[llvm] [AArch64][GlobalISel] More FCmp legalization. (PR #78734)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

G_SELECT shows an optimization opportunity, if the LLT could distinguish between i16 and f16. i16 would never be legal and f16 would sometimes be legal for G_SELECT. The costs are that we have to legalize G_SELECT for i64 and f64.

https://github.com/llvm/llvm-project/pull/78734