Address of SymPy-Function `address_of`

Some CUDA functions (like atomic_add) require pointers to data. This PR adds a SymPy function representing the C address-of operator (&).

I tried to trigger cse to show a problem related to this function (dummy variables were not typed correctly as pointer). I'll include the fix in a follow-up PR.

pystencils/backends/cbackend.py

@@ -5,7 +5,11 @@ from typing import Set
 from sympy.printing.ccode import C89CodePrinter
 
 from pystencils.cpu.vectorization import vec_any, vec_all
-from pystencils.fast_approximation import fast_division, fast_sqrt, fast_inv_sqrt
+from pystencils.data_types import (PointerType, VectorType, address_of,
+                                   cast_func, create_type, reinterpret_cast_func,
+                                   get_type_of_expression,
+                                   vector_memory_access)
+from pystencils.fast_approximation import fast_division, fast_inv_sqrt, fast_sqrt
 
 try:
     from sympy.printing.ccode import C99CodePrinter as CCodePrinter
@@ -15,8 +19,6 @@ except ImportError:
 from pystencils.integer_functions import bitwise_xor, bit_shift_right, bit_shift_left, bitwise_and, \
     bitwise_or, modulo_ceil, int_div, int_power_of_2
 from pystencils.astnodes import Node, KernelFunction
-from pystencils.data_types import create_type, PointerType, get_type_of_expression, VectorType, cast_func, \
-    vector_memory_access, reinterpret_cast_func
 
 __all__ = ['generate_c', 'CustomCodeNode', 'PrintNode', 'get_headers', 'CustomSympyPrinter']
 
@@ -276,6 +278,9 @@ class CustomSympyPrinter(CCodePrinter):
         if isinstance(expr, reinterpret_cast_func):
             arg, data_type = expr.args
             return "*((%s)(& %s))" % (PointerType(data_type, restrict=False), self._print(arg))
+        elif isinstance(expr, address_of):
+            assert len(expr.args) == 1, "address_of must only have one argument"
+            return "&(%s)" % self._print(expr.args[0])
         elif isinstance(expr, cast_func):
             arg, data_type = expr.args
             if isinstance(arg, sp.Number):