compiler: add None type support

artiq/compiler/ir_ast_body.py

@@ -34,7 +34,9 @@ class Visitor:
 
 	def _visit_expr_NameConstant(self, node):
 		v = node.value
-		if isinstance(v, bool):
+		if v is None:
+			r = ir_values.VNone()
+		elif isinstance(v, bool):
 			r = ir_values.VBool()
 		else:
 			raise NotImplementedError

artiq/compiler/ir_infer_types.py

@@ -51,6 +51,7 @@ d = 4          # stays int32
 x = int64(7)
 a += x         # promotes a to int64
 foo = True
+bar = None
 """
 	ns = infer_types(ast.parse(testcode))
 	for k, v in sorted(ns.items(), key=itemgetter(0)):

artiq/compiler/ir_values.py

@@ -2,6 +2,28 @@ from types import SimpleNamespace
 
 from llvm import core as lc
 
+# None type
+
+class VNone:
+	def __repr__(self):
+		return "<VNone>"
+
+	def same_type(self, other):
+		return isinstance(other, VNone)
+
+	def merge(self, other):
+		if not isinstance(other, VNone):
+			raise TypeError
+
+	def create_alloca(self, builder, name):
+		pass
+
+	def o_bool(self, builder):
+		r = VBool()
+		if builder is not None:
+			r.create_constant(False)
+		return r
+
 # Integer type
 
 class VInt: