Author: Sjoerd Meijer Date: 2025-02-20T10:10:23Z New Revision: dc326d0b01f63e49f4f11c0c332369bf109721df
URL: https://github.com/llvm/llvm-project/commit/dc326d0b01f63e49f4f11c0c332369bf109721df DIFF: https://github.com/llvm/llvm-project/commit/dc326d0b01f63e49f4f11c0c332369bf109721df.diff LOG: [Clang][doc] -ffp-contract options and standard compliance (#127621) We had an discussion about -ffp-contract, how it compared to GCC which defaults to fast, and standard compliance. Looking at our docs, most information is there, but this clarifies when this option is and isn't standard compliant. Added: Modified: clang/docs/UsersManual.rst Removed: ################################################################################ diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst index d977868b8a2c6..8213334b61c22 100644 --- a/clang/docs/UsersManual.rst +++ b/clang/docs/UsersManual.rst @@ -1681,19 +1681,27 @@ for more details. permitted to produce more precise results than performing the same operations separately. - The C standard permits intermediate floating-point results within an + The C and C++ standards permit intermediate floating-point results within an expression to be computed with more precision than their type would normally allow. This permits operation fusing, and Clang takes advantage - of this by default. This behavior can be controlled with the ``FP_CONTRACT`` - and ``clang fp contract`` pragmas. Please refer to the pragma documentation - for a description of how the pragmas interact with this option. + of this by default (``on``). Fusion across statements is not compliant with + the C and C++ standards but can be enabled using ``-ffp-contract=fast``. + + Fusion can be controlled with the ``FP_CONTRACT`` and ``clang fp contract`` + pragmas. Please note that pragmas will be ingored with + ``-ffp-contract=fast``, and refer to the pragma documentation for a + description of how the pragmas interact with the diff erent ``-ffp-contract`` + option values. Valid values are: - * ``fast`` (fuse across statements disregarding pragmas, default for CUDA) - * ``on`` (fuse in the same statement unless dictated by pragmas, default for languages other than CUDA/HIP) - * ``off`` (never fuse) - * ``fast-honor-pragmas`` (fuse across statements unless dictated by pragmas, default for HIP) + * ``fast``: enable fusion across statements disregarding pragmas, breaking + compliance with the C and C++ standards (default for CUDA). + * ``on``: enable C and C++ standard complaint fusion in the same statement + unless dictated by pragmas (default for languages other than CUDA/HIP) + * ``off``: disable fusion + * ``fast-honor-pragmas``: fuse across statements unless dictated by pragmas + (default for HIP) .. option:: -f[no-]honor-infinities _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
