[BugFix] Fix missing comunicated PDFs for FreeSlip

When the LBM communication is used special slices for the sides and the corners are created. These contain not enough information for the FreeSlip BCs.

lbmpy/advanced_streaming/communication.py

 import itertools
-from pystencils import Field, Assignment
+from pystencils import CreateKernelConfig, Field, Assignment, AssignmentCollection
 from pystencils.slicing import shift_slice, get_slice_before_ghost_layer, normalize_slice
-from lbmpy.advanced_streaming.utility import is_inplace, get_accessor, numeric_index, \
-    numeric_offsets, Timestep, get_timesteps
+from lbmpy.advanced_streaming.utility import is_inplace, get_accessor, numeric_index, Timestep, get_timesteps
 from pystencils.datahandling import SerialDataHandling
 from pystencils.enums import Target
 from itertools import chain
 
 
-def _trim_slice_in_direction(slices, direction):
-    assert len(slices) == len(direction)
+class LBMPeriodicityHandling:
 
-    result = []
-    for s, d in zip(slices, direction):
-        if isinstance(s, int):
-            result.append(s)
-            continue
-        start = s.start + 1 if d == -1 else s.start
-        stop = s.stop - 1 if d == 1 else s.stop
-        result.append(slice(start, stop, s.step))
+    def __init__(self, stencil, data_handling, pdf_field_name,
+                 streaming_pattern='pull', ghost_layers=1,
+                 pycuda_direct_copy=True):
+        """
+            Periodicity Handling for Lattice Boltzmann Streaming.
 
-    return tuple(result)
+            **On the usage with cuda:**
+            - pycuda allows the copying of sliced arrays within device memory using the numpy syntax,
+            e.g. `dst[:,0] = src[:,-1]`. In this implementation, this is the default for periodicity
+            handling. Alternatively, if you set `pycuda_direct_copy=False`, GPU kernels are generated and
+            compiled. The compiled kernels are almost twice as fast in execution as pycuda array copying,
+            but especially for large stencils like D3Q27, their compilation can take up to 20 seconds.
+            Choose your weapon depending on your use case.
+        """
+        if not isinstance(data_handling, SerialDataHandling):
+            raise ValueError('Only serial data handling is supported!')
 
+        self.stencil = stencil
+        self.dim = stencil.D
+        self.dh = data_handling
 
-def _extend_dir(direction):
-    if len(direction) == 0:
-        yield tuple()
-    elif direction[0] == 0:
-        for d in [-1, 0, 1]:
-            for rest in _extend_dir(direction[1:]):
-                yield (d, ) + rest
-    else:
-        for rest in _extend_dir(direction[1:]):
-            yield (direction[0], ) + rest
+        assert data_handling.default_target in [Target.CPU, Target.GPU]
+        self.target = data_handling.default_target
 
+        self.pdf_field_name = pdf_field_name
+        self.ghost_layers = ghost_layers
+        self.periodicity = data_handling.periodicity
+        self.inplace_pattern = is_inplace(streaming_pattern)
 
-def _get_neighbour_transform(direction, ghost_layers):
-    return tuple(d * (ghost_layers + 1) for d in direction)
+        self.cpu = self.target == Target.CPU
+        self.pycuda_direct_copy = self.target == Target.GPU and pycuda_direct_copy
 
+        def is_copy_direction(direction):
+            s = 0
+            for d, p in zip(direction, self.periodicity):
+                s += abs(d)
+                if d != 0 and not p:
+                    return False
 
-def _fix_length_one_slices(slices):
-    """Slices of length one are replaced by their start value for correct periodic shifting"""
-    if isinstance(slices, int):
-        return slices
-    elif isinstance(slices, slice):
-        if slices.stop is not None and abs(slices.start - slices.stop) == 1:
-            return slices.start
-        elif slices.stop is None and slices.start == -1:
-            return -1  # [-1:] also has length one
+            return s != 0
+
+        full_stencil = itertools.product(*([-1, 0, 1] for _ in range(self.dim)))
+        copy_directions = tuple(filter(is_copy_direction, full_stencil))
+        self.comm_slices = []
+        timesteps = get_timesteps(streaming_pattern)
+        for timestep in timesteps:
+            slices_per_comm_dir = get_communication_slices(stencil=stencil,
+                                                           comm_stencil=copy_directions,
+                                                           streaming_pattern=streaming_pattern,
+                                                           prev_timestep=timestep,
+                                                           ghost_layers=ghost_layers)
+            self.comm_slices.append(list(chain.from_iterable(v for k, v in slices_per_comm_dir.items())))
+
+        if self.target == Target.GPU and not pycuda_direct_copy:
+            self.device_copy_kernels = list()
+            for timestep in timesteps:
+                self.device_copy_kernels.append(self._compile_copy_kernels(timestep))
+
+    def __call__(self, prev_timestep=Timestep.BOTH):
+        if self.cpu:
+            self._periodicity_handling_cpu(prev_timestep)
         else:
-            return slices
-    else:
-        return tuple(_fix_length_one_slices(s) for s in slices)
+            self._periodicity_handling_gpu(prev_timestep)
+
+    def _periodicity_handling_cpu(self, prev_timestep):
+        arr = self.dh.cpu_arrays[self.pdf_field_name]
+        comm_slices = self.comm_slices[prev_timestep.idx]
+        for src, dst in comm_slices:
+            arr[dst] = arr[src]
+
+    def _compile_copy_kernels(self, timestep):
+        pdf_field = self.dh.fields[self.pdf_field_name]
+        kernels = []
+        for src, dst in self.comm_slices[timestep.idx]:
+            kernels.append(
+                periodic_pdf_copy_kernel(pdf_field, src, dst, target=self.target))
+        return kernels
+
+    def _periodicity_handling_gpu(self, prev_timestep):
+        arr = self.dh.gpu_arrays[self.pdf_field_name]
+        if self.pycuda_direct_copy:
+            for src, dst in self.comm_slices[prev_timestep.idx]:
+                arr[dst] = arr[src]
+        else:
+            kernel_args = {self.pdf_field_name: arr}
+            for kernel in self.device_copy_kernels[prev_timestep.idx]:
+                kernel(**kernel_args)
 
 
 def get_communication_slices(
@@ -60,7 +104,7 @@ def get_communication_slices(
     Return the source and destination slices for periodicity handling or communication between blocks.
 
     :param stencil: The stencil used by the LB method.
-    :param comm_stencil: The stencil defining the communication directions. If None, it will be set to the 
+    :param comm_stencil: The stencil defining the communication directions. If None, it will be set to the
                          full stencil (D2Q9 in 2D, D3Q27 in 3D, etc.).
     :param streaming_pattern: The streaming pattern.
     :param prev_timestep: Timestep after which communication is run.
@@ -83,13 +127,10 @@ def get_communication_slices(
 
         for streaming_dir in set(_extend_dir(comm_dir)) & set(stencil):
             d = stencil.index(streaming_dir)
-            write_offsets = numeric_offsets(write_accesses[d])
             write_index = numeric_index(write_accesses[d])[0]
 
-            tangential_dir = tuple(s - c for s, c in zip(streaming_dir, comm_dir))
             origin_slice = get_slice_before_ghost_layer(comm_dir, ghost_layers=ghost_layers, thickness=1)
-            origin_slice = _fix_length_one_slices(origin_slice)
-            src_slice = shift_slice(_trim_slice_in_direction(origin_slice, tangential_dir), write_offsets)
+            src_slice = _fix_length_one_slices(origin_slice)
 
             neighbour_transform = _get_neighbour_transform(comm_dir, ghost_layers)
             dst_slice = shift_slice(src_slice, neighbour_transform)
@@ -130,8 +171,9 @@ def periodic_pdf_copy_kernel(pdf_field, src_slice, dst_slice,
     assert offset == [_stop(s1) - _stop(s2) for s1, s2 in zip(normalized_from_slice, normalized_to_slice)], \
         "Slices have to have same size"
 
-    copy_eq = Assignment(pdf_field(pdf_idx), pdf_field[tuple(offset)](pdf_idx))
-    ast = create_cuda_kernel([copy_eq], iteration_slice=dst_slice, skip_independence_check=True)
+    copy_eq = AssignmentCollection(main_assignments=[Assignment(pdf_field(pdf_idx), pdf_field[tuple(offset)](pdf_idx))])
+    config = CreateKernelConfig(iteration_slice=dst_slice, skip_independence_check=True)
+    ast = create_cuda_kernel(copy_eq, config=config)
     if target == Target.GPU:
         from pystencils.gpucuda import make_python_function
         return make_python_function(ast)
@@ -139,92 +181,32 @@ def periodic_pdf_copy_kernel(pdf_field, src_slice, dst_slice,
         raise ValueError('Invalid target:', target)
 
 
-class LBMPeriodicityHandling:
-
-    def __init__(self, stencil, data_handling, pdf_field_name,
-                 streaming_pattern='pull', ghost_layers=1,
-                 pycuda_direct_copy=True):
-        """
-            Periodicity Handling for Lattice Boltzmann Streaming.
-
-            **On the usage with cuda:**
-            - pycuda allows the copying of sliced arrays within device memory using the numpy syntax,
-            e.g. `dst[:,0] = src[:,-1]`. In this implementation, this is the default for periodicity
-            handling. Alternatively, if you set `pycuda_direct_copy=False`, GPU kernels are generated and
-            compiled. The compiled kernels are almost twice as fast in execution as pycuda array copying,
-            but especially for large stencils like D3Q27, their compilation can take up to 20 seconds. 
-            Choose your weapon depending on your use case.
-        """
-        if not isinstance(data_handling, SerialDataHandling):
-            raise ValueError('Only serial data handling is supported!')
-
-        self.stencil = stencil
-        self.dim = stencil.D
-        self.dh = data_handling
-
-        target = data_handling.default_target
-        assert target in [Target.CPU, Target.GPU]
-
-        self.pdf_field_name = pdf_field_name
-        self.ghost_layers = ghost_layers
-        periodicity = data_handling.periodicity
-        self.inplace_pattern = is_inplace(streaming_pattern)
-        self.target = target
-        self.cpu = target == Target.CPU
-        self.pycuda_direct_copy = target == Target.GPU and pycuda_direct_copy
-
-        def is_copy_direction(direction):
-            s = 0
-            for d, p in zip(direction, periodicity):
-                s += abs(d)
-                if d != 0 and not p:
-                    return False
-
-            return s != 0
-
-        full_stencil = itertools.product(*([-1, 0, 1] for _ in range(self.dim)))
-        copy_directions = tuple(filter(is_copy_direction, full_stencil))
-        self.comm_slices = []
-        timesteps = get_timesteps(streaming_pattern)
-        for timestep in timesteps:
-            slices_per_comm_dir = get_communication_slices(stencil=stencil,
-                                                           comm_stencil=copy_directions,
-                                                           streaming_pattern=streaming_pattern,
-                                                           prev_timestep=timestep,
-                                                           ghost_layers=ghost_layers)
-            self.comm_slices.append(list(chain.from_iterable(v for k, v in slices_per_comm_dir.items())))
-
-        if target == Target.GPU and not pycuda_direct_copy:
-            self.device_copy_kernels = []
-            for timestep in timesteps:
-                self.device_copy_kernels.append(self._compile_copy_kernels(timestep))
+def _extend_dir(direction):
+    if len(direction) == 0:
+        yield tuple()
+    elif direction[0] == 0:
+        for d in [-1, 0, 1]:
+            for rest in _extend_dir(direction[1:]):
+                yield (d, ) + rest
+    else:
+        for rest in _extend_dir(direction[1:]):
+            yield (direction[0], ) + rest
 
-    def __call__(self, prev_timestep=Timestep.BOTH):
-        if self.cpu:
-            self._periodicity_handling_cpu(prev_timestep)
-        else:
-            self._periodicity_handling_gpu(prev_timestep)
 
-    def _periodicity_handling_cpu(self, prev_timestep):
-        arr = self.dh.cpu_arrays[self.pdf_field_name]
-        comm_slices = self.comm_slices[prev_timestep.idx]
-        for src, dst in comm_slices:
-            arr[dst] = arr[src]
+def _get_neighbour_transform(direction, ghost_layers):
+    return tuple(d * (ghost_layers + 1) for d in direction)
 
-    def _compile_copy_kernels(self, timestep):
-        pdf_field = self.dh.fields[self.pdf_field_name]
-        kernels = []
-        for src, dst in self.comm_slices[timestep.idx]:
-            kernels.append(
-                periodic_pdf_copy_kernel(pdf_field, src, dst, target=self.target))
-        return kernels
 
-    def _periodicity_handling_gpu(self, prev_timestep):
-        arr = self.dh.gpu_arrays[self.pdf_field_name]
-        if self.pycuda_direct_copy:
-            for src, dst in self.comm_slices[prev_timestep.idx]:
-                arr[dst] = arr[src]
+def _fix_length_one_slices(slices):
+    """Slices of length one are replaced by their start value for correct periodic shifting"""
+    if isinstance(slices, int):
+        return slices
+    elif isinstance(slices, slice):
+        if slices.stop is not None and abs(slices.start - slices.stop) == 1:
+            return slices.start
+        elif slices.stop is None and slices.start == -1:
+            return -1  # [-1:] also has length one
         else:
-            kernel_args = {self.pdf_field_name: arr}
-            for kernel in self.device_copy_kernels[prev_timestep.idx]:
-                kernel(**kernel_args)
+            return slices
+    else:
+        return tuple(_fix_length_one_slices(s) for s in slices)