nvlink warning caused by recursion in RandomGamma

[stevenhofmeyr]

On my laptop (nvidia CUDA compiler release 12.4, V12.4.131), I get the following warnings at link time when building the CUDA version:

nvlink warning : Stack size for entry function '_ZN5amrex13launch_globalILi256EZNS_14ParallelForRNGIiZNK13DiseaseStatusI14AgentContainerNS_12ParticleTileINS_8ParticleILi0ELi0EEELi0ELi20ENS_14ArenaAllocatorEEENS_16ParticleTileDataIS6_Li0ELi20EEES6_E12updateAgentsERS3_RSt6vectorISt10unique_ptrINS_8MultiFabESt14default_deleteISF_EESaISI_EEEUliRKNS_12RandomEngineEE_vEENSt9enable_ifIXsr5amrex19MaybeDeviceRunnableIT0_vEE5valueEvE4typeET_RKSR_EUlvE_EEvSR_' cannot be statically determined
nvlink warning : Stack size for entry function '_ZN5amrex13launch_globalILi256EZNS_14ParallelForRNGIiZN14AgentContainer12infectAgentsEvEUliRKNS_12RandomEngineEE_vEENSt9enable_ifIXsr5amrex19MaybeDeviceRunnableIT0_vEE5valueEvE4typeET_RKS8_EUlvE_EEvS8_' cannot be statically determined
nvlink warning : Stack size for entry function '_ZN5amrex13launch_globalILi256EZNS_14ParallelForRNGIiZN13HospitalModelI14AgentContainerNS_16ParticleTileDataINS_8ParticleILi0ELi0EEELi0ELi20EEES6_E11treatAgentsERS3_RSt6vectorISt10unique_ptrINS_8MultiFabESt14default_deleteISC_EESaISF_EEEUliRKNS_12RandomEngineEE_vEENSt9enable_ifIXsr5amrex19MaybeDeviceRunnableIT0_vEE5valueEvE4typeET_RKSO_EUlvE_EEvSO_' cannot be statically determined
nvlink warning : Stack size for entry function '_ZN5amrex13launch_globalILi256EZNS_14ParallelForRNGIZN63_INTERNAL_8f05c69d_24_InitializeInfections_cpp_aaef0290_316053423infect_random_communityER14AgentContainerRKNS_6VectorIiSaIiEEERNS_9iMultiFabERSt3mapISt4pairIiiENS_9DenseBinsINS_8ParticleILi0ELi0EEEEESt4lessISE_ESaISD_IKSE_SI_EEEiiibEUliiiRKNS_12RandomEngineEE_Li2EEENSt9enable_ifIXsr5amrex19MaybeDeviceRunnableIT_vEE5valueEvE4typeERKNS_5BoxNDIXT0_EEERKSV_EUlvE_EEvT0_' cannot be statically determined

Turns out these warnings are generated by recursion in CUDA code and are not necessarily a problem. They are generated by the new RandomGamma function which uses recursion. Need to either implement that without recursion or suppress this warning (with the knowledge that the recursion can never cause stack overflow).

[atmyers]

I think I can fix this by adding an extra template parameter to make the function non-recursive.

[atmyers]

AMReX-Codes/amrex#4324