RFR(S): 8209639: assert failure in coalesce.cpp: attempted to spill a non-spillable item

[Roland Westrelin]

> The core issue is that the matcher creates a compound testN_mem_reg0 
> node, that is forced to be scheduled early by the mem access. This 
> forces the test-node far away from the jmp-node. We need to be able to 
> detect this already at matching, and match a load + test_reg_reg instead.

That matches my understanding.

Thanks for the review!

Roland.