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| -rw-r--r-- | llvm/docs/LangRef.rst | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst index 325f95788e1..de07c34b1bd 100644 --- a/llvm/docs/LangRef.rst +++ b/llvm/docs/LangRef.rst @@ -1238,10 +1238,17 @@ example: function call are also considered to be cold; and, thus, given low weight. ``convergent`` - This attribute indicates that the callee is dependent on a convergent - thread execution pattern under certain parallel execution models. - Transformations that are execution model agnostic may not make the execution - of a convergent operation control dependent on any additional values. + In some parallel execution models, there exist operations that cannot be + made control-dependent on any additional values. We call such operations + ``convergent``, and mark them with this function attribute. + + For example, the intrinsic ``llvm.cuda.syncthreads`` is ``convergent``, so + calls to this intrinsic cannot be made control-dependent on additional + values. Other functions may also be marked as convergent; this prevents + the same optimization on those functions. + + The optimizer may remove the ``convergent`` attribute when it can prove + that the function does not execute any convergent operations. ``inaccessiblememonly`` This attribute indicates that the function may only access memory that is not accessible by the module being compiled. This is a weaker form |
