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embed-bitcode is no longer used in iOS

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DianQK 2024-11-20 22:45:32 +08:00
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19
compiler/rustc_codegen_llvm/src/back/write.rs
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@ -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. /// Embed the bitcode of an LLVM module for LTO 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.
unsafe fn embed_bitcode( unsafe fn embed_bitcode(
cgcx: &CodegenContext<LlvmCodegenBackend>, cgcx: &CodegenContext<LlvmCodegenBackend>,
llcx: &llvm::Context, llcx: &llvm::Context,

13
src/doc/rustc/src/codegen-options/index.md
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@ -119,17 +119,14 @@ files. It takes one of the following values:
* `n`, `no`, `off` or `false`: omit bitcode from rlibs. * `n`, `no`, `off` or `false`: omit bitcode from rlibs.
LLVM bitcode is required when rustc is performing link-time optimization (LTO). 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 Embedded bitcode will appear in rustc-generated object files inside of a section
bitcode. Embedded bitcode will appear in rustc-generated object files inside of whose name is defined by the target platform. Most of the time this is `.llvmbc`.
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 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 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 (e.g. if you're not performing LTO). For these reasons, Cargo uses `-C embed-bitcode=no`
reasons, Cargo uses `-C embed-bitcode=no` whenever possible. Likewise, if you whenever possible. Likewise, if you are building directly with `rustc` we recommend
are building directly with `rustc` we recommend using `-C embed-bitcode=no` using `-C embed-bitcode=no` whenever you are not using LTO.
whenever you are not using LTO.
If combined with `-C lto`, `-C embed-bitcode=no` will cause `rustc` to abort If combined with `-C lto`, `-C embed-bitcode=no` will cause `rustc` to abort
at start-up, because the combination is invalid. at start-up, because the combination is invalid.