[llvm] [LV] Cost EVL width-adjusting zext/trunc as free (PR #225016)

[Luke Lau via llvm-commits]

https://github.com/lukel97 commented:

I think it being free is RISC-V specific, is it possible to do this from TTI somehow? 

I've also separately wondered why the return type for get.vector.length is hardcoded to i32, since the input AVL argument can be overloaded to any scalar integer type. Relaxing this to allow returning i64 would probably make life a lot easier, since there's a lot of places in the LV where we have to cast the EVL IIRC

https://github.com/llvm/llvm-project/pull/225016