We propose an operational semantics where the execution of instructions of a program is not necessarily in the order in which they are given in the program. In other words, an instruction might be executed before its preceding instructions have been executed. The idea is that such an execution mechanism can capture some optimizations that a compiler or a runtime environment might apply to the program. In our framework, the allowed reorderings are described by a binary commutation relation on the set of instructions, or, more generally, by a semicommutation relation. We then further extend this basic framework to allow more intricate reordering behaviours. As an experiment, we describe a fragment of the multicopy-atomic ARM memory model in this framework and validate a prototype of it against a number of litmus-tests.

我们提出一种操作语义，其中程序指令的执行不一定按照它们在程序中给出的顺序执行。换句话说，一条指令可能在其先前的指令已被执行之前被执行。想法是，这种执行机制可以捕获编译器或运行时环境可能应用于该程序的某些优化。在我们的框架中，允许的重排序通过指令集上的二进制换向关系或更一般地通过半换向关系来描述。然后，我们进一步扩展此基本框架，以允许进行更复杂的重新排序行为。作为实验，我们在此框架中描述了多原子原子ARM内存模型的一部分，并针对大量石蕊试验验证了其原型。