[llvm] [AArch64] Optimize vector multiplications by certain constants for v2i64 (PR #183827)

[Aly ElAshram via llvm-commits]

AlyElashram wrote:

A bit of a delay due to work , but I updated the code together with the test cases. I think we now cover all of the cases? @davemgreen 

https://github.com/llvm/llvm-project/pull/183827