How can I handle collision detection between many objects efficiently? [duplicate]

Question

I have made a game that runs poorly. I suspect that the way that I programmed the collision detection in the game loop could be the problem.

My game has two player-controlled tanks which fire missiles; there are also power-ups, "gifts", that tanks can collect from the field. At every iteration of my game loop, I detect collisions like this:

1. Loop through all the missiles on the screen, and update their location (move them).
2. Loop through all of tank 1's missiles, and for every one check if collides with tank 2.
3. Loop through all of tank 2's missiles, and for every one check if collide with tank 1.
4. Loop through all the missiles on the screen, and check if collide with screen boundaries.
5. Check if the two tanks collide with each other.
6. Loop through all of the four "gifts" on the screen, and check if they touch a tank.

This method is presumably inefficient. How can I implement collision detection for all of these objects in a better fashion?