sim._pyrtl: fix masking for bitwise operands and muxes.

Fixes #926.

Author: wanda-phi

amaranth/sim/_pyrtl.py

@@ -170,11 +170,11 @@ def sign(value):
             if value.operator == "%":
                 return f"zmod({sign(lhs)}, {sign(rhs)})"
             if value.operator == "&":
-                return f"({mask(lhs)} & {mask(rhs)})"
+                return f"({sign(lhs)} & {sign(rhs)})"
             if value.operator == "|":
-                return f"({mask(lhs)} | {mask(rhs)})"
+                return f"({sign(lhs)} | {sign(rhs)})"
             if value.operator == "^":
-                return f"({mask(lhs)} ^ {mask(rhs)})"
+                return f"({sign(lhs)} ^ {sign(rhs)})"
             if value.operator == "<<":
                 return f"({sign(lhs)} << {sign(rhs)})"
             if value.operator == ">>":
@@ -194,7 +194,7 @@ def sign(value):
         elif len(value.operands) == 3:
             if value.operator == "m":
                 sel, val1, val0 = value.operands
-                return f"({self(val1)} if {mask(sel)} else {self(val0)})"
+                return f"({sign(val1)} if {mask(sel)} else {sign(val0)})"
         raise NotImplementedError("Operator '{}' not implemented".format(value.operator)) # :nocov:
 
     def on_Slice(self, value):

tests/test_sim.py

@@ -152,6 +152,9 @@ def test_mod_neg(self):
     def test_and(self):
         stmt = lambda y, a, b: y.eq(a & b)
         self.assertStatement(stmt, [C(0b1100, 4), C(0b1010, 4)], C(0b1000, 4))
+        self.assertStatement(stmt, [C(0b1010, 4), C(0b10, signed(2))], C(0b1010, 4))
+        stmt = lambda y, a: y.eq(a)
+        self.assertStatement(stmt, [C(0b1010, 4) & C(-2, 2).as_unsigned()], C(0b0010, 4))
 
     def test_or(self):
         stmt = lambda y, a, b: y.eq(a | b)
@@ -211,6 +214,9 @@ def test_mux(self):
         stmt = lambda y, a, b, c: y.eq(Mux(c, a, b))
         self.assertStatement(stmt, [C(2, 4), C(3, 4), C(0)], C(3, 4))
         self.assertStatement(stmt, [C(2, 4), C(3, 4), C(1)], C(2, 4))
+        stmt = lambda y, a: y.eq(a)
+        self.assertStatement(stmt, [Mux(0, C(0b1010, 4), C(0b10, 2).as_signed())], C(0b1110, 4))
+        self.assertStatement(stmt, [Mux(0, C(0b1010, 4), C(-2, 2).as_unsigned())], C(0b0010, 4))
 
     def test_mux_invert(self):
         stmt = lambda y, a, b, c: y.eq(Mux(~c, a, b))