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Re: S/390: -march= and -mcpu= options
- From: "Hartmut Penner" <HPENNER at de dot ibm dot com>
- To: Fergus Henderson <fjh at cs dot mu dot oz dot au>
- Cc: Alexandre Oliva <aoliva at redhat dot com>, dje at watson dot ibm dot com, drow at mvista dot com, Fergus Henderson <fjh at ceres dot cs dot mu dot OZ dot AU>, gcc-patches at gcc dot gnu dot org, Ulrich Weigand <weigand at immd1 dot informatik dot uni-erlangen dot de>
- Date: Fri, 27 Dec 2002 14:26:27 +0100
- Subject: Re: S/390: -march= and -mcpu= options
>Here I don't agree.
>For example, consider x86.
>The default arch should be 386, to ensure wide compatibility.
>The default tuning should be for something a lot more modern,
>e.g. Pentium-<mumble>.
>If an application is compiled with the arch set to 486 (-march=486),
>this should not alter the default tuning.
,
Yes, the tune should be the maximum from default tune and arch, if not
explicit set.
But with that I don't see any reason for the mcpu-option.
If I want to compile my program for a recent architecture, I'm using the
march option only,
with the algorithm above, the tune will be at least for this architecture.
The only advantage
the mcpu option has is to potentially lower the tune to the same level as
the architecture.
But for this I can't see anybody, except us backend maintainer, who may
need this. But
this can be done with the explicit tune option.
Hartmut Penner