[llvm] [AMDGPU] Improve codegen for copysign(x, fneg(y)) (PR #207178)

[Jay Foad via llvm-commits]

https://github.com/jayfoad commented:

It is not clear to me what the patch to DAGCombiner::visitBITCAST is for. Instead of adding an ad hoc exception to a generic combine, can we handle this by improving selection patterns in the AMDGPU backend?

https://github.com/llvm/llvm-project/pull/207178