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  68. <h3 class="section">13.1 Annotations</h3>
  69. <a name="index-annotations"></a>
  70. <p>The optimizers need to associate attributes with variables during the
  71. optimization process. For instance, we need to know whether a
  72. variable has aliases. All these attributes are stored in data
  73. structures called annotations which are then linked to the field
  74. <code>ann</code> in <code>struct tree_common</code>.
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