[compiler-rt] [compiler-rt] Implement __extendxftf2 and __trunctfxf2 for x86_64 (PR #66918)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

I don't see any tests for denormal numbers?

I'm a little concerned that mixing together fp80 and non-fp80 codepaths is going to be confusing for anyone unfamiliar with fp80 because the rules for fp80 significands are different... can you try to pull out the differences into helper methods, so it's more clear what's the IEEE codepath, and what's the non-IEEE codepath?

https://github.com/llvm/llvm-project/pull/66918