[TableGen][NFCI] Change TableGenMain() to take function_ref.

It was switched from a function pointer to std::function in

TableGen: Make 2nd arg MainFn of TableGenMain(argv0, MainFn) optional.
f675ec6

but there's no mention of any particular reason for that.

Author: kosarev

llvm/include/llvm/TableGen/Main.h

@@ -14,7 +14,6 @@
 #define LLVM_TABLEGEN_MAIN_H
 
 #include "llvm/Support/CommandLine.h"
-#include <functional>
 #include <map>
 
 namespace llvm {
@@ -30,18 +29,17 @@ struct TableGenOutputFiles {
 };
 
 /// Returns true on error, false otherwise.
-using TableGenMainFn = bool(raw_ostream &OS, const RecordKeeper &Records);
+using TableGenMainFn =
+    function_ref<bool(raw_ostream &OS, const RecordKeeper &Records)>;
 
 /// Perform the action using Records, and store output in OutFiles.
 /// Returns true on error, false otherwise.
-using MultiFileTableGenMainFn = bool(TableGenOutputFiles &OutFiles,
-                                     const RecordKeeper &Records);
+using MultiFileTableGenMainFn = function_ref<bool(TableGenOutputFiles &OutFiles,
+                                                  const RecordKeeper &Records)>;
 
-int TableGenMain(const char *argv0,
-                 std::function<TableGenMainFn> MainFn = nullptr);
+int TableGenMain(const char *argv0, TableGenMainFn MainFn = nullptr);
 
-int TableGenMain(const char *argv0,
-                 std::function<MultiFileTableGenMainFn> MainFn = nullptr);
+int TableGenMain(const char *argv0, MultiFileTableGenMainFn MainFn = nullptr);
 
 /// Controls emitting large character arrays as strings or character arrays.
 /// Typically set to false when building with MSVC.

llvm/lib/TableGen/Main.cpp

@@ -127,8 +127,7 @@ static int WriteOutput(const TGParser &Parser, const char *argv0,
   return 0;
 }
 
-int llvm::TableGenMain(const char *argv0,
-                       std::function<MultiFileTableGenMainFn> MainFn) {
+int llvm::TableGenMain(const char *argv0, MultiFileTableGenMainFn MainFn) {
   RecordKeeper Records;
   TGTimer &Timer = Records.getTimer();
 
@@ -210,8 +209,7 @@ int llvm::TableGenMain(const char *argv0,
   return 0;
 }
 
-int llvm::TableGenMain(const char *argv0,
-                       std::function<TableGenMainFn> MainFn) {
+int llvm::TableGenMain(const char *argv0, TableGenMainFn MainFn) {
   return TableGenMain(argv0, [&MainFn](TableGenOutputFiles &OutFiles,
                                        const RecordKeeper &Records) {
     std::string S;

llvm/utils/TableGen/Basic/TableGen.cpp

@@ -73,7 +73,7 @@ int tblgen_main(int argc, char **argv) {
   InitLLVM X(argc, argv);
   cl::ParseCommandLineOptions(argc, argv);
 
-  std::function<MultiFileTableGenMainFn> MainFn = nullptr;
+  MultiFileTableGenMainFn MainFn = nullptr;
   return TableGenMain(argv[0], MainFn);
 }