What kinds of optimizations does 'volatile' prevent in C++?

Question

I was looking up the keyword volatile and what it\'s for, and the answer I got was pretty much:

It\'s used to prevent the compiler from o

Answer 1

Unless you are on an embedded system, or you are writing hardware drivers where memory mapping is used as the means of communication, you should never ever ever be using volatile

Consider:

int main()
{
    volatile int SomeHardwareMemory; //This is a platform specific INT location. 
    for(int idx=0; idx < 56; ++idx)
    {
        printf("%d", SomeHardwareMemory);
    }
}

Has to produce code like:

loadIntoRegister3 56
loadIntoRegister2 "%d"
loopTop:
loadIntoRegister1 <
pushRegister2
pushRegister1
call printf
decrementRegister3
ifRegister3LessThan 56 goto loopTop

whereas without volatile it could be:

loadIntoRegister3 56
loadIntoRegister2 "%d"
loadIntoRegister1 <
loopTop:
pushRegister2
pushRegister1
call printf
decrementRegister3
ifRegister3LessThan 56 goto loopTop

The assumption about volatile is that the memory location of the variable may be changed. You are forcing the compiler to load the actual value from memory each time the variable is used; and you tell the compiler that reuse of that value in a register is not allowed.