Re: x86 abi for complex.

[Joseph Koshy <jkoshy%netbsd.org@localhost>]

On Thu, Feb 02, 2023 at 07:59:32PM +0100, Anders Magnusson wrote:

> I looked at the "complex" abi code generated on NetBSD/i386
> for function calls, and noticed a slight discrepancy.

> For functions returning double or long double complex, the complex 
> numbers are handled as returning of structs with the same content.
> But; for functions returning float complex, the return values are 
> returned in eax/edx and not as the corresponding struct.

I believe that is how the i386 ABI is defined:

  https://www.uclibc.org/docs/psABI-i386.pdf (page 14)

> What is the reason for;
> 1) return floats in eax/edx instead as a struct?

My guess: passing these values in registers helps
reduce memory traffic.

Regards,
Joseph Koshy