Improve bitcode generation for Apple platforms

src/librustc_codegen_llvm/back/write.rs

@@ -651,10 +651,8 @@ pub(crate) unsafe fn codegen(
                     "LLVM_module_codegen_embed_bitcode",
                     &module.name[..],
                 );
-                embed_bitcode(cgcx, llcx, llmod, Some(data));
+                embed_bitcode(cgcx, llcx, llmod, &config.bc_cmdline, data);
             }
-        } else if config.emit_obj == EmitObj::ObjectCode(BitcodeSection::Marker) {
-            embed_bitcode(cgcx, llcx, llmod, None);
         }
 
         if config.emit_ir {
@@ -777,8 +775,8 @@ pub(crate) unsafe fn codegen(
 /// * __LLVM,__cmdline
 ///
 /// It appears *both* of these sections are necessary to get the linker to
-/// recognize what's going on. For us though we just always throw in an empty
-/// cmdline section.
+/// 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.
@@ -789,9 +787,10 @@ unsafe fn embed_bitcode(
     cgcx: &CodegenContext<LlvmCodegenBackend>,
     llcx: &llvm::Context,
     llmod: &llvm::Module,
-    bitcode: Option<&[u8]>,
+    cmdline: &str,
+    bitcode: &[u8],
 ) {
-    let llconst = common::bytes_in_context(llcx, bitcode.unwrap_or(&[]));
+    let llconst = common::bytes_in_context(llcx, bitcode);
     let llglobal = llvm::LLVMAddGlobal(
         llmod,
         common::val_ty(llconst),
@@ -800,14 +799,15 @@ unsafe fn embed_bitcode(
     llvm::LLVMSetInitializer(llglobal, llconst);
 
     let is_apple = cgcx.opts.target_triple.triple().contains("-ios")
-        || cgcx.opts.target_triple.triple().contains("-darwin");
+        || cgcx.opts.target_triple.triple().contains("-darwin")
+        || cgcx.opts.target_triple.triple().contains("-tvos");
 
     let section = if is_apple { "__LLVM,__bitcode\0" } else { ".llvmbc\0" };
     llvm::LLVMSetSection(llglobal, section.as_ptr().cast());
     llvm::LLVMRustSetLinkage(llglobal, llvm::Linkage::PrivateLinkage);
     llvm::LLVMSetGlobalConstant(llglobal, llvm::True);
 
-    let llconst = common::bytes_in_context(llcx, &[]);
+    let llconst = common::bytes_in_context(llcx, cmdline.as_bytes());
     let llglobal = llvm::LLVMAddGlobal(
         llmod,
         common::val_ty(llconst),

src/librustc_codegen_ssa/back/write.rs

@@ -68,10 +68,6 @@ pub enum BitcodeSection {
     // No bitcode section.
     None,
 
-    // An empty bitcode section (to placate tools such as the iOS linker that
-    // require this section even if they don't use it).
-    Marker,
-
     // A full, uncompressed bitcode section.
     Full,
 }
@@ -101,6 +97,7 @@ pub struct ModuleConfig {
     pub emit_ir: bool,
     pub emit_asm: bool,
     pub emit_obj: EmitObj,
+    pub bc_cmdline: String,
 
     // Miscellaneous flags.  These are mostly copied from command-line
     // options.
@@ -147,14 +144,8 @@ impl ModuleConfig {
             || sess.opts.cg.linker_plugin_lto.enabled()
         {
             EmitObj::Bitcode
-        } else if need_crate_bitcode_for_rlib(sess) {
-            let force_full = need_crate_bitcode_for_rlib(sess);
-            match sess.opts.optimize {
-                config::OptLevel::No | config::OptLevel::Less if !force_full => {
-                    EmitObj::ObjectCode(BitcodeSection::Marker)
-                }
-                _ => EmitObj::ObjectCode(BitcodeSection::Full),
-            }
+        } else if need_bitcode_in_object(sess) {
+            EmitObj::ObjectCode(BitcodeSection::Full)
         } else {
             EmitObj::ObjectCode(BitcodeSection::None)
         };
@@ -211,6 +202,7 @@ impl ModuleConfig {
                 false
             ),
             emit_obj,
+            bc_cmdline: sess.target.target.options.bitcode_llvm_cmdline.clone(),
 
             verify_llvm_ir: sess.verify_llvm_ir(),
             no_prepopulate_passes: sess.opts.cg.no_prepopulate_passes,
@@ -372,10 +364,12 @@ pub struct CompiledModules {
     pub allocator_module: Option<CompiledModule>,
 }
 
-fn need_crate_bitcode_for_rlib(sess: &Session) -> bool {
-    sess.opts.cg.embed_bitcode
+fn need_bitcode_in_object(sess: &Session) -> bool {
+    let requested_for_rlib = sess.opts.cg.embed_bitcode
         && sess.crate_types.borrow().contains(&CrateType::Rlib)
-        && sess.opts.output_types.contains_key(&OutputType::Exe)
+        && sess.opts.output_types.contains_key(&OutputType::Exe);
+    let forced_by_target = sess.target.target.options.forces_embed_bitcode;
+    requested_for_rlib || forced_by_target
 }
 
 fn need_pre_lto_bitcode_for_incr_comp(sess: &Session) -> bool {

src/librustc_target/spec/aarch64_apple_ios.rs

@@ -19,6 +19,18 @@ pub fn target() -> TargetResult {
             eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            forces_embed_bitcode: true,
+            // Taken from a clang build on Xcode 11.4.1.
+            // These arguments are not actually invoked - they just have
+            // to look right to pass App Store validation.
+            bitcode_llvm_cmdline: "-triple\0\
+                arm64-apple-ios11.0.0\0\
+                -emit-obj\0\
+                -disable-llvm-passes\0\
+                -target-abi\0\
+                darwinpcs\0\
+                -Os\0"
+                .to_string(),
             ..base
         },
     })

src/librustc_target/spec/aarch64_apple_tvos.rs

@@ -19,6 +19,7 @@ pub fn target() -> TargetResult {
             eliminate_frame_pointer: false,
             max_atomic_width: Some(128),
             abi_blacklist: super::arm_base::abi_blacklist(),
+            forces_embed_bitcode: true,
             ..base
         },
     })

src/librustc_target/spec/mod.rs

@@ -783,6 +783,10 @@ 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: String,
 
     /// Don't use this field; instead use the `.min_atomic_width()` method.
     pub min_atomic_width: Option<u64>,
@@ -939,6 +943,8 @@ impl Default for TargetOptions {
             allow_asm: true,
             has_elf_tls: false,
             obj_is_bitcode: false,
+            forces_embed_bitcode: false,
+            bitcode_llvm_cmdline: String::new(),
             min_atomic_width: None,
             max_atomic_width: None,
             atomic_cas: true,
@@ -1278,6 +1284,8 @@ impl Target {
         key!(main_needs_argc_argv, bool);
         key!(has_elf_tls, 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>);
         key!(atomic_cas, bool);
@@ -1505,6 +1513,8 @@ impl ToJson for Target {
         target_option_val!(main_needs_argc_argv);
         target_option_val!(has_elf_tls);
         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);
         target_option_val!(atomic_cas);