Matthew S. Hallacy wrote:

>Programs that can take advantage of optimizations usually are, the kernel,
>glibc, mplayer, etc. Randomly using optimization flags on all your software
>will lead to an unstable system with bugs that you simply can't find.

Generating code for a specific processor (.i.e Athlon) rather than 80386
code just makes sense if a machine has this specific processor.  That is
a trivial (safe) optimization.  It should not be considered a complex
(potentially unsafe) optimization.

Randomly selecting gcc optimization flags without extensive testing is
certainly not a good idea and I doubt that Gentoo uses such an approach.
Hopefully, Gentoo doesn't use rarely used optimizations by default
unless there is a significant performance benefit and no known bugs as a
result.  The Gentoo approach of compiling all software probably does aid
in fixing optimization related bugs more effectively and faster than any
binary distribution approach does.

While it is true that most software will not benefit from new processor
instructions there are some areas in addition to those Matthew
mentioned where there is a significant performance benefit.  For
example, in the Sparc architecture, there is a huge advantage in using
Sparc v8 or v9 instructions over just using the base Sparc v7
instructions in openssl for those processors that support the v8 or v9
instructions.

Sincerely,

Ken Fuchs <kfuchs at winternet.com>

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