GNU Compiler Collection (GCC) Internals: Small IPA passes

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#### 9.4.1 Small IPA passes

A small IPA pass is a pass derived from `simple_ipa_opt_pass`. As described in IPA, it does everything at once and defines only the Execute stage. During this stage it accesses and modifies the function bodies. No `generate_summary`, `read_summary`, or `write_summary` hooks are defined.

- IPA free lang data

  This pass frees resources that are used by the front end but are not needed once it is done. It is located in `tree.cc` and is described by `pass_ipa_free_lang_data`.

- IPA function and variable visibility

  This is a local function pass handling visibilities of all symbols. This happens before LTO streaming, so `-fwhole-program` should be ignored at this level. It is located in `ipa-visibility.cc` and is described by `pass_ipa_function_and_variable_visibility`.

- IPA remove symbols

  This pass performs reachability analysis and reclaims all unreachable nodes. It is located in `passes.cc` and is described by `pass_ipa_remove_symbols`.

- IPA OpenACC

  This is a pass group for OpenACC processing. It is located in `tree-ssa-loop.cc` and is described by `pass_ipa_oacc`.

- IPA points-to analysis

  This is a tree-based points-to analysis pass. The idea behind this analyzer is to generate set constraints from the program, then solve the resulting constraints in order to generate the points-to sets. It is located in `tree-ssa-structalias.cc` and is described by `pass_ipa_pta`.

- IPA OpenACC kernels

  This is a pass group for processing OpenACC kernels regions. It is a subpass of the IPA OpenACC pass group that runs on offloaded functions containing OpenACC kernels loops. It is located in `tree-ssa-loop.cc` and is described by `pass_ipa_oacc_kernels`.

- Target clone

  This is a pass for parsing functions with multiple target attributes. It is located in `multiple_target.cc` and is described by `pass_target_clone`.

- IPA auto profile

  This pass uses AutoFDO profiling data to annotate the control flow graph. It is located in `auto-profile.cc` and is described by `pass_ipa_auto_profile`.

- IPA tree profile

  This pass does profiling for all functions in the call graph. It calculates branch probabilities and basic block execution counts. It is located in `tree-profile.cc` and is described by `pass_ipa_tree_profile`.

- IPA free function summary

  This pass is a small IPA pass when argument `small_p` is true. It releases inline function summaries and call summaries. It is located in `ipa-fnsummary.cc` and is described by `pass_ipa_free_free_fn_summary`.

- IPA increase alignment

  This pass increases the alignment of global arrays to improve vectorization. It is located in `tree-vectorizer.cc` and is described by `pass_ipa_increase_alignment`.

- IPA transactional memory

  This pass is for transactional memory support. It is located in `trans-mem.cc` and is described by `pass_ipa_tm`.

- IPA lower emulated TLS

  This pass lowers thread-local storage (TLS) operations to emulation functions provided by libgcc. It is located in `tree-emutls.cc` and is described by `pass_ipa_lower_emutls`.

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