Cs 152 Computer Architecture and Engineering Lecture 22 – Advanced Processors Iii Last Time: Dynamic Scheduling

● Load hit store: A younger load that executes before an older store to the same memory location has written its data to the caches must retrieve the data from the SDQ. As loads execute, they check the SRQ to see whether there is any older store to the same memory location with data in the SDQ. If one is found, the data is forwarded from the SDQ rather than from the cache. If the data cannot be forwarded (as is the case if the load and store instructions operate on overlapping memory locations and the load data is not the same as or contained within the store data), the group containing the load instruction is flushed; that is, it and all younger groups are discarded and refetched from the instruction cache. If we can tell that there is an older store instruction that will write to the same memory location but has yet to write its result to the SDQ, the load instruction is rejected and reissued, again waiting for the store instruction to execute.