never attempt to vectorize the tail loop

pystencils/backends/cbackend.py

@@ -192,7 +192,9 @@ class CBackend:
     def __init__(self, sympy_printer=None, signature_only=False, vector_instruction_set=None, dialect='c'):
         if sympy_printer is None:
             if vector_instruction_set is not None:
-                self.sympy_printer = VectorizedCustomSympyPrinter(vector_instruction_set)
+                self.vector_sympy_printer = VectorizedCustomSympyPrinter(vector_instruction_set)
+                self.scalar_sympy_printer = CustomSympyPrinter()
+                self.sympy_printer = self.vector_sympy_printer
             else:
                 self.sympy_printer = CustomSympyPrinter()
         else:
@@ -259,6 +261,12 @@ class CBackend:
         prefix = "\n".join(node.prefix_lines)
         if prefix:
             prefix += "\n"
+        if self._vector_instruction_set and hasattr(node, 'instruction_set') and node.instruction_set is None:
+            # the tail loop must not be vectorized
+            self.sympy_printer = self.scalar_sympy_printer
+            code = f"{prefix}{loop_str}\n{self._print(node.body)}"
+            self.sympy_printer = self.vector_sympy_printer
+            return code
         return f"{prefix}{loop_str}\n{self._print(node.body)}"
 
     def _print_SympyAssignment(self, node):

pystencils/cpu/vectorization.py

@@ -173,6 +173,8 @@ def vectorize_inner_loops_and_adapt_load_stores(ast_node, vector_width, assume_a
             cutting_point = modulo_floor(loop_range, vector_width) + loop_node.start
             loop_nodes = [l for l in cut_loop(loop_node, [cutting_point]).args if isinstance(l, ast.LoopOverCoordinate)]
             assert len(loop_nodes) in (0, 1, 2)  # 2 for main and tail loop, 1 if loop range divisible by vector width
+            if len(loop_nodes) == 2:
+                loop_nodes[1].instruction_set = None
             if len(loop_nodes) == 0:
                 continue
             loop_node = loop_nodes[0]
@@ -322,6 +324,9 @@ def insert_vector_casts(ast_node):
             return expr
 
     def visit_node(node, substitution_dict):
+        if hasattr(node, 'instruction_set') and node.instruction_set is None:
+            # the tail loop must not be vectorized
+            return
         substitution_dict = substitution_dict.copy()
         for arg in node.args:
             if isinstance(arg, ast.SympyAssignment):