GNU Compiler Collection (GCC) Internals: Annotations

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### 13.1 Annotations

The optimizers need to associate attributes with variables during the optimization process. For instance, we need to know whether a variable has aliases. All these attributes are stored in data structures called annotations which are then linked to the field `ann` in `struct tree_common`.

Presently, we define annotations for variables (`var_ann_t`). Annotations are defined and documented in `tree-flow.h`.