Function rustc_codegen_llvm::back::write::embed_bitcode

unsafe fn embed_bitcode(
    cgcx: &CodegenContext<LlvmCodegenBackend>,
    llcx: &Context,
    llmod: &Module,
    cmdline: &str,
    bitcode: &[u8],
)

Embed the bitcode of an LLVM module in the LLVM module itself.

This is done primarily for iOS where it appears to be standard to compile C code at least with -fembed-bitcode which creates two sections in the executable:

• __LLVM,__bitcode
• __LLVM,__cmdline

It appears both of these sections are necessary to get the linker to recognize what’s going on. A suitable cmdline value is taken from the target spec.

Furthermore debug/O1 builds don’t actually embed bitcode but rather just embed an empty section.

Basically all of this is us attempting to follow in the footsteps of clang on iOS. See #35968 for lots more info.