Three types of instructions • Incorrectly predicted branch – Indicates speculation was wrong ROB Execution restarts at proper location Store – Update memory Remove store from ROB Everything else – Update registers Remove instruction from ROB You will be using this tool after Spring Break – Architecture similar to speculative Tomasulo’s Register Update Unit (RUU) Controls instructions scheduling and dispatching to functional units Stores intermediate source values for instructions – – Ensures instruction commit occurs in order! Needs to be of appropriate size Minimum of issue width * number of pipeline stages Too small of an RUU can be a structural hazard! Result bus could be a structural hazard UNIT 8 1. Explain in detail the hardware support for preserving exception behavior during Speculation. July 14) (June 2013) (June 2015) H/W Support : Conditional Execution Also as Predicated Execution Enhancement to instruction set Can be used to eliminate branches All control dependences are converted to data dependences Instruction refers to a condition Evaluated as part of the execution True? Executed normally False? Execution continues as if the instruction were a no-op Example :
• Three types of instructions – Incorrectly predicted branch Indicates speculation was wrong ROB Execution restarts at proper location – Store Update memory Remove store from ROB – Everything else Update registers Remove instruction from ROB – You will be using this tool after Spring Break Architecture similar to speculative Tomasulo’s Register Update Unit (RUU) Controls instructions scheduling and dispatching to functional units – Stores intermediate source values for instructions – Ensures instruction commit occurs in order! Needs to be of appropriate size Minimum of issue width * number of pipeline stages Too small of an RUU can be a structural hazard! Result bus could be a structural hazard UNIT 8 1. Explain in detail the hardware support for preserving exception behavior during Speculation. July 14) (June 2013) (June 2015) H/W Support : Conditional Execution Also as Predicated Execution Enhancement to instruction set Can be used to eliminate branches All control dependences are converted to data dependences Instruction refers to a condition Evaluated as part of the execution True? Executed normally False? Execution continues as if the instruction were a no-op Example :
Unit-IV-VIII.docx