Complex numbers support: discussions summary

[Toon Moene]

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).
> 
> 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.

Some thought I came up with (of course, only after the end of the 
conference):

In what way is the handling of the complex type different from that of 
the 128 bit real (i.e., float) type ?

Both are not implemented on most architectures; on most they require two 
registers (or possibly two memory location that do not necessarily have 
to be adjacent) to be implemented.

Yet both are supported by the middle end - consider the clear 
equivalence of the handling of variables a and b when looking at the 
result of -fdump-tree-ssa (on x86_64) for:

cat 128.f90
parameter (iq=kind(1q0))
real(kind=iq) :: a, b
read*, a, b
print*, a / b
end

and:

cat complex.f90
complex a,b
read*,a,b
print*,a/b
end

Hope this helps for a continuing fruitful discussion.

Kind regards,

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands