+    x, y, z = grid.dimensions
+
+    f = Function(name='f', grid=grid)
+    g = Function(name='g', grid=grid)
+
+    i = StencilDimension('i0', 0, 2)
+    w = Weights(name='w0', dimensions=i, initvalue=[1.0, 2.0, 3.0])
+
+    fi = f[x, y + i, z]
+    wi = w[i]
+    cf = ComponentAccess(fi, 0)
+
+    assert (ccode(1.0*f[x, y, z] + 2.0*f[x, y + 1, z] + 3.0*f[x, y + 2, z]) ==
+            '1.0F*f[x][y][z] + 2.0F*f[x][y + 1][z] + 3.0F*f[x][y + 2][z]')
+    assert ccode(fi*wi) == 'w0[i0]*f[x][y + i0][z]'
+    assert ccode(cf*wi) == 'w0[i0]*f[x][y + i0][z].x'
+
+
 def test_symbolic_printing():
     b = Symbol('b')