From be9022c50229b3491afe550a938384db75fe62b6 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Thu, 6 Aug 2015 20:56:55 +0000
Subject: [PATCH] [ItaniumCXXABI] Don't import RTTI data for classes with key
 functions

MinGW has some pretty strange behvaior around RTTI and
dllimport/dllexport:
- RTTI data is never imported
- RTTI data is only exported if the class has no key function.

llvm-svn: 244266
---
 clang/lib/CodeGen/ItaniumCXXABI.cpp      | 18 ++++++++++++++----
 clang/test/CodeGenCXX/dllimport-rtti.cpp |  7 +++++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index cb506c3..115bf19 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -2450,10 +2450,13 @@ static bool ShouldUseExternalRTTIDescriptor(CodeGenModule &CGM,
 
     // FIXME: this may need to be reconsidered if the key function
     // changes.
+    // N.B. We must always emit the RTTI data ourselves if there exists a key
+    // function.
+    bool IsDLLImport = RD->hasAttr<DLLImportAttr>();
     if (CGM.getVTables().isVTableExternal(RD))
-      return true;
+      return IsDLLImport ? false : true;
 
-    if (RD->hasAttr<DLLImportAttr>())
+    if (IsDLLImport)
       return true;
   }
 
@@ -2683,8 +2686,15 @@ static llvm::GlobalVariable::LinkageTypes getTypeInfoLinkage(CodeGenModule &CGM,
       const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
       if (RD->hasAttr<WeakAttr>())
         return llvm::GlobalValue::WeakODRLinkage;
-      if (RD->isDynamicClass())
-        return CGM.getVTableLinkage(RD);
+      if (RD->isDynamicClass()) {
+        llvm::GlobalValue::LinkageTypes LT = CGM.getVTableLinkage(RD);
+        // MinGW won't export the RTTI information when there is a key function.
+        // Make sure we emit our own copy instead of attempting to dllimport it.
+        if (RD->hasAttr<DLLImportAttr>() &&
+            llvm::GlobalValue::isAvailableExternallyLinkage(LT))
+          LT = llvm::GlobalValue::LinkOnceODRLinkage;
+        return LT;
+      }
     }
 
     return llvm::GlobalValue::LinkOnceODRLinkage;
diff --git a/clang/test/CodeGenCXX/dllimport-rtti.cpp b/clang/test/CodeGenCXX/dllimport-rtti.cpp
index 8c0f863..609ad16 100644
--- a/clang/test/CodeGenCXX/dllimport-rtti.cpp
+++ b/clang/test/CodeGenCXX/dllimport-rtti.cpp
@@ -15,3 +15,10 @@ struct __declspec(dllimport) S {
 
 struct U : S {
 } u;
+
+struct __declspec(dllimport) V {
+  virtual void f();
+} v;
+// GNU-DAG: @_ZTV1V = available_externally dllimport
+// GNU-DAG: @_ZTS1V = linkonce_odr
+// GNU-DAG: @_ZTI1V = linkonce_odr
-- 
2.7.4