back.pysim: create unique ResetSynchronizer internal domains.

Commit 300d47ca introduced the same bug commit 779f3ee9 was trying to
avoid, but now only in the simulator. Since the names in simulator
don't have to make any sense, just use DUID to generate them.

nmigen/back/pysim.py

@@ -10,6 +10,7 @@ from ..tools import flatten
 from ..hdl.ast import *
 from ..hdl.ir import *
 from ..hdl.xfrm import ValueVisitor, StatementVisitor
+from ..hdl.ast import DUID
 from ..hdl.dsl import Module
 from ..hdl.cd import ClockDomain
 
@@ -356,12 +357,13 @@ class _StatementCompiler(StatementVisitor):
 class _SimulatorPlatform:
     def get_reset_sync(self, reset_sync):
         m = Module()
-        m.domains += ClockDomain("_reset_sync", async_reset=True)
+        cd = ClockDomain("_reset_sync_{}".format(DUID().duid), async_reset=True)
+        m.domains += cd
         for i, o in zip((0, *reset_sync._regs), reset_sync._regs):
-            m.d._reset_sync += o.eq(i)
+            m.d[cd.name] += o.eq(i)
         m.d.comb += [
-            ClockSignal("_reset_sync").eq(ClockSignal(reset_sync.domain)),
-            ResetSignal("_reset_sync").eq(reset_sync.arst),
+            ClockSignal(cd.name).eq(ClockSignal(reset_sync.domain)),
+            ResetSignal(cd.name).eq(reset_sync.arst),
             ResetSignal(reset_sync.domain).eq(reset_sync._regs[-1])
         ]
         return m