This has been like that forever, this is not new with 3.9. Note also that the system ar/ranlib are sensitive to the environment DYLD_LIBRARY_PATH and will look for libLTO appropriately (since they aren’t invoked with clang, we haven’t been able to do any “magic” here yet).
— Mehdi > On Nov 22, 2016, at 6:31 AM, Jack Howarth <howarth.mailing.li...@gmail.com> > wrote: > > I would also note that llvm 3.9.x and 4.0svn also require use of their > own llvm-ar and llvm-ranlib for archiving under -flto as well (beyond > using the matching libLTO.dylib). > > On Tue, Nov 22, 2016 at 12:59 AM, Mehdi Amini <mehdi.am...@apple.com> wrote: >> Double-checked on the latest binary release on llvm.org, it ships with >> clang+llvm-3.9.0-x86_64-apple-darwin/lib/libLTO.dylib >> >> I also can’t find any CMake option that disable LTO support at build time >> for clang. >> >> >> On Nov 21, 2016, at 9:53 PM, Mehdi Amini via cfe-commits >> <cfe-commits@lists.llvm.org> wrote: >> >> AFAIK any clang build open-source ships with libLTO. >> Not having libLTO built with clang is a Chromium oddity, unless I missed the >> obvious somewhere. >> >> >> On Nov 21, 2016, at 9:50 PM, Nico Weber <tha...@chromium.org> wrote: >> >> In what way is this chromium specific? It's "all non-xcode uses of clang on >> mac", no? >> >> >> On Nov 21, 2016 7:29 PM, "Mehdi Amini" <mehdi.am...@apple.com> wrote: >>> >>> >>> On Nov 21, 2016, at 2:44 PM, Nico Weber <tha...@chromium.org> wrote: >>> >>> On Mon, Nov 21, 2016 at 5:34 PM, Mehdi Amini <mehdi.am...@apple.com> >>> wrote: >>>> >>>> >>>> On Nov 21, 2016, at 2:27 PM, Nico Weber <tha...@chromium.org> wrote: >>>> >>>> On Mon, Nov 21, 2016 at 5:19 PM, Mehdi AMINI via cfe-commits >>>> <cfe-commits@lists.llvm.org> wrote: >>>>> >>>>> mehdi_amini added a comment. >>>>> >>>>> In https://reviews.llvm.org/D25932#601842, @rnk wrote: >>>>> >>>>>> In https://reviews.llvm.org/D25932#601820, @mehdi_amini wrote: >>>>>> >>>>>>> We ship `clang + libLTO + ld64` bundled in the toolchain, so even if >>>>>>> you don't package libLTO yourself, it is already accessible from the >>>>>>> linker: >>>>>>> it will use the one in the toolchain when needed. >>>>>>> >>>>>>> I don't have an immediate idea to prevent this and have the linker >>>>>>> issue an error (other than removing manually libLTO from the Xcode >>>>>>> installation). >>>>>> >>>>>> >>>>>> So, even if clang doesn't pass -lto_library to ld64, ld64 will >>>>>> auto-discover the bundled libLTO that happens to be next to it? That >>>>>> could >>>>>> go badly. >>>>> >>>>> >>>>> Right: until LLVM 3.8, clang was *never* passing the `-lto_library` >>>>> option. The only way to have your own libLTO used by ld64 instead of the >>>>> one >>>>> in the Xcode toolchain was setting the environment variable >>>>> "DYLD_LIBRARY_PATH". >>>>> Of course was has many issues, and that's what lead us to have clang >>>>> passing this option to ld64. Initially only when the driver was invoked >>>>> with >>>>> -flto, but recently I had issues with clients that didn't use LTO >>>>> themselves >>>>> but were having static archives they depend on that were containing >>>>> bitcode. >>>> >>>> >>>> Where those archives system libraries, or other things? >>>> >>>> >>>> We have two cases: >>>> >>>> 1) Internal teams producing libraries in an internal SDK with LTO >>>> enabled, and other teams consuming these libraries and linking to the >>>> framework. It seems also something that people out-in-the-wild are doing >>>> according to some bug reports. >>>> 2) Any Xcode user that have a somehow complex project which is split in >>>> multiple targets. Xcode can’t tell clang from one target that it is linking >>>> with LTO even if LTO is disabled just because another dependency has LTO >>>> enabled. And sometimes Xcode is only seeing static archive as an input >>>> anyway. >>> >>> >>> It sounds like this is a pure regression for us then. >>> >>> >>> Right, for you "downstream consumer of clang in chromium”. >>> >>> Since 'it never "hurt" to pass it' isn't true (every link invocation done >>> by the driver now prints a warning), maybe this should be reverted until >>> there's some better approach? >>> >>> Requiring everyone to put a dummy libLTO.dylib at ../lib/libLTO.dylib >>> (while clever) seems pretty unfortunate. >>> >>> >>> Is there a CMake invocation that disable libLTO today and allow to run >>> “make install” and produce a distribution of clang without libLTO? >>> >>> If not, then I’m against reverting this because I consider your Chromium >>> specific incorrect with respect to the support upstream. And I’m fine having >>> it supported in the future, but you should make it supported, for instance >>> with a cmake option (if the cmake option already exists, I haven’t checked, >>> then we could conditionally compile-out the warning based on it). >>> >>> — >>> Mehdi >>> >>> >>> >>> >>> >>>> >>>> >>>> Maybe clang could sniff archives for bitcode and pass only -flto in that >>>> case? >>>> >>>> >>>> That seems like a possibility. It’d have to resolve paths to the static >>>> archives, which it doesn’t do right now I believe (they can be resolved >>>> with >>>> `-Lpath -lfoo`). >>>> >>>> — >>>> Mehdi >>> >>> >> >> _______________________________________________ >> cfe-commits mailing list >> cfe-commits@lists.llvm.org >> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits >> >> _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
