x=x+1 vs. x +=1

Question

I\'m under the impression that these two commands result in the same end, namely incrementing X by 1 but that the latter is probably more efficient.

If this is not c

Answer 1

I wrote a simple console app:

static void Main(string[] args)
{
    int i = 0;
    i += 1;
    i = i + 1;
    Console.WriteLine(i);
}

I disassembled it using Reflector and here's what i got:

private static void Main(string[] args)
{
    int i = 0;
    i++;
    i++;
    Console.WriteLine(i);
}

They are the same.

Answer 2

Back in the early 1980s, one of the really cool optimizations of the Lattice C Compiler was that "x = x + 1;", "x += 1;" and "x++;" all produced exactly the same machine code. If they could do it, a compiler written in this millenium should definitely be able to do it.

Answer 3

If x is a simple integer scalar variable, they should be the same.

If x is a large expression, possibly with side effects, +=1 and ++ should be twice as fast.

Many people concentrate on this kind of low-level optimization as if that's what optimization is all about. I assume you know it's a much bigger subject.

Answer 4

Something worth noting is that +=, -=, *= etc. do an implicit cast.

int i = 0;
i = i + 5.5; // doesn't compile.
i += 5.5; // compiles.

Answer 5

are the same.

x=x+1 

is mathematical seen a contradiction whereas

x+=1

isn't and is light to be typed.

Answer 6

On x86, if x is in register eax, they will both result in something like

inc eax;

So you're right, after some compilation stage, the IL will be the same.

There's a whole class of questions like this that can be answered with "trust your optimizer."

The famous myth is that
x++;
is less efficient than
++x;
because it has to store a temporary value. If you never use the temporary value, the optimizer will remove that store.