[cfe-dev] When to use '-mcpu' versus '-march'

[Eric Christopher via cfe-dev]

Hi Martin,

Sorry about the delay here, but I've got some advice even though a lot of
things aren't solid anywhere.

a) Does this match an out of tree target for gcc? If so, I'd match that.
b) Typically -march/-mtune (though the latter isn't supported in llvm at
the moment, see an earlier post from me to llvm-dev on how to support that)
are what I'd use for new ports. We used it in a number of new/out of tree
ports in gcc as well.
c) -mcpu is occastionally used for "-march+-mtune" when -march by itself is
generally "this architecture, but generic tuning".

Hope this helps and happy to elaborate if you need it anywhere.

-eric

On Wed, Mar 14, 2018 at 7:48 AM ORiordan, Martin via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi CFE Devs,
>
>
>
> For out-of-tree target developers, what is the best practice advice for
> when to use ‘-mcpu’ and when to use ‘-march’ to identify variants or
> various generations of a target?
>
>
>
> Thanks,
>
>
>
>             MartinO
>
>
>
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