[llvm] [Hexagon/LoopIdiom] Protect test against O2 changes (PR #144734)

[Krzysztof Parzyszek via llvm-commits]

kparzysz wrote:

> Hm, in that case, I think we'd have to have the optimization turned off by default, until the necessary work is done to emit pmpy instructions on Hexagon, subsuming HexagonLoopIdiom. We can then turn it on by default, and strip HexagonLoopIdiom, I think.

Maybe for now you could add some sort of a target hook to check if the target wants the CRC optimization?

There are other architectures that support polynomial multiplication[1], so adding a target-agnostic support for it would be worthwhile.

[1] https://en.wikipedia.org/wiki/CLMUL_instruction_set

https://github.com/llvm/llvm-project/pull/144734