The common single-threaded execution model limits processors to exploiting only the relatively small amount of instruction-level parallelism that is available in application programs. The superthreaded processor, on the other hand, is a concurrent multithreaded architecture (CMA) that can exploit the multiple granularities of parallelism that are available in general-purpose application programs. Unlike other CMAs that rely primarily on hardware for run-time dependence detection and speculation, the superthreaded processor combines compiler-directed thread-level speculation of control and data dependences with run-time data dependence verification hardware. This hybrid of a superscalar processor and a multiprocessor-on-a-chip can utilize many of the existing compiler techniques used in traditional parallelizing compilers developed for multiprocessors. Additional unique compiler techniques, such as the conversion of data speculation into control speculation, are also introduced to generate the superthreaded code and to enhance the parallelism between threads. A detailed execution-driven simulator is used to evaluate the performance potential of this new architecture. It is found that a superthreaded processor can achieve good performance on complex application programs through this close coupling of compile-time and run-time information.

The performance of a concurrent multithreaded architectural model, called superthreading, is studied in this paper. It tries to integrate optimizing compilation techniques and run-time hardware support to exploit both thread-level and instruction-level parallelism, as opposed to exploiting only instruction-level parallelism in existing superscalars. The superthreaded architecture uses a thread pipelining execution model to enhance the overlapping between, threads, and to facilitate data dependence enforcement between threads through compiler-directed, hardware-supported, thread-level control speculation and run-time data dependence checking. We also evaluate the performance of the superthreaded processor through a detailed trace-driven simulator. Our results show that the superthreaded execution model can obtain good performance by exploiting both thread-level and instruction-level parallelism in programs. We also study the design parameters of its main system components, such as the size of the memory buffer, the bandwidth requirement of the communication links between thread processing units, and the bandwidth requirement of the shared data cache.

We propose a new universal High-Level Information (HLI) format to effectively integrate front-end and back-end compilers by passing front-end information to the back-end compiler. Importing this information into an existing back-end leverages the state-of-the-art analysis and transformation capabilities of existing front-end compilers to allow the back-end greater optimization potential than it has when relying on only locally-extracted information. A version of the HLI has been implemented in the SUIF parallelizing compiler and the GCC back-end compiler. Experimental results with the SPEC benchmarks show that HLI can provide GCC with substantially more accurate data dependence information than it can obtain on its own. Our results show that the number of dependence edges in GCC can be reduced by an average of 48% for the integer benchmark programs and an average of 54% for the floating-point benchmark programs studied, which provides greater flexibility to GCC's code scheduling pass. Even with the scheduling optimization limited to basic blocks, the use of HLI produces moderate speedups compared to using only GCC's dependence tests when the optimized programs are executed on MIPS R4600 and R10000 processors.