> On 21 Jun 2019, at 13:49, Jan Hubicka <hubi...@ucw.cz> wrote: > >>>>> I should have been clearer about Darwin: >>>>> >>>>> collect2 is required because it wraps the calling of lto-wrapper and ld. >>>>> >>>>> FWIW Darwin also passes all the “-frepo” testcases, however, I’m not >>>>> aware of anyone actually >>>>> using case #2 from Jonathan’s post. >>>>> >>>>> So, AFAIK the tlink capability isn’t required for modern C++ on Darwin; >>>>> but, maybe deprecation is a >>>>> safer step. >>>> >>>> Thank you for the information. >>>> >>>> Yes, I would be fine to deprecate that for GCC 10.1 >>> >>> “thinking aloud” - would it work to deprecate (or even disallow immediately >>> if no-one is using it) LTO + frepo? >>> (so that non-LTO frepo continues as long as anyone needs it) >> >> Does that even work? ;) It would need an intermediate compile-step to >> instantiate templates to >> another LTO object. > > It is iterating the linker executions so it definitly makes no sense. > One problem is that in the collect2 at the time of deciding whether > to open temporary file for the linker output (which is the problem > Martin tries to solve) we do not know yet whether we will do -flto > (because that will be decided by linker plugin later) or repo > (because it works by looking for .repo files only after the link-step > failed).
for “non ELF” (at least for Darwin) we decide by scanning the object files using simple object - if any LTO section is seen, we spawn lto-wrapper, else we just proceed with a normal link. That used to be horribly inefficient (it was a new “nm & grep " process per object)- but we fixed that during 9 - still too heavy? > I suppose we could block -frepo when -flto is on the command line that > is most common case for LTO builds arriving to bit odd situation that at > link-time -flto will effect nothing but colors of diagnostics > (I would really like to have this solved for gcc 10 in some way) the point is - if it can’t work, then it may as well be disallowed - and then the LTO path knows it doesn’t need to do the tlink stuff. (and tlink can remain for non-LTO frepo) Iain
