[llvm] [AArch64][SelectionDAG] Lower multiplication by a constant to shl+add+shl+add (PR #89532)

[David Green via llvm-commits]

davemgreen wrote:

As I said in the ticket, do we have any evidence that these are better as add+shift? As far as I understand GCC optimized it this way because older cpus had slower mul and faster add+lsl, but that has changed in more recent cores and mul is now usually relatively quick.

https://github.com/llvm/llvm-project/pull/89532