[llvm] Allow FP reg conversion when copying Sx to Dx (PR #147559)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Why do you think the compiler should do this?  It's not what gcc does.  And in general implicitly performing floating-point conversions seems like a bad idea.

https://github.com/llvm/llvm-project/pull/147559