Can non-atomic-load be reordered after atomic-acquire-load?

Question

As known in since C++11 there are 6 memory orders, and in documentation written about std::memory_order_acquire:

• http://en.cppreference.com/w/cpp/

Answer 1

The reference you cited is pretty clear: you can't move reads before this load. In your example:

static std::atomic X;
static int L;


void thread_func() 
{
    int local1 = L;  // (1)
    int x_local = X.load(std::memory_order_acquire);  // (2)
    int local2 = L;  // (3)
}

memory_order_acquire means that (3) cannot happen before (2) (the load in (2) is sequenced before thr load in (3)). It says nothing about the relationship between (1) and (2).