Repository: amaranth-lang/amaranth (python)

Issue:
Detect and warn about elaboratables added more than once into the hierarchy

Pull request description:
hdl._ir: raise an error when an elaboratable is duplicated in hierarchy.
Fixes #1194.

Patch:
diff --git a/amaranth/hdl/_ast.py b/amaranth/hdl/_ast.py
index 0b7f15e..57f102e 100644
--- a/amaranth/hdl/_ast.py
+++ b/amaranth/hdl/_ast.py
@@ -18,7 +18,7 @@ from .._unused import *
 __all__ = [
     "SyntaxError", "SyntaxWarning",
     "Shape", "signed", "unsigned", "ShapeCastable", "ShapeLike",
-    "Value", "Const", "C", "AnyConst", "AnySeq", "Operator", "Mux", "Part", "Slice", "Cat", "Concat",
+    "Value", "Const", "C", "AnyConst", "AnySeq", "Operator", "Mux", "Part", "Slice", "Cat", "Concat", "SwitchValue",
     "Array", "ArrayProxy",
     "Signal", "ClockSignal", "ResetSignal",
     "ValueCastable", "ValueLike",
@@ -1892,6 +1892,60 @@ class Concat(Value):
         return "(cat {})".format(" ".join(map(repr, self.parts)))
 
 
+@final
+class SwitchValue(Value):
+    def __init__(self, test, cases, *, src_loc=None, src_loc_at=0):
+        if src_loc is None:
+            super().__init__(src_loc_at=src_loc_at)
+        else:
+            self.src_loc = src_loc
+        self._test = Value.cast(test)
+        new_cases = []
+        for patterns, value in cases:
+            if patterns is not None:
+                if not isinstance(patterns, tuple):
+                    patterns = (patterns,)
+                new_patterns = ()
+                key_mask = (1 << len(self.test)) - 1
+                for key in _normalize_patterns(patterns, self._test.shape()):
+                    if isinstance(key, int):
+                        key = to_binary(key & key_mask, len(self.test))
+                    new_patterns = (*new_patterns, key)
+            else:
+                new_patterns = None
+            new_cases.append((new_patterns, Value.cast(value)))
+        self._cases = tuple(new_cases)
+
+    @property
+    def test(self):
+        return self._test
+
+    @property
+    def cases(self):
+        return self._cases
+
+    def shape(self):
+        return Shape._unify(value.shape() for _patterns, value in self._cases)
+
+    def _lhs_signals(self):
+        return union((value._lhs_signals() for _patterns, value in self.cases), start=SignalSet())
+
+    def _rhs_signals(self):
+        signals = union((value._rhs_signals() for _patterns, value in self.cases), start=SignalSet())
+        return self.test._rhs_signals() | signals
+
+    def __repr__(self):
+        def case_repr(patterns, value):
+            if patterns is None:
+                return f"(default {value!r})"
+            elif len(patterns) == 1:
+                return f"(case {patterns[0]} {value!r})"
+            else:
+                return "(case ({}) {!r})".format(" ".join(patterns), value)
+        case_reprs = (case_repr(patterns, value) for patterns, value in self.cases)
+        return "(switch-value {!r} {})".format(self.test, " ".join(case_reprs))
+
+
 class _SignalMeta(ABCMeta):
     def __call__(cls, shape=None, src_loc_at=0, **kwargs):
         signal = super().__call__(shape, **kwargs, src_loc_at=src_loc_at + 1)
@@ -2356,10 +2410,17 @@ class Array(MutableSequence):
                                        ", ".join(map(repr, self._inner)))
 
 
+def _proxy_value(name):
+    @functools.wraps(getattr(Value, name))
+    def inner(self, *args, **kwargs):
+        return getattr(Value.cast(self), name)(*args, **kwargs)
+    return inner
+
+
 @final
-class ArrayProxy(Value):
+class ArrayProxy(ValueCastable):
     def __init__(self, elems, index, *, src_loc_at=0):
-        super().__init__(src_loc_at=1 + src_loc_at)
+        self.src_loc = tracer.get_src_loc(1 + src_loc_at)
         self._elems = elems
         self._index = Value.cast(index)
 
@@ -2385,19 +2446,73 @@ class ArrayProxy(Value):
         # elements. I.e., shape-wise, an array proxy must be identical to an equivalent mux tree.
         return Shape._unify(elem.shape() for elem in self._iter_as_values())
 
-    def _lhs_signals(self):
-        signals = union((elem._lhs_signals() for elem in self._iter_as_values()),
-                        start=SignalSet())
-        return signals
+    def as_value(self):
+        return SwitchValue(
+            self._index,
+            (
+                (index, value)
+                for index, value in enumerate(self._elems)
+                if index in range(1 << len(self._index))
+            ),
+            src_loc=self.src_loc,
+        )
 
-    def _rhs_signals(self):
-        signals = union((elem._rhs_signals() for elem in self._iter_as_values()),
-                        start=SignalSet())
-        return self.index._rhs_signals() | signals
+    def eq(self, value, *, src_loc_at=0):
+        return self.as_value().eq(value, src_loc_at=1 + src_loc_at)
 
     def __repr__(self):
         return "(proxy (array [{}]) {!r})".format(", ".join(map(repr, self.elems)), self.index)
 
+    as_signed = _proxy_value("as_signed")
+    as_unsigned = _proxy_value("as_unsigned")
+    __len__ = _proxy_value("__len__")
+    __bool__ = _proxy_value("__bool__")
+    bool = _proxy_value("bool")
+    __pos__ = _proxy_value("__pos__")
+    __neg__ = _proxy_value("__neg__")
+    __add__ = _proxy_value("__add__")
+    __radd__ = _proxy_value("__radd__")
+    __sub__ = _proxy_value("__sub__")
+    __rsub__ = _proxy_value("__rsub__")
+    __mul__ = _proxy_value("__mul__")
+    __rmul__ = _proxy_value("__rmul__")
+    __floordiv__ = _proxy_value("__floordiv__")
+    __rfloordiv__ = _proxy_value("__rfloordiv__")
+    __mod__ = _proxy_value("__mod__")
+    __rmod__ = _proxy_value("__rmod__")
+    __eq__ = _proxy_value("__eq__")
+    __ne__ = _proxy_value("__ne__")
+    __lt__ = _proxy_value("__lt__")
+    __le__ = _proxy_value("__le__")
+    __gt__ = _proxy_value("__gt__")
+    __ge__ = _proxy_value("__ge__")
+    __abs__ = _proxy_value("__abs__")
+    __invert__ = _proxy_value("__invert__")
+    __and__ = _proxy_value("__and__")
+    __rand__ = _proxy_value("__rand__")
+    __or__ = _proxy_value("__or__")
+    __ror__ = _proxy_value("__ror__")
+    __xor__ = _proxy_value("__xor__")
+    __rxor__ = _proxy_value("__rxor__")
+    any = _proxy_value("any")
+    all = _proxy_value("all")
+    xor = _proxy_value("xor")
+    implies = _proxy_value("implies")
+    __lshift__ = _proxy_value("__lshift__")
+    __rlshift__ = _proxy_value("__rlshift__")
+    __rshift__ = _proxy_value("__rshift__")
+    __rrshift__ = _proxy_value("__rrshift__")
+    shift_left = _proxy_value("shift_left")
+    shift_right = _proxy_value("shift_right")
+    rotate_left = _proxy_value("rotate_left")
+    rotate_right = _proxy_value("rotate_right")
+    __contains__ = _proxy_value("__contains__")
+    bit_select = _proxy_value("bit_select")
+    word_select = _proxy_value("word_select")
+    replicate = _proxy_value("replicate")
+    matches = _proxy_value("matches")
+    __format__ = _proxy_value("__format__")
+
 
 @final
 class Initial(Value):
@@ -2772,7 +2887,7 @@ class Switch(Statement):
             self.src_loc = src_loc
 
         self._test  = Value.cast(test)
-        self._cases = []
+        new_cases = []
         for patterns, stmts, case_src_loc in cases:
             if patterns is not None:
                 # Map: key -> (key,); (key...) -> (key...)
@@ -2787,10 +2902,8 @@ class Switch(Statement):
                     new_patterns = (*new_patterns, key)
             else:
                 new_patterns = None
-            if not isinstance(stmts, Iterable):
-                stmts = [stmts]
-            self._cases.append((new_patterns, Statement.cast(stmts), case_src_loc))
-        self._cases = tuple(self._cases)
+            new_cases.append((new_patterns, Statement.cast(stmts), case_src_loc))
+        self._cases = tuple(new_cases)
 
     @property
     def test(self):
@@ -2816,7 +2929,7 @@ class Switch(Statement):
                 return f"(case {patterns[0]} {stmts_repr})"
             else:
                 return "(case ({}) {})".format(" ".join(patterns), stmts_repr)
-        case_reprs = [case_repr(patterns, stmts) for patterns, stmts, _src_loc in self.cases]
+        case_reprs = (case_repr(patterns, stmts) for patterns, stmts, _src_loc in self.cases)
         return "(switch {!r} {})".format(self.test, " ".join(case_reprs))
 
 
diff --git a/amaranth/hdl/_ir.py b/amaranth/hdl/_ir.py
index 717db2e..b4c3801 100644
--- a/amaranth/hdl/_ir.py
+++ b/amaranth/hdl/_ir.py
@@ -9,8 +9,8 @@ from . import _ast, _cd, _ir, _nir
 
 
 __all__ = [
-    "UnusedElaboratable", "Elaboratable", "DriverConflict", "Fragment", "Instance",
-    "IOBufferInstance", "PortDirection", "Design", "build_netlist",
+    "UnusedElaboratable", "Elaboratable", "DuplicateElaboratable", "DriverConflict", "Fragment",
+    "Instance", "IOBufferInstance", "PortDirection", "Design", "build_netlist",
 ]
 
 
@@ -30,6 +30,10 @@ class DriverConflict(UserWarning):
     pass
 
 
+class DuplicateElaboratable(Exception):
+    pass
+
+
 class Fragment:
     @staticmethod
     def get(obj, platform):
@@ -430,6 +434,7 @@ class Design:
         self.hierarchy = hierarchy
         self.fragments: dict[Fragment, DesignFragmentInfo] = {}
         self.signal_lca = _ast.SignalDict()
+        self.elaboratables: dict[Elaboratable, Fragment] = {}
         self._compute_fragment_depth_parent(fragment, None, 0)
         self._collect_used_signals(fragment)
         self._add_io_ports()
@@ -598,6 +603,15 @@ class Design:
         frag_info = self.fragments[fragment]
         frag_info.name = hierarchy
 
+        if fragment.origins is not None:
+            for origin in fragment.origins:
+                if origin in self.elaboratables:
+                    other_hierarchy = self.fragments[self.elaboratables[origin]].name
+                    raise DuplicateElaboratable(f"Elaboratable {origin!r} is included twice "
+                                                f"in the hierarchy, as {'.'.join(other_hierarchy)} "
+                                                f"and {'.'.join(hierarchy)}")
+                self.elaboratables[origin] = fragment
+
         if fragment is self.fragment:
             # Reserve names for top-level ports. If equal to the signal name, let the signal share it.
             for name, conn, _dir in self.ports:
@@ -885,30 +899,39 @@ class NetlistEmitter:
                              stride=value.stride, offset=offset, src_loc=value.src_loc)
             result = self.netlist.add_value_cell(value.width, cell)
             signed = False
-        elif isinstance(value, _ast.ArrayProxy):
-            elems = [self.emit_rhs(module_idx, elem) for elem in value.elems]
+        elif isinstance(value, _ast.SwitchValue):
+            test, _signed = self.emit_rhs(module_idx, value.test)
+            conds = []
+            elems = []
+            for patterns, elem, in value.cases:
+                if patterns is not None:
+                    if not patterns:
+                        # Hack: empty pattern set cannot be supported by RTLIL.
+                        continue
+                    for pattern in patterns:
+                        assert len(pattern) == len(test)
+                    cell = _nir.Matches(module_idx, value=test, patterns=patterns,
+                                        src_loc=value.src_loc)
+                    net, = self.netlist.add_value_cell(1, cell)
+                    conds.append(net)
+                else:
+                    conds.append(_nir.Net.from_const(1))
+                elems.append(self.emit_rhs(module_idx, elem))
+            cell = _nir.PriorityMatch(module_idx, en=_nir.Net.from_const(1),
+                                      inputs=_nir.Value(conds),
+                                      src_loc=value.src_loc)
+            conds = self.netlist.add_value_cell(len(conds), cell)
             shape = _ast.Shape._unify(
                 _ast.Shape(len(value), signed)
                 for value, signed in elems
             )
             elems = tuple(self.extend(elem, elem_signed, shape.width) for elem, elem_signed in elems)
-            index, _signed = self.emit_rhs(module_idx, value.index)
-            conds = []
-            for case_index in range(len(elems)):
-                cell = _nir.Matches(module_idx, value=index,
-                                       patterns=(to_binary(case_index, len(index)),),
-                                       src_loc=value.src_loc)
-                subcond, = self.netlist.add_value_cell(1, cell)
-                conds.append(subcond)
-            conds = _nir.Value(conds)
-            cell = _nir.PriorityMatch(module_idx, en=_nir.Net.from_const(1), inputs=conds, src_loc=value.src_loc)
-            conds = self.netlist.add_value_cell(len(conds), cell)
             assignments = [
-                _nir.Assignment(cond=cond, start=0, value=elem, src_loc=value.src_loc)
-                for cond, elem in zip(conds, elems)
+                _nir.Assignment(cond=subcond, start=0, value=elem, src_loc=value.src_loc)
+                for subcond, elem in zip(conds, elems)
             ]
-            cell = _nir.AssignmentList(module_idx, default=elems[0], assignments=assignments,
-                                 src_loc=value.src_loc)
+            cell = _nir.AssignmentList(module_idx, default=_nir.Value.from_const(0, shape.width),
+                                       assignments=assignments, src_loc=value.src_loc)
             result = self.netlist.add_value_cell(shape.width, cell)
             signed = shape.signed
         elif isinstance(value, _ast.Concat):
@@ -1017,19 +1040,29 @@ class NetlistEmitter:
                 else:
                     subrhs = rhs
                 self.emit_assign(module_idx, cd, lhs.value, start, subrhs, subcond, src_loc=src_loc)
-        elif isinstance(lhs, _ast.ArrayProxy):
-            index, _signed = self.emit_rhs(module_idx, lhs.index)
+        elif isinstance(lhs, _ast.SwitchValue):
+            test, _signed = self.emit_rhs(module_idx, lhs.test)
             conds = []
-            for case_index in range(len(lhs.elems)):
-                cell = _nir.Matches(module_idx, value=index,
-                                       patterns=(to_binary(case_index, len(index)),),
-                                       src_loc=lhs.src_loc)
-                subcond, = self.netlist.add_value_cell(1, cell)
-                conds.append(subcond)
+            elems = []
+            for patterns, elem in lhs.cases:
+                if patterns is not None:
+                    if not patterns:
+                        # Hack: empty pattern set cannot be supported by RTLIL.
+                        continue
+                    for pattern in patterns:
+                        assert len(pattern) == len(test)
+                    cell = _nir.Matches(module_idx, value=test, patterns=patterns,
+                                        src_loc=lhs.src_loc)
+                    net, = self.netlist.add_value_cell(1, cell)
+                    conds.append(net)
+                else:
+                    conds.append(_nir.Net.from_const(1))
+                elems.append(elem)
             conds = _nir.Value(conds)
-            cell = _nir.PriorityMatch(module_idx, en=cond, inputs=conds, src_loc=lhs.src_loc)
+            cell = _nir.PriorityMatch(module_idx, en=_nir.Net.from_const(1),
+                                      inputs=conds, src_loc=lhs.src_loc)
             conds = self.netlist.add_value_cell(len(conds), cell)
-            for subcond, val in zip(conds, lhs.elems):
+            for subcond, val in zip(conds, elems):
                 self.emit_assign(module_idx, cd, val, lhs_start, rhs[:len(val)], subcond, src_loc=src_loc)
         elif isinstance(lhs, _ast.Operator):
             assert lhs.operator in ('u', 's')
diff --git a/amaranth/hdl/_xfrm.py b/amaranth/hdl/_xfrm.py
index 01b4fa1..ccc91ae 100644
--- a/amaranth/hdl/_xfrm.py
+++ b/amaranth/hdl/_xfrm.py
@@ -58,7 +58,7 @@ class ValueVisitor(metaclass=ABCMeta):
         pass # :nocov:
 
     @abstractmethod
-    def on_ArrayProxy(self, value):
+    def on_SwitchValue(self, value):
         pass # :nocov:
 
     @abstractmethod
@@ -90,8 +90,8 @@ class ValueVisitor(metaclass=ABCMeta):
             new_value = self.on_Part(value)
         elif type(value) is Concat:
             new_value = self.on_Concat(value)
-        elif type(value) is ArrayProxy:
-            new_value = self.on_ArrayProxy(value)
+        elif type(value) is SwitchValue:
+            new_value = self.on_SwitchValue(value)
         elif type(value) is Initial:
             new_value = self.on_Initial(value)
         else:
@@ -133,9 +133,8 @@ class ValueTransformer(ValueVisitor):
     def on_Concat(self, value):
         return Concat(self.on_value(o) for o in value.parts)
 
-    def on_ArrayProxy(self, value):
-        return ArrayProxy([self.on_value(elem) for elem in value._iter_as_values()],
-                          self.on_value(value.index))
+    def on_SwitchValue(self, value):
+        return SwitchValue(self.on_value(value.test), [(patterns, self.on_value(val)) for patterns, val in value.cases])
 
     def on_Initial(self, value):
         return value
@@ -319,6 +318,7 @@ class FragmentTransformer:
         else:
             new_fragment = Fragment(src_loc=fragment.src_loc)
         new_fragment.attrs = OrderedDict(fragment.attrs)
+        new_fragment.origins = fragment.origins
         self.map_subfragments(fragment, new_fragment)
         self.map_domains(fragment, new_fragment)
         self.map_statements(fragment, new_fragment)
@@ -399,10 +399,10 @@ class DomainCollector(ValueVisitor, StatementVisitor):
         for o in value.parts:
             self.on_value(o)
 
-    def on_ArrayProxy(self, value):
-        for elem in value._iter_as_values():
-            self.on_value(elem)
-        self.on_value(value.index)
+    def on_SwitchValue(self, value):
+        self.on_value(value.test)
+        for patterns, val in value.cases:
+            self.on_value(val)
 
     def on_Initial(self, value):
         pass
diff --git a/amaranth/sim/_pyrtl.py b/amaranth/sim/_pyrtl.py
index 3f41f34..14e8b01 100644
--- a/amaranth/sim/_pyrtl.py
+++ b/amaranth/sim/_pyrtl.py
@@ -67,6 +67,53 @@ class _Compiler:
         self.state = state
         self.emitter = emitter
 
+    def _emit_switch(self, test, cases, case_handler):
+        if not cases:
+            return
+        use_match = _USE_PATTERN_MATCHING
+        for patterns, *_ in cases:
+            if patterns is None:
+                continue
+            for pattern in patterns:
+                if "-" in pattern:
+                    use_match = False
+        if use_match:
+            self.emitter.append(f"match {test}:")
+            with self.emitter.indent():
+                for case in cases:
+                    patterns = case[0]
+                    if patterns is None:
+                        self.emitter.append(f"case _:")
+                    elif not patterns:
+                        self.emitter.append(f"case _ if False:")
+                    else:
+                        self.emitter.append(f"case {' | '.join(f'0b0{pattern}' for pattern in patterns)}:")
+                    with self.emitter.indent():
+                        case_handler(*case)
+        else:
+            for index, case in enumerate(cases):
+                patterns = case[0]
+                gen_checks = []
+                if patterns is None:
+                    gen_checks.append(f"True")
+                elif not patterns:
+                    gen_checks.append(f"False")
+                else:
+                    for pattern in patterns:
+                        if "-" in pattern:
+                            mask  = int("".join("0" if b == "-" else "1" for b in pattern), 2)
+                            value = int("".join("0" if b == "-" else  b  for b in pattern), 2)
+                            gen_checks.append(f"{value} == ({mask} & {test})")
+                        else:
+                            value = int(pattern or "0", 2)
+                            gen_checks.append(f"{value} == {test}")
+                if index == 0:
+                    self.emitter.append(f"if {' or '.join(gen_checks)}:")
+                else:
+                    self.emitter.append(f"elif {' or '.join(gen_checks)}:")
+                with self.emitter.indent():
+                    case_handler(*case)
+
 
 class _ValueCompiler(ValueVisitor, _Compiler):
     helpers = {
@@ -223,36 +270,13 @@ class _RHSValueCompiler(_ValueCompiler):
             return f"({' | '.join(gen_parts)})"
         return f"0"
 
-    def on_ArrayProxy(self, value):
-        index_mask = (1 << len(value.index)) - 1
-        gen_index = self.emitter.def_var("rhs_index", f"{index_mask:#x} & {self(value.index)}")
-        gen_value = self.emitter.gen_var("rhs_proxy")
-        if value.elems:
-            if _USE_PATTERN_MATCHING:
-                self.emitter.append(f"match {gen_index}:")
-                with self.emitter.indent():
-                    for index, elem in enumerate(value.elems):
-                        self.emitter.append(f"case {index}:")
-                        with self.emitter.indent():
-                            self.emitter.append(f"{gen_value} = {self(elem)}")
-                    self.emitter.append("case _:")
-                    with self.emitter.indent():
-                            self.emitter.append(f"{gen_value} = {self(value.elems[-1])}")
-            else:
-                for index, elem in enumerate(value.elems):
-                    if index == 0:
-                        self.emitter.append(f"if {index} == {gen_index}:")
-                    else:
-                        self.emitter.append(f"elif {index} == {gen_index}:")
-                    with self.emitter.indent():
-                        self.emitter.append(f"{gen_value} = {self(elem)}")
-                self.emitter.append(f"else:")
-                with self.emitter.indent():
-                    self.emitter.append(f"{gen_value} = {self(value.elems[-1])}")
-
-            return gen_value
-        else:
-            return f"0"
+    def on_SwitchValue(self, value):
+        gen_test = self.emitter.def_var("test", f"{(1 << len(value.test)) - 1:#x} & {self(value.test)}")
+        gen_value = self.emitter.def_var("rhs_switch", "0")
+        def case_handler(patterns, elem):
+            self.emitter.append(f"{gen_value} = {self(elem)}")
+        self._emit_switch(gen_test, value.cases, case_handler)
+        return gen_value
 
     @classmethod
     def compile(cls, state, value, *, mode):
@@ -323,34 +347,12 @@ class _LHSValueCompiler(_ValueCompiler):
                 offset += len(part)
         return gen
 
-    def on_ArrayProxy(self, value):
+    def on_SwitchValue(self, value):
         def gen(arg):
-            index_mask = (1 << len(value.index)) - 1
-            gen_index = self.emitter.def_var("index", f"{self.rrhs(value.index)} & {index_mask:#x}")
-            if value.elems:
-                if _USE_PATTERN_MATCHING:
-                    self.emitter.append(f"match {gen_index}:")
-                    with self.emitter.indent():
-                        for index, elem in enumerate(value.elems):
-                            self.emitter.append(f"case {index}:")
-                            with self.emitter.indent():
-                                self(elem)(arg)
-                        self.emitter.append("case _:")
-                        with self.emitter.indent():
-                            self(value.elems[-1])(arg)
-                else:
-                    for index, elem in enumerate(value.elems):
-                        if index == 0:
-                            self.emitter.append(f"if {index} == {gen_index}:")
-                        else:
-                            self.emitter.append(f"elif {index} == {gen_index}:")
-                        with self.emitter.indent():
-                            self(elem)(arg)
-                    self.emitter.append(f"else:")
-                    with self.emitter.indent():
-                        self(value.elems[-1])(arg)
-            else:
-                self.emitter.append(f"pass")
+            gen_test = self.emitter.def_var("test", f"{(1 << len(value.test)) - 1:#x} & {self.rrhs(value.test)}")
+            def case_handler(patterns, elem):
+                self(elem)(arg)
+            self._emit_switch(gen_test, value.cases, case_handler)
         return gen
 
 
@@ -396,27 +398,9 @@ class _StatementCompiler(StatementVisitor, _Compiler):
     def on_Switch(self, stmt):
         gen_test_value = self.rhs(stmt.test) # check for oversized value before generating mask
         gen_test = self.emitter.def_var("test", f"{(1 << len(stmt.test)) - 1:#x} & {gen_test_value}")
-        for index, (patterns, stmts, _src_loc) in enumerate(stmt.cases):
-            gen_checks = []
-            if patterns is None:
-                gen_checks.append(f"True")
-            elif not patterns:
-                gen_checks.append(f"False")
-            else:
-                for pattern in patterns:
-                    if "-" in pattern:
-                        mask  = int("".join("0" if b == "-" else "1" for b in pattern), 2)
-                        value = int("".join("0" if b == "-" else  b  for b in pattern), 2)
-                        gen_checks.append(f"{value} == ({mask} & {gen_test})")
-                    else:
-                        value = int(pattern or "0", 2)
-                        gen_checks.append(f"{value} == {gen_test}")
-            if index == 0:
-                self.emitter.append(f"if {' or '.join(gen_checks)}:")
-            else:
-                self.emitter.append(f"elif {' or '.join(gen_checks)}:")
-            with self.emitter.indent():
-                self(stmts)
+        def case_handler(pattern, stmt, src_loc):
+            self(stmt)
+        self._emit_switch(gen_test, stmt.cases, case_handler)
 
     def emit_format(self, format):
         format_string = []


Test patch:
diff --git a/tests/test_hdl_ast.py b/tests/test_hdl_ast.py
index 23e8e76..e17268a 100644
--- a/tests/test_hdl_ast.py
+++ b/tests/test_hdl_ast.py
@@ -1144,6 +1144,7 @@ class ArrayProxyTestCase(FHDLTestCase):
         s = Signal(range(3))
         v = a[s]
         self.assertEqual(repr(v), "(proxy (array [1, 2, 3]) (sig s))")
+        self.assertEqual(repr(v.as_value()), "(switch-value (sig s) (case 00 (const 1'd1)) (case 01 (const 2'd2)) (case 10 (const 2'd3)))")
 
 
 class SignalTestCase(FHDLTestCase):
diff --git a/tests/test_hdl_ir.py b/tests/test_hdl_ir.py
index 07464e3..f54bc08 100644
--- a/tests/test_hdl_ir.py
+++ b/tests/test_hdl_ir.py
@@ -77,6 +77,18 @@ class FragmentDriversTestCase(FHDLTestCase):
         self.assertEqual(list(f.iter_sync()), [])
 
 
+class DuplicateElaboratableTestCase(FHDLTestCase):
+    def test_duplicate(self):
+        sub = Module()
+        m = Module()
+        m.submodules.a = sub
+        m.submodules.b = sub
+        with self.assertRaisesRegex(DuplicateElaboratable,
+                r"^Elaboratable .* is included twice in the hierarchy, as "
+                r"top\.a and top\.b$"):
+            Fragment.get(m, None).prepare()
+
+
 class FragmentPortsTestCase(FHDLTestCase):
     def setUp(self):
         self.s1 = Signal()
@@ -1623,6 +1635,69 @@ class AssignTestCase(FHDLTestCase):
         )
         """)
 
+    def test_switchvalue(self):
+        s1 = Signal(8)
+        s2 = Signal(8)
+        s3 = Signal(8)
+        s4 = Signal(8)
+        s5 = Signal(8)
+        s6 = Signal(8)
+        s7 = Signal(8)
+        f = Fragment()
+        f.add_statements("comb", [
+            SwitchValue(s5[:4], [
+                (1, s1),
+                ((2, 3), s2),
+                ((), s3),
+                ('11--', s4),
+            ]).eq(s6),
+            SwitchValue(s5[4:], [
+                (4, s1),
+                (5, s2),
+                (6, s3),
+                (None, s4),
+            ]).eq(s7),
+        ])
+        f.add_driver(s1, "comb")
+        f.add_driver(s2, "comb")
+        f.add_driver(s3, "comb")
+        f.add_driver(s4, "comb")
+        nl = build_netlist(f, ports=[s1, s2, s3, s4, s5, s6, s7])
+        self.assertRepr(nl, """
+        (
+            (module 0 None ('top')
+                (input 's5' 0.2:10)
+                (input 's6' 0.10:18)
+                (input 's7' 0.18:26)
+                (output 's1' 9.0:8)
+                (output 's2' 10.0:8)
+                (output 's3' 12.0:8)
+                (output 's4' 11.0:8)
+            )
+            (cell 0 0 (top
+                (input 's5' 2:10)
+                (input 's6' 10:18)
+                (input 's7' 18:26)
+                (output 's1' 9.0:8)
+                (output 's2' 10.0:8)
+                (output 's3' 12.0:8)
+                (output 's4' 11.0:8)
+            ))
+            (cell 1 0 (matches 0.2:6 0001))
+            (cell 2 0 (matches 0.2:6 0010 0011))
+            (cell 3 0 (matches 0.2:6 11--))
+            (cell 4 0 (priority_match 1 (cat 1.0 2.0 3.0)))
+            (cell 5 0 (matches 0.6:10 0100))
+            (cell 6 0 (matches 0.6:10 0101))
+            (cell 7 0 (matches 0.6:10 0110))
+            (cell 8 0 (priority_match 1 (cat 5.0 6.0 7.0 1'd1)))
+            (cell 9 0 (assignment_list 8'd0 (4.0 0:8 0.10:18) (8.0 0:8 0.18:26)))
+            (cell 10 0 (assignment_list 8'd0 (4.1 0:8 0.10:18) (8.1 0:8 0.18:26)))
+            (cell 11 0 (assignment_list 8'd0 (4.2 0:8 0.10:18) (8.3 0:8 0.18:26)))
+            (cell 12 0 (assignment_list 8'd0 (8.2 0:8 0.18:26)))
+        )
+        """)
+
     def test_sliced_slice(self):
         s1 = Signal(12)
         s2 = Signal(4)
@@ -2953,7 +3028,7 @@ class RhsTestCase(FHDLTestCase):
             (cell 2 0 (matches 0.50:54 0001))
             (cell 3 0 (matches 0.50:54 0010))
             (cell 4 0 (priority_match 1 (cat 1.0 2.0 3.0)))
-            (cell 5 0 (assignment_list 0.2:10
+            (cell 5 0 (assignment_list 8'd0
                 (4.0 0:8 0.2:10)
                 (4.1 0:8 0.10:18)
                 (4.2 0:8 0.18:26)
@@ -2962,7 +3037,7 @@ class RhsTestCase(FHDLTestCase):
             (cell 7 0 (matches 0.50:54 0001))
             (cell 8 0 (matches 0.50:54 0010))
             (cell 9 0 (priority_match 1 (cat 6.0 7.0 8.0)))
-            (cell 10 0 (assignment_list (cat 0.2:10 1'd0)
+            (cell 10 0 (assignment_list 9'd0
                 (9.0 0:9 (cat 0.2:10 1'd0))
                 (9.1 0:9 (cat 0.10:18 1'd0))
                 (9.2 0:9 (cat 0.42:50 0.49))
@@ -2971,7 +3046,7 @@ class RhsTestCase(FHDLTestCase):
             (cell 12 0 (matches 0.50:54 0001))
             (cell 13 0 (matches 0.50:54 0010))
             (cell 14 0 (priority_match 1 (cat 11.0 12.0 13.0)))
-            (cell 15 0 (assignment_list 0.26:34
+            (cell 15 0 (assignment_list 8'd0
                 (14.0 0:8 0.26:34)
                 (14.1 0:8 0.34:42)
                 (14.2 0:8 0.42:50)
@@ -2980,7 +3055,7 @@ class RhsTestCase(FHDLTestCase):
             (cell 17 0 (matches 0.50:54 0001))
             (cell 18 0 (matches 0.50:54 0010))
             (cell 19 0 (priority_match 1 (cat 16.0 17.0 18.0)))
-            (cell 20 0 (assignment_list 0.26:34
+            (cell 20 0 (assignment_list 8'd0
                 (19.0 0:8 0.26:34)
                 (19.1 0:8 0.34:42)
                 (19.2 0:8 (cat 0.50:54 4'd0))
@@ -2988,6 +3063,67 @@ class RhsTestCase(FHDLTestCase):
         )
         """)
 
+    def test_switchvalue(self):
+        i8ua = Signal(8)
+        i8ub = Signal(8)
+        i8uc = Signal(8)
+        i8ud = Signal(8)
+        i4 = Signal(4)
+        o1 = Signal(10)
+        o2 = Signal(10)
+        m = Module()
+        m.d.comb += o1.eq(SwitchValue(i4, [
+            (1, i8ua),
+            ((2, 3), i8ub),
+            ('11--', i8uc),
+        ]))
+        m.d.comb += o2.eq(SwitchValue(i4, [
+            ((4, 5), i8ua),
+            ((), i8ub),
+            ((6, 7), i8uc),
+            (None, i8ud),
+        ]))
+        nl = build_netlist(Fragment.get(m, None), [i8ua, i8ub, i8uc, i8ud, i4, o1, o2])
+        self.assertRepr(nl, """
+        (
+            (module 0 None ('top')
+                (input 'i8ua' 0.2:10)
+                (input 'i8ub' 0.10:18)
+                (input 'i8uc' 0.18:26)
+                (input 'i8ud' 0.26:34)
+                (input 'i4' 0.34:38)
+                (output 'o1' (cat 5.0:8 2'd0))
+                (output 'o2' (cat 9.0:8 2'd0))
+            )
+            (cell 0 0 (top
+                (input 'i8ua' 2:10)
+                (input 'i8ub' 10:18)
+                (input 'i8uc' 18:26)
+                (input 'i8ud' 26:34)
+                (input 'i4' 34:38)
+                (output 'o1' (cat 5.0:8 2'd0))
+                (output 'o2' (cat 9.0:8 2'd0))
+            ))
+            (cell 1 0 (matches 0.34:38 0001))
+            (cell 2 0 (matches 0.34:38 0010 0011))
+            (cell 3 0 (matches 0.34:38 11--))
+            (cell 4 0 (priority_match 1 (cat 1.0 2.0 3.0)))
+            (cell 5 0 (assignment_list 8'd0
+                (4.0 0:8 0.2:10)
+                (4.1 0:8 0.10:18)
+                (4.2 0:8 0.18:26)
+            ))
+            (cell 6 0 (matches 0.34:38 0100 0101))
+            (cell 7 0 (matches 0.34:38 0110 0111))
+            (cell 8 0 (priority_match 1 (cat 6.0 7.0 1'd1)))
+            (cell 9 0 (assignment_list 8'd0
+                (8.0 0:8 0.2:10)
+                (8.1 0:8 0.18:26)
+                (8.2 0:8 0.26:34)
+            ))
+        )
+        """)
+
     def test_anyvalue(self):
         o1 = Signal(12)
         o2 = Signal(12)
diff --git a/tests/test_sim.py b/tests/test_sim.py
index 9be4299..bb5d495 100644
--- a/tests/test_sim.py
+++ b/tests/test_sim.py
@@ -314,8 +314,8 @@ class SimulatorUnitTestCase(FHDLTestCase):
     def test_array_oob(self):
         array = Array([1, 4, 10])
         stmt = lambda y, a: y.eq(array[a])
-        self.assertStatement(stmt, [C(3)], C(10))
-        self.assertStatement(stmt, [C(4)], C(10))
+        self.assertStatement(stmt, [C(3)], C(0))
+        self.assertStatement(stmt, [C(4)], C(0))
 
     def test_array_lhs(self):
         l = Signal(3, init=1)
@@ -333,8 +333,8 @@ class SimulatorUnitTestCase(FHDLTestCase):
         n = Signal(3)
         array = Array([l, m, n])
         stmt = lambda y, a, b: [array[a].eq(b), y.eq(Cat(*array))]
-        self.assertStatement(stmt, [C(3), C(0b001)], C(0b001000000))
-        self.assertStatement(stmt, [C(4), C(0b010)], C(0b010000000))
+        self.assertStatement(stmt, [C(3), C(0b001)], C(0))
+        self.assertStatement(stmt, [C(4), C(0b010)], C(0))
 
     def test_array_index(self):
         array = Array(Array(x * y for y in range(10)) for x in range(10))
@@ -513,6 +513,8 @@ class SimulatorIntegrationTestCase(FHDLTestCase):
         with self.m.Switch(self.s):
             with self.m.Case(0):
                 self.m.d.sync += self.o.eq(self.a + self.b)
+            with self.m.Case():
+                self.m.d.sync += self.o.eq(self.a * self.b)
             with self.m.Case(1):
                 self.m.d.sync += self.o.eq(self.a - self.b)
             with self.m.Default():