LTO: introduce object file-based on-disk module format.

This format is simply a regular object file with the bitcode stored in a
section named ".llvmbc", plus any number of other (non-allocated) sections.

One immediate use case for this is to accommodate compilation processes
which expect the object file to contain metadata in non-allocated sections,
such as the ".go_export" section used by some Go compilers [1], although I
imagine that in the future we could consider compiling parts of the module
(such as large non-inlinable functions) directly into the object file to
improve LTO efficiency.

[1] http://golang.org/doc/install/gccgo#Imports

Differential Revision: http://reviews.llvm.org/D4371

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218078 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Object/IRObjectFile.h

@@ -22,6 +22,8 @@ class Module;
 class GlobalValue;
 
 namespace object {
+class ObjectFile;
+
 class IRObjectFile : public SymbolicFile {
   std::unique_ptr<Module> M;
   std::unique_ptr<Mangler> Mang;
@@ -49,6 +51,16 @@ public:
     return v->isIR();
   }
 
+  /// \brief Finds and returns bitcode embedded in the given object file, or an
+  /// error code if not found.
+  static ErrorOr<MemoryBufferRef> findBitcodeInObject(const ObjectFile &Obj);
+
+  /// \brief Finds and returns bitcode in the given memory buffer (which may
+  /// be either a bitcode file or a native object file with embedded bitcode),
+  /// or an error code if not found.
+  static ErrorOr<MemoryBufferRef>
+  findBitcodeInMemBuffer(MemoryBufferRef Object);
+
   static ErrorOr<std::unique_ptr<IRObjectFile>>
   createIRObjectFile(MemoryBufferRef Object, LLVMContext &Context);
 };