For PR780:

This change was suggested by Chris so that we can select an alternate
(or even no-op) implementation of the link assurance. I'm committing this
for your review, Chris. If the names and definitions are okay, I'll adjust
all the .h and .cpp files in a later patch.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28712 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 31 insertions, 8 deletions

diff --git a/include/llvm/System/IncludeFile.h b/include/llvm/System/IncludeFile.h
index 2e4f12d..8e96f75 100644
--- a/include/llvm/System/IncludeFile.h
+++ b/include/llvm/System/IncludeFile.h
@@ -7,12 +7,39 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file defines the IncludeFile class.
+// This file defines the FORCE_DEFINING_FILE_TO_BE_LINKED and DEFINE_FILE_FOR
+// macros.
 //
 //===----------------------------------------------------------------------===//
 
-/// This class is used as a facility to make sure that the implementation of a 
-/// header file is included into a tool that uses the header.  This is solely 
+#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) \
+  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) char name
+
+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
@@ -27,14 +54,10 @@
 /// <tt>extern int LinkMyCodeStub;</tt><br/>
 /// <tt>static IncludeFile LinkMyModule(&LinkMyCodeStub);</tt><br/>
 /// @brief Class to ensure linking of corresponding object file.
-
-#ifndef LLVM_SUPPORT_INCLUDEFILE_H
-#define LLVM_SUPPORT_INCLUDEFILE_H
-
-namespace llvm {
 struct IncludeFile {
   IncludeFile(void *);
 };
+
 }
 
 #endif