Is generic tuning adapted to the cpu-type selected with -march ?

Florian Weimer fweimer@redhat.com
Tue Aug 29 07:57:21 GMT 2023


* Paul Richards via Gcc-help:

> I ask, because the documentation doesn't make it clear what happens,
> but at the same time using "-march" with x86-64 psABI levels
> apparently invokes generic tuning and it would be weird if generic
> tuning under "-march=x86-64-v4" wasn't different than generic tuning
> under "-march=x86-64".

The tuning defaults for -march=x86-64-v* need some discussion.  For
example, for -march=x86-64-v4, maybe GCC should tune for 256-bit vector
widths.  For both -march=x86-64-v3 and -march=x86-64-v4, there is some
tuning for FMA that could be applied.  I'm sure there are other
examples.

Thanks,
Florian



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