[GNU ObjC] Fix a regression listing methods twice.

Methods synthesized from declared properties were being added to the
method lists twice.  This came from the change to list them in the
class's method list, which missed removing the place in CGObjCGNU that
added them again.

Reviewed By: lanza

Differential Revision: https://reviews.llvm.org/D91874

clang/lib/CodeGen/CGObjCGNU.cpp

@@ -3512,19 +3512,6 @@ void CGObjCGNU::GenerateClass(const ObjCImplementationDecl *OID) {
   ClassMethods.insert(ClassMethods.begin(), OID->classmeth_begin(),
       OID->classmeth_end());
 
-  // Collect the same information about synthesized properties, which don't
-  // show up in the instance method lists.
-  for (auto *propertyImpl : OID->property_impls())
-    if (propertyImpl->getPropertyImplementation() ==
-        ObjCPropertyImplDecl::Synthesize) {
-      auto addPropertyMethod = [&](const ObjCMethodDecl *accessor) {
-        if (accessor)
-          InstanceMethods.push_back(accessor);
-      };
-      addPropertyMethod(propertyImpl->getGetterMethodDecl());
-      addPropertyMethod(propertyImpl->getSetterMethodDecl());
-    }
-
   llvm::Constant *Properties = GeneratePropertyList(OID, ClassDecl);
 
   // Collect the names of referenced protocols

clang/test/CodeGenObjC/gnu-method-only-once.m

@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -S -emit-llvm -fobjc-runtime=gnustep-2.0 -o - %s | FileCheck %s -check-prefix=CHECK-NEW
+// RUN: %clang_cc1 -triple x86_64-unknown-freebsd -S -emit-llvm -fobjc-runtime=gnustep-1.8 -o - %s | FileCheck %s -check-prefix=CHECK-OLD
+
+// Clang 9 or 10 changed the handling of method lists so that methods provided
+// from synthesised properties showed up in the method list, where previously
+// CGObjCGNU had to collect them and merge them.  One of the places where this
+// merging happened was missed in the move and so we ended up emitting two
+// copies of method metadata for declared properties.
+
+// This class has only instance properties and only one pair of synthesized
+// methods from the property and so we should synthesize only one method list,
+// with precisely two methods on it.
+@interface X
+@property (retain) id iProp;
+@end
+
+@implementation X
+@synthesize iProp;
+@end
+
+// Check that the method list has precisely 2 methods.
+// CHECK-NEW: @.objc_method_list = internal global { i8*, i32, i64, [2 x
+// CHECK-OLD: @.objc_method_list = internal global { i8*, i32, [2 x