Prevent ICE in dllexport class with _Atomic data member

Guard against a null pointer dereference that caused Clang to crash
when processing a class containing an _Atomic qualified data member,
and that is tagged with 'dllexport'.

Differential Revision: https://reviews.llvm.org/D29208


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@293911 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGClass.cpp

@@ -1131,10 +1131,11 @@ namespace {
           RHS = EC->getSubExpr();
         if (!RHS)
           return nullptr;
-        MemberExpr *ME2 = dyn_cast<MemberExpr>(RHS);
-        if (dyn_cast<FieldDecl>(ME2->getMemberDecl()) != Field)
-          return nullptr;
-        return Field;
+        if (MemberExpr *ME2 = dyn_cast<MemberExpr>(RHS)) {
+          if (ME2->getMemberDecl() == Field)
+            return Field;
+        }
+        return nullptr;
       } else if (CXXMemberCallExpr *MCE = dyn_cast<CXXMemberCallExpr>(S)) {
         CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(MCE->getCalleeDecl());
         if (!(MD && isMemcpyEquivalentSpecialMember(MD)))

test/CodeGenCXX/atomic-dllexport.cpp

+// RUN: %clang_cc1 -triple i686-windows-msvc -emit-llvm -std=c++11 -fms-extensions -O0 -o - %s | FileCheck --check-prefix=M32 %s
+// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -std=c++11 -fms-extensions -O0 -o - %s | FileCheck --check-prefix=M64 %s
+
+struct __declspec(dllexport) SomeStruct {
+  // Copy assignment operator should be produced, and exported:
+  // M32: define weak_odr dllexport x86_thiscallcc dereferenceable({{[0-9]+}}) %struct.SomeStruct* @"\01??4SomeStruct@@QAEAAU0@ABU0@@Z"
+  // M64: define weak_odr dllexport                dereferenceable({{[0-9]+}}) %struct.SomeStruct* @"\01??4SomeStruct@@QEAAAEAU0@AEBU0@@Z"
+  _Atomic(int) mData;
+};