hdl.ast: simplify Mux implementation.

nmigen/back/rtlil.py

@@ -562,6 +562,8 @@ class _RHSValueCompiler(_ValueCompiler):
 
     def on_Operator_mux(self, value):
         sel, val1, val0 = value.operands
+        if len(sel) != 1:
+            sel = sel.bool()
         val1_bits, val1_sign = val1.shape()
         val0_bits, val0_sign = val0.shape()
         res_bits, res_sign = value.shape()

nmigen/hdl/ast.py

@@ -735,9 +735,6 @@ def Mux(sel, val1, val0):
     Value, out
         Output ``Value``. If ``sel`` is asserted, the Mux returns ``val1``, else ``val0``.
     """
-    sel = Value.cast(sel)
-    if len(sel) != 1:
-        sel = sel.bool()
     return Operator("m", [sel, val1, val0])