Avoid including FileSystem.h from MemoryBuffer.h

Lots of headers pass around MemoryBuffer objects, but very few open
them. Let those that do include FileSystem.h.

Saves ~250 includes of Chrono.h & FileSystem.h:

$ diff -u thedeps-before.txt thedeps-after.txt | grep '^[-+] ' | sort | uniq -c | sort -nr
    254 -    ../llvm/include/llvm/Support/FileSystem.h
    253 -    ../llvm/include/llvm/Support/Chrono.h
    237 -    ../llvm/include/llvm/Support/NativeFormatting.h
    237 -    ../llvm/include/llvm/Support/FormatProviders.h
    192 -    ../llvm/include/llvm/ADT/StringSwitch.h
    190 -    ../llvm/include/llvm/Support/FormatVariadicDetails.h
...

This requires duplicating the file_t typedef, which is unfortunate. I
sunk the choice of mapping mode down into the cpp file using variable
template specializations instead of class members in headers.

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>

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"

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;

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 {

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"

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"

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;
 

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);

tools/llvm-exegesis/lib/BenchmarkResult.h

@@ -28,6 +28,8 @@
 #include <vector>
 
 namespace llvm {
+class Error;
+
 namespace exegesis {
 
 struct InstructionBenchmarkKey {

tools/llvm-exegesis/lib/Clustering.cpp

@@ -14,6 +14,7 @@
 #include <algorithm>
 #include <string>
 #include <vector>
+#include <deque>
 
 namespace llvm {
 namespace exegesis {

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>

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"

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"

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"

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"