hvdijk added a comment.

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.

> 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.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D86310/new/

https://reviews.llvm.org/D86310

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