add the ability to call InitTargetOptionsFromCodeGenFlags from multiple objects

[inglorion]

Summary

llvm/CodeGen/CommandFlags.h a utility function InitTargetOptionsFromCodeGenFlags which is used to set target options from flags based on the command line. The command line flags are stored in globals defined in the same file, and including the file in multiple places causes the globals to be defined multiple times, leading to linker errors. This change adds a single place in lld where these globals are defined and exports only the utility function. This makes it possible to call InitTargetOptionsFromCodeGenFlags from multiple places in lld, which a follow-up change will do.

[ruiu]

Are you actually going to use InitTargetOptionsFromCodeGenFlag function defined in this patch in future?

[inglorion]

D29059 uses this.

[davide]

The code LGTM. If Rui/Peter think it's OK to ship this for COFF, I'm fine with this going in.

[ruiu]

Sorry for the belated response. I think this should live under lld/lib/Core instead of lld/lib/Config because this is not a configuration or something.

[inglorion]

Good point, @ruiu. Moved this to Core.

[ruiu]

LGTM

lib/Core/TargetOptionsCommandFlags.cpp

28

I'd remove the outer namespace and s/InitTarget/lld::InitTarget/.

[davide]

LGTM assuming you plan to use this in the COFF lld backend.

[inglorion]

removed outer namespace and put it on the function instead

ELF/LTO.cpp

 //===- LTO.cpp ------------------------------------------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "LTO.h"
 #include "Config.h"
 #include "Error.h"
 #include "InputFiles.h"
 #include "Symbols.h"
+#include "lld/Core/TargetOptionsCommandFlags.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
-#include "llvm/CodeGen/CommandFlags.h"
 #include "llvm/IR/DiagnosticPrinter.h"
 #include "llvm/LTO/Config.h"
 #include "llvm/LTO/LTO.h"
 #include "llvm/Object/SymbolicFile.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/ELF.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"

include/lld/Core/TargetOptionsCommandFlags.h

+//===-- TargetOptionsCommandFlags.h ----------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// Helper to create TargetOptions from command line flags.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Target/TargetOptions.h"
+
+namespace lld {
+llvm::TargetOptions InitTargetOptionsFromCodeGenFlags();
+}

lib/Core/CMakeLists.txt

 add_lld_library(lldCore
   DefinedAtom.cpp
   Error.cpp
   File.cpp
   LinkingContext.cpp
   Reader.cpp
   Reproduce.cpp
   Resolver.cpp
   SymbolTable.cpp
+  TargetOptionsCommandFlags.cpp
   Writer.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLD_INCLUDE_DIR}/lld/Core
 
   LINK_COMPONENTS
     Support
   )

lib/Core/TargetOptionsCommandFlags.cpp

+//===-- TargetOptionsCommandFlags.cpp ---------------------------*- C++ -*-===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file exists as a place for global variables defined in LLVM's
+// CodeGen/CommandFlags.h. By putting the resulting object file in
+// an archive and linking with it, the definitions will automatically be
+// included when needed and skipped when already present.
+//
+//===----------------------------------------------------------------------===//
+
+#include "lld/Core/TargetOptionsCommandFlags.h"
+
+#include "llvm/CodeGen/CommandFlags.h"
+#include "llvm/Target/TargetOptions.h"
+
+namespace lld {
+
+// Define an externally visible version of
+// InitTargetOptionsFromCodeGenFlags, so that its functionality can be
+// used without having to include llvm/CodeGen/CommandFlags.h, which
+// would lead to multiple definitions of the command line flags.
+llvm::TargetOptions InitTargetOptionsFromCodeGenFlags() {
+  return ::InitTargetOptionsFromCodeGenFlags();
+}
+}