Complex numbers support: discussions summary

[Sylvain Noiry]

> On 9/26/23 20:40, Toon Moene wrote:
>
>>/On 9/26/23 09:30, Richard Biener via Gcc wrote: />>//>>>/On Mon, Sep 25, 2023 at 5:17 PM Sylvain Noiry via Gcc />>>/<gcc@gcc.gnu.org> wrote: />>//>>>>/As I said at the end of the presentation, we have written a paper which />>>>/explains />>>>/our implementation in details. You can find it on the wiki page of the />>>>/Cauldron />>>>/(https://gcc.gnu.org/wiki/cauldron2023talks?action=AttachFile&do=view&target=Exposing+Complex+Numbers+to+Target+Back-ends+%28paper%29.pdf 
<https://gcc.gnu.org/wiki/cauldron2023talks?action=AttachFile&do=view&target=Exposing+Complex+Numbers+to+Target+Back-ends+%28paper%29.pdf>). 
/>>>//>>>/Thanks for the detailed presentation at the Cauldron. />>>//>>>/My personal summary is that I'm less convinced delaying lowering is />>>/the way to go. />>//>>/Thanks Sylvain for the quick summary of the discussion - it helps a />>/great deal now that the discussion is still fresh in our memory. />
> I found time today to run some tests.
>
> First of all, the result of the gcc test harness as applied to the top 
> of the complex/kvx branch in the https://github.com/kalray/gcc  repository:
>
 > https://gcc.gnu.org/pipermail/gcc-testresults/2023-October/797627.html  <https://gcc.gnu.org/pipermail/gcc-testresults/2023-October/797627.html>
>
> I think there are several complex failures here that are not in 
> "standard" 12.2 release (for x86_64-linux-gnu).

We have removed some special cases for complex operations outside the cplxlower pass (especially in tree-ssa-forwprop.cc), because of it ruined our efforts to maintain it not lowered. So the performance is fine on the KVX target, but some (SLP) vectorization cases are missed for other targets which do not exploit complex patterns.

It may be interesting to add a conditions on theses cases rather than just remove them.

> I also compiled all of lapack-3.11.0 with that compiler and obtained the 
> same results as with gcc/gfortran 13.2:
>
>			-->   LAPACK TESTING SUMMARY  <--
>		Processing LAPACK Testing output found in the TESTING directory
> SUMMARY             	nb test run 	numerical error   	other error
> ================   	===========	=================	================
> REAL             	1327023		0	(0.000%)	0	(0.000%)	
> DOUBLE PRECISION	1300917		6	(0.000%)	0	(0.000%)	
> COMPLEX          	786775		0	(0.000%)	0	(0.000%)	
> COMPLEX16         	787842		0	(0.000%)	0	(0.000%)	
>
> --> ALL PRECISIONS	4202557		6	(0.000%)	0	(0.000%)	

Thank you! It doesn't surprise me because GCC still processed complex operations like before when the backend does not exploit complex patterns.

Best regards,

Sylvain