Implementing Extended subwords in Simplescalar

TIPPINST - Implementing new instructions on Simplescalar is a slow and tedious process as I outlined in an article a few months back.

The CoMP research group in the Dep. Math. and Comp. Science at the University of Antwerp realise and appreciate this as a result they are working on a project that amongst other things simplifies this process.

Their research into implementing extended subwordsin Simplescalar. The goal of their project is to merge the two tools they have developed called SSIT and SAT into one tool, to extend the resulting tool, to employ the tool to evaluate extended subwords, and to investigate if extended subwords can be used to increase the performance of applications other than the applications currently considered.

The two tools called SSIT (SimpleScalar Instruction Tool) and SAT (SimpleScalar Architecture Tool) have been developed by CoMP to simplify adding new instructions to the SimpleScalar toolset.

Extended subwords is a novel micro-architectural technique designed to improve the performance of SIMD extensions such as MMX. MMX instructions can process eight 8-bit values in parallel. However, 8 bits is often too small for intermediate computations to be performed without overflow. Because of this, data often needs to be unpacked to a larger computational format. This implies a performance loss due to (un)packing overhead and loss of parallelism. Extended subwords are 12 bits wide, allowing many intermediate computations to be performed without overflow.

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