The Transitioning to ARC Release Notes makes this statement:
One issue to be aware of is that the optimizer is not run in common
debug configurations, so expect to see a lot more retain/release
traffic at -O0 than at -Os.
How can we enable the optimizer in a default debug configuration?
You can set the optimization level in Xcode’s Build Settings independently of for the Debug and Release configurations – just go to build settings, scroll down till you find the optimization setting, and pick the one you want from the menu.
Note: You should probably only do this for curiosity (which is to be encouraged :-)), as optimization can (re)move code etc. debugging may become a little harder, e.g. a variable may “disappear” so you can’t so easily track its value as its been assigned to a register.