[compiler-rt] [compiler-rt][ARM] Optimized double precision FP add/sub (PR #179921)

[Simon Tatham via llvm-commits]

statham-arm wrote:

This is now the patch at the head of my queue of optimized FP implementations.

I'm pleased to say that we're now into the optimized FP implementations! All the preliminary patches are done, and further patches will actually make things run faster. :slightly_smiling_face: 

https://github.com/llvm/llvm-project/pull/179921