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A data dependency in computer science is a situation in which a program statement (instruction) refers to the data of a preceding statement. In compiler theory, the technique used to discover data dependencies among statements (or instructions) is called dependence analysis. There are three types of dependencies: data, name, and control. == Data dependencies == Assuming statement S1 and S2, S2 depends on S1 if: (∩ O(S2) ) ∪ (∩ I(S2) ) ∪ (∩ O(S2) ) ≠ Ø where: * I(Si) is the set of memory locations read by Si and * O(Sj) is the set of memory locations written by Sj * and there is a feasible run-time execution path from S1 to S2 This Condition is called Bernstein Condition, named by A. J. Bernstein. Three cases exist: * Flow (data) dependence: O(S1) ∩ I (S2), S1 → S2 and S1 writes after something read by S2 * Anti-dependence: I(S1) ∩ O(S2), S1 → S2 and S1 reads something before S2 overwrites it * Output dependence: O(S1) ∩ O(S2), S1 → S2 and both write the same memory location. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「data dependency」の詳細全文を読む スポンサード リンク
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