Author: Arthur Eubanks Date: 2022-02-28T12:53:09-08:00 New Revision: f1315c61a03ea6ef72ec11522f9abecd782f4856
URL: https://github.com/llvm/llvm-project/commit/f1315c61a03ea6ef72ec11522f9abecd782f4856 DIFF: https://github.com/llvm/llvm-project/commit/f1315c61a03ea6ef72ec11522f9abecd782f4856.diff LOG: [docs] Add note about interaction between clang plugins and -clear-ast-before-backend Reviewed By: rnk Differential Revision: https://reviews.llvm.org/D120666 Added: Modified: clang/docs/ClangPlugins.rst Removed: ################################################################################ diff --git a/clang/docs/ClangPlugins.rst b/clang/docs/ClangPlugins.rst index cf2c8721c12ae..001e66e434efb 100644 --- a/clang/docs/ClangPlugins.rst +++ b/clang/docs/ClangPlugins.rst @@ -200,3 +200,17 @@ action (i.e. the same as using `-add-plugin`): PluginASTAction::ActionType getActionType() override { return AddAfterMainAction; } + +Interaction with ``-clear-ast-before-backend`` +---------------------------------------------- + +To reduce peak memory usage of the compiler, plugins are recommended to run +*before* the main action, which is usually code generation. This is because +having any plugins that run after the codegen action automatically turns off +``-clear-ast-before-backend``. ``-clear-ast-before-backend`` reduces peak +memory by clearing the Clang AST after generating IR and before running IR +optimizations. Use ``CmdlineBeforeMainAction`` or ``AddBeforeMainAction`` as +``getActionType`` to run plugins while still benefitting from +``-clear-ast-before-backend``. Plugins must make sure not to modify the AST, +otherwise they should run after the main action. + _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
