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Conservative 0-o-0 Load Execution str1,ldr3,(r2)(r4) - Split execution of store instruction into two phases: address calculation and data write - Can execute load before store, if addresses known and r4!=r2 - Each load address compared with addresses of all previous uncommitted stores (can use partial conservative check i.e., bottom 12 bits of address) - Don't execute load if any previous store address not known (MIPS R10K, 16 entry address queue) October. 31, 2005 Address Speculation str1,ldr3,(r2)(r4) - Guess that r 4!=r2 - Execute load before store address known - Need to hold all completed but uncommitted load/store addresses in program order - If subsequently find r4==r2, squash load and all following instructions Large penalty for inaccurate address speculation Memory Dependence Prediction (Alpha 21264) str1,ldr3,(r2)(r4) - Guess that r4!=r2 and execute load before store - If later find r4==r2, squash load and all following instructions, but mark load instruction as store-wait - Subsequent executions of the same load instruction will wait for all previous stores to complete - Perindically clear store-inait bits