embed-bitcode is no longer used in iOS

Author: dianqk

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -955,24 +955,7 @@ pub(crate) fn bitcode_section_name(cgcx: &CodegenContext<LlvmCodegenBackend>) ->
     }
 }
 
-/// 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.
+/// Embed the bitcode of an LLVM module for LTO in the LLVM module itself.
 unsafe fn embed_bitcode(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     llcx: &llvm::Context,

src/doc/rustc/src/codegen-options/index.md

@@ -119,17 +119,14 @@ files. It takes one of the following values:
 * `n`, `no`, `off` or `false`: omit bitcode from rlibs.
 
 LLVM bitcode is required when rustc is performing link-time optimization (LTO).
-It is also required on some targets like iOS ones where vendors look for LLVM
-bitcode. Embedded bitcode will appear in rustc-generated object files inside of
-a section whose name is defined by the target platform. Most of the time this is
-`.llvmbc`.
+Embedded bitcode will appear in rustc-generated object files inside of a section
+whose name is defined by the target platform. Most of the time this is `.llvmbc`.
 
 The use of `-C embed-bitcode=no` can significantly improve compile times and
 reduce generated file sizes if your compilation does not actually need bitcode
-(e.g. if you're not compiling for iOS or you're not performing LTO). For these
-reasons, Cargo uses `-C embed-bitcode=no` whenever possible. Likewise, if you
-are building directly with `rustc` we recommend using `-C embed-bitcode=no`
-whenever you are not using LTO.
+(e.g. if you're not performing LTO). For these reasons, Cargo uses `-C embed-bitcode=no`
+whenever possible. Likewise, if you are building directly with `rustc` we recommend
+using `-C embed-bitcode=no` whenever you are not using LTO.
 
 If combined with `-C lto`, `-C embed-bitcode=no` will cause `rustc` to abort
 at start-up, because the combination is invalid.