The future of Int128 support in D language

[Iain Buclaw]

On Monday, 9 January 2023 at 18:10:43 UTC, Patrick Schluter wrote:
> On Monday, 9 January 2023 at 16:51:45 UTC, Iain Buclaw wrote:
>> On Sunday, 8 January 2023 at 17:36:07 UTC, Johan wrote:
>>> [...]
>>
>> Actually, I had implemented core.int128 as compiler-recognized 
>> intrinsics that do the necessary conversion to/from native on 
>> the fly.
>>
>> I ran into some problems when testing this on SPARC though (to 
>> name one non-x86 target that I use for sanity checking new 
>> code-gen features).  Never found the time to get to the bottom 
>> of what was causing it to crash, so left it as a TBD patch set.
>>
>> I suspect I am going wrong somewhere with all the concatenated 
>> `*cast(cent*)&c` and `*cast(core.int128.Cent*)&c` going on all 
>> around the place when you chain these functions together with 
>> UFCS.  Maybe should investigate using a `union` instead, but 
>> not enough bandwidth to do that at the moment.
>
> SPARC is big endian. Probably somewhere an intermediate value 
> that is truncated to 64 bits which passes in LE but not in BE.
> Talking completely out of my a.s. :-)

Endianess is already covered.

https://github.com/dlang/dmd/blob/ee1acbb62dc4a65e72d7bf27e61761fb34d497e2/druntime/src/core/int128.d#L24-L36

At some point the backend dies on receiving invalid code, or 
something it cannot reasonably expand/lower.  So I must be doing 
something wrong. :-)