[clang] [CIR] Fix alignment when lowering set/get bitfield operations (PR #148999)

[Henrich Lauko via cfe-commits]

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@@ -1720,20 +1720,24 @@ def SetBitfieldOp : CIR_Op<"set_bitfield"> {
     %2 = cir.load %0 : !cir.ptr<!cir.ptr<!record_type>>, !cir.ptr<!record_type>
     %3 = cir.get_member %2[1] {name = "e"} : !cir.ptr<!record_type>
                                                              -> !cir.ptr<!u16i>
-    %4 = cir.set_bitfield(#bfi_e, %3 : !cir.ptr<!u16i>, %1 : !s32i) -> !s32i
+    %4 = cir.set_bitfield align(4) (#bfi_e, %3 : !cir.ptr<!u16i>, %1 : !s32i)
+                                                                       -> !s32i
     ```
    }];
 
   let arguments = (ins
     Arg<CIR_PointerType, "the address to store the value", [MemWrite]>:$addr,
     CIR_AnyType:$src,
     BitfieldInfoAttr:$bitfield_info,
+    OptionalAttr<I64Attr>:$alignment,
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xlauko wrote:

Maybe even `DefaultValuedOptionalAttr` would be better, which would eliminate unnecessary ternary in builders and `op.getAlignment().value()` should be reduced to `op.getAlignment()`.

https://github.com/llvm/llvm-project/pull/148999