To be clear: the assignment isn&#x27;t the optimization; its the use of a symbol for &#x27;x&#x27; on the rhs so that the compiler can recognize it. To illustrate that<p><pre><code>    X &amp;x = { complex reference expression for x }
    y = (x + 1) &#x2F; atan(x) - x;
</code></pre>
Now the compiler has the clues it needs to write good code.
And with language support I don&#x27;t have to introduce new names for each occurrence; just one name like &lt;LHS&gt; that readers can quickly learn.