[llvm] [Offload]: Skip copying of unused kernel-mapped data (PR #124723)

[Johannes Doerfert via llvm-commits]

================
@@ -1197,6 +1197,97 @@ class PrivateArgumentManagerTy {
   }
 };
 
+/// Try to determine if kernel argument is unused. This method
+/// takes a conservative approach, i.e. it may return false
+/// negatives but it should never return a false positive.
----------------
jdoerfert wrote:

This deserves some more explanation. Why are these arg types "unused". Basically explain that they have no explicit or implicit variable use in the region.

https://github.com/llvm/llvm-project/pull/124723