Xcode stuck at `Compile Swift source files` stage

Using Swift
1

I'm trying to adopt the Xcode new build system in our project, which contain a development pod. After performing a clean build, I modify one of the swift file in the pod (just adding a empty line), and perform a Incremental build. In the Xcode report navigator, I check the latest building progress, and found out something is weird:

  1. Xcode stuck at Compile Swift source files for a few seconds without compiling any swift file
  2. Xcode compile the changed swift file, merge swiftmodule, and stuck for addition nearly 60 seconds
    20%20AM
    20%20AM850×59 7.92 KB
  3. Xcode continue the building process
    20%20AM
    20%20AM847×58 7.43 KB

Any idea why Xcode stuck for such a long time?