hdl: allow driving individual bits of signals from multiple modules o…

…r domains.

Fixes #1454.

amaranth/hdl/_dsl.py

@@ -19,82 +19,78 @@
 __all__ = ["SyntaxError", "SyntaxWarning", "Module"]
 
 
-class _Visitor:
-    def __init__(self):
-        self.driven_signals = SignalSet()
-
-    def visit_stmt(self, stmt):
-        if isinstance(stmt, _StatementList):
-            for s in stmt:
-                self.visit_stmt(s)
-        elif isinstance(stmt, Assign):
-            self.visit_lhs(stmt.lhs)
-            self.visit_rhs(stmt.rhs)
-        elif isinstance(stmt, Print):
+def _check_stmt(stmt):
+    if isinstance(stmt, _StatementList):
+        for s in stmt:
+            _check_stmt(s)
+    elif isinstance(stmt, Assign):
+        _check_lhs(stmt.lhs)
+        _check_rhs(stmt.rhs)
+    elif isinstance(stmt, Print):
+        for chunk in stmt.message._chunks:
+            if not isinstance(chunk, str):
+                obj, format_spec = chunk
+                _check_rhs(obj)
+    elif isinstance(stmt, Property):
+        _check_rhs(stmt.test)
+        if stmt.message is not None:
             for chunk in stmt.message._chunks:
                 if not isinstance(chunk, str):
                     obj, format_spec = chunk
-                    self.visit_rhs(obj)
-        elif isinstance(stmt, Property):
-            self.visit_rhs(stmt.test)
-            if stmt.message is not None:
-                for chunk in stmt.message._chunks:
-                    if not isinstance(chunk, str):
-                        obj, format_spec = chunk
-                        self.visit_rhs(obj)
-        elif isinstance(stmt, Switch):
-            self.visit_rhs(stmt.test)
-            for _patterns, stmts, _src_loc in stmt.cases:
-                self.visit_stmt(stmts)
-        elif isinstance(stmt, _LateBoundStatement):
-            pass
-        else:
-            assert False # :nocov:
-
-    def visit_lhs(self, value):
-        if isinstance(value, Operator) and value.operator in ("u", "s"):
-            self.visit_lhs(value.operands[0])
-        elif isinstance(value, (Signal, ClockSignal, ResetSignal)):
-            self.driven_signals.add(value)
-        elif isinstance(value, Slice):
-            self.visit_lhs(value.value)
-        elif isinstance(value, Part):
-            self.visit_lhs(value.value)
-            self.visit_rhs(value.offset)
-        elif isinstance(value, Concat):
-            for part in value.parts:
-                self.visit_lhs(part)
-        elif isinstance(value, SwitchValue):
-            self.visit_rhs(value.test)
-            for _patterns, elem in value.cases:
-                self.visit_lhs(elem)
-        elif isinstance(value, MemoryData._Row):
-            raise ValueError(f"Value {value!r} can only be used in simulator processes")
-        else:
-            raise ValueError(f"Value {value!r} cannot be assigned to")
-
-    def visit_rhs(self, value):
-        if isinstance(value, (Const, Signal, ClockSignal, ResetSignal, Initial, AnyValue)):
-            pass
-        elif isinstance(value, Operator):
-            for op in value.operands:
-                self.visit_rhs(op)
-        elif isinstance(value, Slice):
-            self.visit_rhs(value.value)
-        elif isinstance(value, Part):
-            self.visit_rhs(value.value)
-            self.visit_rhs(value.offset)
-        elif isinstance(value, Concat):
-            for part in value.parts:
-                self.visit_rhs(part)
-        elif isinstance(value, SwitchValue):
-            self.visit_rhs(value.test)
-            for _patterns, elem in value.cases:
-                self.visit_rhs(elem)
-        elif isinstance(value, MemoryData._Row):
-            raise ValueError(f"Value {value!r} can only be used in simulator processes")
-        else:
-            assert False # :nocov:
+                    _check_rhs(obj)
+    elif isinstance(stmt, Switch):
+        _check_rhs(stmt.test)
+        for _patterns, stmts, _src_loc in stmt.cases:
+            _check_stmt(stmts)
+    elif isinstance(stmt, _LateBoundStatement):
+        pass
+    else:
+        assert False # :nocov:
+
+def _check_lhs(value):
+    if isinstance(value, Operator) and value.operator in ("u", "s"):
+        _check_lhs(value.operands[0])
+    elif isinstance(value, (Signal, ClockSignal, ResetSignal)):
+        pass
+    elif isinstance(value, Slice):
+        _check_lhs(value.value)
+    elif isinstance(value, Part):
+        _check_lhs(value.value)
+        _check_rhs(value.offset)
+    elif isinstance(value, Concat):
+        for part in value.parts:
+            _check_lhs(part)
+    elif isinstance(value, SwitchValue):
+        _check_rhs(value.test)
+        for _patterns, elem in value.cases:
+            _check_lhs(elem)
+    elif isinstance(value, MemoryData._Row):
+        raise ValueError(f"Value {value!r} can only be used in simulator processes")
+    else:
+        raise ValueError(f"Value {value!r} cannot be assigned to")
+
+def _check_rhs(value):
+    if isinstance(value, (Const, Signal, ClockSignal, ResetSignal, Initial, AnyValue)):
+        pass
+    elif isinstance(value, Operator):
+        for op in value.operands:
+            _check_rhs(op)
+    elif isinstance(value, Slice):
+        _check_rhs(value.value)
+    elif isinstance(value, Part):
+        _check_rhs(value.value)
+        _check_rhs(value.offset)
+    elif isinstance(value, Concat):
+        for part in value.parts:
+            _check_rhs(part)
+    elif isinstance(value, SwitchValue):
+        _check_rhs(value.test)
+        for _patterns, elem in value.cases:
+            _check_rhs(elem)
+    elif isinstance(value, MemoryData._Row):
+        raise ValueError(f"Value {value!r} can only be used in simulator processes")
+    else:
+        assert False # :nocov:
 
 
 class _ModuleBuilderProxy:
@@ -632,16 +628,27 @@ def _add_statement(self, assigns, domain, depth):
 
             stmt._MustUse__used = True
 
-            visitor = _Visitor()
-            visitor.visit_stmt(stmt)
-            for signal in visitor.driven_signals:
-                if signal not in self._driving:
-                    self._driving[signal] = domain
-                elif self._driving[signal] != domain:
-                    cd_curr = self._driving[signal]
-                    raise SyntaxError(
-                        f"Driver-driver conflict: trying to drive {signal!r} from d.{domain}, but it is "
-                        f"already driven from d.{cd_curr}")
+            _check_stmt(stmt)
+
+            lhs_masks = LHSMaskCollector()
+            # This is an opportunistic early check — not much harm skipping it, since
+            # the whole-design check will be later done in NIR emitter.
+            if not isinstance(stmt, _LateBoundStatement):
+                lhs_masks.visit_stmt(stmt)
+
+            for sig, mask in lhs_masks.masks():
+                if sig not in self._driving:
+                    self._driving[sig] = [None] * len(sig)
+                sig_domain = self._driving[sig]
+                for bit in range(len(sig)):
+                    if not (mask & (1 << bit)):
+                        continue
+                    if sig_domain[bit] is None:
+                        sig_domain[bit] = domain
+                    if sig_domain[bit] != domain:
+                        raise SyntaxError(
+                            f"Driver-driver conflict: trying to drive {sig!r} bit {bit} from d.{domain}, but it is "
+                            f"already driven from d.{sig_domain[bit]}")
 
             self._statements.setdefault(domain, []).append(stmt)