Re: Validity of SUBREG+AND-imm transformations

[Jeff Law <law at redhat dot com>]

On 03/04/2016 09:33 AM, Kyrill Tkachov wrote:
> On 04/03/16 16:21, Jeff Law wrote:
> > On 03/04/2016 08:05 AM, Richard Biener wrote:
> > > > does that mean that the shift amount should be DImode?
> > > > Seems like a more flexible approach would be for the midend to be able
> > > > to handle these things...
> > >
> > > Or macroize for all integer modes?
> > That's probably worth exploring.  I wouldn't be at all surprised if it
> > that turns out to be better than any individual mode,  not just for
> > arm & aarch64, but would help a variety of targets.
>
> What do you mean by 'macroize' here? Do you mean use iterators to create
> multple variants of patterns with different
> modes on the shift amount?
> I believe we'd still run into the issue at
> https://gcc.gnu.org/ml/gcc/2016-03/msg00036.html.
We might, but I would expect the the number of incidences to be fewer.

Essentially we're giving the compiler multiple options when it comes to 
representation of the shift amount -- allowing the compiler (combine in 
particular) to use the shift amount in whatever mode is most natural. 
ie, if the count is sitting in a QI, HI, SI or possibly even a DI 
register, then it can be used as-is.  No subregs, no zero/sign 
extensions, or and-imm masking.

jeff