Tagged references for thread-local data

Method and apparatus for tagged references for identifying thread-local data in multithreaded applications. Embodiments may provide a dynamic mechanism that identifies thread-local objects by "tagging" references to the objects. In embodiments, in an application, if an object is to be allocated as a thread-local object, one or more bits of the object reference may be "tagged" to indicate that the object is a thread-local object. In one embodiment, the lowest-order bit of the object reference may be set to indicate that the object is a thread-local object. In embodiments, thread locality of an object may be determined by testing the reference itself rather than loading a bit or field from the referenced object or by checking address ranges. Further, embodiments do not rely on address ranges to identify objects as thread-local, and so the allocation of thread-local objects may not be restricted to thread-local heaps.