I have a fairly simple project with only two XIBs, 5 custom classes and 5 frameworks (CFNetwork, QuartzCore, UIKit, Foundation, CoreGraphics). I was using XCode 3.x before and recently updated to XCode 4. After I did, build times are sometimes up to a minute, typically about 30 seconds. I have an 2.4 GHz MBP with 4GB of memory.
Looking at the build log in log navigator, I see "check dependencies..." come up for a long time, everything else happens nearly instantly. However clicking on this log entry doesn't reveal any more details. Where could I find more detailed info about what is causing this?
Update:
After rebooting, build returned to normal speed. There was possibly something happening in the background that was causing the slowdown.
What you can do is turn off implicit dependencies. Edit the build scheme that is slow and find the build option called Find Implicit Dependencies. You will see the schemes at the top-left. Just select Edit Scheme and once that sheet comes down select Build on the left as you see in the attached screenshot. Then click OK and try your build again. (You may want to disable it for other schemes as well.)
For anyone else that stumbles upon this question because they have really slow build times. I managed to avoid the 2 minute long "Check Dependencies" stage by unchecking the following in this image http://i.stack.imgur.com/taXVc.png
- analyze, test & archive checkboxes
- parallize build
- find implicit dependencies
I think it was just compiling really slowly because it was trying to build every single product at once.
来源：https://stackoverflow.com/questions/5533799/build-slow-on-xcode4-because-of-check-dependencies