What I've observed is that, with egcs (old toolchain) on i386, you
   normally see:
   
   	-Os < -O < -O2
   
   but you sometimes see:
   
   	-O < -Os < -O2
   
   -Os turns off certain optimizations which tend to bloat code size and
   increase instruction count; it turned out that, for i386, it reduced
   instruction count but increased object code size for the one case I
   looked at in detail.
   
   The differences were often small, but with our install media commonly
   very close to the limit, a few bytes can make a difference..



this is different to my tests on the sparc a while back.  i think this
is with egcs 1.1.x or so.  i found that

	-Os < -O2 << -O1

or

	-O2 < -Os << -O1


ie, that -Os and -O2 were very very similar, but -O1 was a LOT worse.
-O0 is worse again as to be expected.


this is all from memory so i could be mis-remembering.


.mrg.