jhuber6 wrote: > > This patch, which simply makes it legal on all architectures but do nothing > > is it's older than sm_70. > > I do not think this is the right thing to do. "do nothing" is not what one > would expect from a `nanosleep`.
Thanks, I made this a draft because I figured it wasn't the correct thing to do but wanted to pose the question. > Let's unpack your problem a bit. > > __nvvm_reflect() is probably closest to what you would need. However, IIUIC, > if you use it to provide nanosleep-based variant and an alternative for the > older GPUs, the `nanosleep` variant code will still hang off the dead branch > of if(__nvvm_reflect()) and if it's not eliminated by DCE (which it would not > if optimizations are off), the resulting PTX will be invalid for the older > GPUs. > > In other words, pushing nanosleep implementation into an intrinsic makes > things compile everywhere at the expense of doing a wrong thing on the older > GPUs. I do not think it's a good trade-off. > > Perhaps a better approach would be to incorporate dead branch elimination > onto NVVMReflect pass itself. We do know that it is the explicit intent of > `__nvvm_reflect()`. If NVVMReflect explicitly guarantees that the dead branch > will be gone, it should allow you to use approach `#1` w/o concerns for > whether optimizations are enabled and you should be able to provide whatever > alternative implementation you need (even if it's a null one), without > affecting correctness of LLVM itself. I think that would be a good solution if possible. Would this simply mean scheduling a global DCE pass right after the NVVM reflect pass? Since that seems to be run at `O0` that seems like the easiest solution, though it somewhat breaks `O0` semantics. Or, maybe we just have a really shallow implementation in the NVVM reflect pass that collapses the branch? https://github.com/llvm/llvm-project/pull/81033 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
