How much is known about -Os on X86_64?

[Steve Bergman <steve rueb com>]

I have a few questions.  How much work has been done to benchmark the 
advantages/disadvantages of using -Os for various FC packages on 
X86_64?  I know that on x86 -Os is used fort he kernel.  On X86_64, it 
looks to me like -Os is not used.  In fact, it seems that I read 
somewhere that one should not use -Os on X86_64, or shouldn't use it on 
the kernel, or shouldn't use it in FC4, or something like that and I 
can't seem to relocate that reference.  Anyone know anything about that?

Also, how useful would it be if  did some real world benchmarking on my 
Athlon64 2800+ system running FC4/X86_64?  Would I be wasting my time, 
duplicating someone else's previous efforts?  What packages might 
benefit?  Is it possible that compilintg the whole distro -Os might be a 
win? (Intuitively, it seems that everything being a little smaller could 
have a cummulative effect on the speed of the whole system, saving disk 
reads, main memory, cache memory, etc.)

I'm no expert at this stuff, so I figured asking on the list before I do 
much work would be a good idea.  Searches of the archives don't seem to 
turn up much except that "-Os can sometimes help".

So far, I've just played around a little bit with bzip2.  -Os seems to 
be a pretty good win for bzip2 compression, giving over about a 12% 
improvement.

Thank you for any input.

-Steve Bergman