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Re: S/390: -march= and -mcpu= options
- From: David Edelsohn <dje at watson dot ibm dot com>
- To: Daniel Jacobowitz <drow at mvista dot com>
- Cc: Hartmut Penner <HPENNER at de dot ibm dot com>, gcc-patches at gcc dot gnu dot org
- Date: Mon, 23 Dec 2002 15:15:07 -0500
- Subject: Re: S/390: -march= and -mcpu= options
>>>>> Daniel Jacobowitz writes:
Daniel> Then why is -mcpu= necessary, if there is no backwards compatibility
Daniel> issue on S/390? It's a shorthand for -march=z900 -mtune=z900, if I'm
Daniel> reading your comments above correctly.
First there are backward compatibility issues in a complete s390
port.
Second, the people who participated in the earlier discussion
agreed that there should be a shorthand.
When not accepting the defaults, most GCC end-users want a single
option which means "give me optimal code for the processor on which I will
be running the application". Software distributors or system
administrators are more likely to want backward compatibility with optimal
tuning for the latest installed base of systems and are willing to
investigate options. And computer geeks will test all combinations.
Why force most users to set multiple commandline options for the
common case? That's bad interface design and asking for users to complain
about poor performance of GCC-compiled applications due to user error.
The point is think about this from the user perspective, not a
geek perspective. The complexity of the options should scale with the
expertise necessary to use them. -Wall is just shorthand for a useful
subset of GCC -Wxxx options after all.
David