[llvm] [RFC][LangRef] Specify that the accessed bytes of concurrent atomics must be either disjoint or the same (PR #204329)

[Ralf Jung via llvm-commits]

================
@@ -4100,6 +4105,12 @@ address. See that instruction's documentation for details.
 For a simpler introduction to the ordering constraints, see the
 {doc}`Atomics`.
 
+For the following, we call two or more accesses *perfectly overlapping*
+if they all access the exact same set of bytes, i.e., they access the
+same address and have the same access size. By the constraints of the
+previous section, racing atomic accesses must be perfectly overlapping
----------------
RalfJung wrote:

I suppose "racing" here is meant to exclude reads?

https://github.com/llvm/llvm-project/pull/204329