Generating vptr assume loads

[Prazek]

Summary

Generating vptr assumption loads for better devirtualization.

More here: http://lists.llvm.org/pipermail/cfe-dev/2015-July/044227.html

[majnemer]

Some first round review comments.

lib/CodeGen/CGClass.cpp

1831–1832

Sentences should start with a capital letter and end with a period.

1838

Variables should be capitalized.

1842

The return should be on it's own line, please clang-format this.
Also, under which conditions is this case possible?

2101–2102

This kind of initialization is not very common in LLVM.

lib/CodeGen/CodeGenFunction.h

1312

Capital letter and period missing here.

1326–1333

Would it make more sense for these to live in CGClass ?

lib/CodeGen/ItaniumCXXABI.cpp

193–194

I'm not sure what this function is supposed to compute. Needed for what?

1404

Check what?

lib/CodeGen/MicrosoftCXXABI.cpp

223–228

In the MS ABI, derived classes never share vtables with bases. Why do you need to do anything other than check that the most derived class doesn't have the __declspec(novtable) ?

[Prazek]

lib/CodeGen/CGClass.cpp

1842

Unfortunatelly clang-format puts short instructions in the same line

2101–2102

is It worth adding constructor just to change { with ( ?

lib/CodeGen/MicrosoftCXXABI.cpp

223–228

I don't know, I just took previous code assuming it is correct.

[rsmith]

include/clang/AST/VTableBuilder.h

387–391 ↗

(On Diff #31571)

Please commit this cleanup separately.

lib/CodeGen/CGCXXABI.h

349–357

Please add documentation comments for these.

352

Typo Initilize -> Initialize

364–365

Comment is out of date.

lib/CodeGen/CGClass.cpp

1831–1832

Please start comments with a capital letter and end them with a full stop.

lib/CodeGen/ItaniumCXXABI.cpp

1404

Is this done? :)

[rsmith]

lib/CodeGen/CGClass.cpp

2101–2102

No, just add an = before the {.

[djasper]

lib/CodeGen/CGClass.cpp

1842

Not, it doesn't. At least not if you properly configure LLVM style.

[Prazek]

lib/CodeGen/CGClass.cpp

1842

So mb I am doing something wrong, but I am using git-clang-format and get things like this

[Prazek]

lib/CodeGen/CodeGenFunction.h

1326–1333

What do You mean? These functions are defined in CGClass.cpp

lib/CodeGen/MicrosoftCXXABI.cpp

223–228

ok, I see. I just took code that suposed to work with microsoft and itanium abi. You are right

[nwilson]

lib/CodeGen/CGClass.cpp

1862

Looks like another formatting/tab issue here.

2157

Looks like the same formatting/tab as above.

This is what I've done when using clang-format, maybe it will fix the issues you've had:
./clang-format -style=llvm -lines="N:M" <FileToFormat> > tmp && cp tmp <FileToFormat>

(Just don't include the less than and greater around the FileToFormat.)

[djasper]

lib/CodeGen/CGClass.cpp

2157

You shouldn't need to do this by "hand". There is clang-format-diff.py / git-clang-format for that.

[nwilson]

lib/CodeGen/CGClass.cpp

2157

Good to know. Thanks!

[Prazek]

lib/CodeGen/ItaniumCXXABI.cpp

193–194

isVirtualOffsetNeededForVtableField good enough?

[rsmith]

lib/CodeGen/CGCXXABI.h

349–357

Please also add documentation comments for the other two. =)

[hfinkel]

lib/CodeGen/CGClass.cpp

1832

I think this comment should be a little more verbose. How about this:

// Generate vtable assumptions if we are calling dynamic-class's ctor, except when doing so as part of a derived class's ctor's base-class initialization. Doing so in this latter case would be useless, because the vtable is about to be overwritten by the derived class's vtable.

test/CodeGenCXX/vtable-assume-load.cpp

33

Will these IR values still have names even when compiling an -Asserts (NDEBUG) build? If not, you'll need to have better pattern matching.

Also, please match the load instructions that calculate %vtable (and the call to the ctor so that we know that the call to the assumption comes after it).

I think it would be nicer to put the checks for each function adjacent to the function definitions themselves. So put these CHECK lines right next to fooA().

39

Don't match the TBAA metadata (leaving off everything after the comma before !tbaa should be fine).

[Prazek]

lib/CodeGen/CGClass.cpp

1832

The main point of not calling this function, is because it is useless to have assumption loads inside constructor, when they are generated also outside of ctor. I guess You could have case when You are not overriding base vptr, and You are calling base ctor from dynamic class

[rsmith]

lib/CodeGen/CGClass.cpp

1832

It might also be worth including in the comment that it is not correct to call EmitVTableAssumptionLoads here, because it assumes the object's vptr points to the complete object vtable; during a constructor call it will probably have a construction vtable instead.

[Prazek]

lib/CodeGen/CGClass.cpp

1832

Well, it would be correct, but it would be useless. Just after calling base constructor, assume loads would appear, and after there would be new store to vptr.

[rsmith]

lib/CodeGen/CGClass.cpp

1832

EmitVTableAssumptionLoads assumes that the This pointer points to an object whose most-derived type is ClassDecl, and it assumes that the object is not under construction. Both of those assumptions can be violated for a base class constructor call, and can result in it emitting incorrect assumptions (because virtual bases may be at different offsets and because the vptr of an object under construction may be different from the corresponding vptr of a fully-constructed object).

[Prazek]

lib/CodeGen/CGClass.cpp

1832

ok, now I get it

[rjmccall]

Mostly LGTM. Are you going to emit assumptions for vbptrs in a separate patch?

lib/CodeGen/CGCXXABI.h

349–357

In contrast, this does not need to be as general as it is, and making it this general is actively harmful; just pass the vtable class.

Also, I suggest calling it "doStructorsInitializeVTables".

352

This method does not need to be passed a CodeGenFunction&, but it should take a complete CodeGenFunction::VPtr, not just this one random field from it.

lib/CodeGen/CGClass.cpp

1862

As mentioned elsewhere, you can skip this entire loop if doStructorsInitializeVTables returns false.

2157

Please call doStructorsInitializeVTables for RD above the call to getVTablePointers and then just skip the rest of the function if it returns false.

[majnemer]

test/CodeGenCXX/vtable-assume-load.cpp

40

This check line looks misspelled.

[Prazek]

In D11859#225025, @rjmccall wrote:

Mostly LGTM. Are you going to emit assumptions for vbptrs in a separate patch?

I wasn't planning to. I am focusing now on upgrading GVN for using new invariant.barrier metadata.

[rjmccall]

In D11859#225384, @Prazek wrote:

In D11859#225025, @rjmccall wrote:

Mostly LGTM. Are you going to emit assumptions for vbptrs in a separate patch?

I wasn't planning to. I am focusing now on upgrading GVN for using new invariant.barrier metadata.

I won't argue with prioritizing Itanium over MS work, if that's your motivation, because that's obviously your call to make, and certainly that's how I would weigh things if I were doing this work. If you're interested in both, though, I would guess that vbptr assumptions would be particularly valuable — constructing objects and immediately converting them to a base class is pretty common in a lot of idioms.

[Prazek]

lib/CodeGen/CGCXXABI.h

352

yep, I thought that there will be problem with placing VPtr class, but I haven't noticed that CGCXXAABI includes CodeGenFunction.

CodeGenFunction is required for ItaniumABI
return NeedsVTTParameter(CGF.CurGD);

lib/CodeGen/CGClass.cpp

1862

hmm, I think it is not true. This code checks if each base that we are initilizing/generating vptr assumption don't have novtable specifier. If one base has it, it doesn't mean that we don't have to do it for other base

[Prazek]

In D11859#225404, @rjmccall wrote:

In D11859#225384, @Prazek wrote:

In D11859#225025, @rjmccall wrote:

Mostly LGTM. Are you going to emit assumptions for vbptrs in a separate patch?

I wasn't planning to. I am focusing now on upgrading GVN for using new invariant.barrier metadata.

I won't argue with prioritizing Itanium over MS work, if that's your motivation, because that's obviously your call to make, and certainly that's how I would weigh things if I were doing this work. If you're interested in both, though, I would guess that vbptr assumptions would be particularly valuable — constructing objects and immediately converting them to a base class is pretty common in a lot of idioms.

It just wasn't in our plans. Main target was to devirtualize function calls much better, and I think that finishing the work from proposed paper will be much more valuable.

[rjmccall]

lib/CodeGen/CGClass.cpp

1862

No, it only checks whether VTableClass has novtable. VTableClass is the derived class for which we're initializing subobject v-tables, and it's invariant during getVTablePointers; that's why it's passed separately from BaseSubobject.

And if you think about how novtable works as a language feature, you'll see that it has to be that way. The purpose of "novtable" is to avoid emitting v-tables just for the short-term purposes of construction and destruction. It's not supposed to apply when initializing derived classes: eventually, the complete object does need all the v-tables to be initialized, or else you'll never be able to call virtual methods on it, meaning that it might as well not have any.

[Prazek]

lib/CodeGen/CGClass.cpp

1862

You are right. I changed things like You said - I only named it doStructorsInitilizeVPtrs

[rjmccall]

Just a couple tweaks and then LGTM.

lib/CodeGen/CGClass.cpp

1833

Please use this comment:

// Generate vtable assumptions if we're constructing a complete object
// with a vtable.  We don't do this for base subobjects for two reasons:
// first, it's incorrect for classes with virtual bases, and second, we're
// about to overwrite the vptrs anyway.

2157

Please also skip the call to getVTablePointers when doStructorsInitializeVPtrs, thanks.

lib/CodeGen/ItaniumCXXABI.cpp

196

Typo: "Initialize".

[Prazek]

Fix for the PR24479

[rsmith]

LGTM

test/CodeGenCXX/vtable-assume-load.cpp

25

While you're here, maybe also remove the %"struct.test1::A"* (and likewise for the tests below).

lib/CodeGen/CGCXXABI.h

virtual void EmitDestructorCall(CodeGenFunction &CGF,
                                   const CXXDestructorDecl *DD, CXXDtorType Type,
                                   bool ForVirtualBase, bool Delegating,
                                   llvm::Value *This) = 0;
 
   /// Emits the VTable definitions required for the given record type.
   virtual void emitVTableDefinitions(CodeGenVTables &CGVT,
                                      const CXXRecordDecl *RD) = 0;
 
+  /// Checks if ABI requires extra virtual offset for vtable field.
+  virtual bool
+  isVirtualOffsetNeededForVTableField(CodeGenFunction &CGF,
+                                      const CXXRecordDecl *NearestVBase) = 0;
+
+  /// Checks if ABI allows to initilize vptr for given class.
+  virtual bool canInitializeVPtr(const CXXRecordDecl *VTableClass,
+                                 const CXXRecordDecl *Base,
+                                 const CXXRecordDecl *NearestVBase) = 0;
+
+  /// Get the address point of the vtable for the given base subobject.
+  virtual llvm::Constant *
+  getVTableAddressPoint(BaseSubobject Base,
+                        const CXXRecordDecl *VTableClass) = 0;
+
   /// Get the address point of the vtable for the given base subobject while
-  /// building a constructor or a destructor. On return, NeedsVirtualOffset
-  /// tells if a virtual base adjustment is needed in order to get the offset
-  /// of the base subobject.
-  virtual llvm::Value *getVTableAddressPointInStructor(
-      CodeGenFunction &CGF, const CXXRecordDecl *RD, BaseSubobject Base,
-      const CXXRecordDecl *NearestVBase, bool &NeedsVirtualOffset) = 0;
+  /// building a constructor or a destructor.
+  virtual llvm::Value *
+  getVTableAddressPointInStructor(CodeGenFunction &CGF, const CXXRecordDecl *RD,
+                                  BaseSubobject Base,
+                                  const CXXRecordDecl *NearestVBase) = 0;
 
   /// Get the address point of the vtable for the given base subobject while
   /// building a constexpr.
   virtual llvm::Constant *
   getVTableAddressPointForConstExpr(BaseSubobject Base,
                                     const CXXRecordDecl *VTableClass) = 0;
 
   /// Get the address of the vtable for the given record decl which should be

lib/CodeGen/CGClass.cpp

CGF.EmitCXXDestructorCall(dtor, Dtor_Complete, /*for vbase*/ false,
                             /*Delegating=*/false, addr);
 }
 
 void CodeGenFunction::EmitCXXConstructorCall(const CXXConstructorDecl *D,
                                              CXXCtorType Type,
                                              bool ForVirtualBase,
                                              bool Delegating, llvm::Value *This,
                                              const CXXConstructExpr *E) {
+  const CXXRecordDecl *ClassDecl = D->getParent();
+
   // C++11 [class.mfct.non-static]p2:
   //   If a non-static member function of a class X is called for an object that
   //   is not of type X, or of a type derived from X, the behavior is undefined.
   // FIXME: Provide a source location here.
   EmitTypeCheck(CodeGenFunction::TCK_ConstructorCall, SourceLocation(), This,
-                getContext().getRecordType(D->getParent()));
+                getContext().getRecordType(ClassDecl));
 
   if (D->isTrivial() && D->isDefaultConstructor()) {
     assert(E->getNumArgs() == 0 && "trivial default ctor with args");
     return;
   }
 
   // If this is a trivial constructor, just emit what's needed. If this is a
   // union copy constructor, we must emit a memcpy, because the AST does not
   // model that copy.
   if (isMemcpyEquivalentSpecialMember(D)) {
     assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
 
     const Expr *Arg = E->getArg(0);
     QualType SrcTy = Arg->getType();
     llvm::Value *Src = EmitLValue(Arg).getAddress();
-    QualType DestTy = getContext().getTypeDeclType(D->getParent());
+    QualType DestTy = getContext().getTypeDeclType(ClassDecl);
     EmitAggregateCopyCtor(This, Src, DestTy, SrcTy);
     return;
   }
 
   CallArgList Args;
 
   // Push the this ptr.
   Args.add(RValue::get(This), D->getThisType(getContext()));
 
   // Add the rest of the user-supplied arguments.
   const FunctionProtoType *FPT = D->getType()->castAs<FunctionProtoType>();
   EmitCallArgs(Args, FPT, E->arguments(), E->getConstructor());
 
   // Insert any ABI-specific implicit constructor arguments.
   unsigned ExtraArgs = CGM.getCXXABI().addImplicitConstructorArgs(
       *this, D, Type, ForVirtualBase, Delegating, Args);
 
   // Emit the call.
   llvm::Value *Callee = CGM.getAddrOfCXXStructor(D, getFromCtorType(Type));
   const CGFunctionInfo &Info =
       CGM.getTypes().arrangeCXXConstructorCall(Args, D, Type, ExtraArgs);
   EmitCall(Info, Callee, ReturnValueSlot(), Args, D);
+
+  // Generate vtable assumptions if we are calling dynamic class ctor,
+  // unless we are calling base constructor - we don't want to generating
+  // assumption loads for not completed because vptr may still change.
+  if (CGM.getCodeGenOpts().OptimizationLevel > 0 &&
+      ClassDecl->isDynamicClass() && Type != Ctor_Base)
+    EmitVTableAssumptionLoads(ClassDecl, This);
+}
+
+void CodeGenFunction::EmitVTableAssumptionLoad(const VPtr &Vptr,
+                                               llvm::Value *This) {
+  llvm::Value *VTableGlobal =
+      CGM.getCXXABI().getVTableAddressPoint(Vptr.Base, Vptr.VTableClass);
+  if (!VTableGlobal)
+    return;
+
+  // We can just use the base offset in the complete class.
+  CharUnits NonVirtualOffset = Vptr.Base.getBaseOffset();
+
+  if (!NonVirtualOffset.isZero())
+    This =
+        ApplyNonVirtualAndVirtualOffset(*this, This, NonVirtualOffset, nullptr);
+
+  llvm::Value *VPtrValue = GetVTablePtr(This, VTableGlobal->getType());
+  llvm::Value *Cmp =
+      Builder.CreateICmpEQ(VPtrValue, VTableGlobal, "cmp.vtables");
+  Builder.CreateAssumption(Cmp);
+}
+
+void CodeGenFunction::EmitVTableAssumptionLoads(const CXXRecordDecl *ClassDecl,
+                                                llvm::Value *This) {
+  for (const VPtr &vptr : getVTablePointers(ClassDecl))
+    if (CGM.getCXXABI().canInitializeVPtr(vptr.VTableClass, vptr.Base.getBase(),
+                                          vptr.NearestVBase))
+      EmitVTableAssumptionLoad(vptr, This);
 }
 
 void
 CodeGenFunction::EmitSynthesizedCXXCopyCtorCall(const CXXConstructorDecl *D,
                                         llvm::Value *This, llvm::Value *Src,
                                         const CXXConstructExpr *E) {
   if (isMemcpyEquivalentSpecialMember(D)) {
     assert(E->getNumArgs() == 1 && "unexpected argcount for trivial ctor");
void CodeGenFunction::PushDestructorCleanup(QualType T, llvm::Value *Addr) {
   if (!ClassDecl) return;
   if (ClassDecl->hasTrivialDestructor()) return;
 
   const CXXDestructorDecl *D = ClassDecl->getDestructor();
   assert(D && D->isUsed() && "destructor not marked as used!");
   PushDestructorCleanup(D, Addr);
 }
 
-void
-CodeGenFunction::InitializeVTablePointer(BaseSubobject Base,
-                                         const CXXRecordDecl *NearestVBase,
-                                         CharUnits OffsetFromNearestVBase,
-                                         const CXXRecordDecl *VTableClass) {
-  const CXXRecordDecl *RD = Base.getBase();
-
-  // Don't initialize the vtable pointer if the class is marked with the
-  // 'novtable' attribute.
-  if ((RD == VTableClass || RD == NearestVBase) &&
-      VTableClass->hasAttr<MSNoVTableAttr>())
-    return;
-
+void CodeGenFunction::InitializeVTablePointer(const VPtr &Vptr) {
   // Compute the address point.
-  bool NeedsVirtualOffset;
   llvm::Value *VTableAddressPoint =
       CGM.getCXXABI().getVTableAddressPointInStructor(
-          *this, VTableClass, Base, NearestVBase, NeedsVirtualOffset);
+          *this, Vptr.VTableClass, Vptr.Base, Vptr.NearestVBase);
+
   if (!VTableAddressPoint)
     return;
 
   // Compute where to store the address point.
   llvm::Value *VirtualOffset = nullptr;
   CharUnits NonVirtualOffset = CharUnits::Zero();
 
-  if (NeedsVirtualOffset) {
+  if (CGM.getCXXABI().isVirtualOffsetNeededForVTableField(*this,
+                                                          Vptr.NearestVBase)) {
     // We need to use the virtual base offset offset because the virtual base
     // might have a different offset in the most derived class.
-    VirtualOffset = CGM.getCXXABI().GetVirtualBaseClassOffset(*this,
-                                                              LoadCXXThis(),
-                                                              VTableClass,
-                                                              NearestVBase);
-    NonVirtualOffset = OffsetFromNearestVBase;
+    VirtualOffset = CGM.getCXXABI().GetVirtualBaseClassOffset(
+        *this, LoadCXXThis(), Vptr.VTableClass, Vptr.NearestVBase);
+    NonVirtualOffset = Vptr.OffsetFromNearestVBase;
   } else {
     // We can just use the base offset in the complete class.
-    NonVirtualOffset = Base.getBaseOffset();
+    NonVirtualOffset = Vptr.Base.getBaseOffset();
   }
 
   // Apply the offsets.
   llvm::Value *VTableField = LoadCXXThis();
 
   if (!NonVirtualOffset.isZero() || VirtualOffset)
     VTableField = ApplyNonVirtualAndVirtualOffset(*this, VTableField,
                                                   NonVirtualOffset,
                                                   VirtualOffset);
 
   // Finally, store the address point. Use the same LLVM types as the field to
   // support optimization.
   llvm::Type *VTablePtrTy =
       llvm::FunctionType::get(CGM.Int32Ty, /*isVarArg=*/true)
           ->getPointerTo()
           ->getPointerTo();
   VTableField = Builder.CreateBitCast(VTableField, VTablePtrTy->getPointerTo());
   VTableAddressPoint = Builder.CreateBitCast(VTableAddressPoint, VTablePtrTy);
+
   llvm::StoreInst *Store = Builder.CreateStore(VTableAddressPoint, VTableField);
   CGM.DecorateInstruction(Store, CGM.getTBAAInfoForVTablePtr());
 }
 
-void
-CodeGenFunction::InitializeVTablePointers(BaseSubobject Base,
-                                          const CXXRecordDecl *NearestVBase,
-                                          CharUnits OffsetFromNearestVBase,
-                                          bool BaseIsNonVirtualPrimaryBase,
-                                          const CXXRecordDecl *VTableClass,
-                                          VisitedVirtualBasesSetTy& VBases) {
+CodeGenFunction::VPtrsVector
+CodeGenFunction::getVTablePointers(const CXXRecordDecl *VTableClass) {
+  CodeGenFunction::VPtrsVector VPtrsResult;
+  VisitedVirtualBasesSetTy VBases;
+  getVTablePointers(BaseSubobject(VTableClass, CharUnits::Zero()),
+                    /*NearestVBase=*/nullptr,
+                    /*OffsetFromNearestVBase=*/CharUnits::Zero(),
+                    /*BaseIsNonVirtualPrimaryBase=*/false, VTableClass, VBases,
+                    VPtrsResult);
+  return VPtrsResult;
+}
+
+void CodeGenFunction::getVTablePointers(BaseSubobject Base,
+                                        VisitedVirtualBasesSetTy &VBases,
+                                        VPtrsVector &Vptrs) {
   // If this base is a non-virtual primary base the address point has already
   // been set.
   if (!BaseIsNonVirtualPrimaryBase) {
     // Initialize the vtable pointer for this base.
-    InitializeVTablePointer(Base, NearestVBase, OffsetFromNearestVBase,
-                            VTableClass);
+    VPtr Vptr = {Base, NearestVBase, OffsetFromNearestVBase, VTableClass};
+    Vptrs.push_back(Vptr);
   }
 
   const CXXRecordDecl *RD = Base.getBase();
 
   // Traverse bases.
   for (const auto &I : RD->bases()) {
     CXXRecordDecl *BaseDecl
       = cast<CXXRecordDecl>(I.getType()->getAs<RecordType>()->getDecl());
if (I.isVirtual()) {
       const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
 
       BaseOffset = Base.getBaseOffset() + Layout.getBaseClassOffset(BaseDecl);
       BaseOffsetFromNearestVBase =
         OffsetFromNearestVBase + Layout.getBaseClassOffset(BaseDecl);
       BaseDeclIsNonVirtualPrimaryBase = Layout.getPrimaryBase() == BaseDecl;
     }
 
-    InitializeVTablePointers(BaseSubobject(BaseDecl, BaseOffset),
-                             I.isVirtual() ? BaseDecl : NearestVBase,
-                             BaseOffsetFromNearestVBase,
-                             BaseDeclIsNonVirtualPrimaryBase,
-                             VTableClass, VBases);
+    getVTablePointers(
+        BaseSubobject(BaseDecl, BaseOffset),
+        I.isVirtual() ? BaseDecl : NearestVBase, BaseOffsetFromNearestVBase,
+        BaseDeclIsNonVirtualPrimaryBase, VTableClass, VBases, Vptrs);
   }
 }
 
 void CodeGenFunction::InitializeVTablePointers(const CXXRecordDecl *RD) {
   // Ignore classes without a vtable.
   if (!RD->isDynamicClass())
     return;
 
+  auto Vptrs = getVTablePointers(RD);
+
   // Initialize the vtable pointers for this class and all of its bases.
-  VisitedVirtualBasesSetTy VBases;
-  InitializeVTablePointers(BaseSubobject(RD, CharUnits::Zero()),
-                           /*NearestVBase=*/nullptr,
-                           /*OffsetFromNearestVBase=*/CharUnits::Zero(),
-                           /*BaseIsNonVirtualPrimaryBase=*/false, RD, VBases);
+  for (const VPtr &Vptr : Vptrs)
+    if (CGM.getCXXABI().canInitializeVPtr(Vptr.VTableClass, Vptr.Base.getBase(),
+                                          Vptr.NearestVBase))
+      InitializeVTablePointer(Vptr);
 
   if (RD->getNumVBases())
     CGM.getCXXABI().initializeHiddenVirtualInheritanceMembers(*this, RD);
 }
 
 llvm::Value *CodeGenFunction::GetVTablePtr(llvm::Value *This,
                                            llvm::Type *Ty) {
   llvm::Value *VTablePtrSrc = Builder.CreateBitCast(This, Ty->getPointerTo());

lib/CodeGen/CodeGenFunction.h

llvm::Function *GenerateVarArgsThunk(llvm::Function *Fn,
                                        GlobalDecl GD, const ThunkInfo &Thunk);
 
   void EmitCtorPrologue(const CXXConstructorDecl *CD, CXXCtorType Type,
                         FunctionArgList &Args);
 
   void EmitInitializerForField(FieldDecl *Field, LValue LHS, Expr *Init,
                                ArrayRef<VarDecl *> ArrayIndexes);
 
-  /// InitializeVTablePointer - Initialize the vtable pointer of the given
-  /// subobject.
-  ///
-  void InitializeVTablePointer(BaseSubobject Base,
-                               const CXXRecordDecl *NearestVBase,
-                               CharUnits OffsetFromNearestVBase,
-                               const CXXRecordDecl *VTableClass);
+  /// Struct containg all informations needed to initilize vptrs.
+  struct VPtr {
+    BaseSubobject Base;
+    const CXXRecordDecl *NearestVBase;
+    CharUnits OffsetFromNearestVBase;
+    const CXXRecordDecl *VTableClass;
+  };
+
+  /// Initialize the vtable pointer of the given subobject.
+  void InitializeVTablePointer(const VPtr &vptr);
+
+  typedef llvm::SmallVector<VPtr, 4> VPtrsVector;
 
   typedef llvm::SmallPtrSet<const CXXRecordDecl *, 4> VisitedVirtualBasesSetTy;
-  void InitializeVTablePointers(BaseSubobject Base,
-                                const CXXRecordDecl *NearestVBase,
-                                CharUnits OffsetFromNearestVBase,
-                                bool BaseIsNonVirtualPrimaryBase,
-                                const CXXRecordDecl *VTableClass,
-                                VisitedVirtualBasesSetTy& VBases);
+  VPtrsVector getVTablePointers(const CXXRecordDecl *VTableClass);
+
+  void getVTablePointers(BaseSubobject Base, const CXXRecordDecl *NearestVBase,
+                         VisitedVirtualBasesSetTy &VBases, VPtrsVector &vptrs);
 
   void InitializeVTablePointers(const CXXRecordDecl *ClassDecl);
 
   /// GetVTablePtr - Return the Value of the vtable pointer member pointed
   /// to by This.
   llvm::Value *GetVTablePtr(llvm::Value *This, llvm::Type *Ty);
 
   enum CFITypeCheckKind {
     CFITCK_VCall,
void EmitDelegateCXXConstructorCall(const CXXConstructorDecl *Ctor,
                                       const FunctionArgList &Args,
                                       SourceLocation Loc);
   // It's important not to confuse this and the previous function. Delegating
   // constructors are the C++0x feature. The constructor delegate optimization
   // is used to reduce duplication in the base and complete consturctors where
   // they are substantially the same.
   void EmitDelegatingCXXConstructorCall(const CXXConstructorDecl *Ctor,
                                         const FunctionArgList &Args);
+
   void EmitCXXConstructorCall(const CXXConstructorDecl *D, CXXCtorType Type,
                               bool ForVirtualBase, bool Delegating,
                               llvm::Value *This, const CXXConstructExpr *E);
 
+  /// Emit assumption load for all bases. Requires to be be called only on
+  /// most-derived class and not under construction of the object.
+  void EmitVTableAssumptionLoads(const CXXRecordDecl *ClassDecl,
+                                 llvm::Value *This);
+
+  /// Emit assumption that vptr load == global vtable.
+  void EmitVTableAssumptionLoad(const VPtr &vptr, llvm::Value *This);
+
   void EmitSynthesizedCXXCopyCtorCall(const CXXConstructorDecl *D,
                               llvm::Value *This, llvm::Value *Src,
                               const CXXConstructExpr *E);
 
   void EmitCXXAggrConstructorCall(const CXXConstructorDecl *D,
                                   const ConstantArrayType *ArrayTy,
                                   llvm::Value *ArrayPtr,
                                   const CXXConstructExpr *E,

lib/CodeGen/ItaniumCXXABI.cpp

public:
 
   void EmitDestructorCall(CodeGenFunction &CGF, const CXXDestructorDecl *DD,
                           CXXDtorType Type, bool ForVirtualBase,
                           bool Delegating, llvm::Value *This) override;
 
   void emitVTableDefinitions(CodeGenVTables &CGVT,
                              const CXXRecordDecl *RD) override;
 
+  bool isVirtualOffsetNeededForVTableField(
+      CodeGenFunction &CGF, const CXXRecordDecl *NearestVBase) override;
+
+  bool canInitializeVPtr(const CXXRecordDecl *VTableClass,
+                         const CXXRecordDecl *Base,
+                         const CXXRecordDecl *NearestVBase) override {
+    return true;
+  }
+
+  llvm::Constant *
+  getVTableAddressPoint(BaseSubobject Base,
+                        const CXXRecordDecl *VTableClass) override;
+
   llvm::Value *getVTableAddressPointInStructor(
       CodeGenFunction &CGF, const CXXRecordDecl *VTableClass,
-      BaseSubobject Base, const CXXRecordDecl *NearestVBase,
-      bool &NeedsVirtualOffset) override;
+      BaseSubobject Base, const CXXRecordDecl *NearestVBase) override;
+
+  llvm::Value *getVTableAddressPointInStructorWithVTT(
+      CodeGenFunction &CGF, const CXXRecordDecl *VTableClass,
+      BaseSubobject Base, const CXXRecordDecl *NearestVBase);
 
   llvm::Constant *
   getVTableAddressPointForConstExpr(BaseSubobject Base,
                                     const CXXRecordDecl *VTableClass) override;
 
   llvm::GlobalVariable *getAddrOfVTable(const CXXRecordDecl *RD,
                                         CharUnits VPtrOffset) override;
 
if (RD->getIdentifier() &&
       isa<NamespaceDecl>(DC) && cast<NamespaceDecl>(DC)->getIdentifier() &&
       cast<NamespaceDecl>(DC)->getIdentifier()->isStr("__cxxabiv1") &&
       DC->getParent()->isTranslationUnit())
     EmitFundamentalRTTIDescriptors();
 
   CGM.EmitVTableBitSetEntries(VTable, VTLayout);
 }
 
+bool ItaniumCXXABI::isVirtualOffsetNeededForVTableField(
+    CodeGenFunction &CGF, const CXXRecordDecl *NearestVBase) {
+  if (NearestVBase == nullptr)
+    return false;
+  return NeedsVTTParameter(CGF.CurGD);
+}
+
 llvm::Value *ItaniumCXXABI::getVTableAddressPointInStructor(
     CodeGenFunction &CGF, const CXXRecordDecl *VTableClass, BaseSubobject Base,
-    const CXXRecordDecl *NearestVBase, bool &NeedsVirtualOffset) {
-  bool NeedsVTTParam = CGM.getCXXABI().NeedsVTTParameter(CGF.CurGD);
-  NeedsVirtualOffset = (NeedsVTTParam && NearestVBase);
+    const CXXRecordDecl *NearestVBase) {
 
-  llvm::Value *VTableAddressPoint;
-  if (NeedsVTTParam && (Base.getBase()->getNumVBases() || NearestVBase)) {
-    // Get the secondary vpointer index.
-    uint64_t VirtualPointerIndex =
-        CGM.getVTables().getSecondaryVirtualPointerIndex(VTableClass, Base);
-
-    /// Load the VTT.
-    llvm::Value *VTT = CGF.LoadCXXVTT();
-    if (VirtualPointerIndex)
-      VTT = CGF.Builder.CreateConstInBoundsGEP1_64(VTT, VirtualPointerIndex);
-
-    // And load the address point from the VTT.
-    VTableAddressPoint = CGF.Builder.CreateLoad(VTT);
-  } else {
-    llvm::Constant *VTable =
-        CGM.getCXXABI().getAddrOfVTable(VTableClass, CharUnits());
-    uint64_t AddressPoint = CGM.getItaniumVTableContext()
-                                .getVTableLayout(VTableClass)
-                                .getAddressPoint(Base);
-    VTableAddressPoint =
-        CGF.Builder.CreateConstInBoundsGEP2_64(VTable, 0, AddressPoint);
+  if ((Base.getBase()->getNumVBases() || NearestVBase != nullptr) &&
+      NeedsVTTParameter(CGF.CurGD)) {
+    return getVTableAddressPointInStructorWithVTT(CGF, VTableClass, Base,
+                                                  NearestVBase);
   }
-
-  return VTableAddressPoint;
+  return getVTableAddressPoint(Base, VTableClass);
 }
 
-llvm::Constant *ItaniumCXXABI::getVTableAddressPointForConstExpr(
-    BaseSubobject Base, const CXXRecordDecl *VTableClass) {
-  auto *VTable = getAddrOfVTable(VTableClass, CharUnits());
+llvm::Constant *
+ItaniumCXXABI::getVTableAddressPoint(BaseSubobject Base,
+                                     const CXXRecordDecl *VTableClass) {
+  llvm::GlobalValue *VTable = getAddrOfVTable(VTableClass, CharUnits());
 
   // Find the appropriate vtable within the vtable group.
   uint64_t AddressPoint = CGM.getItaniumVTableContext()
                               .getVTableLayout(VTableClass)
                               .getAddressPoint(Base);
   llvm::Value *Indices[] = {
     llvm::ConstantInt::get(CGM.Int64Ty, 0),
     llvm::ConstantInt::get(CGM.Int64Ty, AddressPoint)
   };
 
   return llvm::ConstantExpr::getInBoundsGetElementPtr(VTable->getValueType(),
                                                       VTable, Indices);
 }
 
+llvm::Value *ItaniumCXXABI::getVTableAddressPointInStructorWithVTT(
+    CodeGenFunction &CGF, const CXXRecordDecl *VTableClass, BaseSubobject Base,
+    const CXXRecordDecl *NearestVBase) {
+  assert((Base.getBase()->getNumVBases() || NearestVBase != nullptr) &&
+         NeedsVTTParameter(CGF.CurGD) && "This class doesn't have VTT");
+
+  // Get the secondary vpointer index.
+  uint64_t VirtualPointerIndex =
+      CGM.getVTables().getSecondaryVirtualPointerIndex(VTableClass, Base);
+
+  /// Load the VTT.
+  llvm::Value *VTT = CGF.LoadCXXVTT();
+  if (VirtualPointerIndex)
+    VTT = CGF.Builder.CreateConstInBoundsGEP1_64(VTT, VirtualPointerIndex);
+
+  // And load the address point from the VTT.
+  return CGF.Builder.CreateLoad(VTT);
+}
+
+llvm::Constant *ItaniumCXXABI::getVTableAddressPointForConstExpr(
+    BaseSubobject Base, const CXXRecordDecl *VTableClass) {
+  return getVTableAddressPoint(Base, VTableClass);
+}
+
 llvm::GlobalVariable *ItaniumCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
                                                      CharUnits VPtrOffset) {
   assert(VPtrOffset.isZero() && "Itanium ABI only supports zero vptr offsets");
 
   llvm::GlobalVariable *&VTable = VTables[RD];
   if (VTable)
     return VTable;
 

lib/CodeGen/MicrosoftCXXABI.cpp

void EmitDestructorCall(CodeGenFunction &CGF, const CXXDestructorDecl *DD,
                           bool Delegating, llvm::Value *This) override;
 
   void emitVTableBitSetEntries(VPtrInfo *Info, const CXXRecordDecl *RD,
                                llvm::GlobalVariable *VTable);
 
   void emitVTableDefinitions(CodeGenVTables &CGVT,
                              const CXXRecordDecl *RD) override;
 
+  bool isVirtualOffsetNeededForVTableField(
+      CodeGenFunction &CGF, const CXXRecordDecl *NearestVBase) override;
+
+  // Can't initialize the vtable pointer if the class is marked
+  // with the 'novtable' attribute.
+  bool canInitializeVPtr(const CXXRecordDecl *VTableClass,
+                         const CXXRecordDecl *Base,
+                         const CXXRecordDecl *NearestVBase) override {
+    return !VTableClass->hasAttr<MSNoVTableAttr>();
+  }
+
+  llvm::Constant *
+  getVTableAddressPoint(BaseSubobject Base,
+                        const CXXRecordDecl *VTableClass) override;
+
   llvm::Value *getVTableAddressPointInStructor(
       CodeGenFunction &CGF, const CXXRecordDecl *VTableClass,
-      BaseSubobject Base, const CXXRecordDecl *NearestVBase,
-      bool &NeedsVirtualOffset) override;
+      BaseSubobject Base, const CXXRecordDecl *NearestVBase) override;
 
   llvm::Constant *
   getVTableAddressPointForConstExpr(BaseSubobject Base,
                                     const CXXRecordDecl *VTableClass) override;
 
   llvm::GlobalVariable *getAddrOfVTable(const CXXRecordDecl *RD,
                                         CharUnits VPtrOffset) override;
 
llvm::Constant *Init = CGVT.CreateVTableInitializer(
         VTLayout.getNumVTableThunks(), RTTI);
 
     VTable->setInitializer(Init);
 
     emitVTableBitSetEntries(Info, RD, VTable);
   }
 }
 
+bool MicrosoftCXXABI::isVirtualOffsetNeededForVTableField(
+    CodeGenFunction &CGF, const CXXRecordDecl *NearestVBase) {
+  return (NearestVBase != nullptr);
+}
+
 llvm::Value *MicrosoftCXXABI::getVTableAddressPointInStructor(
     CodeGenFunction &CGF, const CXXRecordDecl *VTableClass, BaseSubobject Base,
-    const CXXRecordDecl *NearestVBase, bool &NeedsVirtualOffset) {
-  NeedsVirtualOffset = (NearestVBase != nullptr);
-
-  (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
-  VFTableIdTy ID(VTableClass, Base.getBaseOffset());
-  llvm::GlobalValue *VTableAddressPoint = VFTablesMap[ID];
+    const CXXRecordDecl *NearestVBase) {
+  llvm::Constant *VTableAddressPoint = getVTableAddressPoint(Base, VTableClass);
   if (!VTableAddressPoint) {
     assert(Base.getBase()->getNumVBases() &&
            !getContext().getASTRecordLayout(Base.getBase()).hasOwnVFPtr());
   }
   return VTableAddressPoint;
 }
 
 static void mangleVFTableName(MicrosoftMangleContext &MangleContext,
                               const CXXRecordDecl *RD, const VPtrInfo *VFPtr,
                               SmallString<256> &Name) {
   llvm::raw_svector_ostream Out(Name);
   MangleContext.mangleCXXVFTable(RD, VFPtr->MangledPath, Out);
 }
 
-llvm::Constant *MicrosoftCXXABI::getVTableAddressPointForConstExpr(
-    BaseSubobject Base, const CXXRecordDecl *VTableClass) {
+llvm::Constant *
+MicrosoftCXXABI::getVTableAddressPoint(BaseSubobject Base,
+                                       const CXXRecordDecl *VTableClass) {
   (void)getAddrOfVTable(VTableClass, Base.getBaseOffset());
   VFTableIdTy ID(VTableClass, Base.getBaseOffset());
-  llvm::GlobalValue *VFTable = VFTablesMap[ID];
+  return VFTablesMap[ID];
+}
+
+llvm::Constant *MicrosoftCXXABI::getVTableAddressPointForConstExpr(
+    BaseSubobject Base, const CXXRecordDecl *VTableClass) {
+  llvm::Constant *VFTable = getVTableAddressPoint(Base, VTableClass);
   assert(VFTable && "Couldn't find a vftable for the given base?");
   return VFTable;
 }
 
 llvm::GlobalVariable *MicrosoftCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
                                                        CharUnits VPtrOffset) {
   // getAddrOfVTable may return 0 if asked to get an address of a vtable which
   // shouldn't be used in the given record type. We want to cache this result in
   // VFTablesMap, thus a simple zero check is not sufficient.
+
   VFTableIdTy ID(RD, VPtrOffset);
   VTablesMapTy::iterator I;
   bool Inserted;
   std::tie(I, Inserted) = VTablesMap.insert(std::make_pair(ID, nullptr));
   if (!Inserted)
     return I->second;
 
   llvm::GlobalVariable *&VTable = I->second;
bool VFTableComesFromAnotherTU =
       llvm::GlobalValue::isAvailableExternallyLinkage(VFTableLinkage) ||
       llvm::GlobalValue::isExternalLinkage(VFTableLinkage);
   bool VTableAliasIsRequred =
       !VFTableComesFromAnotherTU && getContext().getLangOpts().RTTIData;
 
   if (llvm::GlobalValue *VFTable =
           CGM.getModule().getNamedGlobal(VFTableName)) {
     VFTablesMap[ID] = VFTable;
-    return VTableAliasIsRequred
+    VTable = VTableAliasIsRequred
                  ? cast<llvm::GlobalVariable>(
                        cast<llvm::GlobalAlias>(VFTable)->getBaseObject())
                  : cast<llvm::GlobalVariable>(VFTable);
+    return VTable;
   }
 
   uint64_t NumVTableSlots =
       VTContext.getVFTableLayout(RD, VFPtr->FullOffsetInMDC)
           .getNumVTableComponents();
   llvm::GlobalValue::LinkageTypes VTableLinkage =
       VTableAliasIsRequred ? llvm::GlobalValue::PrivateLinkage : VFTableLinkage;
 

test/CodeGen/available-externally-hidden.cpp

  public:
   bool Send(Message* message) override;
 };
 
 class TestSyncMessageFilter : public SyncMessageFilter {
 };
 
 int main() {
-TestSyncMessageFilter*  f = new TestSyncMessageFilter;
+  TestSyncMessageFilter *f = new TestSyncMessageFilter;
   f->Send(new Message);
 }

test/CodeGenCXX/ctor-globalopt.cpp

 // RUN: %clang_cc1 -triple %itanium_abi_triple -emit-llvm -o - %s | FileCheck %s
-// RUN: %clang_cc1 -triple %itanium_abi_triple -emit-llvm -o - %s -O1 | FileCheck %s --check-prefix=O1
+// RUN: %clang_cc1 -triple %itanium_abi_triple -emit-llvm -o - %s -O2 | opt - -S -globalopt -o - | FileCheck %s --check-prefix=O1
 // RUN: %clang_cc1 -triple %ms_abi_triple -emit-llvm -o - %s | FileCheck %s
-// RUN: %clang_cc1 -triple %ms_abi_triple -emit-llvm -o - %s -O1 | FileCheck %s --check-prefix=O1
+// RUN: %clang_cc1 -triple %ms_abi_triple -emit-llvm -o - %s -O2 | opt - -S -globalopt -o - | FileCheck %s --check-prefix=O1
 
 // Check that GlobalOpt can eliminate static constructors for simple implicit
 // constructors. This is a targetted integration test to make sure that LLVM's
 // optimizers are able to process Clang's IR. GlobalOpt in particular is
 // sensitive to the casts we emit.
 
 // CHECK: @llvm.global_ctors = appending global [1 x { i32, void ()*, i8* }] 
 // CHECK: [{ i32, void ()*, i8* } { i32 65535, void ()* @_GLOBAL__sub_I_ctor_globalopt.cpp, i8* null }]

test/CodeGenCXX/template-instantiation.cpp

 // RUN: %clang_cc1 %s -O1 -disable-llvm-optzns -triple=x86_64-apple-darwin10 -emit-llvm -o - | FileCheck %s
 
+// CHECK:     @_ZTVN5test018stdio_sync_filebufIA4_iEE = linkonce_odr unnamed_addr constant
+
 // CHECK: @_ZN7PR100011xE = global
 // CHECK-NOT: @_ZN7PR100014kBarE = external global i32
 //
 // CHECK-NOT: @_ZTVN5test118stdio_sync_filebufIwEE = constant
 // CHECK-NOT: _ZTVN5test315basic_fstreamXXIcEE
 // CHECK-NOT: @_ZTVN5test018stdio_sync_filebufIA1_iEE
 // CHECK-NOT: @_ZTVN5test018stdio_sync_filebufIA2_iEE
 // CHECK:     @_ZTVN5test018stdio_sync_filebufIA3_iEE = weak_odr unnamed_addr constant
 
 // CHECK: @_ZN7PR100011SIiE3arrE = linkonce_odr global [3 x i32]
 // CHECK-NOT: @_ZN7PR100011SIiE3arr2E = linkonce_odr global [3 x i32]A
 
-// CHECK:     @_ZTVN5test018stdio_sync_filebufIA4_iEE = linkonce_odr unnamed_addr constant
 
 // CHECK-NOT: _ZTVN5test31SIiEE
 // CHECK-NOT: _ZTSN5test31SIiEE
 
 // CHECK-LABEL: define linkonce_odr void @_ZN5test21CIiEC1Ev(%"class.test2::C"* %this) unnamed_addr
 // CHECK-LABEL: define linkonce_odr void @_ZN5test21CIiE6foobarIdEEvT_(
 // CHECK-LABEL: define available_externally void @_ZN5test21CIiE6zedbarEd(
 

test/CodeGenCXX/thunks.cpp

-// RUN: %clang_cc1 %s -triple=x86_64-pc-linux-gnu -munwind-tables -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 %s -triple=x86_64-pc-linux-gnu -munwind-tables -emit-llvm -o - -O1 -disable-llvm-optzns | FileCheck %s
+// RUN: %clang_cc1 %s -triple=x86_64-pc-linux-gnu -munwind-tables -emit-llvm -o %t
+// RUN: %clang_cc1 %s -triple=x86_64-pc-linux-gnu -munwind-tables -emit-llvm -o %t.opt -O1 -disable-llvm-optzns
+// RUN: FileCheck %s < %t
+// RUN: FileCheck %s < %t.opt
+// RUN: FileCheck --check-prefix=CHECK-NONOPT %s < %t
+// RUN: FileCheck --check-prefix=CHECK-OPT %s < %t.opt
 
 namespace Test1 {
 
 // Check that we emit a non-virtual thunk for C::f.
 
 struct A {
   virtual void f();
 };
struct D : public C {
   ~D();
 };
 D::~D() {}
 // CHECK: define linkonce_odr void @_ZThn8_N6Test161C3fooEv({{.*}}) {{.*}} comdat
 }
 
 /**** The following has to go at the end of the file ****/
 
+// checking without opt
+// CHECK-NONOPT-LABEL: define internal void @_ZThn8_N6Test4B12_GLOBAL__N_11C1fEv(
+// CHECK-NONOPT-NOT: comdat
+
 // This is from Test5:
-// CHECK-LABEL: define internal void @_ZThn8_N6Test4B12_GLOBAL__N_11C1fEv(
-// CHECK-NOT: comdat
-// CHECK-LABEL: define linkonce_odr void @_ZTv0_n24_N5Test51B1fEv
+// CHECK-NONOPT-LABEL: define linkonce_odr void @_ZTv0_n24_N5Test51B1fEv
+
+// This is from Test10:
+// CHECK-NONOPT-LABEL: define linkonce_odr void @_ZN6Test101C3fooEv
+// CHECK-NONOPT-LABEL: define linkonce_odr void @_ZThn8_N6Test101C3fooEv
+
+// Checking with opt
+// CHECK-OPT-LABEL: define internal void @_ZThn8_N6Test4B12_GLOBAL__N_11C1fEv(%"struct.Test4B::(anonymous namespace)::C"* %this) unnamed_addr #0 align 2
 
 // This is from Test10:
-// CHECK-LABEL: define linkonce_odr void @_ZN6Test101C3fooEv
-// CHECK-LABEL: define linkonce_odr void @_ZThn8_N6Test101C3fooEv
+// CHECK-OPT-LABEL: define linkonce_odr void @_ZN6Test101C3fooEv
+// CHECK-OPT-LABEL: define linkonce_odr void @_ZThn8_N6Test101C3fooEv
+
+// This is from Test5:
+// CHECK-OPT-LABEL: define linkonce_odr void @_ZTv0_n24_N5Test51B1fEv
 
 // CHECK: attributes [[NUW]] = { nounwind uwtable{{.*}} }

test/CodeGenCXX/virtual-base-ctor.cpp

-// RUN: %clang_cc1 %s -emit-llvm -triple %itanium_abi_triple -o - -O2 | FileCheck %s
+// RUN: %clang_cc1 %s -emit-llvm -triple %itanium_abi_triple -o - -O2 | opt - -S -globalopt -o - | FileCheck %s
 
 struct B;
 extern B x;
 char y;
 typedef __typeof(sizeof(int)) size_t;
 struct A { int a; A() { y = ((size_t)this - (size_t)&x) / sizeof(void*); } };
 struct B : virtual A { void* x; };    
 B x;
 
 // CHECK: @y = global i8 2

test/CodeGenCXX/vtable-assume-load.cpp

+// RUN: %clang_cc1 %s -triple x86_64-apple-darwin10 -emit-llvm -o %t.ll -O1 -disable-llvm-optzns -fms-extensions
+// RUN: %clang_cc1 %s -triple i686-pc-win32 -emit-llvm -o %t.ms.ll -O1 -disable-llvm-optzns -fms-extensions
+
+// RUN: FileCheck --check-prefix=CHECK1 --input-file=%t.ll %s
+// RUN: FileCheck --check-prefix=CHECK2 --input-file=%t.ll %s
+// RUN: FileCheck --check-prefix=CHECK3 --input-file=%t.ll %s
+// RUN: FileCheck --check-prefix=CHECK4 --input-file=%t.ll %s
+// RUN: FileCheck --check-prefix=CHECK-MS --input-file=%t.ms.ll %s
+
+namespace test1 {
+
+struct A {
+  A();
+  virtual void foo();
+};
+
+struct B : A {
+  virtual void foo();
+};
+
+void g(A *a) { a->foo(); }
+
+// CHECK1-LABEL: define void @_ZN5test14fooAEv()
+// CHECK1: call void @_ZN5test11AC1Ev(%"struct.test1::A"* %a)
+// CHECK1: %vtable = load i8**, i8*** %1
+// CHECK1: %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([3 x i8*], [3 x i8*]* @_ZTVN5test11AE, i64 0, i64 2)
+// CHECK1: call void @llvm.assume(i1 %cmp.vtables)
+// CHECK1-LABEL: }
+
+void fooA() {
+  A a;
+  g(&a);
+}
+
+// CHECK1-LABEL: define void @_ZN5test14fooBEv()
+// CHECK1: call void @_ZN5test11BC1Ev(%"struct.test1::B"* %b)
+// CHECK1: %vtable = load i8**, i8*** %1
+// CHECK1: %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([3 x i8*], [3 x i8*]* @_ZTVN5test11BE, i64 0, i64 2)
+// CHECK1: call void @llvm.assume(i1 %cmp.vtables)
+// CHECK1-LABLE: }
+
+void fooB() {
+  B b;
+  g(&b);
+}
+// there should not be any assumes in the ctor that calls base ctor
+// CHECK1-LABEL: define linkonce_odr void @_ZN5test11BC2Ev(%"struct.test1::B"* %this)
+// CHECK1-NOT: @llvm.assume(
+// CHECK1-LABEL: }
+}
+namespace test2 {
+struct A {
+  A();
+  virtual void foo();
+};
+
+struct B {
+  B();
+  virtual void bar();
+};
+
+struct C : A, B {
+  C();
+  virtual void foo();
+};
+void g(A *a) { a->foo(); }
+void h(B *b) { b->bar(); }
+
+// CHECK2-LABEL: define void @_ZN5test24testEv()
+// CHECK2: call void @_ZN5test21CC1Ev(%"struct.test2::C"* %c)
+// CHECK2: vtable = load i8**, i8*** %1
+// CHECK2: %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([6 x i8*], [6 x i8*]* @_ZTVN5test21CE, i64 0, i64 2)
+// CHECK2: call void @llvm.assume(i1 %cmp.vtables)
+
+// CHECK2: %2 = bitcast %"struct.test2::C"* %c to i8*
+// CHECK2: %add.ptr = getelementptr inbounds i8, i8* %2, i64 8
+// CHECK2: %3 = bitcast i8* %add.ptr to i8***
+// CHECK2: %vtable1 = load i8**, i8*** %3
+// CHECK2: %cmp.vtables2 = icmp eq i8** %vtable1, getelementptr inbounds ([6 x i8*], [6 x i8*]* @_ZTVN5test21CE, i64 0, i64 5)
+// CHECK2: call void @llvm.assume(i1 %cmp.vtables2)
+
+// CHECK2: call void @_ZN5test21gEPNS_1AE(
+// CHECK2-LABEL: }
+
+void test() {
+  C c;
+  g(&c);
+  h(&c);
+}
+}
+
+namespace test3 {
+struct A {
+  A();
+};
+
+struct B : A {
+  B();
+  virtual void foo();
+};
+
+struct C : virtual A, B {
+  C();
+  virtual void foo();
+};
+void g(B *a) { a->foo(); }
+
+// CHECK3-LABEL: define void @_ZN5test34testEv()
+// CHECK3: call void @_ZN5test31CC1Ev(%"struct.test3::C"* %c)
+// CHECK3: %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([4 x i8*], [4 x i8*]* @_ZTVN5test31CE, i64 0, i64 3)
+// CHECK3: call void @llvm.assume(i1 %cmp.vtables)
+// CHECK3-LABLEL: }
+void test() {
+  C c;
+  g(&c);
+}
+} // test3
+
+namespace test4 {
+struct A {
+  A();
+  virtual void foo();
+};
+
+struct B : virtual A {
+  B();
+  virtual void foo();
+};
+struct C : B {
+  C();
+  virtual void foo();
+};
+
+void g(C *c) { c->foo(); }
+
+// CHECK4-LABEL: define void @_ZN5test44testEv()
+// CHECK4: call void @_ZN5test41CC1Ev(%"struct.test4::C"* %c)
+// CHECK4: %vtable = load i8**, i8*** %1
+// CHECK4: %cmp.vtables = icmp eq i8** %vtable, getelementptr inbounds ([5 x i8*], [5 x i8*]* @_ZTVN5test41CE, i64 0, i64 4)
+// CHECK4: call void @llvm.assume(i1 %cmp.vtables)
+
+// CHECK4: %2 = bitcast %"struct.test4::C"* %c to i8***
+// CHECK4: %vtable1 = load i8**, i8*** %2
+// CHECK4: %cmp.vtables2 = icmp eq i8** %vtable1, getelementptr inbounds ([5 x i8*], [5 x i8*]* @_ZTVN5test41CE, i64 0, i64 4)
+// CHECK4: call void @llvm.assume(i1 %cmp.vtables2)
+// CHECK4-LABEL: }
+
+void test() {
+  C c;
+  g(&c);
+}
+} // test4
+
+namespace test5 {
+
+struct __declspec(novtable) S {
+  virtual void foo();
+};
+
+void g(S &s) { s.foo(); }
+
+// if struct has novtable specifier, then we can't generate assumes
+// CHECK-MS-LABEL: define void @"\01?test@test5@@YAXXZ"()
+// CHECK-MS: call x86_thiscallcc %"struct.test5::S"* @"\01??0S@test5@@QAE@XZ"(
+// CHECK-MS-NOT: @llvm.assume
+// CHECK-MS-LABEL: }
+
+void test() {
+  S s;
+  g(s);
+}
+
+} // test5

test/CodeGenCXX/vtable-available-externally.cpp

void f() {
   g(&x);
 }
 
 }  // Test8
 
 namespace Test9 {
 // all virtual functions are outline, so we can assume that it will
 // be generated in translation unit where foo is defined
-// CHECK-TEST9: @_ZTVN5Test91AE = available_externally unnamed_addr constant
-// CHECK-TEST9: @_ZTVN5Test91BE = available_externally unnamed_addr constant
+// CHECK-TEST9-DAG: @_ZTVN5Test91AE = available_externally unnamed_addr constant
+// CHECK-TEST9-DAG: @_ZTVN5Test91BE = available_externally unnamed_addr constant
 struct A {
   virtual void foo();
   virtual void bar();
 };
 void A::bar() {}
 
 struct B : A {
   void foo();
 };
 
 void g() {
   A a;
   a.foo();
   B b;
   b.foo();
 }
 
 }  // Test9
 
 namespace Test10 {
 
 // because A's key function is defined here, vtable is generated in this TU
-// CHECK-TEST10: @_ZTVN6Test101AE = unnamed_addr constant
+// CHECK-TEST10-DAG: @_ZTVN6Test101AE = unnamed_addr constant
 struct A {
   virtual void foo();
   virtual void bar();
 };
 void A::foo() {}
 
 // Because key function is inline we will generate vtable as linkonce_odr
-// CHECK-TEST10: @_ZTVN6Test101DE = linkonce_odr unnamed_addr constant
+// CHECK-TEST10-DAG: @_ZTVN6Test101DE = linkonce_odr unnamed_addr constant
 struct D : A {
   void bar();
 };
 inline void D::bar() {}
 
 // because B has outline key function then we can refer to
-// CHECK-TEST10: @_ZTVN6Test101BE = available_externally unnamed_addr constant
+// CHECK-TEST10-DAG: @_ZTVN6Test101BE = available_externally unnamed_addr constant
 struct B : A {
   void foo();
   void bar();
 };
 
 // C's key function (car) is outline, but C has inline virtual function so we
 // can't guarantee that we will be able to refer to bar from name
 // so (at the moment) we can't emit vtable available_externally
-// CHECK-TEST10: @_ZTVN6Test101CE = external unnamed_addr constant
+// CHECK-TEST10-DAG: @_ZTVN6Test101CE = external unnamed_addr constant
 struct C : A {
   void bar() {}               // defined in body - not key function
   virtual inline void gar();  // inline in body - not key function
   virtual void car();
 };
 
 // no key function, vtable will be generated everywhere it will be used
-// CHECK-TEST10: @_ZTVN6Test101EE = linkonce_odr unnamed_addr constant
+// CHECK-TEST10-DAG: @_ZTVN6Test101EE = linkonce_odr unnamed_addr constant
 struct E : A {};
 
 void g(A& a) {
   a.foo();
   a.bar();
 }
 
 void f() {