[clang] [CIR] Upstream support for accessing structure members (PR #136383)

[Erich Keane via cfe-commits]

================
@@ -1310,6 +1310,70 @@ def GetGlobalOp : CIR_Op<"get_global",
   let hasVerifier = 0;
 }
 
+//===----------------------------------------------------------------------===//
+// GetMemberOp
+//===----------------------------------------------------------------------===//
+
+def GetMemberOp : CIR_Op<"get_member"> {
+  let summary = "Get the address of a member of a record";
+  let description = [{
+    The `cir.get_member` operation gets the address of a particular named
+    member from the input record.
+
+    It expects a pointer to the base record as well as the name of the member
+    and its field index.
----------------
erichkeane wrote:

There is a bunch of 'legal' vs 'UB' things with common-initial sequence, particularly in C that might be interesting to opt based on, but I don't have any good ideas.

https://github.com/llvm/llvm-project/pull/136383