tcg/optimize: Simplify sign bit test in fold_shift

Merge the two conditions, sign != 0 && !(z_mask & sign),
by testing ~z_mask & sign.   If sign == 0, the logical and
will produce false.

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