Realize special instructions on clustering VLIW DSP: multiplication-accumulation instruction

BWDSP is a 32bit static scalar digital signal processor with VLIW and SIMD features, which is designed for high-performance computing. Associated special instructions are designed for its special architecture and application scenarios. However, the existing compilation framework doesn't meet these special instructions. Therefore, in the context of traditional Open64 compiler, proposed a special instruction algorithm. Through this algorithm implements the multiplication-accumulation operation with BWDSP structure, to improve the performance of algorithms with multiply-accumulate requirements. Experimental results show that the algorithm, which can make an maximum of 8.85 speedup on BWDSP.