Is x += 1 more efficient than x = x + 1?

Question

In x = x + 1, is x evaluated twice? If so, does that mean in x += 1, x is only evaluated once? How are the two expression

Answer 1

With gcc, you can get the assembler code with gcc -S foo.c. I tried it with x += 1 and x = x + 1 and it was the same.