Cleanup include dependencies for LLVMTableGen

Based on the output of include-what-you-use. No other library seems affected by
the new forward declaration.

$ clang++ -E  -Iinclude -I../llvm/include ../llvm/lib/TableGen/*.cpp -std=c++14 -fno-rtti -fno-exceptions | wc -l
before: 795231
after: 750654

Related Discourse thread: https://llvm.discourse.group/t/include-what-you-use-include-cleanup
Differential Revision: https://reviews.llvm.org/D118374

llvm/lib/TableGen/DetailedRecordsBackend.cpp

@@ -13,15 +13,16 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/StringExtras.h"
-#include "llvm/Support/Format.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FormatVariadic.h"
-#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/SMLoc.h"
 #include "llvm/Support/SourceMgr.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
-#include "llvm/TableGen/TableGenBackend.h"
+#include <map>
+#include <memory>
 #include <string>
 #include <utility>
 

llvm/lib/TableGen/JSONBackend.cpp

@@ -11,12 +11,12 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/BitVector.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/Debug.h"
-#include "llvm/TableGen/Error.h"
-#include "llvm/TableGen/Record.h"
-#include "llvm/TableGen/TableGenBackend.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/JSON.h"
+#include "llvm/TableGen/Record.h"
 
 #define DEBUG_TYPE "json-emitter"
 

llvm/lib/TableGen/Main.cpp

@@ -16,7 +16,6 @@
 
 #include "llvm/TableGen/Main.h"
 #include "TGParser.h"
-#include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -24,7 +23,6 @@
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
 #include <algorithm>
-#include <cstdio>
 #include <system_error>
 using namespace llvm;
 

llvm/lib/TableGen/Record.cpp

@@ -10,16 +10,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/TableGen/Record.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/StringSet.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/Casting.h"
@@ -29,11 +28,10 @@
 #include "llvm/Support/SMLoc.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
-#include "llvm/TableGen/Record.h"
 #include <cassert>
 #include <cstdint>
-#include <memory>
 #include <map>
+#include <memory>
 #include <string>
 #include <utility>
 #include <vector>
@@ -2289,8 +2287,8 @@ bool RecordVal::setValue(Init *V, SMLoc NewLoc) {
   return false;
 }
 
-#include "llvm/TableGen/Record.h"
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+#include "llvm/TableGen/Record.h"
 LLVM_DUMP_METHOD void RecordVal::dump() const { errs() << *this; }
 #endif
 

llvm/lib/TableGen/SetTheory.cpp

@@ -11,9 +11,9 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/TableGen/SetTheory.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Format.h"
@@ -21,7 +21,6 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/TableGen/Error.h"
 #include "llvm/TableGen/Record.h"
-#include "llvm/TableGen/SetTheory.h"
 #include <algorithm>
 #include <cstdint>
 #include <string>

llvm/lib/TableGen/TGParser.cpp

@@ -11,8 +11,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "TGParser.h"
+#include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/None.h"
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
@@ -21,7 +21,6 @@
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/SourceMgr.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>

llvm/lib/TableGen/TableGenBackendSkeleton.cpp

@@ -10,22 +10,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/ArrayRef.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/StringExtras.h"
-#include "llvm/Support/Format.h"
-#include "llvm/Support/MemoryBuffer.h"
-#include "llvm/Support/SourceMgr.h"
-#include "llvm/TableGen/Error.h"
-#include "llvm/TableGen/Record.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/TableGen/TableGenBackend.h"
-#include <algorithm>
-#include <set>
-#include <string>
-#include <vector>
 
 #define DEBUG_TYPE "skeleton-emitter"
 
+namespace llvm {
+class RecordKeeper;
+class raw_ostream;
+} // namespace llvm
+
 using namespace llvm;
 
 namespace {