Emit invariant.group loads with empty group md

[Prazek]

Summary

As discussed here
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109332.html
having different groups doesn't solve the problem entirly.

[rjmccall]

Okay.

cfe/trunk/lib/CodeGen/CodeGenModule.cpp

if (ConvertTypeToTag && TBAA)
     Inst->setMetadata(llvm::LLVMContext::MD_tbaa,
                       TBAA->getTBAAScalarTagInfo(TBAAInfo));
   else
     Inst->setMetadata(llvm::LLVMContext::MD_tbaa, TBAAInfo);
 }
 
 void CodeGenModule::DecorateInstructionWithInvariantGroup(
     llvm::Instruction *I, const CXXRecordDecl *RD) {
-  llvm::Metadata *MD = CreateMetadataIdentifierForType(QualType(RD->getTypeForDecl(), 0));
-  auto *MetaDataNode = dyn_cast<llvm::MDNode>(MD);
-  // Check if we have to wrap MDString in MDNode.
-  if (!MetaDataNode)
-    MetaDataNode = llvm::MDNode::get(getLLVMContext(), MD);
-  I->setMetadata(llvm::LLVMContext::MD_invariant_group, MetaDataNode);
+  I->setMetadata(llvm::LLVMContext::MD_invariant_group,
+                 llvm::MDNode::get(getLLVMContext(), {}));
 }
 
 void CodeGenModule::Error(SourceLocation loc, StringRef message) {
   unsigned diagID = getDiags().getCustomDiagID(DiagnosticsEngine::Error, "%0");
   getDiags().Report(Context.getFullLoc(loc), diagID) << message;
 }
 
 /// ErrorUnsupported - Print out an error that codegen doesn't support the

cfe/trunk/test/CodeGenCXX/invariant.group-for-vptrs.cpp

 // RUN: %clang_cc1 -triple=x86_64-pc-linux-gnu -emit-llvm %s -fstrict-vtable-pointers -O1 -o - -disable-llvm-passes | FileCheck %s
 
 struct A {
   virtual void foo();
 };
 
 struct D : A {
   void foo();
 };
 
 // CHECK-LABEL: define void @_Z21testExternallyVisiblev()
 void testExternallyVisible() {
   A *a = new A;
 
-  // CHECK: load {{.*}} !invariant.group ![[A_MD:[0-9]+]]
+  // CHECK: load {{.*}} !invariant.group ![[MD:[0-9]+]]
   a->foo();
 
   D *d = new D;
   // CHECK: call void @_ZN1DC1Ev(
-  // CHECK: load {{.*}} !invariant.group ![[D_MD:[0-9]+]]
+  // CHECK: load {{.*}} !invariant.group ![[MD]]
   d->foo();
   A *a2 = d;
-  // CHECK: load {{.*}} !invariant.group ![[A_MD]]
+  // CHECK: load {{.*}} !invariant.group ![[MD]]
   a2->foo();
 }
 // CHECK-LABEL: {{^}}}
 
 namespace {
 
 struct B {
   virtual void bar();
 };
 
 struct C : B {
   void bar();
 };
 
 }
 
 // CHECK-LABEL: define void @_Z21testInternallyVisibleb(
 void testInternallyVisible(bool p) {
   B *b = new B;
-  // CHECK: = load {{.*}}, !invariant.group ![[B_MD:[0-9]+]]
+  // CHECK: = load {{.*}}, !invariant.group ![[MD]]
   b->bar();
 
   // CHECK: call void @_ZN12_GLOBAL__N_11CC1Ev(
   C *c = new C;
-  // CHECK: = load {{.*}}, !invariant.group ![[C_MD:[0-9]+]]
+  // CHECK: = load {{.*}}, !invariant.group ![[MD]]
   c->bar();
 }
 
 // Checking A::A()
 // CHECK-LABEL: define linkonce_odr void @_ZN1AC2Ev(
-// CHECK: store {{.*}}, !invariant.group ![[A_MD]]
+// CHECK: store {{.*}}, !invariant.group ![[MD]]
 // CHECK-LABEL: {{^}}}
 
 // Checking D::D()
 // CHECK-LABEL: define linkonce_odr void @_ZN1DC2Ev(
 // CHECK:  = call i8* @llvm.invariant.group.barrier(i8*
 // CHECK:  call void @_ZN1AC2Ev(%struct.A*
-// CHECK: store {{.*}} !invariant.group ![[D_MD]]
+// CHECK: store {{.*}} !invariant.group ![[MD]]
 
 // Checking B::B()
 // CHECK-LABEL: define internal void @_ZN12_GLOBAL__N_11BC2Ev(
-// CHECK:  store {{.*}}, !invariant.group ![[B_MD]]
+// CHECK:  store {{.*}}, !invariant.group ![[MD]]
 
 // Checking C::C()
 // CHECK-LABEL: define internal void @_ZN12_GLOBAL__N_11CC2Ev(
-// CHECK:  store {{.*}}, !invariant.group ![[C_MD]]
+// CHECK:  store {{.*}}, !invariant.group ![[MD]]
 
-// CHECK: ![[A_MD]] = !{!"_ZTS1A"}
-// CHECK: ![[D_MD]] = !{!"_ZTS1D"}
-// CHECK: ![[B_MD]] = distinct !{}
-// CHECK: ![[C_MD]] = distinct !{}
+// CHECK: ![[MD]] = !{}