On Mon, Feb 22, 2016 at 06:50:44PM -0600, Evandro Menezes wrote:
> In preparation for the patch adding the Newton series also for
> square root, I'd like to propose this patch changing the name of the
> existing tuning flag for the reciprocal square root.
This is fine, other names like sw_rsqrt, expand_rsqrt, nr_rsqrt would also
be OK. Pick your favourite!
One comment on the replacement invoke.texi text below, otherwise this is
OK to apply now.
> diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
> index 5cbd4cd..155d2bd 100644
> --- a/gcc/config/aarch64/aarch64.opt
> +++ b/gcc/config/aarch64/aarch64.opt
> @@ -151,5 +151,5 @@ PC relative literal loads.
>
> mlow-precision-recip-sqrt
> Common Var(flag_mrecip_low_precision_sqrt) Optimization
> -When calculating a sqrt approximation, run fewer steps.
> +Calculate the reciprocal square-root approximation in fewer steps.
> This reduces precision, but can result in faster computation.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index 490df93..eeff24d 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -12879,12 +12879,10 @@ corresponding flag to the linker.
> @item -mno-low-precision-recip-sqrt
> @opindex -mlow-precision-recip-sqrt
> @opindex -mno-low-precision-recip-sqrt
> -The square root estimate uses two steps instead of three for
> double-precision,
> -and one step instead of two for single-precision.
> -Thus reducing latency and precision.
> -This is only relevant if @option{-ffast-math} activates
> -reciprocal square root estimate instructions.
> -Which in turn depends on the target processor.
> +The reciprocal square root approximation uses one step less than otherwise,
> +thus reducing latency and precision.
When calculating the reciprocal square root approximation, use one less
step than otherwise, thus reducing latency and precision.
Thanks,
James
