api: cache subsampling factors to avoid duplicates

Author: mloubout

devito/types/dimension.py

@@ -12,6 +12,7 @@
 from devito.tools import Pickable, is_integer, memoized_meth
 from devito.types.args import ArgProvider
 from devito.types.basic import Symbol, DataSymbol, Scalar
+from devito.types.caching import Cached
 from devito.types.constant import Constant
 
 
@@ -822,6 +823,12 @@ def bound_symbols(self):
         return self.parent.bound_symbols
 
 
+class SubsamplingFactor(Constant, Cached):
+
+    __hash__ = sympy.Symbol.__hash__
+    _cache_key = Symbol._cache_key
+
+
 class ConditionalDimension(DerivedDimension):
 
     """
@@ -913,7 +920,8 @@ def __init_finalize__(self, name, parent=None, factor=None, condition=None,
         if factor is None or factor == 1:
             self._factor = None
         elif is_integer(factor):
-            self._factor = Constant(name="%sf" % name, value=factor, dtype=np.int32)
+            self._factor = SubsamplingFactor(name=f"{name}f", value=factor,
+                                             dtype=np.int32)
         elif factor.is_Constant and is_integer(factor.data):
             self._factor = factor
         else:

tests/test_dimension.py

@@ -1,4 +1,5 @@
 from itertools import product
+from copy import deepcopy
 
 import numpy as np
 from sympy import And, Or
@@ -1896,6 +1897,24 @@ def test_cond_notime(self):
         op(time_m=1, time_M=nt-1, dt=1)
         assert norm(g, order=1) == norm(sum(usaved, dims=time_under), order=1)
 
+    def test_cond_copy(self):
+        grid = Grid((11, 11, 11))
+        time = grid.time_dim
+
+        cd = ConditionalDimension(name='tsub', parent=time, factor=5)
+        u = TimeFunction(name='u', grid=grid, space_order=4, time_order=2, save=Buffer(2))
+        u1 = TimeFunction(name='u1', grid=grid, space_order=0,
+                          time_order=0, save=5, time_dim=cd)
+        u2 = TimeFunction(name='u2', grid=grid, space_order=0,
+                          time_order=0, save=5, time_dim=cd)
+
+        # Mimic what happens when an operator is copied
+        u12 = deepcopy(u1)
+        u22 = deepcopy(u2)
+
+        op = Operator([Eq(u.forward, u.laplace), Eq(u12, u), Eq(u22, u)])
+        assert len([p for p in op.parameters if p.name == 'tsubf']) == 1
+
 
 class TestCustomDimension: