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So, if I enable bitcode it just doubles the size of my binaries currently?

by tobias3 11y ago

simonh 11y ago
It (roughly) doubles the size of the app bundle you upload to Apple. They then compile that down to create normal sized binaries, which are what are actually downloaded to the device. Bear in mind the source->bitcode->binary process (I'm simplifying here) was previously all performed by LLVM on your computer anyway. It's just that now the final bitcode->binary step is done by Apple, to allow device-specific optimizations of the binary for the devices that are downloading it without you having to do all those device specific optimized builds yourself.
- ksk 11y ago
  Do you know what the performance increase is of these optimized builds?
  - simonh 11y ago
    No idea. We'd need to do on-device profiling of 'plain' builds directly from XCode alongside the builds downloaded from the app store, but of course optimizations may only be possible on particular devices, and some apps would benefit more than others, so you'd have to do a huge amount of testing to track down the differences. Also Apple may be doing this due to planned advantages in the future, so testing done now might be pointless anyway.
    - ksk 11y ago
      Its just strange that Apple has not presented any actual numbers on this. Usually you'd expect them to talk about how XYZ is 90% faster, and 100x awesome and what not. It makes me think that they have something else in mind.
      - Glide 11y ago
        It's most likely so you don't have to update the binary when the next version of LLVM comes out. There are a lot of apps that don't get updated with major iOS versions and they would likely see improvement. Conspiracy theories aside, wouldn't it take them more effort to ship a different version of LLVM for Xcode and another one that runs against bitcode?
        ksk 11y ago
        It is not a conspiracy theory per se, I'm just skeptical of their optimization claims. In theory, sure. In practice, I'd have to see hard data.
  - diakritikal 11y ago
    %s/optimized/backdoor'd/g I mean, who can tell right?

So, if I enable bitcode it just doubles the size of my binaries currently?

by tobias3 11y ago

So, if I enable bitcode it just doubles the size of my binaries currently?

It (roughly) doubles the size of the app bundle you upload to Apple. They then compile that down to create normal sized binaries, which are what are actually downloaded to the device. Bear in mind the source->bitcode->binary process (I'm simplifying here) was previously all performed by LLVM on your computer anyway. It's just that now the final bitcode->binary step is done by Apple, to allow device-specific optimizations of the binary for the devices that are downloading it without you having to do all those device specific optimized builds yourself.

ksk 11y ago
Do you know what the performance increase is of these optimized builds?
- simonh 11y ago
  No idea. We'd need to do on-device profiling of 'plain' builds directly from XCode alongside the builds downloaded from the app store, but of course optimizations may only be possible on particular devices, and some apps would benefit more than others, so you'd have to do a huge amount of testing to track down the differences. Also Apple may be doing this due to planned advantages in the future, so testing done now might be pointless anyway.
  - ksk 11y ago
    Its just strange that Apple has not presented any actual numbers on this. Usually you'd expect them to talk about how XYZ is 90% faster, and 100x awesome and what not. It makes me think that they have something else in mind.
    - Glide 11y ago
      It's most likely so you don't have to update the binary when the next version of LLVM comes out. There are a lot of apps that don't get updated with major iOS versions and they would likely see improvement. Conspiracy theories aside, wouldn't it take them more effort to ship a different version of LLVM for Xcode and another one that runs against bitcode?
      - ksk 11y ago
        It is not a conspiracy theory per se, I'm just skeptical of their optimization claims. In theory, sure. In practice, I'd have to see hard data.
- diakritikal 11y ago
  %s/optimized/backdoor'd/g I mean, who can tell right?