Don't emit an internal destructor that is identical to an external one.

It is not safe to emit alias to undefined (not supported by ELF or COFF), but
it is safe to rauw when the alias would have been internal or linkonce_odr.

llvm-svn: 194307

clang/lib/CodeGen/CGCXX.cpp

@@ -82,18 +82,12 @@ bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
   if (!UniqueBase)
     return true;
 
-  /// If we don't have a definition for the destructor yet, don't
-  /// emit.  We can't emit aliases to declarations; that's just not
-  /// how aliases work.
-  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
-  if (!BaseD->isImplicit() && !BaseD->hasBody())
-    return true;
-
   // If the base is at a non-zero offset, give up.
   const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
   if (!ClassLayout.getBaseClassOffset(UniqueBase).isZero())
     return true;
 
+  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor();
   return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
                                   GlobalDecl(BaseD, Dtor_Base),
                                   false);
@@ -146,14 +140,20 @@ bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
     return false;
   }
 
-  // Don't create an alias to a linker weak symbol unless we know we can do
-  // that in every TU. This avoids producing different COMDATs in different
-  // TUs.
-  if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) {
-    if (!InEveryTU)
+  if (!InEveryTU) {
+    /// If we don't have a definition for the destructor yet, don't
+    /// emit.  We can't emit aliases to declarations; that's just not
+    /// how aliases work.
+    if (Ref->isDeclaration())
       return true;
 
-    assert(Linkage == TargetLinkage);
+    // Don't create an alias to a linker weak symbol unless we know we can do
+    // that in every TU. This avoids producing different COMDATs in different
+    // TUs.
+    if (llvm::GlobalValue::isWeakForLinker(TargetLinkage)) {
+      assert(Linkage == TargetLinkage);
+      return true;
+    }
   }
 
   // Create the alias with no name.

clang/test/CodeGenCXX/ctor-dtor-alias.cpp

@@ -73,3 +73,18 @@ namespace test5 {
   }
   B X;
 }
+
+namespace test6 {
+  // Test that we use ~A directly, even when ~A is not defined. The symbol for
+  // ~B would have been internal and still contain a reference to ~A.
+  struct A {
+    virtual ~A();
+  };
+  namespace {
+  struct B : public A {
+    ~B() {}
+  };
+  }
+  B X;
+  // CHECK-DAG: call i32 @__cxa_atexit({{.*}}@_ZN5test61AD2Ev
+}