Re: [PATCH] rs6000: Use rldimi for vec init instead of shift + ior

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

Hi!

On Tue, Dec 22, 2020 at 04:08:26PM +0800, Kewen.Lin wrote:
> This patch is to make unsigned int vector init go with
> rldimi to merge two integers instead of shift and ior.
> 
> I tried to use nonzero_bits in md file to make it more
> general, but the testing shows it isn't doable.  The
> reason is that some passes would replace some pseudos
> with other pseudos and do the recog again, but at that
> time the nonzero_bits could get rough information and
> lead the recog fails unexpectedly.

Aha.  So nonzero_bits is unusable for most purposes as well.  Great :-/

> btw, the test case would reply on the combine patch[1].

Can you make a different testcase perhaps?  This patch looks fine
otherwise.

(Ideally the compiler would just form those insert insns itself, of
course.  Why doesn't that work?  This is important for quite a lot of
code, we really can advantageously use the rl*imi insns often!)


Segher