Re: [PR25529] Convert (unsigned t * 2)/2 into unsigned (t & 0x7FFFFFFF)

[Richard Biener <richard.guenther@gmail.com>]

On Tue, Jul 7, 2015 at 8:06 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
> On Tue, 7 Jul 2015, Hurugalawadi, Naveen wrote:
>
>> Please find attached the patch "PR25529.patch" that converts the pattern:-
>> (unsigned * 2)/2 is into unsigned &0x7FFFFFFF
>
>
> +/* Simplify (unsigned t * 2)/2 -> unsigned t & 0x7FFFFFFF.  */
> +(for div (trunc_div ceil_div floor_div round_div exact_div)
> + (simplify
> +  (div (mult @0 INTEGER_CST@1) INTEGER_CST@1)
>
> You don't need to repeat INTEGER_CST, the second time @1 is enough.
>
> +  (with { tree n2 = build_int_cst (TREE_TYPE (@0),
> +                                  wi::exact_log2 (@1)); }
> +  (if (TYPE_UNSIGNED (TREE_TYPE (@0)))
> +   (bit_and @0 (rshift (lshift { build_minus_one_cst (TREE_TYPE (@0)); }
> +                              { n2; }) { n2; }))))))
>
> What happens if you write t*3/3?

Huh, and you posted this patch twice?  See my reply to the other copy
for the correctness issues and better handling of exact_div

Richard.

> --
> Marc Glisse