[llvm-exegesis] Move native target initialization code to a separate file.

[courbet]

Summary

This helps building internal tools on top of the library.

[courbet]

add missing inline

llvm/tools/llvm-exegesis/lib/TargetSelect.h

+//===-- TargetSelect.h ------------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+///
+/// Utilities to handle the creation of the native exegesis target.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_TOOLS_LLVM_EXEGESIS_TARGET_SELECT_H
+#define LLVM_TOOLS_LLVM_EXEGESIS_TARGET_SELECT_H
+
+namespace llvm {
+namespace exegesis {
+
+#ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
+void LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
+#endif
+
+// Initializes the native exegesis target, or returns false if there is no
+// native target (either because llvm-exegesis does not support the target or
+// because it's not linked in).
+bool InitializeNativeExegesisTarget() {
+#ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
+  LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
+  return true;
+#else
+  return false;
+#endif
+}
+
+} // namespace exegesis
+} // namespace llvm
+
+#endif // LLVM_TOOLS_LLVM_EXEGESIS_TARGET_SELECT_H

llvm/tools/llvm-exegesis/llvm-exegesis.cpp

 
 #include "lib/Analysis.h"
 #include "lib/BenchmarkResult.h"
 #include "lib/BenchmarkRunner.h"
 #include "lib/Clustering.h"
 #include "lib/LlvmState.h"
 #include "lib/PerfHelper.h"
 #include "lib/Target.h"
+#include "lib/TargetSelect.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/MC/MCInstBuilder.h"
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCParser/MCAsmParser.h"
 #include "llvm/MC/MCParser/MCTargetAsmParser.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/MC/MCStreamer.h"

 static cl::opt<bool>
     DumpObjectToDisk("dump-object-to-disk",
                      cl::desc("dumps the generated benchmark object to disk "
                               "and prints a message to access it"),
                      cl::cat(BenchmarkOptions), cl::init(true));
 
 static ExitOnError ExitOnErr;
 
-#ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
-void LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
-#endif
-
 // Checks that only one of OpcodeNames, OpcodeIndex or SnippetsFile is provided,
 // and returns the opcode indices or {} if snippets should be read from
 // `SnippetsFile`.
 static std::vector<unsigned>
 getOpcodesOrDie(const llvm::MCInstrInfo &MCInstrInfo) {
   const size_t NumSetFlags = (OpcodeNames.empty() ? 0 : 1) +
                              (OpcodeIndex == 0 ? 0 : 1) +
                              (SnippetsFile.empty() ? 0 : 1);

 #endif
 
   if (exegesis::pfm::pfmInitialize())
     llvm::report_fatal_error("cannot initialize libpfm");
 
   llvm::InitializeNativeTarget();
   llvm::InitializeNativeTargetAsmPrinter();
   llvm::InitializeNativeTargetAsmParser();
-#ifdef LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET
-  LLVM_EXEGESIS_INITIALIZE_NATIVE_TARGET();
-#endif
+  InitializeNativeExegesisTarget();
 
   const LLVMState State(CpuName);
   const auto Opcodes = getOpcodesOrDie(State.getInstrInfo());
 
   std::vector<BenchmarkCode> Configurations;
   if (!Opcodes.empty()) {
     for (const unsigned Opcode : Opcodes) {
       // Ignore instructions without a sched class if