Re: [PATCH] Optimize certain end of loop conditions into min/max operation

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Jul 27, 2015 at 5:41 AM, Michael Collison
<michael.collison@linaro.org> wrote:
> This patch is designed to optimize end of loop conditions involving of the
> form
>  i < x && i < y into i < min (x, y). Loop condition involving '>' are
> handled similarly using max(x,y).
> As an example:
>
> #define N 1024
>
> int  a[N], b[N], c[N];
>
> void add (unsignedint  m, unsignedint  n)
> {
>   unsignedint  i, bound = (m < n) ? m : n;
>   for  (i = 0; i < m && i < n; ++i)
>     a[i] = b[i] + c[i];
> }
>
>
> Performed bootstrap and make check on: x86_64_unknown-linux-gnu,
> arm-linux-gnueabihf, and aarch64-linux-gnu.
> Okay for trunk?

So this works only for && that has been lowered to non-CFG form
(I suppose phiopt would catch that?  If not, ifcombine would be the
place to implement it I guess).

Furthermore it doesn't work for three such ops which would require
an additional pattern like

 (simplfiy
  (bit_and:c (op @0 (min @1 @2)) (op @0 @3))
  (op @0 (min (min @1 @2) @3))))

if that's profitable?

Richard.

> 2015-07-24  Michael Collison  <michael.collison@linaro.org>
>                     Andrew Pinski <andrew.pinski@caviumnetworks.com>
>
>                 * match.pd ((x < y) && (x < z) -> x < min (y,z),
>                 (x > y) and (x > z) -> x > max (y,z))
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 5e8fd32..8691710 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -1793,3 +1793,17 @@ along with GCC; see the file COPYING3.  If not see
>      (convert (bit_and (op (convert:utype @0) (convert:utype @1))
>                (convert:utype @4)))))))
>
> +
> +/* Transform (@0 < @1 and @0 < @2) to use min */
> +(for op (lt le)
> +(simplify
> +(bit_and:c (op @0 @1) (op @0 @2))
> +(if (INTEGRAL_TYPE_P (TREE_TYPE (@0)))
> +(op @0 (min @1 @2)))))
> +
> +/* Transform (@0 > @1 and @0 > @2) to use max */
> +(for op (gt ge)
> +(simplify
> +(bit_and:c (op @0 @1) (op @0 @2))
> +(if (INTEGRAL_TYPE_P (TREE_TYPE (@0)))
> +(op @0 (max @1 @2)))))
> --
>
> --
> Michael Collison
> Linaro Toolchain Working Group
> michael.collison@linaro.org
>