(simplify_shift_const): Leave only the fallback
case when no simplification is possible. Extract to...
(simplify_shift_const_1): ... here. Always create a new
RTX instead of substituting. Remove the signed_count variable.
Return NULL_RTX if no substitution is possible.
(simplify_and_const_int): Leave only the fallback
case when no simplification is possible. Extract to...
(simplify_and_const_int_1): ... here. Always create a new
RTX instead of substituting. Return NULL_RTX if no substitution
is possible.
(force_to_mode, simplify_comparison): Don't pass a non-NULL first
parameter to simplify_and_const_int and simplify_shift_const,
unless it is equal to the expected non-simplified result.