chapter3-m2-ziavras

D f0 f2 f4 addd subd muld f6 f0 f8 f8 f10 f14 f6 f10

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Unformatted text preview: ata dependence stalls the pipeline To improve performance: execute out-of-order if program produces correct results S. Ziavras Out-Of-Order Execution Out-Of-Order Completion • • Introduces possibility of WAR & WAW hazards Example: DIV.D F0, F2, F4 ADD.D SUB.D MUL.D F6, F0, F8 F8, F10, F14 F6, F10, F8 F10 F8 • ADD.D waits for DIV.D result • Antidependence between ADD.D & SUB.D • WAR hazard will appear if SUB.D is executed before ADD.D • Output dependence between ADD.D & MUL.D • WAW hazard will appear if MUL.D before ADD.D S. Ziavras Out-Of-Order Completion & Exceptions • • • Dynamic scheduling with out-of-order completion must preserve exception behavior – Exactly those exceptions that would arise if the exceptions that would arise if the program were executed in strict program order actually do arise Ensure that no instr. can generate an exception until processor knows that the instr. raising the exception will be executed will be executed Although exception beha...
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