tcg/optimize: Simplify fold_and constant checks

If operand 2 is constant, then the computation of z_mask
and a_mask will produce the same results as the explicit
checks via fold_xi_to_i and fold_xi_to_x.  Shift the call
of fold_xx_to_x down below the ti_is_const(t2) check.

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
1 file changed