tbaeder added a comment. In D90457#2390519 <https://reviews.llvm.org/D90457#2390519>, @MaskRay wrote:
> Is the motivation just to avoid -flto or -flto=lto at link time? Essentially, yes. Lots of projects seem to depend on this behavior of GCC. I.e. the pass -flto when compiling but not when linking. > I am afraid that the advantage probably is not large enough to justify the > potentially costly object file parsing in the driver. Before this, as I > understand it, object files are opaque to the driver. The driver just passes > all file names to the linker. With this change, every object file will be > opened and `llvm::getBitcodeFileContents` will be called on every object file. I thought about the potential performance penalties as well. All of this only matters if -flto is really missing of course, otherwise the driver is not going to do any more work than it did before. > Other thoughts include: > > - An LTO link can mix regular and thin LTO bitcode files. I am not very > familiar with the thinlto internals so I don't know whether it is appropriate > to stop after we immediately see a full LTO bitcode file. > - This provides a convenience method in the most simplest link (no other LTO > related option). If you specify any other LTO related option (e.g > --thinlto-index-only, --thinlto-cache-dir), the save of a `-flto` option > appears to give too small of a value with an extra parsing. Right, the purpose of this is not to save typing a "-flto", but to make linking in the simplest cast just work. ================ Comment at: clang/lib/Driver/Driver.cpp:1205 + setLTOModeFromInputFiles(&Inputs); + ---------------- MaskRay wrote: > On line 1133, there is a similar setLTOMode. If we are going to add the > logic, probably consider unifying the logic. However, I am concerned with the > cost, see my main comment Setting the LTO mode from the input files requires the Inputs list, but calling the existing setLTOMode() this late causes problems. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D90457/new/ https://reviews.llvm.org/D90457 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
