Introduce a string_ostream string builder facilty

string_ostream is a safe and efficient string builder that combines opaque
stack storage with a built-in ostream interface.

small_string_ostream<bytes> additionally permits an explicit stack storage size
other than the default 128 bytes to be provided. Beyond that, storage is
transferred to the heap.

This convenient class can be used in most places an
std::string+raw_string_ostream pair or SmallString<>+raw_svector_ostream pair
would previously have been used, in order to guarantee consistent access
without byte truncation.

The patch also converts much of LLVM to use the new facility. These changes
include several probable bug fixes for truncated output, a programming error
that's no longer possible with the new interface.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211749 91177308-0d34-0410-b5e6-96231b3b80d8

43 files changed, 155 insertions, 224 deletions

diff --git a/lib/Analysis/Analysis.cpp b/lib/Analysis/Analysis.cpp
index ade940a7d3..7b6397679d 100644
--- a/lib/Analysis/Analysis.cpp
+++ b/lib/Analysis/Analysis.cpp
@@ -75,8 +75,7 @@ void LLVMInitializeAnalysis(LLVMPassRegistryRef R) {
 LLVMBool LLVMVerifyModule(LLVMModuleRef M, LLVMVerifierFailureAction Action,
                           char **OutMessages) {
   raw_ostream *DebugOS = Action != LLVMReturnStatusAction ? &errs() : nullptr;
-  std::string Messages;
-  raw_string_ostream MsgsOS(Messages);
+  string_ostream MsgsOS;
 
   LLVMBool Result = verifyModule(*unwrap(M), OutMessages ? &MsgsOS : DebugOS);
 
@@ -88,7 +87,7 @@ LLVMBool LLVMVerifyModule(LLVMModuleRef M, LLVMVerifierFailureAction Action,
     report_fatal_error("Broken module found, compilation aborted!");
 
   if (OutMessages)
-    *OutMessages = strdup(MsgsOS.str().c_str());
+    *OutMessages = strndup(MsgsOS.str().data(), MsgsOS.str().size());
 
   return Result;
 }
diff --git a/lib/Analysis/BlockFrequencyInfo.cpp b/lib/Analysis/BlockFrequencyInfo.cpp
index 8ed8e3e4c2..7e702c3143 100644
--- a/lib/Analysis/BlockFrequencyInfo.cpp
+++ b/lib/Analysis/BlockFrequencyInfo.cpp
@@ -82,10 +82,9 @@ struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
 
   std::string getNodeLabel(const BasicBlock *Node,
                            const BlockFrequencyInfo *Graph) {
-    std::string Result;
-    raw_string_ostream OS(Result);
+    string_ostream OS;
 
-    OS << Node->getName().str() << ":";
+    OS << Node->getName() << ":";
     switch (ViewBlockFreqPropagationDAG) {
     case GVDT_Fraction:
       Graph->printBlockFreq(OS, Node);
@@ -98,7 +97,7 @@ struct DOTGraphTraits<BlockFrequencyInfo*> : public DefaultDOTGraphTraits {
                        "never reach this point.");
     }
 
-    return Result;
+    return OS.str();
   }
 };
 
diff --git a/lib/Analysis/Lint.cpp b/lib/Analysis/Lint.cpp
index b14f3292e9..806a1fdee5 100644
--- a/lib/Analysis/Lint.cpp
+++ b/lib/Analysis/Lint.cpp
@@ -105,11 +105,10 @@ namespace {
     const DataLayout *DL;
     TargetLibraryInfo *TLI;
 
-    std::string Messages;
-    raw_string_ostream MessagesStr;
+    string_ostream MessagesStr;
 
     static char ID; // Pass identification, replacement for typeid
-    Lint() : FunctionPass(ID), MessagesStr(Messages) {
+    Lint() : FunctionPass(ID) {
       initializeLintPass(*PassRegistry::getPassRegistry());
     }
 
@@ -181,7 +180,7 @@ bool Lint::runOnFunction(Function &F) {
   TLI = &getAnalysis<TargetLibraryInfo>();
   visit(F);
   dbgs() << MessagesStr.str();
-  Messages.clear();
+  MessagesStr.clear();
   return false;
 }
 
diff --git a/lib/AsmParser/LLParser.cpp b/lib/AsmParser/LLParser.cpp
index f444206852..840f764d3a 100644
--- a/lib/AsmParser/LLParser.cpp
+++ b/lib/AsmParser/LLParser.cpp
@@ -28,10 +28,9 @@
 using namespace llvm;
 
 static std::string getTypeString(Type *T) {
-  std::string Result;
-  raw_string_ostream Tmp(Result);
-  Tmp << *T;
-  return Tmp.str();
+  string_ostream Result;
+  Result << *T;
+  return Result.str();
 }
 
 /// Run: module ::= toplevelentity*
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
index 799ee92d3a..ebb49c34a7 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -1585,8 +1585,7 @@ static const MCExpr *lowerConstant(const Constant *CV, AsmPrinter &AP) {
 
     // Otherwise report the problem to the user.
     {
-      std::string S;
-      raw_string_ostream OS(S);
+      string_ostream OS;
       OS << "Unsupported expression in static initializer: ";
       CE->printAsOperand(OS, /*PrintType=*/false,
                      !AP.MF ? nullptr : AP.MF->getFunction()->getParent());
diff --git a/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp b/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
index 46ee0c856b..01f26d0c4c 100644
--- a/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
+++ b/lib/CodeGen/AsmPrinter/AsmPrinterInlineAsm.cpp
@@ -241,8 +241,7 @@ static void EmitMSInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
         }
       }
       if (Error) {
-        std::string msg;
-        raw_string_ostream Msg(msg);
+        string_ostream Msg;
         Msg << "invalid operand in inline asm: '" << AsmStr << "'";
         MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
       }
@@ -413,8 +412,7 @@ static void EmitGCCInlineAsmStr(const char *AsmStr, const MachineInstr *MI,
           }
         }
         if (Error) {
-          std::string msg;
-          raw_string_ostream Msg(msg);
+          string_ostream Msg;
           Msg << "invalid operand in inline asm: '" << AsmStr << "'";
           MMI->getModule()->getContext().emitError(LocCookie, Msg.str());
         }
@@ -471,8 +469,7 @@ void AsmPrinter::EmitInlineAsm(const MachineInstr *MI) const {
 
   // Emit the inline asm to a temporary string so we can emit it through
   // EmitInlineAsm.
-  SmallString<256> StringData;
-  raw_svector_ostream OS(StringData);
+  small_string_ostream<256> OS;
 
   // The variant of the current asmprinter.
   int AsmPrinterVariant = MAI->getAssemblerDialect();
@@ -517,8 +514,7 @@ void AsmPrinter::PrintSpecial(const MachineInstr *MI, raw_ostream &OS,
     }
     OS << Counter;
   } else {
-    std::string msg;
-    raw_string_ostream Msg(msg);
+    string_ostream Msg;
     Msg << "Unknown special formatter '" << Code
          << "' for machine instr: " << *MI;
     report_fatal_error(Msg.str());
diff --git a/lib/CodeGen/MachineBlockFrequencyInfo.cpp b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
index 9151d99089..35e4a56cec 100644
--- a/lib/CodeGen/MachineBlockFrequencyInfo.cpp
+++ b/lib/CodeGen/MachineBlockFrequencyInfo.cpp
@@ -89,10 +89,9 @@ struct DOTGraphTraits<MachineBlockFrequencyInfo*> :
 
   std::string getNodeLabel(const MachineBasicBlock *Node,
                            const MachineBlockFrequencyInfo *Graph) {
-    std::string Result;
-    raw_string_ostream OS(Result);
+    string_ostream OS;
 
-    OS << Node->getName().str() << ":";
+    OS << Node->getName() << ":";
     switch (ViewMachineBlockFreqPropagationDAG) {
     case GVDT_Fraction:
       Graph->printBlockFreq(OS, Node);
@@ -105,7 +104,7 @@ struct DOTGraphTraits<MachineBlockFrequencyInfo*> :
                        "never reach this point.");
     }
 
-    return Result;
+    return OS.str();
   }
 };
 
diff --git a/lib/CodeGen/MachineBlockPlacement.cpp b/lib/CodeGen/MachineBlockPlacement.cpp
index 74af1e2d64..891f605e2a 100644
--- a/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/lib/CodeGen/MachineBlockPlacement.cpp
@@ -264,23 +264,19 @@ INITIALIZE_PASS_END(MachineBlockPlacement, "block-placement2",
 ///
 /// Only used by debug logging.
 static std::string getBlockName(MachineBasicBlock *BB) {
-  std::string Result;
-  raw_string_ostream OS(Result);
+  string_ostream OS;
   OS << "BB#" << BB->getNumber()
      << " (derived from LLVM BB '" << BB->getName() << "')";
-  OS.flush();
-  return Result;
+  return OS.str();
 }
 
 /// \brief Helper to print the number of a MBB.
 ///
 /// Only used by debug logging.
 static std::string getBlockNum(MachineBasicBlock *BB) {
-  std::string Result;
-  raw_string_ostream OS(Result);
+  string_ostream OS;
   OS << "BB#" << BB->getNumber();
-  OS.flush();
-  return Result;
+  return OS.str();
 }
 #endif
 
diff --git a/lib/CodeGen/MachineFunction.cpp b/lib/CodeGen/MachineFunction.cpp
index 6138aef4ad..20210adf30 100644
--- a/lib/CodeGen/MachineFunction.cpp
+++ b/lib/CodeGen/MachineFunction.cpp
@@ -465,9 +465,8 @@ MCSymbol *MachineFunction::getJTISymbol(unsigned JTI, MCContext &Ctx,
 
   const char *Prefix = isLinkerPrivate ? DL->getLinkerPrivateGlobalPrefix() :
                                          DL->getPrivateGlobalPrefix();
-  SmallString<60> Name;
-  raw_svector_ostream(Name)
-    << Prefix << "JTI" << getFunctionNumber() << '_' << JTI;
+  small_string_ostream<60> Name;
+  Name << Prefix << "JTI" << getFunctionNumber() << '_' << JTI;
   return Ctx.GetOrCreateSymbol(Name.str());
 }
 
diff --git a/lib/CodeGen/MachineScheduler.cpp b/lib/CodeGen/MachineScheduler.cpp
index 0baf2a6c1c..f7459bbf6f 100644
--- a/lib/CodeGen/MachineScheduler.cpp
+++ b/lib/CodeGen/MachineScheduler.cpp
@@ -3235,8 +3235,7 @@ struct DOTGraphTraits<ScheduleDAGMI*> : public DefaultDOTGraphTraits {
   }
 
   static std::string getNodeLabel(const SUnit *SU, const ScheduleDAG *G) {
-    std::string Str;
-    raw_string_ostream SS(Str);
+    string_ostream SS;
     const ScheduleDAGMI *DAG = static_cast<const ScheduleDAGMI*>(G);
     const SchedDFSResult *DFS = DAG->hasVRegLiveness() ?
       static_cast<const ScheduleDAGMILive*>(G)->getDFSResult() : nullptr;
diff --git a/lib/CodeGen/ScheduleDAGInstrs.cpp b/lib/CodeGen/ScheduleDAGInstrs.cpp
index 92a9a30f24..baf4af6aba 100644
--- a/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -1197,8 +1197,7 @@ void ScheduleDAGInstrs::dumpNode(const SUnit *SU) const {
 }
 
 std::string ScheduleDAGInstrs::getGraphNodeLabel(const SUnit *SU) const {
-  std::string s;
-  raw_string_ostream oss(s);
+  string_ostream oss;
   if (SU == &EntrySU)
     oss << "<entry>";
   else if (SU == &ExitSU)
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 57e22e21c3..a2cc290816 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -3245,8 +3245,7 @@ SelectCodeCommon(SDNode *NodeToMatch, const unsigned char *MatcherTable,
 
 
 void SelectionDAGISel::CannotYetSelect(SDNode *N) {
-  std::string msg;
-  raw_string_ostream Msg(msg);
+  string_ostream Msg;
   Msg << "Cannot select: ";
 
   if (N->getOpcode() != ISD::INTRINSIC_W_CHAIN &&
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
index 4df5ede388..680a7ec5dd 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGPrinter.cpp
@@ -268,8 +268,7 @@ void SelectionDAG::setSubgraphColor(SDNode *N, const char *Color) {
 }
 
 std::string ScheduleDAGSDNodes::getGraphNodeLabel(const SUnit *SU) const {
-  std::string s;
-  raw_string_ostream O(s);
+  string_ostream O;
   O << "SU(" << SU->NodeNum << "): ";
   if (SU->getNode()) {
     SmallVector<SDNode *, 4> GluedNodes;
diff --git a/lib/CodeGen/TargetSchedule.cpp b/lib/CodeGen/TargetSchedule.cpp
index b0f2ca6888..d18a514a85 100644
--- a/lib/CodeGen/TargetSchedule.cpp
+++ b/lib/CodeGen/TargetSchedule.cpp
@@ -212,11 +212,10 @@ unsigned TargetSchedModel::computeOperandLatency(
   if (SCDesc->isValid() && !DefMI->getOperand(DefOperIdx).isImplicit()
       && !DefMI->getDesc().OpInfo[DefOperIdx].isOptionalDef()
       && SchedModel.isComplete()) {
-    std::string Err;
-    raw_string_ostream ss(Err);
-    ss << "DefIdx " << DefIdx << " exceeds machine model writes for "
-       << *DefMI;
-    report_fatal_error(ss.str());
+    string_ostream Err;
+    Err << "DefIdx " << DefIdx << " exceeds machine model writes for "
+        << *DefMI;
+    report_fatal_error(Err.str());
   }
 #endif
   // FIXME: Automatically giving all implicit defs defaultDefLatency is
diff --git a/lib/DebugInfo/DWARFDebugFrame.cpp b/lib/DebugInfo/DWARFDebugFrame.cpp
index a33548e95b..2227260bb0 100644
--- a/lib/DebugInfo/DWARFDebugFrame.cpp
+++ b/lib/DebugInfo/DWARFDebugFrame.cpp
@@ -353,10 +353,9 @@ void DWARFDebugFrame::parse(DataExtractor Data) {
     Entries.back()->parseInstructions(Data, &Offset, EndStructureOffset);
 
     if (Offset != EndStructureOffset) {
-      std::string Str;
-      raw_string_ostream OS(Str);
-      OS << format("Parsing entry instructions at %lx failed", StartOffset);
-      report_fatal_error(Str);
+      string_ostream Str;
+      Str << format("Parsing entry instructions at %lx failed", StartOffset);
+      report_fatal_error(Str.str());
     }
   }
 }
diff --git a/lib/IR/Core.cpp b/lib/IR/Core.cpp
index 2c49d5b949..bf936d6dc7 100644
--- a/lib/IR/Core.cpp
+++ b/lib/IR/Core.cpp
@@ -62,6 +62,11 @@ void LLVMShutdown() {
 
 /*===-- Error handling ----------------------------------------------------===*/
 
+static char *LLVMCreateMessage(StringRef Message) {
+  assert(Message.find('\0') == Message.npos);
+  return strndup(Message.data(), Message.size());
+}
+
 char *LLVMCreateMessage(const char *Message) {
   return strdup(Message);
 }
@@ -110,14 +115,10 @@ unsigned LLVMGetMDKindID(const char* Name, unsigned SLen) {
 }
 
 char *LLVMGetDiagInfoDescription(LLVMDiagnosticInfoRef DI) {
-  std::string MsgStorage;
-  raw_string_ostream Stream(MsgStorage);
-  DiagnosticPrinterRawOStream DP(Stream);
-
+  string_ostream Msg;
+  DiagnosticPrinterRawOStream DP(Msg);
   unwrap(DI)->print(DP);
-  Stream.flush();
-
-  return LLVMCreateMessage(MsgStorage.c_str());
+  return LLVMCreateMessage(Msg.str());
 }
 
 LLVMDiagnosticSeverity LLVMGetDiagInfoSeverity(LLVMDiagnosticInfoRef DI){
@@ -201,13 +202,9 @@ LLVMBool LLVMPrintModuleToFile(LLVMModuleRef M, const char *Filename,
 }
 
 char *LLVMPrintModuleToString(LLVMModuleRef M) {
-  std::string buf;
-  raw_string_ostream os(buf);
-
+  string_ostream os;
   unwrap(M)->print(os, nullptr);
-  os.flush();
-
-  return strdup(buf.c_str());
+  return LLVMCreateMessage(os.str());
 }
 
 /*--.. Operations on inline assembler ......................................--*/
@@ -278,17 +275,14 @@ void LLVMDumpType(LLVMTypeRef Ty) {
 }
 
 char *LLVMPrintTypeToString(LLVMTypeRef Ty) {
-  std::string buf;
-  raw_string_ostream os(buf);
+  string_ostream os;
 
   if (unwrap(Ty))
     unwrap(Ty)->print(os);
   else
     os << "Printing <null> Type";
 
-  os.flush();
-
-  return strdup(buf.c_str());
+  return strndup(os.str().data(), os.str().size());
 }
 
 /*--.. Operations on integer types .........................................--*/
@@ -532,17 +526,14 @@ void LLVMDumpValue(LLVMValueRef Val) {
 }
 
 char* LLVMPrintValueToString(LLVMValueRef Val) {
-  std::string buf;
-  raw_string_ostream os(buf);
+  string_ostream os;
 
   if (unwrap(Val))
     unwrap(Val)->print(os);
   else
     os << "Printing <null> Value";
 
-  os.flush();
-
-  return strdup(buf.c_str());
+  return strndup(os.str().data(), os.str().size());
 }
 
 void LLVMReplaceAllUsesWith(LLVMValueRef OldVal, LLVMValueRef NewVal) {
diff --git a/lib/IR/DataLayout.cpp b/lib/IR/DataLayout.cpp
index dea05fbef4..3aa775097d 100644
--- a/lib/IR/DataLayout.cpp
+++ b/lib/IR/DataLayout.cpp
@@ -519,8 +519,7 @@ const StructLayout *DataLayout::getStructLayout(StructType *Ty) const {
 }
 
 std::string DataLayout::getStringRepresentation() const {
-  std::string Result;
-  raw_string_ostream OS(Result);
+  string_ostream OS;
 
   OS << (LittleEndian ? "e" : "E");
 
diff --git a/lib/IR/LLVMContext.cpp b/lib/IR/LLVMContext.cpp
index de825f00b2..201b278285 100644
--- a/lib/IR/LLVMContext.cpp
+++ b/lib/IR/LLVMContext.cpp
@@ -164,23 +164,22 @@ void LLVMContext::diagnose(const DiagnosticInfo &DI) {
   }
 
   // Otherwise, print the message with a prefix based on the severity.
-  std::string MsgStorage;
-  raw_string_ostream Stream(MsgStorage);
-  DiagnosticPrinterRawOStream DP(Stream);
+  string_ostream Msg;
+  DiagnosticPrinterRawOStream DP(Msg);
   DI.print(DP);
-  Stream.flush();
+
   switch (DI.getSeverity()) {
   case DS_Error:
-    errs() << "error: " << MsgStorage << "\n";
+    errs() << "error: " << Msg.str() << "\n";
     exit(1);
   case DS_Warning:
-    errs() << "warning: " << MsgStorage << "\n";
+    errs() << "warning: " << Msg.str() << "\n";
     break;
   case DS_Remark:
-    errs() << "remark: " << MsgStorage << "\n";
+    errs() << "remark: " << Msg.str() << "\n";
     break;
   case DS_Note:
-    errs() << "note: " << MsgStorage << "\n";
+    errs() << "note: " << Msg.str() << "\n";
     break;
   }
 }
diff --git a/lib/IRReader/IRReader.cpp b/lib/IRReader/IRReader.cpp
index 01aa074aba..6d389d4dc4 100644
--- a/lib/IRReader/IRReader.cpp
+++ b/lib/IRReader/IRReader.cpp
@@ -108,13 +108,9 @@ LLVMBool LLVMParseIRInContext(LLVMContextRef ContextRef,
 
   if(!*OutM) {
     if (OutMessage) {
-      std::string buf;
-      raw_string_ostream os(buf);
-
+      string_ostream os;
       Diag.print(nullptr, os, false);
-      os.flush();
-
-      *OutMessage = strdup(buf.c_str());
+      *OutMessage = strndup(os.str().data(), os.str().size());
     }
     return 1;
   }
diff --git a/lib/LTO/LTOCodeGenerator.cpp b/lib/LTO/LTOCodeGenerator.cpp
index a1709f60ff..d87299b5c7 100644
--- a/lib/LTO/LTOCodeGenerator.cpp
+++ b/lib/LTO/LTOCodeGenerator.cpp
@@ -549,16 +549,17 @@ void LTOCodeGenerator::DiagnosticHandler2(const DiagnosticInfo &DI) {
     break;
   }
   // Create the string that will be reported to the external diagnostic handler.
-  std::string MsgStorage;
-  raw_string_ostream Stream(MsgStorage);
-  DiagnosticPrinterRawOStream DP(Stream);
+  string_ostream Msg;
+  DiagnosticPrinterRawOStream DP(Msg);
   DI.print(DP);
-  Stream.flush();
+
+  // Null-terminate the C string.
+  Msg << '\0';
 
   // If this method has been called it means someone has set up an external
   // diagnostic handler. Assert on that.
   assert(DiagHandler && "Invalid diagnostic handler");
-  (*DiagHandler)(Severity, MsgStorage.c_str(), DiagContext);
+  (*DiagHandler)(Severity, Msg.str().data(), DiagContext);
 }
 
 void
diff --git a/lib/MC/MCAsmStreamer.cpp b/lib/MC/MCAsmStreamer.cpp
index da235ec1d3..a3a81a6bc7 100644
--- a/lib/MC/MCAsmStreamer.cpp
+++ b/lib/MC/MCAsmStreamer.cpp
@@ -1175,9 +1175,10 @@ void MCAsmStreamer::AddEncodingComment(const MCInst &Inst,
   raw_ostream &OS = GetCommentOS();
   SmallString<256> Code;
   SmallVector<MCFixup, 4> Fixups;
-  raw_svector_ostream VecOS(Code);
-  Emitter->EncodeInstruction(Inst, VecOS, Fixups, STI);
-  VecOS.flush();
+  {
+    raw_svector_ostream VecOS(Code);
+    Emitter->EncodeInstruction(Inst, VecOS, Fixups, STI);
+  }
 
   // If we are showing fixups, create symbolic markers in the encoded
   // representation. We do this by making a per-bit map to the fixup item index,
diff --git a/lib/MC/MCContext.cpp b/lib/MC/MCContext.cpp
index bd2c4e960a..3a8cfaa947 100644
--- a/lib/MC/MCContext.cpp
+++ b/lib/MC/MCContext.cpp
@@ -140,17 +140,15 @@ MCSymbol *MCContext::GetOrCreateSymbol(const Twine &Name) {
 }
 
 MCSymbol *MCContext::CreateLinkerPrivateTempSymbol() {
-  SmallString<128> NameSV;
-  raw_svector_ostream(NameSV)
-    << MAI->getLinkerPrivateGlobalPrefix() << "tmp" << NextUniqueID++;
-  return CreateSymbol(NameSV);
+  small_string_ostream<128> NameSV;
+  NameSV << MAI->getLinkerPrivateGlobalPrefix() << "tmp" << NextUniqueID++;
+  return CreateSymbol(NameSV.str());
 }
 
 MCSymbol *MCContext::CreateTempSymbol() {
-  SmallString<128> NameSV;
-  raw_svector_ostream(NameSV)
-    << MAI->getPrivateGlobalPrefix() << "tmp" << NextUniqueID++;
-  return CreateSymbol(NameSV);
+  small_string_ostream<128> NameSV;
+  NameSV << MAI->getPrivateGlobalPrefix() << "tmp" << NextUniqueID++;
+  return CreateSymbol(NameSV.str());
 }
 
 unsigned MCContext::NextInstance(unsigned LocalLabelVal) {
diff --git a/lib/MC/MCDisassembler/Disassembler.cpp b/lib/MC/MCDisassembler/Disassembler.cpp
index 0530c26369..e3ec4eb30d 100644
--- a/lib/MC/MCDisassembler/Disassembler.cpp
+++ b/lib/MC/MCDisassembler/Disassembler.cpp
@@ -270,8 +270,7 @@ size_t LLVMDisasmInstruction(LLVMDisasmContextRef DCR, uint8_t *Bytes,
   const MCDisassembler *DisAsm = DC->getDisAsm();
   MCInstPrinter *IP = DC->getIP();
   MCDisassembler::DecodeStatus S;
-  SmallVector<char, 64> InsnStr;
-  raw_svector_ostream Annotations(InsnStr);
+  small_string_ostream<64> Annotations;
   S = DisAsm->getInstruction(Inst, Size, MemoryObject, PC,
                              /*REMOVE*/ nulls(), Annotations);
   switch (S) {
@@ -281,13 +280,10 @@ size_t LLVMDisasmInstruction(LLVMDisasmContextRef DCR, uint8_t *Bytes,
     return 0;
 
   case MCDisassembler::Success: {
-    Annotations.flush();
-    StringRef AnnotationsStr = Annotations.str();
-
     SmallVector<char, 64> InsnStr;
     raw_svector_ostream OS(InsnStr);
     formatted_raw_ostream FormattedOS(OS);
-    IP->printInst(&Inst, FormattedOS, AnnotationsStr);
+    IP->printInst(&Inst, FormattedOS, Annotations.str());
 
     if (DC->getOptions() & LLVMDisassembler_Option_PrintLatency)
       emitLatency(DC, Inst);
diff --git a/lib/MC/MCDwarf.cpp b/lib/MC/MCDwarf.cpp
index bddbf578d8..eab4d88f25 100644
--- a/lib/MC/MCDwarf.cpp
+++ b/lib/MC/MCDwarf.cpp
@@ -420,8 +420,7 @@ unsigned MCDwarfLineTableHeader::getFile(StringRef &Directory,
 void MCDwarfLineAddr::Emit(MCStreamer *MCOS, int64_t LineDelta,
                            uint64_t AddrDelta) {
   MCContext &Context = MCOS->getContext();
-  SmallString<256> Tmp;
-  raw_svector_ostream OS(Tmp);
+  small_string_ostream<256> OS;
   MCDwarfLineAddr::Encode(Context, LineDelta, AddrDelta, OS);
   MCOS->EmitBytes(OS.str());
 }
@@ -1647,8 +1646,7 @@ void MCDwarfFrameEmitter::Emit(MCObjectStreamer &Streamer, MCAsmBackend *MAB,
 void MCDwarfFrameEmitter::EmitAdvanceLoc(MCObjectStreamer &Streamer,
                                          uint64_t AddrDelta) {
   MCContext &Context = Streamer.getContext();
-  SmallString<256> Tmp;
-  raw_svector_ostream OS(Tmp);
+  small_string_ostream<256> OS;
   MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OS);
   Streamer.EmitBytes(OS.str());
 }
diff --git a/lib/MC/MCParser/AsmParser.cpp b/lib/MC/MCParser/AsmParser.cpp
index fa5dfdc9fe..7bfbbf4932 100644
--- a/lib/MC/MCParser/AsmParser.cpp
+++ b/lib/MC/MCParser/AsmParser.cpp
@@ -4580,8 +4580,7 @@ bool AsmParser::parseMSInlineAsm(
   }
 
   // Build the IR assembly string.
-  std::string AsmStringIR;
-  raw_string_ostream OS(AsmStringIR);
+  string_ostream OS;
   const char *AsmStart = SrcMgr.getMemoryBuffer(0)->getBufferStart();
   const char *AsmEnd = SrcMgr.getMemoryBuffer(0)->getBufferEnd();
   array_pod_sort(AsmStrRewrites.begin(), AsmStrRewrites.end(), rewritesSort);
@@ -4646,8 +4645,7 @@ bool AsmParser::parseMSInlineAsm(
     }
     case AOK_DotOperator:
       // Insert the dot if the user omitted it.
-      OS.flush();
-      if (AsmStringIR.back() != '.')
+      if (OS.str().back() != '.')
         OS << '.';
       OS << AR.Val;
       break;
diff --git a/lib/Object/MachOObjectFile.cpp b/lib/Object/MachOObjectFile.cpp
index dbfc07270a..2511a4a3fa 100644
--- a/lib/Object/MachOObjectFile.cpp
+++ b/lib/Object/MachOObjectFile.cpp
@@ -301,7 +301,7 @@ static unsigned getCPUType(const MachOObjectFile *O) {
 
 static void printRelocationTargetName(const MachOObjectFile *O,
                                       const MachO::any_relocation_info &RE,
-                                      raw_string_ostream &fmt) {
+                                      raw_ostream &fmt) {
   bool IsScattered = O->isRelocationScattered(RE);
 
   // Target of a scattered relocation is an address.  In the interest of
@@ -1010,8 +1010,7 @@ MachOObjectFile::getRelocationValueString(DataRefImpl Rel,
 
   unsigned Arch = this->getArch();
 
-  std::string fmtbuf;
-  raw_string_ostream fmt(fmtbuf);
+  string_ostream fmt;
   unsigned Type = this->getAnyRelocationType(RE);
   bool IsPCRel = this->getAnyRelocationPCRel(RE);
 
@@ -1174,7 +1173,7 @@ MachOObjectFile::getRelocationValueString(DataRefImpl Rel,
   } else
     printRelocationTargetName(this, RE, fmt);
 
-  fmt.flush();
+  StringRef fmtbuf = fmt.str();
   Result.append(fmtbuf.begin(), fmtbuf.end());
   return object_error::success;
 }
diff --git a/lib/Option/Arg.cpp b/lib/Option/Arg.cpp
index 4c8da58f53..30a6922973 100644
--- a/lib/Option/Arg.cpp
+++ b/lib/Option/Arg.cpp
@@ -62,8 +62,7 @@ void Arg::dump() const {
 }
 
 std::string Arg::getAsString(const ArgList &Args) const {
-  SmallString<256> Res;
-  llvm::raw_svector_ostream OS(Res);
+  small_string_ostream<256> OS;
 
   ArgStringList ASL;
   render(Args, ASL);
@@ -95,8 +94,7 @@ void Arg::render(const ArgList &Args, ArgStringList &Output) const {
     break;
 
   case Option::RenderCommaJoinedStyle: {
-    SmallString<256> Res;
-    llvm::raw_svector_ostream OS(Res);
+    small_string_ostream<256> OS;
     OS << getSpelling();
     for (unsigned i = 0, e = getNumValues(); i != e; ++i) {
       if (i) OS << ',';
diff --git a/lib/Support/CommandLine.cpp b/lib/Support/CommandLine.cpp
index c2b739fa73..e28e1d1763 100644
--- a/lib/Support/CommandLine.cpp
+++ b/lib/Support/CommandLine.cpp
@@ -1342,25 +1342,21 @@ printGenericOptionDiff(const Option &O, const GenericOptionValue &Value,
 
 // printOptionDiff - Specializations for printing basic value types.
 //
-#define PRINT_OPT_DIFF(T)                                               \
-  void parser<T>::                                                      \
-  printOptionDiff(const Option &O, T V, OptionValue<T> D,               \
-                  size_t GlobalWidth) const {                           \
-    printOptionName(O, GlobalWidth);                                    \
-    std::string Str;                                                    \
-    {                                                                   \
-      raw_string_ostream SS(Str);                                       \
-      SS << V;                                                          \
-    }                                                                   \
-    outs() << "= " << Str;                                              \
-    size_t NumSpaces = MaxOptWidth > Str.size() ? MaxOptWidth - Str.size() : 0;\
-    outs().indent(NumSpaces) << " (default: ";                          \
-    if (D.hasValue())                                                   \
-      outs() << D.getValue();                                           \
-    else                                                                \
-      outs() << "*no default*";                                         \
-    outs() << ")\n";                                                    \
-  }                                                                     \
+#define PRINT_OPT_DIFF(T)                                                      \
+  void parser<T>::printOptionDiff(const Option &O, T V, OptionValue<T> D,      \
+                                  size_t GlobalWidth) const {                  \
+    printOptionName(O, GlobalWidth);                                           \
+    string_ostream SS;                                                         \
+    SS << V;                                                                   \
+    outs() << "= " << SS.str();                                                \
+    size_t NumSpaces = MaxOptWidth > SS.tell() ? MaxOptWidth - SS.tell() : 0;  \
+    outs().indent(NumSpaces) << " (default: ";                                 \
+    if (D.hasValue())                                                          \
+      outs() << D.getValue();                                                  \
+    else                                                                       \
+      outs() << "*no default*";                                                \
+    outs() << ")\n";                                                           \
+  }
 
 PRINT_OPT_DIFF(bool)
 PRINT_OPT_DIFF(boolOrDefault)
diff --git a/lib/Support/raw_ostream.cpp b/lib/Support/raw_ostream.cpp
index f7c213ac2b..b3f3056ba6 100644
--- a/lib/Support/raw_ostream.cpp
+++ b/lib/Support/raw_ostream.cpp
@@ -704,6 +704,10 @@ void raw_string_ostream::write_impl(const char *Ptr, size_t Size) {
 // and we only need to set the vector size when the data is flushed.
 
 raw_svector_ostream::raw_svector_ostream(SmallVectorImpl<char> &O) : OS(O) {
+  init();
+}
+
+void raw_svector_ostream::init() {
   // Set up the initial external buffer. We make sure that the buffer has at
   // least 128 bytes free; raw_ostream itself only requires 64, but we want to
   // make sure that we don't grow the buffer unnecessarily on destruction (when
diff --git a/lib/TableGen/SetTheory.cpp b/lib/TableGen/SetTheory.cpp
index c99c2bab45..594d4d9a94 100644
--- a/lib/TableGen/SetTheory.cpp
+++ b/lib/TableGen/SetTheory.cpp
@@ -209,13 +209,12 @@ struct SequenceOp : public SetTheory::Operator {
         break;
       else if (Step < 0 && From < To)
         break;
-      std::string Name;
-      raw_string_ostream OS(Name);
-      OS << format(Format.c_str(), unsigned(From));
-      Record *Rec = Records.getDef(OS.str());
+      string_ostream Name;
+      Name << format(Format.c_str(), unsigned(From));
+      Record *Rec = Records.getDef(Name.str());
       if (!Rec)
-        PrintFatalError(Loc, "No def named '" + Name + "': " +
-          Expr->getAsString());
+        PrintFatalError(Loc, "No def named '" + Name.str() + "': " +
+                                 Expr->getAsString());
       // Try to reevaluate Rec in case it is a set.
       if (const RecVec *Result = ST.expand(Rec))
         Elts.insert(Result->begin(), Result->end());
diff --git a/lib/TableGen/TGParser.cpp b/lib/TableGen/TGParser.cpp
index 0550692ebc..76ef696c68 100644
--- a/lib/TableGen/TGParser.cpp
+++ b/lib/TableGen/TGParser.cpp
@@ -1307,8 +1307,7 @@ Init *TGParser::ParseSimpleValue(Record *CurRec, RecTy *ItemType,
     if (ItemType) {
       ListRecTy *ListType = dyn_cast<ListRecTy>(ItemType);
       if (!ListType) {
-        std::string s;
-        raw_string_ostream ss(s);
+        string_ostream ss;
         ss << "Type mismatch for list, expected list type, got "
            << ItemType->getAsString();
         TokError(ss.str());
diff --git a/lib/Target/NVPTX/NVPTXAsmPrinter.cpp b/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
index 195b3c0fe9..eee2f9264f 100644
--- a/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
+++ b/lib/Target/NVPTX/NVPTXAsmPrinter.cpp
@@ -146,8 +146,7 @@ const MCExpr *nvptx::LowerConstant(const Constant *CV, AsmPrinter &AP) {
 
     // Otherwise report the problem to the user.
     {
-      std::string S;
-      raw_string_ostream OS(S);
+      string_ostream OS;
       OS << "Unsupported expression in static initializer: ";
       CE->printAsOperand(OS, /*PrintType=*/ false,
                          !AP.MF ? nullptr : AP.MF->getFunction()->getParent());
diff --git a/lib/Target/TargetMachineC.cpp b/lib/Target/TargetMachineC.cpp
index 20923c97ec..0b0a09a0ad 100644
--- a/lib/Target/TargetMachineC.cpp
+++ b/lib/Target/TargetMachineC.cpp
@@ -237,15 +237,13 @@ LLVMBool LLVMTargetMachineEmitToFile(LLVMTargetMachineRef T, LLVMModuleRef M,
 LLVMBool LLVMTargetMachineEmitToMemoryBuffer(LLVMTargetMachineRef T,
   LLVMModuleRef M, LLVMCodeGenFileType codegen, char** ErrorMessage,
   LLVMMemoryBufferRef *OutMemBuf) {
-  std::string CodeString;
-  raw_string_ostream OStream(CodeString);
-  formatted_raw_ostream Out(OStream);
+  string_ostream Code;
+  formatted_raw_ostream Out(Code);
   bool Result = LLVMTargetMachineEmit(T, M, Out, codegen, ErrorMessage);
-  OStream.flush();
 
-  std::string &Data = OStream.str();
-  *OutMemBuf = LLVMCreateMemoryBufferWithMemoryRangeCopy(Data.c_str(),
-                                                     Data.length(), "");
+  StringRef Buffer = Code.str();
+  *OutMemBuf = LLVMCreateMemoryBufferWithMemoryRangeCopy(Buffer.data(),
+                                                         Buffer.size(), "");
   return Result;
 }
 
diff --git a/lib/Target/X86/AsmParser/X86AsmParser.cpp b/lib/Target/X86/AsmParser/X86AsmParser.cpp
index 3e57914f9e..7e04608d99 100644
--- a/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -2412,8 +2412,7 @@ bool X86AsmParser::MatchAndEmitInstruction(SMLoc IDLoc, unsigned &Opcode,
     if (Match3 == Match_Success) MatchChars[NumMatches++] = Suffixes[2];
     if (Match4 == Match_Success) MatchChars[NumMatches++] = Suffixes[3];
 
-    SmallString<126> Msg;
-    raw_svector_ostream OS(Msg);
+    small_string_ostream<128> OS;
     OS << "ambiguous instructions require an explicit suffix (could be ";
     for (unsigned i = 0; i != NumMatches; ++i) {
       if (i != 0)
diff --git a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 78403424da..3f9eb07d83 100644
--- a/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -281,8 +281,7 @@ void X86AsmBackend::relaxInstruction(const MCInst &Inst, MCInst &Res) const {
   unsigned RelaxedOp = getRelaxedOpcode(Inst.getOpcode());
 
   if (RelaxedOp == Inst.getOpcode()) {
-    SmallString<256> Tmp;
-    raw_svector_ostream OS(Tmp);
+    small_string_ostream<256> OS;
     Inst.dump_pretty(OS);
     OS << "\n";
     report_fatal_error("unexpected instruction to relax: " + OS.str());
diff --git a/lib/Target/X86/X86AsmPrinter.cpp b/lib/Target/X86/X86AsmPrinter.cpp
index 1dca5689ad..cdfff82143 100644
--- a/lib/Target/X86/X86AsmPrinter.cpp
+++ b/lib/Target/X86/X86AsmPrinter.cpp
@@ -550,8 +550,7 @@ emitNonLazySymbolPointer(MCStreamer &OutStreamer, MCSymbol *StubLabel,
 }
 
 void X86AsmPrinter::GenerateExportDirective(const MCSymbol *Sym, bool IsData) {
-  SmallString<128> Directive;
-  raw_svector_ostream OS(Directive);
+  small_string_ostream<128> OS;
   StringRef Name = Sym->getName();
 
   if (Subtarget->isTargetKnownWindowsMSVC())
@@ -572,8 +571,7 @@ void X86AsmPrinter::GenerateExportDirective(const MCSymbol *Sym, bool IsData) {
       OS << ",data";
   }
 
-  OS.flush();
-  OutStreamer.EmitBytes(Directive);
+  OutStreamer.EmitBytes(OS.str());
 }
 
 void X86AsmPrinter::EmitEndOfAsmFile(Module &M) {
diff --git a/lib/Target/XCore/XCoreAsmPrinter.cpp b/lib/Target/XCore/XCoreAsmPrinter.cpp
index e98d4f933d..7b5da33496 100644
--- a/lib/Target/XCore/XCoreAsmPrinter.cpp
+++ b/lib/Target/XCore/XCoreAsmPrinter.cpp
@@ -267,8 +267,7 @@ PrintAsmMemoryOperand(const MachineInstr *MI, unsigned OpNum,
 }
 
 void XCoreAsmPrinter::EmitInstruction(const MachineInstr *MI) {
-  SmallString<128> Str;
-  raw_svector_ostream O(Str);
+  small_string_ostream<128> O;
 
   switch (MI->getOpcode()) {
   case XCore::DBG_VALUE:
diff --git a/lib/Transforms/Instrumentation/DebugIR.cpp b/lib/Transforms/Instrumentation/DebugIR.cpp
index f2f1738808..56e60e6984 100644
--- a/lib/Transforms/Instrumentation/DebugIR.cpp
+++ b/lib/Transforms/Instrumentation/DebugIR.cpp
@@ -352,14 +352,12 @@ private:
   }
 
   std::string getTypeName(Type *T) {
-    std::string TypeName;
-    raw_string_ostream TypeStream(TypeName);
+    string_ostream OS;
     if (T)
-      T->print(TypeStream);
+      T->print(OS);
     else
-      TypeStream << "Printing <null> Type";
-    TypeStream.flush();
-    return TypeName;
+      OS << "Printing <null> Type";
+    return OS.str();
   }
 
   /// Returns the MDNode that represents type T if it is already created, or 0
diff --git a/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/lib/Transforms/Instrumentation/GCOVProfiling.cpp
index cfeb62eb1f..5af938beae 100644
--- a/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -316,11 +316,9 @@ namespace {
       }
       ReturnBlock = new GCOVBlock(i++, os);
 
-      std::string FunctionNameAndLine;
-      raw_string_ostream FNLOS(FunctionNameAndLine);
-      FNLOS << getFunctionName(SP) << SP.getLineNumber();
-      FNLOS.flush();
-      FuncChecksum = hash_value(FunctionNameAndLine);
+      string_ostream FnNameLine;
+      FnNameLine << getFunctionName(SP) << SP.getLineNumber();
+      FuncChecksum = hash_value(FnNameLine.str());
     }
 
     ~GCOVFunction() {
@@ -337,15 +335,14 @@ namespace {
     }
 
     std::string getEdgeDestinations() {
-      std::string EdgeDestinations;
-      raw_string_ostream EDOS(EdgeDestinations);
+      string_ostream EdgeDestinations;
       Function *F = Blocks.begin()->first->getParent();
       for (Function::iterator I = F->begin(), E = F->end(); I != E; ++I) {
         GCOVBlock &Block = *Blocks[I];
         for (int i = 0, e = Block.OutEdges.size(); i != e; ++i)
-          EDOS << Block.OutEdges[i]->Number;
+          EdgeDestinations << Block.OutEdges[i]->Number;
       }
-      return EdgeDestinations;
+      return EdgeDestinations.str();
     }
 
     uint32_t getFuncChecksum() {
diff --git a/lib/Transforms/Instrumentation/MemorySanitizer.cpp b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
index 4ca0323807..bb88bc00ba 100644
--- a/lib/Transforms/Instrumentation/MemorySanitizer.cpp
+++ b/lib/Transforms/Instrumentation/MemorySanitizer.cpp
@@ -2424,8 +2424,7 @@ struct MemorySanitizerVisitor : public InstVisitor<MemorySanitizerVisitor> {
 
     if (PoisonStack && MS.TrackOrigins) {
       setOrigin(&I, getCleanOrigin());
-      SmallString<2048> StackDescriptionStorage;
-      raw_svector_ostream StackDescription(StackDescriptionStorage);
+      small_string_ostream<2048> StackDescription;
       // We create a string with a description of the stack allocation and
       // pass it into __msan_set_alloca_origin.
       // It will be printed by the run-time if stack-originated UMR is found.
diff --git a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
index dd4dd50f0b..744fb24048 100644
--- a/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
+++ b/lib/Transforms/ObjCARC/ObjCARCOpts.cpp
@@ -835,8 +835,7 @@ static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
       // of line at the module level and to provide a very simple format
       // encoding the information herein. Both of these makes it simpler to
       // parse the annotations by a simple external program.
-      std::string Str;
-      raw_string_ostream os(Str);
+      string_ostream os;
       os << "(" << Inst->getParent()->getParent()->getName() << ",%"
          << Inst->getName() << ")";
 
@@ -849,8 +848,7 @@ static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
       Hash = cast<MDString>(Node->getOperand(0));
     }
   } else if (Argument *Arg = dyn_cast<Argument>(Ptr)) {
-    std::string str;
-    raw_string_ostream os(str);
+    string_ostream os;
     os << "(" << Arg->getParent()->getName() << ",%" << Arg->getName()
        << ")";
     Hash = MDString::get(Arg->getContext(), os.str());
@@ -860,8 +858,7 @@ static MDString *AppendMDNodeToSourcePtr(unsigned NodeId,
 }
 
 static std::string SequenceToString(Sequence A) {
-  std::string str;
-  raw_string_ostream os(str);
+  string_ostream os;
   os << A;
   return os.str();
 }
diff --git a/lib/Transforms/Utils/ASanStackFrameLayout.cpp b/lib/Transforms/Utils/ASanStackFrameLayout.cpp
index cce016aafd..42fd398d5f 100644
--- a/lib/Transforms/Utils/ASanStackFrameLayout.cpp
+++ b/lib/Transforms/Utils/ASanStackFrameLayout.cpp
@@ -65,8 +65,7 @@ ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars,
     Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment);
 
   std::stable_sort(Vars.begin(), Vars.end(), CompareVars);
-  SmallString<2048> StackDescriptionStorage;
-  raw_svector_ostream StackDescription(StackDescriptionStorage);
+  small_string_ostream<2048> StackDescription;
   StackDescription << NumVars;
   Layout->FrameAlignment = std::max(Granularity, Vars[0].Alignment);
   SmallVector<uint8_t, 64> &SB(Layout->ShadowBytes);
diff --git a/lib/Transforms/Vectorize/LoopVectorize.cpp b/lib/Transforms/Vectorize/LoopVectorize.cpp
index cb8a41dbea..2338d296cc 100644
--- a/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ b/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -212,24 +212,23 @@ class LoopVectorizationCostModel;
 /// Optimization analysis message produced during vectorization. Messages inform
 /// the user why vectorization did not occur.
 class Report {
-  std::string Message;
-  raw_string_ostream Out;
+  string_ostream Message;
   Instruction *Instr;
 
 public:
-  Report(Instruction *I = nullptr) : Out(Message), Instr(I) {
-    Out << "loop not vectorized: ";
+  Report(Instruction *I = nullptr) : Instr(I) {
+    Message << "loop not vectorized: ";
   }
 
   template <typename A> Report &operator<<(const A &Value) {
-    Out << Value;
+    Message << Value;
     return *this;
   }
 
   Instruction *getInstr() { return Instr; }
 
-  std::string &str() { return Out.str(); }
-  operator Twine() { return Out.str(); }
+  StringRef str() { return Message.str(); }
+  operator Twine() { return Message.str(); }
 };
 
 /// InnerLoopVectorizer vectorizes loops which contain only one basic
@@ -503,18 +502,17 @@ static void setDebugLocFromInst(IRBuilder<> &B, const Value *Ptr) {
 #ifndef NDEBUG
 /// \return string containing a file name and a line # for the given loop.
 static std::string getDebugLocString(const Loop *L) {
-  std::string Result;
-  if (L) {
-    raw_string_ostream OS(Result);
-    const DebugLoc LoopDbgLoc = L->getStartLoc();
-    if (!LoopDbgLoc.isUnknown())
-      LoopDbgLoc.print(L->getHeader()->getContext(), OS);
-    else
-      // Just print the module name.
-      OS << L->getHeader()->getParent()->getParent()->getModuleIdentifier();
-    OS.flush();
-  }
-  return Result;
+  if (!L)
+    return std::string();
+
+  string_ostream OS;
+  const DebugLoc LoopDbgLoc = L->getStartLoc();
+  if (!LoopDbgLoc.isUnknown())
+    LoopDbgLoc.print(L->getHeader()->getContext(), OS);
+  else
+    // Just print the module name.
+    OS << L->getHeader()->getParent()->getParent()->getModuleIdentifier();
+  return OS.str();
 }
 #endif