diff --git a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
index 8042b52ddc03..e3ca8fdec393 100644
--- a/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
+++ b/clang/lib/Frontend/SerializedDiagnosticPrinter.cpp
@@ -22,6 +22,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Bitstream/BitCodes.h"
 #include "llvm/Bitstream/BitstreamReader.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include <utility>
 
diff --git a/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp b/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
index 029bfe1cd600..cdb4a79fa11a 100644
--- a/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
+++ b/clang/lib/Lex/DependencyDirectivesSourceMinimizer.cpp
@@ -18,6 +18,7 @@
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Lex/LexDiagnostic.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/MemoryBuffer.h"
 
diff --git a/clang/tools/libclang/CIndexer.cpp b/clang/tools/libclang/CIndexer.cpp
index 57acb4d0d84b..3d8c00cf2115 100644
--- a/clang/tools/libclang/CIndexer.cpp
+++ b/clang/tools/libclang/CIndexer.cpp
@@ -17,6 +17,7 @@
 #include "clang/Driver/Driver.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MD5.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
diff --git a/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp b/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
index eb1fb8d0d8df..76d412203009 100644
--- a/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
+++ b/clang/utils/TableGen/ClangDiagnosticsEmitter.cpp
@@ -19,6 +19,7 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/TableGen/Error.h"
diff --git a/clang/utils/TableGen/MveEmitter.cpp b/clang/utils/TableGen/MveEmitter.cpp
index 6a34f1ff1b24..bc3c21f3a44f 100644
--- a/clang/utils/TableGen/MveEmitter.cpp
+++ b/clang/utils/TableGen/MveEmitter.cpp
@@ -60,6 +60,7 @@
 
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
diff --git a/llvm/include/llvm/BinaryFormat/MsgPackReader.h b/llvm/include/llvm/BinaryFormat/MsgPackReader.h
index 2d332f531b23..bd760f7d7c87 100644
--- a/llvm/include/llvm/BinaryFormat/MsgPackReader.h
+++ b/llvm/include/llvm/BinaryFormat/MsgPackReader.h
@@ -33,6 +33,7 @@
 #ifndef LLVM_SUPPORT_MSGPACKREADER_H
 #define LLVM_SUPPORT_MSGPACKREADER_H
 
+#include "llvm/Support/Error.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdint>
diff --git a/llvm/include/llvm/Bitstream/BitstreamReader.h b/llvm/include/llvm/Bitstream/BitstreamReader.h
index c476f60420fa..0393d1a51866 100644
--- a/llvm/include/llvm/Bitstream/BitstreamReader.h
+++ b/llvm/include/llvm/Bitstream/BitstreamReader.h
@@ -18,6 +18,7 @@
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Bitstream/BitCodes.h"
 #include "llvm/Support/Endian.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
diff --git a/llvm/include/llvm/Support/MemoryBuffer.h b/llvm/include/llvm/Support/MemoryBuffer.h
index b5196cd84cb4..f47a8d2d334b 100644
--- a/llvm/include/llvm/Support/MemoryBuffer.h
+++ b/llvm/include/llvm/Support/MemoryBuffer.h
@@ -19,7 +19,6 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/ErrorOr.h"
-#include "llvm/Support/FileSystem.h"
 #include <cstddef>
 #include <cstdint>
 #include <memory>
@@ -28,6 +27,18 @@ namespace llvm {
 
 class MemoryBufferRef;
 
+namespace sys {
+namespace fs {
+// Duplicated from FileSystem.h to avoid a dependency.
+#if defined(_WIN32)
+// A Win32 HANDLE is a typedef of void*
+using file_t = void *;
+#else
+using file_t = int;
+#endif
+} // namespace fs
+} // namespace sys
+
 /// This interface provides simple read-only access to a block of memory, and
 /// provides simple methods for reading files and standard input into a memory
 /// buffer.  In addition to basic access to the characters in the file, this
@@ -48,9 +59,6 @@ protected:
   void init(const char *BufStart, const char *BufEnd,
             bool RequiresNullTerminator);
 
-  static constexpr sys::fs::mapped_file_region::mapmode Mapmode =
-      sys::fs::mapped_file_region::readonly;
-
 public:
   MemoryBuffer(const MemoryBuffer &) = delete;
   MemoryBuffer &operator=(const MemoryBuffer &) = delete;
@@ -156,9 +164,6 @@ class WritableMemoryBuffer : public MemoryBuffer {
 protected:
   WritableMemoryBuffer() = default;
 
-  static constexpr sys::fs::mapped_file_region::mapmode Mapmode =
-      sys::fs::mapped_file_region::priv;
-
 public:
   using MemoryBuffer::getBuffer;
   using MemoryBuffer::getBufferEnd;
@@ -218,9 +223,6 @@ class WriteThroughMemoryBuffer : public MemoryBuffer {
 protected:
   WriteThroughMemoryBuffer() = default;
 
-  static constexpr sys::fs::mapped_file_region::mapmode Mapmode =
-      sys::fs::mapped_file_region::readwrite;
-
 public:
   using MemoryBuffer::getBuffer;
   using MemoryBuffer::getBufferEnd;
diff --git a/llvm/lib/BinaryFormat/AMDGPUMetadataVerifier.cpp b/llvm/lib/BinaryFormat/AMDGPUMetadataVerifier.cpp
index d927171d556c..e8b9e12ce4c8 100644
--- a/llvm/lib/BinaryFormat/AMDGPUMetadataVerifier.cpp
+++ b/llvm/lib/BinaryFormat/AMDGPUMetadataVerifier.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/BinaryFormat/AMDGPUMetadataVerifier.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/AMDGPUMetadata.h"
 
 namespace llvm {
diff --git a/llvm/lib/ExecutionEngine/Orc/DebugUtils.cpp b/llvm/lib/ExecutionEngine/Orc/DebugUtils.cpp
index c9e87ff737fc..8d4a8107a71c 100644
--- a/llvm/lib/ExecutionEngine/Orc/DebugUtils.cpp
+++ b/llvm/lib/ExecutionEngine/Orc/DebugUtils.cpp
@@ -8,6 +8,7 @@
 
 #include "llvm/ExecutionEngine/Orc/DebugUtils.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
diff --git a/llvm/lib/IR/Attributes.cpp b/llvm/lib/IR/Attributes.cpp
index c41d6c8260b7..6c3464abd36f 100644
--- a/llvm/lib/IR/Attributes.cpp
+++ b/llvm/lib/IR/Attributes.cpp
@@ -23,6 +23,7 @@
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/LLVMContext.h"
diff --git a/llvm/lib/IR/LLVMRemarkStreamer.cpp b/llvm/lib/IR/LLVMRemarkStreamer.cpp
index 326523eaa102..96001ab42c38 100644
--- a/llvm/lib/IR/LLVMRemarkStreamer.cpp
+++ b/llvm/lib/IR/LLVMRemarkStreamer.cpp
@@ -15,6 +15,7 @@
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
+#include "llvm/Support/FileSystem.h"
 
 using namespace llvm;
 
diff --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index e4027ca7bbfd..e467daf42a33 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -162,6 +162,20 @@ MemoryBuffer::getFileSlice(const Twine &FilePath, uint64_t MapSize,
 //===----------------------------------------------------------------------===//
 
 namespace {
+
+template <typename MB>
+constexpr sys::fs::mapped_file_region::mapmode Mapmode =
+    sys::fs::mapped_file_region::readonly;
+template <>
+constexpr sys::fs::mapped_file_region::mapmode Mapmode<MemoryBuffer> =
+    sys::fs::mapped_file_region::readonly;
+template <>
+constexpr sys::fs::mapped_file_region::mapmode Mapmode<WritableMemoryBuffer> =
+    sys::fs::mapped_file_region::priv;
+template <>
+constexpr sys::fs::mapped_file_region::mapmode
+    Mapmode<WriteThroughMemoryBuffer> = sys::fs::mapped_file_region::readwrite;
+
 /// Memory maps a file descriptor using sys::fs::mapped_file_region.
 ///
 /// This handles converting the offset into a legal offset on the platform.
@@ -184,7 +198,7 @@ class MemoryBufferMMapFile : public MB {
 public:
   MemoryBufferMMapFile(bool RequiresNullTerminator, sys::fs::file_t FD, uint64_t Len,
                        uint64_t Offset, std::error_code &EC)
-      : MFR(FD, MB::Mapmode, getLegalMapSize(Len, Offset),
+      : MFR(FD, Mapmode<MB>, getLegalMapSize(Len, Offset),
             getLegalMapOffset(Offset), EC) {
     if (!EC) {
       const char *Start = getStart(Len, Offset);
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
index 29bf9963c995..1788e7490685 100644
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkResult.h
@@ -28,6 +28,8 @@
 #include <vector>
 
 namespace llvm {
+class Error;
+
 namespace exegesis {
 
 struct InstructionBenchmarkKey {
diff --git a/llvm/tools/llvm-exegesis/lib/Clustering.cpp b/llvm/tools/llvm-exegesis/lib/Clustering.cpp
index 33a8e018f515..c9070ef554dd 100644
--- a/llvm/tools/llvm-exegesis/lib/Clustering.cpp
+++ b/llvm/tools/llvm-exegesis/lib/Clustering.cpp
@@ -14,6 +14,7 @@
 #include <algorithm>
 #include <string>
 #include <vector>
+#include <deque>
 
 namespace llvm {
 namespace exegesis {
diff --git a/llvm/tools/llvm-mca/CodeRegion.h b/llvm/tools/llvm-mca/CodeRegion.h
index cabb4a5d4484..d2b05fa80c54 100644
--- a/llvm/tools/llvm-mca/CodeRegion.h
+++ b/llvm/tools/llvm-mca/CodeRegion.h
@@ -35,8 +35,10 @@
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/MC/MCInst.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
 #include <vector>
diff --git a/llvm/unittests/ProfileData/SampleProfTest.cpp b/llvm/unittests/ProfileData/SampleProfTest.cpp
index 4c58d25cedbc..866a9ec21f7a 100644
--- a/llvm/unittests/ProfileData/SampleProfTest.cpp
+++ b/llvm/unittests/ProfileData/SampleProfTest.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ProfileData/SampleProfWriter.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
 #include "gtest/gtest.h"
diff --git a/llvm/unittests/Support/YAMLIOTest.cpp b/llvm/unittests/Support/YAMLIOTest.cpp
index df111e7f6ea8..d86489cf7560 100644
--- a/llvm/unittests/Support/YAMLIOTest.cpp
+++ b/llvm/unittests/Support/YAMLIOTest.cpp
@@ -9,6 +9,7 @@
 #include "llvm/ADT/BitmaskEnum.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Endian.h"
diff --git a/llvm/utils/TableGen/GlobalISel/GIMatchTree.cpp b/llvm/utils/TableGen/GlobalISel/GIMatchTree.cpp
index 4884bdadea91..8eef93393a1e 100644
--- a/llvm/utils/TableGen/GlobalISel/GIMatchTree.cpp
+++ b/llvm/utils/TableGen/GlobalISel/GIMatchTree.cpp
@@ -10,6 +10,7 @@
 
 #include "../CodeGenInstruction.h"
 
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/raw_ostream.h"
diff --git a/llvm/utils/TableGen/OptRSTEmitter.cpp b/llvm/utils/TableGen/OptRSTEmitter.cpp
index 3102f378bc1e..5e44d033109a 100644
--- a/llvm/utils/TableGen/OptRSTEmitter.cpp
+++ b/llvm/utils/TableGen/OptRSTEmitter.cpp
@@ -9,6 +9,7 @@
 #include "OptEmitter.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"