The way this works behind the scenes isn't via NGEN (Native Image Generator) reimagined. (Ugh. Did I really just use the "R" word?)
NGEN is a tool for improving performance of managed applications byusing native images stored in cache rather than a just-in-time compiler. Instead, according to the Going Deep presentation, Machine Dependent Intermediate Language (MDIL) is at the core of Microsoft's compiler-in-the-cloud solution. Microsoft officials are claiming that the linking step on devices that convert MDIL assembly to a native image takes one-fifth of the time as traditional NGEN on device.
"Thus, we get some of the benefits of both pre-compilation (since we are executing off the native image where all instructions are assembly instructions) and JIT-compilation (no heavy compilation on the device during framework updates)," the Channel 9 session abstract says.
"When you build your app in Visual Studio, the code is not compiled into a native image, but into a machine-independent Common Intermediate Language (CIL) binary file. (CIL was formerly known as Microsoft Intermediate Language, or MSIL.) This CIL file is what you submit to the Store when you’re ready to sell your app. At that time, the binary file is converted from CIL to optimized Machine Dependent Intermediate Language, or MDIL. Finally, when the user downloads your app to a device, the MDIL file is linked to produce a native image. These steps are repeated in your development environment whenever you deploy your app to a Windows Phone 8 device.
"The functionality of your app is not affected by the conversion to native code. However, the native image typically starts and runs faster."