On Tue, Oct 17, 2017 at 6:30 PM, Wilco Dijkstra <wilco.dijks...@arm.com> wrote:
> This patch implements some of the optimizations discussed in
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71026.
>
> Canonicalize x / (- y) into (-x) / y.
>
> This moves negates out of the RHS of a division in order to
> allow further simplifications and potentially more reciprocal CSEs.
>
> OK for commit?
Ok.
Richard.
> ChangeLog
> 2017-10-17 Wilco Dijkstra <wdijk...@arm.com>
> Jackson Woodruff <jackson.woodr...@arm.com>
>
> gcc/
> PR 71026/tree-optimization
> * match.pd: Canonicalize negate in division.
>
> gcc/testsuite/
> PR 71026/tree-optimization
> * gcc.dg/div_neg: New test.
> --
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index
> cb48f079b4a310272e49cc319a1b3b0ff2023ba4..ade851f78fb9ac6ce03b752f63e03f3b5a19cda9
> 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -352,6 +352,11 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
> (rdiv @0 (rdiv:s @1 @2))
> (mult (rdiv @0 @1) @2)))
>
> +/* Simplify x / (- y) to -x / y. */
> +(simplify
> + (rdiv @0 (negate @1))
> + (rdiv (negate @0) @1))
> +
> (if (flag_unsafe_math_optimizations)
> /* Simplify (C / x op 0.0) to x op 0.0 for C > 0. */
> (for op (lt le gt ge)
> diff --git a/gcc/testsuite/gcc.dg/div_neg.c b/gcc/testsuite/gcc.dg/div_neg.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..da499cda2fba6c943ec99c55cae2ea389f9e1cca
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/div_neg.c
> @@ -0,0 +1,10 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +
> +float
> +div_neg (float x, float y)
> +{
> + return (-x / y) * (x / -y);
> +}
> +
> +/* { dg-final { scan-tree-dump-times " / " 1 "optimized" } } */
