[llvm] AMDGPU: Fix asserting in DAG kernel argument lowering on v6i32 (PR #100528)

[Carl Ritson via llvm-commits]

perlfu wrote:

> What was this assert about?! LGTM anyway.

Assertion pre-dates when we had MVTs to cover all of those vector sizes.
It should have been removed when the associated MVTs were added.


https://github.com/llvm/llvm-project/pull/100528