hdl.xfrm: consider fragment's own domains in DomainLowerer.

Changed in preparation for introducing local clock domains.

nmigen/hdl/ir.py

@@ -395,7 +395,7 @@ class Fragment:
     def _lower_domain_signals(self):
         from .xfrm import DomainLowerer
 
-        return DomainLowerer(self.domains)(self)
+        return DomainLowerer()(self)
 
     def _prepare_use_def_graph(self, parent, level, uses, defs, ios, top):
         def add_uses(*sigs, self=self):

nmigen/hdl/xfrm.py

@@ -337,6 +337,11 @@ class TransformedElaboratable(Elaboratable):
 class DomainCollector(ValueVisitor, StatementVisitor):
     def __init__(self):
         self.domains = set()
+        self._local_domains = set()
+
+    def _add_domain(self, domain_name):
+        if domain_name not in self._local_domains:
+            self.domains.add(domain_name)
 
     def on_ignore(self, value):
         pass
@@ -347,10 +352,10 @@ class DomainCollector(ValueVisitor, StatementVisitor):
     on_Signal = on_ignore
 
     def on_ClockSignal(self, value):
-        self.domains.add(value.domain)
+        self._add_domain(value.domain)
 
     def on_ResetSignal(self, value):
-        self.domains.add(value.domain)
+        self._add_domain(value.domain)
 
     on_Record = on_ignore
 
@@ -406,11 +411,20 @@ class DomainCollector(ValueVisitor, StatementVisitor):
         if isinstance(fragment, Instance):
             for name, (value, dir) in fragment.named_ports.items():
                 self.on_value(value)
+
+        old_local_domains, self._local_domains = self._local_domains, set(self._local_domains)
+        for domain_name, domain in fragment.domains.items():
+            if domain.local:
+                self._local_domains.add(domain_name)
+
         self.on_statements(fragment.statements)
-        self.domains.update(fragment.drivers.keys())
+        for domain_name in fragment.drivers:
+            self._add_domain(domain_name)
         for subfragment, name in fragment.subfragments:
             self.on_fragment(subfragment)
 
+        self._local_domains = old_local_domains
+
     def __call__(self, fragment):
         self.on_fragment(fragment)
         return self.domains
@@ -457,8 +471,8 @@ class DomainRenamer(FragmentTransformer, ValueTransformer, StatementTransformer)
 
 
 class DomainLowerer(FragmentTransformer, ValueTransformer, StatementTransformer):
-    def __init__(self, domains):
-        self.domains = domains
+    def __init__(self):
+        self.domains = None
 
     def _resolve(self, domain, context):
         if domain not in self.domains:
@@ -487,6 +501,11 @@ class DomainLowerer(FragmentTransformer, ValueTransformer, StatementTransformer)
                                   .format(value, value.domain))
         return cd.rst
 
+    def on_fragment(self, fragment):
+        self.domains = fragment.domains
+        new_fragment = super().on_fragment(fragment)
+        return new_fragment
+
 
 class SampleDomainInjector(ValueTransformer, StatementTransformer):
     def __init__(self, domain):