XCore target: Add TypeString meta data to IR output.

This includes the addition of the virtual function:
	TargetCodeGenInfo::EmitTargetMD()

llvm-svn: 207832

3 files changed, 551 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ac97bdac601..11f69cc0fce 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1463,6 +1463,8 @@ CodeGenModule::GetOrCreateLLVMFunction(StringRef MangledName,
     }
   }
 
+  getTargetCodeGenInfo().emitTargetMD(D, F, *this);
+
   // Make sure the result is of the requested type.
   if (!IsIncompleteFunction) {
     assert(F->getType()->getElementType() == Ty);
@@ -1616,6 +1618,8 @@ CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName,
       isExternallyVisible(D->getLinkageAndVisibility().getLinkage()))
     GV->setSection(".cp.rodata");
 
+  getTargetCodeGenInfo().emitTargetMD(D, GV, *this);
+
   return GV;
 }
 
diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 5ad940d157b..b283ccbaba5 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -23,6 +23,9 @@
 #include "llvm/IR/DataLayout.h"
 #include "llvm/IR/Type.h"
 #include "llvm/Support/raw_ostream.h"
+
+#include <algorithm>    // std::sort
+
 using namespace clang;
 using namespace CodeGen;
 
@@ -6105,7 +6108,100 @@ SparcV9TargetCodeGenInfo::initDwarfEHRegSizeTable(CodeGen::CodeGenFunction &CGF,
 //===----------------------------------------------------------------------===//
 // XCore ABI Implementation
 //===----------------------------------------------------------------------===//
+
 namespace {
+
+/// A SmallStringEnc instance is used to build up the TypeString by passing
+/// it by reference between functions that append to it.
+typedef llvm::SmallString<128> SmallStringEnc;
+
+/// TypeStringCache caches the meta encodings of Types.
+///
+/// The reason for caching TypeStrings is two fold:
+///   1. To cache a type's encoding for later uses;
+///   2. As a means to break recursive member type inclusion.
+///
+/// A cache Entry can have a Status of:
+///   NonRecursive:   The type encoding is not recursive;
+///   Recursive:      The type encoding is recursive;
+///   Incomplete:     An incomplete TypeString;
+///   IncompleteUsed: An incomplete TypeString that has been used in a
+///                   Recursive type encoding.
+///
+/// A NonRecursive entry will have all of its sub-members expanded as fully
+/// as possible. Whilst it may contain types which are recursive, the type
+/// itself is not recursive and thus its encoding may be safely used whenever
+/// the type is encountered.
+///
+/// A Recursive entry will have all of its sub-members expanded as fully as
+/// possible. The type itself is recursive and it may contain other types which
+/// are recursive. The Recursive encoding must not be used during the expansion
+/// of a recursive type's recursive branch. For simplicity the code uses
+/// IncompleteCount to reject all usage of Recursive encodings for member types.
+///
+/// An Incomplete entry is always a RecordType and only encodes its
+/// identifier e.g. "s(S){}". Incomplete 'StubEnc' entries are ephemeral and
+/// are placed into the cache during type expansion as a means to identify and
+/// handle recursive inclusion of types as sub-members. If there is recursion
+/// the entry becomes IncompleteUsed.
+///
+/// During the expansion of a RecordType's members:
+///
+///   If the cache contains a NonRecursive encoding for the member type, the
+///   cached encoding is used;
+///
+///   If the cache contains a Recursive encoding for the member type, the
+///   cached encoding is 'Swapped' out, as it may be incorrect, and...
+///
+///   If the member is a RecordType, an Incomplete encoding is placed into the
+///   cache to break potential recursive inclusion of itself as a sub-member;
+///
+///   Once a member RecordType has been expanded, its temporary incomplete
+///   entry is removed from the cache. If a Recursive encoding was swapped out
+///   it is swapped back in;
+///
+///   If an incomplete entry is used to expand a sub-member, the incomplete
+///   entry is marked as IncompleteUsed. The cache keeps count of how many
+///   IncompleteUsed entries it currently contains in IncompleteUsedCount;
+///
+///   If a member's encoding is found to be a NonRecursive or Recursive viz:
+///   IncompleteUsedCount==0, the member's encoding is added to the cache.
+///   Else the member is part of a recursive type and thus the recursion has
+///   been exited too soon for the encoding to be correct for the member.
+///
+class TypeStringCache {
+  enum Status {NonRecursive, Recursive, Incomplete, IncompleteUsed};
+  struct Entry {
+    std::string Str;     // The encoded TypeString for the type.
+    enum Status State;   // Information about the encoding in 'Str'.
+    std::string Swapped; // A temporary place holder for a Recursive encoding
+                         // during the expansion of RecordType's members.
+  };
+  std::map<const IdentifierInfo *, struct Entry> Map;
+  unsigned IncompleteCount;     // Number of Incomplete entries in the Map.
+  unsigned IncompleteUsedCount; // Number of IncompleteUsed entries in the Map.
+public:
+  void addIncomplete(const IdentifierInfo *ID, std::string StubEnc);
+  bool removeIncomplete(const IdentifierInfo *ID);
+  void addIfComplete(const IdentifierInfo *ID, StringRef Str,
+                     bool IsRecursive);
+  StringRef lookupStr(const IdentifierInfo *ID);
+};
+
+/// TypeString encodings for union fields must be order.
+/// FieldEncoding is a helper for this ordering process.
+class FieldEncoding {
+  bool HasName;
+  std::string Enc;
+public:
+  FieldEncoding(bool b, SmallStringEnc &e) : HasName(b), Enc(e.c_str()) {};
+  StringRef str() {return Enc.c_str();};
+  bool operator<(const FieldEncoding &rhs) const {
+    if (HasName != rhs.HasName) return HasName;
+    return Enc < rhs.Enc;
+  }
+};
+
 class XCoreABIInfo : public DefaultABIInfo {
 public:
   XCoreABIInfo(CodeGen::CodeGenTypes &CGT) : DefaultABIInfo(CGT) {}
@@ -6114,10 +6210,14 @@ public:
 };
 
 class XCoreTargetCodeGenInfo : public TargetCodeGenInfo {
+  mutable TypeStringCache TSC;
 public:
   XCoreTargetCodeGenInfo(CodeGenTypes &CGT)
     :TargetCodeGenInfo(new XCoreABIInfo(CGT)) {}
+  virtual void emitTargetMD(const Decl *D, llvm::GlobalValue *GV,
+                            CodeGen::CodeGenModule &M) const;
 };
+
 } // End anonymous namespace.
 
 llvm::Value *XCoreABIInfo::EmitVAArg(llvm::Value *VAListAddr, QualType Ty,
@@ -6169,6 +6269,448 @@ llvm::Value *XCoreABIInfo::EmitVAArg(llvm::Value *VAListAddr, QualType Ty,
   return Val;
 }
 
+/// During the expansion of a RecordType, an incomplete TypeString is placed
+/// into the cache as a means to identify and break recursion.
+/// If there is a Recursive encoding in the cache, it is swapped out and will
+/// be reinserted by removeIncomplete().
+/// All other types of encoding should have been used rather than arriving here.
+void TypeStringCache::addIncomplete(const IdentifierInfo *ID,
+                                    std::string StubEnc) {
+  if (!ID)
+    return;
+  Entry &E = Map[ID];
+  assert( (E.Str.empty() || E.State == Recursive) &&
+         "Incorrectly use of addIncomplete");
+  assert(!StubEnc.empty() && "Passing an empty string to addIncomplete()");
+  E.Swapped.swap(E.Str); // swap out the Recursive
+  E.Str.swap(StubEnc);
+  E.State = Incomplete;
+  ++IncompleteCount;
+}
+
+/// Once the RecordType has been expanded, the temporary incomplete TypeString
+/// must be removed from the cache.
+/// If a Recursive was swapped out by addIncomplete(), it will be replaced.
+/// Returns true if the RecordType was defined recursively.
+bool TypeStringCache::removeIncomplete(const IdentifierInfo *ID) {
+  if (!ID)
+    return false;
+  auto I = Map.find(ID);
+  assert(I != Map.end() && "Entry not present");
+  Entry &E = I->second;
+  assert( (E.State == Incomplete ||
+           E.State == IncompleteUsed) &&
+         "Entry must be an incomplete type");
+  bool IsRecursive = false;
+  if (E.State == IncompleteUsed) {
+    // We made use of our Incomplete encoding, thus we are recursive.
+    IsRecursive = true;
+    --IncompleteUsedCount;
+  }
+  if (E.Swapped.empty())
+    Map.erase(I);
+  else {
+    // Swap the Recursive back.
+    E.Swapped.swap(E.Str);
+    E.Swapped.clear();
+    E.State = Recursive;
+  }
+  --IncompleteCount;
+  return IsRecursive;
+}
+
+/// Add the encoded TypeString to the cache only if it is NonRecursive or
+/// Recursive (viz: all sub-members were expanded as fully as possible).
+void TypeStringCache::addIfComplete(const IdentifierInfo *ID, StringRef Str,
+                                    bool IsRecursive) {
+  if (!ID || IncompleteUsedCount)
+    return; // No key or it is is an incomplete sub-type so don't add.
+  Entry &E = Map[ID];
+  if (IsRecursive && !E.Str.empty()) {
+    assert(E.State==Recursive && E.Str.size() == Str.size() &&
+           "This is not the same Recursive entry");
+    // The parent container was not recursive after all, so we could have used
+    // this Recursive sub-member entry after all, but we assumed the worse when
+    // we started viz: IncompleteCount!=0.
+    return;
+  }
+  assert(E.Str.empty() && "Entry already present");
+  E.Str = Str.str();
+  E.State = IsRecursive? Recursive : NonRecursive;
+}
+
+/// Return a cached TypeString encoding for the ID. If there isn't one, or we
+/// are recursively expanding a type (IncompleteCount != 0) and the cached
+/// encoding is Recursive, return an empty StringRef.
+StringRef TypeStringCache::lookupStr(const IdentifierInfo *ID) {
+  if (!ID)
+    return StringRef();   // We have no key.
+  auto I = Map.find(ID);
+  if (I == Map.end())
+    return StringRef();   // We have no encoding.
+  Entry &E = I->second;
+  if (E.State == Recursive && IncompleteCount)
+    return StringRef();   // We don't use Recursive encodings for member types.
+
+  if (E.State == Incomplete) {
+    // The incomplete type is being used to break out of recursion.
+    E.State = IncompleteUsed;
+    ++IncompleteUsedCount;
+  }
+  return E.Str.c_str();
+}
+
+/// The XCore ABI includes a type information section that communicates symbol
+/// type information to the linker. The linker uses this information to verify
+/// safety/correctness of things such as array bound and pointers et al.
+/// The ABI only requires C (and XC) language modules to emit TypeStrings.
+/// This type information (TypeString) is emitted into meta data for all global
+/// symbols: definitions, declarations, functions & variables.
+///
+/// The TypeString carries type, qualifier, name, size & value details.
+/// Please see 'Tools Development Guide' section 2.16.2 for format details:
+/// <https://www.xmos.com/download/public/Tools-Development-Guide%28X9114A%29.pdf>
+/// The output is tested by test/CodeGen/xcore-stringtype.c.
+///
+static bool getTypeString(SmallStringEnc &Enc, const Decl *D,
+                          CodeGen::CodeGenModule &CGM, TypeStringCache &TSC);
+
+/// XCore uses emitTargetMD to emit TypeString metadata for global symbols.
+void XCoreTargetCodeGenInfo::emitTargetMD(const Decl *D, llvm::GlobalValue *GV,
+                                          CodeGen::CodeGenModule &CGM) const {
+  SmallStringEnc Enc;
+  if (getTypeString(Enc, D, CGM, TSC)) {
+    llvm::LLVMContext &Ctx = CGM.getModule().getContext();
+    llvm::SmallVector<llvm::Value *, 2> MDVals;
+    MDVals.push_back(GV);
+    MDVals.push_back(llvm::MDString::get(Ctx, Enc.str()));
+    llvm::NamedMDNode *MD =
+      CGM.getModule().getOrInsertNamedMetadata("xcore.typestrings");
+    MD->addOperand(llvm::MDNode::get(Ctx, MDVals));
+  }
+}
+
+static bool appendType(SmallStringEnc &Enc, QualType QType,
+                       const CodeGen::CodeGenModule &CGM,
+                       TypeStringCache &TSC);
+
+/// Helper function for appendRecordType().
+/// Builds a SmallVector containing the encoded field types in declaration order.
+static bool extractFieldType(SmallVectorImpl<FieldEncoding> &FE,
+                             const RecordDecl *RD,
+                             const CodeGen::CodeGenModule &CGM,
+                             TypeStringCache &TSC) {
+  for (RecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
+       I != E; ++I) {
+    SmallStringEnc Enc;
+    Enc += "m(";
+    Enc += I->getName();
+    Enc += "){";
+    if (I->isBitField()) {
+      Enc += "b(";
+      llvm::raw_svector_ostream OS(Enc);
+      OS.resync();
+      OS << I->getBitWidthValue(CGM.getContext());
+      OS.flush();
+      Enc += ':';
+    }
+    if (!appendType(Enc, I->getType(), CGM, TSC))
+      return false;
+    if (I->isBitField())
+      Enc += ')';
+    Enc += '}';
+    FE.push_back(FieldEncoding(!I->getName().empty(), Enc));
+  }
+  return true;
+}
+
+/// Appends structure and union types to Enc and adds encoding to cache.
+/// Recursively calls appendType (via extractFieldType) for each field.
+/// Union types have their fields ordered according to the ABI.
+static bool appendRecordType(SmallStringEnc &Enc, const RecordType *RT,
+                             const CodeGen::CodeGenModule &CGM,
+                             TypeStringCache &TSC, const IdentifierInfo *ID) {
+  // Append the cached TypeString if we have one.
+  StringRef TypeString = TSC.lookupStr(ID);
+  if (!TypeString.empty()) {
+    Enc += TypeString;
+    return true;
+  }
+
+  // Start to emit an incomplete TypeString.
+  size_t Start = Enc.size();
+  Enc += (RT->isUnionType()? 'u' : 's');
+  Enc += '(';
+  if (ID)
+    Enc += ID->getName();
+  Enc += "){";
+
+  // We collect all encoded fields and order as necessary.
+  bool IsRecursive = false;
+  SmallVector<FieldEncoding, 16> FE;
+  const RecordDecl *RD = RT->getDecl()->getDefinition();
+  if (RD && !RD->field_empty()) {
+    // An incomplete TypeString stub is placed in the cache for this RecordType
+    // so that recursive calls to this RecordType will use it whilst building a
+    // complete TypeString for this RecordType.
+    std::string StubEnc(Enc.substr(Start).str());
+    StubEnc += '}';  // StubEnc now holds a valid incomplete TypeString.
+    TSC.addIncomplete(ID, std::move(StubEnc));
+    if (!extractFieldType(FE, RD, CGM, TSC)) {
+      (void) TSC.removeIncomplete(ID);
+      return false;
+    }
+    IsRecursive = TSC.removeIncomplete(ID);
+    // The ABI requires unions to be sorted but not structures.
+    // See FieldEncoding::operator< for sort algorithm.
+    if (RT->isUnionType())
+      std::sort(FE.begin(), FE.end());
+  }
+
+  // We can now complete the TypeString.
+  if (unsigned E = FE.size())
+    for (unsigned I = 0; I != E; ++I) {
+      if (I)
+        Enc += ',';
+      Enc += FE[I].str();
+    }
+  Enc += '}';
+  TSC.addIfComplete(ID, Enc.substr(Start), IsRecursive);
+  return true;
+}
+
+/// Appends enum types to Enc and adds the encoding to the cache.
+static bool appendEnumType(SmallStringEnc &Enc, const EnumType *ET,
+                           TypeStringCache &TSC,
+                           const IdentifierInfo *ID) {
+  // Append the cached TypeString if we have one.
+  StringRef TypeString = TSC.lookupStr(ID);
+  if (!TypeString.empty()) {
+    Enc += TypeString;
+    return true;
+  }
+
+  size_t Start = Enc.size();
+  Enc += "e(";
+  if (ID)
+    Enc += ID->getName();
+  Enc += "){";
+  if (const EnumDecl *ED = ET->getDecl()->getDefinition()) {
+    auto I = ED->enumerator_begin();
+    auto E = ED->enumerator_end();
+    while (I != E) {
+      Enc += "m(";
+      Enc += I->getName();
+      Enc += "){";
+      I->getInitVal().toString(Enc);
+      Enc += '}';
+      ++I;
+      if (I != E)
+        Enc += ',';
+    }
+  }
+  Enc += '}';
+  TSC.addIfComplete(ID, Enc.substr(Start), false);
+  return true;
+}
+
+/// Appends type's qualifier to Enc.
+/// This is done prior to appending the type's encoding.
+static void appendQualifier(SmallStringEnc &Enc, QualType QT) {
+  // Qualifiers are emitted in alphabetical order.
+  static const char *Table[] = {"","c:","r:","cr:","v:","cv:","rv:","crv:"};
+  int Lookup = 0;
+  if (QT.isConstQualified())
+    Lookup += 1<<0;
+  if (QT.isRestrictQualified())
+    Lookup += 1<<1;
+  if (QT.isVolatileQualified())
+    Lookup += 1<<2;
+  Enc += Table[Lookup];
+}
+
+/// Appends built-in types to Enc.
+static bool appendBuiltinType(SmallStringEnc &Enc, const BuiltinType *BT) {
+  const char *EncType;
+  switch (BT->getKind()) {
+    case BuiltinType::Void:
+      EncType = "0";
+      break;
+    case BuiltinType::Bool:
+      EncType = "b";
+      break;
+    case BuiltinType::Char_U:
+      EncType = "uc";
+      break;
+    case BuiltinType::UChar:
+      EncType = "uc";
+      break;
+    case BuiltinType::SChar:
+      EncType = "sc";
+      break;
+    case BuiltinType::UShort:
+      EncType = "us";
+      break;
+    case BuiltinType::Short:
+      EncType = "ss";
+      break;
+    case BuiltinType::UInt:
+      EncType = "ui";
+      break;
+    case BuiltinType::Int:
+      EncType = "si";
+      break;
+    case BuiltinType::ULong:
+      EncType = "ul";
+      break;
+    case BuiltinType::Long:
+      EncType = "sl";
+      break;
+    case BuiltinType::ULongLong:
+      EncType = "ull";
+      break;
+    case BuiltinType::LongLong:
+      EncType = "sll";
+      break;
+    case BuiltinType::Float:
+      EncType = "ft";
+      break;
+    case BuiltinType::Double:
+      EncType = "d";
+      break;
+    case BuiltinType::LongDouble:
+      EncType = "ld";
+      break;
+    default:
+      return false;
+  }
+  Enc += EncType;
+  return true;
+}
+
+/// Appends a pointer encoding to Enc before calling appendType for the pointee.
+static bool appendPointerType(SmallStringEnc &Enc, const PointerType *PT,
+                              const CodeGen::CodeGenModule &CGM,
+                              TypeStringCache &TSC) {
+  Enc += "p(";
+  if (!appendType(Enc, PT->getPointeeType(), CGM, TSC))
+    return false;
+  Enc += ')';
+  return true;
+}
+
+/// Appends array encoding to Enc before calling appendType for the element.
+static bool appendArrayType(SmallStringEnc &Enc, const ArrayType *AT,
+                            const CodeGen::CodeGenModule &CGM,
+                            TypeStringCache &TSC, StringRef NoSizeEnc) {
+  if (AT->getSizeModifier() != ArrayType::Normal)
+    return false;
+  Enc += "a(";
+  if (const ConstantArrayType *CAT = dyn_cast<ConstantArrayType>(AT))
+    CAT->getSize().toStringUnsigned(Enc);
+  else
+    Enc += NoSizeEnc; // Global arrays use "*", otherwise it is "".
+  Enc += ':';
+  if (!appendType(Enc, AT->getElementType(), CGM, TSC))
+    return false;
+  Enc += ')';
+  return true;
+}
+
+/// Appends a function encoding to Enc, calling appendType for the return type
+/// and the arguments.
+static bool appendFunctionType(SmallStringEnc &Enc, const FunctionType *FT,
+                             const CodeGen::CodeGenModule &CGM,
+                             TypeStringCache &TSC) {
+  Enc += "f{";
+  if (!appendType(Enc, FT->getReturnType(), CGM, TSC))
+    return false;
+  Enc += "}(";
+  if (const FunctionProtoType *FPT = FT->getAs<FunctionProtoType>()) {
+    // N.B. we are only interested in the adjusted param types.
+    auto I = FPT->param_type_begin();
+    auto E = FPT->param_type_end();
+    if (I != E) {
+      do {
+        if (!appendType(Enc, *I, CGM, TSC))
+          return false;
+        ++I;
+        if (I != E)
+          Enc += ',';
+      } while (I != E);
+      if (FPT->isVariadic())
+        Enc += ",va";
+    } else {
+      if (FPT->isVariadic())
+        Enc += "va";
+      else
+        Enc += '0';
+    }
+  }
+  Enc += ')';
+  return true;
+}
+
+/// Handles the type's qualifier before dispatching a call to handle specific
+/// type encodings.
+static bool appendType(SmallStringEnc &Enc, QualType QType,
+                       const CodeGen::CodeGenModule &CGM,
+                       TypeStringCache &TSC) {
+
+  QualType QT = QType.getCanonicalType();
+
+  appendQualifier(Enc, QT);
+
+  if (const BuiltinType *BT = QT->getAs<BuiltinType>())
+    return appendBuiltinType(Enc, BT);
+
+  if (const ArrayType *AT = QT->getAsArrayTypeUnsafe())
+    return appendArrayType(Enc, AT, CGM, TSC, "");
+
+  if (const PointerType *PT = QT->getAs<PointerType>())
+    return appendPointerType(Enc, PT, CGM, TSC);
+
+  if (const EnumType *ET = QT->getAs<EnumType>())
+    return appendEnumType(Enc, ET, TSC, QT.getBaseTypeIdentifier());
+
+  if (const RecordType *RT = QT->getAsStructureType())
+    return appendRecordType(Enc, RT, CGM, TSC, QT.getBaseTypeIdentifier());
+
+  if (const RecordType *RT = QT->getAsUnionType())
+    return appendRecordType(Enc, RT, CGM, TSC, QT.getBaseTypeIdentifier());
+
+  if (const FunctionType *FT = QT->getAs<FunctionType>())
+    return appendFunctionType(Enc, FT, CGM, TSC);
+
+  return false;
+}
+
+static bool getTypeString(SmallStringEnc &Enc, const Decl *D,
+                          CodeGen::CodeGenModule &CGM, TypeStringCache &TSC) {
+  if (!D)
+    return false;
+
+  if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
+    if (FD->getLanguageLinkage() != CLanguageLinkage)
+      return false;
+    return appendType(Enc, FD->getType(), CGM, TSC);
+  }
+
+  if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
+    if (VD->getLanguageLinkage() != CLanguageLinkage)
+      return false;
+    QualType QT = VD->getType().getCanonicalType();
+    if (const ArrayType *AT = QT->getAsArrayTypeUnsafe()) {
+      // Global ArrayTypes are given a size of '*' if the size is unknown.
+      appendQualifier(Enc, QT);
+      return appendArrayType(Enc, AT, CGM, TSC, "*");
+    }
+    return appendType(Enc, QT, CGM, TSC);
+  }
+  return false;
+}
+
+
 //===----------------------------------------------------------------------===//
 // Driver code
 //===----------------------------------------------------------------------===//
diff --git a/clang/lib/CodeGen/TargetInfo.h b/clang/lib/CodeGen/TargetInfo.h
index 6c3ab64834b..b092426d832 100644
--- a/clang/lib/CodeGen/TargetInfo.h
+++ b/clang/lib/CodeGen/TargetInfo.h
@@ -56,6 +56,11 @@ namespace clang {
     virtual void SetTargetAttributes(const Decl *D, llvm::GlobalValue *GV,
                                      CodeGen::CodeGenModule &M) const { }
 
+    /// EmitTargetMD - Provides a convenient hook to handle extra
+    /// target-specific metadata for the given global.
+    virtual void emitTargetMD(const Decl *D, llvm::GlobalValue *GV,
+                              CodeGen::CodeGenModule &M) const { }
+
     /// Determines the size of struct _Unwind_Exception on this platform,
     /// in 8-bit units.  The Itanium ABI defines this as:
     ///   struct _Unwind_Exception {