Use the same reg or memory location called a name but

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Unformatted text preview: e reg. names are fixed) • Difficult with memory locations (because 2+ addresses may refer to same location & be different) S. Ziavras Name Dependence • • Definition: 2 instrs. use the same reg. or memory location, called a name, but there is no flow of data between the instrs. associated with that name th th 2 types of name dependences between an instr. i that precedes that precedes instruction j in program order: program order: – Antidependence: j writes a reg. or memory location that i reads – Output dependence: i & j write the same reg. or memory location SOLUTION SOLUTION • REGISTER RENAMING can remove name dependences S. Ziavras Unknown Dependence • Dependence relation between 2 instrs. cannot be determined in the following situations: – Subscript of variable is itself subscribed (indirect addressing) – Subscript doesn’t contain loop index variable – Variable appears more than once with subscripts having different coefficients of loop variable – Subscript is nonlinear in loop index variable S. Ziavras Dependence Graphs • Nodes: instructions • Data dependence: i j • Name dependence dependence – Antidependence: i j – Output dependence: i S. Ziavras j Dependence...
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This document was uploaded on 02/09/2014.

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