That depends on the speed of your computer. The first phase usually takes some time. Do you still have the build.log of that particular session? If yes; you can verify no binaries had been deleted yet and no source code had been built yet. In you don't have the build log of that session then there is no way to know for sure. In that case the only way to know if your tree is not corrupt is a full clean and reinstall.
RE: blddemo
That depends on the speed of your computer. The first phase usually takes some time. Do you still have the build.log of that particular session? If yes; you can verify no binaries had been deleted yet and no source code had been built yet. In you don't have the build log of that session then there is no way to know for sure. In that case the only way to know if your tree is not corrupt is a full clean and reinstall.