On Tue, Oct 13, 2020 at 11:47:10AM -0500, Segher Boessenkool wrote:
> On Tue, Oct 13, 2020 at 09:44:25AM +0200, Jakub Jelinek wrote:
> > The following testcases are miscompiled (the first one since my improvements
> > to rotate discovery on GIMPLE, the other one for many years) because
> > combiner optimizes nested ROTATEs with narrowing SUBREG in between (i.e.
> > the outer rotate is performed in shorter precision than the inner one) to
> > just one ROTATE of the rotated constant. While that (under certain
> > conditions) can work for shifts, it can't work for rotates where we can only
> > do that with rotates of the same precision.
>
> > OT, on the other side I wonder why the code doesn't handle ROTATERT. While
>
> ROTATERT is a relatively recent invention, and isn't handled in many
> places.
Depends on how we define recent.
I see ROTATERT already in 1994 code ;)
Jakub
