Basic support for OpenCL (experimental)

Basic support for OpenCL

Problem: OpenCL cannot import stdint.h. Temporary fix: define custom opencl_stdint.h (defines currently only int64_t `)

TODO:

• implement opencl_stdint.h
• implement shard_mem, textures, built-in functions
• avoid CUDA intrinsics (fast_div)

pystencils/backends/opencl_backend.py

 import pystencils.data_types
 from pystencils.astnodes import Node
-from pystencils.backends.cbackend import generate_c
+from pystencils.backends.cbackend import CustomSympyPrinter, generate_c
 from pystencils.backends.cuda_backend import CudaBackend, CudaSympyPrinter
 
 
@@ -35,6 +35,12 @@ class OpenClBackend(CudaBackend):
         else:
             return code
 
+    def _print_ThreadBlockSynchronization(self, node):
+        raise NotImplementedError()
+
+    def _print_TextureDeclaration(self, node):
+        raise NotImplementedError()
+
 
 class OpenClSympyPrinter(CudaSympyPrinter):
     language = "OpenCL"
@@ -57,3 +63,9 @@ class OpenClSympyPrinter(CudaSympyPrinter):
         dimension = self.DIMENSION_MAPPING[dimension]
         function_name = self.INDEXING_FUNCTION_MAPPING[function_name]
         return f"{function_name}({dimension})"
+
+    def _print_TextureAccess(self, node):
+        raise NotImplementedError()
+
+    # Avoid usage of CUDA intrinsics
+    _print_Function = CustomSympyPrinter._print_Function