compiler: fix empty node

Author: mloubout

devito/ir/iet/nodes.py

@@ -30,7 +30,7 @@
            'Increment', 'Return', 'While', 'ListMajor', 'ParallelIteration',
            'ParallelBlock', 'Dereference', 'Lambda', 'SyncSpot', 'Pragma',
            'DummyExpr', 'BlankLine', 'ParallelTree', 'BusyWait', 'UsingNamespace',
-           'Using', 'CallableBody', 'Transfer']
+           'Using', 'CallableBody', 'Transfer', 'EmptyList']
 
 # First-class IET nodes
 
@@ -218,6 +218,11 @@ def __repr__(self):
                                       len(self.body), len(self.footer))
 
 
+class EmptyList(List):
+    """A plain List node without a body, such as a header/footer only"""
+    _traversable = []
+
+
 class Block(List):
 
     """A sequence of Nodes, wrapped in a block {...}."""

devito/ir/iet/visitors.py

@@ -1331,7 +1331,7 @@ def visit_Node(self, o, **kwargs):
             handle = self.mapper[o]
             return self.transform(o, handle, **kwargs)
         children = [self._visit(i, **kwargs) for i in o.children]
-        if o._traversable and not any(children) and not o.args_frozen:
+        if o._traversable and not any(children) and any(o.children):
             return None
         return o._rebuild(*children, **o.args_frozen)
 

devito/passes/iet/misc.py

@@ -7,7 +7,7 @@
 from devito.finite_differences import Max, Min
 from devito.finite_differences.differentiable import SafeInv
 from devito.logger import warning
-from devito.ir import (Any, Forward, DummyExpr, Iteration, List, Prodder,
+from devito.ir import (Any, Forward, DummyExpr, Iteration, EmptyList, Prodder,
                        FindApplications, FindNodes, FindSymbols, Transformer,
                        Uxreplace, filter_iterations, retrieve_iteration_tree,
                        pull_dims)
@@ -47,7 +47,7 @@ def avoid_denormals(iet, platform=None, **kwargs):
               cgen.Statement('_MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON)'),
               cgen.Line())
 
-    body = iet.body._rebuild(body=(List(header=header),) + iet.body.body)
+    body = iet.body._rebuild(body=(EmptyList(header=header),) + iet.body.body)
     iet = iet._rebuild(body=body)
 
     return iet, {'includes': ('xmmintrin.h', 'pmmintrin.h')}

examples/performance/01_gpu.ipynb

@@ -288,6 +288,7 @@
       "\n",
       "  const int x_fsz0 = u_vec->size[1];\n",
       "  const int y_fsz0 = u_vec->size[2];\n",
+      "\n",
       "  const int x_stride0 = x_fsz0*y_fsz0;\n",
       "  const int y_stride0 = y_fsz0;\n",
       "\n",