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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
2 types of name dependences between an instr. i
that precedes instruction j in program order:
– Antidependence: j writes a reg. or memory
location that i reads
– Output dependence: i & j write the same reg. or
SOLUTION • REGISTER RENAMING can remove name
S. Ziavras Unknown Dependence
• Dependence relation between 2 instrs. cannot be
determined in the following situations:
– Subscript of variable is itself subscribed
– Subscript doesn’t contain loop index variable
– Variable appears more than once with
subscripts having different coefficients of loop
– Subscript is nonlinear in loop index variable S. Ziavras Dependence Graphs
• Nodes: instructions
• Data dependence: i j • Name dependence
– Antidependence: i j – Output dependence: i S. Ziavras j Dependence...
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This document was uploaded on 02/09/2014.
- Fall '09