This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Validity of SUBREG+AND-imm transformations


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


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]