diff --git a/clang/lib/ARCMigrate/ARCMT.cpp b/clang/lib/ARCMigrate/ARCMT.cpp
index e32884218597..7eb01fb93db0 100644
--- a/clang/lib/ARCMigrate/ARCMT.cpp
+++ b/clang/lib/ARCMigrate/ARCMT.cpp
@@ -600,7 +600,6 @@ bool MigrationProcess::applyTransform(TransformFn trans,
     SmallString<512> newText;
     llvm::raw_svector_ostream vecOS(newText);
     buf.write(vecOS);
-    vecOS.flush();
     std::unique_ptr<llvm::MemoryBuffer> memBuf(
         llvm::MemoryBuffer::getMemBufferCopy(
             StringRef(newText.data(), newText.size()), newFname));
diff --git a/clang/lib/ARCMigrate/ObjCMT.cpp b/clang/lib/ARCMigrate/ObjCMT.cpp
index b61a421ce415..8271023eed20 100644
--- a/clang/lib/ARCMigrate/ObjCMT.cpp
+++ b/clang/lib/ARCMigrate/ObjCMT.cpp
@@ -1982,7 +1982,6 @@ void ObjCMigrateASTConsumer::HandleTranslationUnit(ASTContext &Ctx) {
     SmallString<512> newText;
     llvm::raw_svector_ostream vecOS(newText);
     buf.write(vecOS);
-    vecOS.flush();
     std::unique_ptr<llvm::MemoryBuffer> memBuf(
         llvm::MemoryBuffer::getMemBufferCopy(
             StringRef(newText.data(), newText.size()), file->getName()));
@@ -2215,7 +2214,6 @@ static std::string applyEditsToTemp(const FileEntry *FE,
   SmallString<512> NewText;
   llvm::raw_svector_ostream OS(NewText);
   Buf->write(OS);
-  OS.flush();
 
   SmallString<64> TempPath;
   int FD;
diff --git a/clang/lib/AST/ASTDiagnostic.cpp b/clang/lib/AST/ASTDiagnostic.cpp
index 5b66f583442c..0544ccbef7a0 100644
--- a/clang/lib/AST/ASTDiagnostic.cpp
+++ b/clang/lib/AST/ASTDiagnostic.cpp
@@ -445,8 +445,6 @@ void clang::FormatASTNodeDiagnosticArgument(
 
   }
 
-  OS.flush();
-
   if (NeedQuotes) {
     Output.insert(Output.begin()+OldEnd, '\'');
     Output.push_back('\'');
diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 89f47f980c9c..3327fb3ef1db 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -498,7 +498,6 @@ std::string PredefinedExpr::ComputeName(IdentType IT, const Decl *CurrentDecl) {
         else
           MC->mangleName(ND, Out);
 
-        Out.flush();
         if (!Buffer.empty() && Buffer.front() == '\01')
           return Buffer.substr(1);
         return Buffer.str();
@@ -660,7 +659,6 @@ std::string PredefinedExpr::ComputeName(IdentType IT, const Decl *CurrentDecl) {
 
     Out << Proto;
 
-    Out.flush();
     return Name.str().str();
   }
   if (const CapturedDecl *CD = dyn_cast<CapturedDecl>(CurrentDecl)) {
@@ -692,7 +690,6 @@ std::string PredefinedExpr::ComputeName(IdentType IT, const Decl *CurrentDecl) {
     MD->getSelector().print(Out);
     Out <<  ']';
 
-    Out.flush();
     return Name.str().str();
   }
   if (isa<TranslationUnitDecl>(CurrentDecl) && IT == PrettyFunction) {
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index 1fcf466a1f6f..1e777a51d9fa 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -2405,7 +2405,6 @@ void CXXNameMangler::mangleType(const ObjCObjectType *T) {
       StringRef name = I->getName();
       QualOS << name.size() << name;
     }
-    QualOS.flush();
     Out << 'U' << QualStr.size() << QualStr;
   }
 
diff --git a/clang/lib/AST/Mangle.cpp b/clang/lib/AST/Mangle.cpp
index 1a061c4f6632..014338f0490f 100644
--- a/clang/lib/AST/Mangle.cpp
+++ b/clang/lib/AST/Mangle.cpp
@@ -206,7 +206,6 @@ void MangleContext::mangleCtorBlock(const CXXConstructorDecl *CD,
   SmallString<64> Buffer;
   llvm::raw_svector_ostream Out(Buffer);
   mangleCXXCtor(CD, CT, Out);
-  Out.flush();
   mangleFunctionBlock(*this, Buffer, BD, ResStream);
 }
 
@@ -216,7 +215,6 @@ void MangleContext::mangleDtorBlock(const CXXDestructorDecl *DD,
   SmallString<64> Buffer;
   llvm::raw_svector_ostream Out(Buffer);
   mangleCXXDtor(DD, DT, Out);
-  Out.flush();
   mangleFunctionBlock(*this, Buffer, BD, ResStream);
 }
 
@@ -253,7 +251,6 @@ void MangleContext::mangleBlock(const DeclContext *DC, const BlockDecl *BD,
       }
     }
   }
-  Stream.flush();
   mangleFunctionBlock(*this, Buffer, BD, Out);
 }
 
diff --git a/clang/lib/AST/MicrosoftMangle.cpp b/clang/lib/AST/MicrosoftMangle.cpp
index a5f75ec0b17a..1be02f5e23c7 100644
--- a/clang/lib/AST/MicrosoftMangle.cpp
+++ b/clang/lib/AST/MicrosoftMangle.cpp
@@ -721,7 +721,6 @@ void MicrosoftCXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
     llvm::raw_svector_ostream Stream(TemplateMangling);
     MicrosoftCXXNameMangler Extra(Context, Stream);
     Extra.mangleTemplateInstantiationName(TD, *TemplateArgs);
-    Stream.flush();
 
     mangleSourceName(TemplateMangling);
     return;
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index ac31722899a8..eaa1e250eb3a 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -613,7 +613,6 @@ static SmallString<256> getUniqueTagTypeName(const TagType *Ty,
   // a unique string for a type?
   llvm::raw_svector_ostream Out(FullName);
   CGM.getCXXABI().getMangleContext().mangleCXXRTTIName(QualType(Ty, 0), Out);
-  Out.flush();
   return FullName;
 }
 
diff --git a/clang/lib/CodeGen/CGVTT.cpp b/clang/lib/CodeGen/CGVTT.cpp
index e3df5a4c05e3..4fb76710d2ad 100644
--- a/clang/lib/CodeGen/CGVTT.cpp
+++ b/clang/lib/CodeGen/CGVTT.cpp
@@ -108,7 +108,6 @@ llvm::GlobalVariable *CodeGenVTables::GetAddrOfVTT(const CXXRecordDecl *RD) {
   llvm::raw_svector_ostream Out(OutName);
   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
       .mangleCXXVTT(RD, Out);
-  Out.flush();
   StringRef Name = OutName.str();
 
   // This will also defer the definition of the VTT.
diff --git a/clang/lib/CodeGen/CGVTables.cpp b/clang/lib/CodeGen/CGVTables.cpp
index 83f45b5da2c3..fcb5c3664943 100644
--- a/clang/lib/CodeGen/CGVTables.cpp
+++ b/clang/lib/CodeGen/CGVTables.cpp
@@ -44,7 +44,6 @@ llvm::Constant *CodeGenModule::GetAddrOfThunk(GlobalDecl GD,
                                                       Thunk.This, Out);
   else
     getCXXABI().getMangleContext().mangleThunk(MD, Thunk, Out);
-  Out.flush();
 
   llvm::Type *Ty = getTypes().GetFunctionTypeForVTable(GD);
   return GetOrCreateLLVMFunction(Name, Ty, GD, /*ForVTable=*/true,
@@ -644,7 +643,6 @@ CodeGenVTables::GenerateConstructionVTable(const CXXRecordDecl *RD,
   cast<ItaniumMangleContext>(CGM.getCXXABI().getMangleContext())
       .mangleCXXCtorVTable(RD, Base.getBaseOffset().getQuantity(),
                            Base.getBase(), Out);
-  Out.flush();
   StringRef Name = OutName.str();
 
   llvm::ArrayType *ArrayType = 
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index fe1f9bae7848..5ce25a29d488 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -2953,7 +2953,6 @@ CodeGenModule::GetAddrOfConstantStringFromLiteral(const StringLiteral *S,
       getCXXABI().getMangleContext().shouldMangleStringLiteral(S)) {
     llvm::raw_svector_ostream Out(MangledNameBuffer);
     getCXXABI().getMangleContext().mangleStringLiteral(S, Out);
-    Out.flush();
 
     LT = llvm::GlobalValue::LinkOnceODRLinkage;
     GlobalVariableName = MangledNameBuffer;
@@ -3041,7 +3040,6 @@ llvm::Constant *CodeGenModule::GetAddrOfGlobalTemporary(
   llvm::raw_svector_ostream Out(Name);
   getCXXABI().getMangleContext().mangleReferenceTemporary(
       VD, E->getManglingNumber(), Out);
-  Out.flush();
 
   APValue *Value = nullptr;
   if (E->getStorageDuration() == SD_Static) {
diff --git a/clang/lib/CodeGen/CodeGenTBAA.cpp b/clang/lib/CodeGen/CodeGenTBAA.cpp
index 53ba02a81397..c3c925cde2fd 100644
--- a/clang/lib/CodeGen/CodeGenTBAA.cpp
+++ b/clang/lib/CodeGen/CodeGenTBAA.cpp
@@ -155,7 +155,6 @@ CodeGenTBAA::getTBAAInfo(QualType QTy) {
     SmallString<256> OutName;
     llvm::raw_svector_ostream Out(OutName);
     MContext.mangleTypeName(QualType(ETy, 0), Out);
-    Out.flush();
     return MetadataCache[Ty] = createTBAAScalarType(OutName, getChar());
   }
 
@@ -271,7 +270,6 @@ CodeGenTBAA::getTBAAStructTypeInfo(QualType QTy) {
       // Don't use the mangler for C code.
       llvm::raw_svector_ostream Out(OutName);
       MContext.mangleTypeName(QualType(Ty, 0), Out);
-      Out.flush();
     } else {
       OutName = RD->getName();
     }
diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 115bf19d97fd..3948b2447ebb 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -1439,7 +1439,6 @@ llvm::GlobalVariable *ItaniumCXXABI::getAddrOfVTable(const CXXRecordDecl *RD,
   SmallString<256> Name;
   llvm::raw_svector_ostream Out(Name);
   getMangleContext().mangleCXXVTable(RD, Out);
-  Out.flush();
 
   ItaniumVTableContext &VTContext = CGM.getItaniumVTableContext();
   llvm::ArrayType *ArrayType = llvm::ArrayType::get(
@@ -1814,7 +1813,6 @@ void ItaniumCXXABI::EmitGuardedInit(CodeGenFunction &CGF,
     {
       llvm::raw_svector_ostream out(guardName);
       getMangleContext().mangleStaticGuardVariable(&D, out);
-      out.flush();
     }
 
     // Create the guard variable with a zero-initializer.
@@ -2038,7 +2036,6 @@ ItaniumCXXABI::getOrCreateThreadLocalWrapper(const VarDecl *VD,
   {
     llvm::raw_svector_ostream Out(WrapperName);
     getMangleContext().mangleItaniumThreadLocalWrapper(VD, Out);
-    Out.flush();
   }
 
   if (llvm::Value *V = CGM.getModule().getNamedValue(WrapperName))
@@ -2094,7 +2091,6 @@ void ItaniumCXXABI::EmitThreadLocalInitFuncs(
     {
       llvm::raw_svector_ostream Out(InitFnName);
       getMangleContext().mangleItaniumThreadLocalInit(VD, Out);
-      Out.flush();
     }
 
     // If we have a definition for the variable, emit the initialization
@@ -2290,7 +2286,6 @@ llvm::GlobalVariable *ItaniumRTTIBuilder::GetAddrOfTypeName(
   SmallString<256> Name;
   llvm::raw_svector_ostream Out(Name);
   CGM.getCXXABI().getMangleContext().mangleCXXRTTIName(Ty, Out);
-  Out.flush();
 
   // We know that the mangled name of the type starts at index 4 of the
   // mangled name of the typename, so we can just index into it in order to
@@ -2312,7 +2307,6 @@ ItaniumRTTIBuilder::GetAddrOfExternalRTTIDescriptor(QualType Ty) {
   SmallString<256> Name;
   llvm::raw_svector_ostream Out(Name);
   CGM.getCXXABI().getMangleContext().mangleCXXRTTI(Ty, Out);
-  Out.flush();
 
   // Look for an existing global.
   llvm::GlobalVariable *GV = CGM.getModule().getNamedGlobal(Name);
@@ -2711,7 +2705,6 @@ llvm::Constant *ItaniumRTTIBuilder::BuildTypeInfo(QualType Ty, bool Force) {
   SmallString<256> Name;
   llvm::raw_svector_ostream Out(Name);
   CGM.getCXXABI().getMangleContext().mangleCXXRTTI(Ty, Out);
-  Out.flush();
 
   llvm::GlobalVariable *OldGV = CGM.getModule().getNamedGlobal(Name);
   if (OldGV && !OldGV->isDeclaration()) {
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 3084446795e8..e62bbae46664 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -257,7 +257,6 @@ public:
     SmallString<256> OutName;
     llvm::raw_svector_ostream Out(OutName);
     getMangleContext().mangleCXXVirtualDisplacementMap(SrcRD, DstRD, Out);
-    Out.flush();
     StringRef MangledName = OutName.str();
 
     if (auto *VDispMap = CGM.getModule().getNamedGlobal(MangledName))
@@ -1854,7 +1853,6 @@ llvm::Function *MicrosoftCXXABI::EmitVirtualMemPtrThunk(
   SmallString<256> ThunkName;
   llvm::raw_svector_ostream Out(ThunkName);
   getMangleContext().mangleVirtualMemPtrThunk(MD, Out);
-  Out.flush();
 
   // If the thunk has been generated previously, just return it.
   if (llvm::GlobalValue *GV = CGM.getModule().getNamedValue(ThunkName))
@@ -1930,7 +1928,6 @@ MicrosoftCXXABI::getAddrOfVBTable(const VPtrInfo &VBT, const CXXRecordDecl *RD,
   SmallString<256> OutName;
   llvm::raw_svector_ostream Out(OutName);
   getMangleContext().mangleCXXVBTable(RD, VBT.MangledPath, Out);
-  Out.flush();
   StringRef Name = OutName.str();
 
   llvm::ArrayType *VBTableType =
@@ -2342,7 +2339,6 @@ void MicrosoftCXXABI::EmitGuardedInit(CodeGenFunction &CGF, const VarDecl &D,
                                                                Out);
       else
         getMangleContext().mangleStaticGuardVariable(&D, Out);
-      Out.flush();
     }
 
     // Create the guard variable with a zero-initializer. Just absorb linkage,
@@ -3747,7 +3743,6 @@ MicrosoftCXXABI::getAddrOfCXXCtorClosure(const CXXConstructorDecl *CD,
   SmallString<256> ThunkName;
   llvm::raw_svector_ostream Out(ThunkName);
   getMangleContext().mangleCXXCtor(CD, CT, Out);
-  Out.flush();
 
   // If the thunk has been generated previously, just return it.
   if (llvm::GlobalValue *GV = CGM.getModule().getNamedValue(ThunkName))
diff --git a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
index d0e857be3ca2..526c0c71de56 100644
--- a/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
+++ b/clang/lib/CodeGen/ObjectFilePCHContainerOperations.cpp
@@ -139,7 +139,6 @@ public:
       clang::EmitBackendOutput(Diags, CodeGenOpts, TargetOpts, LangOpts,
                                Ctx.getTargetInfo().getDataLayoutString(),
                                M.get(), BackendAction::Backend_EmitLL, &OS);
-      OS.flush();
       llvm::dbgs() << Buffer;
     });
 
diff --git a/clang/lib/Index/CommentToXML.cpp b/clang/lib/Index/CommentToXML.cpp
index ef6aeefa6526..d5c225ecad6c 100644
--- a/clang/lib/Index/CommentToXML.cpp
+++ b/clang/lib/Index/CommentToXML.cpp
@@ -481,7 +481,6 @@ void CommentASTToHTMLConverter::visitFullComment(const FullComment *C) {
     Result << "</div>";
   }
 
-  Result.flush();
 }
 
 void CommentASTToHTMLConverter::visitNonStandaloneParagraphComment(
@@ -1078,8 +1077,6 @@ void CommentASTToXMLConverter::visitFullComment(const FullComment *C) {
   }
 
   Result << RootEndTag;
-
-  Result.flush();
 }
 
 void CommentASTToXMLConverter::appendToResultWithXMLEscaping(StringRef S) {
diff --git a/clang/lib/Index/USRGeneration.cpp b/clang/lib/Index/USRGeneration.cpp
index 8cdd283ba5c5..cc98a719a62b 100644
--- a/clang/lib/Index/USRGeneration.cpp
+++ b/clang/lib/Index/USRGeneration.cpp
@@ -156,10 +156,8 @@ public:
 //===----------------------------------------------------------------------===//
 
 bool USRGenerator::EmitDeclName(const NamedDecl *D) {
-  Out.flush();
   const unsigned startSize = Buf.size();
   D->printName(Out);
-  Out.flush();
   const unsigned endSize = Buf.size();
   return startSize == endSize;
 }
@@ -462,7 +460,6 @@ void USRGenerator::VisitTagDecl(const TagDecl *D) {
   }
   
   Out << '@';
-  Out.flush();
   assert(Buf.size() > 0);
   const unsigned off = Buf.size() - 1;
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index e25b1608064b..7c54986f5681 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -11461,7 +11461,6 @@ static FixItHint createFriendTagNNSFixIt(Sema &SemaRef, NamedDecl *ND, Scope *S,
   std::reverse(Namespaces.begin(), Namespaces.end());
   for (auto *II : Namespaces)
     OS << II->getName() << "::";
-  OS.flush();
   return FixItHint::CreateInsertion(NameLoc, Insertion);
 }
 
diff --git a/clang/lib/Sema/SemaExceptionSpec.cpp b/clang/lib/Sema/SemaExceptionSpec.cpp
index ec3d9fd82fe6..7d03ac4b2497 100644
--- a/clang/lib/Sema/SemaExceptionSpec.cpp
+++ b/clang/lib/Sema/SemaExceptionSpec.cpp
@@ -318,7 +318,6 @@ bool Sema::CheckEquivalentExceptionSpec(FunctionDecl *Old, FunctionDecl *New) {
   default:
     llvm_unreachable("This spec type is compatible with none.");
   }
-  OS.flush();
 
   SourceLocation FixItLoc;
   if (TypeSourceInfo *TSInfo = New->getTypeSourceInfo()) {
diff --git a/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
index 2ba7ea4a4e4d..3f27c3954fa0 100644
--- a/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/DereferenceChecker.cpp
@@ -159,7 +159,6 @@ void DereferenceChecker::reportBug(ProgramStateRef State, const Stmt *S,
     break;
   }
 
-  os.flush();
   auto report = llvm::make_unique<BugReport>(
       *BT_null, buf.empty() ? BT_null->getDescription() : StringRef(buf), N);
 
diff --git a/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
index 4e3f9b73acb2..db4fbca36deb 100644
--- a/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
@@ -276,7 +276,6 @@ void ASTFieldVisitor::ReportError(QualType T) {
     }
   }
   os << " (type " << FieldChain.back()->getType().getAsString() << ")";
-  os.flush();
 
   // Note that this will fire for every translation unit that uses this
   // class.  This is suboptimal, but at least scan-build will merge
diff --git a/clang/tools/libclang/CIndex.cpp b/clang/tools/libclang/CIndex.cpp
index 1fb62d259cd7..46125e3a52b6 100644
--- a/clang/tools/libclang/CIndex.cpp
+++ b/clang/tools/libclang/CIndex.cpp
@@ -7364,8 +7364,6 @@ Logger &cxindex::Logger::operator<<(const llvm::format_object_base &Fmt) {
 static llvm::ManagedStatic<llvm::sys::Mutex> LoggingMutex;
 
 cxindex::Logger::~Logger() {
-  LogOS.flush();
-
   llvm::sys::ScopedLock L(*LoggingMutex);
 
   static llvm::TimeRecord sBeginTR = llvm::TimeRecord::getCurrentTime();
diff --git a/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h b/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
index 49a1fbadb295..1e7d211196f5 100644
--- a/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
+++ b/llvm/include/llvm/ExecutionEngine/Orc/CompileUtils.h
@@ -40,7 +40,6 @@ public:
     if (TM.addPassesToEmitMC(PM, Ctx, ObjStream))
       llvm_unreachable("Target does not support MC emission.");
     PM.run(M);
-    ObjStream.flush();
     std::unique_ptr<MemoryBuffer> ObjBuffer(
         new ObjectMemoryBuffer(std::move(ObjBufferSV)));
     ErrorOr<std::unique_ptr<object::ObjectFile>> Obj =
diff --git a/llvm/include/llvm/Support/raw_ostream.h b/llvm/include/llvm/Support/raw_ostream.h
index 138d811a44a6..d5374d4447a6 100644
--- a/llvm/include/llvm/Support/raw_ostream.h
+++ b/llvm/include/llvm/Support/raw_ostream.h
@@ -509,6 +509,8 @@ public:
   }
   ~raw_svector_ostream() override {}
 
+  void flush() = delete;
+
   /// Return a StringRef for the vector contents.
   StringRef str() { return StringRef(OS.data(), OS.size()); }
 };
diff --git a/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp b/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp
index c201f39a375e..bbe4432d36b3 100644
--- a/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp
+++ b/llvm/lib/ExecutionEngine/MCJIT/MCJIT.cpp
@@ -159,7 +159,6 @@ std::unique_ptr<MemoryBuffer> MCJIT::emitObject(Module *M) {
   // Initialize passes.
   PM.run(*M);
   // Flush the output buffer to get the generated code into memory
-  ObjStream.flush();
 
   std::unique_ptr<MemoryBuffer> CompiledObjBuffer(
                                 new ObjectMemoryBuffer(std::move(ObjBufferSV)));
diff --git a/llvm/lib/MC/MCAsmStreamer.cpp b/llvm/lib/MC/MCAsmStreamer.cpp
index ae482a0fd00d..e33063694e6e 100644
--- a/llvm/lib/MC/MCAsmStreamer.cpp
+++ b/llvm/lib/MC/MCAsmStreamer.cpp
@@ -253,9 +253,6 @@ public:
 void MCAsmStreamer::AddComment(const Twine &T) {
   if (!IsVerboseAsm) return;
 
-  // Make sure that CommentStream is flushed.
-  CommentStream.flush();
-
   T.toVector(CommentToEmit);
   // Each comment goes on its own line.
   CommentToEmit.push_back('\n');
@@ -267,7 +264,6 @@ void MCAsmStreamer::EmitCommentsAndEOL() {
     return;
   }
 
-  CommentStream.flush();
   StringRef Comments = CommentToEmit;
 
   assert(Comments.back() == '\n' &&
@@ -1223,7 +1219,6 @@ void MCAsmStreamer::AddEncodingComment(const MCInst &Inst,
   SmallVector<MCFixup, 4> Fixups;
   raw_svector_ostream VecOS(Code);
   Emitter->encodeInstruction(Inst, VecOS, Fixups, STI);
-  VecOS.flush();
 
   // 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/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 38e126191c1f..4ec81b3c3bb0 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -986,7 +986,6 @@ bool MCAssembler::relaxInstruction(MCAsmLayout &Layout,
   SmallString<256> Code;
   raw_svector_ostream VecOS(Code);
   getEmitter().encodeInstruction(Relaxed, VecOS, Fixups, F.getSubtargetInfo());
-  VecOS.flush();
 
   // Update the fragment.
   F.setInst(Relaxed);
@@ -1009,7 +1008,6 @@ bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
     encodeSLEB128(Value, OSE);
   else
     encodeULEB128(Value, OSE);
-  OSE.flush();
   return OldSize != LF.getContents().size();
 }
 
@@ -1028,7 +1026,6 @@ bool MCAssembler::relaxDwarfLineAddr(MCAsmLayout &Layout,
   raw_svector_ostream OSE(Data);
   MCDwarfLineAddr::Encode(Context, getDWARFLinetableParams(), LineDelta,
                           AddrDelta, OSE);
-  OSE.flush();
   return OldSize != Data.size();
 }
 
@@ -1044,7 +1041,6 @@ bool MCAssembler::relaxDwarfCallFrameFragment(MCAsmLayout &Layout,
   Data.clear();
   raw_svector_ostream OSE(Data);
   MCDwarfFrameEmitter::EncodeAdvanceLoc(Context, AddrDelta, OSE);
-  OSE.flush();
   return OldSize != Data.size();
 }
 
diff --git a/llvm/lib/MC/MCDisassembler/Disassembler.cpp b/llvm/lib/MC/MCDisassembler/Disassembler.cpp
index f8260af53c90..82063fb74696 100644
--- a/llvm/lib/MC/MCDisassembler/Disassembler.cpp
+++ b/llvm/lib/MC/MCDisassembler/Disassembler.cpp
@@ -125,7 +125,6 @@ void LLVMDisasmDispose(LLVMDisasmContextRef DCR){
 static void emitComments(LLVMDisasmContext *DC,
                          formatted_raw_ostream &FormattedOS) {
   // Flush the stream before taking its content.
-  DC->CommentStream.flush();
   StringRef Comments = DC->CommentsToEmit.str();
   // Get the default information for printing a comment.
   const MCAsmInfo *MAI = DC->getAsmInfo();
@@ -260,7 +259,6 @@ size_t LLVMDisasmInstruction(LLVMDisasmContextRef DCR, uint8_t *Bytes,
     return 0;
 
   case MCDisassembler::Success: {
-    Annotations.flush();
     StringRef AnnotationsStr = Annotations.str();
 
     SmallVector<char, 64> InsnStr;
@@ -272,7 +270,6 @@ size_t LLVMDisasmInstruction(LLVMDisasmContextRef DCR, uint8_t *Bytes,
       emitLatency(DC, Inst);
 
     emitComments(DC, FormattedOS);
-    OS.flush();
 
     assert(OutStringSize != 0 && "Output buffer cannot be zero size");
     size_t OutputSize = std::min(OutStringSize-1, InsnStr.size());
diff --git a/llvm/lib/MC/MCELFStreamer.cpp b/llvm/lib/MC/MCELFStreamer.cpp
index 7588ea388238..9a64baa4f13c 100644
--- a/llvm/lib/MC/MCELFStreamer.cpp
+++ b/llvm/lib/MC/MCELFStreamer.cpp
@@ -68,7 +68,6 @@ void MCELFStreamer::mergeFragment(MCDataFragment *DF,
       EF->setBundlePadding(static_cast<uint8_t>(RequiredBundlePadding));
 
       Assembler.writeFragmentPadding(*EF, FSize, OW);
-      VecOS.flush();
       delete OW;
 
       DF->getContents().append(Code.begin(), Code.end());
@@ -480,7 +479,6 @@ void MCELFStreamer::EmitInstToData(const MCInst &Inst,
   SmallString<256> Code;
   raw_svector_ostream VecOS(Code);
   Assembler.getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
-  VecOS.flush();
 
   for (unsigned i = 0, e = Fixups.size(); i != e; ++i)
     fixSymbolsInTLSFixups(Fixups[i].getValue());
diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
index 116ef094d18e..33045d0fcf7b 100644
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -443,7 +443,6 @@ void MCMachOStreamer::EmitInstToData(const MCInst &Inst,
   SmallString<256> Code;
   raw_svector_ostream VecOS(Code);
   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
-  VecOS.flush();
 
   // Add the fixups and data.
   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
diff --git a/llvm/lib/MC/MCObjectStreamer.cpp b/llvm/lib/MC/MCObjectStreamer.cpp
index 3906464ed8b2..49b8358e6e8e 100644
--- a/llvm/lib/MC/MCObjectStreamer.cpp
+++ b/llvm/lib/MC/MCObjectStreamer.cpp
@@ -276,7 +276,6 @@ void MCObjectStreamer::EmitInstToFragment(const MCInst &Inst,
   raw_svector_ostream VecOS(Code);
   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, IF->getFixups(),
                                                 STI);
-  VecOS.flush();
   IF->getContents().append(Code.begin(), Code.end());
 }
 
diff --git a/llvm/lib/MC/WinCOFFStreamer.cpp b/llvm/lib/MC/WinCOFFStreamer.cpp
index 36dd691f07b8..a6e084439106 100644
--- a/llvm/lib/MC/WinCOFFStreamer.cpp
+++ b/llvm/lib/MC/WinCOFFStreamer.cpp
@@ -49,7 +49,6 @@ void MCWinCOFFStreamer::EmitInstToData(const MCInst &Inst,
   SmallString<256> Code;
   raw_svector_ostream VecOS(Code);
   getAssembler().getEmitter().encodeInstruction(Inst, VecOS, Fixups, STI);
-  VecOS.flush();
 
   // Add the fixups and data.
   for (unsigned i = 0, e = Fixups.size(); i != e; ++i) {
@@ -228,7 +227,6 @@ void MCWinCOFFStreamer::EmitCommonSymbol(MCSymbol *Symbol, uint64_t Size,
 
     OS << " -aligncomm:\"" << Symbol->getName() << "\","
        << Log2_32_Ceil(ByteAlignment);
-    OS.flush();
 
     PushSection();
     SwitchSection(MFI->getDrectveSection());
diff --git a/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp b/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
index 20831460b933..15e42abb0b72 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUMCInstLower.cpp
@@ -136,8 +136,6 @@ void AMDGPUAsmPrinter::EmitInstruction(const MachineInstr *MI) {
       MCCodeEmitter &InstEmitter = ObjStreamer.getAssembler().getEmitter();
       InstEmitter.encodeInstruction(TmpInst, CodeStream, Fixups,
                                     MF->getSubtarget<MCSubtargetInfo>());
-      CodeStream.flush();
-
       HexLines.resize(HexLines.size() + 1);
       std::string &HexLine = HexLines.back();
       raw_string_ostream HexStream(HexLine);
diff --git a/llvm/lib/Target/TargetMachineC.cpp b/llvm/lib/Target/TargetMachineC.cpp
index 5913822de235..b2bd8fae423e 100644
--- a/llvm/lib/Target/TargetMachineC.cpp
+++ b/llvm/lib/Target/TargetMachineC.cpp
@@ -243,7 +243,6 @@ LLVMBool LLVMTargetMachineEmitToMemoryBuffer(LLVMTargetMachineRef T,
   SmallString<0> CodeString;
   raw_svector_ostream OStream(CodeString);
   bool Result = LLVMTargetMachineEmit(T, M, OStream, codegen, ErrorMessage);
-  OStream.flush();
 
   StringRef Data = OStream.str();
   *OutMemBuf =
diff --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index 2b30ce6d362b..36c74023d7bb 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -92,7 +92,6 @@ namespace llvm {
       SmallVector<MCFixup, 4> Fixups;
       raw_svector_ostream VecOS(Code);
       CodeEmitter->encodeInstruction(Inst, VecOS, Fixups, STI);
-      VecOS.flush();
       CurrentShadowSize += Code.size();
       if (CurrentShadowSize >= RequiredShadowSize)
         InShadow = false; // The shadow is big enough. Stop counting.
diff --git a/llvm/tools/llvm-objdump/MachODump.cpp b/llvm/tools/llvm-objdump/MachODump.cpp
index 8171a3e9815c..fe3a10ed183b 100644
--- a/llvm/tools/llvm-objdump/MachODump.cpp
+++ b/llvm/tools/llvm-objdump/MachODump.cpp
@@ -5867,7 +5867,6 @@ static void emitComments(raw_svector_ostream &CommentStream,
                          formatted_raw_ostream &FormattedOS,
                          const MCAsmInfo &MAI) {
   // Flush the stream before taking its content.
-  CommentStream.flush();
   StringRef Comments = CommentsToEmit.str();
   // Get the default information for printing a comment.
   const char *CommentBegin = MAI.getCommentString();
@@ -6248,7 +6247,6 @@ static void DisassembleMachO(StringRef Filename, MachOObjectFile *MachOOF,
             dumpBytes(ArrayRef<uint8_t>(Bytes.data() + Index, Size), outs());
           }
           formatted_raw_ostream FormattedOS(outs());
-          Annotations.flush();
           StringRef AnnotationsStr = Annotations.str();
           if (isThumb)
             ThumbIP->printInst(&Inst, FormattedOS, AnnotationsStr, *ThumbSTI);
diff --git a/llvm/utils/TableGen/AsmWriterEmitter.cpp b/llvm/utils/TableGen/AsmWriterEmitter.cpp
index bc7cdc7570f9..4b543d3f9fc6 100644
--- a/llvm/utils/TableGen/AsmWriterEmitter.cpp
+++ b/llvm/utils/TableGen/AsmWriterEmitter.cpp
@@ -727,7 +727,6 @@ public:
         ++I;
       }
     }
-    OS.flush();
 
     // Emit the string.
     O.indent(6) << "AsmString = \"" << OutString << "\";\n";
diff --git a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
index 994039e7c395..f78c6ca6d217 100644
--- a/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
+++ b/llvm/utils/TableGen/FixedLenDecoderEmitter.cpp
@@ -1120,7 +1120,6 @@ unsigned FilterChooser::getDecoderIndex(DecoderSet &Decoders,
   raw_svector_ostream S(Decoder);
   unsigned I = 4;
   emitDecoder(S, I, Opc, HasCompleteDecoder);
-  S.flush();
 
   // Using the full decoder string as the key value here is a bit
   // heavyweight, but is effective. If the string comparisons become a
@@ -1231,7 +1230,6 @@ void FilterChooser::emitPredicateTableEntry(DecoderTableInfo &TableInfo,
   SmallString<16> PBytes;
   raw_svector_ostream S(PBytes);
   encodeULEB128(PIdx, S);
-  S.flush();
 
   TableInfo.Table.push_back(MCD::OPC_CheckPredicate);
   // Predicate index
@@ -1297,7 +1295,6 @@ void FilterChooser::emitSoftFailTableEntry(DecoderTableInfo &TableInfo,
   if (NeedNegativeMask) {
     MaskBytes.clear();
     encodeULEB128(NegativeMask.getZExtValue(), S);
-    S.flush();
     for (unsigned i = 0, e = MaskBytes.size(); i != e; ++i)
       TableInfo.Table.push_back(MaskBytes[i]);
   } else
@@ -1367,7 +1364,6 @@ void FilterChooser::emitSingletonTableEntry(DecoderTableInfo &TableInfo,
   SmallString<16> Bytes;
   raw_svector_ostream S(Bytes);
   encodeULEB128(DIdx, S);
-  S.flush();
 
   // Decoder index
   for (unsigned i = 0, e = Bytes.size(); i != e; ++i)