[llvm] [BasicTTIImpl] Add cost entries for ldexp, [l]lround (PR #146373)

[David Green via llvm-commits]

davemgreen wrote:

I've added some tests, can you rebase? I'm pretty sure this LGTM, providing that the SVE tests still produce an invalid cost. (We will need to add lowering).

https://github.com/llvm/llvm-project/pull/146373