IRGen: Add method lists of generic class patterns to their own section

Put the method lists in generic class patterns in a section __objc_methodlist such that they are discoverable by the linker.
The linker can then make them relative like it can for regular objective c class metadata.

rdar://66634459

Author: aschwaighofer

lib/IRGen/GenClass.cpp

@@ -1436,9 +1436,10 @@ namespace {
                                  weakLinkage);
     }
 
-    void emitRODataFields(ConstantStructBuilder &b,
-                          ForMetaClass_t forMeta,
-                          HasUpdateCallback_t hasUpdater) {
+    void emitRODataFields(
+        ConstantStructBuilder &b, ForMetaClass_t forMeta,
+        HasUpdateCallback_t hasUpdater,
+        ForGenericPattern_t isForGeneric = IsNotForGenericPattern) {
       assert(FieldLayout && "can't emit rodata for a category");
 
       // struct _class_ro_t {
@@ -1497,7 +1498,7 @@ namespace {
       emitAndAddMethodList(b,
                            forMeta ? MethodListKind::ClassMethods
                                    : MethodListKind::InstanceMethods,
-                           llvm::GlobalVariable::InternalLinkage);
+                           llvm::GlobalVariable::InternalLinkage, isForGeneric);
 
       //   const protocol_list_t *baseProtocols;
       // Apparently, this list is the same in the class and the metaclass.
@@ -1530,7 +1531,7 @@ namespace {
 
       // };
     }
-    
+
     llvm::Constant *emitROData(ForMetaClass_t forMeta,
                                HasUpdateCallback_t hasUpdater) {
       ConstantInitBuilder builder(IGM);
@@ -1763,9 +1764,10 @@ namespace {
     };
 
     /// Emit the method list and add the pointer to the `builder`.
-    void emitAndAddMethodList(ConstantInitBuilder::StructBuilder &builder,
-                              MethodListKind kind,
-                              llvm::GlobalValue::LinkageTypes linkage) {
+    void emitAndAddMethodList(
+        ConstantInitBuilder::StructBuilder &builder, MethodListKind kind,
+        llvm::GlobalValue::LinkageTypes linkage,
+        ForGenericPattern_t isForGeneric = IsNotForGenericPattern) {
       ArrayRef<MethodDescriptor> methods;
       StringRef namePrefix;
       switch (kind) {
@@ -1791,7 +1793,7 @@ namespace {
         break;
       }
       llvm::Constant *methodListPtr =
-          buildMethodList(methods, namePrefix, linkage);
+          buildMethodList(methods, namePrefix, linkage, isForGeneric);
       builder.add(methodListPtr);
     }
 
@@ -1837,7 +1839,8 @@ namespace {
     /// This method does not return a value of a predictable type.
     llvm::Constant *buildMethodList(ArrayRef<MethodDescriptor> methods,
                                     StringRef name,
-                                    llvm::GlobalValue::LinkageTypes linkage) {
+                                    llvm::GlobalValue::LinkageTypes linkage,
+                                    ForGenericPattern_t isForGeneric) {
       return buildOptionalList(
           methods, 3 * IGM.getPointerSize(), name,
           /*isConst*/ false, linkage,
@@ -2146,10 +2149,11 @@ namespace {
     /// \param optionalEltSize - if non-zero, a size which needs
     ///   to be placed in the list header
     template <class C, class Fn>
-    llvm::Constant *buildOptionalList(const C &objects, Size optionalEltSize,
-                                      StringRef nameBase, bool isConst,
-                                      llvm::GlobalValue::LinkageTypes linkage,
-                                      Fn &&buildElement) {
+    llvm::Constant *buildOptionalList(
+        const C &objects, Size optionalEltSize, StringRef nameBase,
+        bool isConst, llvm::GlobalValue::LinkageTypes linkage,
+        Fn &&buildElement,
+        ForGenericPattern_t isForGeneric = IsNotForGenericPattern) {
       if (objects.empty())
         return null();
 
@@ -2187,7 +2191,8 @@ namespace {
 
       fields.fillPlaceholderWithInt(countPosition, countType, count);
 
-      return buildGlobalVariable(fields, nameBase, isConst, linkage);
+      return buildGlobalVariable(fields, nameBase, isConst, linkage,
+                                 isForGeneric);
     }
 
     /// Get the name of the class or protocol to mangle into the ObjC symbol
@@ -2216,9 +2221,10 @@ namespace {
     /// Build a private global variable as a structure containing the
     /// given fields.
     template <class B>
-    llvm::Constant *
-    buildGlobalVariable(B &fields, StringRef nameBase, bool isConst,
-                        llvm::GlobalValue::LinkageTypes linkage) {
+    llvm::Constant *buildGlobalVariable(
+        B &fields, StringRef nameBase, bool isConst,
+        llvm::GlobalValue::LinkageTypes linkage,
+        ForGenericPattern_t isForGeneric = IsNotForGenericPattern) {
       llvm::SmallString<64> nameBuffer;
       auto var =
         fields.finishAndCreateGlobal(Twine(nameBase) 
@@ -2235,8 +2241,12 @@ namespace {
 
       switch (IGM.TargetInfo.OutputObjectFormat) {
       case llvm::Triple::MachO:
-        var->setSection(isConst ? "__DATA, __objc_const"
-                                : "__DATA, __objc_data");
+        if (isForGeneric) {
+          var->setSection("__DATA, __objc_methlist,regular");
+        } else {
+          var->setSection(isConst ? "__DATA, __objc_const"
+                                  : "__DATA, __objc_data");
+        }
         break;
       case llvm::Triple::XCOFF:
       case llvm::Triple::COFF:
@@ -2447,17 +2457,17 @@ irgen::emitClassPrivateDataFields(IRGenModule &IGM,
 
     // Note: an update callback is only ever used with the in-place
     // initialization pattern, which precludes generic classes.
-    builder.emitRODataFields(classRO,
-                             ForClass,
-                             DoesNotHaveUpdateCallback);
+    builder.emitRODataFields(classRO, ForClass, DoesNotHaveUpdateCallback,
+                             IsForGenericPattern);
     classRO.finishAndAddTo(init);
   }
 
   Size startOfMetaclassRO = init.getNextOffsetFromGlobal();
   assert(startOfMetaclassRO.isMultipleOf(IGM.getPointerSize()));
   {
     auto classRO = init.beginStruct();
-    builder.emitRODataFields(classRO, ForMetaClass, DoesNotHaveUpdateCallback);
+    builder.emitRODataFields(classRO, ForMetaClass, DoesNotHaveUpdateCallback,
+                             IsForGenericPattern);
     classRO.finishAndAddTo(init);
   }
 

lib/IRGen/GenClass.h

@@ -78,6 +78,11 @@ namespace irgen {
     HasUpdateCallback = true
   };
 
+  enum ForGenericPattern_t : bool {
+    IsNotForGenericPattern = false,
+    IsForGenericPattern = true
+  };
+
   /// Creates a layout for the class \p classType with allocated tail elements
   /// \p tailTypes.
   ///