compiler: add source location to SSA arguments.

Fixes #1006.

artiq/compiler/ir.py

@@ -410,7 +410,13 @@ class BasicBlock(NamedValue):
 class Argument(NamedValue):
     """
     A function argument.
+
+    :ivar loc: (:class:`pythonparser.source.Range` or None)
+        source location
     """
+    def __init__(self, typ, name):
+        super().__init__(typ, name)
+        self.loc = None
 
     def as_entity(self, type_printer):
         return self.as_operand(type_printer)

artiq/compiler/transforms/artiq_ir_generator.py

@@ -268,6 +268,9 @@ class ARTIQIRGenerator(algorithm.Visitor):
                 self.current_args[arg_name] = arg
                 optargs.append(arg)
 
+            for (arg, arg_node) in zip(args + optargs, node.args.args):
+                arg.loc = arg_node.loc
+
             func = ir.Function(typ, ".".join(self.name), [env_arg] + args + optargs,
                                loc=node.lambda_loc if is_lambda else node.keyword_loc)
             func.is_internal = is_internal