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### 16.23 Iterators

Ports often need to define similar patterns for more than one machine mode or for more than one rtx code. GCC provides some simple iterator facilities to make this process easier.

- Mode Iterators: Generating variations of patterns for different modes.
- Code Iterators: Doing the same for codes.
- Int Iterators: Doing the same for integers.
- Subst Iterators: Generating variations of patterns for define_subst.