diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 2a2f96cd1d3..d571fd897a4 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -450,12 +450,12 @@ static void decodeLLVMAttributesForBitcode(AttrBuilder &B,
                 (EncodedAttrs & 0xffff));
 }
 
-bool BitcodeReader::ParseAttributeBlock() {
+error_code BitcodeReader::ParseAttributeBlock() {
   if (Stream.EnterSubBlock(bitc::PARAMATTR_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   if (!MAttributes.empty())
-    return Error("Multiple PARAMATTR blocks found!");
+    return Error(InvalidMultipleBlocks);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -468,9 +468,9 @@ bool BitcodeReader::ParseAttributeBlock() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("Error at end of PARAMATTR block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -484,7 +484,7 @@ bool BitcodeReader::ParseAttributeBlock() {
     case bitc::PARAMATTR_CODE_ENTRY_OLD: { // ENTRY: [paramidx0, attr0, ...]
       // FIXME: Remove in 4.0.
       if (Record.size() & 1)
-        return Error("Invalid ENTRY record");
+        return Error(InvalidRecord);
 
       for (unsigned i = 0, e = Record.size(); i != e; i += 2) {
         AttrBuilder B;
@@ -508,130 +508,131 @@ bool BitcodeReader::ParseAttributeBlock() {
   }
 }
 
-bool BitcodeReader::ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind) {
+error_code BitcodeReader::ParseAttrKind(uint64_t Code,
+                                        Attribute::AttrKind *Kind) {
   switch (Code) {
   case bitc::ATTR_KIND_ALIGNMENT:
     *Kind = Attribute::Alignment;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_ALWAYS_INLINE:
     *Kind = Attribute::AlwaysInline;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_BUILTIN:
     *Kind = Attribute::Builtin;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_BY_VAL:
     *Kind = Attribute::ByVal;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_COLD:
     *Kind = Attribute::Cold;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_INLINE_HINT:
     *Kind = Attribute::InlineHint;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_IN_REG:
     *Kind = Attribute::InReg;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_MIN_SIZE:
     *Kind = Attribute::MinSize;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NAKED:
     *Kind = Attribute::Naked;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NEST:
     *Kind = Attribute::Nest;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_ALIAS:
     *Kind = Attribute::NoAlias;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_BUILTIN:
     *Kind = Attribute::NoBuiltin;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_CAPTURE:
     *Kind = Attribute::NoCapture;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_DUPLICATE:
     *Kind = Attribute::NoDuplicate;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_IMPLICIT_FLOAT:
     *Kind = Attribute::NoImplicitFloat;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_INLINE:
     *Kind = Attribute::NoInline;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NON_LAZY_BIND:
     *Kind = Attribute::NonLazyBind;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_RED_ZONE:
     *Kind = Attribute::NoRedZone;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_RETURN:
     *Kind = Attribute::NoReturn;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_NO_UNWIND:
     *Kind = Attribute::NoUnwind;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_OPTIMIZE_FOR_SIZE:
     *Kind = Attribute::OptimizeForSize;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_OPTIMIZE_NONE:
     *Kind = Attribute::OptimizeNone;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_READ_NONE:
     *Kind = Attribute::ReadNone;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_READ_ONLY:
     *Kind = Attribute::ReadOnly;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_RETURNED:
     *Kind = Attribute::Returned;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_RETURNS_TWICE:
     *Kind = Attribute::ReturnsTwice;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_S_EXT:
     *Kind = Attribute::SExt;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_STACK_ALIGNMENT:
     *Kind = Attribute::StackAlignment;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_STACK_PROTECT:
     *Kind = Attribute::StackProtect;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_STACK_PROTECT_REQ:
     *Kind = Attribute::StackProtectReq;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_STACK_PROTECT_STRONG:
     *Kind = Attribute::StackProtectStrong;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_STRUCT_RET:
     *Kind = Attribute::StructRet;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_SANITIZE_ADDRESS:
     *Kind = Attribute::SanitizeAddress;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_SANITIZE_THREAD:
     *Kind = Attribute::SanitizeThread;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_SANITIZE_MEMORY:
     *Kind = Attribute::SanitizeMemory;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_UW_TABLE:
     *Kind = Attribute::UWTable;
-    return false;
+    return error_code::success();
   case bitc::ATTR_KIND_Z_EXT:
     *Kind = Attribute::ZExt;
-    return false;
+    return error_code::success();
   default:
-    return Error("Unknown attribute kind");
+    return Error(InvalidValue);
   }
 }
 
-bool BitcodeReader::ParseAttributeGroupBlock() {
+error_code BitcodeReader::ParseAttributeGroupBlock() {
   if (Stream.EnterSubBlock(bitc::PARAMATTR_GROUP_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   if (!MAttributeGroups.empty())
-    return Error("Multiple PARAMATTR_GROUP blocks found!");
+    return Error(InvalidMultipleBlocks);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -642,9 +643,9 @@ bool BitcodeReader::ParseAttributeGroupBlock() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("Error at end of PARAMATTR_GROUP block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -657,7 +658,7 @@ bool BitcodeReader::ParseAttributeGroupBlock() {
       break;
     case bitc::PARAMATTR_GRP_CODE_ENTRY: { // ENTRY: [grpid, idx, a0, a1, ...]
       if (Record.size() < 3)
-        return Error("Invalid ENTRY record");
+        return Error(InvalidRecord);
 
       uint64_t GrpID = Record[0];
       uint64_t Idx = Record[1]; // Index of the object this attribute refers to.
@@ -666,14 +667,14 @@ bool BitcodeReader::ParseAttributeGroupBlock() {
       for (unsigned i = 2, e = Record.size(); i != e; ++i) {
         if (Record[i] == 0) {        // Enum attribute
           Attribute::AttrKind Kind;
-          if (ParseAttrKind(Record[++i], &Kind))
-            return true;
+          if (error_code EC = ParseAttrKind(Record[++i], &Kind))
+            return EC;
 
           B.addAttribute(Kind);
         } else if (Record[i] == 1) { // Align attribute
           Attribute::AttrKind Kind;
-          if (ParseAttrKind(Record[++i], &Kind))
-            return true;
+          if (error_code EC = ParseAttrKind(Record[++i], &Kind))
+            return EC;
           if (Kind == Attribute::Alignment)
             B.addAlignmentAttr(Record[++i]);
           else
@@ -708,16 +709,16 @@ bool BitcodeReader::ParseAttributeGroupBlock() {
   }
 }
 
-bool BitcodeReader::ParseTypeTable() {
+error_code BitcodeReader::ParseTypeTable() {
   if (Stream.EnterSubBlock(bitc::TYPE_BLOCK_ID_NEW))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   return ParseTypeTableBody();
 }
 
-bool BitcodeReader::ParseTypeTableBody() {
+error_code BitcodeReader::ParseTypeTableBody() {
   if (!TypeList.empty())
-    return Error("Multiple TYPE_BLOCKs found!");
+    return Error(InvalidMultipleBlocks);
 
   SmallVector<uint64_t, 64> Record;
   unsigned NumRecords = 0;
@@ -731,12 +732,11 @@ bool BitcodeReader::ParseTypeTableBody() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      Error("Error in the type table block");
-      return true;
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
       if (NumRecords != TypeList.size())
-        return Error("Invalid type forward reference in TYPE_BLOCK");
-      return false;
+        return Error(MalformedBlock);
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -746,12 +746,13 @@ bool BitcodeReader::ParseTypeTableBody() {
     Record.clear();
     Type *ResultTy = 0;
     switch (Stream.readRecord(Entry.ID, Record)) {
-    default: return Error("unknown type in type table");
+    default:
+      return Error(InvalidValue);
     case bitc::TYPE_CODE_NUMENTRY: // TYPE_CODE_NUMENTRY: [numentries]
       // TYPE_CODE_NUMENTRY contains a count of the number of types in the
       // type list.  This allows us to reserve space.
       if (Record.size() < 1)
-        return Error("Invalid TYPE_CODE_NUMENTRY record");
+        return Error(InvalidRecord);
       TypeList.resize(Record[0]);
       continue;
     case bitc::TYPE_CODE_VOID:      // VOID
@@ -786,19 +787,20 @@ bool BitcodeReader::ParseTypeTableBody() {
       break;
     case bitc::TYPE_CODE_INTEGER:   // INTEGER: [width]
       if (Record.size() < 1)
-        return Error("Invalid Integer type record");
+        return Error(InvalidRecord);
 
       ResultTy = IntegerType::get(Context, Record[0]);
       break;
     case bitc::TYPE_CODE_POINTER: { // POINTER: [pointee type] or
                                     //          [pointee type, address space]
       if (Record.size() < 1)
-        return Error("Invalid POINTER type record");
+        return Error(InvalidRecord);
       unsigned AddressSpace = 0;
       if (Record.size() == 2)
         AddressSpace = Record[1];
       ResultTy = getTypeByID(Record[0]);
-      if (ResultTy == 0) return Error("invalid element type in pointer type");
+      if (ResultTy == 0)
+        return Error(InvalidType);
       ResultTy = PointerType::get(ResultTy, AddressSpace);
       break;
     }
@@ -806,7 +808,7 @@ bool BitcodeReader::ParseTypeTableBody() {
       // FIXME: attrid is dead, remove it in LLVM 4.0
       // FUNCTION: [vararg, attrid, retty, paramty x N]
       if (Record.size() < 3)
-        return Error("Invalid FUNCTION type record");
+        return Error(InvalidRecord);
       SmallVector<Type*, 8> ArgTys;
       for (unsigned i = 3, e = Record.size(); i != e; ++i) {
         if (Type *T = getTypeByID(Record[i]))
@@ -817,7 +819,7 @@ bool BitcodeReader::ParseTypeTableBody() {
 
       ResultTy = getTypeByID(Record[2]);
       if (ResultTy == 0 || ArgTys.size() < Record.size()-3)
-        return Error("invalid type in function type");
+        return Error(InvalidType);
 
       ResultTy = FunctionType::get(ResultTy, ArgTys, Record[0]);
       break;
@@ -825,7 +827,7 @@ bool BitcodeReader::ParseTypeTableBody() {
     case bitc::TYPE_CODE_FUNCTION: {
       // FUNCTION: [vararg, retty, paramty x N]
       if (Record.size() < 2)
-        return Error("Invalid FUNCTION type record");
+        return Error(InvalidRecord);
       SmallVector<Type*, 8> ArgTys;
       for (unsigned i = 2, e = Record.size(); i != e; ++i) {
         if (Type *T = getTypeByID(Record[i]))
@@ -836,14 +838,14 @@ bool BitcodeReader::ParseTypeTableBody() {
 
       ResultTy = getTypeByID(Record[1]);
       if (ResultTy == 0 || ArgTys.size() < Record.size()-2)
-        return Error("invalid type in function type");
+        return Error(InvalidType);
 
       ResultTy = FunctionType::get(ResultTy, ArgTys, Record[0]);
       break;
     }
     case bitc::TYPE_CODE_STRUCT_ANON: {  // STRUCT: [ispacked, eltty x N]
       if (Record.size() < 1)
-        return Error("Invalid STRUCT type record");
+        return Error(InvalidRecord);
       SmallVector<Type*, 8> EltTys;
       for (unsigned i = 1, e = Record.size(); i != e; ++i) {
         if (Type *T = getTypeByID(Record[i]))
@@ -852,21 +854,21 @@ bool BitcodeReader::ParseTypeTableBody() {
           break;
       }
       if (EltTys.size() != Record.size()-1)
-        return Error("invalid type in struct type");
+        return Error(InvalidType);
       ResultTy = StructType::get(Context, EltTys, Record[0]);
       break;
     }
     case bitc::TYPE_CODE_STRUCT_NAME:   // STRUCT_NAME: [strchr x N]
       if (ConvertToString(Record, 0, TypeName))
-        return Error("Invalid STRUCT_NAME record");
+        return Error(InvalidRecord);
       continue;
 
     case bitc::TYPE_CODE_STRUCT_NAMED: { // STRUCT: [ispacked, eltty x N]
       if (Record.size() < 1)
-        return Error("Invalid STRUCT type record");
+        return Error(InvalidRecord);
 
       if (NumRecords >= TypeList.size())
-        return Error("invalid TYPE table");
+        return Error(InvalidTYPETable);
 
       // Check to see if this was forward referenced, if so fill in the temp.
       StructType *Res = cast_or_null<StructType>(TypeList[NumRecords]);
@@ -885,17 +887,17 @@ bool BitcodeReader::ParseTypeTableBody() {
           break;
       }
       if (EltTys.size() != Record.size()-1)
-        return Error("invalid STRUCT type record");
+        return Error(InvalidRecord);
       Res->setBody(EltTys, Record[0]);
       ResultTy = Res;
       break;
     }
     case bitc::TYPE_CODE_OPAQUE: {       // OPAQUE: []
       if (Record.size() != 1)
-        return Error("Invalid OPAQUE type record");
+        return Error(InvalidRecord);
 
       if (NumRecords >= TypeList.size())
-        return Error("invalid TYPE table");
+        return Error(InvalidTYPETable);
 
       // Check to see if this was forward referenced, if so fill in the temp.
       StructType *Res = cast_or_null<StructType>(TypeList[NumRecords]);
@@ -910,33 +912,33 @@ bool BitcodeReader::ParseTypeTableBody() {
     }
     case bitc::TYPE_CODE_ARRAY:     // ARRAY: [numelts, eltty]
       if (Record.size() < 2)
-        return Error("Invalid ARRAY type record");
+        return Error(InvalidRecord);
       if ((ResultTy = getTypeByID(Record[1])))
         ResultTy = ArrayType::get(ResultTy, Record[0]);
       else
-        return Error("Invalid ARRAY type element");
+        return Error(InvalidType);
       break;
     case bitc::TYPE_CODE_VECTOR:    // VECTOR: [numelts, eltty]
       if (Record.size() < 2)
-        return Error("Invalid VECTOR type record");
+        return Error(InvalidRecord);
       if ((ResultTy = getTypeByID(Record[1])))
         ResultTy = VectorType::get(ResultTy, Record[0]);
       else
-        return Error("Invalid ARRAY type element");
+        return Error(InvalidType);
       break;
     }
 
     if (NumRecords >= TypeList.size())
-      return Error("invalid TYPE table");
+      return Error(InvalidTYPETable);
     assert(ResultTy && "Didn't read a type?");
     assert(TypeList[NumRecords] == 0 && "Already read type?");
     TypeList[NumRecords++] = ResultTy;
   }
 }
 
-bool BitcodeReader::ParseValueSymbolTable() {
+error_code BitcodeReader::ParseValueSymbolTable() {
   if (Stream.EnterSubBlock(bitc::VALUE_SYMTAB_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -948,9 +950,9 @@ bool BitcodeReader::ParseValueSymbolTable() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("malformed value symbol table block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -963,10 +965,10 @@ bool BitcodeReader::ParseValueSymbolTable() {
       break;
     case bitc::VST_CODE_ENTRY: {  // VST_ENTRY: [valueid, namechar x N]
       if (ConvertToString(Record, 1, ValueName))
-        return Error("Invalid VST_ENTRY record");
+        return Error(InvalidRecord);
       unsigned ValueID = Record[0];
       if (ValueID >= ValueList.size())
-        return Error("Invalid Value ID in VST_ENTRY record");
+        return Error(InvalidRecord);
       Value *V = ValueList[ValueID];
 
       V->setName(StringRef(ValueName.data(), ValueName.size()));
@@ -975,10 +977,10 @@ bool BitcodeReader::ParseValueSymbolTable() {
     }
     case bitc::VST_CODE_BBENTRY: {
       if (ConvertToString(Record, 1, ValueName))
-        return Error("Invalid VST_BBENTRY record");
+        return Error(InvalidRecord);
       BasicBlock *BB = getBasicBlock(Record[0]);
       if (BB == 0)
-        return Error("Invalid BB ID in VST_BBENTRY record");
+        return Error(InvalidRecord);
 
       BB->setName(StringRef(ValueName.data(), ValueName.size()));
       ValueName.clear();
@@ -988,11 +990,11 @@ bool BitcodeReader::ParseValueSymbolTable() {
   }
 }
 
-bool BitcodeReader::ParseMetadata() {
+error_code BitcodeReader::ParseMetadata() {
   unsigned NextMDValueNo = MDValueList.size();
 
   if (Stream.EnterSubBlock(bitc::METADATA_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -1003,10 +1005,9 @@ bool BitcodeReader::ParseMetadata() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      Error("malformed metadata block");
-      return true;
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -1035,7 +1036,7 @@ bool BitcodeReader::ParseMetadata() {
       for (unsigned i = 0; i != Size; ++i) {
         MDNode *MD = dyn_cast<MDNode>(MDValueList.getValueFwdRef(Record[i]));
         if (MD == 0)
-          return Error("Malformed metadata record");
+          return Error(InvalidRecord);
         NMD->addOperand(MD);
       }
       break;
@@ -1045,13 +1046,14 @@ bool BitcodeReader::ParseMetadata() {
       // fall-through
     case bitc::METADATA_NODE: {
       if (Record.size() % 2 == 1)
-        return Error("Invalid METADATA_NODE record");
+        return Error(InvalidRecord);
 
       unsigned Size = Record.size();
       SmallVector<Value*, 8> Elts;
       for (unsigned i = 0; i != Size; i += 2) {
         Type *Ty = getTypeByID(Record[i]);
-        if (!Ty) return Error("Invalid METADATA_NODE record");
+        if (!Ty)
+          return Error(InvalidRecord);
         if (Ty->isMetadataTy())
           Elts.push_back(MDValueList.getValueFwdRef(Record[i+1]));
         else if (!Ty->isVoidTy())
@@ -1072,14 +1074,14 @@ bool BitcodeReader::ParseMetadata() {
     }
     case bitc::METADATA_KIND: {
       if (Record.size() < 2)
-        return Error("Invalid METADATA_KIND record");
+        return Error(InvalidRecord);
 
       unsigned Kind = Record[0];
       SmallString<8> Name(Record.begin()+1, Record.end());
 
       unsigned NewKind = TheModule->getMDKindID(Name.str());
       if (!MDKindMap.insert(std::make_pair(Kind, NewKind)).second)
-        return Error("Conflicting METADATA_KIND records");
+        return Error(ConflictingMETADATA_KINDRecords);
       break;
     }
     }
@@ -1099,7 +1101,7 @@ uint64_t BitcodeReader::decodeSignRotatedValue(uint64_t V) {
 
 /// ResolveGlobalAndAliasInits - Resolve all of the initializers for global
 /// values and aliases that we can.
-bool BitcodeReader::ResolveGlobalAndAliasInits() {
+error_code BitcodeReader::ResolveGlobalAndAliasInits() {
   std::vector<std::pair<GlobalVariable*, unsigned> > GlobalInitWorklist;
   std::vector<std::pair<GlobalAlias*, unsigned> > AliasInitWorklist;
   std::vector<std::pair<Function*, unsigned> > FunctionPrefixWorklist;
@@ -1117,7 +1119,7 @@ bool BitcodeReader::ResolveGlobalAndAliasInits() {
       if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
         GlobalInitWorklist.back().first->setInitializer(C);
       else
-        return Error("Global variable initializer is not a constant!");
+        return Error(ExpectedConstant);
     }
     GlobalInitWorklist.pop_back();
   }
@@ -1130,7 +1132,7 @@ bool BitcodeReader::ResolveGlobalAndAliasInits() {
       if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
         AliasInitWorklist.back().first->setAliasee(C);
       else
-        return Error("Alias initializer is not a constant!");
+        return Error(ExpectedConstant);
     }
     AliasInitWorklist.pop_back();
   }
@@ -1143,12 +1145,12 @@ bool BitcodeReader::ResolveGlobalAndAliasInits() {
       if (Constant *C = dyn_cast<Constant>(ValueList[ValID]))
         FunctionPrefixWorklist.back().first->setPrefixData(C);
       else
-        return Error("Function prefix is not a constant!");
+        return Error(ExpectedConstant);
     }
     FunctionPrefixWorklist.pop_back();
   }
 
-  return false;
+  return error_code::success();
 }
 
 static APInt ReadWideAPInt(ArrayRef<uint64_t> Vals, unsigned TypeBits) {
@@ -1159,9 +1161,9 @@ static APInt ReadWideAPInt(ArrayRef<uint64_t> Vals, unsigned TypeBits) {
   return APInt(TypeBits, Words);
 }
 
-bool BitcodeReader::ParseConstants() {
+error_code BitcodeReader::ParseConstants() {
   if (Stream.EnterSubBlock(bitc::CONSTANTS_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -1174,15 +1176,15 @@ bool BitcodeReader::ParseConstants() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("malformed block record in AST file");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
       if (NextCstNo != ValueList.size())
-        return Error("Invalid constant reference!");
+        return Error(InvalidConstantReference);
 
       // Once all the constants have been read, go through and resolve forward
       // references.
       ValueList.ResolveConstantForwardRefs();
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -1199,9 +1201,9 @@ bool BitcodeReader::ParseConstants() {
       break;
     case bitc::CST_CODE_SETTYPE:   // SETTYPE: [typeid]
       if (Record.empty())
-        return Error("Malformed CST_SETTYPE record");
+        return Error(InvalidRecord);
       if (Record[0] >= TypeList.size())
-        return Error("Invalid Type ID in CST_SETTYPE record");
+        return Error(InvalidRecord);
       CurTy = TypeList[Record[0]];
       continue;  // Skip the ValueList manipulation.
     case bitc::CST_CODE_NULL:      // NULL
@@ -1209,12 +1211,12 @@ bool BitcodeReader::ParseConstants() {
       break;
     case bitc::CST_CODE_INTEGER:   // INTEGER: [intval]
       if (!CurTy->isIntegerTy() || Record.empty())
-        return Error("Invalid CST_INTEGER record");
+        return Error(InvalidRecord);
       V = ConstantInt::get(CurTy, decodeSignRotatedValue(Record[0]));
       break;
     case bitc::CST_CODE_WIDE_INTEGER: {// WIDE_INTEGER: [n x intval]
       if (!CurTy->isIntegerTy() || Record.empty())
-        return Error("Invalid WIDE_INTEGER record");
+        return Error(InvalidRecord);
 
       APInt VInt = ReadWideAPInt(Record,
                                  cast<IntegerType>(CurTy)->getBitWidth());
@@ -1224,7 +1226,7 @@ bool BitcodeReader::ParseConstants() {
     }
     case bitc::CST_CODE_FLOAT: {    // FLOAT: [fpval]
       if (Record.empty())
-        return Error("Invalid FLOAT record");
+        return Error(InvalidRecord);
       if (CurTy->isHalfTy())
         V = ConstantFP::get(Context, APFloat(APFloat::IEEEhalf,
                                              APInt(16, (uint16_t)Record[0])));
@@ -1254,7 +1256,7 @@ bool BitcodeReader::ParseConstants() {
 
     case bitc::CST_CODE_AGGREGATE: {// AGGREGATE: [n x value number]
       if (Record.empty())
-        return Error("Invalid CST_AGGREGATE record");
+        return Error(InvalidRecord);
 
       unsigned Size = Record.size();
       SmallVector<Constant*, 16> Elts;
@@ -1282,7 +1284,7 @@ bool BitcodeReader::ParseConstants() {
     case bitc::CST_CODE_STRING:    // STRING: [values]
     case bitc::CST_CODE_CSTRING: { // CSTRING: [values]
       if (Record.empty())
-        return Error("Invalid CST_STRING record");
+        return Error(InvalidRecord);
 
       SmallString<16> Elts(Record.begin(), Record.end());
       V = ConstantDataArray::getString(Context, Elts,
@@ -1291,7 +1293,7 @@ bool BitcodeReader::ParseConstants() {
     }
     case bitc::CST_CODE_DATA: {// DATA: [n x value]
       if (Record.empty())
-        return Error("Invalid CST_DATA record");
+        return Error(InvalidRecord);
 
       Type *EltTy = cast<SequentialType>(CurTy)->getElementType();
       unsigned Size = Record.size();
@@ -1336,13 +1338,14 @@ bool BitcodeReader::ParseConstants() {
         else
           V = ConstantDataArray::get(Context, Elts);
       } else {
-        return Error("Unknown element type in CE_DATA");
+        return Error(InvalidTypeForValue);
       }
       break;
     }
 
     case bitc::CST_CODE_CE_BINOP: {  // CE_BINOP: [opcode, opval, opval]
-      if (Record.size() < 3) return Error("Invalid CE_BINOP record");
+      if (Record.size() < 3)
+        return Error(InvalidRecord);
       int Opc = GetDecodedBinaryOpcode(Record[0], CurTy);
       if (Opc < 0) {
         V = UndefValue::get(CurTy);  // Unknown binop.
@@ -1372,13 +1375,15 @@ bool BitcodeReader::ParseConstants() {
       break;
     }
     case bitc::CST_CODE_CE_CAST: {  // CE_CAST: [opcode, opty, opval]
-      if (Record.size() < 3) return Error("Invalid CE_CAST record");
+      if (Record.size() < 3)
+        return Error(InvalidRecord);
       int Opc = GetDecodedCastOpcode(Record[0]);
       if (Opc < 0) {
         V = UndefValue::get(CurTy);  // Unknown cast.
       } else {
         Type *OpTy = getTypeByID(Record[1]);
-        if (!OpTy) return Error("Invalid CE_CAST record");
+        if (!OpTy)
+          return Error(InvalidRecord);
         Constant *Op = ValueList.getConstantFwdRef(Record[2], OpTy);
         V = ConstantExpr::getCast(Opc, Op, CurTy);
       }
@@ -1386,11 +1391,13 @@ bool BitcodeReader::ParseConstants() {
     }
     case bitc::CST_CODE_CE_INBOUNDS_GEP:
     case bitc::CST_CODE_CE_GEP: {  // CE_GEP:        [n x operands]
-      if (Record.size() & 1) return Error("Invalid CE_GEP record");
+      if (Record.size() & 1)
+        return Error(InvalidRecord);
       SmallVector<Constant*, 16> Elts;
       for (unsigned i = 0, e = Record.size(); i != e; i += 2) {
         Type *ElTy = getTypeByID(Record[i]);
-        if (!ElTy) return Error("Invalid CE_GEP record");
+        if (!ElTy)
+          return Error(InvalidRecord);
         Elts.push_back(ValueList.getConstantFwdRef(Record[i+1], ElTy));
       }
       ArrayRef<Constant *> Indices(Elts.begin() + 1, Elts.end());
@@ -1400,7 +1407,8 @@ bool BitcodeReader::ParseConstants() {
       break;
     }
     case bitc::CST_CODE_CE_SELECT: {  // CE_SELECT: [opval#, opval#, opval#]
-      if (Record.size() < 3) return Error("Invalid CE_SELECT record");
+      if (Record.size() < 3)
+        return Error(InvalidRecord);
 
       Type *SelectorTy = Type::getInt1Ty(Context);
 
@@ -1417,10 +1425,12 @@ bool BitcodeReader::ParseConstants() {
       break;
     }
     case bitc::CST_CODE_CE_EXTRACTELT: { // CE_EXTRACTELT: [opty, opval, opval]
-      if (Record.size() < 3) return Error("Invalid CE_EXTRACTELT record");
+      if (Record.size() < 3)
+        return Error(InvalidRecord);
       VectorType *OpTy =
         dyn_cast_or_null<VectorType>(getTypeByID(Record[0]));
-      if (OpTy == 0) return Error("Invalid CE_EXTRACTELT record");
+      if (OpTy == 0)
+        return Error(InvalidRecord);
       Constant *Op0 = ValueList.getConstantFwdRef(Record[1], OpTy);
       Constant *Op1 = ValueList.getConstantFwdRef(Record[2],
                                                   Type::getInt32Ty(Context));
@@ -1430,7 +1440,7 @@ bool BitcodeReader::ParseConstants() {
     case bitc::CST_CODE_CE_INSERTELT: { // CE_INSERTELT: [opval, opval, opval]
       VectorType *OpTy = dyn_cast<VectorType>(CurTy);
       if (Record.size() < 3 || OpTy == 0)
-        return Error("Invalid CE_INSERTELT record");
+        return Error(InvalidRecord);
       Constant *Op0 = ValueList.getConstantFwdRef(Record[0], OpTy);
       Constant *Op1 = ValueList.getConstantFwdRef(Record[1],
                                                   OpTy->getElementType());
@@ -1442,7 +1452,7 @@ bool BitcodeReader::ParseConstants() {
     case bitc::CST_CODE_CE_SHUFFLEVEC: { // CE_SHUFFLEVEC: [opval, opval, opval]
       VectorType *OpTy = dyn_cast<VectorType>(CurTy);
       if (Record.size() < 3 || OpTy == 0)
-        return Error("Invalid CE_SHUFFLEVEC record");
+        return Error(InvalidRecord);
       Constant *Op0 = ValueList.getConstantFwdRef(Record[0], OpTy);
       Constant *Op1 = ValueList.getConstantFwdRef(Record[1], OpTy);
       Type *ShufTy = VectorType::get(Type::getInt32Ty(Context),
@@ -1456,7 +1466,7 @@ bool BitcodeReader::ParseConstants() {
       VectorType *OpTy =
         dyn_cast_or_null<VectorType>(getTypeByID(Record[0]));
       if (Record.size() < 4 || RTy == 0 || OpTy == 0)
-        return Error("Invalid CE_SHUFVEC_EX record");
+        return Error(InvalidRecord);
       Constant *Op0 = ValueList.getConstantFwdRef(Record[1], OpTy);
       Constant *Op1 = ValueList.getConstantFwdRef(Record[2], OpTy);
       Type *ShufTy = VectorType::get(Type::getInt32Ty(Context),
@@ -1466,9 +1476,11 @@ bool BitcodeReader::ParseConstants() {
       break;
     }
     case bitc::CST_CODE_CE_CMP: {     // CE_CMP: [opty, opval, opval, pred]
-      if (Record.size() < 4) return Error("Invalid CE_CMP record");
+      if (Record.size() < 4)
+        return Error(InvalidRecord);
       Type *OpTy = getTypeByID(Record[0]);
-      if (OpTy == 0) return Error("Invalid CE_CMP record");
+      if (OpTy == 0)
+        return Error(InvalidRecord);
       Constant *Op0 = ValueList.getConstantFwdRef(Record[1], OpTy);
       Constant *Op1 = ValueList.getConstantFwdRef(Record[2], OpTy);
 
@@ -1481,16 +1493,17 @@ bool BitcodeReader::ParseConstants() {
     // This maintains backward compatibility, pre-asm dialect keywords.
     // FIXME: Remove with the 4.0 release.
     case bitc::CST_CODE_INLINEASM_OLD: {
-      if (Record.size() < 2) return Error("Invalid INLINEASM record");
+      if (Record.size() < 2)
+        return Error(InvalidRecord);
       std::string AsmStr, ConstrStr;
       bool HasSideEffects = Record[0] & 1;
       bool IsAlignStack = Record[0] >> 1;
       unsigned AsmStrSize = Record[1];
       if (2+AsmStrSize >= Record.size())
-        return Error("Invalid INLINEASM record");
+        return Error(InvalidRecord);
       unsigned ConstStrSize = Record[2+AsmStrSize];
       if (3+AsmStrSize+ConstStrSize > Record.size())
-        return Error("Invalid INLINEASM record");
+        return Error(InvalidRecord);
 
       for (unsigned i = 0; i != AsmStrSize; ++i)
         AsmStr += (char)Record[2+i];
@@ -1504,17 +1517,18 @@ bool BitcodeReader::ParseConstants() {
     // This version adds support for the asm dialect keywords (e.g.,
     // inteldialect).
     case bitc::CST_CODE_INLINEASM: {
-      if (Record.size() < 2) return Error("Invalid INLINEASM record");
+      if (Record.size() < 2)
+        return Error(InvalidRecord);
       std::string AsmStr, ConstrStr;
       bool HasSideEffects = Record[0] & 1;
       bool IsAlignStack = (Record[0] >> 1) & 1;
       unsigned AsmDialect = Record[0] >> 2;
       unsigned AsmStrSize = Record[1];
       if (2+AsmStrSize >= Record.size())
-        return Error("Invalid INLINEASM record");
+        return Error(InvalidRecord);
       unsigned ConstStrSize = Record[2+AsmStrSize];
       if (3+AsmStrSize+ConstStrSize > Record.size())
-        return Error("Invalid INLINEASM record");
+        return Error(InvalidRecord);
 
       for (unsigned i = 0; i != AsmStrSize; ++i)
         AsmStr += (char)Record[2+i];
@@ -1527,12 +1541,15 @@ bool BitcodeReader::ParseConstants() {
       break;
     }
     case bitc::CST_CODE_BLOCKADDRESS:{
-      if (Record.size() < 3) return Error("Invalid CE_BLOCKADDRESS record");
+      if (Record.size() < 3)
+        return Error(InvalidRecord);
       Type *FnTy = getTypeByID(Record[0]);
-      if (FnTy == 0) return Error("Invalid CE_BLOCKADDRESS record");
+      if (FnTy == 0)
+        return Error(InvalidRecord);
       Function *Fn =
         dyn_cast_or_null<Function>(ValueList.getConstantFwdRef(Record[1],FnTy));
-      if (Fn == 0) return Error("Invalid CE_BLOCKADDRESS record");
+      if (Fn == 0)
+        return Error(InvalidRecord);
 
       // If the function is already parsed we can insert the block address right
       // away.
@@ -1540,7 +1557,7 @@ bool BitcodeReader::ParseConstants() {
         Function::iterator BBI = Fn->begin(), BBE = Fn->end();
         for (size_t I = 0, E = Record[2]; I != E; ++I) {
           if (BBI == BBE)
-            return Error("Invalid blockaddress block #");
+            return Error(InvalidID);
           ++BBI;
         }
         V = BlockAddress::get(Fn, BBI);
@@ -1563,9 +1580,9 @@ bool BitcodeReader::ParseConstants() {
   }
 }
 
-bool BitcodeReader::ParseUseLists() {
+error_code BitcodeReader::ParseUseLists() {
   if (Stream.EnterSubBlock(bitc::USELIST_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -1576,9 +1593,9 @@ bool BitcodeReader::ParseUseLists() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("malformed use list block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -1592,7 +1609,7 @@ bool BitcodeReader::ParseUseLists() {
     case bitc::USELIST_CODE_ENTRY: { // USELIST_CODE_ENTRY: TBD.
       unsigned RecordLength = Record.size();
       if (RecordLength < 1)
-        return Error ("Invalid UseList reader!");
+        return Error(InvalidRecord);
       UseListRecords.push_back(Record);
       break;
     }
@@ -1603,10 +1620,10 @@ bool BitcodeReader::ParseUseLists() {
 /// RememberAndSkipFunctionBody - When we see the block for a function body,
 /// remember where it is and then skip it.  This lets us lazily deserialize the
 /// functions.
-bool BitcodeReader::RememberAndSkipFunctionBody() {
+error_code BitcodeReader::RememberAndSkipFunctionBody() {
   // Get the function we are talking about.
   if (FunctionsWithBodies.empty())
-    return Error("Insufficient function protos");
+    return Error(InsufficientFunctionProtos);
 
   Function *Fn = FunctionsWithBodies.back();
   FunctionsWithBodies.pop_back();
@@ -1617,15 +1634,15 @@ bool BitcodeReader::RememberAndSkipFunctionBody() {
 
   // Skip over the function block for now.
   if (Stream.SkipBlock())
-    return Error("Malformed block record");
-  return false;
+    return Error(InvalidRecord);
+  return error_code::success();
 }
 
-bool BitcodeReader::GlobalCleanup() {
+error_code BitcodeReader::GlobalCleanup() {
   // Patch the initializers for globals and aliases up.
   ResolveGlobalAndAliasInits();
   if (!GlobalInits.empty() || !AliasInits.empty())
-    return Error("Malformed global initializer set");
+    return Error(MalformedGlobalInitializerSet);
 
   // Look for intrinsic functions which need to be upgraded at some point
   for (Module::iterator FI = TheModule->begin(), FE = TheModule->end();
@@ -1644,14 +1661,14 @@ bool BitcodeReader::GlobalCleanup() {
   // want lazy deserialization.
   std::vector<std::pair<GlobalVariable*, unsigned> >().swap(GlobalInits);
   std::vector<std::pair<GlobalAlias*, unsigned> >().swap(AliasInits);
-  return false;
+  return error_code::success();
 }
 
-bool BitcodeReader::ParseModule(bool Resume) {
+error_code BitcodeReader::ParseModule(bool Resume) {
   if (Resume)
     Stream.JumpToBit(NextUnreadBit);
   else if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
   std::vector<std::string> SectionTable;
@@ -1663,8 +1680,7 @@ bool BitcodeReader::ParseModule(bool Resume) {
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
-      Error("malformed module block");
-      return true;
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
       return GlobalCleanup();
 
@@ -1672,49 +1688,51 @@ bool BitcodeReader::ParseModule(bool Resume) {
       switch (Entry.ID) {
       default:  // Skip unknown content.
         if (Stream.SkipBlock())
-          return Error("Malformed block record");
+          return Error(InvalidRecord);
         break;
       case bitc::BLOCKINFO_BLOCK_ID:
         if (Stream.ReadBlockInfoBlock())
-          return Error("Malformed BlockInfoBlock");
+          return Error(MalformedBlock);
         break;
       case bitc::PARAMATTR_BLOCK_ID:
-        if (ParseAttributeBlock())
-          return true;
+        if (error_code EC = ParseAttributeBlock())
+          return EC;
         break;
       case bitc::PARAMATTR_GROUP_BLOCK_ID:
-        if (ParseAttributeGroupBlock())
-          return true;
+        if (error_code EC = ParseAttributeGroupBlock())
+          return EC;
         break;
       case bitc::TYPE_BLOCK_ID_NEW:
-        if (ParseTypeTable())
-          return true;
+        if (error_code EC = ParseTypeTable())
+          return EC;
         break;
       case bitc::VALUE_SYMTAB_BLOCK_ID:
-        if (ParseValueSymbolTable())
-          return true;
+        if (error_code EC = ParseValueSymbolTable())
+          return EC;
         SeenValueSymbolTable = true;
         break;
       case bitc::CONSTANTS_BLOCK_ID:
-        if (ParseConstants() || ResolveGlobalAndAliasInits())
-          return true;
+        if (error_code EC = ParseConstants())
+          return EC;
+        if (error_code EC = ResolveGlobalAndAliasInits())
+          return EC;
         break;
       case bitc::METADATA_BLOCK_ID:
-        if (ParseMetadata())
-          return true;
+        if (error_code EC = ParseMetadata())
+          return EC;
         break;
       case bitc::FUNCTION_BLOCK_ID:
         // If this is the first function body we've seen, reverse the
         // FunctionsWithBodies list.
         if (!SeenFirstFunctionBody) {
           std::reverse(FunctionsWithBodies.begin(), FunctionsWithBodies.end());
-          if (GlobalCleanup())
-            return true;
+          if (error_code EC = GlobalCleanup())
+            return EC;
           SeenFirstFunctionBody = true;
         }
 
-        if (RememberAndSkipFunctionBody())
-          return true;
+        if (error_code EC = RememberAndSkipFunctionBody())
+          return EC;
         // For streaming bitcode, suspend parsing when we reach the function
         // bodies. Subsequent materialization calls will resume it when
         // necessary. For streaming, the function bodies must be at the end of
@@ -1723,12 +1741,12 @@ bool BitcodeReader::ParseModule(bool Resume) {
         // just finish the parse now.
         if (LazyStreamer && SeenValueSymbolTable) {
           NextUnreadBit = Stream.GetCurrentBitNo();
-          return false;
+          return error_code::success();
         }
         break;
       case bitc::USELIST_BLOCK_ID:
-        if (ParseUseLists())
-          return true;
+        if (error_code EC = ParseUseLists())
+          return EC;
         break;
       }
       continue;
@@ -1744,11 +1762,12 @@ bool BitcodeReader::ParseModule(bool Resume) {
     default: break;  // Default behavior, ignore unknown content.
     case bitc::MODULE_CODE_VERSION: {  // VERSION: [version#]
       if (Record.size() < 1)
-        return Error("Malformed MODULE_CODE_VERSION");
+        return Error(InvalidRecord);
       // Only version #0 and #1 are supported so far.
       unsigned module_version = Record[0];
       switch (module_version) {
-        default: return Error("Unknown bitstream version!");
+        default:
+          return Error(InvalidValue);
         case 0:
           UseRelativeIDs = false;
           break;
@@ -1761,21 +1780,21 @@ bool BitcodeReader::ParseModule(bool Resume) {
     case bitc::MODULE_CODE_TRIPLE: {  // TRIPLE: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_TRIPLE record");
+        return Error(InvalidRecord);
       TheModule->setTargetTriple(S);
       break;
     }
     case bitc::MODULE_CODE_DATALAYOUT: {  // DATALAYOUT: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_DATALAYOUT record");
+        return Error(InvalidRecord);
       TheModule->setDataLayout(S);
       break;
     }
     case bitc::MODULE_CODE_ASM: {  // ASM: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_ASM record");
+        return Error(InvalidRecord);
       TheModule->setModuleInlineAsm(S);
       break;
     }
@@ -1783,21 +1802,21 @@ bool BitcodeReader::ParseModule(bool Resume) {
       // FIXME: Remove in 4.0.
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_DEPLIB record");
+        return Error(InvalidRecord);
       // Ignore value.
       break;
     }
     case bitc::MODULE_CODE_SECTIONNAME: {  // SECTIONNAME: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_SECTIONNAME record");
+        return Error(InvalidRecord);
       SectionTable.push_back(S);
       break;
     }
     case bitc::MODULE_CODE_GCNAME: {  // SECTIONNAME: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_GCNAME record");
+        return Error(InvalidRecord);
       GCTable.push_back(S);
       break;
     }
@@ -1806,11 +1825,12 @@ bool BitcodeReader::ParseModule(bool Resume) {
     //             unnamed_addr]
     case bitc::MODULE_CODE_GLOBALVAR: {
       if (Record.size() < 6)
-        return Error("Invalid MODULE_CODE_GLOBALVAR record");
+        return Error(InvalidRecord);
       Type *Ty = getTypeByID(Record[0]);
-      if (!Ty) return Error("Invalid MODULE_CODE_GLOBALVAR record");
+      if (!Ty)
+        return Error(InvalidRecord);
       if (!Ty->isPointerTy())
-        return Error("Global not a pointer type!");
+        return Error(InvalidTypeForValue);
       unsigned AddressSpace = cast<PointerType>(Ty)->getAddressSpace();
       Ty = cast<PointerType>(Ty)->getElementType();
 
@@ -1820,7 +1840,7 @@ bool BitcodeReader::ParseModule(bool Resume) {
       std::string Section;
       if (Record[5]) {
         if (Record[5]-1 >= SectionTable.size())
-          return Error("Invalid section ID");
+          return Error(InvalidID);
         Section = SectionTable[Record[5]-1];
       }
       GlobalValue::VisibilityTypes Visibility = GlobalValue::DefaultVisibility;
@@ -1859,15 +1879,16 @@ bool BitcodeReader::ParseModule(bool Resume) {
     //             alignment, section, visibility, gc, unnamed_addr]
     case bitc::MODULE_CODE_FUNCTION: {
       if (Record.size() < 8)
-        return Error("Invalid MODULE_CODE_FUNCTION record");
+        return Error(InvalidRecord);
       Type *Ty = getTypeByID(Record[0]);
-      if (!Ty) return Error("Invalid MODULE_CODE_FUNCTION record");
+      if (!Ty)
+        return Error(InvalidRecord);
       if (!Ty->isPointerTy())
-        return Error("Function not a pointer type!");
+        return Error(InvalidTypeForValue);
       FunctionType *FTy =
         dyn_cast<FunctionType>(cast<PointerType>(Ty)->getElementType());
       if (!FTy)
-        return Error("Function not a pointer to function type!");
+        return Error(InvalidTypeForValue);
 
       Function *Func = Function::Create(FTy, GlobalValue::ExternalLinkage,
                                         "", TheModule);
@@ -1880,13 +1901,13 @@ bool BitcodeReader::ParseModule(bool Resume) {
       Func->setAlignment((1 << Record[5]) >> 1);
       if (Record[6]) {
         if (Record[6]-1 >= SectionTable.size())
-          return Error("Invalid section ID");
+          return Error(InvalidID);
         Func->setSection(SectionTable[Record[6]-1]);
       }
       Func->setVisibility(GetDecodedVisibility(Record[7]));
       if (Record.size() > 8 && Record[8]) {
         if (Record[8]-1 > GCTable.size())
-          return Error("Invalid GC ID");
+          return Error(InvalidID);
         Func->setGC(GCTable[Record[8]-1].c_str());
       }
       bool UnnamedAddr = false;
@@ -1909,11 +1930,12 @@ bool BitcodeReader::ParseModule(bool Resume) {
     // ALIAS: [alias type, aliasee val#, linkage, visibility]
     case bitc::MODULE_CODE_ALIAS: {
       if (Record.size() < 3)
-        return Error("Invalid MODULE_ALIAS record");
+        return Error(InvalidRecord);
       Type *Ty = getTypeByID(Record[0]);
-      if (!Ty) return Error("Invalid MODULE_ALIAS record");
+      if (!Ty)
+        return Error(InvalidRecord);
       if (!Ty->isPointerTy())
-        return Error("Function not a pointer type!");
+        return Error(InvalidTypeForValue);
 
       GlobalAlias *NewGA = new GlobalAlias(Ty, GetDecodedLinkage(Record[2]),
                                            "", 0, TheModule);
@@ -1928,7 +1950,7 @@ bool BitcodeReader::ParseModule(bool Resume) {
     case bitc::MODULE_CODE_PURGEVALS:
       // Trim down the value list to the specified size.
       if (Record.size() < 1 || Record[0] > ValueList.size())
-        return Error("Invalid MODULE_PURGEVALS record");
+        return Error(InvalidRecord);
       ValueList.shrinkTo(Record[0]);
       break;
     }
@@ -1936,10 +1958,11 @@ bool BitcodeReader::ParseModule(bool Resume) {
   }
 }
 
-bool BitcodeReader::ParseBitcodeInto(Module *M) {
+error_code BitcodeReader::ParseBitcodeInto(Module *M) {
   TheModule = 0;
 
-  if (InitStream()) return true;
+  if (error_code EC = InitStream())
+    return EC;
 
   // Sniff for the signature.
   if (Stream.Read(8) != 'B' ||
@@ -1948,42 +1971,42 @@ bool BitcodeReader::ParseBitcodeInto(Module *M) {
       Stream.Read(4) != 0xC ||
       Stream.Read(4) != 0xE ||
       Stream.Read(4) != 0xD)
-    return Error("Invalid bitcode signature");
+    return Error(InvalidBitcodeSignature);
 
   // We expect a number of well-defined blocks, though we don't necessarily
   // need to understand them all.
   while (1) {
     if (Stream.AtEndOfStream())
-      return false;
+      return error_code::success();
 
     BitstreamEntry Entry =
       Stream.advance(BitstreamCursor::AF_DontAutoprocessAbbrevs);
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
-      Error("malformed module file");
-      return true;
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
 
     case BitstreamEntry::SubBlock:
       switch (Entry.ID) {
       case bitc::BLOCKINFO_BLOCK_ID:
         if (Stream.ReadBlockInfoBlock())
-          return Error("Malformed BlockInfoBlock");
+          return Error(MalformedBlock);
         break;
       case bitc::MODULE_BLOCK_ID:
         // Reject multiple MODULE_BLOCK's in a single bitstream.
         if (TheModule)
-          return Error("Multiple MODULE_BLOCKs in same stream");
+          return Error(InvalidMultipleBlocks);
         TheModule = M;
-        if (ParseModule(false))
-          return true;
-        if (LazyStreamer) return false;
+        if (error_code EC = ParseModule(false))
+          return EC;
+        if (LazyStreamer)
+          return error_code::success();
         break;
       default:
         if (Stream.SkipBlock())
-          return Error("Malformed block record");
+          return Error(InvalidRecord);
         break;
       }
       continue;
@@ -1996,16 +2019,16 @@ bool BitcodeReader::ParseBitcodeInto(Module *M) {
       if (Stream.getAbbrevIDWidth() == 2 && Entry.ID == 2 &&
           Stream.Read(6) == 2 && Stream.Read(24) == 0xa0a0a &&
           Stream.AtEndOfStream())
-        return false;
+        return error_code::success();
 
-      return Error("Invalid record at top-level");
+      return Error(InvalidRecord);
     }
   }
 }
 
-bool BitcodeReader::ParseModuleTriple(std::string &Triple) {
+error_code BitcodeReader::ParseModuleTriple(std::string &Triple) {
   if (Stream.EnterSubBlock(bitc::MODULE_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
 
@@ -2016,9 +2039,9 @@ bool BitcodeReader::ParseModuleTriple(std::string &Triple) {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("malformed module block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -2030,7 +2053,7 @@ bool BitcodeReader::ParseModuleTriple(std::string &Triple) {
     case bitc::MODULE_CODE_TRIPLE: {  // TRIPLE: [strchr x N]
       std::string S;
       if (ConvertToString(Record, 0, S))
-        return Error("Invalid MODULE_CODE_TRIPLE record");
+        return Error(InvalidRecord);
       Triple = S;
       break;
     }
@@ -2039,8 +2062,9 @@ bool BitcodeReader::ParseModuleTriple(std::string &Triple) {
   }
 }
 
-bool BitcodeReader::ParseTriple(std::string &Triple) {
-  if (InitStream()) return true;
+error_code BitcodeReader::ParseTriple(std::string &Triple) {
+  if (error_code EC = InitStream())
+    return EC;
 
   // Sniff for the signature.
   if (Stream.Read(8) != 'B' ||
@@ -2049,7 +2073,7 @@ bool BitcodeReader::ParseTriple(std::string &Triple) {
       Stream.Read(4) != 0xC ||
       Stream.Read(4) != 0xE ||
       Stream.Read(4) != 0xD)
-    return Error("Invalid bitcode signature");
+    return Error(InvalidBitcodeSignature);
 
   // We expect a number of well-defined blocks, though we don't necessarily
   // need to understand them all.
@@ -2058,20 +2082,17 @@ bool BitcodeReader::ParseTriple(std::string &Triple) {
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
-      Error("malformed module file");
-      return true;
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
 
     case BitstreamEntry::SubBlock:
       if (Entry.ID == bitc::MODULE_BLOCK_ID)
         return ParseModuleTriple(Triple);
 
       // Ignore other sub-blocks.
-      if (Stream.SkipBlock()) {
-        Error("malformed block record in AST file");
-        return true;
-      }
+      if (Stream.SkipBlock())
+        return Error(MalformedBlock);
       continue;
 
     case BitstreamEntry::Record:
@@ -2082,9 +2103,9 @@ bool BitcodeReader::ParseTriple(std::string &Triple) {
 }
 
 /// ParseMetadataAttachment - Parse metadata attachments.
-bool BitcodeReader::ParseMetadataAttachment() {
+error_code BitcodeReader::ParseMetadataAttachment() {
   if (Stream.EnterSubBlock(bitc::METADATA_ATTACHMENT_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   SmallVector<uint64_t, 64> Record;
   while (1) {
@@ -2093,9 +2114,9 @@ bool BitcodeReader::ParseMetadataAttachment() {
     switch (Entry.Kind) {
     case BitstreamEntry::SubBlock: // Handled for us already.
     case BitstreamEntry::Error:
-      return Error("malformed metadata block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
-      return false;
+      return error_code::success();
     case BitstreamEntry::Record:
       // The interesting case.
       break;
@@ -2109,14 +2130,14 @@ bool BitcodeReader::ParseMetadataAttachment() {
     case bitc::METADATA_ATTACHMENT: {
       unsigned RecordLength = Record.size();
       if (Record.empty() || (RecordLength - 1) % 2 == 1)
-        return Error ("Invalid METADATA_ATTACHMENT reader!");
+        return Error(InvalidRecord);
       Instruction *Inst = InstructionList[Record[0]];
       for (unsigned i = 1; i != RecordLength; i = i+2) {
         unsigned Kind = Record[i];
         DenseMap<unsigned, unsigned>::iterator I =
           MDKindMap.find(Kind);
         if (I == MDKindMap.end())
-          return Error("Invalid metadata kind ID");
+          return Error(InvalidID);
         Value *Node = MDValueList.getValueFwdRef(Record[i+1]);
         Inst->setMetadata(I->second, cast<MDNode>(Node));
         if (I->second == LLVMContext::MD_tbaa)
@@ -2129,9 +2150,9 @@ bool BitcodeReader::ParseMetadataAttachment() {
 }
 
 /// ParseFunctionBody - Lazily parse the specified function body block.
-bool BitcodeReader::ParseFunctionBody(Function *F) {
+error_code BitcodeReader::ParseFunctionBody(Function *F) {
   if (Stream.EnterSubBlock(bitc::FUNCTION_BLOCK_ID))
-    return Error("Malformed block record");
+    return Error(InvalidRecord);
 
   InstructionList.clear();
   unsigned ModuleValueListSize = ValueList.size();
@@ -2154,7 +2175,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
 
     switch (Entry.Kind) {
     case BitstreamEntry::Error:
-      return Error("Bitcode error in function block");
+      return Error(MalformedBlock);
     case BitstreamEntry::EndBlock:
       goto OutOfRecordLoop;
 
@@ -2162,20 +2183,24 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       switch (Entry.ID) {
       default:  // Skip unknown content.
         if (Stream.SkipBlock())
-          return Error("Malformed block record");
+          return Error(InvalidRecord);
         break;
       case bitc::CONSTANTS_BLOCK_ID:
-        if (ParseConstants()) return true;
+        if (error_code EC = ParseConstants())
+          return EC;
         NextValueNo = ValueList.size();
         break;
       case bitc::VALUE_SYMTAB_BLOCK_ID:
-        if (ParseValueSymbolTable()) return true;
+        if (error_code EC = ParseValueSymbolTable())
+          return EC;
         break;
       case bitc::METADATA_ATTACHMENT_ID:
-        if (ParseMetadataAttachment()) return true;
+        if (error_code EC = ParseMetadataAttachment())
+          return EC;
         break;
       case bitc::METADATA_BLOCK_ID:
-        if (ParseMetadata()) return true;
+        if (error_code EC = ParseMetadata())
+          return EC;
         break;
       }
       continue;
@@ -2191,10 +2216,10 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     unsigned BitCode = Stream.readRecord(Entry.ID, Record);
     switch (BitCode) {
     default: // Default behavior: reject
-      return Error("Unknown instruction");
+      return Error(InvalidValue);
     case bitc::FUNC_CODE_DECLAREBLOCKS:     // DECLAREBLOCKS: [nblocks]
       if (Record.size() < 1 || Record[0] == 0)
-        return Error("Invalid DECLAREBLOCKS record");
+        return Error(InvalidRecord);
       // Create all the basic blocks for the function.
       FunctionBBs.resize(Record[0]);
       for (unsigned i = 0, e = FunctionBBs.size(); i != e; ++i)
@@ -2214,7 +2239,8 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
                !FunctionBBs[CurBBNo-1]->empty())
         I = &FunctionBBs[CurBBNo-1]->back();
 
-      if (I == 0) return Error("Invalid DEBUG_LOC_AGAIN record");
+      if (I == 0)
+        return Error(InvalidRecord);
       I->setDebugLoc(LastLoc);
       I = 0;
       continue;
@@ -2227,7 +2253,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
                !FunctionBBs[CurBBNo-1]->empty())
         I = &FunctionBBs[CurBBNo-1]->back();
       if (I == 0 || Record.size() < 4)
-        return Error("Invalid FUNC_CODE_DEBUG_LOC record");
+        return Error(InvalidRecord);
 
       unsigned Line = Record[0], Col = Record[1];
       unsigned ScopeID = Record[2], IAID = Record[3];
@@ -2247,10 +2273,11 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       if (getValueTypePair(Record, OpNum, NextValueNo, LHS) ||
           popValue(Record, OpNum, NextValueNo, LHS->getType(), RHS) ||
           OpNum+1 > Record.size())
-        return Error("Invalid BINOP record");
+        return Error(InvalidRecord);
 
       int Opc = GetDecodedBinaryOpcode(Record[OpNum++], LHS->getType());
-      if (Opc == -1) return Error("Invalid BINOP record");
+      if (Opc == -1)
+        return Error(InvalidRecord);
       I = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
       InstructionList.push_back(I);
       if (OpNum < Record.size()) {
@@ -2292,12 +2319,12 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       Value *Op;
       if (getValueTypePair(Record, OpNum, NextValueNo, Op) ||
           OpNum+2 != Record.size())
-        return Error("Invalid CAST record");
+        return Error(InvalidRecord);
 
       Type *ResTy = getTypeByID(Record[OpNum]);
       int Opc = GetDecodedCastOpcode(Record[OpNum+1]);
       if (Opc == -1 || ResTy == 0)
-        return Error("Invalid CAST record");
+        return Error(InvalidRecord);
       I = CastInst::Create((Instruction::CastOps)Opc, Op, ResTy);
       InstructionList.push_back(I);
       break;
@@ -2307,13 +2334,13 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 0;
       Value *BasePtr;
       if (getValueTypePair(Record, OpNum, NextValueNo, BasePtr))
-        return Error("Invalid GEP record");
+        return Error(InvalidRecord);
 
       SmallVector<Value*, 16> GEPIdx;
       while (OpNum != Record.size()) {
         Value *Op;
         if (getValueTypePair(Record, OpNum, NextValueNo, Op))
-          return Error("Invalid GEP record");
+          return Error(InvalidRecord);
         GEPIdx.push_back(Op);
       }
 
@@ -2329,14 +2356,14 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 0;
       Value *Agg;
       if (getValueTypePair(Record, OpNum, NextValueNo, Agg))
-        return Error("Invalid EXTRACTVAL record");
+        return Error(InvalidRecord);
 
       SmallVector<unsigned, 4> EXTRACTVALIdx;
       for (unsigned RecSize = Record.size();
            OpNum != RecSize; ++OpNum) {
         uint64_t Index = Record[OpNum];
         if ((unsigned)Index != Index)
-          return Error("Invalid EXTRACTVAL index");
+          return Error(InvalidValue);
         EXTRACTVALIdx.push_back((unsigned)Index);
       }
 
@@ -2350,17 +2377,17 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 0;
       Value *Agg;
       if (getValueTypePair(Record, OpNum, NextValueNo, Agg))
-        return Error("Invalid INSERTVAL record");
+        return Error(InvalidRecord);
       Value *Val;
       if (getValueTypePair(Record, OpNum, NextValueNo, Val))
-        return Error("Invalid INSERTVAL record");
+        return Error(InvalidRecord);
 
       SmallVector<unsigned, 4> INSERTVALIdx;
       for (unsigned RecSize = Record.size();
            OpNum != RecSize; ++OpNum) {
         uint64_t Index = Record[OpNum];
         if ((unsigned)Index != Index)
-          return Error("Invalid INSERTVAL index");
+          return Error(InvalidValue);
         INSERTVALIdx.push_back((unsigned)Index);
       }
 
@@ -2377,7 +2404,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       if (getValueTypePair(Record, OpNum, NextValueNo, TrueVal) ||
           popValue(Record, OpNum, NextValueNo, TrueVal->getType(), FalseVal) ||
           popValue(Record, OpNum, NextValueNo, Type::getInt1Ty(Context), Cond))
-        return Error("Invalid SELECT record");
+        return Error(InvalidRecord);
 
       I = SelectInst::Create(Cond, TrueVal, FalseVal);
       InstructionList.push_back(I);
@@ -2392,18 +2419,18 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       if (getValueTypePair(Record, OpNum, NextValueNo, TrueVal) ||
           popValue(Record, OpNum, NextValueNo, TrueVal->getType(), FalseVal) ||
           getValueTypePair(Record, OpNum, NextValueNo, Cond))
-        return Error("Invalid SELECT record");
+        return Error(InvalidRecord);
 
       // select condition can be either i1 or [N x i1]
       if (VectorType* vector_type =
           dyn_cast<VectorType>(Cond->getType())) {
         // expect <n x i1>
         if (vector_type->getElementType() != Type::getInt1Ty(Context))
-          return Error("Invalid SELECT condition type");
+          return Error(InvalidTypeForValue);
       } else {
         // expect i1
         if (Cond->getType() != Type::getInt1Ty(Context))
-          return Error("Invalid SELECT condition type");
+          return Error(InvalidTypeForValue);
       }
 
       I = SelectInst::Create(Cond, TrueVal, FalseVal);
@@ -2416,7 +2443,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       Value *Vec, *Idx;
       if (getValueTypePair(Record, OpNum, NextValueNo, Vec) ||
           popValue(Record, OpNum, NextValueNo, Type::getInt32Ty(Context), Idx))
-        return Error("Invalid EXTRACTELT record");
+        return Error(InvalidRecord);
       I = ExtractElementInst::Create(Vec, Idx);
       InstructionList.push_back(I);
       break;
@@ -2429,7 +2456,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo,
                    cast<VectorType>(Vec->getType())->getElementType(), Elt) ||
           popValue(Record, OpNum, NextValueNo, Type::getInt32Ty(Context), Idx))
-        return Error("Invalid INSERTELT record");
+        return Error(InvalidRecord);
       I = InsertElementInst::Create(Vec, Elt, Idx);
       InstructionList.push_back(I);
       break;
@@ -2440,10 +2467,10 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       Value *Vec1, *Vec2, *Mask;
       if (getValueTypePair(Record, OpNum, NextValueNo, Vec1) ||
           popValue(Record, OpNum, NextValueNo, Vec1->getType(), Vec2))
-        return Error("Invalid SHUFFLEVEC record");
+        return Error(InvalidRecord);
 
       if (getValueTypePair(Record, OpNum, NextValueNo, Mask))
-        return Error("Invalid SHUFFLEVEC record");
+        return Error(InvalidRecord);
       I = new ShuffleVectorInst(Vec1, Vec2, Mask);
       InstructionList.push_back(I);
       break;
@@ -2461,7 +2488,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       if (getValueTypePair(Record, OpNum, NextValueNo, LHS) ||
           popValue(Record, OpNum, NextValueNo, LHS->getType(), RHS) ||
           OpNum+1 != Record.size())
-        return Error("Invalid CMP record");
+        return Error(InvalidRecord);
 
       if (LHS->getType()->isFPOrFPVectorTy())
         I = new FCmpInst((FCmpInst::Predicate)Record[OpNum], LHS, RHS);
@@ -2483,9 +2510,9 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         unsigned OpNum = 0;
         Value *Op = NULL;
         if (getValueTypePair(Record, OpNum, NextValueNo, Op))
-          return Error("Invalid RET record");
+          return Error(InvalidRecord);
         if (OpNum != Record.size())
-          return Error("Invalid RET record");
+          return Error(InvalidRecord);
 
         I = ReturnInst::Create(Context, Op);
         InstructionList.push_back(I);
@@ -2493,10 +2520,10 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       }
     case bitc::FUNC_CODE_INST_BR: { // BR: [bb#, bb#, opval] or [bb#]
       if (Record.size() != 1 && Record.size() != 3)
-        return Error("Invalid BR record");
+        return Error(InvalidRecord);
       BasicBlock *TrueDest = getBasicBlock(Record[0]);
       if (TrueDest == 0)
-        return Error("Invalid BR record");
+        return Error(InvalidRecord);
 
       if (Record.size() == 1) {
         I = BranchInst::Create(TrueDest);
@@ -2507,7 +2534,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         Value *Cond = getValue(Record, 2, NextValueNo,
                                Type::getInt1Ty(Context));
         if (FalseDest == 0 || Cond == 0)
-          return Error("Invalid BR record");
+          return Error(InvalidRecord);
         I = BranchInst::Create(TrueDest, FalseDest, Cond);
         InstructionList.push_back(I);
       }
@@ -2527,7 +2554,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         Value *Cond = getValue(Record, 2, NextValueNo, OpTy);
         BasicBlock *Default = getBasicBlock(Record[3]);
         if (OpTy == 0 || Cond == 0 || Default == 0)
-          return Error("Invalid SWITCH record");
+          return Error(InvalidRecord);
 
         unsigned NumCases = Record[4];
 
@@ -2579,12 +2606,12 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       // Old SwitchInst format without case ranges.
 
       if (Record.size() < 3 || (Record.size() & 1) == 0)
-        return Error("Invalid SWITCH record");
+        return Error(InvalidRecord);
       Type *OpTy = getTypeByID(Record[0]);
       Value *Cond = getValue(Record, 1, NextValueNo, OpTy);
       BasicBlock *Default = getBasicBlock(Record[2]);
       if (OpTy == 0 || Cond == 0 || Default == 0)
-        return Error("Invalid SWITCH record");
+        return Error(InvalidRecord);
       unsigned NumCases = (Record.size()-3)/2;
       SwitchInst *SI = SwitchInst::Create(Cond, Default, NumCases);
       InstructionList.push_back(SI);
@@ -2594,7 +2621,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         BasicBlock *DestBB = getBasicBlock(Record[1+3+i*2]);
         if (CaseVal == 0 || DestBB == 0) {
           delete SI;
-          return Error("Invalid SWITCH record!");
+          return Error(InvalidRecord);
         }
         SI->addCase(CaseVal, DestBB);
       }
@@ -2603,11 +2630,11 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     }
     case bitc::FUNC_CODE_INST_INDIRECTBR: { // INDIRECTBR: [opty, op0, op1, ...]
       if (Record.size() < 2)
-        return Error("Invalid INDIRECTBR record");
+        return Error(InvalidRecord);
       Type *OpTy = getTypeByID(Record[0]);
       Value *Address = getValue(Record, 1, NextValueNo, OpTy);
       if (OpTy == 0 || Address == 0)
-        return Error("Invalid INDIRECTBR record");
+        return Error(InvalidRecord);
       unsigned NumDests = Record.size()-2;
       IndirectBrInst *IBI = IndirectBrInst::Create(Address, NumDests);
       InstructionList.push_back(IBI);
@@ -2616,7 +2643,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           IBI->addDestination(DestBB);
         } else {
           delete IBI;
-          return Error("Invalid INDIRECTBR record!");
+          return Error(InvalidRecord);
         }
       }
       I = IBI;
@@ -2625,7 +2652,8 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
 
     case bitc::FUNC_CODE_INST_INVOKE: {
       // INVOKE: [attrs, cc, normBB, unwindBB, fnty, op0,op1,op2, ...]
-      if (Record.size() < 4) return Error("Invalid INVOKE record");
+      if (Record.size() < 4)
+        return Error(InvalidRecord);
       AttributeSet PAL = getAttributes(Record[0]);
       unsigned CCInfo = Record[1];
       BasicBlock *NormalBB = getBasicBlock(Record[2]);
@@ -2634,7 +2662,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 4;
       Value *Callee;
       if (getValueTypePair(Record, OpNum, NextValueNo, Callee))
-        return Error("Invalid INVOKE record");
+        return Error(InvalidRecord);
 
       PointerType *CalleeTy = dyn_cast<PointerType>(Callee->getType());
       FunctionType *FTy = !CalleeTy ? 0 :
@@ -2643,24 +2671,25 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       // Check that the right number of fixed parameters are here.
       if (FTy == 0 || NormalBB == 0 || UnwindBB == 0 ||
           Record.size() < OpNum+FTy->getNumParams())
-        return Error("Invalid INVOKE record");
+        return Error(InvalidRecord);
 
       SmallVector<Value*, 16> Ops;
       for (unsigned i = 0, e = FTy->getNumParams(); i != e; ++i, ++OpNum) {
         Ops.push_back(getValue(Record, OpNum, NextValueNo,
                                FTy->getParamType(i)));
-        if (Ops.back() == 0) return Error("Invalid INVOKE record");
+        if (Ops.back() == 0)
+          return Error(InvalidRecord);
       }
 
       if (!FTy->isVarArg()) {
         if (Record.size() != OpNum)
-          return Error("Invalid INVOKE record");
+          return Error(InvalidRecord);
       } else {
         // Read type/value pairs for varargs params.
         while (OpNum != Record.size()) {
           Value *Op;
           if (getValueTypePair(Record, OpNum, NextValueNo, Op))
-            return Error("Invalid INVOKE record");
+            return Error(InvalidRecord);
           Ops.push_back(Op);
         }
       }
@@ -2676,7 +2705,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned Idx = 0;
       Value *Val = 0;
       if (getValueTypePair(Record, Idx, NextValueNo, Val))
-        return Error("Invalid RESUME record");
+        return Error(InvalidRecord);
       I = ResumeInst::Create(Val);
       InstructionList.push_back(I);
       break;
@@ -2687,9 +2716,10 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       break;
     case bitc::FUNC_CODE_INST_PHI: { // PHI: [ty, val0,bb0, ...]
       if (Record.size() < 1 || ((Record.size()-1)&1))
-        return Error("Invalid PHI record");
+        return Error(InvalidRecord);
       Type *Ty = getTypeByID(Record[0]);
-      if (!Ty) return Error("Invalid PHI record");
+      if (!Ty)
+        return Error(InvalidRecord);
 
       PHINode *PN = PHINode::Create(Ty, (Record.size()-1)/2);
       InstructionList.push_back(PN);
@@ -2704,7 +2734,8 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         else
           V = getValue(Record, 1+i, NextValueNo, Ty);
         BasicBlock *BB = getBasicBlock(Record[2+i]);
-        if (!V || !BB) return Error("Invalid PHI record");
+        if (!V || !BB)
+          return Error(InvalidRecord);
         PN->addIncoming(V, BB);
       }
       I = PN;
@@ -2715,12 +2746,13 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       // LANDINGPAD: [ty, val, val, num, (id0,val0 ...)?]
       unsigned Idx = 0;
       if (Record.size() < 4)
-        return Error("Invalid LANDINGPAD record");
+        return Error(InvalidRecord);
       Type *Ty = getTypeByID(Record[Idx++]);
-      if (!Ty) return Error("Invalid LANDINGPAD record");
+      if (!Ty)
+        return Error(InvalidRecord);
       Value *PersFn = 0;
       if (getValueTypePair(Record, Idx, NextValueNo, PersFn))
-        return Error("Invalid LANDINGPAD record");
+        return Error(InvalidRecord);
 
       bool IsCleanup = !!Record[Idx++];
       unsigned NumClauses = Record[Idx++];
@@ -2733,7 +2765,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
 
         if (getValueTypePair(Record, Idx, NextValueNo, Val)) {
           delete LP;
-          return Error("Invalid LANDINGPAD record");
+          return Error(InvalidRecord);
         }
 
         assert((CT != LandingPadInst::Catch ||
@@ -2752,13 +2784,14 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
 
     case bitc::FUNC_CODE_INST_ALLOCA: { // ALLOCA: [instty, opty, op, align]
       if (Record.size() != 4)
-        return Error("Invalid ALLOCA record");
+        return Error(InvalidRecord);
       PointerType *Ty =
         dyn_cast_or_null<PointerType>(getTypeByID(Record[0]));
       Type *OpTy = getTypeByID(Record[1]);
       Value *Size = getFnValueByID(Record[2], OpTy);
       unsigned Align = Record[3];
-      if (!Ty || !Size) return Error("Invalid ALLOCA record");
+      if (!Ty || !Size)
+        return Error(InvalidRecord);
       I = new AllocaInst(Ty->getElementType(), Size, (1 << Align) >> 1);
       InstructionList.push_back(I);
       break;
@@ -2768,7 +2801,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       Value *Op;
       if (getValueTypePair(Record, OpNum, NextValueNo, Op) ||
           OpNum+2 != Record.size())
-        return Error("Invalid LOAD record");
+        return Error(InvalidRecord);
 
       I = new LoadInst(Op, "", Record[OpNum+1], (1 << Record[OpNum]) >> 1);
       InstructionList.push_back(I);
@@ -2780,15 +2813,15 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       Value *Op;
       if (getValueTypePair(Record, OpNum, NextValueNo, Op) ||
           OpNum+4 != Record.size())
-        return Error("Invalid LOADATOMIC record");
+        return Error(InvalidRecord);
 
 
       AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+2]);
       if (Ordering == NotAtomic || Ordering == Release ||
           Ordering == AcquireRelease)
-        return Error("Invalid LOADATOMIC record");
+        return Error(InvalidRecord);
       if (Ordering != NotAtomic && Record[OpNum] == 0)
-        return Error("Invalid LOADATOMIC record");
+        return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[OpNum+3]);
 
       I = new LoadInst(Op, "", Record[OpNum+1], (1 << Record[OpNum]) >> 1,
@@ -2803,7 +2836,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo,
                     cast<PointerType>(Ptr->getType())->getElementType(), Val) ||
           OpNum+2 != Record.size())
-        return Error("Invalid STORE record");
+        return Error(InvalidRecord);
 
       I = new StoreInst(Val, Ptr, Record[OpNum+1], (1 << Record[OpNum]) >> 1);
       InstructionList.push_back(I);
@@ -2817,15 +2850,15 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo,
                     cast<PointerType>(Ptr->getType())->getElementType(), Val) ||
           OpNum+4 != Record.size())
-        return Error("Invalid STOREATOMIC record");
+        return Error(InvalidRecord);
 
       AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+2]);
       if (Ordering == NotAtomic || Ordering == Acquire ||
           Ordering == AcquireRelease)
-        return Error("Invalid STOREATOMIC record");
+        return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[OpNum+3]);
       if (Ordering != NotAtomic && Record[OpNum] == 0)
-        return Error("Invalid STOREATOMIC record");
+        return Error(InvalidRecord);
 
       I = new StoreInst(Val, Ptr, Record[OpNum+1], (1 << Record[OpNum]) >> 1,
                         Ordering, SynchScope);
@@ -2842,10 +2875,10 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo,
                     cast<PointerType>(Ptr->getType())->getElementType(), New) ||
           OpNum+3 != Record.size())
-        return Error("Invalid CMPXCHG record");
+        return Error(InvalidRecord);
       AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+1]);
       if (Ordering == NotAtomic || Ordering == Unordered)
-        return Error("Invalid CMPXCHG record");
+        return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[OpNum+2]);
       I = new AtomicCmpXchgInst(Ptr, Cmp, New, Ordering, SynchScope);
       cast<AtomicCmpXchgInst>(I)->setVolatile(Record[OpNum]);
@@ -2860,14 +2893,14 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
           popValue(Record, OpNum, NextValueNo,
                     cast<PointerType>(Ptr->getType())->getElementType(), Val) ||
           OpNum+4 != Record.size())
-        return Error("Invalid ATOMICRMW record");
+        return Error(InvalidRecord);
       AtomicRMWInst::BinOp Operation = GetDecodedRMWOperation(Record[OpNum]);
       if (Operation < AtomicRMWInst::FIRST_BINOP ||
           Operation > AtomicRMWInst::LAST_BINOP)
-        return Error("Invalid ATOMICRMW record");
+        return Error(InvalidRecord);
       AtomicOrdering Ordering = GetDecodedOrdering(Record[OpNum+2]);
       if (Ordering == NotAtomic || Ordering == Unordered)
-        return Error("Invalid ATOMICRMW record");
+        return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[OpNum+3]);
       I = new AtomicRMWInst(Operation, Ptr, Val, Ordering, SynchScope);
       cast<AtomicRMWInst>(I)->setVolatile(Record[OpNum+1]);
@@ -2876,11 +2909,11 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     }
     case bitc::FUNC_CODE_INST_FENCE: { // FENCE:[ordering, synchscope]
       if (2 != Record.size())
-        return Error("Invalid FENCE record");
+        return Error(InvalidRecord);
       AtomicOrdering Ordering = GetDecodedOrdering(Record[0]);
       if (Ordering == NotAtomic || Ordering == Unordered ||
           Ordering == Monotonic)
-        return Error("Invalid FENCE record");
+        return Error(InvalidRecord);
       SynchronizationScope SynchScope = GetDecodedSynchScope(Record[1]);
       I = new FenceInst(Context, Ordering, SynchScope);
       InstructionList.push_back(I);
@@ -2889,7 +2922,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     case bitc::FUNC_CODE_INST_CALL: {
       // CALL: [paramattrs, cc, fnty, fnid, arg0, arg1...]
       if (Record.size() < 3)
-        return Error("Invalid CALL record");
+        return Error(InvalidRecord);
 
       AttributeSet PAL = getAttributes(Record[0]);
       unsigned CCInfo = Record[1];
@@ -2897,13 +2930,13 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
       unsigned OpNum = 2;
       Value *Callee;
       if (getValueTypePair(Record, OpNum, NextValueNo, Callee))
-        return Error("Invalid CALL record");
+        return Error(InvalidRecord);
 
       PointerType *OpTy = dyn_cast<PointerType>(Callee->getType());
       FunctionType *FTy = 0;
       if (OpTy) FTy = dyn_cast<FunctionType>(OpTy->getElementType());
       if (!FTy || Record.size() < FTy->getNumParams()+OpNum)
-        return Error("Invalid CALL record");
+        return Error(InvalidRecord);
 
       SmallVector<Value*, 16> Args;
       // Read the fixed params.
@@ -2913,18 +2946,19 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
         else
           Args.push_back(getValue(Record, OpNum, NextValueNo,
                                   FTy->getParamType(i)));
-        if (Args.back() == 0) return Error("Invalid CALL record");
+        if (Args.back() == 0)
+          return Error(InvalidRecord);
       }
 
       // Read type/value pairs for varargs params.
       if (!FTy->isVarArg()) {
         if (OpNum != Record.size())
-          return Error("Invalid CALL record");
+          return Error(InvalidRecord);
       } else {
         while (OpNum != Record.size()) {
           Value *Op;
           if (getValueTypePair(Record, OpNum, NextValueNo, Op))
-            return Error("Invalid CALL record");
+            return Error(InvalidRecord);
           Args.push_back(Op);
         }
       }
@@ -2939,12 +2973,12 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     }
     case bitc::FUNC_CODE_INST_VAARG: { // VAARG: [valistty, valist, instty]
       if (Record.size() < 3)
-        return Error("Invalid VAARG record");
+        return Error(InvalidRecord);
       Type *OpTy = getTypeByID(Record[0]);
       Value *Op = getValue(Record, 1, NextValueNo, OpTy);
       Type *ResTy = getTypeByID(Record[2]);
       if (!OpTy || !Op || !ResTy)
-        return Error("Invalid VAARG record");
+        return Error(InvalidRecord);
       I = new VAArgInst(Op, ResTy);
       InstructionList.push_back(I);
       break;
@@ -2955,7 +2989,7 @@ bool BitcodeReader::ParseFunctionBody(Function *F) {
     // this file.
     if (CurBB == 0) {
       delete I;
-      return Error("Invalid instruction with no BB");
+      return Error(InvalidInstructionWithNoBB);
     }
     CurBB->getInstList().push_back(I);
 
@@ -2982,7 +3016,7 @@ OutOfRecordLoop:
           delete A;
         }
       }
-      return Error("Never resolved value found in function!");
+      return Error(NeverResolvedValueFoundInFunction);
     }
   }
 
@@ -2998,7 +3032,7 @@ OutOfRecordLoop:
     for (unsigned i = 0, e = RefList.size(); i != e; ++i) {
       unsigned BlockIdx = RefList[i].first;
       if (BlockIdx >= FunctionBBs.size())
-        return Error("Invalid blockaddress block #");
+        return Error(InvalidID);
 
       GlobalVariable *FwdRef = RefList[i].second;
       FwdRef->replaceAllUsesWith(BlockAddress::get(F, FunctionBBs[BlockIdx]));
@@ -3012,7 +3046,7 @@ OutOfRecordLoop:
   ValueList.shrinkTo(ModuleValueListSize);
   MDValueList.shrinkTo(ModuleMDValueListSize);
   std::vector<BasicBlock*>().swap(FunctionBBs);
-  return false;
+  return error_code::success();
 }
 
 /// FindFunctionInStream - Find the function body in the bitcode stream
@@ -3020,7 +3054,7 @@ bool BitcodeReader::FindFunctionInStream(Function *F,
        DenseMap<Function*, uint64_t>::iterator DeferredFunctionInfoIterator) {
   while (DeferredFunctionInfoIterator->second == 0) {
     if (Stream.AtEndOfStream())
-      return Error("Could not find Function in stream");
+      return Error(CouldNotFindFunctionInStream);
     // ParseModule will parse the next body in the stream and set its
     // position in the DeferredFunctionInfo map.
     if (ParseModule(true)) return true;
@@ -3056,8 +3090,9 @@ bool BitcodeReader::Materialize(GlobalValue *GV, std::string *ErrInfo) {
   // Move the bit stream to the saved position of the deferred function body.
   Stream.JumpToBit(DFII->second);
 
-  if (ParseFunctionBody(F)) {
-    if (ErrInfo) *ErrInfo = ErrorString;
+  if (error_code EC = ParseFunctionBody(F)) {
+    if (ErrInfo)
+      *ErrInfo = EC.message();
     return true;
   }
 
@@ -3138,35 +3173,36 @@ bool BitcodeReader::MaterializeModule(Module *M, std::string *ErrInfo) {
   return false;
 }
 
-bool BitcodeReader::InitStream() {
-  if (LazyStreamer) return InitLazyStream();
+error_code BitcodeReader::InitStream() {
+  if (LazyStreamer)
+    return InitLazyStream();
   return InitStreamFromBuffer();
 }
 
-bool BitcodeReader::InitStreamFromBuffer() {
+error_code BitcodeReader::InitStreamFromBuffer() {
   const unsigned char *BufPtr = (const unsigned char*)Buffer->getBufferStart();
   const unsigned char *BufEnd = BufPtr+Buffer->getBufferSize();
 
   if (Buffer->getBufferSize() & 3) {
     if (!isRawBitcode(BufPtr, BufEnd) && !isBitcodeWrapper(BufPtr, BufEnd))
-      return Error("Invalid bitcode signature");
+      return Error(InvalidBitcodeSignature);
     else
-      return Error("Bitcode stream should be a multiple of 4 bytes in length");
+      return Error(BitcodeStreamInvalidSize);
   }
 
   // If we have a wrapper header, parse it and ignore the non-bc file contents.
   // The magic number is 0x0B17C0DE stored in little endian.
   if (isBitcodeWrapper(BufPtr, BufEnd))
     if (SkipBitcodeWrapperHeader(BufPtr, BufEnd, true))
-      return Error("Invalid bitcode wrapper header");
+      return Error(InvalidBitcodeWrapperHeader);
 
   StreamFile.reset(new BitstreamReader(BufPtr, BufEnd));
   Stream.init(*StreamFile);
 
-  return false;
+  return error_code::success();
 }
 
-bool BitcodeReader::InitLazyStream() {
+error_code BitcodeReader::InitLazyStream() {
   // Check and strip off the bitcode wrapper; BitstreamReader expects never to
   // see it.
   StreamingMemoryObject *Bytes = new StreamingMemoryObject(LazyStreamer);
@@ -3175,10 +3211,10 @@ bool BitcodeReader::InitLazyStream() {
 
   unsigned char buf[16];
   if (Bytes->readBytes(0, 16, buf) == -1)
-    return Error("Bitcode stream must be at least 16 bytes in length");
+    return Error(BitcodeStreamInvalidSize);
 
   if (!isBitcode(buf, buf + 16))
-    return Error("Invalid bitcode signature");
+    return Error(InvalidBitcodeSignature);
 
   if (isBitcodeWrapper(buf, buf + 4)) {
     const unsigned char *bitcodeStart = buf;
@@ -3187,7 +3223,63 @@ bool BitcodeReader::InitLazyStream() {
     Bytes->dropLeadingBytes(bitcodeStart - buf);
     Bytes->setKnownObjectSize(bitcodeEnd - bitcodeStart);
   }
-  return false;
+  return error_code::success();
+}
+
+namespace {
+class BitcodeErrorCategoryType : public _do_message {
+  const char *name() const LLVM_OVERRIDE {
+    return "llvm.bitcode";
+  }
+  std::string message(int IE) const LLVM_OVERRIDE {
+    BitcodeReader::ErrorType E = static_cast<BitcodeReader::ErrorType>(IE);
+    switch (E) {
+    case BitcodeReader::BitcodeStreamInvalidSize:
+      return "Bitcode stream length should be >= 16 bytes and a multiple of 4";
+    case BitcodeReader::ConflictingMETADATA_KINDRecords:
+      return "Conflicting METADATA_KIND records";
+    case BitcodeReader::CouldNotFindFunctionInStream:
+      return "Could not find function in stream";
+    case BitcodeReader::ExpectedConstant:
+      return "Expected a constant";
+    case BitcodeReader::InsufficientFunctionProtos:
+      return "Insufficient function protos";
+    case BitcodeReader::InvalidBitcodeSignature:
+      return "Invalid bitcode signature";
+    case BitcodeReader::InvalidBitcodeWrapperHeader:
+      return "Invalid bitcode wrapper header";
+    case BitcodeReader::InvalidConstantReference:
+      return "Invalid ronstant reference";
+    case BitcodeReader::InvalidID:
+      return "Invalid ID";
+    case BitcodeReader::InvalidInstructionWithNoBB:
+      return "Invalid instruction with no BB";
+    case BitcodeReader::InvalidRecord:
+      return "Invalid record";
+    case BitcodeReader::InvalidTypeForValue:
+      return "Invalid type for value";
+    case BitcodeReader::InvalidTYPETable:
+      return "Invalid TYPE table";
+    case BitcodeReader::InvalidType:
+      return "Invalid type";
+    case BitcodeReader::MalformedBlock:
+      return "Malformed block";
+    case BitcodeReader::MalformedGlobalInitializerSet:
+      return "Malformed global initializer set";
+    case BitcodeReader::InvalidMultipleBlocks:
+      return "Invalid multiple blocks";
+    case BitcodeReader::NeverResolvedValueFoundInFunction:
+      return "Never resolved value found in function";
+    case BitcodeReader::InvalidValue:
+      return "Invalid value";
+    }
+  }
+};
+}
+
+const error_category &BitcodeReader::BitcodeErrorCategory() {
+  static BitcodeErrorCategoryType O;
+  return O;
 }
 
 //===----------------------------------------------------------------------===//
@@ -3202,9 +3294,9 @@ Module *llvm::getLazyBitcodeModule(MemoryBuffer *Buffer,
   Module *M = new Module(Buffer->getBufferIdentifier(), Context);
   BitcodeReader *R = new BitcodeReader(Buffer, Context);
   M->setMaterializer(R);
-  if (R->ParseBitcodeInto(M)) {
+  if (error_code EC = R->ParseBitcodeInto(M)) {
     if (ErrMsg)
-      *ErrMsg = R->getErrorString();
+      *ErrMsg = EC.message();
 
     delete M;  // Also deletes R.
     return 0;
@@ -3225,9 +3317,9 @@ Module *llvm::getStreamedBitcodeModule(const std::string &name,
   Module *M = new Module(name, Context);
   BitcodeReader *R = new BitcodeReader(streamer, Context);
   M->setMaterializer(R);
-  if (R->ParseBitcodeInto(M)) {
+  if (error_code EC = R->ParseBitcodeInto(M)) {
     if (ErrMsg)
-      *ErrMsg = R->getErrorString();
+      *ErrMsg = EC.message();
     delete M;  // Also deletes R.
     return 0;
   }
@@ -3266,9 +3358,9 @@ std::string llvm::getBitcodeTargetTriple(MemoryBuffer *Buffer,
   R->setBufferOwned(false);
 
   std::string Triple("");
-  if (R->ParseTriple(Triple))
+  if (error_code EC = R->ParseTriple(Triple))
     if (ErrMsg)
-      *ErrMsg = R->getErrorString();
+      *ErrMsg = EC.message();
 
   delete R;
   return Triple;
diff --git a/lib/Bitcode/Reader/BitcodeReader.h b/lib/Bitcode/Reader/BitcodeReader.h
index b284e8cac1e..0a8bb0147d7 100644
--- a/lib/Bitcode/Reader/BitcodeReader.h
+++ b/lib/Bitcode/Reader/BitcodeReader.h
@@ -21,6 +21,7 @@
 #include "llvm/IR/Attributes.h"
 #include "llvm/IR/OperandTraits.h"
 #include "llvm/IR/Type.h"
+#include "llvm/Support/system_error.h"
 #include "llvm/Support/ValueHandle.h"
 #include <vector>
 
@@ -132,8 +133,6 @@ class BitcodeReader : public GVMaterializer {
   uint64_t NextUnreadBit;
   bool SeenValueSymbolTable;
 
-  const char *ErrorString;
-
   std::vector<Type*> TypeList;
   BitcodeReaderValueList ValueList;
   BitcodeReaderMDValueList MDValueList;
@@ -194,17 +193,46 @@ class BitcodeReader : public GVMaterializer {
   /// not need this flag.
   bool UseRelativeIDs;
 
+  static const error_category &BitcodeErrorCategory();
+
 public:
+  enum ErrorType {
+    BitcodeStreamInvalidSize,
+    ConflictingMETADATA_KINDRecords,
+    CouldNotFindFunctionInStream,
+    ExpectedConstant,
+    InsufficientFunctionProtos,
+    InvalidBitcodeSignature,
+    InvalidBitcodeWrapperHeader,
+    InvalidConstantReference,
+    InvalidID, // A read identifier is not found in the table it should be in.
+    InvalidInstructionWithNoBB,
+    InvalidRecord, // A read record doesn't have the expected size or structure
+    InvalidTypeForValue, // Type read OK, but is invalid for its use
+    InvalidTYPETable,
+    InvalidType, // We were unable to read a type
+    MalformedBlock, // We are unable to advance in the stream.
+    MalformedGlobalInitializerSet,
+    InvalidMultipleBlocks, // We found multiple blocks of a kind that should
+                           // have only one
+    NeverResolvedValueFoundInFunction,
+    InvalidValue // Invalid version, inst number, attr number, etc
+  };
+
+  error_code Error(ErrorType E) {
+    return error_code(E, BitcodeErrorCategory());
+  }
+
   explicit BitcodeReader(MemoryBuffer *buffer, LLVMContext &C)
     : Context(C), TheModule(0), Buffer(buffer), BufferOwned(false),
       LazyStreamer(0), NextUnreadBit(0), SeenValueSymbolTable(false),
-      ErrorString(0), ValueList(C), MDValueList(C),
+      ValueList(C), MDValueList(C),
       SeenFirstFunctionBody(false), UseRelativeIDs(false) {
   }
   explicit BitcodeReader(DataStreamer *streamer, LLVMContext &C)
     : Context(C), TheModule(0), Buffer(0), BufferOwned(false),
       LazyStreamer(streamer), NextUnreadBit(0), SeenValueSymbolTable(false),
-      ErrorString(0), ValueList(C), MDValueList(C),
+      ValueList(C), MDValueList(C),
       SeenFirstFunctionBody(false), UseRelativeIDs(false) {
   }
   ~BitcodeReader() {
@@ -225,19 +253,13 @@ public:
   virtual bool MaterializeModule(Module *M, std::string *ErrInfo = 0);
   virtual void Dematerialize(GlobalValue *GV);
 
-  bool Error(const char *Str) {
-    ErrorString = Str;
-    return true;
-  }
-  const char *getErrorString() const { return ErrorString; }
-
   /// @brief Main interface to parsing a bitcode buffer.
   /// @returns true if an error occurred.
-  bool ParseBitcodeInto(Module *M);
+  error_code ParseBitcodeInto(Module *M);
 
   /// @brief Cheap mechanism to just extract module triple
   /// @returns true if an error occurred.
-  bool ParseTriple(std::string &Triple);
+  error_code ParseTriple(std::string &Triple);
 
   static uint64_t decodeSignRotatedValue(uint64_t V);
 
@@ -324,26 +346,26 @@ private:
     return getFnValueByID(ValNo, Ty);
   }
 
-  bool ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind);
-  bool ParseModule(bool Resume);
-  bool ParseAttributeBlock();
-  bool ParseAttributeGroupBlock();
-  bool ParseTypeTable();
-  bool ParseTypeTableBody();
+  error_code ParseAttrKind(uint64_t Code, Attribute::AttrKind *Kind);
+  error_code ParseModule(bool Resume);
+  error_code ParseAttributeBlock();
+  error_code ParseAttributeGroupBlock();
+  error_code ParseTypeTable();
+  error_code ParseTypeTableBody();
 
-  bool ParseValueSymbolTable();
-  bool ParseConstants();
-  bool RememberAndSkipFunctionBody();
-  bool ParseFunctionBody(Function *F);
-  bool GlobalCleanup();
-  bool ResolveGlobalAndAliasInits();
-  bool ParseMetadata();
-  bool ParseMetadataAttachment();
-  bool ParseModuleTriple(std::string &Triple);
-  bool ParseUseLists();
-  bool InitStream();
-  bool InitStreamFromBuffer();
-  bool InitLazyStream();
+  error_code ParseValueSymbolTable();
+  error_code ParseConstants();
+  error_code RememberAndSkipFunctionBody();
+  error_code ParseFunctionBody(Function *F);
+  error_code GlobalCleanup();
+  error_code ResolveGlobalAndAliasInits();
+  error_code ParseMetadata();
+  error_code ParseMetadataAttachment();
+  error_code ParseModuleTriple(std::string &Triple);
+  error_code ParseUseLists();
+  error_code InitStream();
+  error_code InitStreamFromBuffer();
+  error_code InitLazyStream();
   bool FindFunctionInStream(Function *F,
          DenseMap<Function*, uint64_t>::iterator DeferredFunctionInfoIterator);
 };
diff --git a/test/Bitcode/invalid.ll b/test/Bitcode/invalid.ll
index 51d8cf2f9e1..1d4a82bf2b6 100644
--- a/test/Bitcode/invalid.ll
+++ b/test/Bitcode/invalid.ll
@@ -1,6 +1,6 @@
 ; RUN:  not llvm-dis < %s.bc 2>&1 | FileCheck %s
 
-; CHECK: llvm-dis{{(\.EXE|\.exe)?}}: Unknown attribute kind
+; CHECK: llvm-dis{{(\.EXE|\.exe)?}}: Invalid value
 
 ; invalid.ll.bc has an invalid attribute number.
 ; The test checks that LLVM reports the error and doesn't access freed memory
diff --git a/test/Bitcode/null-type.ll b/test/Bitcode/null-type.ll
index d01488c4263..a620fab8cc3 100644
--- a/test/Bitcode/null-type.ll
+++ b/test/Bitcode/null-type.ll
@@ -1,4 +1,4 @@
 ; RUN: not llvm-dis < %s.bc 2>&1 | FileCheck %s
 ; PR8494
 
-; CHECK: Invalid MODULE_CODE_FUNCTION record
+; CHECK: Invalid record