[RFC] Adds a target hook

[Kugan Vivekanandarajah]

Hi Kyrill,

Thanks for the review.

On 13 February 2018 at 20:58, Kyrill  Tkachov
<kyrylo.tkachov@foss.arm.com> wrote:
> Hi Kugan,
>
> On 12/02/18 23:53, Kugan Vivekanandarajah wrote:
>>
>> Adds a target hook TARGET_HW_MAX_MEM_READ_STREAMS. Loop unroller, if
>> defined, will try to limit the unrolling factor based on this.
>>
>
> Could you elaborate a bit on this, in particular how is this different
> from the PARAM_SIMULTANEOUS_PREFETCHES param that describes
> "the number of prefetches that can run at the same time".
> The descriptions seem very similar to me...

You are right that they are similar. I wanted to keep it separate
because not all the micro-architectures might prefer limiting unroll
factor this way. If we keep this separate, we will have the option to
disable this without affecting the rest.

> Incidentally, since this is expected to always be an integer, maybe
> make it into a param so it is consistent with the other prefetch-related
> tuning numbers?

Ok, I will change it into param in the next iteration.

Thanks,
Kugan
>
> Thanks,
> Kyrill
>
>
>>
>> gcc/ChangeLog:
>>
>> 2018-02-12  Kugan Vivekanandarajah <kuganv@linaro.org>
>>
>>     * doc/tm.texi.in (TARGET_HW_MAX_MEM_READ_STREAMS): Dcoument.
>>     * doc/tm.texi: Regenerate.
>>     * target.def (hw_max_mem_read_streams): New target hook.
>
>