RFC: Idea for code size reduction

[Richard Guenther]

On Fri, Mar 7, 2008 at 12:46 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Fri, Mar 07, 2008 at 11:10:53AM +0100, Richard Guenther wrote:
>  > On Fri, Mar 7, 2008 at 11:02 AM, Philipp Marek <philipp@marek.priv.at> wrote:
>
> > >  I wrote some perl scripts to test this.  I took a "alldefconfig" i686
>  > >  kernel, let objdump disassemble it, and on "iret", "ret", "ljmp" or "jmp"
>  > >  with a 4 byte address I store the last few bytes.  Another script goes
>  > >  through these block-ends, and estimates the number of bytes saved, if
>  > >  identical sequences get changed into a 5 byte opcode (jump with 32bit
>  > >  address).
>  >
>
> > Sounds like what -frtl-abstract-sequences is trying to do.
>
>  Not exactly.  AFAIK -frtl-abstract-sequences works at a function level, only
>  same sequences within one function are abstracted.

Right - "trying to do" - you'd need to move this to whole-program level
with LTO (preferably on the tree level), but the basic idea of outlining
same sequences is the same.

Richard.