[clang] [ObjC] Recursively check superclasses to see if any inherit from NSObject (PR #81335)

[via cfe-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/81335

>From 18987af24d2f53d00e2ac42998a8f1580e35afdf Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Fri, 9 Feb 2024 17:51:15 -0500
Subject: [PATCH 1/2] [ObjC] Add pre-commit tests [NFC]

---
 .../CodeGenObjC/constant-non-fragile-ivar-offset.m  | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
index 788b3220af3067..40a97ba62ec6cf 100644
--- a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
+++ b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -emit-llvm %s -o - | FileCheck %s
 
 // CHECK: @"OBJC_IVAR_$_StaticLayout.static_layout_ivar" = hidden constant i64 20
+// CHECK: @"OBJC_IVAR_$_StaticLayoutSubClass.static_layout_ivar2" = hidden global i64 24
 // CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden global i64 12
 
 @interface NSObject {
@@ -20,6 +21,18 @@ -(void)meth {
 }
 @end
 
+ at interface StaticLayoutSubClass : StaticLayout
+ at end
+
+ at implementation StaticLayoutSubClass {
+  int static_layout_ivar2;
+}
+-(void)meth2 {
+  static_layout_ivar2 = 0;
+  // CHECK: load i64, ptr @"OBJC_IVAR_$_StaticLayoutSubClass
+}
+ at end
+
 @interface NotNSObject {
   int these, might, change;
 }

>From 193bec6224c2a04f486c24a7d262cbcb058cc1c3 Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Fri, 9 Feb 2024 17:47:59 -0500
Subject: [PATCH 2/2] [ObjC] Recursively check superclasses to see if any
 inherit from NSObject

If an NSObject subclass has fixed offsets, then so must the subclasses of that subclass!
---
 clang/lib/CodeGen/CGObjCMac.cpp               | 22 ++++++++++++++-----
 .../constant-non-fragile-ivar-offset.m        |  4 ++--
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index 27d77e9a8a5511..ceee70a5d79b3e 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1593,12 +1593,22 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
   }
 
   bool isClassLayoutKnownStatically(const ObjCInterfaceDecl *ID) {
-    // NSObject is a fixed size. If we can see the @implementation of a class
-    // which inherits from NSObject then we know that all it's offsets also must
-    // be fixed. FIXME: Can we do this if see a chain of super classes with
-    // implementations leading to NSObject?
-    return ID->getImplementation() && ID->getSuperClass() &&
-           ID->getSuperClass()->getName() == "NSObject";
+    // Test a class by checking its superclasses up to its base class if it has
+    // one
+    while (ID) {
+      // The base class NSObject is a fixed size
+      if (ID->getName() == "NSObject")
+        return true;
+
+      // If we cannot see the @implementation of a class, we cannot assume fixed
+      // offsets
+      if (!ID->getImplementation())
+        return false;
+
+      // Test superclass
+      ID = ID->getSuperClass();
+    }
+    return false;
   }
 
 public:
diff --git a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
index 40a97ba62ec6cf..c5bc2be0dfdb84 100644
--- a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
+++ b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -triple x86_64-apple-macosx10.14.0 -emit-llvm %s -o - | FileCheck %s
 
 // CHECK: @"OBJC_IVAR_$_StaticLayout.static_layout_ivar" = hidden constant i64 20
-// CHECK: @"OBJC_IVAR_$_StaticLayoutSubClass.static_layout_ivar2" = hidden global i64 24
+// CHECK: @"OBJC_IVAR_$_StaticLayoutSubClass.static_layout_ivar2" = hidden constant i64 24
 // CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden global i64 12
 
 @interface NSObject {
@@ -29,7 +29,7 @@ @implementation StaticLayoutSubClass {
 }
 -(void)meth2 {
   static_layout_ivar2 = 0;
-  // CHECK: load i64, ptr @"OBJC_IVAR_$_StaticLayoutSubClass
+  // CHECK-NOT: load i64, ptr @"OBJC_IVAR_$_StaticLayoutSubClass
 }
 @end