llvm-project

b2322772 - [libc] Reduce reference counter to a 32-bit integer (#150961)

[libc] Reduce reference counter to a 32-bit integer (#150961) Summary: This reference counter tracks how many threads are using a given slab. Currently it's a 64-bit integer, this patch reduces it to a 32-bit integer. The benefit of this is that we save a few registers now that we no longer need to use two for these operations. This increases the risk of overflow, but given that the largest value we accept for a single slab is ~131,000 it is a long way off of the maximum of four billion or so. Obviously we can oversubscribe the reference count by having threads attempt to claim the lock and then try to free it, but I assert that it is exceedingly unlikely that we will somehow have over four billion GPU threads stalled in the same place. A later optimization could be done to split the reference counter and pointers into a struct of arrays, that will save 128 KiB of static memory (as we currently use 512 KiB for the slab array).