t := left.X.Type()
			nf := t.NumFields()
			idx := fieldIdx(left)

			// Grab old value of structure.
			old := s.expr(left.X)

			// Make new structure.
			new := s.newValue0(ssa.StructMakeOp(t.NumFields()), t)

			// Add fields as args.
			for i := 0; i < nf; i++ {
				if i == idx {
					new.AddArg(right)
				} else {