yaxunl added a comment. In D123441#3446408 <https://reviews.llvm.org/D123441#3446408>, @tra wrote:
> LGTM in principle. This will keep around the GPU code we do need. > > That said, it seems to be a rather blunt hammer. I think we'll end up linking > almost everything in an archive into the final executable as we'll likely > have a host-visible symbol in most of the GPU objects (e.g. most of them > would have a kernel). > Device-side linking would also be unaware of which objects were actually > linked into the host executable and thus would link in more objects than > necessary. We could have achieved about the same result by linking with > `--whole-archive`. > > The root of the problem here is that in isolation GPU-side linking does not > know what will really be needed by the host and thus has to link in > everything, except, maybe, object files where we may have `__device__` > functions only. > Ideally, the linking should be a two-phase process -- link CPU side, extract > references to the GPU symbols (host-side compilation would have to be > augmented to place them in a well known location) and pass them to the > GPU-side linker which would then have all the info necessary to pull in > relevant GPU-side objects without compiler having to force having nearly all > of them linked in. > > I realize that this would be a nontrivial change to the compilation pipeline. > As a short-to-medium term solution, this patch may do, though I'd probably > prefer just linking with `--whole-archive` as it would, in theory, be simpler. This approach will only link in kernels and device variables used by host code, whereas --whole-archive will keep everything in the archive. There are use cases where the archive contains a large amount of kernels that the application only use a few of them. Also, --whole-archive will require users to carefully arrange --whole-archive and --no-whole-archive options for the archives they use. This approach avoids that. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D123441/new/ https://reviews.llvm.org/D123441 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
