Re: [PATCH] Optimize divmod expansion (PR middle-end/79665)

[Jeff Law <law@redhat.com>]

On 02/22/2017 02:40 PM, Jakub Jelinek wrote:
> Hi!
>
> If both arguments of integer division or modulo are known to be non-negative
> in corresponding signed type, then signed as well as unsigned division/modulo
> shall have the exact same result and therefore we can choose between those
> two depending on which one is faster (or shorter for -Os), which varries
> a lot depending on target and especially for constant divisors on the exact
> divisor.  expand_divmod itself is too complicated and we don't even have
> the ability to ask about costs e.g. for highpart multiplication without
> actually expanding it, so this patch just in that case tries both sequences,
> computes their costs and uses the cheaper (and for equal cost honors the
> actual original signedness of the operation).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
>
> 2017-02-22  Jakub Jelinek  <jakub@redhat.com>
>
> 	PR middle-end/79665
> 	* internal-fn.c (get_range_pos_neg): Moved to ...
> 	* tree.c (get_range_pos_neg): ... here.  No longer static.
> 	* tree.h (get_range_pos_neg): New prototype.
> 	* expr.c (expand_expr_real_2) <case TRUNC_DIV_EXPR>: If both arguments
> 	are known to be in between 0 and signed maximum inclusive, try to
> 	expand both unsigned and signed divmod and use the cheaper one from
> 	those.
OK.
jeff