[CodeView] Initial support for emitting S_THUNK32 symbols for compiler-generated thunk routines

[bwyma]

Summary

Compiler-generated thunk routines are currently emitted using S_GPROC32_ID symbols. This causes Visual Studio to believe the thunk is user code, and when stepping into them Visual Studio opens a "Source Not Found" window because the thunk is correlated with source line zero (0).

By emitting these as S_THUNK32 symbols instead, Visual Studio will recognize these as compiler-generated thunks and step through them into the user code they call.

This initial support only handles standard thunk ordinals.

[rnk]

Thanks! Can you add a clang IRGen test that checks the DISubprogram flags set for thunks?

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

869

This throws away all the local variables and inlined call sites in the thunk. I guess that's good enough for -O0, and optimized debug info is best effort anyway, but it's worth a comment, either here or at the point where we return early for thunks.

874

I noticed that MSVC emits S_PROC_ID_END. Should we do that too?

llvm/test/DebugInfo/COFF/thunk.ll

20

Can you add a member pointer thunk to this test? Add something like:

bool (A::*mp)() = &A::MyMethod;

The ??_9 function should be a thunk.

[bwyma]

Can you add a clang IRGen test that checks the DISubprogram flags set for thunks?

I extended the existing test debug-info-thunk.cpp to make sure the DIFlagThunk flag is set on the thunk routines.

... it's worth a comment, either here ...

Comment added.

I noticed that MSVC emits S_PROC_ID_END. Should we do that too?

Fixed.

Can you add a member pointer thunk to this test?

Done.

[bwyma]

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

2360

Some thunks are (correctly) not given any source correlation by CLANG. When this happens it does not have line info and the entire thunk was being thrown away here. This change prevents the compiler from throwing away the thunk.

[rnk]

lgtm

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

2360

I think this might be a hold-over from when the only reason we emitted ProcSym records was for line table info. We might want to re-evaluate this check completely at some point, but for now, sounds good.

llvm/include/llvm/IR/DebugInfoFlags.def

 HANDLE_DI_FLAG((3 << 16), VirtualInheritance)
 HANDLE_DI_FLAG((1 << 18), IntroducedVirtual)
 HANDLE_DI_FLAG((1 << 19), BitField)
 HANDLE_DI_FLAG((1 << 20), NoReturn)
 HANDLE_DI_FLAG((1 << 21), MainSubprogram)
 HANDLE_DI_FLAG((1 << 22), TypePassByValue)
 HANDLE_DI_FLAG((1 << 23), TypePassByReference)
 HANDLE_DI_FLAG((1 << 24), FixedEnum)
+HANDLE_DI_FLAG((1 << 25), Thunk)
 
 // To avoid needing a dedicated value for IndirectVirtualBase, we use
 // the bitwise or of Virtual and FwdDecl, which does not otherwise
 // make sense for inheritance.
 HANDLE_DI_FLAG((1 << 2) | (1 << 5), IndirectVirtualBase)
 
 #ifdef DI_FLAG_LARGEST_NEEDED
 // intended to be used with ADT/BitmaskEnum.h
 // NOTE: always must be equal to largest flag, check this when adding new flag
-HANDLE_DI_FLAG((1 << 24), Largest)
+HANDLE_DI_FLAG((1 << 25), Largest)
 #undef DI_FLAG_LARGEST_NEEDED
 #endif
 
 #undef HANDLE_DI_FLAG

llvm/include/llvm/IR/DebugInfoMetadata.h

public:
   /// non-static member function (void foo() &&).
   bool isRValueReference() const { return getFlags() & FlagRValueReference; }
 
   /// Check if this is marked as noreturn.
   ///
   /// Return true if this subprogram is C++11 noreturn or C11 _Noreturn
   bool isNoReturn() const { return getFlags() & FlagNoReturn; }
 
+  // Check if this routine is a compiler-generated thunk.
+  //
+  // Returns true if this subprogram is a thunk generated by the compiler.
+  bool isThunk() const { return getFlags() & FlagThunk; }
+
   DIScopeRef getScope() const { return DIScopeRef(getRawScope()); }
 
   StringRef getName() const { return getStringOperand(2); }
   StringRef getLinkageName() const { return getStringOperand(3); }
 
   DISubroutineType *getType() const {
     return cast_or_null<DISubroutineType>(getRawType());
   }

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.h

class LLVM_LIBRARY_VISIBILITY CodeViewDebug : public DebugHandlerBase {
   void emitTypeInformation();
 
   void emitTypeGlobalHashes();
 
   void emitCompilerInformation();
 
   void emitInlineeLinesSubsection();
 
+  void emitDebugInfoForThunk(const Function *GV,
+                             FunctionInfo &FI,
+                             const MCSymbol *Fn);
+
   void emitDebugInfoForFunction(const Function *GV, FunctionInfo &FI);
 
   void emitDebugInfoForGlobals();
 
   void emitDebugInfoForRetainedTypes();
 
   void
   emitDebugInfoForUDTs(ArrayRef<std::pair<std::string, const DIType *>> UDTs);

llvm/lib/CodeGen/AsmPrinter/CodeViewDebug.cpp

void CodeViewDebug::switchToDebugSectionForSymbol(const MCSymbol *GVSym) {
   OS.SwitchSection(DebugSec);
 
   // Emit the magic version number if this is the first time we've switched to
   // this section.
   if (ComdatDebugSections.insert(DebugSec).second)
     emitCodeViewMagicVersion();
 }
 
+// Emit an S_THUNK32/S_END symbol pair for a thunk routine.
+// The only supported thunk ordinal is currently the standard type.
+void CodeViewDebug::emitDebugInfoForThunk(const Function *GV,
+                                          FunctionInfo &FI,
+                                          const MCSymbol *Fn) {
+  std::string FuncName = GlobalValue::dropLLVMManglingEscape(GV->getName());
+  const ThunkOrdinal ordinal = ThunkOrdinal::Standard; // Only supported kind.
+
+  OS.AddComment("Symbol subsection for " + Twine(FuncName));
+  MCSymbol *SymbolsEnd = beginCVSubsection(DebugSubsectionKind::Symbols);
+
+  // Emit S_THUNK32
+  MCSymbol *ThunkRecordBegin = MMI->getContext().createTempSymbol(),
+           *ThunkRecordEnd   = MMI->getContext().createTempSymbol();
+  OS.AddComment("Record length");
+  OS.emitAbsoluteSymbolDiff(ThunkRecordEnd, ThunkRecordBegin, 2);
+  OS.EmitLabel(ThunkRecordBegin);
+  OS.AddComment("Record kind: S_THUNK32");
+  OS.EmitIntValue(unsigned(SymbolKind::S_THUNK32), 2);
+  OS.AddComment("PtrParent");
+  OS.EmitIntValue(0, 4);
+  OS.AddComment("PtrEnd");
+  OS.EmitIntValue(0, 4);
+  OS.AddComment("PtrNext");
+  OS.EmitIntValue(0, 4);
+  OS.AddComment("Thunk section relative address");
+  OS.EmitCOFFSecRel32(Fn, /*Offset=*/0);
+  OS.AddComment("Thunk section index");
+  OS.EmitCOFFSectionIndex(Fn);
+  OS.AddComment("Code size");
+  OS.emitAbsoluteSymbolDiff(FI.End, Fn, 2);
+  OS.AddComment("Ordinal");
+  OS.EmitIntValue(unsigned(ordinal), 1);
+  OS.AddComment("Function name");
+  emitNullTerminatedSymbolName(OS, FuncName);
+  // Additional fields specific to the thunk ordinal would go here.
+  OS.EmitLabel(ThunkRecordEnd);
+
+  // Emit S_END
+  const unsigned RecordLengthForSymbolEnd = 2;
+  OS.AddComment("Record length");
+  OS.EmitIntValue(RecordLengthForSymbolEnd, 2);
+  OS.AddComment("Record kind: S_END");
+  OS.EmitIntValue(unsigned(SymbolKind::S_END), 2);
+
+  endCVSubsection(SymbolsEnd);
+}
+
 void CodeViewDebug::emitDebugInfoForFunction(const Function *GV,
                                              FunctionInfo &FI) {
   // For each function there is a separate subsection which holds the PC to
   // file:line table.
   const MCSymbol *Fn = Asm->getSymbol(GV);
   assert(Fn);
 
   // Switch to the to a comdat section, if appropriate.
   switchToDebugSectionForSymbol(Fn);
 
   std::string FuncName;
   auto *SP = GV->getSubprogram();
   assert(SP);
   setCurrentSubprogram(SP);
 
+  if (SP->isThunk()) {
+    emitDebugInfoForThunk(GV, FI, Fn);
+    return;
+  }
+
   // If we have a display name, build the fully qualified name by walking the
   // chain of scopes.
   if (!SP->getName().empty())
     FuncName =
         getFullyQualifiedName(SP->getScope().resolve(), SP->getName());
 
   // If our DISubprogram name is empty, use the mangled name.
   if (FuncName.empty())
void CodeViewDebug::endFunctionImpl(const MachineFunction *MF) {
   const Function &GV = MF->getFunction();
   assert(FnDebugInfo.count(&GV));
   assert(CurFn == &FnDebugInfo[&GV]);
 
   collectVariableInfo(GV.getSubprogram());
 
   // Don't emit anything if we don't have any line tables.
   if (!CurFn->HaveLineInfo) {
     FnDebugInfo.erase(&GV);
     CurFn = nullptr;
     return;
   }
 
   CurFn->Annotations = MF->getCodeViewAnnotations();
 
   CurFn->End = Asm->getFunctionEnd();
 

llvm/lib/DebugInfo/CodeView/SymbolDumper.cpp

Error CVSymbolDumperImpl::visitKnownRecord(CVSymbol &CVR, BlockSym &Block) {
   }
   W.printHex("Segment", Block.Segment);
   W.printString("BlockName", Block.Name);
   W.printString("LinkageName", LinkageName);
   return Error::success();
 }
 
 Error CVSymbolDumperImpl::visitKnownRecord(CVSymbol &CVR, Thunk32Sym &Thunk) {
+  W.printString("Name", Thunk.Name);
   W.printNumber("Parent", Thunk.Parent);
   W.printNumber("End", Thunk.End);
   W.printNumber("Next", Thunk.Next);
   W.printNumber("Off", Thunk.Offset);
   W.printNumber("Seg", Thunk.Segment);
   W.printNumber("Len", Thunk.Length);
   W.printEnum("Ordinal", uint8_t(Thunk.Thunk), getThunkOrdinalNames());
   return Error::success();

llvm/test/DebugInfo/COFF/thunk.ll

+; RUN: llc < %s -filetype=obj | llvm-readobj - -codeview | FileCheck %s
+; RUN: llc < %s | FileCheck %s --check-prefix=ASM
+; RUN: opt -S -debugger-tune=lldb %s | FileCheck -check-prefix=OPT %s
+;
+; -- "thunk.cpp" begin --------------------------------------------------------
+; class A { public: virtual bool MyMethod() { return true; } }; 
+; class B { public: virtual bool MyMethod() { return true; } }; 
+; class C : public virtual A, public virtual B { 
+; public: 
+;     virtual bool MyMethod() { return true; } 
+; }; 
+; 
+; int main() 
+; { 
+;     A* a = new C(); 
+;     B* b = new C(); 
+;     C* c = new C(); 
+;     a->MyMethod();
+;     b->MyMethod();
+;     c->MyMethod();
+;     return 0;
+; } 
+; -- "thunk.cpp" end ----------------------------------------------------------
+;
+; Build command:
+;   $ clang -S -emit-llvm -g -gcodeview thunk.cpp
+;
+; CHECK:       Thunk32Sym {
+; CHECK-NEXT:    Kind: S_THUNK32 ({{.*}})
+; CHECK-NEXT:    Name: {{.*MyMethod.*C.*}}
+; CHECK-NEXT:    Parent: 0
+; CHECK-NEXT:    End: 0
+; CHECK-NEXT:    Next: 0
+; CHECK-NEXT:    Off: 0
+; CHECK-NEXT:    Seg: 0
+; CHECK-NEXT:    Len: {{[0-9]+}}
+; CHECK-NEXT:    Ordinal: Standard (0x0)
+; CHECK-NEXT:  }
+; CHECK-NEXT:  ScopeEndSym {
+; CHECK-NEXT:    Kind: S_END ({{.*}})
+; CHECK-NEXT:  }
+
+;
+; ASM:          .long 241                     # Symbol subsection for ?MyMethod@C@@W7EAA_NXZ
+; ASM-NEXT:     .long {{.*}}                  # Subsection size
+; ASM-NEXT: {{\.L.*}}:
+; ASM-NEXT:   .short  [[END:.?L.*]]-[[BEGIN:.?L.*]] # Record length
+; ASM-NEXT: [[BEGIN]]:
+; ASM-NEXT:   .short  4354                    # Record kind: S_THUNK32
+; ASM-NEXT:   .long 0                       # PtrParent
+; ASM-NEXT:   .long 0                       # PtrEnd
+; ASM-NEXT:   .long 0                       # PtrNext
+; ASM-NEXT:   .secrel32 "{{.*MyMethod.*C.*}}" # Thunk section relative address
+; ASM-NEXT:   .secidx "{{.*MyMethod.*C.*}}" # Thunk section index
+; ASM-NEXT:   .short  .Lfunc_end{{.*}}-"{{.*MyMethod.*C.*}}" # Code size
+; ASM-NEXT:   .byte 0                       # Ordinal
+; ASM-NEXT:   .asciz  "{{.*MyMethod.*C.*}}" # Function name
+; ASM-NEXT: [[END]]:
+; ASM-NEXT:   .short  2                       # Record length
+; ASM-NEXT:   .short  6                       # Record kind: S_END
+;
+; OPT: DISubprogram(linkageName: "{{.*MyMethod.*C.*}}",{{.*}} line: 5,{{.*}} flags: DIFlagArtificial | DIFlagThunk{{.*}})
+;
+
+; ModuleID = 'thunk.cpp'
+source_filename = "thunk.cpp"
+target datalayout = "e-m:w-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-pc-windows-msvc19.0.24210"
+
+%rtti.CompleteObjectLocator = type { i32, i32, i32, i32, i32, i32 }
+%rtti.TypeDescriptor7 = type { i8**, i8*, [8 x i8] }
+%rtti.ClassHierarchyDescriptor = type { i32, i32, i32, i32 }
+%rtti.BaseClassDescriptor = type { i32, i32, i32, i32, i32, i32, i32 }
+%class.A = type { i32 (...)** }
+%class.B = type { i32 (...)** }
+%class.C = type { i32*, %class.A, %class.B }
+
+$"\01??0C@@QEAA@XZ" = comdat any
+
+$"\01??0A@@QEAA@XZ" = comdat any
+
+$"\01??0B@@QEAA@XZ" = comdat any
+
+$"\01?MyMethod@C@@UEAA_NXZ" = comdat any
+
+$"\01?MyMethod@C@@W7EAA_NXZ" = comdat any
+
+$"\01?MyMethod@A@@UEAA_NXZ" = comdat any
+
+$"\01?MyMethod@B@@UEAA_NXZ" = comdat any
+
+$"\01??_8C@@7B@" = comdat any
+
+$"\01??_7C@@6BA@@@" = comdat largest
+
+$"\01??_7C@@6BB@@@" = comdat largest
+
+$"\01??_R4C@@6BA@@@" = comdat any
+
+$"\01??_R0?AVC@@@8" = comdat any
+
+$"\01??_R3C@@8" = comdat any
+
+$"\01??_R2C@@8" = comdat any
+
+$"\01??_R1A@?0A@EA@C@@8" = comdat any
+
+$"\01??_R1A@A@3FA@A@@8" = comdat any
+
+$"\01??_R0?AVA@@@8" = comdat any
+
+$"\01??_R3A@@8" = comdat any
+
+$"\01??_R2A@@8" = comdat any
+
+$"\01??_R1A@?0A@EA@A@@8" = comdat any
+
+$"\01??_R1A@A@7FA@B@@8" = comdat any
+
+$"\01??_R0?AVB@@@8" = comdat any
+
+$"\01??_R3B@@8" = comdat any
+
+$"\01??_R2B@@8" = comdat any
+
+$"\01??_R1A@?0A@EA@B@@8" = comdat any
+
+$"\01??_R4C@@6BB@@@" = comdat any
+
+$"\01??_7A@@6B@" = comdat largest
+
+$"\01??_R4A@@6B@" = comdat any
+
+$"\01??_7B@@6B@" = comdat largest
+
+$"\01??_R4B@@6B@" = comdat any
+
+@"\01??_8C@@7B@" = linkonce_odr unnamed_addr constant [3 x i32] [i32 0, i32 8, i32 16], comdat
+@0 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"\01??_R4C@@6BA@@@" to i8*), i8* bitcast (i1 (i8*)* @"\01?MyMethod@C@@UEAA_NXZ" to i8*)] }, comdat($"\01??_7C@@6BA@@@")
+@1 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"\01??_R4C@@6BB@@@" to i8*), i8* bitcast (i1 (i8*)* @"\01?MyMethod@C@@W7EAA_NXZ" to i8*)] }, comdat($"\01??_7C@@6BB@@@")
+@"\01??_R4C@@6BA@@@" = linkonce_odr constant %rtti.CompleteObjectLocator { i32 1, i32 8, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVC@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3C@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.CompleteObjectLocator* @"\01??_R4C@@6BA@@@" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_7type_info@@6B@" = external constant i8*
+@"\01??_R0?AVC@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AVC@@\00" }, comdat
+@__ImageBase = external constant i8
+@"\01??_R3C@@8" = linkonce_odr constant %rtti.ClassHierarchyDescriptor { i32 0, i32 3, i32 3, i32 trunc (i64 sub nuw nsw (i64 ptrtoint ([4 x i32]* @"\01??_R2C@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R2C@@8" = linkonce_odr constant [4 x i32] [i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@?0A@EA@C@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@A@3FA@A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@A@7FA@B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0], comdat
+@"\01??_R1A@?0A@EA@C@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVC@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 2, i32 0, i32 -1, i32 0, i32 64, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3C@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R1A@A@3FA@A@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVA@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0, i32 0, i32 0, i32 4, i32 80, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R0?AVA@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AVA@@\00" }, comdat
+@"\01??_R3A@@8" = linkonce_odr constant %rtti.ClassHierarchyDescriptor { i32 0, i32 0, i32 1, i32 trunc (i64 sub nuw nsw (i64 ptrtoint ([2 x i32]* @"\01??_R2A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R2A@@8" = linkonce_odr constant [2 x i32] [i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@?0A@EA@A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0], comdat
+@"\01??_R1A@?0A@EA@A@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVA@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0, i32 0, i32 -1, i32 0, i32 64, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R1A@A@7FA@B@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVB@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0, i32 0, i32 0, i32 8, i32 80, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R0?AVB@@@8" = linkonce_odr global %rtti.TypeDescriptor7 { i8** @"\01??_7type_info@@6B@", i8* null, [8 x i8] c".?AVB@@\00" }, comdat
+@"\01??_R3B@@8" = linkonce_odr constant %rtti.ClassHierarchyDescriptor { i32 0, i32 0, i32 1, i32 trunc (i64 sub nuw nsw (i64 ptrtoint ([2 x i32]* @"\01??_R2B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R2B@@8" = linkonce_odr constant [2 x i32] [i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.BaseClassDescriptor* @"\01??_R1A@?0A@EA@B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0], comdat
+@"\01??_R1A@?0A@EA@B@@8" = linkonce_odr constant %rtti.BaseClassDescriptor { i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVB@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 0, i32 0, i32 -1, i32 0, i32 64, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@"\01??_R4C@@6BB@@@" = linkonce_odr constant %rtti.CompleteObjectLocator { i32 1, i32 16, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVC@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3C@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.CompleteObjectLocator* @"\01??_R4C@@6BB@@@" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@2 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"\01??_R4A@@6B@" to i8*), i8* bitcast (i1 (%class.A*)* @"\01?MyMethod@A@@UEAA_NXZ" to i8*)] }, comdat($"\01??_7A@@6B@")
+@"\01??_R4A@@6B@" = linkonce_odr constant %rtti.CompleteObjectLocator { i32 1, i32 0, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVA@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3A@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.CompleteObjectLocator* @"\01??_R4A@@6B@" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+@3 = private unnamed_addr constant { [2 x i8*] } { [2 x i8*] [i8* bitcast (%rtti.CompleteObjectLocator* @"\01??_R4B@@6B@" to i8*), i8* bitcast (i1 (%class.B*)* @"\01?MyMethod@B@@UEAA_NXZ" to i8*)] }, comdat($"\01??_7B@@6B@")
+@"\01??_R4B@@6B@" = linkonce_odr constant %rtti.CompleteObjectLocator { i32 1, i32 0, i32 0, i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.TypeDescriptor7* @"\01??_R0?AVB@@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.ClassHierarchyDescriptor* @"\01??_R3B@@8" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32), i32 trunc (i64 sub nuw nsw (i64 ptrtoint (%rtti.CompleteObjectLocator* @"\01??_R4B@@6B@" to i64), i64 ptrtoint (i8* @__ImageBase to i64)) to i32) }, comdat
+
+@"\01??_7C@@6BA@@@" = unnamed_addr alias i8*, getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @0, i32 0, i32 0, i32 1)
+@"\01??_7C@@6BB@@@" = unnamed_addr alias i8*, getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @1, i32 0, i32 0, i32 1)
+@"\01??_7A@@6B@" = unnamed_addr alias i8*, getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @2, i32 0, i32 0, i32 1)
+@"\01??_7B@@6B@" = unnamed_addr alias i8*, getelementptr inbounds ({ [2 x i8*] }, { [2 x i8*] }* @3, i32 0, i32 0, i32 1)
+
+; Function Attrs: noinline norecurse uwtable
+define i32 @main() #0 !dbg !7 {
+entry:
+  %retval = alloca i32, align 4
+  %a = alloca %class.A*, align 8
+  %b = alloca %class.B*, align 8
+  %c = alloca %class.C*, align 8
+  store i32 0, i32* %retval, align 4
+  call void @llvm.dbg.declare(metadata %class.A** %a, metadata !11, metadata !23), !dbg !24
+  %call = call i8* @"\01??2@YAPEAX_K@Z"(i64 24) #6, !dbg !25
+  %0 = bitcast i8* %call to %class.C*, !dbg !25
+  %1 = bitcast %class.C* %0 to i8*, !dbg !26
+  call void @llvm.memset.p0i8.i64(i8* %1, i8 0, i64 24, i32 8, i1 false), !dbg !26
+  %call1 = call %class.C* @"\01??0C@@QEAA@XZ"(%class.C* %0, i32 1) #7, !dbg !27
+  %2 = icmp eq %class.C* %0, null, !dbg !25
+  br i1 %2, label %cast.end, label %cast.notnull, !dbg !25
+
+cast.notnull:                                     ; preds = %entry
+  %3 = bitcast %class.C* %0 to i8*, !dbg !29
+  %vbptr = getelementptr inbounds i8, i8* %3, i64 0, !dbg !29
+  %4 = bitcast i8* %vbptr to i32**, !dbg !29
+  %vbtable = load i32*, i32** %4, align 8, !dbg !29
+  %5 = getelementptr inbounds i32, i32* %vbtable, i32 1, !dbg !29
+  %vbase_offs = load i32, i32* %5, align 4, !dbg !29
+  %6 = sext i32 %vbase_offs to i64, !dbg !29
+  %7 = add nsw i64 0, %6, !dbg !29
+  %8 = bitcast %class.C* %0 to i8*, !dbg !29
+  %add.ptr = getelementptr inbounds i8, i8* %8, i64 %7, !dbg !29
+  %9 = bitcast i8* %add.ptr to %class.A*, !dbg !29
+  br label %cast.end, !dbg !29
+
+cast.end:                                         ; preds = %cast.notnull, %entry
+  %cast.result = phi %class.A* [ %9, %cast.notnull ], [ null, %entry ], !dbg !31
+  store %class.A* %cast.result, %class.A** %a, align 8, !dbg !33
+  call void @llvm.dbg.declare(metadata %class.B** %b, metadata !34, metadata !23), !dbg !43
+  %call2 = call i8* @"\01??2@YAPEAX_K@Z"(i64 24) #6, !dbg !44
+  %10 = bitcast i8* %call2 to %class.C*, !dbg !44
+  %11 = bitcast %class.C* %10 to i8*, !dbg !45
+  call void @llvm.memset.p0i8.i64(i8* %11, i8 0, i64 24, i32 8, i1 false), !dbg !45
+  %call3 = call %class.C* @"\01??0C@@QEAA@XZ"(%class.C* %10, i32 1) #7, !dbg !46
+  %12 = icmp eq %class.C* %10, null, !dbg !44
+  br i1 %12, label %cast.end9, label %cast.notnull4, !dbg !44
+
+cast.notnull4:                                    ; preds = %cast.end
+  %13 = bitcast %class.C* %10 to i8*, !dbg !47
+  %vbptr5 = getelementptr inbounds i8, i8* %13, i64 0, !dbg !47
+  %14 = bitcast i8* %vbptr5 to i32**, !dbg !47
+  %vbtable6 = load i32*, i32** %14, align 8, !dbg !47
+  %15 = getelementptr inbounds i32, i32* %vbtable6, i32 2, !dbg !47
+  %vbase_offs7 = load i32, i32* %15, align 4, !dbg !47
+  %16 = sext i32 %vbase_offs7 to i64, !dbg !47
+  %17 = add nsw i64 0, %16, !dbg !47
+  %18 = bitcast %class.C* %10 to i8*, !dbg !47
+  %add.ptr8 = getelementptr inbounds i8, i8* %18, i64 %17, !dbg !47
+  %19 = bitcast i8* %add.ptr8 to %class.B*, !dbg !47
+  br label %cast.end9, !dbg !47
+
+cast.end9:                                        ; preds = %cast.notnull4, %cast.end
+  %cast.result10 = phi %class.B* [ %19, %cast.notnull4 ], [ null, %cast.end ], !dbg !48
+  store %class.B* %cast.result10, %class.B** %b, align 8, !dbg !49
+  call void @llvm.dbg.declare(metadata %class.C** %c, metadata !50, metadata !23), !dbg !60
+  %call11 = call i8* @"\01??2@YAPEAX_K@Z"(i64 24) #6, !dbg !61
+  %20 = bitcast i8* %call11 to %class.C*, !dbg !61
+  %21 = bitcast %class.C* %20 to i8*, !dbg !62
+  call void @llvm.memset.p0i8.i64(i8* %21, i8 0, i64 24, i32 8, i1 false), !dbg !62
+  %call12 = call %class.C* @"\01??0C@@QEAA@XZ"(%class.C* %20, i32 1) #7, !dbg !63
+  store %class.C* %20, %class.C** %c, align 8, !dbg !60
+  %22 = load %class.A*, %class.A** %a, align 8, !dbg !64
+  %23 = bitcast %class.A* %22 to i1 (%class.A*)***, !dbg !65
+  %vtable = load i1 (%class.A*)**, i1 (%class.A*)*** %23, align 8, !dbg !65
+  %vfn = getelementptr inbounds i1 (%class.A*)*, i1 (%class.A*)** %vtable, i64 0, !dbg !65
+  %24 = load i1 (%class.A*)*, i1 (%class.A*)** %vfn, align 8, !dbg !65
+  %call13 = call zeroext i1 %24(%class.A* %22), !dbg !65
+  %25 = load %class.B*, %class.B** %b, align 8, !dbg !66
+  %26 = bitcast %class.B* %25 to i1 (%class.B*)***, !dbg !67
+  %vtable14 = load i1 (%class.B*)**, i1 (%class.B*)*** %26, align 8, !dbg !67
+  %vfn15 = getelementptr inbounds i1 (%class.B*)*, i1 (%class.B*)** %vtable14, i64 0, !dbg !67
+  %27 = load i1 (%class.B*)*, i1 (%class.B*)** %vfn15, align 8, !dbg !67
+  %call16 = call zeroext i1 %27(%class.B* %25), !dbg !67
+  %28 = load %class.C*, %class.C** %c, align 8, !dbg !68
+  %29 = bitcast %class.C* %28 to i8*, !dbg !69
+  %vbptr17 = getelementptr inbounds i8, i8* %29, i64 0, !dbg !69
+  %30 = bitcast i8* %vbptr17 to i32**, !dbg !69
+  %vbtable18 = load i32*, i32** %30, align 8, !dbg !69
+  %31 = getelementptr inbounds i32, i32* %vbtable18, i32 1, !dbg !69
+  %vbase_offs19 = load i32, i32* %31, align 4, !dbg !69
+  %32 = sext i32 %vbase_offs19 to i64, !dbg !69
+  %33 = add nsw i64 0, %32, !dbg !69
+  %34 = getelementptr inbounds i8, i8* %29, i64 %33, !dbg !69
+  %35 = bitcast i8* %34 to i1 (i8*)***, !dbg !69
+  %vtable20 = load i1 (i8*)**, i1 (i8*)*** %35, align 8, !dbg !69
+  %vfn21 = getelementptr inbounds i1 (i8*)*, i1 (i8*)** %vtable20, i64 0, !dbg !69
+  %36 = load i1 (i8*)*, i1 (i8*)** %vfn21, align 8, !dbg !69
+  %37 = bitcast %class.C* %28 to i8*, !dbg !69
+  %vbptr22 = getelementptr inbounds i8, i8* %37, i64 0, !dbg !69
+  %38 = bitcast i8* %vbptr22 to i32**, !dbg !69
+  %vbtable23 = load i32*, i32** %38, align 8, !dbg !69
+  %39 = getelementptr inbounds i32, i32* %vbtable23, i32 1, !dbg !69
+  %vbase_offs24 = load i32, i32* %39, align 4, !dbg !69
+  %40 = sext i32 %vbase_offs24 to i64, !dbg !69
+  %41 = add nsw i64 0, %40, !dbg !69
+  %42 = getelementptr inbounds i8, i8* %37, i64 %41, !dbg !69
+  %call25 = call zeroext i1 %36(i8* %42), !dbg !69
+  ret i32 0, !dbg !70
+}
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
+
+; Function Attrs: nobuiltin
+declare noalias i8* @"\01??2@YAPEAX_K@Z"(i64) #2
+
+; Function Attrs: argmemonly nounwind
+declare void @llvm.memset.p0i8.i64(i8* nocapture writeonly, i8, i64, i32, i1) #3
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr %class.C* @"\01??0C@@QEAA@XZ"(%class.C* returned %this, i32 %is_most_derived) unnamed_addr #4 comdat align 2 !dbg !71 {
+entry:
+  %retval = alloca %class.C*, align 8
+  %is_most_derived.addr = alloca i32, align 4
+  %this.addr = alloca %class.C*, align 8
+  store i32 %is_most_derived, i32* %is_most_derived.addr, align 4
+  call void @llvm.dbg.declare(metadata i32* %is_most_derived.addr, metadata !75, metadata !23), !dbg !76
+  store %class.C* %this, %class.C** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.C** %this.addr, metadata !77, metadata !23), !dbg !76
+  %this1 = load %class.C*, %class.C** %this.addr, align 8
+  store %class.C* %this1, %class.C** %retval, align 8
+  %is_most_derived2 = load i32, i32* %is_most_derived.addr, align 4
+  %is_complete_object = icmp ne i32 %is_most_derived2, 0, !dbg !78
+  br i1 %is_complete_object, label %ctor.init_vbases, label %ctor.skip_vbases, !dbg !78
+
+ctor.init_vbases:                                 ; preds = %entry
+  %this.int8 = bitcast %class.C* %this1 to i8*, !dbg !79
+  %0 = getelementptr inbounds i8, i8* %this.int8, i64 0, !dbg !79
+  %vbptr.C = bitcast i8* %0 to i32**, !dbg !79
+  store i32* getelementptr inbounds ([3 x i32], [3 x i32]* @"\01??_8C@@7B@", i32 0, i32 0), i32** %vbptr.C, align 8, !dbg !79
+  %1 = bitcast %class.C* %this1 to i8*, !dbg !79
+  %2 = getelementptr inbounds i8, i8* %1, i64 8, !dbg !79
+  %3 = bitcast i8* %2 to %class.A*, !dbg !79
+  %call = call %class.A* @"\01??0A@@QEAA@XZ"(%class.A* %3) #7, !dbg !79
+  %4 = bitcast %class.C* %this1 to i8*, !dbg !79
+  %5 = getelementptr inbounds i8, i8* %4, i64 16, !dbg !79
+  %6 = bitcast i8* %5 to %class.B*, !dbg !79
+  %call3 = call %class.B* @"\01??0B@@QEAA@XZ"(%class.B* %6) #7, !dbg !81
+  br label %ctor.skip_vbases, !dbg !79
+
+ctor.skip_vbases:                                 ; preds = %ctor.init_vbases, %entry
+  %7 = bitcast %class.C* %this1 to i8*, !dbg !83
+  %vbptr = getelementptr inbounds i8, i8* %7, i64 0, !dbg !83
+  %8 = bitcast i8* %vbptr to i32**, !dbg !83
+  %vbtable = load i32*, i32** %8, align 8, !dbg !83
+  %9 = getelementptr inbounds i32, i32* %vbtable, i32 1, !dbg !83
+  %vbase_offs = load i32, i32* %9, align 4, !dbg !83
+  %10 = sext i32 %vbase_offs to i64, !dbg !83
+  %11 = add nsw i64 0, %10, !dbg !83
+  %12 = bitcast %class.C* %this1 to i8*, !dbg !83
+  %add.ptr = getelementptr inbounds i8, i8* %12, i64 %11, !dbg !83
+  %13 = bitcast i8* %add.ptr to i32 (...)***, !dbg !83
+  store i32 (...)** bitcast (i8** @"\01??_7C@@6BA@@@" to i32 (...)**), i32 (...)*** %13, align 8, !dbg !83
+  %14 = bitcast %class.C* %this1 to i8*, !dbg !83
+  %vbptr4 = getelementptr inbounds i8, i8* %14, i64 0, !dbg !83
+  %15 = bitcast i8* %vbptr4 to i32**, !dbg !83
+  %vbtable5 = load i32*, i32** %15, align 8, !dbg !83
+  %16 = getelementptr inbounds i32, i32* %vbtable5, i32 2, !dbg !83
+  %vbase_offs6 = load i32, i32* %16, align 4, !dbg !83
+  %17 = sext i32 %vbase_offs6 to i64, !dbg !83
+  %18 = add nsw i64 0, %17, !dbg !83
+  %19 = bitcast %class.C* %this1 to i8*, !dbg !83
+  %add.ptr7 = getelementptr inbounds i8, i8* %19, i64 %18, !dbg !83
+  %20 = bitcast i8* %add.ptr7 to i32 (...)***, !dbg !83
+  store i32 (...)** bitcast (i8** @"\01??_7C@@6BB@@@" to i32 (...)**), i32 (...)*** %20, align 8, !dbg !83
+  %21 = load %class.C*, %class.C** %retval, align 8, !dbg !83
+  ret %class.C* %21, !dbg !83
+}
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr %class.A* @"\01??0A@@QEAA@XZ"(%class.A* returned %this) unnamed_addr #4 comdat align 2 !dbg !85 {
+entry:
+  %this.addr = alloca %class.A*, align 8
+  store %class.A* %this, %class.A** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.A** %this.addr, metadata !89, metadata !23), !dbg !90
+  %this1 = load %class.A*, %class.A** %this.addr, align 8
+  %0 = bitcast %class.A* %this1 to i32 (...)***, !dbg !91
+  store i32 (...)** bitcast (i8** @"\01??_7A@@6B@" to i32 (...)**), i32 (...)*** %0, align 8, !dbg !91
+  ret %class.A* %this1, !dbg !91
+}
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr %class.B* @"\01??0B@@QEAA@XZ"(%class.B* returned %this) unnamed_addr #4 comdat align 2 !dbg !92 {
+entry:
+  %this.addr = alloca %class.B*, align 8
+  store %class.B* %this, %class.B** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.B** %this.addr, metadata !96, metadata !23), !dbg !97
+  %this1 = load %class.B*, %class.B** %this.addr, align 8
+  %0 = bitcast %class.B* %this1 to i32 (...)***, !dbg !98
+  store i32 (...)** bitcast (i8** @"\01??_7B@@6B@" to i32 (...)**), i32 (...)*** %0, align 8, !dbg !98
+  ret %class.B* %this1, !dbg !98
+}
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr zeroext i1 @"\01?MyMethod@C@@UEAA_NXZ"(i8*) unnamed_addr #4 comdat align 2 !dbg !99 {
+entry:
+  %this.addr = alloca %class.C*, align 8
+  %this = bitcast i8* %0 to %class.C*
+  %1 = bitcast %class.C* %this to i8*
+  %2 = getelementptr inbounds i8, i8* %1, i32 -8
+  %3 = bitcast i8* %2 to %class.C*
+  store %class.C* %3, %class.C** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.C** %this.addr, metadata !100, metadata !23), !dbg !101
+  %this1 = load %class.C*, %class.C** %this.addr, align 8
+  ret i1 true, !dbg !102
+}
+
+; Function Attrs: noinline uwtable
+define linkonce_odr zeroext i1 @"\01?MyMethod@C@@W7EAA_NXZ"(i8*) unnamed_addr #5 comdat align 2 !dbg !103 {
+entry:
+  %this.addr = alloca %class.C*, align 8
+  %this = bitcast i8* %0 to %class.C*
+  store %class.C* %this, %class.C** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.C** %this.addr, metadata !105, metadata !23), !dbg !106
+  %this1 = load %class.C*, %class.C** %this.addr, align 8, !dbg !106
+  %1 = bitcast %class.C* %this1 to i8*, !dbg !106
+  %2 = getelementptr i8, i8* %1, i32 -8, !dbg !106
+  %call = tail call zeroext i1 @"\01?MyMethod@C@@UEAA_NXZ"(i8* %2), !dbg !106
+  ret i1 %call, !dbg !106
+}
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr zeroext i1 @"\01?MyMethod@A@@UEAA_NXZ"(%class.A* %this) unnamed_addr #4 comdat align 2 !dbg !107 {
+entry:
+  %this.addr = alloca %class.A*, align 8
+  store %class.A* %this, %class.A** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.A** %this.addr, metadata !108, metadata !23), !dbg !109
+  %this1 = load %class.A*, %class.A** %this.addr, align 8
+  ret i1 true, !dbg !110
+}
+
+; Function Attrs: noinline nounwind uwtable
+define linkonce_odr zeroext i1 @"\01?MyMethod@B@@UEAA_NXZ"(%class.B* %this) unnamed_addr #4 comdat align 2 !dbg !111 {
+entry:
+  %this.addr = alloca %class.B*, align 8
+  store %class.B* %this, %class.B** %this.addr, align 8
+  call void @llvm.dbg.declare(metadata %class.B** %this.addr, metadata !112, metadata !23), !dbg !113
+  %this1 = load %class.B*, %class.B** %this.addr, align 8
+  ret i1 true, !dbg !114
+}
+
+attributes #0 = { noinline norecurse uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { nounwind readnone }
+attributes #2 = { nobuiltin "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #3 = { argmemonly nounwind }
+attributes #4 = { noinline nounwind uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #5 = { noinline uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #6 = { builtin }
+attributes #7 = { nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, producer: "clang version 5.0.0", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "thunk.cpp", directory: "C:/path/to/directory", checksumkind: CSK_MD5, checksum: "f5c2ef3ded84645a49347c61948c7970")
+!2 = !{}
+!3 = !{i32 2, !"CodeView", i32 1}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"PIC Level", i32 2}
+!6 = !{!"clang version 5.0.0"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 8, type: !8, isLocal: false, isDefinition: true, scopeLine: 9, flags: DIFlagPrototyped, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocalVariable(name: "a", scope: !7, file: !1, line: 10, type: !12)
+!12 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64)
+!13 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "A", file: !1, line: 1, size: 64, elements: !14, vtableHolder: !13, identifier: ".?AVA@@")
+!14 = !{!15, !16, !18}
+!15 = !DIDerivedType(tag: DW_TAG_pointer_type, name: "__vtbl_ptr_type", baseType: null, size: 64)
+!16 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$A", scope: !1, file: !1, baseType: !17, size: 64, flags: DIFlagArtificial)
+!17 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !15, size: 64)
+!18 = !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@A@@UEAA_NXZ", scope: !13, file: !1, line: 1, type: !19, isLocal: false, isDefinition: false, scopeLine: 1, containingType: !13, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPublic | DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: false)
+!19 = !DISubroutineType(types: !20)
+!20 = !{!21, !22}
+!21 = !DIBasicType(name: "bool", size: 8, encoding: DW_ATE_boolean)
+!22 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !13, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!23 = !DIExpression()
+!24 = !DILocation(line: 10, column: 8, scope: !7)
+!25 = !DILocation(line: 10, column: 12, scope: !7)
+!26 = !DILocation(line: 10, column: 16, scope: !7)
+!27 = !DILocation(line: 10, column: 16, scope: !28)
+!28 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 6)
+!29 = !DILocation(line: 10, column: 12, scope: !30)
+!30 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 2)
+!31 = !DILocation(line: 10, column: 12, scope: !32)
+!32 = !DILexicalBlockFile(scope: !7, file: !1, discriminator: 4)
+!33 = !DILocation(line: 10, column: 8, scope: !32)
+!34 = !DILocalVariable(name: "b", scope: !7, file: !1, line: 11, type: !35)
+!35 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !36, size: 64)
+!36 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "B", file: !1, line: 2, size: 64, elements: !37, vtableHolder: !36, identifier: ".?AVB@@")
+!37 = !{!15, !38, !39}
+!38 = !DIDerivedType(tag: DW_TAG_member, name: "_vptr$B", scope: !1, file: !1, baseType: !17, size: 64, flags: DIFlagArtificial)
+!39 = !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@B@@UEAA_NXZ", scope: !36, file: !1, line: 2, type: !40, isLocal: false, isDefinition: false, scopeLine: 2, containingType: !36, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, flags: DIFlagPublic | DIFlagPrototyped | DIFlagIntroducedVirtual, isOptimized: false)
+!40 = !DISubroutineType(types: !41)
+!41 = !{!21, !42}
+!42 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !36, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!43 = !DILocation(line: 11, column: 8, scope: !7)
+!44 = !DILocation(line: 11, column: 12, scope: !7)
+!45 = !DILocation(line: 11, column: 16, scope: !7)
+!46 = !DILocation(line: 11, column: 16, scope: !28)
+!47 = !DILocation(line: 11, column: 12, scope: !30)
+!48 = !DILocation(line: 11, column: 12, scope: !32)
+!49 = !DILocation(line: 11, column: 8, scope: !32)
+!50 = !DILocalVariable(name: "c", scope: !7, file: !1, line: 12, type: !51)
+!51 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !52, size: 64)
+!52 = distinct !DICompositeType(tag: DW_TAG_class_type, name: "C", file: !1, line: 3, size: 192, elements: !53, vtableHolder: !52, identifier: ".?AVC@@")
+!53 = !{!54, !55, !56}
+!54 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !52, baseType: !13, offset: 4, flags: DIFlagPublic | DIFlagVirtual)
+!55 = !DIDerivedType(tag: DW_TAG_inheritance, scope: !52, baseType: !36, offset: 8, flags: DIFlagPublic | DIFlagVirtual)
+!56 = !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@C@@UEAA_NXZ", scope: !52, file: !1, line: 5, type: !57, isLocal: false, isDefinition: false, scopeLine: 5, containingType: !52, virtuality: DW_VIRTUALITY_virtual, virtualIndex: 0, thisAdjustment: 8, flags: DIFlagPublic | DIFlagPrototyped, isOptimized: false)
+!57 = !DISubroutineType(types: !58)
+!58 = !{!21, !59}
+!59 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !52, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!60 = !DILocation(line: 12, column: 8, scope: !7)
+!61 = !DILocation(line: 12, column: 12, scope: !7)
+!62 = !DILocation(line: 12, column: 16, scope: !7)
+!63 = !DILocation(line: 12, column: 16, scope: !30)
+!64 = !DILocation(line: 13, column: 5, scope: !7)
+!65 = !DILocation(line: 13, column: 8, scope: !7)
+!66 = !DILocation(line: 14, column: 5, scope: !7)
+!67 = !DILocation(line: 14, column: 8, scope: !7)
+!68 = !DILocation(line: 15, column: 5, scope: !7)
+!69 = !DILocation(line: 15, column: 8, scope: !7)
+!70 = !DILocation(line: 16, column: 5, scope: !7)
+!71 = distinct !DISubprogram(name: "C", linkageName: "\01??0C@@QEAA@XZ", scope: !52, file: !1, line: 3, type: !72, isLocal: false, isDefinition: true, scopeLine: 3, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !74, variables: !2)
+!72 = !DISubroutineType(types: !73)
+!73 = !{null, !59}
+!74 = !DISubprogram(name: "C", scope: !52, type: !72, isLocal: false, isDefinition: false, flags: DIFlagPublic | DIFlagArtificial | DIFlagPrototyped, isOptimized: false)
+!75 = !DILocalVariable(name: "is_most_derived", arg: 2, scope: !71, type: !10, flags: DIFlagArtificial)
+!76 = !DILocation(line: 0, scope: !71)
+!77 = !DILocalVariable(name: "this", arg: 1, scope: !71, type: !51, flags: DIFlagArtificial | DIFlagObjectPointer)
+!78 = !DILocation(line: 3, column: 7, scope: !71)
+!79 = !DILocation(line: 3, column: 7, scope: !80)
+!80 = !DILexicalBlockFile(scope: !71, file: !1, discriminator: 2)
+!81 = !DILocation(line: 3, column: 7, scope: !82)
+!82 = !DILexicalBlockFile(scope: !71, file: !1, discriminator: 6)
+!83 = !DILocation(line: 3, column: 7, scope: !84)
+!84 = !DILexicalBlockFile(scope: !71, file: !1, discriminator: 4)
+!85 = distinct !DISubprogram(name: "A", linkageName: "\01??0A@@QEAA@XZ", scope: !13, file: !1, line: 1, type: !86, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !88, variables: !2)
+!86 = !DISubroutineType(types: !87)
+!87 = !{null, !22}
+!88 = !DISubprogram(name: "A", scope: !13, type: !86, isLocal: false, isDefinition: false, flags: DIFlagPublic | DIFlagArtificial | DIFlagPrototyped, isOptimized: false)
+!89 = !DILocalVariable(name: "this", arg: 1, scope: !85, type: !12, flags: DIFlagArtificial | DIFlagObjectPointer)
+!90 = !DILocation(line: 0, scope: !85)
+!91 = !DILocation(line: 1, column: 7, scope: !85)
+!92 = distinct !DISubprogram(name: "B", linkageName: "\01??0B@@QEAA@XZ", scope: !36, file: !1, line: 2, type: !93, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagArtificial | DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !95, variables: !2)
+!93 = !DISubroutineType(types: !94)
+!94 = !{null, !42}
+!95 = !DISubprogram(name: "B", scope: !36, type: !93, isLocal: false, isDefinition: false, flags: DIFlagPublic | DIFlagArtificial | DIFlagPrototyped, isOptimized: false)
+!96 = !DILocalVariable(name: "this", arg: 1, scope: !92, type: !35, flags: DIFlagArtificial | DIFlagObjectPointer)
+!97 = !DILocation(line: 0, scope: !92)
+!98 = !DILocation(line: 2, column: 7, scope: !92)
+!99 = distinct !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@C@@UEAA_NXZ", scope: !52, file: !1, line: 5, type: !57, isLocal: false, isDefinition: true, scopeLine: 5, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !56, variables: !2)
+!100 = !DILocalVariable(name: "this", arg: 1, scope: !99, type: !51, flags: DIFlagArtificial | DIFlagObjectPointer)
+!101 = !DILocation(line: 0, scope: !99)
+!102 = !DILocation(line: 5, column: 31, scope: !99)
+!103 = distinct !DISubprogram(linkageName: "\01?MyMethod@C@@W7EAA_NXZ", scope: !1, file: !1, line: 5, type: !104, isLocal: false, isDefinition: true, flags: DIFlagArtificial | DIFlagThunk, isOptimized: false, unit: !0, variables: !2)
+!104 = !DISubroutineType(types: !2)
+!105 = !DILocalVariable(name: "this", arg: 1, scope: !103, type: !51, flags: DIFlagArtificial | DIFlagObjectPointer)
+!106 = !DILocation(line: 0, scope: !103)
+!107 = distinct !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@A@@UEAA_NXZ", scope: !13, file: !1, line: 1, type: !19, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !18, variables: !2)
+!108 = !DILocalVariable(name: "this", arg: 1, scope: !107, type: !12, flags: DIFlagArtificial | DIFlagObjectPointer)
+!109 = !DILocation(line: 0, scope: !107)
+!110 = !DILocation(line: 1, column: 45, scope: !107)
+!111 = distinct !DISubprogram(name: "MyMethod", linkageName: "\01?MyMethod@B@@UEAA_NXZ", scope: !36, file: !1, line: 2, type: !40, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !0, declaration: !39, variables: !2)
+!112 = !DILocalVariable(name: "this", arg: 1, scope: !111, type: !35, flags: DIFlagArtificial | DIFlagObjectPointer)
+!113 = !DILocation(line: 0, scope: !111)
+!114 = !DILocation(line: 2, column: 45, scope: !111)
+

llvm/tools/clang/lib/CodeGen/CGDebugInfo.h

public:
   void EmitLocation(CGBuilderTy &Builder, SourceLocation Loc);
 
   /// Emit a call to llvm.dbg.function.start to indicate
   /// start of a new function.
   /// \param Loc       The location of the function header.
   /// \param ScopeLoc  The location of the function body.
   void EmitFunctionStart(GlobalDecl GD, SourceLocation Loc,
                          SourceLocation ScopeLoc, QualType FnType,
-                         llvm::Function *Fn, CGBuilderTy &Builder);
+                         llvm::Function *Fn, bool CurFnIsThunk,
+                         CGBuilderTy &Builder);
 
   /// Start a new scope for an inlined function.
   void EmitInlineFunctionStart(CGBuilderTy &Builder, GlobalDecl GD);
   /// End an inlined function scope.
   void EmitInlineFunctionEnd(CGBuilderTy &Builder);
 
   /// Emit debug info for a function declaration.
   void EmitFunctionDecl(GlobalDecl GD, SourceLocation Loc, QualType FnType);

llvm/tools/clang/lib/CodeGen/CGDebugInfo.cpp

if (FD->isVariadic()) {
                                            getDwarfCC(CC));
     }
 
   return cast<llvm::DISubroutineType>(getOrCreateType(FnType, F));
 }
 
 void CGDebugInfo::EmitFunctionStart(GlobalDecl GD, SourceLocation Loc,
                                     SourceLocation ScopeLoc, QualType FnType,
-                                    llvm::Function *Fn, CGBuilderTy &Builder) {
+                                    llvm::Function *Fn, bool CurFuncIsThunk,
+                                    CGBuilderTy &Builder) {
 
   StringRef Name;
   StringRef LinkageName;
 
   FnBeginRegionCount.push_back(LexicalBlockStack.size());
 
   const Decl *D = GD.getDecl();
   bool HasDecl = (D != nullptr);
void CGDebugInfo::EmitFunctionStart(GlobalDecl GD, SourceLocation Loc,
   if (Name.startswith("\01"))
     Name = Name.substr(1);
 
   if (!HasDecl || D->isImplicit() || D->hasAttr<ArtificialAttr>()) {
     Flags |= llvm::DINode::FlagArtificial;
     // Artificial functions should not silently reuse CurLoc.
     CurLoc = SourceLocation();
   }
+
+  if (CurFuncIsThunk)
+    Flags |= llvm::DINode::FlagThunk;
+
   unsigned LineNo = getLineNumber(Loc);
   unsigned ScopeLine = getLineNumber(ScopeLoc);
 
   // FIXME: The function declaration we're constructing here is mostly reusing
   // declarations from CXXMethodDecl and not constructing new ones for arbitrary
   // FunctionDecls. When/if we fix this we can have FDContext be TheCU/null for
   // all subprograms instead of the actual context since subprogram definitions
   // are emitted as CU level entities by the backend.

llvm/tools/clang/lib/CodeGen/CodeGenFunction.cpp

if (CGDebugInfo *DI = getDebugInfo()) {
     if (auto *FD = dyn_cast_or_null<FunctionDecl>(D))
       if (const auto *SrcFnTy = FD->getType()->getAs<FunctionType>())
         CC = SrcFnTy->getCallConv();
     SmallVector<QualType, 16> ArgTypes;
     for (const VarDecl *VD : Args)
       ArgTypes.push_back(VD->getType());
     QualType FnType = getContext().getFunctionType(
         RetTy, ArgTypes, FunctionProtoType::ExtProtoInfo(CC));
-    DI->EmitFunctionStart(GD, Loc, StartLoc, FnType, CurFn, Builder);
+    DI->EmitFunctionStart(GD, Loc, StartLoc, FnType, CurFn, CurFuncIsThunk,
+                          Builder);
   }
 
   if (ShouldInstrumentFunction()) {
     if (CGM.getCodeGenOpts().InstrumentFunctions)
       CurFn->addFnAttr("instrument-function-entry", "__cyg_profile_func_enter");
     if (CGM.getCodeGenOpts().InstrumentFunctionsAfterInlining)
       CurFn->addFnAttr("instrument-function-entry-inlined",
                        "__cyg_profile_func_enter");