On Fri, Apr 01, 2016 at 02:47:05PM +0100, Wilco Dijkstra wrote:
> Evandro Menezes wrote:
> >
> > Ping^1
>
> I haven't seen a newer version that incorporates my feedback. To recap what
> I'd like to see is a more general way to select approximations based on mode.
> I don't believe that looking at the inner mode works in general, and it
> doesn't make sense to add internal tune flags for all possible combinations.
Agreed. I don't think that a flag for each of the cartesian product of
{rsqrt,sqrt,div} X {SF,DF,V2SF,V4SF,V2DF} is a scalable solution - that's
at least 15 flags we'll need.
As I said earlier in the discussion, this particular split (between SF and
DF mode) seems strange to me. I'd expect the V4SF vs. SF would also be
interesting, and that a distinction between vector modes and scalar
modes would be more likely to be useful.
> To give an idea what I mean, it would be easiest to add a single field to the
> CPU tuning structure that contains a mask for all the combinations. Then we
> call a single function with approximation kind ie. sqrt, rsqrt, div (x/y),
> recip (1/x) and mode which uses the CPU tuning field to decide whether it
> should be inlined.
I like the idea of a single cost function.
These patches are well and truly on my radar for GCC 7, but as we're still
in bugfixing mode (and there's still plenty to do!), I'm not going to get
round to giving them a more detailed review until after the release. Feel
free to ping them again once GCC 6 has shipped.
Thanks,
James
