On Fri, Mar 7, 2008 at 11:02 AM, Philipp Marek <[EMAIL PROTECTED]> wrote: > Hello everybody, > > I have a feature request. > > > I'd like to (manually) define some byte blocks, eg. as functions with an > identifier. Then, if GCC would emit exactly these bytes, it puts a JMP > identifier there instead. > > This would help by sharing many identical (text/code) byte sequences, to > make a smaller image - like -fmerge-constants does for data - and therefor > helps for cache locality, too. > > > 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). > > > The original kernel has > $ size vmlinux > text data bss dec hex filename > 4802166 446554 606208 5854928 5956d0 vmlinux > > and my scripts emit space savings of about 30kB. Now that's not > that much, but for embedded systems it means another userspace > binary more. > [ If anyone's interested, I can post my scripts here ... they're not > that large. ] > > And, of course, the same can be used for other binaries too - which could > save other space as well. (blender-bin, text size 8664025, gives 97KB > savings) > > > I'd imagine the use that such: > - Built the binary > - Run my scripts, to find some common code sequences > - Give them to gcc > - Rebuild, using the optimizations > > I don't know whether some new optimize switch could be used, to do all > that internally in the compiler and linker. > > > What do you think about that? > [ Please keep at least *me* cc'ed - don't know whether that's that > interesting for linux-tiny. ]
Sounds like what -frtl-abstract-sequences is trying to do. Richard.
