[clang] [CIR] Upstream new SetBitfieldOp for handling C and C++ struct bitfields (PR #147609)

[Bruno Cardoso Lopes via cfe-commits]

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@@ -1669,6 +1669,90 @@ def GetGlobalOp : CIR_Op<"get_global",
   }];
 }
 
+//===----------------------------------------------------------------------===//
+// SetBitfieldOp
+//===----------------------------------------------------------------------===//
+
+def SetBitfieldOp : CIR_Op<"set_bitfield"> {
+  let summary = "Set the value of a bitfield member";
+  let description = [{
+    The `cir.set_bitfield` operation provides a store-like access to
+    a bit field of a record.
+
+    It expects an address of a storage where to store, a type of the storage,
+    a value being stored, a name of a bit field, a pointer to the storage in the
+    base record, a size of the storage, a size the bit field, an offset
+    of the bit field and a sign. Returns a value being stored.
+
+    A unit attribute `volatile` can be used to indicate a volatile load of the
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bcardosolopes wrote:

Perhaps adding an example would also be helpful

https://github.com/llvm/llvm-project/pull/147609