[javaCompiler-users] one more feature request :)

[john s. <kmk...@ya...>]

"john sonal wrote:
 > I have one more feature request...
 > 
 > -> Add an optimization option. To do this you just
 > pass -O2 after each compile command. ie. gcj -c
 > blah.jar -O2
 
 Crap. I looked that up, but it didn't seem to exist;
so I didn't use it. 
 Either I screw that up or it just wasn't there with
GCJ 3.x.
 Thanks, I'll add that.
 
 > It usually makes a difference in binary size
(smaller)
 
 Really? I have different experience. As higher the
optimisation, as 
 bigger the executables... Depends on the strengh of
the optimisation.
 Anyway, it doesn't make big changes :-) What we
really need is the 
 ability to remove AWT/Swing and XML from the binaries
when not needed. 
 That would drastically reduce the binary size...
 
 > and makes a big difference in performance. 
 
 Yes, -O2 should really have been there...
 
 
 Marco"

I wasn't sure if it existed either for gcj but then I
manually compiled a program and it accepted the flag.
Right away I noticed the optimized binary was 2 mb
less than the non optimized one. The optimized binary
also performs nearly 300% quicker in parsing a 25k xml
document (from 1205 ms to 430ms). 

About optimization and the binary size. According to
gcc's site: "-O2: Optimize even more. GCC performs
nearly all supported optimizations that do not involve
a space-speed tradeoff." Based on that it would seem
that binary size should not increase but if it does,
only slightly. I had read somewhere else that -O2
usually shrinks the binary. -O3 on the other hand will
make it bigger. There's also -Os which might be the
best solution to use with GCJ: "Optimize for size. -Os
enables all -O2 optimizations that do not typically
increase code size. It also performs further
optimizations designed to reduce code size." I haven't
tried -Os yet. I'll do that today and see how much of
a difference in binary size it makes. 

I think it would be nice to remove the xml stuff from
the binary in all situations since most people will
typically want to use their own xml parser. As far as
the AWT/Swing stuff, I believe what that guy at
thisiscool.com did was to compile different versions
of "libgcj". One with Swing/AWT stripped out and one
with that "SwingWT" library included. Here's a quote
from his site: "To integrate SwingWT, I first
surgically removed the GNU AWT and Swing sources from
the libgcj build (see noawt.diff in the patch list
below)." 
Not sure how difficult it would be to do that.



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