Investigation On Code Optimization Techniques Of Register Pair For Vector VLIW DSP

This thesis studies the code optimization of register pair of vector VLIW DSP,including three code optimization problems: register pair operand processing,register pair assignment,and register pair use in automatic vectorization.In this thesis,a modified algorithm of register pair operands is proposed,which eliminates the requirement that the paired symbol register in the instruction operands must obtain the register pair as a whole when the register is allocated,and improves the flexibility of the use of registers.This thesis provides a flexible register pair assignment algorithm for the paired symbol registers in the operands of instructions,which can improve the success rate of register assignment process and reduce the number of insert overflow recovery instructions.This thesis presents a code optimization algorithm for register pair in automatic vectorization based on the processing and hardware features of the algorithm.The specific research contents are as follows:(1)Code optimization algorithm of register pair operands.Combining with the data flow information,the source operands and target operands of the instruction are modified in different ways according to the register allocation results.In this algorithm,the register pair that does not meet the register pair constraint condition in the instruction operands is called the error register pair.During instruction operand correction,single instruction is taken as the basic object,the handle mode is analyzed,and the data in the error register pairs in the instruction is temporarily stored in the legal register pair found by heuristic method by inserting data transfer instruction.The data forwarding instruction is then added after the instruction to transfer the stored data back to the original register.The instruction operand correction algorithm makes the use of register pair operands conform to the constraint condition of physical register pairs use and ensures that the semantics of input code does not change.(2)Code optimization algorithm of register pair assignment.According to the number characteristics of candidate physical register set and the constraints of register pair,the register assignment in register allocation process is optimized.When there are free physical register pair that meet the use constraints of register pair,this optimization algorithm will assign the free physical register pair to symbol register pair as much as possible.When there is no such pair of free physical registers,assign any two free physical registers to the pair symbol registers to avoid the failure of register assignment.(3)Code optimization algorithm of register pair in automatic vectorization.In this algorithm,a cost model based on the number of instruction packages executed by code fragments is established to guide code conversion,and some instructions using single register operands are mapped to operands using register pair.This method can help improve the utilization of instructions with more data processing power.