[clang] [CIR] Use data size in emitAggregateCopy for overlapping copies (PR #186702)

[Erich Keane via cfe-commits]

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@@ -4149,21 +4149,32 @@ def CIR_CopyOp : CIR_Op<"copy",[
 
     The `volatile` keyword indicates that the operation is volatile.
 
+    The `skip_tail_padding` keyword indicates that only the data bytes should
+    be copied, excluding any tail padding. This is used when copying
+    potentially-overlapping subobjects where the tail padding might be occupied
+    by other objects (e.g. fields marked with `[[no_unique_address]]`). This
+    is only valid when the pointee type is a record type.
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erichkeane wrote:

Can we put this in the verifier? 

https://github.com/llvm/llvm-project/pull/186702