Set dllimport on Objective C ivar offsets (llvm#107604)

Ensures that offsets for instance variables are marked with `dllimport`
if the interface to which they belong has this attribute.

Author: qmfrederik

clang/lib/CodeGen/CGObjCGNU.cpp

@@ -1699,11 +1699,18 @@ class CGObjCGNUstep2 : public CGObjCGNUstep {
   llvm::Value *EmitIvarOffset(CodeGenFunction &CGF,
                               const ObjCInterfaceDecl *Interface,
                               const ObjCIvarDecl *Ivar) override {
-    const std::string Name = GetIVarOffsetVariableName(Ivar->getContainingInterface(), Ivar);
+    const ObjCInterfaceDecl *ContainingInterface =
+        Ivar->getContainingInterface();
+    const std::string Name =
+        GetIVarOffsetVariableName(ContainingInterface, Ivar);
     llvm::GlobalVariable *IvarOffsetPointer = TheModule.getNamedGlobal(Name);
-    if (!IvarOffsetPointer)
+    if (!IvarOffsetPointer) {
       IvarOffsetPointer = new llvm::GlobalVariable(TheModule, IntTy, false,
               llvm::GlobalValue::ExternalLinkage, nullptr, Name);
+      if (Ivar->getAccessControl() != ObjCIvarDecl::Private &&
+          Ivar->getAccessControl() != ObjCIvarDecl::Package)
+        CGM.setGVProperties(IvarOffsetPointer, ContainingInterface);
+    }
     CharUnits Align = CGM.getIntAlign();
     llvm::Value *Offset =
         CGF.Builder.CreateAlignedLoad(IntTy, IvarOffsetPointer, Align);

clang/test/CodeGenObjC/dllstorage.m

@@ -112,7 +112,7 @@ @interface M : I {
 // CHECK-IR-DAG: @"OBJC_IVAR_$_M._ivar" = external dllimport global i32
 
 // CHECK-NF-DAG: @"$_OBJC_REF_CLASS_M" = external dllimport global ptr
-// CHECK-NF-DAG: @"__objc_ivar_offset_M._ivar.@" = external global i32
+// CHECK-NF-DAG: @"__objc_ivar_offset_M._ivar.@" = external dllimport global i32
 
 __declspec(dllexport)
 __attribute__((__objc_exception__))
@@ -151,7 +151,7 @@ id f(Q *q) {
 
 // CHECK-IR-DAG: @"OBJC_IVAR_$_M._ivar" = external dllimport global i32
 
-// CHECK-NF-DAG: @"__objc_ivar_offset_M._ivar.@" = external global i32
+// CHECK-NF-DAG: @"__objc_ivar_offset_M._ivar.@" = external dllimport global i32
 
 int g(void) {
   @autoreleasepool {

clang/test/SemaObjC/ivar-access-tests.m

@@ -2,6 +2,8 @@
 
 @interface MySuperClass
 {
+  int unmarked;
+
 @private
   int private;
 
@@ -17,6 +19,7 @@ @implementation MySuperClass
 - (void) test {
     int access;
     MySuperClass *s = 0;
+    access = s->unmarked;
     access = s->private;   
     access = s->protected;
 }
@@ -30,9 +33,11 @@ @implementation MyClass
 - (void) test {
     int access;
     MySuperClass *s = 0;
+    access = s->unmarked;
     access = s->private; // expected-error {{instance variable 'private' is private}}
     access = s->protected;
     MyClass *m=0;
+    access = m->unmarked;
     access = m->private; // expected-error {{instance variable 'private' is private}}
     access = m->protected;
 }
@@ -46,9 +51,11 @@ @implementation Deeper
 - (void) test {
     int access;
     MySuperClass *s = 0;
+    access = s->unmarked;
     access = s->private; // expected-error {{instance variable 'private' is private}}
     access = s->protected;
     MyClass *m=0;
+    access = m->unmarked;
     access = m->private; // expected-error {{instance variable 'private' is private}}
     access = m->protected;
 }
@@ -61,9 +68,11 @@ @implementation Unrelated
 - (void) test {
     int access;
     MySuperClass *s = 0;
+    access = s->unmarked; // expected-error {{instance variable 'unmarked' is protected}}
     access = s->private; // expected-error {{instance variable 'private' is private}}
     access = s->protected; // expected-error {{instance variable 'protected' is protected}}
     MyClass *m=0;
+    access = m->unmarked; // expected-error {{instance variable 'unmarked' is protected}}
     access = m->private; // expected-error {{instance variable 'private' is private}}
     access = m->protected; // expected-error {{instance variable 'protected' is protected}}
 }
@@ -73,6 +82,7 @@ int main (void)
 {
   MySuperClass *s = 0;
   int access;
+  access = s->unmarked; // expected-error {{instance variable 'unmarked' is protected}}
   access = s->private;   // expected-error {{instance variable 'private' is private}}
   access = s->protected; // expected-error {{instance variable 'protected' is protected}}
   return 0;