1. A system for simultaneous multithreading (SMT), the system comprising: a shared cache; a processor core comprising circuitry configured to execute threads by SMT, the threads including a first thread, a second thread, and a third thread, each of the first, second, and third threads having its own load queue and store queue such that the first thread has a first load queue and a first store queue, the second thread has a second load queue and a second store queue, and the third thread has a third load queue and a third store queue, the processor comprising an instruction cache, wherein in response to the processor core having control for writing and reading of a cache line in the shared cache, the processor core is configured to execute a store instruction for the first thread of the threads on the processor core comprising: placing an entry of the store instruction in the first store queue belonging to the first thread, the entry for the store instruction having a starting memory address and an ending memory address on the cache line; comparing starting memory addresses through ending memory addresses of the second and third load queues of the second and third threads on a byte-per-byte basis against the starting memory address through the ending memory address of the store instruction of the first store queue of the first thread; in response to at least one memory address byte in the starting through ending memory addresses in any of the second and third load queues of the second and third threads overlapping with a memory address byte in the starting through ending memory address of the store instruction, flushing the second thread or the third thread having the at least one memory address byte; in response to no overlap, permitting entries in the second and third load queues of the threads to remain; wherein the second and third threads for the second and third store queues have overlapping memory address bytes in the cache line; and storing to the cache line concurrently for both the second and third threads, the storing concurrently being permitted based on the second and third threads being on the processor core together, wherein the second and third threads are not permitted to both store concurrently to the cache line if on separate processor cores; an other processor core comprising circuitry to execute other threads by SMT, each of the other threads having its own load queue and store queue, wherein the other processor core having the other threads cannot control writing and reading of the cache line while the processor core having the first, second, and third threads controls writing and reading of the cache line.