> On Tue, 8 May 2018, Jan Hubicka wrote: > > > > On Tue, May 8, 2018 at 8:14 AM, Jan Hubicka <hubi...@ucw.cz> wrote: > > > > Hi, > > > > with lto, incremental linking can be meaninfuly done in three ways: > > > > 1) read LTO file and produce non-LTO .o file > > > > this is current behaviour of gcc -r or ld -r with plugin > > > > 2) read LTO files and merge section for later LTO > > > > this is current behaviour of ld -r w/o plugin > > > > 3) read LTO files into the compiler, link them and produce > > > > incrementaly linked LTO object. > > > > > > > > 3 makes most sense and I am maing it new default for gcc -r. For > > > > testing purposes > > > > and perhaps in order to have tool to turn LTO object into real object, > > > > we want > > > > to have 1) available as well. GCC currently have -flinker-output > > > > option that > > > > decides between modes that is decided by linker plugin and can be > > > > overwritten > > > > by user (I have forgot to document this). > > > > > > > > I am targeting for -flinker-output=rel to be incremental linking into > > > > LTO > > > > and adding -flinker-output=nolto-rel for 1). > > > > > > > > The main limitation of 2 and 3 is that you can not link LTO and non-LTO > > > > object files theger. For 2 HJ's binutils patchset has support and I > > > > think > > > > it can be extended to handle 3 as well. But with default binutils we > > > > want > > > > to warn users. This patch implements the warning (and prevents linker > > > > plugin > > > > to add redundat linker-ouptut options. > > > > > > > > > My users/hjl/lto-mixed/master branch is quite flexible. I can extend > > > it if needed. > > > > I think once the main patchset settles down we could add a way to > > communicate > > to lto-plugin if combined lto+non-lto .o files are supported by linker and > > sillence > > the warning. > > How does the patchset deal with partially linking fat objects? How
Currently it will turn them into slim LTO merged object. I can add code path that will optimize them into binary. That will be additional fun because we probably want to WPA them, but it should not be that hard to implement: WPA will produce one object file with merged LTO data that will be passed to linker plus partitions that will be turned to final binary. > do HJs binutils deal with them when you consider a fat object partially > linked with a non-LTO object? HJ? Honza > > Richard. > > -- > Richard Biener <rguent...@suse.de> > SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB > 21284 (AG Nuernberg)
