Comment by dooglius

You are strawmanning the parent, he did not claim that compilers will go "oh, you wrote to this variable without synchronization! Now I'll show you, hehehe!". Your description of the compiler's behavior matches his description; the compilers detect a case where the program might exhibit behavior defined ISO C spec (signed integer overflow), see it as a potential for optimization because they are allowed to do anything (certain passes can be made if overflow is assumed not to happen), then do that optimization.