diff --git a/llvm/include/llvm/Bitcode/BitcodeWriter.h b/llvm/include/llvm/Bitcode/BitcodeWriter.h
--- a/llvm/include/llvm/Bitcode/BitcodeWriter.h
+++ b/llvm/include/llvm/Bitcode/BitcodeWriter.h
@@ -30,7 +30,7 @@
 class raw_ostream;
 
   class BitcodeWriter {
-    SmallVectorImpl<char> &Buffer;
+    std::vector<char> &Buffer;
     std::unique_ptr<BitstreamWriter> Stream;
 
     StringTableBuilder StrtabBuilder{StringTableBuilder::RAW};
@@ -47,7 +47,7 @@
 
   public:
     /// Create a BitcodeWriter that writes to Buffer.
-    BitcodeWriter(SmallVectorImpl<char> &Buffer);
+    BitcodeWriter(std::vector<char> &Buffer);
 
     ~BitcodeWriter();
 
diff --git a/llvm/include/llvm/Bitstream/BitstreamWriter.h b/llvm/include/llvm/Bitstream/BitstreamWriter.h
--- a/llvm/include/llvm/Bitstream/BitstreamWriter.h
+++ b/llvm/include/llvm/Bitstream/BitstreamWriter.h
@@ -25,7 +25,7 @@
 namespace llvm {
 
 class BitstreamWriter {
-  SmallVectorImpl<char> &Out;
+  std::vector<char> &Out;
 
   /// CurBit - Always between 0 and 31 inclusive, specifies the next bit to use.
   unsigned CurBit;
@@ -68,7 +68,7 @@
 
   void WriteWord(unsigned Value) {
     Value = support::endian::byte_swap<uint32_t, support::little>(Value);
-    Out.append(reinterpret_cast<const char *>(&Value),
+    Out.insert(Out.end(), reinterpret_cast<const char *>(&Value),
                reinterpret_cast<const char *>(&Value + 1));
   }
 
@@ -81,8 +81,8 @@
   }
 
 public:
-  explicit BitstreamWriter(SmallVectorImpl<char> &O)
-    : Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {}
+  explicit BitstreamWriter(std::vector<char> &O)
+      : Out(O), CurBit(0), CurValue(0), CurCodeSize(2) {}
 
   ~BitstreamWriter() {
     assert(CurBit == 0 && "Unflushed data remaining");
diff --git a/llvm/include/llvm/Remarks/BitstreamRemarkSerializer.h b/llvm/include/llvm/Remarks/BitstreamRemarkSerializer.h
--- a/llvm/include/llvm/Remarks/BitstreamRemarkSerializer.h
+++ b/llvm/include/llvm/Remarks/BitstreamRemarkSerializer.h
@@ -49,7 +49,7 @@
 struct BitstreamRemarkSerializerHelper {
   /// Buffer used for encoding the bitstream before writing it to the final
   /// stream.
-  SmallVector<char, 1024> Encoded;
+  std::vector<char> Encoded;
   /// Buffer used to construct records and pass to the bitstream writer.
   SmallVector<uint64_t, 64> R;
   /// The Bitstream writer.
diff --git a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
--- a/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
+++ b/llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
@@ -244,7 +244,7 @@
 /// Class to manage the bitcode writing for a module.
 class ModuleBitcodeWriter : public ModuleBitcodeWriterBase {
   /// Pointer to the buffer allocated by caller for bitcode writing.
-  const SmallVectorImpl<char> &Buffer;
+  const std::vector<char> &Buffer;
 
   /// True if a module hash record should be written.
   bool GenerateHash;
@@ -261,7 +261,7 @@
 public:
   /// Constructs a ModuleBitcodeWriter object for the given Module,
   /// writing to the provided \p Buffer.
-  ModuleBitcodeWriter(const Module &M, SmallVectorImpl<char> &Buffer,
+  ModuleBitcodeWriter(const Module &M, std::vector<char> &Buffer,
                       StringTableBuilder &StrtabBuilder,
                       BitstreamWriter &Stream, bool ShouldPreserveUseListOrder,
                       const ModuleSummaryIndex *Index, bool GenerateHash,
@@ -1987,7 +1987,7 @@
   Record.push_back(Strings.size());
 
   // Emit the sizes of the strings in the blob.
-  SmallString<256> Blob;
+  std::vector<char> Blob;
   {
     BitstreamWriter W(Blob);
     for (const Metadata *MD : Strings)
@@ -1999,11 +1999,14 @@
   Record.push_back(Blob.size());
 
   // Add the strings to the blob.
-  for (const Metadata *MD : Strings)
-    Blob.append(cast<MDString>(MD)->getString());
+  for (const Metadata *MD : Strings) {
+    StringRef s = cast<MDString>(MD)->getString();
+    Blob.insert(Blob.end(), s.begin(), s.end());
+  }
 
   // Emit the final record.
-  Stream.EmitRecordWithBlob(createMetadataStringsAbbrev(), Record, Blob);
+  StringRef BlobStr(Blob.data(), Blob.size());
+  Stream.EmitRecordWithBlob(createMetadataStringsAbbrev(), Record, BlobStr);
   Record.clear();
 }
 
@@ -4285,7 +4288,7 @@
   Stream.ExitBlock();
 }
 
-static void writeInt32ToBuffer(uint32_t Value, SmallVectorImpl<char> &Buffer,
+static void writeInt32ToBuffer(uint32_t Value, std::vector<char> &Buffer,
                                uint32_t &Position) {
   support::endian::write32le(&Buffer[Position], Value);
   Position += 4;
@@ -4304,7 +4307,7 @@
 ///   uint32_t CPUType;       // CPU specifier.
 ///   ... potentially more later ...
 /// };
-static void emitDarwinBCHeaderAndTrailer(SmallVectorImpl<char> &Buffer,
+static void emitDarwinBCHeaderAndTrailer(std::vector<char> &Buffer,
                                          const Triple &TT) {
   unsigned CPUType = ~0U;
 
@@ -4361,7 +4364,7 @@
   Stream.Emit(0xD, 4);
 }
 
-BitcodeWriter::BitcodeWriter(SmallVectorImpl<char> &Buffer)
+BitcodeWriter::BitcodeWriter(std::vector<char> &Buffer)
     : Buffer(Buffer), Stream(new BitstreamWriter(Buffer)) {
   writeBitcodeHeader(*Stream);
 }
@@ -4464,7 +4467,7 @@
                               bool ShouldPreserveUseListOrder,
                               const ModuleSummaryIndex *Index,
                               bool GenerateHash, ModuleHash *ModHash) {
-  SmallVector<char, 0> Buffer;
+  std::vector<char> Buffer;
   Buffer.reserve(256*1024);
 
   // If this is darwin or another generic macho target, reserve space for the
@@ -4507,7 +4510,7 @@
 void llvm::WriteIndexToFile(
     const ModuleSummaryIndex &Index, raw_ostream &Out,
     const std::map<std::string, GVSummaryMapTy> *ModuleToSummariesForIndex) {
-  SmallVector<char, 0> Buffer;
+  std::vector<char> Buffer;
   Buffer.reserve(256 * 1024);
 
   BitcodeWriter Writer(Buffer);
@@ -4667,7 +4670,7 @@
 void llvm::WriteThinLinkBitcodeToFile(const Module &M, raw_ostream &Out,
                                       const ModuleSummaryIndex &Index,
                                       const ModuleHash &ModHash) {
-  SmallVector<char, 0> Buffer;
+  std::vector<char> Buffer;
   Buffer.reserve(256 * 1024);
 
   BitcodeWriter Writer(Buffer);
diff --git a/llvm/lib/ExecutionEngine/Orc/ThreadSafeModule.cpp b/llvm/lib/ExecutionEngine/Orc/ThreadSafeModule.cpp
--- a/llvm/lib/ExecutionEngine/Orc/ThreadSafeModule.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/ThreadSafeModule.cpp
@@ -24,7 +24,7 @@
     ShouldCloneDef = [](const GlobalValue &) { return true; };
 
   return TSM.withModuleDo([&](Module &M) {
-    SmallVector<char, 1> ClonedModuleBuffer;
+    std::vector<char> ClonedModuleBuffer;
 
     {
       std::set<GlobalValue *> ClonedDefsInSrc;
diff --git a/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp b/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
--- a/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
+++ b/llvm/lib/Transforms/IPO/ThinLTOBitcodeWriter.cpp
@@ -397,7 +397,7 @@
   ModuleSummaryIndex MergedMIndex =
       buildModuleSummaryIndex(*MergedM, nullptr, &PSI);
 
-  SmallVector<char, 0> Buffer;
+  std::vector<char> Buffer;
 
   BitcodeWriter W(Buffer);
   // Save the module hash produced for the full bitcode, which will
@@ -409,7 +409,7 @@
   W.writeModule(*MergedM, /*ShouldPreserveUseListOrder=*/false, &MergedMIndex);
   W.writeSymtab();
   W.writeStrtab();
-  OS << Buffer;
+  OS.write(Buffer.data(), Buffer.size());
 
   // If a minimized bitcode module was requested for the thin link, only
   // the information that is needed by thin link will be written in the
@@ -423,7 +423,7 @@
                    &MergedMIndex);
     W2.writeSymtab();
     W2.writeStrtab();
-    *ThinLinkOS << Buffer;
+    ThinLinkOS->write(Buffer.data(), Buffer.size());
   }
 }
 
diff --git a/llvm/tools/llvm-cat/llvm-cat.cpp b/llvm/tools/llvm-cat/llvm-cat.cpp
--- a/llvm/tools/llvm-cat/llvm-cat.cpp
+++ b/llvm/tools/llvm-cat/llvm-cat.cpp
@@ -54,7 +54,7 @@
   ExitOnError ExitOnErr("llvm-cat: ");
   LLVMContext Context;
 
-  SmallVector<char, 0> Buffer;
+  std::vector<char> Buffer;
   BitcodeWriter Writer(Buffer);
   if (BinaryCat) {
     for (const auto &InputFilename : InputFilenames) {
diff --git a/llvm/tools/llvm-modextract/llvm-modextract.cpp b/llvm/tools/llvm-modextract/llvm-modextract.cpp
--- a/llvm/tools/llvm-modextract/llvm-modextract.cpp
+++ b/llvm/tools/llvm-modextract/llvm-modextract.cpp
@@ -58,12 +58,12 @@
   ExitOnErr(errorCodeToError(EC));
 
   if (BinaryExtract) {
-    SmallVector<char, 0> Result;
+    std::vector<char> Result;
     BitcodeWriter Writer(Result);
-    Result.append(Ms[ModuleIndex].getBuffer().begin(),
+    Result.insert(Result.end(), Ms[ModuleIndex].getBuffer().begin(),
                   Ms[ModuleIndex].getBuffer().end());
     Writer.copyStrtab(Ms[ModuleIndex].getStrtab());
-    Out->os() << Result;
+    Out->os().write(Result.data(), Result.size());
     Out->keep();
     return 0;
   }