aaron.ballman added a comment. Thanks for this new documentation! I'm by no means an expert in these builtins, so I had some questions on places we might want to expand things a bit more.
================ Comment at: clang/docs/LanguageExtensions.rst:2183 + n * sizeof(float), + 8 * alignof(float)); + init(mem, n); ---------------- ================ Comment at: clang/docs/LanguageExtensions.rst:2569-2570 + +``__builtin_expect`` is used to indicate that an expression is expected (I;e. +very likely to) take a given value. + ---------------- ================ Comment at: clang/docs/LanguageExtensions.rst:2588 + +The ``__builtin_expect()`` builtin is expected to be used with control flow +conditions such as in ``if`` and ``switch`` statements to help branch ---------------- ================ Comment at: clang/docs/LanguageExtensions.rst:2617 + +The ``__builtin_expect_with_probability()`` builtin is expected to be used with control flow +conditions such as in ``if`` and ``switch`` statements to help branch ---------------- ================ Comment at: clang/docs/LanguageExtensions.rst:2620 +prediction. It means that its first argument ``expr`` is expected to take the +value of its second argument ``val`` with probability ``p``. It always returns ``expr``. + ---------------- Should we mention that the probability should be specified as a value between [0.0, 1.0]? ================ Comment at: clang/docs/LanguageExtensions.rst:2627-2628 + +``__builtin_prefetch`` is used to communicate with the cache handler and bring +data in cache before it gets used. + ---------------- ================ Comment at: clang/docs/LanguageExtensions.rst:2647-2648 +are going to be used next. ``addr`` is the address that needs to be brought into +the cache. ``rw`` indicates the expected access mode: ``0`` for *read* and ``1`` +for *write*. ``locality`` indicates the expected persistance of data in cache, +from ``0`` which means that data can be discarded from cache after its next use ---------------- Is there a way to specify both read and write at the same time? Or does write access imply read access? (If so, it'd be good to make that explicit.) ================ Comment at: clang/docs/LanguageExtensions.rst:2649-2650 +for *write*. ``locality`` indicates the expected persistance of data in cache, +from ``0`` which means that data can be discarded from cache after its next use +to ``3`` which means that data is going to be resued a lot once in cache. + ---------------- How do users know whether to pick `1` or `2`? Should we list the values in table form with some prose describing when to use each value? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D117296/new/ https://reviews.llvm.org/D117296 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
