error：Failed to find or create execution context for description ‘<IBCocoaTouchPlatformToolDescription: 0x7fe0ddceada0> System content for IBCocoaTouchFramework-ElevenAndLater <IBScaleFactorDeviceTypeDescription: 0x7fe0dd8606b0> scaleFactor=2x’. These intermediate objects were non-nil
这是升级完xcode后，全局的xib报错
使用终端进行解决：
kill掉所有的模拟器的进程
$ sudo killall -9 com.apple.CoreSimulator.CoreSimulatorService
重新打开xcode，运行即可正常；如果仍然异常，需要重置所有的模拟器操作
$ xcrun simctl erase all
