lib.cdc: add tests for MultiReg.

nmigen/back/pysim.py

@@ -7,6 +7,7 @@ from vcd.gtkw import GTKWSave
 
 from ..tools import flatten
 from ..hdl.ast import *
+from ..hdl.ir import *
 from ..hdl.xfrm import ValueVisitor, StatementVisitor
 
 
@@ -359,6 +360,9 @@ class Simulator:
         self._gtkw_file       = gtkw_file
         self._traces          = traces
 
+        while not isinstance(self._fragment, Fragment):
+            self._fragment = self._fragment.get_fragment(platform=None)
+
     @staticmethod
     def _check_process(process):
         if inspect.isgeneratorfunction(process):