On 6/15/2022 5:36 AM, Richard Sandiford wrote:
Jeff Law via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
On 6/13/2022 5:54 AM, Richard Biener wrote:
On Sun, Jun 12, 2022 at 7:27 PM Jeff Law via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
[...]
On a related topic, any thoughts on keeping complex objects as complex
types/modes through gimple and into at least parts of the RTL pipeline?
The way complex arithmetic instructions work on our chip is going to be
extremely tough to utilize in GCC -- we really need to the complex
types/arithmetic up through RTL generation at the least. Ideally we'd
even expose complex modes all the way to final. Is that something
y'all could benefit from as well? Have y'all poked at this problem at all?
Since you are going to need to "recover" complex operations from people
open-coding them (both fortran and C and also C++ with std::complex) it
should be less work to just do that ;) I think that complex modes and types
exist solely for ABI purposes.
I don't see any reasonable way to do that. Without going into all the
details, our complex ops work on low elements within a vector
register. Trying to recover them after gimple->rtl expansion would be
similar to trying to SLP vectorize on RTL, something I'm not keen to chase.
It would be a hell of a lot easier to leave the complex ops as complex
ops to the expanders, then make the decision to use the complex
instructions or decompose into components.
Realise you might not be in a position to answer this for confidentiality
reasons, but: would normal tree SLP not help here? We already try to
recognise complex add & multiply, and in principle we could do the same
for other operations as well. It shouldn't matter that a vector
multiply on 2 elements is really just a single-data operation.
That's the only viable option I see for our target if we keep the model
where complex operations are broken down into their component operations
in the gimple passes.
jeff
