Re: [PATCH v3 2/3] Add predict_doloop_p target hook

[Segher Boessenkool <segher@kernel.crashing.org>]

On Mon, May 20, 2019 at 08:43:59AM -0600, Jeff Law wrote:
> > I think we should have two hooks: one is called with the struct loop as
> > parameter; and the other is called for every statement in the loop, if
> > the hook isn't null anyway.  Or perhaps we do not need that second one.
> I'd wait to see a compelling example from real world code where we need
> to scan the statements.  Otherwise we're just dragging in more target
> specific decisions which in fact we want to minimize target stuff.

The ivopts pass will be too optimistic about what loops will end up as a
doloop, and cost things accordingly.  The cases where we cannot later
actually use a doloop are doing pretty much per iteration, so I think
ivopts will still make good decisions.  We'll need to make the rtl part
not actually do a doloop then, but we probably still need that logic
anyway.

Kewen, Bin, will that work satisfactorily do you think?


Segher