private void updateComposite(long sourceDtID, Composite sourceDt, Composite destDt,
			MyIdentityHashMap<Long, DataType> resolvedDataTypes) {

		if (sourceDt instanceof Structure) {
			updateStructure(sourceDtID, (Structure) sourceDt, (Structure) destDt,
				resolvedDataTypes);
		}
		else {
			updateUnion(sourceDtID, (Union) sourceDt, (Union) destDt, resolvedDataTypes);
		}

	}
Bitfield insertions can cause excess growth of structure which must be trimmed.
@param struct structure to be trimmed
@param preferredSize preferred structure size
Ghidra/Features/Base/src/main/java/ghidra/app/merge/datatypes/DataTypeMergeManager.java