[clang] [ObjC] Expand isClassLayoutKnownStatically to base classes as long as the implementation of it is known (PR #85465)

[via cfe-commits]

https://github.com/AtariDreams updated 
https://github.com/llvm/llvm-project/pull/85465

>From 274838e83e20d073b326387a1d319dd60ad32568 Mon Sep 17 00:00:00 2001
From: Rose <gfunni...@gmail.com>
Date: Fri, 15 Mar 2024 16:43:10 -0400
Subject: [PATCH] [ObjC] Expand isClassLayoutKnownStatically to base classes as
 long as the implementation of it is known

Only NSObject we can trust the layout of won't change even though we cannot 
directly see its @implementation
---
 clang/lib/CodeGen/CGObjCMac.cpp               |  9 +++++-
 .../constant-non-fragile-ivar-offset.m        | 30 ++++++++++++++++++-
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index e815e097e1fb48..da47ef786cf816 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -1595,6 +1595,11 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
   bool isClassLayoutKnownStatically(const ObjCInterfaceDecl *ID) {
     // Test a class by checking its superclasses up to
     // its base class if it has one.
+
+    // Cannot check a null class
+    if (!ID)
+      return false;
+
     for (; ID; ID = ID->getSuperClass()) {
       // The layout of base class NSObject
       // is guaranteed to be statically known
@@ -1606,7 +1611,9 @@ class CGObjCNonFragileABIMac : public CGObjCCommonMac {
       if (!ID->getImplementation())
         return false;
     }
-    return false;
+
+    // We know the layout of all the intermediate classes and superclasses.
+    return true;
   }
 
 public:
diff --git a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m 
b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
index 8d55e6c7d23081..ee4034e4b7f205 100644
--- a/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
+++ b/clang/test/CodeGenObjC/constant-non-fragile-ivar-offset.m
@@ -8,6 +8,12 @@
 // CHECK: @"OBJC_IVAR_$_IntermediateClass._intermediateProperty" = hidden 
constant i64 48
 // CHECK: @"OBJC_IVAR_$_SubClass.subClassIvar" = constant i64 56
 // CHECK: @"OBJC_IVAR_$_SubClass._subClassProperty" = hidden constant i64 64
+
+// CHECK: @"OBJC_IVAR_$_RootClass.these" = constant i64 0
+// CHECK: @"OBJC_IVAR_$_RootClass.dont" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_RootClass.change" = constant i64 4
+// CHECK: @"OBJC_IVAR_$_StillStaticLayout.static_layout_ivar" = hidden global 
i32 12
+
 // CHECK: @"OBJC_IVAR_$_NotStaticLayout.not_static_layout_ivar" = hidden 
global i64 12
 
 @interface NSObject {
@@ -120,7 +126,29 @@ -(void)intermediateSubclassVar {
 // CHECK: getelementptr inbounds i8, ptr %1, i64 64
 @end
 
-@interface NotNSObject {
+ __attribute((objc_root_class))  @interface RootClass {
+  int these, dont, change;
+}
+@end
+
+@implementation RootClass 
+@end
+
+@interface StillStaticLayout : RootClass
+@end
+
+@implementation StillStaticLayout {
+  int static_layout_ivar;
+}
+
+// CHECK-LABEL: define internal void @"\01-[StillStaticLayout meth]"
+-(void)meth {
+  static_layout_ivar = 0;
+  // CHECK-NOT: load i64, ptr @"OBJC_IVAR_$StillStaticLayout.static_layout_ivar
+}
+@end
+
+__attribute((objc_root_class))  @interface NotNSObject {
   int these, might, change;
 }
 @end

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