TL:DR: memory ordering is not the same thing as out of order execution. It happens even on in-order pipelined CPUs. In-order commit is necessary1 for precise exceptions that can roll-back to exactly the instruction that faulted, without any instructions after that having already retired. The cardinal rule of out-of-order execution is don’t break single-threaded code. … Read more
A core is usually the basic computation unit of the CPU – it can run a single program context (or multiple ones if it supports hardware threads such as hyperthreading on Intel CPUs), maintaining the correct program state, registers, and correct execution order, and performing the operations through ALUs. For optimization purposes, a core can … Read more
Simple answer – it doesn’t. Machine code instructions are just binary numbers, as are data. More complicated answer – your processor may (or may not) provide segmentation of memory, meaning that attempting to execute what has been specified as data causes a trap of some sort. This is one of the the meaning of a … Read more
The cardinal rules of speculative out-of-order (OoO) execution are: Preserve the illusion of instructions running sequentially, in program order Make sure speculation is contained to things that can be rolled back if mis-speculation is detected, and that can’t be observed by other cores to be holding a wrong value. Physical registers, the back-end itself that … Read more