compiler: add rudimentary support for multi-cond buffering

Author: mloubout

devito/ir/clusters/algorithms.py

@@ -254,6 +254,7 @@ def guard(clusters):
 
             # Chain together all `cds` conditions from all expressions in `c`
             guards = {}
+            mode = sympy.Or
             for cd in cds:
                 # `BOTTOM` parent implies a guard that lives outside of
                 # any iteration space, which corresponds to the placeholder None
@@ -270,6 +271,7 @@ def guard(clusters):
 
                 # Pull `cd` from any expr
                 condition = guards.setdefault(k, [])
+                mode = mode and cd.relation
                 for e in exprs:
                     try:
                         condition.append(e.conditionals[cd])
@@ -284,7 +286,8 @@ def guard(clusters):
                     conditionals.pop(cd, None)
                     exprs[i] = e.func(*e.args, conditionals=conditionals)
 
-            guards = {d: sympy.And(*v, evaluate=False) for d, v in guards.items()}
+            # Combination mode is And by default and Or if all conditions are
+            guards = {d: mode(*v, evaluate=False) for d, v in guards.items()}
 
             # Construct a guarded Cluster
             processed.append(c.rebuild(exprs=exprs, guards=guards))

devito/ir/equations/equation.py

@@ -223,7 +223,7 @@ def __new__(cls, *args, **kwargs):
             else:
                 cond = diff2sympy(lower_exprs(d.condition))
                 if d._factor is not None:
-                    cond = sympy.And(cond, GuardFactor(d))
+                    cond = d.relation(cond, GuardFactor(d))
                 conditionals[d] = cond
             # Replace dimension with index
             index = d.index

devito/types/dimension.py

@@ -860,6 +860,8 @@ class ConditionalDimension(DerivedDimension):
         If True, use `self`, rather than the parent Dimension, to
         index into arrays. A typical use case is when arrays are accessed
         indirectly via the ``condition`` expression.
+    relation: Or/And, default=And
+        How this ConditionalDimension will be combined with other ones.
 
     Examples
     --------
@@ -913,10 +915,10 @@ class ConditionalDimension(DerivedDimension):
     is_Conditional = True
 
     __rkwargs__ = DerivedDimension.__rkwargs__ + \
-        ('factor', 'condition', 'indirect')
+        ('factor', 'condition', 'indirect', 'relation')
 
     def __init_finalize__(self, name, parent=None, factor=None, condition=None,
-                          indirect=False, **kwargs):
+                          indirect=False, relation=sympy.And, **kwargs):
         # `parent=None` degenerates to a ConditionalDimension outside of
         # any iteration space
         if parent is None:
@@ -937,6 +939,7 @@ def __init_finalize__(self, name, parent=None, factor=None, condition=None,
 
         self._condition = condition
         self._indirect = indirect
+        self._relation = relation
 
     @property
     def uses_symbolic_factor(self):
@@ -978,6 +981,10 @@ def condition(self):
     def indirect(self):
         return self._indirect
 
+    @property
+    def relation(self):
+        return self._relation
+
     @cached_property
     def free_symbols(self):
         retval = set(super().free_symbols)