Apparatus and method for tracking out of order load instructions to

Abstract

The present invention is directed towards a means to detect and reorder out of order instructions that may violate data coherency. The invention comprises a mis-queue table for holding entries of instruction data, each entry corresponding to an instruction in a computer microprocesor. The instruction data in each entry comprises: i) address information for the instruction; ii) ordering information for the instruction, indicating the order of the instruction relative to other instructions in the mis-queue table; iii) data modification information for the instruction, for indicating a possibility of modified data; and iv) out of order information, for indicating that a newer instruction has completed before the corresponding older instruction to the entry. The invention also comprises an out of order comparator for comparing an address of a completed instruction to any address information entries in the miss queue. If a completed instruction accesses the same address as another instruction, as indicated in the address information in the mis-queue table, and the completed instruction is newer than the matched instruction, the out of order field is marked indicating this condition exists. The invention comprises a modification comparator. This compares addresses from data altering events to those addresses in the entries in the mis-queue table. On a match, the modification field of the corresponding entry is marked to indicate this condition exists. When an instruction entry indicates that the corresponding instruction's data is modified, and that the instruction is out of order, all subsequent instructions are canceled.