s390 port

[Paul Edwards]

Hi Ulrich.

I just checked my copy of s390.md and I don’t see
LA being used for arithmetic.

If your copy of s390.md is using LA for arithmetic
then would it be possible to have an option to
use a normal mathematics instruction instead of
LA?

Do you have any more examples besides LA being
used for maths instead of a proper maths instruction?

Also, I just realized – if GCC is using LA for maths
for 32-bit registers, then values will be limited to
2 GiB instead of 4 GiB for unsigned, but that is not
the case.

BFN. Paul.




From: Ulrich Weigand 
Sent: Friday, September 3, 2021 12:53 AM
To: Paul Edwards 
Cc: gcc@gcc.gnu.org ; Ulrich Weigand 
Subject: Re: s390 port

"Paul Edwards" <mutazilah@gmail.com> wrote on 02.09.2021 16:50:35:

> Could you give me an example of an instruction
> generated by –m31 that is not expected to work
> on an AM64 system?

Well, everything related to address computation, of course.

For example, GCC may use LA on -m31 to implement a
31-bit addition, while it may use LA on -m64 to
implement a 64-bit addition.

Bye,
Ulrich