lenary added a comment. In D57450#1641308 <https://reviews.llvm.org/D57450#1641308>, @jyknight wrote:
> In D57450#1641190 <https://reviews.llvm.org/D57450#1641190>, @lenary wrote: > > > @jyknight I hear where you're coming from. I'll see what I can do about the > > psABI document. > > > > In that ticket, it's mentioned that the Darwin ABI explicitly says that > > non-power-of-two atomic types should be padded and realigned, but I cannot > > find any documentation explaining this. That would be useful, given > > presumably GCC does have to pad/align on Darwin. > > > AFAIK, there is no such documentation, at least publicly. Possibly Apple has > some internally, but I suspect it more likely just some in-person > conversation or something. > > GCC is not really supported on Darwin, so I suspect it just gets it wrong. To keep everyone updated, this has bubbled over into a thread on the GCC Mailing list: https://gcc.gnu.org/ml/gcc/2019-08/msg00191.html - Potentially this is a route to a resolution on non-RISC-V platforms (specifically x86). > > >> Then the only outstanding question relates to zero-sized atomics, which GCC >> does not pad, but I think Clang has to pad to get the semantics correct, >> based on this comment: >> https://github.com/llvm/llvm-project/blob/master/clang/lib/AST/ASTContext.cpp#L2176 > > The semantics in GCC are that you can create such an object, but any attempt > to load or store it will result in a compile-time error. E.g., "error: > argument 1 of ‘__atomic_load’ must be a pointer to a nonzero size object". So > I don't think there's really an issue there. Neat, ok. I think the feeling with this ticket and the RISC-V backend is: - We match GCC for power-of-two-sized atomics - We don't match for non-power-of-two sized atomics (as on any other platform) This feels like that should be enough for this patch to be merged, and in a future patch we can address the fall-out of ABIs changing across GCC and clang on more platforms than just RISC-V? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D57450/new/ https://reviews.llvm.org/D57450 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
