How to fake 1000 registers

Large numbers of logical registers can improve performance by allowing fast access to multiple subroutine contexts (register windows) and multiple thread contexts (multithreading). Support for both of these together requires a multiplicative number of registers that quickly becomes prohibitive. We overcome this limitation with the virtual context architecture (VCA), a new register-file architecture that virtualizes logical register contexts. VCA works by treating the physical registers as a cache of a much larger memory-mapped logical register space. Complete contexts, whether activation records or threads, are no longer required to reside in their entirety in the physical register file. A VCA implementation of register windows on a single-threaded machine reduces data cache accesses by 20%, providing the same performance as a conventional machine while requiring one fewer cache port. Using VCA to support multithreading enables a four-thread machine to use half as many physical registers without a significant performance loss. VCA naturally extends to support both multithreading and register windows, providing higher performance with significantly fewer registers than a conventional machine