llvmlink-time-optimization

Does monolithic link-time optimization work with static libraries?

This article discusses how object files can contain LLVM IR that is used for link-time optimization. But what if the linker is compiling a project that includes a static library, do static libraries have the information as well? If so, under which circumstances?

Solution

  • Yes. Static libraries can contain llvm-IR-bitcode also.

    A. Step for build static libs with llvm-IR-bitcode

    1. In Xcode Static Lib Project:
      Build Settings->Enable Bitcode , Switch to Yes
    2. Product->Archive

    B. Check if a static lib contains llvm-IR-bitcode or not.

    1. otool -l libDemo.a
    2. In the output, search for __bitcode and check whether the size is bigger than 000001 or not.
      if size > 000001 : then the static lib contain llvm-IR-bitcode
      else: the static lib do not contain llvm-IR-bitcode.

    Wish this answers your question.