[PATCH] D153519: [LegalizeTypes] Widen insert_subvector ops for fixed insert into scalable

[Luke Lau via Phabricator via llvm-commits]

luke added a comment.

In D153519#4441716 <https://reviews.llvm.org/D153519#4441716>, @craig.topper wrote:

> In D153519#4441673 <https://reviews.llvm.org/D153519#4441673>, @luke wrote:
>
>> In D153519#4441316 <https://reviews.llvm.org/D153519#4441316>, @craig.topper wrote:
>>
>>> Is it possible for the widened type to exceed the minimum vscale?
>>
>> Yes, but I think that would still fall under the "If this condition cannot be determined statically but is
>> false at runtime, then the result vector is undefined." part of insert_subvector's definition. Since we currently already lower an insert_subvector of e.g. v8i32 into nxv4i32
>
> What if vscale min is 3(not possible for RISC-V but this is generic code), and the types are nxv1i64 and v3i64. The operation is defined for those types, but when v3i64 gets widened to v4i64 it becomes undefined.

Right, I see now. Could we then lower it as a series of insert_vector_elt?


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