diff --git a/clang/lib/Tooling/JSONCompilationDatabase.cpp b/clang/lib/Tooling/JSONCompilationDatabase.cpp
--- a/clang/lib/Tooling/JSONCompilationDatabase.cpp
+++ b/clang/lib/Tooling/JSONCompilationDatabase.cpp
@@ -198,7 +198,7 @@
                                       JSONCommandLineSyntax Syntax) {
   // Don't mmap: if we're a long-lived process, the build system may overwrite.
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> DatabaseBuffer =
-      llvm::MemoryBuffer::getFile(FilePath, /*FileSize=*/-1,
+      llvm::MemoryBuffer::getFile(FilePath, /*IsText=*/false,
                                   /*RequiresNullTerminator=*/true,
                                   /*IsVolatile=*/true);
   if (std::error_code Result = DatabaseBuffer.getError()) {
diff --git a/clang/tools/arcmt-test/arcmt-test.cpp b/clang/tools/arcmt-test/arcmt-test.cpp
--- a/clang/tools/arcmt-test/arcmt-test.cpp
+++ b/clang/tools/arcmt-test/arcmt-test.cpp
@@ -207,15 +207,13 @@
 static bool filesCompareEqual(StringRef fname1, StringRef fname2) {
   using namespace llvm;
 
-  ErrorOr<std::unique_ptr<MemoryBuffer>> file1 = MemoryBuffer::getFile(
-      fname1, /*FileSize=*/-1, /*RequiresNullTerminator=*/true,
-      /*IsVolatile=*/false, /*IsText=*/true);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> file1 =
+      MemoryBuffer::getFile(fname1, /*IsText=*/true);
   if (!file1)
     return false;
 
-  ErrorOr<std::unique_ptr<MemoryBuffer>> file2 = MemoryBuffer::getFile(
-      fname2, /*FileSize=*/-1, /*RequiresNullTerminator=*/true,
-      /*IsVolatile=*/false, /*IsText=*/true);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> file2 =
+      MemoryBuffer::getFile(fname2, /*IsText=*/true);
   if (!file2)
     return false;
 
@@ -244,9 +242,7 @@
   if (RemappingsFile.empty())
     inputBuf = MemoryBuffer::getSTDIN();
   else
-    inputBuf = MemoryBuffer::getFile(RemappingsFile, /*FileSize=*/-1,
-                                     /*RequiresNullTerminator=*/true,
-                                     /*IsVolatile=*/false, /*IsText=*/true);
+    inputBuf = MemoryBuffer::getFile(RemappingsFile, /*IsText=*/true);
   if (!inputBuf) {
     errs() << "error: could not read remappings input\n";
     return true;
diff --git a/lld/COFF/Driver.cpp b/lld/COFF/Driver.cpp
--- a/lld/COFF/Driver.cpp
+++ b/lld/COFF/Driver.cpp
@@ -157,9 +157,8 @@
   auto strategy = std::launch::deferred;
 #endif
   return std::async(strategy, [=]() {
-    auto mbOrErr = MemoryBuffer::getFile(path,
-                                         /*FileSize*/ -1,
-                                         /*RequiresNullTerminator*/ false);
+    auto mbOrErr = MemoryBuffer::getFile(path, /*IsText=*/false,
+                                         /*RequiresNullTerminator=*/false);
     if (!mbOrErr)
       return MBErrPair{nullptr, mbOrErr.getError()};
     return MBErrPair{std::move(*mbOrErr), std::error_code()};
@@ -829,7 +828,7 @@
   // If the import library already exists, replace it only if the contents
   // have changed.
   ErrorOr<std::unique_ptr<MemoryBuffer>> oldBuf = MemoryBuffer::getFile(
-      path, /*FileSize*/ -1, /*RequiresNullTerminator*/ false);
+      path, /*IsText=*/false, /*RequiresNullTerminator=*/false);
   if (!oldBuf) {
     handleError(writeImportLibrary(libName, path, exports, config->machine,
                                    config->mingw));
@@ -849,7 +848,7 @@
   }
 
   std::unique_ptr<MemoryBuffer> newBuf = check(MemoryBuffer::getFile(
-      tmpName, /*FileSize*/ -1, /*RequiresNullTerminator*/ false));
+      tmpName, /*IsText=*/false, /*RequiresNullTerminator=*/false));
   if ((*oldBuf)->getBuffer() != newBuf->getBuffer()) {
     oldBuf->reset();
     handleError(errorCodeToError(sys::fs::rename(tmpName, path)));
@@ -859,8 +858,11 @@
 }
 
 static void parseModuleDefs(StringRef path) {
-  std::unique_ptr<MemoryBuffer> mb = CHECK(
-      MemoryBuffer::getFile(path, -1, false, true), "could not open " + path);
+  std::unique_ptr<MemoryBuffer> mb =
+      CHECK(MemoryBuffer::getFile(path, /*IsText=*/false,
+                                  /*RequiresNullTerminator=*/false,
+                                  /*IsVolatile=*/true),
+            "could not open " + path);
   COFFModuleDefinition m = check(parseCOFFModuleDefinition(
       mb->getMemBufferRef(), config->machine, config->mingw));
 
@@ -948,8 +950,11 @@
 
   // Open a file.
   StringRef path = arg.substr(1);
-  std::unique_ptr<MemoryBuffer> mb = CHECK(
-      MemoryBuffer::getFile(path, -1, false, true), "could not open " + path);
+  std::unique_ptr<MemoryBuffer> mb =
+      CHECK(MemoryBuffer::getFile(path, /*IsText=*/false,
+                                  /*RequiresNullTerminator=*/false,
+                                  /*IsVolatile=*/true),
+            "could not open " + path);
 
   // Parse a file. An order file contains one symbol per line.
   // All symbols that were not present in a given order file are
@@ -973,8 +978,11 @@
 }
 
 static void parseCallGraphFile(StringRef path) {
-  std::unique_ptr<MemoryBuffer> mb = CHECK(
-      MemoryBuffer::getFile(path, -1, false, true), "could not open " + path);
+  std::unique_ptr<MemoryBuffer> mb =
+      CHECK(MemoryBuffer::getFile(path, /*IsText=*/false,
+                                  /*RequiresNullTerminator=*/false,
+                                  /*IsVolatile=*/true),
+            "could not open " + path);
 
   // Build a map from symbol name to section.
   DenseMap<StringRef, Symbol *> map;
diff --git a/lld/COFF/DriverUtils.cpp b/lld/COFF/DriverUtils.cpp
--- a/lld/COFF/DriverUtils.cpp
+++ b/lld/COFF/DriverUtils.cpp
@@ -350,7 +350,7 @@
   // is called (you cannot remove an opened file on Windows.)
   std::unique_ptr<MemoryBuffer> getMemoryBuffer() {
     // IsVolatile=true forces MemoryBuffer to not use mmap().
-    return CHECK(MemoryBuffer::getFile(path, /*FileSize=*/-1,
+    return CHECK(MemoryBuffer::getFile(path, /*IsText=*/false,
                                        /*RequiresNullTerminator=*/false,
                                        /*IsVolatile=*/true),
                  "could not open " + path);
diff --git a/lld/ELF/InputFiles.cpp b/lld/ELF/InputFiles.cpp
--- a/lld/ELF/InputFiles.cpp
+++ b/lld/ELF/InputFiles.cpp
@@ -115,7 +115,8 @@
   log(path);
   config->dependencyFiles.insert(llvm::CachedHashString(path));
 
-  auto mbOrErr = MemoryBuffer::getFile(path, -1, false);
+  auto mbOrErr = MemoryBuffer::getFile(path, /*IsText=*/false,
+                                       /*RequiresNullTerminator=*/false);
   if (auto ec = mbOrErr.getError()) {
     error("cannot open " + path + ": " + ec.message());
     return None;
diff --git a/lldb/source/Host/common/FileSystem.cpp b/lldb/source/Host/common/FileSystem.cpp
--- a/lldb/source/Host/common/FileSystem.cpp
+++ b/lldb/source/Host/common/FileSystem.cpp
@@ -307,7 +307,7 @@
   std::unique_ptr<llvm::WritableMemoryBuffer> buffer;
   if (size == 0) {
     auto buffer_or_error =
-        llvm::WritableMemoryBuffer::getFile(*external_path, -1, is_volatile);
+        llvm::WritableMemoryBuffer::getFile(*external_path, is_volatile);
     if (!buffer_or_error)
       return nullptr;
     buffer = std::move(*buffer_or_error);
diff --git a/lldb/source/Plugins/ObjectFile/PDB/ObjectFilePDB.cpp b/lldb/source/Plugins/ObjectFile/PDB/ObjectFilePDB.cpp
--- a/lldb/source/Plugins/ObjectFile/PDB/ObjectFilePDB.cpp
+++ b/lldb/source/Plugins/ObjectFile/PDB/ObjectFilePDB.cpp
@@ -173,7 +173,7 @@
   if (ec || magic != llvm::file_magic::pdb)
     return nullptr;
   llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> ErrorOrBuffer =
-      llvm::MemoryBuffer::getFile(PdbPath, /*FileSize=*/-1,
+      llvm::MemoryBuffer::getFile(PdbPath, /*IsText=*/false,
                                   /*RequiresNullTerminator=*/false);
   if (!ErrorOrBuffer)
     return nullptr;
diff --git a/lldb/unittests/TestingSupport/TestUtilities.cpp b/lldb/unittests/TestingSupport/TestUtilities.cpp
--- a/lldb/unittests/TestingSupport/TestUtilities.cpp
+++ b/lldb/unittests/TestingSupport/TestUtilities.cpp
@@ -38,8 +38,8 @@
 
 llvm::Expected<TestFile> TestFile::fromYamlFile(const llvm::Twine &Name) {
   auto BufferOrError =
-      llvm::MemoryBuffer::getFile(GetInputFilePath(Name), /*FileSize*/ -1,
-                                  /*RequiresNullTerminator*/ false);
+      llvm::MemoryBuffer::getFile(GetInputFilePath(Name), /*IsText=*/false,
+                                  /*RequiresNullTerminator=*/false);
   if (!BufferOrError)
     return llvm::errorCodeToError(BufferOrError.getError());
   return fromYaml(BufferOrError.get()->getBuffer());
diff --git a/llvm/include/llvm/Support/MemoryBuffer.h b/llvm/include/llvm/Support/MemoryBuffer.h
--- a/llvm/include/llvm/Support/MemoryBuffer.h
+++ b/llvm/include/llvm/Support/MemoryBuffer.h
@@ -75,20 +75,17 @@
   virtual StringRef getBufferIdentifier() const { return "Unknown buffer"; }
 
   /// Open the specified file as a MemoryBuffer, returning a new MemoryBuffer
-  /// if successful, otherwise returning null. If FileSize is specified, this
-  /// means that the client knows that the file exists and that it has the
-  /// specified size.
+  /// if successful, otherwise returning null.
+  ///
+  /// \param IsText Set to true to indicate that the file should be read in
+  /// text mode.
   ///
   /// \param IsVolatile Set to true to indicate that the contents of the file
   /// can change outside the user's control, e.g. when libclang tries to parse
   /// while the user is editing/updating the file or if the file is on an NFS.
-  ///
-  /// \param IsText Set to true to indicate that the file should be read in
-  /// text mode.
   static ErrorOr<std::unique_ptr<MemoryBuffer>>
-  getFile(const Twine &Filename, int64_t FileSize = -1,
-          bool RequiresNullTerminator = true, bool IsVolatile = false,
-          bool IsText = false);
+  getFile(const Twine &Filename, bool IsText = false,
+          bool RequiresNullTerminator = true, bool IsVolatile = false);
 
   /// Read all of the specified file into a MemoryBuffer as a stream
   /// (i.e. until EOF reached). This is useful for special files that
@@ -133,8 +130,8 @@
   /// Open the specified file as a MemoryBuffer, or open stdin if the Filename
   /// is "-".
   static ErrorOr<std::unique_ptr<MemoryBuffer>>
-  getFileOrSTDIN(const Twine &Filename, int64_t FileSize = -1,
-                 bool RequiresNullTerminator = true, bool IsText = false);
+  getFileOrSTDIN(const Twine &Filename, bool IsText = false,
+                 bool RequiresNullTerminator = true);
 
   /// Map a subrange of the specified file as a MemoryBuffer.
   static ErrorOr<std::unique_ptr<MemoryBuffer>>
@@ -184,8 +181,7 @@
   }
 
   static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
-  getFile(const Twine &Filename, int64_t FileSize = -1,
-          bool IsVolatile = false);
+  getFile(const Twine &Filename, bool IsVolatile = false);
 
   /// Map a subrange of the specified file as a WritableMemoryBuffer.
   static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
diff --git a/llvm/lib/BinaryFormat/Magic.cpp b/llvm/lib/BinaryFormat/Magic.cpp
--- a/llvm/lib/BinaryFormat/Magic.cpp
+++ b/llvm/lib/BinaryFormat/Magic.cpp
@@ -223,7 +223,8 @@
 }
 
 std::error_code llvm::identify_magic(const Twine &Path, file_magic &Result) {
-  auto FileOrError = MemoryBuffer::getFile(Path, -1LL, false);
+  auto FileOrError = MemoryBuffer::getFile(Path, /*IsText=*/false,
+                                           /*RequiresNullTerminator=*/false);
   if (!FileOrError)
     return FileOrError.getError();
 
diff --git a/llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp b/llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp
--- a/llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp
+++ b/llvm/lib/DebugInfo/PDB/Native/NativeSession.cpp
@@ -83,7 +83,7 @@
 static Expected<std::unique_ptr<PDBFile>>
 loadPdbFile(StringRef PdbPath, std::unique_ptr<BumpPtrAllocator> &Allocator) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> ErrorOrBuffer =
-      MemoryBuffer::getFile(PdbPath, /*FileSize=*/-1,
+      MemoryBuffer::getFile(PdbPath, /*IsText=*/false,
                             /*RequiresNullTerminator=*/false);
   if (!ErrorOrBuffer)
     return make_error<RawError>(ErrorOrBuffer.getError());
diff --git a/llvm/lib/FuzzMutate/FuzzerCLI.cpp b/llvm/lib/FuzzMutate/FuzzerCLI.cpp
--- a/llvm/lib/FuzzMutate/FuzzerCLI.cpp
+++ b/llvm/lib/FuzzMutate/FuzzerCLI.cpp
@@ -153,7 +153,7 @@
       continue;
     }
 
-    auto BufOrErr = MemoryBuffer::getFile(Arg, /*FileSize-*/ -1,
+    auto BufOrErr = MemoryBuffer::getFile(Arg, /*IsText=*/false,
                                           /*RequiresNullTerminator=*/false);
     if (std::error_code EC = BufOrErr.getError()) {
       errs() << "Error reading file: " << Arg << ": " << EC.message() << "\n";
diff --git a/llvm/lib/IRReader/IRReader.cpp b/llvm/lib/IRReader/IRReader.cpp
--- a/llvm/lib/IRReader/IRReader.cpp
+++ b/llvm/lib/IRReader/IRReader.cpp
@@ -92,9 +92,7 @@
 llvm::parseIRFile(StringRef Filename, SMDiagnostic &Err, LLVMContext &Context,
                   DataLayoutCallbackTy DataLayoutCallback) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(Filename, /*FileSize=*/-1,
-                                   /*RequiresNullTerminator=*/true,
-                                   /*IsText=*/true);
+      MemoryBuffer::getFileOrSTDIN(Filename, /*IsText=*/true);
   if (std::error_code EC = FileOrErr.getError()) {
     Err = SMDiagnostic(Filename, SourceMgr::DK_Error,
                        "Could not open input file: " + EC.message());
diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -285,8 +285,8 @@
     return nullptr;
 
   // read .o file into memory buffer
-  ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
-      MemoryBuffer::getFile(name, -1, false);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr = MemoryBuffer::getFile(
+      name, /*IsText=*/false, /*RequiresNullTerminator=*/false);
   if (std::error_code EC = BufferOrErr.getError()) {
     emitError(EC.message());
     sys::fs::remove(NativeObjectPath);
diff --git a/llvm/lib/Object/Binary.cpp b/llvm/lib/Object/Binary.cpp
--- a/llvm/lib/Object/Binary.cpp
+++ b/llvm/lib/Object/Binary.cpp
@@ -97,7 +97,7 @@
 Expected<OwningBinary<Binary>>
 object::createBinary(StringRef Path, LLVMContext *Context, bool InitContent) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(Path, /*FileSize=*/-1,
+      MemoryBuffer::getFileOrSTDIN(Path, /*IsText=*/false,
                                    /*RequiresNullTerminator=*/false);
   if (std::error_code EC = FileOrErr.getError())
     return errorCodeToError(EC);
diff --git a/llvm/lib/ProfileData/GCOV.cpp b/llvm/lib/ProfileData/GCOV.cpp
--- a/llvm/lib/ProfileData/GCOV.cpp
+++ b/llvm/lib/ProfileData/GCOV.cpp
@@ -564,7 +564,7 @@
     // Open source files without requiring a NUL terminator. The concurrent
     // modification may nullify the NUL terminator condition.
     ErrorOr<std::unique_ptr<MemoryBuffer>> BufferOrErr =
-        MemoryBuffer::getFileOrSTDIN(Filename, -1,
+        MemoryBuffer::getFileOrSTDIN(Filename, /*IsText=*/false,
                                      /*RequiresNullTerminator=*/false);
     if (std::error_code EC = BufferOrErr.getError()) {
       errs() << Filename << ": " << EC.message() << "\n";
diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -105,9 +105,8 @@
 
 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
-getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
-           uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile,
-           bool IsText);
+getFileAux(const Twine &Filename, uint64_t MapSize, uint64_t Offset,
+           bool IsText, bool RequiresNullTerminator, bool IsVolatile);
 
 std::unique_ptr<MemoryBuffer>
 MemoryBuffer::getMemBuffer(StringRef InputData, StringRef BufferName,
@@ -141,21 +140,22 @@
 }
 
 ErrorOr<std::unique_ptr<MemoryBuffer>>
-MemoryBuffer::getFileOrSTDIN(const Twine &Filename, int64_t FileSize,
-                             bool RequiresNullTerminator, bool IsText) {
+MemoryBuffer::getFileOrSTDIN(const Twine &Filename, bool IsText,
+                             bool RequiresNullTerminator) {
   SmallString<256> NameBuf;
   StringRef NameRef = Filename.toStringRef(NameBuf);
 
   if (NameRef == "-")
     return getSTDIN();
-  return getFile(Filename, FileSize, RequiresNullTerminator, false, IsText);
+  return getFile(Filename, IsText, RequiresNullTerminator,
+                 /*IsVolatile=*/false);
 }
 
 ErrorOr<std::unique_ptr<MemoryBuffer>>
 MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
                            uint64_t Offset, bool IsVolatile) {
-  return getFileAux<MemoryBuffer>(FilePath, -1, MapSize, Offset, false,
-                                  IsVolatile, false);
+  return getFileAux<MemoryBuffer>(FilePath, MapSize, Offset, /*IsText=*/false,
+                                  /*RequiresNullTerminator=*/false, IsVolatile);
 }
 
 //===----------------------------------------------------------------------===//
@@ -242,11 +242,10 @@
 }
 
 ErrorOr<std::unique_ptr<MemoryBuffer>>
-MemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
-                      bool RequiresNullTerminator, bool IsVolatile,
-                      bool IsText) {
-  return getFileAux<MemoryBuffer>(Filename, FileSize, FileSize, 0,
-                                  RequiresNullTerminator, IsVolatile, IsText);
+MemoryBuffer::getFile(const Twine &Filename, bool IsText,
+                      bool RequiresNullTerminator, bool IsVolatile) {
+  return getFileAux<MemoryBuffer>(Filename, /*MapSize=*/-1, /*Offset=*/0,
+                                  IsText, RequiresNullTerminator, IsVolatile);
 }
 
 template <typename MB>
@@ -257,33 +256,32 @@
 
 template <typename MB>
 static ErrorOr<std::unique_ptr<MB>>
-getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
-           uint64_t Offset, bool RequiresNullTerminator, bool IsVolatile,
-           bool IsText) {
+getFileAux(const Twine &Filename, uint64_t MapSize, uint64_t Offset,
+           bool IsText, bool RequiresNullTerminator, bool IsVolatile) {
   Expected<sys::fs::file_t> FDOrErr = sys::fs::openNativeFileForRead(
       Filename, IsText ? sys::fs::OF_Text : sys::fs::OF_None);
   if (!FDOrErr)
     return errorToErrorCode(FDOrErr.takeError());
   sys::fs::file_t FD = *FDOrErr;
-  auto Ret = getOpenFileImpl<MB>(FD, Filename, FileSize, MapSize, Offset,
+  auto Ret = getOpenFileImpl<MB>(FD, Filename, /*FileSize=*/-1, MapSize, Offset,
                                  RequiresNullTerminator, IsVolatile);
   sys::fs::closeFile(FD);
   return Ret;
 }
 
 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
-WritableMemoryBuffer::getFile(const Twine &Filename, int64_t FileSize,
-                              bool IsVolatile) {
-  return getFileAux<WritableMemoryBuffer>(Filename, FileSize, FileSize, 0,
-                                          /*RequiresNullTerminator*/ false,
-                                          IsVolatile, false);
+WritableMemoryBuffer::getFile(const Twine &Filename, bool IsVolatile) {
+  return getFileAux<WritableMemoryBuffer>(
+      Filename, /*MapSize=*/-1, /*Offset=*/0, /*IsText=*/false,
+      /*RequiresNullTerminator=*/false, IsVolatile);
 }
 
 ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 WritableMemoryBuffer::getFileSlice(const Twine &Filename, uint64_t MapSize,
                                    uint64_t Offset, bool IsVolatile) {
-  return getFileAux<WritableMemoryBuffer>(Filename, -1, MapSize, Offset, false,
-                                          IsVolatile, false);
+  return getFileAux<WritableMemoryBuffer>(
+      Filename, MapSize, Offset, /*IsText=*/false,
+      /*RequiresNullTerminator=*/false, IsVolatile);
 }
 
 std::unique_ptr<WritableMemoryBuffer>
diff --git a/llvm/lib/TableGen/Main.cpp b/llvm/lib/TableGen/Main.cpp
--- a/llvm/lib/TableGen/Main.cpp
+++ b/llvm/lib/TableGen/Main.cpp
@@ -93,9 +93,7 @@
 
   Records.startTimer("Parse, build records");
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(InputFilename, /*FileSize=*/-1,
-                                   /*RequiresNullTerminator=*/true,
-                                   /*IsText=*/true);
+      MemoryBuffer::getFileOrSTDIN(InputFilename, /*IsText=*/true);
   if (std::error_code EC = FileOrErr.getError())
     return reportError(argv0, "Could not open input file '" + InputFilename +
                                   "': " + EC.message() + "\n");
@@ -139,9 +137,8 @@
     // Only updates the real output file if there are any differences.
     // This prevents recompilation of all the files depending on it if there
     // aren't any.
-    if (auto ExistingOrErr = MemoryBuffer::getFile(
-            OutputFilename, /*FileSize=*/-1, /*RequiresNullTerminator=*/true,
-            /*IsVolatile=*/false, /*IsText=*/true))
+    if (auto ExistingOrErr =
+            MemoryBuffer::getFile(OutputFilename, /*IsText=*/true))
       if (std::move(ExistingOrErr.get())->getBuffer() == Out.str())
         WriteFile = false;
   }
diff --git a/llvm/lib/ToolDrivers/llvm-lib/LibDriver.cpp b/llvm/lib/ToolDrivers/llvm-lib/LibDriver.cpp
--- a/llvm/lib/ToolDrivers/llvm-lib/LibDriver.cpp
+++ b/llvm/lib/ToolDrivers/llvm-lib/LibDriver.cpp
@@ -112,8 +112,8 @@
   std::unique_ptr<MemoryBuffer> B;
   for (auto *Arg : Args.filtered(OPT_INPUT)) {
     // Create or open the archive object.
-    ErrorOr<std::unique_ptr<MemoryBuffer>> MaybeBuf =
-        MemoryBuffer::getFile(Arg->getValue(), -1, false);
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MaybeBuf = MemoryBuffer::getFile(
+        Arg->getValue(), /*IsText=*/false, /*RequiresNullTerminator=*/false);
     fatalOpenError(errorCodeToError(MaybeBuf.getError()), Arg->getValue());
 
     if (identify_magic(MaybeBuf.get()->getBuffer()) == file_magic::archive) {
@@ -339,8 +339,8 @@
       continue;
 
     // Open a file.
-    ErrorOr<std::unique_ptr<MemoryBuffer>> MOrErr =
-        MemoryBuffer::getFile(Path, -1, false);
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MOrErr = MemoryBuffer::getFile(
+        Path, /*IsText=*/false, /*RequiresNullTerminator=*/false);
     fatalOpenError(errorCodeToError(MOrErr.getError()), Path);
     MemoryBufferRef MBRef = (*MOrErr)->getMemBufferRef();
 
diff --git a/llvm/tools/lli/lli.cpp b/llvm/tools/lli/lli.cpp
--- a/llvm/tools/lli/lli.cpp
+++ b/llvm/tools/lli/lli.cpp
@@ -327,7 +327,8 @@
       return nullptr;
     // Load the object from the cache filename
     ErrorOr<std::unique_ptr<MemoryBuffer>> IRObjectBuffer =
-        MemoryBuffer::getFile(CacheName, -1, false);
+        MemoryBuffer::getFile(CacheName, /*IsText=*/false,
+                              /*RequiresNullTerminator=*/false);
     // If the file isn't there, that's OK.
     if (!IRObjectBuffer)
       return nullptr;
diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -270,7 +270,8 @@
 }
 
 static object::Archive &readLibrary(const Twine &Library) {
-  auto BufOrErr = MemoryBuffer::getFile(Library, -1, false);
+  auto BufOrErr = MemoryBuffer::getFile(Library, /*IsText=*/false,
+                                        /*RequiresNullTerminator=*/false);
   failIfError(BufOrErr.getError(), "could not open library " + Library);
   ArchiveBuffers.push_back(std::move(*BufOrErr));
   auto LibOrErr =
@@ -995,8 +996,8 @@
 static int performOperation(ArchiveOperation Operation,
                             std::vector<NewArchiveMember> *NewMembers) {
   // Create or open the archive object.
-  ErrorOr<std::unique_ptr<MemoryBuffer>> Buf =
-      MemoryBuffer::getFile(ArchiveName, -1, false);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> Buf = MemoryBuffer::getFile(
+      ArchiveName, /*IsText=*/false, /*RequiresNullTerminator=*/false);
   std::error_code EC = Buf.getError();
   if (EC && EC != errc::no_such_file_or_directory)
     fail("unable to open '" + ArchiveName + "': " + EC.message());
diff --git a/llvm/tools/llvm-cov/gcov.cpp b/llvm/tools/llvm-cov/gcov.cpp
--- a/llvm/tools/llvm-cov/gcov.cpp
+++ b/llvm/tools/llvm-cov/gcov.cpp
@@ -46,7 +46,8 @@
   // Open .gcda and .gcda without requiring a NUL terminator. The concurrent
   // modification may nullify the NUL terminator condition.
   ErrorOr<std::unique_ptr<MemoryBuffer>> GCNO_Buff =
-      MemoryBuffer::getFileOrSTDIN(GCNO, -1, /*RequiresNullTerminator=*/false);
+      MemoryBuffer::getFileOrSTDIN(GCNO, /*IsText=*/false,
+                                   /*RequiresNullTerminator=*/false);
   if (std::error_code EC = GCNO_Buff.getError()) {
     errs() << GCNO << ": " << EC.message() << "\n";
     return;
@@ -58,7 +59,8 @@
   }
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> GCDA_Buff =
-      MemoryBuffer::getFileOrSTDIN(GCDA, -1, /*RequiresNullTerminator=*/false);
+      MemoryBuffer::getFileOrSTDIN(GCDA, /*IsText=*/false,
+                                   /*RequiresNullTerminator=*/false);
   if (std::error_code EC = GCDA_Buff.getError()) {
     if (EC != errc::no_such_file_or_directory) {
       errs() << GCDA << ": " << EC.message() << "\n";
diff --git a/llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp b/llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
--- a/llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
+++ b/llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
@@ -147,7 +147,7 @@
   std::tie(FileName, DirName) = StringRef(FileList).rsplit(",");
 
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(FileName, /*FileSize=*/-1,
+      MemoryBuffer::getFileOrSTDIN(FileName, /*IsText=*/false,
                                    /*RequiresNullTerminator=*/false);
   if (std::error_code EC = FileOrErr.getError())
     return createFileError(FileName, errorCodeToError(EC));
diff --git a/llvm/tools/llvm-pdbutil/InputFile.cpp b/llvm/tools/llvm-pdbutil/InputFile.cpp
--- a/llvm/tools/llvm-pdbutil/InputFile.cpp
+++ b/llvm/tools/llvm-pdbutil/InputFile.cpp
@@ -288,7 +288,8 @@
         formatv("File {0} is not a supported file type", Path),
         inconvertibleErrorCode());
 
-  auto Result = MemoryBuffer::getFile(Path, -1LL, false);
+  auto Result = MemoryBuffer::getFile(Path, /*IsText=*/false,
+                                      /*RequiresNullTerminator=*/false);
   if (!Result)
     return make_error<StringError>(
         formatv("File {0} could not be opened", Path), Result.getError());
diff --git a/llvm/tools/llvm-pdbutil/llvm-pdbutil.cpp b/llvm/tools/llvm-pdbutil/llvm-pdbutil.cpp
--- a/llvm/tools/llvm-pdbutil/llvm-pdbutil.cpp
+++ b/llvm/tools/llvm-pdbutil/llvm-pdbutil.cpp
@@ -748,7 +748,7 @@
 static void yamlToPdb(StringRef Path) {
   BumpPtrAllocator Allocator;
   ErrorOr<std::unique_ptr<MemoryBuffer>> ErrorOrBuffer =
-      MemoryBuffer::getFileOrSTDIN(Path, /*FileSize=*/-1,
+      MemoryBuffer::getFileOrSTDIN(Path, /*IsText=*/false,
                                    /*RequiresNullTerminator=*/false);
 
   if (ErrorOrBuffer.getError()) {
diff --git a/llvm/tools/llvm-rc/ResourceFileWriter.cpp b/llvm/tools/llvm-rc/ResourceFileWriter.cpp
--- a/llvm/tools/llvm-rc/ResourceFileWriter.cpp
+++ b/llvm/tools/llvm-rc/ResourceFileWriter.cpp
@@ -1524,14 +1524,16 @@
   // properly though, so if using that to append paths below, this early
   // exception case could be removed.)
   if (sys::path::has_root_directory(File))
-    return errorOrToExpected(MemoryBuffer::getFile(File, -1, false));
+    return errorOrToExpected(MemoryBuffer::getFile(
+        File, /*IsText=*/false, /*RequiresNullTerminator=*/false));
 
   // 1. The current working directory.
   sys::fs::current_path(Cwd);
   Path.assign(Cwd.begin(), Cwd.end());
   sys::path::append(Path, File);
   if (sys::fs::exists(Path))
-    return errorOrToExpected(MemoryBuffer::getFile(Path, -1, false));
+    return errorOrToExpected(MemoryBuffer::getFile(
+        Path, /*IsText=*/false, /*RequiresNullTerminator=*/false));
 
   // 2. The directory of the input resource file, if it is different from the
   // current working directory.
@@ -1539,19 +1541,22 @@
   Path.assign(InputFileDir.begin(), InputFileDir.end());
   sys::path::append(Path, File);
   if (sys::fs::exists(Path))
-    return errorOrToExpected(MemoryBuffer::getFile(Path, -1, false));
+    return errorOrToExpected(MemoryBuffer::getFile(
+        Path, /*IsText=*/false, /*RequiresNullTerminator=*/false));
 
   // 3. All of the include directories specified on the command line.
   for (StringRef ForceInclude : Params.Include) {
     Path.assign(ForceInclude.begin(), ForceInclude.end());
     sys::path::append(Path, File);
     if (sys::fs::exists(Path))
-      return errorOrToExpected(MemoryBuffer::getFile(Path, -1, false));
+      return errorOrToExpected(MemoryBuffer::getFile(
+          Path, /*IsText=*/false, /*RequiresNullTerminator=*/false));
   }
 
   if (auto Result =
           llvm::sys::Process::FindInEnvPath("INCLUDE", File, Params.NoInclude))
-    return errorOrToExpected(MemoryBuffer::getFile(*Result, -1, false));
+    return errorOrToExpected(MemoryBuffer::getFile(
+        *Result, /*IsText=*/false, /*RequiresNullTerminator=*/false));
 
   return make_error<StringError>("error : file not found : " + Twine(File),
                                  inconvertibleErrorCode());
diff --git a/llvm/tools/llvm-readobj/llvm-readobj.cpp b/llvm/tools/llvm-readobj/llvm-readobj.cpp
--- a/llvm/tools/llvm-readobj/llvm-readobj.cpp
+++ b/llvm/tools/llvm-readobj/llvm-readobj.cpp
@@ -653,7 +653,7 @@
 /// Opens \a File and dumps it.
 static void dumpInput(StringRef File, ScopedPrinter &Writer) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(File, /*FileSize=*/-1,
+      MemoryBuffer::getFileOrSTDIN(File, /*IsText=*/false,
                                    /*RequiresNullTerminator=*/false);
   if (std::error_code EC = FileOrErr.getError())
     return reportError(errorCodeToError(EC), File);
diff --git a/llvm/tools/obj2yaml/obj2yaml.cpp b/llvm/tools/obj2yaml/obj2yaml.cpp
--- a/llvm/tools/obj2yaml/obj2yaml.cpp
+++ b/llvm/tools/obj2yaml/obj2yaml.cpp
@@ -36,7 +36,7 @@
 
 static Error dumpInput(StringRef File) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> FileOrErr =
-      MemoryBuffer::getFileOrSTDIN(File, /*FileSize=*/-1,
+      MemoryBuffer::getFileOrSTDIN(File, /*IsText=*/false,
                                    /*RequiresNullTerminator=*/false);
   if (std::error_code EC = FileOrErr.getError())
     return errorCodeToError(EC);
diff --git a/llvm/tools/sanstats/sanstats.cpp b/llvm/tools/sanstats/sanstats.cpp
--- a/llvm/tools/sanstats/sanstats.cpp
+++ b/llvm/tools/sanstats/sanstats.cpp
@@ -125,8 +125,8 @@
   cl::ParseCommandLineOptions(argc, argv,
                               "Sanitizer Statistics Processing Tool");
 
-  ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
-      MemoryBuffer::getFile(ClInputFile, -1, false);
+  ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr = MemoryBuffer::getFile(
+      ClInputFile, /*IsText=*/false, /*RequiresNullTerminator=*/false);
   if (!MBOrErr) {
     errs() << argv[0] << ": " << ClInputFile << ": "
            << MBOrErr.getError().message() << '\n';
diff --git a/llvm/utils/FileCheck/FileCheck.cpp b/llvm/utils/FileCheck/FileCheck.cpp
--- a/llvm/utils/FileCheck/FileCheck.cpp
+++ b/llvm/utils/FileCheck/FileCheck.cpp
@@ -821,9 +821,7 @@
 
   // Read the expected strings from the check file.
   ErrorOr<std::unique_ptr<MemoryBuffer>> CheckFileOrErr =
-      MemoryBuffer::getFileOrSTDIN(CheckFilename, /*FileSize=*/-1,
-                                   /*RequiresNullTerminator=*/true,
-                                   /*IsText=*/true);
+      MemoryBuffer::getFileOrSTDIN(CheckFilename, /*IsText=*/true);
   if (std::error_code EC = CheckFileOrErr.getError()) {
     errs() << "Could not open check file '" << CheckFilename
            << "': " << EC.message() << '\n';
@@ -845,9 +843,7 @@
 
   // Open the file to check and add it to SourceMgr.
   ErrorOr<std::unique_ptr<MemoryBuffer>> InputFileOrErr =
-      MemoryBuffer::getFileOrSTDIN(InputFilename, /*FileSize=*/-1,
-                                   /*RequiresNullTerminator=*/true,
-                                   /*IsText=*/true);
+      MemoryBuffer::getFileOrSTDIN(InputFilename, /*IsText=*/true);
   if (InputFilename == "-")
     InputFilename = "<stdin>"; // Overwrite for improved diagnostic messages
   if (std::error_code EC = InputFileOrErr.getError()) {