[OBJC] Add attribute to mark Objective C class as non-lazy

A non-lazy class will be initialized eagerly when the Objective-C runtime is
loaded. This is required for certain system classes which have instances allocated in
non-standard ways, such as the classes for blocks and constant strings.
Adding this attribute is essentially equivalent to providing a trivial
+load method but avoids the (fairly small) load-time overheads associated
with defining and calling such a method.

Differential Revision: https://reviews.llvm.org/D56555

llvm-svn: 353116

1 files changed, 4 insertions, 3 deletions

diff --git a/clang/lib/CodeGen/CGObjCMac.cpp b/clang/lib/CodeGen/CGObjCMac.cpp
index 20b5a86cae4..7822a95285b 100644
--- a/clang/lib/CodeGen/CGObjCMac.cpp
+++ b/clang/lib/CodeGen/CGObjCMac.cpp
@@ -6261,9 +6261,10 @@ CGObjCNonFragileABIMac::BuildClassObject(const ObjCInterfaceDecl *CI,
   return GV;
 }
 
-bool
-CGObjCNonFragileABIMac::ImplementationIsNonLazy(const ObjCImplDecl *OD) const {
-  return OD->getClassMethod(GetNullarySelector("load")) != nullptr;
+bool CGObjCNonFragileABIMac::ImplementationIsNonLazy(
+    const ObjCImplDecl *OD) const {
+  return OD->getClassMethod(GetNullarySelector("load")) != nullptr ||
+         OD->getClassInterface()->hasAttr<ObjCNonLazyClassAttr>();
 }
 
 void CGObjCNonFragileABIMac::GetClassSizeInfo(const ObjCImplementationDecl *OID,