Lec12a - COMP 4300 Computer Architecture Control...

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1 COMP 4300 Computer Architecture Control Dependencies Dr. Xiao Qin Auburn University http://www.eng.auburn.edu/~xqin xqin@auburn.edu Fall, 2010
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2 Instruction Dependence Example Instruction Dependence Example For the following code identify all data and name dependence between instructions and give the dependency graph L.D F0, 0 (R1) ADD.D F4, F0, F2 S.D F4, 0(R1) L.D F0, -8(R1) ADD.D F4, F0, F2 S.D F4, -8(R1) 1 2 3 4 5 6 True Data Dependence: Instruction 2 depends on instruction 1 (instruction 1 result in F0 used by instruction 2), Similarly, instructions (4,5) Instruction 3 depends on instruction 2 (instruction 2 result in F4 used by instruction 3), Similarly, instructions (5,6) Name Dependence: Output Name Dependence (WAW): Instruction 1 has an output name dependence over result register (name) F0 with instructions 4 Instruction 2 has an output name dependence over result register (name) F4 with instructions 5 Anti-dependence (WAR): Instruction 2 has an anti-dependence with instruction 4 over register (name) F0 which is an operand of instruction 1 and the result of instruction 4 Instruction 3 has an anti-dependence with instruction 5 over register (name) F4 which is an operand of instruction 3 and the result of instruction 5
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Lec12a - COMP 4300 Computer Architecture Control...

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