On Fri, Jul 12, 2013 at 12:30 PM, Jakub Jelinek <ja...@redhat.com> wrote: > On Fri, Jul 12, 2013 at 12:25:16PM -0700, Ian Lance Taylor wrote: >> For gold I think it has two effects. If you use compressed debug >> sections, it will compress them with zlib level 9 rather than 1. If > > Marc's patch enabled it only for -O3/-Ofast (which are already compile time > expensive options, thus it perhaps it doesn't hurt that much to spend extra > time in the linker too) and -Os (then you are really looking for small, > and if ld -O2 provides that, then perhaps it is desirable too).
OK, let me put it this way: perhaps there is some set of linker options that we should enable by default when linking with -O. But I don't see any particular reason that they are specifically the linker options that are selected by -O. >> you use -O2 or greater it will optimize string tables (e.g., the table >> holding the names of symbols) such that if the table stores two >> strings S1 and S2, and S2 is a suffix of S1, it will store only S1, >> and change pointers to S2 to point to the suffix of S1. So you are >> correct that the result will be smaller, but not faster to link. > > Oh, gold doesn't do this by default? ld.bfd does (unless it changed since > I've implemented many years ago). Correct: gold does not do it by default. For us link time matters most for large C++ programs. For those programs, the optimization only fired a tiny percentage of the time, but it took something like 4% of total link time. It wasn't worth it by default. Ian
