It’s a funny register: you don’t want to read it (and before Ivy Bridge, user code couldn’t read it). The base is added by the CPU when you dereference the poi

It’s a funny register: you don’t want to read it (and before Ivy Bridge, user code couldn’t read it). The base is added by the CPU when you dereference the pointer. So code like: __thread int array[100]; array[n] += 5: Effectively computes the offset portion of array+n and then, using CPU assistance, accesses that memory relative to the segment.