llvm-6502/include/llvm/System/IncludeFile.h
Reid Spencer 4f1bd9e996 For PR780:
1. Fix the macros in IncludeFile.h to put everything in the llvm namespace
2. Replace the previous explicit mechanism in all the .h and .cpp files
   with the macros in IncludeFile.h
This gets us a consistent mechanism throughout LLVM for ensuring linkage.
Next step is to make sure its used in enough places.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28715 91177308-0d34-0410-b5e6-96231b3b80d8
2006-06-07 22:00:26 +00:00

66 lines
2.8 KiB
C++

//===- llvm/Support/IncludeFile.h - Ensure Linking Of Library ---*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file was developed by Reid Spencer and is distributed under the
// University of Illinois Open Source License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file defines the FORCE_DEFINING_FILE_TO_BE_LINKED and DEFINE_FILE_FOR
// macros.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_SUPPORT_INCLUDEFILE_H
#define LLVM_SUPPORT_INCLUDEFILE_H
/// This macro is the public interface that IncludeFile.h exports. This gives
/// us the option to implement the "link the definition" capability in any
/// manner that we choose. All header files that depend on a specific .cpp
/// file being linked at run time should use this macro instead of the
/// IncludeFile class directly.
///
/// For example, foo.h would use:<br/>
/// <tt>FORCE_DEFINING_FILE_TO_BE_LINKED(foo)</tt><br/>
///
/// And, foo.cp would use:<br/>
/// <tt>DEFINING_FILE_FOR(foo)</tt><br/>
#define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \
namespace llvm { \
extern char name ## LinkVar; \
static IncludeFile name ## LinkObj ( &name ## LinkVar ); \
}
/// This macro is the counterpart to FORCE_DEFINING_FILE_TO_BE_LINKED. It should
/// be used in a .cpp file to define the name referenced in a header file that
/// will cause linkage of the .cpp file. It should only be used at extern level.
#define DEFINING_FILE_FOR(name) namespace llvm { char name ## LinkVar; }
namespace llvm {
/// This class is used in the implementation of FORCE_DEFINING_FILE_TO_BE_LINKED
/// macro to make sure that the implementation of a header file is included
/// into a tool that uses the header. This is solely
/// to overcome problems linking .a files and not getting the implementation
/// of compilation units we need. This is commonly an issue with the various
/// Passes but also occurs elsewhere in LLVM. We like to use .a files because
/// they link faster and provide the smallest executables. However, sometimes
/// those executables are too small, if the program doesn't reference something
/// that might be needed, especially by a loaded share object. This little class
/// helps to resolve that problem. The basic strategy is to use this class in
/// a header file and pass the address of a variable to the constructor. If the
/// variable is defined in the header file's corresponding .cpp file then all
/// tools/libraries that #include the header file will require the .cpp as well.
/// For example:<br/>
/// <tt>extern int LinkMyCodeStub;</tt><br/>
/// <tt>static IncludeFile LinkMyModule(&LinkMyCodeStub);</tt><br/>
/// @brief Class to ensure linking of corresponding object file.
struct IncludeFile {
IncludeFile(void *);
};
}
#endif