Building iOS apps with Xcode involves a myriad of build settings, and “Enable Bitcode” is one that often raises questions. This setting, seemingly innocuous, can significantly impact your app’s size, performance, and future compatibility. Understanding its implications is crucial for developers seeking to optimize their app development process. This article dives deep into the impact of enabling or disabling bitcode in your Xcode project, offering insights and best practices for making informed decisions.

What is Bitcode?

Bitcode is an intermediate representation of your compiled program. Instead of submitting fully compiled machine code to the App Store, enabling bitcode allows Apple to re-optimize your app for future architectures and potentially improve performance without requiring a new build from you. Think of it as future-proofing your application.

Apple can also use bitcode to perform app thinning, tailoring the download to the specific device architecture the user is downloading to. This results in smaller download sizes and faster installation times.

Crucially, bitcode is not just for iOS; watchOS and tvOS apps are also affected by this setting. Maintaining consistency across your Apple platforms is essential for a smooth user experience.

Advantages of Enabling Bitcode

Enabling bitcode offers several key advantages. First, it allows Apple to perform app slicing, delivering optimized binaries tailored to each device. This results in smaller downloads and potentially faster installations for your users.

Secondly, bitcode allows for future optimizations without requiring resubmission. As new processor architectures emerge, Apple can recompile your app from the bitcode, ensuring optimal performance on the latest hardware.

Finally, some security features, like potential malware scanning, are enabled by bitcode, contributing to a safer app ecosystem.

• Smaller app downloads
• Future performance enhancements

Disadvantages of Enabling Bitcode

While the benefits are compelling, enabling bitcode comes with its own set of challenges. Debugging can become more complex, as you’ll need to symbolicate crash reports using bitcode symbols provided by Apple.

Furthermore, all libraries and frameworks used in your project must also include bitcode. If a third-party library doesn’t support bitcode, you won’t be able to enable it for your app.

Another consideration is the slight increase in compile times when bitcode is enabled. While usually negligible, this can be a factor in large projects.

• Debugging complexity
• Third-party library compatibility

Making the Right Choice: Enable or Disable?

The decision of whether to enable or disable bitcode depends on your specific project. For new projects, enabling bitcode is generally recommended. It future-proofs your app and offers significant advantages in terms of app size and potential performance improvements.

For existing projects, especially those with complex dependency chains, carefully consider the implications for third-party library compatibility. If you’re unsure, test thoroughly before making the switch.

It’s worth noting that Apple has deprecated bitcode for watchOS and tvOS apps, so focus on iOS when making this decision. Learn more about bitcode compatibility.

Featured Snippet: Bitcode is an intermediate representation of your compiled code. Enabling it allows Apple to optimize your app for future hardware and perform app thinning, resulting in smaller downloads. However, it can also complicate debugging and requires bitcode support from all linked libraries.

Best Practices and Troubleshooting

When working with bitcode, follow these best practices: Regularly check for updates to third-party libraries to ensure ongoing bitcode compatibility. Test your app thoroughly after enabling or disabling bitcode to identify any potential issues.

If you encounter problems, consult Apple’s documentation and community forums for troubleshooting tips. Understanding the nuances of bitcode can save you valuable time and effort during the app development process.

1. Check library compatibility.
2. Test thoroughly.
3. Consult documentation.

FAQ

Q: Is bitcode mandatory for App Store submission?

A: While not strictly mandatory for all apps, it is generally recommended, especially for new projects targeting iOS.

[Infographic Placeholder] Choosing the correct bitcode setting is an important step in optimizing your iOS app. By carefully weighing the pros and cons and following best practices, you can ensure your app is well-positioned for future success. Explore further resources like Apple’s official documentation and developer forums for the latest information and best practices. Investing time in understanding this setting will pay dividends in the long run, resulting in a more efficient and performant app for your users. Take the time to analyze your project’s specific needs and make an informed decision about bitcode. This will contribute to a smoother development process and a higher quality app.

Question & Answer :
Yesterday I recognized a ton of warnings regarding the parse.com library:

URGENT: all bitcode will be dropped because ‘[path]/Parse.framework/Parse(PFAnalytics.o)’ was built without bitcode. You must rebuild it with bitcode enabled (Xcode setting ENABLE_BITCODE), obtain an updated library from the vendor, or disable bitcode for this target. Note: This will be an error in the future.

I am aware of the fact that I can remove those warning with this answer but am now wondering if it will have any negative impact in regards to AppStore submission and / or actual performance of my app.

Xcode informs you regarding bitcode

Activating this setting indicates that the target or project should generate bitcode during compilation for platforms and architectures which support it. For Archive builds, bitcode will be generated in the linked binary for submission to the app store. For other builds, the compiler and linker will check whether the code complies with the requirements for bitcode generation, but will not generate actual bitcode. [ENABLE_BITCODE]

But I am not getting any really useful information out of this text.

• Can I use the linked answer to circumvent the issue without any negative impact and without compromising a future AppStore submission?
• What does the ENABLE_BITCODE actually do, will it be a non-optional requirement in the future?
• Are there any performance impacts if I enable / disable it?

• What does the ENABLE_BITCODE actually do, will it be a non-optional requirement in the future?

I’m not sure at what level you are looking for an answer at, so let’s take a little trip. Some of this you may already know.

When you build your project, Xcode invokes clang for Objective-C targets and swift/swiftc for Swift targets. Both of these compilers compile the app to an intermediate representation (IR), one of these IRs is bitcode. From this IR, a program called LLVM takes over and creates the binaries needed for x86 32 and 64 bit modes (for the simulator) and arm6/arm7/arm7s/arm64 (for the device). Normally, all of these different binaries are lumped together in a single file called a fat binary.

The ENABLE_BITCODE option cuts out this final step. It creates a version of the app with an IR bitcode binary. This has a number of nice features, but one giant drawback: it can’t run anywhere. In order to get an app with a bitcode binary to run, the bitcode needs to be recompiled (maybe assembled or transcoded… I’m not sure of the correct verb) into an x86 or ARM binary.

When a bitcode app is submitted to the App Store, Apple will do this final step and create the finished binaries.

Right now, bitcode apps are optional, but history has shown Apple turns optional things into requirements (like 64 bit support). This usually takes a few years, so third party developers (like Parse) have time to update.

• can I use the above method without any negative impact and without compromising a future appstore submission?

Yes, you can turn off ENABLE_BITCODE and everything will work just like before. Until Apple makes bitcode apps a requirement for the App Store, you will be fine.

• Are there any performance impacts if I enable / disable it?

There will never be negative performance impacts for enabling it, but internal distribution of an app for testing may get more complicated.

As for positive impacts… well that’s complicated.

For distribution in the App Store, Apple will create separate versions of your app for each machine architecture (arm6/arm7/arm7s/arm64) instead of one app with a fat binary. This means the app installed on iOS devices will be smaller.

In addition, when bitcode is recompiled (maybe assembled or transcoded… again, I’m not sure of the correct verb), it is optimized. LLVM is always working on creating new a better optimizations. In theory, the App Store could recreate the separate version of the app in the App Store with each new release of LLVM, so your app could be re-optimized with the latest LLVM technology.