hdl.ast: remove dead code. NFC.

See #548.

Author: whitequark

nmigen/hdl/ast.py

@@ -702,17 +702,11 @@ def _bitwise_binary_shape(a_shape, b_shape):
             if self.operator in ("&", "^", "|"):
                 return _bitwise_binary_shape(*op_shapes)
             if self.operator == "<<":
-                if b_signed:
-                    extra = 2 ** (b_width - 1) - 1
-                else:
-                    extra = 2 ** (b_width)     - 1
-                return Shape(a_width + extra, a_signed)
+                assert not b_signed
+                return Shape(a_width + 2 ** b_width - 1, a_signed)
             if self.operator == ">>":
-                if b_signed:
-                    extra = 2 ** (b_width - 1)
-                else:
-                    extra = 0
-                return Shape(a_width + extra, a_signed)
+                assert not b_signed
+                return Shape(a_width, a_signed)
         elif len(op_shapes) == 3:
             if self.operator == "m":
                 s_shape, a_shape, b_shape = op_shapes