[llvm] [RFC] IR: Define noalias.addrspace metadata (PR #102461)

[Matt Arsenault via llvm-commits]

================
@@ -8021,6 +8021,43 @@ it will contain a list of ids, including the ids of the callsites in the
 full inline sequence, in order from the leaf-most call's id to the outermost
 inlined call.
 
+
+'``noalias.addrspace``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``noalias.addrspace`` metadata is used to identify memory
+operations which cannot access a range of address spaces. It is
----------------
arsenm wrote:

I was not planning on touching alias analysis for this, but in principle it should be possible. We probably should have an address space AA. Currently we deal with this with target specific backend analyses, but this has the drawback that it's after the heavier AA passes in the pipeline when we can give cheaper addrspace checks in many cases.

TargetTransformInfo already has addrspacesMayAlias and isValidAddrSpaceCast 

https://github.com/llvm/llvm-project/pull/102461