I noticed that various Thread Statics helpers constantly pop up in native traces in micro and macro benchmarks, e.g. Platform-JSON TE benchmark:

A simple demo:

while (true)
{
    var arr = ArrayPool<int>.Shared.Rent(10000);
    ArrayPool<int>.Shared.Return(arr);
}

when it spins it spends most of the time in JIT_GetSharedGCThreadStaticBaseDynamicClass:

where it just early outs:

if only we had a dedicated register (I think we can afford one at least on arm) which always pointed to current thread we could avoid that kind of overhead. Something like this (pseudocode):

if (!CTreg->tlsInited)
  initTls();
var field = CTreg->field;

making TLS access super cheap. As a bonus it might help with some pinvoke/safepoints routine?
Thoughts?
cc @jkotas

category:cq
theme:runtime
skill-level:intermediate
cost:small
impact:medium