[llvm] [AArch64] Fix #94909: Optimize vector fmul(sitofp(x), 0.5) -> scvtf(x, 2) (PR #141480)

[David Green via llvm-commits]

https://github.com/davemgreen commented:

It looks like this got quite far. I've left a few comments inline, tablegen can be finicky at times.

https://github.com/llvm/llvm-project/pull/141480