[PATCH] D16239: Fix PR25526 by adding back limited cmpxchg pseudo-Insts

[Tim Northover via llvm-commits]

> Comment at: lib/Target/AArch64/AArch64ISelDAGToDAG.cpp:2360
> @@ -2325,1 +2359,3 @@
> +    SelectCMP_SWAP(Node);
> +    return 0;
>    case ISD::READ_REGISTER:
> ----------------
> return nullptr;

Thanks Chad. Will do, sorry about that. I also realised I'd not
updated the comments properly yet. The one in AArch64InstrAtomics.td
is misleading and more elsewhere would probably help.

Tim.