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

tools/llvm-nm/llvm-nm.cpp

@@ -149,6 +149,9 @@ cl::list<std::string> SegSect("s", cl::Positional, cl::ZeroOrMore,
 cl::opt<bool> FormatMachOasHex("x", cl::desc("Print symbol entry in hex, "
                                              "Mach-O only"));
 
+cl::opt<bool> NoLLVMBitcode("no-llvm-bc",
+                            cl::desc("Disable LLVM bitcode reader"));
+
 bool PrintAddress = true;
 
 bool MultipleFiles = false;
@@ -1009,8 +1012,8 @@ static void dumpSymbolNamesFromFile(std::string &Filename) {
     return;
 
   LLVMContext &Context = getGlobalContext();
-  ErrorOr<std::unique_ptr<Binary>> BinaryOrErr =
-      createBinary(BufferOrErr.get()->getMemBufferRef(), &Context);
+  ErrorOr<std::unique_ptr<Binary>> BinaryOrErr = createBinary(
+      BufferOrErr.get()->getMemBufferRef(), NoLLVMBitcode ? nullptr : &Context);
   if (error(BinaryOrErr.getError(), Filename))
     return;
   Binary &Bin = *BinaryOrErr.get();