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.

Author: rnk

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>
 

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"
 

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"

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"

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"

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>

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"

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 @@ class MemoryBuffer {
   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;

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 {

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"