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80 lines
3.3 KiB
C++
80 lines
3.3 KiB
C++
//===- llvm/System/IncludeFile.h - Ensure Linking Of Library ---*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines the FORCE_DEFINING_FILE_TO_BE_LINKED and DEFINE_FILE_FOR
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// macros.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SYSTEM_INCLUDEFILE_H
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#define LLVM_SYSTEM_INCLUDEFILE_H
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/// This macro is the public interface that IncludeFile.h exports. This gives
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/// us the option to implement the "link the definition" capability in any
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/// manner that we choose. All header files that depend on a specific .cpp
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/// file being linked at run time should use this macro instead of the
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/// IncludeFile class directly.
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///
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/// For example, foo.h would use:<br/>
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/// <tt>FORCE_DEFINING_FILE_TO_BE_LINKED(foo)</tt><br/>
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///
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/// And, foo.cp would use:<br/>
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/// <tt>DEFINING_FILE_FOR(foo)</tt><br/>
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#ifdef __GNUC__
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// If the `used' attribute is available, use it to create a variable
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// with an initializer that will force the linking of the defining file.
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#define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \
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namespace llvm { \
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extern const char name ## LinkVar; \
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__attribute__((used)) static const char *const name ## LinkObj = \
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&name ## LinkVar; \
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}
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#else
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// Otherwise use a constructor call.
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#define FORCE_DEFINING_FILE_TO_BE_LINKED(name) \
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namespace llvm { \
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extern const char name ## LinkVar; \
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static const IncludeFile name ## LinkObj ( &name ## LinkVar ); \
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}
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#endif
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/// This macro is the counterpart to FORCE_DEFINING_FILE_TO_BE_LINKED. It should
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/// be used in a .cpp file to define the name referenced in a header file that
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/// will cause linkage of the .cpp file. It should only be used at extern level.
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#define DEFINING_FILE_FOR(name) \
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namespace llvm { const char name ## LinkVar = 0; }
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namespace llvm {
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/// This class is used in the implementation of FORCE_DEFINING_FILE_TO_BE_LINKED
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/// macro to make sure that the implementation of a header file is included
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/// into a tool that uses the header. This is solely
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/// to overcome problems linking .a files and not getting the implementation
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/// of compilation units we need. This is commonly an issue with the various
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/// Passes but also occurs elsewhere in LLVM. We like to use .a files because
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/// they link faster and provide the smallest executables. However, sometimes
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/// those executables are too small, if the program doesn't reference something
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/// that might be needed, especially by a loaded share object. This little class
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/// helps to resolve that problem. The basic strategy is to use this class in
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/// a header file and pass the address of a variable to the constructor. If the
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/// variable is defined in the header file's corresponding .cpp file then all
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/// tools/libraries that \#include the header file will require the .cpp as
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/// well.
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/// For example:<br/>
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/// <tt>extern int LinkMyCodeStub;</tt><br/>
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/// <tt>static IncludeFile LinkMyModule(&LinkMyCodeStub);</tt><br/>
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/// @brief Class to ensure linking of corresponding object file.
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struct IncludeFile {
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explicit IncludeFile(const void *);
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};
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}
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#endif
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