[llvm] [NVPTX] Don't use stack memory when bitcasting to/from v2i8 (PR #113928)

[Justin Fargnoli via llvm-commits]

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+; RUN: llc < %s -mtriple=nvptx64-nvidia-cuda -mcpu=sm_90 -mattr=+ptx80 -asm-verbose=false \
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justinfargnoli wrote:

I think you need to delete all the existing `CHECK` statements first. 

If that doesn't work (and the rest of the MR looks good), I'll just submit a follow-up patch that auto-generates the test. 

https://github.com/llvm/llvm-project/pull/113928