Index: llvm/trunk/docs/LangRef.rst =================================================================== --- llvm/trunk/docs/LangRef.rst +++ llvm/trunk/docs/LangRef.rst @@ -1240,15 +1240,24 @@ ``convergent`` 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. + ``convergent``, and mark them with this attribute. + The ``convergent`` attribute may appear on functions or call/invoke + instructions. When it appears on a function, it indicates that calls to + this function should not be made control-dependent on additional values. 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. + values. - The optimizer may remove the ``convergent`` attribute when it can prove - that the function does not execute any convergent operations. + When it appears on a call/invoke, the ``convergent`` attribute indicates + that we should treat the call as though we're calling a convergent + function. This is particularly useful on indirect calls; without this we + may treat such calls as though the target is non-convergent. + + The optimizer may remove the ``convergent`` attribute on functions when it + can prove that the function does not execute any convergent operations. + Similarly, the optimizer may remove ``convergent`` on calls/invokes when it + can prove that the call/invoke cannot call a convergent function. ``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