hdl.ast: warn on unused property statements (Assert, Assume, etc).

A property statement that is created but not added to a module is
virtually always a serious bug, since it can make formal verification
pass when it should not. Therefore, add a warning to it, similar to
UnusedElaboratable.

Doing this to all statements is possible, but many temporary ones are
created internally by nMigen, and the extensive changes required to
remove false positives are likely not worth the true positives.
We can revisit this in the future.

Fixes #303.

diff --git a/nmigen/hdl/ast.py b/nmigen/hdl/ast.py
index d26c3c3d9c154f03dd4a2d0ba941c1fd07f969ae..efaeb0ff7d48635bcea5724bc0345064d6bbe92a 100644 (file)
--- a/nmigen/hdl/ast.py
+++ b/nmigen/hdl/ast.py
@@ -8,6 +8,7 @@ from enum import Enum
 
 from .. import tracer
 from .._utils import *
+from .._unused import *
 
 
 __all__ = [
@@ -17,9 +18,9 @@ __all__ = [
     "Signal", "ClockSignal", "ResetSignal",
     "UserValue",
     "Sample", "Past", "Stable", "Rose", "Fell", "Initial",
-    "Statement", "Assign", "Assert", "Assume", "Cover", "Switch",
-    "ValueKey", "ValueDict", "ValueSet", "SignalKey", "SignalDict",
-    "SignalSet",
+    "Statement", "Switch",
+    "Property", "Assign", "Assert", "Assume", "Cover",
+    "ValueKey", "ValueDict", "ValueSet", "SignalKey", "SignalDict", "SignalSet",
 ]
 
 
@@ -493,13 +494,13 @@ class AnyValue(Value, DUID):
 @final
 class AnyConst(AnyValue):
     def __repr__(self):
-        return "(anyconst {}'{})".format(self.nbits, "s" if self.signed else "")
+        return "(anyconst {}'{})".format(self.width, "s" if self.signed else "")
 
 
 @final
 class AnySeq(AnyValue):
     def __repr__(self):
-        return "(anyseq {}'{})".format(self.nbits, "s" if self.signed else "")
+        return "(anyseq {}'{})".format(self.width, "s" if self.signed else "")
 
 
 @final
@@ -1221,7 +1222,13 @@ class Assign(Statement):
         return "(eq {!r} {!r})".format(self.lhs, self.rhs)
 
 
-class Property(Statement):
+class UnusedProperty(UnusedMustUse):
+    pass
+
+
+class Property(Statement, MustUse):
+    _MustUse__warning = UnusedProperty
+
     def __init__(self, test, *, _check=None, _en=None, src_loc_at=0):
         super().__init__(src_loc_at=src_loc_at)
         self.test   = Value.cast(test)

diff --git a/nmigen/hdl/dsl.py b/nmigen/hdl/dsl.py
index b8f7692ec63454279cab8af96849e378c2d8ec68..986ecc0c4efe34a8b836eba2bac10334d8d02aa8 100644 (file)
--- a/nmigen/hdl/dsl.py
+++ b/nmigen/hdl/dsl.py
@@ -462,14 +462,16 @@ class Module(_ModuleBuilderRoot, Elaboratable):
         while len(self._ctrl_stack) > self.domain._depth:
             self._pop_ctrl()
 
-        for assign in Statement.cast(assigns):
-            if not compat_mode and not isinstance(assign, (Assign, Assert, Assume, Cover)):
+        for stmt in Statement.cast(assigns):
+            if not compat_mode and not isinstance(stmt, (Assign, Assert, Assume, Cover)):
                 raise SyntaxError(
                     "Only assignments and property checks may be appended to d.{}"
                     .format(domain_name(domain)))
 
-            assign = SampleDomainInjector(domain)(assign)
-            for signal in assign._lhs_signals():
+            stmt._MustUse__used = True
+            stmt = SampleDomainInjector(domain)(stmt)
+
+            for signal in stmt._lhs_signals():
                 if signal not in self._driving:
                     self._driving[signal] = domain
                 elif self._driving[signal] != domain:
@@ -479,7 +481,7 @@ class Module(_ModuleBuilderRoot, Elaboratable):
                         "already driven from d.{}"
                         .format(signal, domain_name(domain), domain_name(cd_curr)))
 
-            self._statements.append(assign)
+            self._statements.append(stmt)
 
     def _add_submodule(self, submodule, name=None):
         if not hasattr(submodule, "elaborate"):

diff --git a/nmigen/hdl/ir.py b/nmigen/hdl/ir.py
index 5d4a1c57d9afda472721edd18a51fbe84968968e..cea9b4034d7f9755d942fd8cb814340e77e90379 100644 (file)
--- a/nmigen/hdl/ir.py
+++ b/nmigen/hdl/ir.py
@@ -121,7 +121,9 @@ class Fragment:
         yield from self.domains
 
     def add_statements(self, *stmts):
-        self.statements += Statement.cast(stmts)
+        for stmt in Statement.cast(stmts):
+            stmt._MustUse__used = True
+            self.statements.append(stmt)
 
     def add_subfragment(self, subfragment, name=None):
         assert isinstance(subfragment, Fragment)

diff --git a/nmigen/hdl/xfrm.py b/nmigen/hdl/xfrm.py
index 75f85ba6a24be76746ceb1418ea9c425c159ff8d..fb4dad954b704313e56ec73c5eb3da8340cdf4f4 100644 (file)
--- a/nmigen/hdl/xfrm.py
+++ b/nmigen/hdl/xfrm.py
@@ -234,6 +234,8 @@ class StatementVisitor(metaclass=ABCMeta):
             new_stmt.src_loc = stmt.src_loc
             if isinstance(new_stmt, Switch) and isinstance(stmt, Switch):
                 new_stmt.case_src_locs = stmt.case_src_locs
+        if isinstance(new_stmt, Property):
+            new_stmt._MustUse__used = True
         return new_stmt
 
     def __call__(self, stmt):