On 2020-08-24 19:16, Jan Hubicka wrote:
On Thu, Aug 20, 2020 at 6:35 AM guojiufu via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> This patch is checking the _average_ number of calls which is the
> summary of call numbers multiply the possibility of the call maybe
> executed. The _average_ number could be a fraction, to keep the
> precision, the param is the threshold number multiply 10000.
>
Can you try mimicking what try_unroll_loop_completely on GIMPLE does
instead? IIRC the main motivation to not unroll calls is the spilling
code
around it which we cannot estimate very well. And that spilling
happens
irrespective of whether the call is in a hot or cold path so I'm not
sure
it makes sense to use the "average" number of calls here.
In try_unroll_loop_completely, it is checking the calls in the hot path:
num_non_pure_calls_on_hot_path), and avoid unrolling if there is.
This is one reason for here to use "average".
As long as I remember, we excluded calls simply becuase it is/was an
expensive intruction so it was an indication that the loop overhead is
small compared to the overhead of loop body.
Thanks, Honza and Richard!
Honza
