I've been going backwards in Git history to find the cause of a humongous file size change, but the only real reason I can find is the switch from Xcode 6 to Xcode 7 GM.

I've found that these are the top 10 file size contributors in an .ipa created from the Archive operation on a Release build configuration:

$ unzip -lv Roger\ Release.ipa | sort -k +3nr | head 41802768 Defl:N 16887199 60% 09-14-15 23:47 dc24cdc1 Payload/Roger.app/Frameworks/libswiftCore.dylib 41802400 Defl:N 16886076 60% 09-06-15 18:33 f939ea6a SwiftSupport/iphoneos/libswiftCore.dylib 11184032 Defl:N 5915625 47% 09-14-15 23:48 6ceac4a2 Payload/Roger.app/Roger 6399584 Defl:N 2670275 58% 09-14-15 23:47 0ac52d3f Payload/Roger.app/Frameworks/libPhoneNumber_iOS.framework/libPhoneNumber_iOS 5410384 Defl:N 2334189 57% 09-14-15 23:47 7a8cb03f Payload/Roger.app/Frameworks/Alamofire.framework/Alamofire 4521904 Defl:N 2292789 49% 09-14-15 23:47 95da0882 Payload/Roger.app/Frameworks/FBSDKCoreKit.framework/FBSDKCoreKit 4731552 Defl:N 1926357 59% 09-14-15 23:48 e05337de Payload/Roger.app/Frameworks/libswiftFoundation.dylib 4731168 Defl:N 1925355 59% 09-06-15 18:33 19a5c3c4 SwiftSupport/iphoneos/libswiftFoundation.dylib 2659232 Defl:N 1232897 54% 09-14-15 23:47 1a53a401 Payload/Roger.app/Frameworks/AFNetworking.framework/AFNetworking 1196624 Defl:N 545343 54% 09-14-15 23:47 19a063cb Payload/Roger.app/Frameworks/Bolts.framework/Bolts

By far the largest files are the two (slightly different) libswiftCore.dylib files, which total over 32 MB. In the bundle built by Xcode 6 these two files totaled only 3 MB.

So question #1 is: Why are the Swift core files there twice? (Embedded Content Contains Swift Code is set to No).

And question #2 is: What happened? Why did the Swift core size increase by 15 MB? Is this permanent?

Some additional notes: