Re: [Patch] Add option to reduce amount of reflection data to gcj...

[Andrew Haley <aph at redhat dot com>]

David Daney writes:
 > Andrew Haley wrote:
 > > David Daney writes:
 > >  > Here is my patch to optionally reduce the amount of reflection data 
 > >  > generated by gcj.  When applied to libgcj on i686 I see about 5% 
 > >  > reduction in memory image size.
 > >  > 
 > >  >     text    data     bss     dec     hex filename
 > >  > 18937435        3615244  260644 22813323        15c1a8b 
 > >  > /home/daney/gccsvn/native_clean/i686-pc-linux-gnu/libjava/.libs/libgcj.so.7.0.0
 > >  > 18284867        3254316  260644 21799827        14ca393 libgcj.so.7.0.0
 > >  > 
 > >  > On my GCC-3.4.3/mipsel-linux port of the patch when used in conjunction 
 > >  > with static linking I am getting about 12-15% savings on a fairly large 
 > >  > (1000 classes) application.
 > >  > 
 > >  > There are of course several caveats:  By eliminating a lot of reflection 
 > >  > meta-data, a lot of reflection operations will fail.  No big surprize 
 > >  > there.  JNI and the binary compatibility ABI depend on complete 
 > >  > reflection meta-data, so they cannot be used in conjunction with reduced 
 > >  > reflection meta-data.  The byte code interpereter, and the gij program 
 > >  > work on some, but not all, programs with reduced reflection meta-data.
 > >  > 
 > >  > Tested on i686-pc-linux-gnu (FC3).
 > >  > 
 > >  > When -freflection-data= is not specified, no regressions with full 
 > >  > bootstrap of all default languages.  I generated assembly language for a 
 > >  > 122 class package with and without the patch and the *only* differences 
 > >  > were the movement of the vtables from after to before the reflection 
 > >  > data.  This is to be expected from the patch.  Adding 
 > >  > -freflection-data=reduced to my libgcj.spec.in, resulted in many (about 
 > >  > 180) failures in the libgcj testsuite.  These were in some, but not all, 
 > >  > gij compilation tests as well as JNI, BC and some specific reflection 
 > >  > tests.  I am considering this a pass as some things are not expected to 
 > >  > work with the -freflection-data=reduced option enabled.
 > >  > 
 > >  > OK to commit?
 > > 
 > > I don't think the -freflection-data=none option should be there in its
 > > current form, since it breaks so much.  Perhaps this option could be
 > > enhanced so that we don't silently generate incorrect code.  We should
 > > report an error instead.
 > > 
 > > If it's incompatible with -findirect-dispatch, it should error if
 > > these options are combined on the command line.
 > 
 > Both issues fixed with this new version of the patch.
 > 
 > The new option is '-freduced-reflection'.
 > 
 > Tested as before.  No regressions without new -freduced-reflection 
 > option. with %{fjni|findirect-dispatch:;:-freduced-reflection} added to 
 > libgcj.spec.in I get 125 new failures, but they are all expected as the 
 > patch makes this sacrifice to save space.
 > 
 > OK to commit?

I'm going to approve this with the proviso that it's an experimental
option that we don't guarantee to support in future releases.  I'll
add some wordage to that effect.

Andrew.