He actually references that pretty specifically saying that indeed it can't be used to move 32bit -> 64bit [0]
> Bitcode is not [12:30] a magic solution, though. You can't take a 32-bit app, for example, and run it on a 64-bit device. That kind of portability isn’t something that Bitcode can give you, notably because that is something that's visible in C. As you're writing C code, you can write #ifdef pointer size equals 32, and that’s something that Bitcode can't abstract over. It's useful for very specific, low-level kinds of enhancements, but it isn't a panacea that makes everything [13:00] magically portable
> Bitcode is not [12:30] a magic solution, though. You can't take a 32-bit app, for example, and run it on a 64-bit device. That kind of portability isn’t something that Bitcode can give you, notably because that is something that's visible in C. As you're writing C code, you can write #ifdef pointer size equals 32, and that’s something that Bitcode can't abstract over. It's useful for very specific, low-level kinds of enhancements, but it isn't a panacea that makes everything [13:00] magically portable
[0]: http://atp.fm/205-chris-lattner-interview-transcript/#portab...