comments linking to Clang's CGObjCMac.cpp

Author: jbatez

compiler/rustc_codegen_llvm/src/consts.rs

@@ -550,6 +550,9 @@ impl<'ll> CodegenCx<'ll, '_> {
         self.compiler_used_statics.borrow_mut().push(global);
     }
 
+    // We do our best here to match what Clang does when compiling Objective-C natively.
+    // See Clang's `CGObjCCommonMac::CreateCStringLiteral`:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L4134
     fn define_objc_classname(&self, classname: &str) -> &'ll Value {
         assert_eq!(self.objc_abi_version(), 1);
 
@@ -570,13 +573,24 @@ impl<'ll> CodegenCx<'ll, '_> {
         g
     }
 
+    // We do our best here to match what Clang does when compiling Objective-C natively.
+    // See Clang's `ObjCNonFragileABITypesHelper`:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L6052
     fn get_objc_class_t(&self) -> &'ll Type {
         if let Some(class_t) = self.objc_class_t.get() {
             return class_t;
         }
 
         assert_eq!(self.objc_abi_version(), 2);
 
+        // struct _class_t {
+        //     struct _class_t* isa;
+        //     struct _class_t* const superclass;
+        //     void* cache;
+        //     IMP* vtable;
+        //     struct class_ro_t* ro;
+        // }
+
         let class_t = self.type_named_struct("struct._class_t");
         let els = [self.type_ptr(); 5];
         let packed = false;
@@ -598,6 +612,8 @@ impl<'ll> CodegenCx<'ll, '_> {
 
         let g = match self.objc_abi_version() {
             1 => {
+                // See Clang's `CGObjCMac::EmitClassRefFromId`:
+                // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L5205
                 let llval = self.define_objc_classname(classname.as_str());
                 let llty = self.type_ptr();
                 let sym = self.generate_local_symbol_name("OBJC_CLASS_REFERENCES_");
@@ -612,7 +628,8 @@ impl<'ll> CodegenCx<'ll, '_> {
                 g
             }
             2 => {
-                assert!(self.tcx.sess.target.is_like_darwin);
+                // See Clang's `CGObjCNonFragileABIMac::EmitClassRefFromId`:
+                // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L7423
                 let llval = {
                     let extern_sym = format!("OBJC_CLASS_$_{}", classname.as_str());
                     let extern_llty = self.get_objc_class_t();
@@ -649,6 +666,8 @@ impl<'ll> CodegenCx<'ll, '_> {
 
         let abi_version = self.objc_abi_version();
 
+        // See Clang's `CGObjCCommonMac::CreateCStringLiteral`:
+        // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L4134
         let methname_llval = self.null_terminate_const_bytes(methname.as_str().as_bytes());
         let methname_llty = self.val_ty(methname_llval);
         let methname_sym = self.generate_local_symbol_name("OBJC_METH_VAR_NAME_");
@@ -670,6 +689,10 @@ impl<'ll> CodegenCx<'ll, '_> {
         llvm::LLVMSetUnnamedAddress(methname_g, llvm::UnnamedAddr::Global);
         self.add_compiler_used_global(methname_g);
 
+        // See Clang's `CGObjCMac::EmitSelectorAddr`:
+        // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L5243
+        // And Clang's `CGObjCNonFragileABIMac::EmitSelectorAddr`:
+        // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L7586
         let selref_llval = methname_g;
         let selref_llty = self.type_ptr();
         let selref_sym = self.generate_local_symbol_name("OBJC_SELECTOR_REFERENCES_");
@@ -701,13 +724,18 @@ impl<'ll> CodegenCx<'ll, '_> {
         selref_g
     }
 
+    // We do our best here to match what Clang does when compiling Objective-C natively.
+    // See Clang's `ObjCTypesHelper`:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L5936
+    // And Clang's `CGObjCMac::EmitModuleInfo`:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L5151
     pub(crate) fn define_objc_module_info(&mut self) {
         assert_eq!(self.objc_abi_version(), 1);
 
         // struct _objc_module {
         //     long version;                // Hardcoded to 7 in Clang.
         //     long size;                   // sizeof(struct _objc_module)
-        //     char *name;                  // Hardcoded to classname "" in Clang.
+        //     char* name;                  // Hardcoded to classname "" in Clang.
         //     struct _objc_symtab* symtab; // Null without class or category definitions.
         //  }
 

compiler/rustc_codegen_llvm/src/context.rs

@@ -690,17 +690,22 @@ impl<'ll, 'tcx> CodegenCx<'ll, 'tcx> {
 
     pub(crate) fn objc_abi_version(&self) -> u32 {
         if self.tcx.sess.target.arch == "x86" && self.tcx.sess.target.os == "macos" {
-            // 32-bit x86 macOS uses ABI version 1.
+            // 32-bit x86 macOS uses ABI version 1 (a.k.a. the "fragile ABI").
             1
         } else {
-            // All other Darwin-like targets we support use ABI version 2.
+            // All other Darwin-like targets we support use ABI version 2
+            // (a.k.a the "non-fragile ABI").
             assert!(self.tcx.sess.target.is_like_darwin);
             2
         }
     }
 
+    // We do our best here to match what Clang does when compiling Objective-C natively.
+    // See Clang's `CGObjCCommonMac::EmitImageInfo`:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-20.1.8/clang/lib/CodeGen/CGObjCMac.cpp#L5085
     pub(crate) fn add_objc_module_flags(&self) {
         let abi_version = self.objc_abi_version();
+
         llvm::add_module_flag_u32(
             self.llmod,
             llvm::ModuleFlagMergeBehavior::Error,