Let me try to answer a bit here...
On Mon, May 20, 2019 at 11:28:26AM +0200, Richard Biener wrote:
> On Thu, 16 May 2019, li...@linux.ibm.com wrote:
> > +/* Predict whether the given loop in gimple will be transformed in the RTL
> > + doloop_optimize pass. This is for rs6000 target specific. */
> > +
> > +static bool
> > +rs6000_predict_doloop_p (struct loop *loop)
> > +{
> > + gcc_assert (loop);
> > +
> > + /* On rs6000, targetm.can_use_doloop_p is actually
> > + can_use_doloop_if_innermost. Just ensure it's innermost. */
>
> So the point is that ppc only has a single counter register, right?
That, and the register is call-clobbered, and some RTL patterns use it
for other purposes. So we want doloop only for inner loops, and not if
certain constructs are used in the loop (switch statements...)
It may be good enough if we only look at the loop structure? That would
simplify things a lot ;-)
> So the better way would be to expose that via a target hook somehow.
> Or simply restrict IVOPTs processing to innermost loops for now.
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.
Segher
