Rollup merge of rust-lang#133297 - DianQK:embed-bitcode-ios, r=nikic

Remove legacy bitcode for iOS

Follow rust-lang#117364.

Author: jieyouxu

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,

compiler/rustc_codegen_ssa/src/back/write.rs

@@ -432,11 +432,9 @@ struct CompiledModules {
 
 fn need_bitcode_in_object(tcx: TyCtxt<'_>) -> bool {
     let sess = tcx.sess;
-    let requested_for_rlib = sess.opts.cg.embed_bitcode
+    sess.opts.cg.embed_bitcode
         && tcx.crate_types().contains(&CrateType::Rlib)
-        && sess.opts.output_types.contains_key(&OutputType::Exe);
-    let forced_by_target = sess.target.forces_embed_bitcode;
-    requested_for_rlib || forced_by_target
+        && sess.opts.output_types.contains_key(&OutputType::Exe)
 }
 
 fn need_pre_lto_bitcode_for_incr_comp(sess: &Session) -> bool {

compiler/rustc_target/src/spec/mod.rs

@@ -2327,8 +2327,6 @@ pub struct TargetOptions {
     /// If we give emcc .o files that are actually .bc files it
     /// will 'just work'.
     pub obj_is_bitcode: bool,
-    /// Whether the target requires that emitted object code includes bitcode.
-    pub forces_embed_bitcode: bool,
     /// Content of the LLVM cmdline section associated with embedded bitcode.
     pub bitcode_llvm_cmdline: StaticCow<str>,
 
@@ -2671,7 +2669,6 @@ impl Default for TargetOptions {
             allow_asm: true,
             has_thread_local: false,
             obj_is_bitcode: false,
-            forces_embed_bitcode: false,
             bitcode_llvm_cmdline: "".into(),
             min_atomic_width: None,
             max_atomic_width: None,
@@ -3412,7 +3409,6 @@ impl Target {
         key!(main_needs_argc_argv, bool);
         key!(has_thread_local, bool);
         key!(obj_is_bitcode, bool);
-        key!(forces_embed_bitcode, bool);
         key!(bitcode_llvm_cmdline);
         key!(max_atomic_width, Option<u64>);
         key!(min_atomic_width, Option<u64>);
@@ -3687,7 +3683,6 @@ impl ToJson for Target {
         target_option_val!(main_needs_argc_argv);
         target_option_val!(has_thread_local);
         target_option_val!(obj_is_bitcode);
-        target_option_val!(forces_embed_bitcode);
         target_option_val!(bitcode_llvm_cmdline);
         target_option_val!(min_atomic_width);
         target_option_val!(max_atomic_width);

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.