tmgross added a comment. In D86310#4516911 <https://reviews.llvm.org/D86310#4516911>, @hvdijk wrote:
> In D86310#4516876 <https://reviews.llvm.org/D86310#4516876>, @pengfei wrote: > >> Just FYI. There are a few reports about the compatibility issues, e.g., >> #41784 <https://github.com/llvm/llvm-project/issues/41784>. > > Thanks. This is a case where clang breaks up `__int128` into 2x `i64` before > it gets to LLVM. It is therefore not affected by this patch. Your other link > also references #20283 <https://github.com/llvm/llvm-project/issues/20283>, > which is the same issue of clang breaking `__int128` into 2x `i64`. > > Although this patch will not fix those issues, it may make it easier to fix > them later on: it will give clang the ability to use LLVM's `i128` type > rather than trying to emulate it.> Does this happen on the clang side or the LLVM side? I built rustc against LLVM with your patch ([link to source](llvm.org/docs/LangRef.html#floating-point-types)) and it makes rustc compatible with clang (progress!) but it still seems not compatible with GCC. That is, after the patch rustc now seems to have an identical calling behavior to clang, so I'm thinking that maybe this behavior lies somewhere in LLVM and not the frontend? Quick ABI check that demonstrates this https://github.com/tgross35/quick-abi-check, the outputs of note (clang-new is built with this patch): # all caller-foo-callee-samefoo work fine + ./bins/caller-gcc-callee-gcc caller cc: gcc 11.3.0 caller align i128 16 caller arg0 244 caller argval 0xf0e0d0c0b0a09080706050403020100 caller arg15 123456.125000 callee cc: gcc 11.3.0 callee arg0 244 callee arg1 0xf0e0d0c0b0a09080706050403020100 callee arg2 0xf0e0d0c0b0a09080706050403020100 callee arg3 0xf0e0d0c0b0a09080706050403020100 callee arg4 0xf0e0d0c0b0a09080706050403020100 callee arg15 123456.125000 # between clang and gcc arg3+ seem to flip he word order? + ./bins/caller-gcc-callee-clang-old caller cc: gcc 11.3.0 caller align i128 16 caller arg0 244 caller argval 0xf0e0d0c0b0a09080706050403020100 caller arg15 123456.125000 callee cc: clang 14.0.0 callee arg0 244 callee arg1 0xf0e0d0c0b0a09080706050403020100 callee arg2 0xf0e0d0c0b0a09080706050403020100 callee arg3 0x7060504030201000000000000000000 callee arg4 0x7060504030201000f0e0d0c0b0a0908 callee arg15 123456.125000 + ./bins/caller-gcc-callee-clang-new caller cc: gcc 11.3.0 caller align i128 16 caller arg0 244 caller argval 0xf0e0d0c0b0a09080706050403020100 caller arg15 123456.125000 callee cc: clang 17.0.0 (g...@github.com:tgross35/llvm-project.git 1733d949633a61cd0213f63e22d461a39e798946) callee arg0 244 callee arg1 0xf0e0d0c0b0a09080706050403020100 callee arg2 0xf0e0d0c0b0a09080706050403020100 callee arg3 0x7060504030201000000000000000000 callee arg4 0x7060504030201000f0e0d0c0b0a0908 callee arg15 123456.125000 I think this patch can stand on its own even if it doesn't fix the above, but I'm just trying to get a better idea of where it's coming from if anyone knows more details. >> There's also concern about the alignment difference between `_BitInt(128)` >> and `__int128`, see #60925 >> <https://github.com/llvm/llvm-project/issues/60925> > > That references https://gitlab.com/x86-psABIs/x86-64-ABI/-/issues/11, where > the answer four months ago was basically "it's probably already too late for > that" with a suggestion to try and post on the mailing list to try and > convince others that this was important enough to do. Nothing was posted to > the mailing list, and by now GCC has started implementing what the ABI > specifies (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102989). I think we > would need an extraordinary rationale if we want to convince others that the > ABI should be changed. I reached out to the person who authored that. We will follow up with the mailing list to at least make a mild push for `_BitInt(128)` to take the alignment of `__int128` (imagine the stackoverflow confusion if they aren't the same). However, I'm in agreement with the above comment - that is a separate concern from the behavior here since LLVM already complies with the bitint spec. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D86310/new/ https://reviews.llvm.org/D86310 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
