[PATCH] D131547: [Clang][AArch64] Use generic extract/insert vector for svget/svset/svcreate tuples

Wed Aug 17 09:35:18 PDT 2022

sdesmalen added a comment.

In D131547#3728867 <https://reviews.llvm.org/D131547#3728867>, @dmgreen wrote:

> In D131547#3728842 <https://reviews.llvm.org/D131547#3728842>, @sdesmalen wrote:
>
>> In D131547#3723083 <https://reviews.llvm.org/D131547#3723083>, @dmgreen wrote:
>>
>>> I think we usually try to do the same, if the intrinsics have been in released compilers. There is an example in https://reviews.llvm.org/D98487#change-tOTTgECYYAO5, hopefully these would be equally simple.
>>
>> We don't really have the intention in keeping compatibility for intrinsics like these, since the vector.extract/insert intrinsics are the proper way to insert/extract vectors and they have been around for quite some time now. Also these intrinsics are quite specific to the initial SVE ACLE implementation when we first upstreamed it, so it's not very likely that anyone else is using them.
>
> I'm not sure what you mean by "keeping compatibility", they just need to be replaced in the autoupdate code. If there was a release of llvm which emitted the intrinsics, then the default assumption is that someone might have bitcode that uses them.

What I meant with 'keeping compatibility' is exactly what you described; bitcode/IR that uses the old intrinsics remaining to work with newer versions of LLVM.

My point was that these intrinsics have not been in LLVM for that long and have a very limited scope, so are unlikely to have accrued much legacy. I don't really expect a practical use-case where people have legacy SVE ACLE bitcode that they need to compile with a newer version of LLVM. So unless someone explicitly requests the compatibility, we'd rather remove them in favour of adding code that will never be used.

Is there a formal requirement that LLVM must remain backward compatible with older LLVM IR (beyond the target-independent parts)?

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