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### 9.4 Inter-procedural optimization passes

The inter-procedural optimization (IPA) passes use call graph information to perform transformations across function boundaries. IPA is a critical part of link-time optimization (LTO) and whole-program (WHOPR) optimization, and these passes are structured with the needs of LTO and WHOPR in mind by dividing their operations into stages. For detailed discussion of the LTO/WHOPR IPA pass stages and interfaces, see IPA.

The following briefly describes the inter-procedural optimization (IPA) passes, which are split into small IPA passes, regular IPA passes, and late IPA passes, according to the LTO/WHOPR processing model.