Reland r312224 - [ItaniumCXXABI] Always use linkonce_odr linkage for RTTI data on MinGW

[mstorsjo]

Summary

This fixes cases where dynamic classes produced RTTI data with external linkage, producing linker errors about duplicate symbols.

This touches code close to what was changed in SVN r244266, but this change doesn't break the tests added in that revision.

The previous version had missed to update CodeGenCXX/virt-dtor-key.cpp, which had a behaviour change only when running the testsuite on windows.

cfe/trunk/lib/CodeGen/ItaniumCXXABI.cpp

case ExternalLinkage:
     if (const RecordType *Record = dyn_cast<RecordType>(Ty)) {
       const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
       if (RD->hasAttr<WeakAttr>())
         return llvm::GlobalValue::WeakODRLinkage;
       if (CGM.getTriple().isWindowsItaniumEnvironment())
         if (RD->hasAttr<DLLImportAttr>() &&
             ShouldUseExternalRTTIDescriptor(CGM, Ty))
           return llvm::GlobalValue::ExternalLinkage;
-      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;
-      }
+      // MinGW always uses LinkOnceODRLinkage for type info.
+      if (RD->isDynamicClass() &&
+          !CGM.getContext()
+               .getTargetInfo()
+               .getTriple()
+               .isWindowsGNUEnvironment())
+        return CGM.getVTableLinkage(RD);
     }
 
     return llvm::GlobalValue::LinkOnceODRLinkage;
   }
 
   llvm_unreachable("Invalid linkage!");
 }
 

cfe/trunk/test/CodeGenCXX/rtti-mingw64.cpp

 // RUN: %clang_cc1 -triple x86_64-windows-gnu %s -emit-llvm -o - | FileCheck %s
 struct A { int a; };
 struct B : virtual A { int b; };
 B b;
+class C {
+  virtual ~C();
+};
+C::~C() {}
 
+// CHECK: @_ZTI1C = linkonce_odr
 // CHECK: @_ZTI1B = linkonce_odr constant { i8*, i8*, i32, i32, i8*, i64 }
 // CHECK-SAME:  i8* bitcast (i8** getelementptr inbounds (i8*, i8** @_ZTVN10__cxxabiv121__vmi_class_type_infoE, i64 2) to i8*),
 // CHECK-SAME:  i8* getelementptr inbounds ([3 x i8], [3 x i8]* @_ZTS1B, i32 0, i32 0),
 // CHECK-SAME:  i32 0,
 // CHECK-SAME:  i32 1,
 // CHECK-SAME:  i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*),
 //    This i64 is important, it should be an i64, not an i32.
 // CHECK-SAME:  i64 -6141 }, comdat

cfe/trunk/test/CodeGenCXX/virt-dtor-key.cpp

-// RUN: %clang_cc1 -triple %itanium_abi_triple -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i386-linux -emit-llvm %s -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i386-windows-gnu -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-MINGW
 // CHECK: @_ZTI3foo = constant
+// CHECK-MINGW: @_ZTI3foo = linkonce_odr
 class foo {
    foo();
    virtual ~foo();
 };
 
 foo::~foo() {
 }