[llvm] [AArch64] Consider negated powers of 2 when calculating throughput cost (PR #143013)

[David Green via llvm-commits]

davemgreen wrote:

> Not really
> 
> Because the asr is folded into it most of the time

I was looking into https://llvm.godbolt.org/z/xTKTddj73. The vector versions will not generally be able to fold the sub into the other instructions. For the scalar versions, sub+asr is usually a more expensive instruction than a single sub, although exact throughput costs become difficult to be precise about.

https://github.com/llvm/llvm-project/pull/143013