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Re: gcc 3.4.1 and CPU optimization
Orginal message
> On Wed, Dec 01, 2004 at 06:35:08PM +0100, Zbigniew ?uszpi?ski wrote:
> > Remember that default settings are always overwritten by those
> > set in command line (by script or user). The aim of this discussion is to
> > create default gcc configuration which can not be replaced by parameters
> > executed from commandline.
>
> I would oppose such an approach in the official gcc, as it makes the
> compiler more difficult to support. People will then report bugs that we
> can't reproduce, because they are unaware of the settings in a hidden
> configuration file.
This file should be an option for power users. All of its content should be
commented out by default. The power users would delete comment # signs to
enable options they need. In such way the rest of gcc users will be safe.
I have new idea about this issue. gcc should have new option:
-use-current-cpu. This option should have higher priority than other to stop
optimization chaos. The gcc could detect current processor by looking
in: /proc/cpuinfo file.
There are some advatanges:
+ old scripts will not be broken because they do not know new option
+ it is easy to support in new scripts
+ the faulty configure processor detection procedure could be removed from
make scripts
+ it is easy to support in old configure scripts via adding
CFLAGS="-use-current-cpu" to configure in commandline. Thanks to this gcc
will silently clean up its commandline parameters by ignoring old
optimization parameters.
+ it is easier to update gcc processor recognize engine than updating million
configure scripts laying around Internet.
> > Ali Imran have good idea how to resolve this problem. I probably end up
> > with bash script aliased to gcc which will filter out deprecated
> > options, add mine and pass it to orginal gcc renamed to gcc.orginal.
>
> This is the best approach; even better would be to avoid renaming gcc,
> and calling your script gcc-zbigniew or something, so that people who
> run it are constantly aware that they are not running the actual gcc.
> After all, you appear to want to either reject or silently discard some
> options, and add other options that the user did not select.
> With proper Makefiles, you can change the compiler just by specifying
> the value of one variable (CC).
>
The renaming gcc by aliasing it is necessary. Since someone told me
about ./configure CFLAGS="option" I was manually editing houndreds of config
lines (many programs were compiled) to have good optimization. If you
recompile many programs to speed up system a little you will understand what
I am talking about.
If I setup gcc to run with -march=athlon-xp option it would be good to reject
or silently discard bad optimizations from scripts like -m386 or
-mtune=pentium. It is sad that I have to clean chaos made by someone else.
greetings,
Zbigniew