Re: [PATCH] Optimize manual byte swap implementations v3

[Mark Mitchell <mark at codesourcery dot com>]

Andrew Haley wrote:
>> Without speaking to that particular optimization (which I don't know
>> much about), that kind of thing isn't really a counter-argument.  The
>> same can happen to any optional feature of the compiler.  It's up to the
>> people who care about it to maintain it.  Maybe in this particular case,
>> it should have been on by default, but that doesn't mean that all
>> optimizations should be.
> 
> Can't we just turn on this byte swap optimization throughout the gcc test
> suites?  I can't think of any overpowering reason not to.  Would this
> be enough coverage?

I think that's orthogonal to Richard's question of whether there should
be any optimizations at that are not enabled by default at some
optimization level.

But, yes, we could arrange the testsuite to run with this option, or
that some tests run with this option, or have some people who run the
testsuite with this option, or something.  If we decide to include the
byteswap pass, but disable it by default, one of those options may well
be a good idea.

However, my ideal outcome would be to demonstrate the benefits of the
optimization and/or reduce the cost of the optimization so that it could
easily be justified as on by default.  I have every confidence that some
programs will benefit from this optimization, and that very few will
lose, so I think the challenge is to get the cost down.

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713