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

lib/Object/Error.cpp

@@ -41,6 +41,8 @@ std::string _object_error_category::message(int EV) const {
     return "Invalid data was encountered while parsing the file";
   case object_error::unexpected_eof:
     return "The end of the file was unexpectedly encountered";
+  case object_error::bitcode_section_not_found:
+    return "Bitcode section not found in object file";
   }
   llvm_unreachable("An enumerator of object_error does not have a message "
                    "defined.");

lib/Object/IRObjectFile.cpp

@@ -25,6 +25,7 @@
 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCTargetAsmParser.h"
 #include "llvm/MC/MCParser/MCAsmParser.h"
+#include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/TargetRegistry.h"
@@ -264,11 +265,50 @@ basic_symbol_iterator IRObjectFile::symbol_end_impl() const {
   return basic_symbol_iterator(BasicSymbolRef(Ret, this));
 }
 
+ErrorOr<MemoryBufferRef> IRObjectFile::findBitcodeInObject(const ObjectFile &Obj) {
+  for (const SectionRef &Sec : Obj.sections()) {
+    StringRef SecName;
+    if (std::error_code EC = Sec.getName(SecName))
+      return EC;
+    if (SecName == ".llvmbc") {
+      StringRef SecContents;
+      if (std::error_code EC = Sec.getContents(SecContents))
+        return EC;
+      return MemoryBufferRef(SecContents, Obj.getFileName());
+    }
+  }
+
+  return object_error::bitcode_section_not_found;
+}
+
+ErrorOr<MemoryBufferRef> IRObjectFile::findBitcodeInMemBuffer(MemoryBufferRef Object) {
+  sys::fs::file_magic Type = sys::fs::identify_magic(Object.getBuffer());
+  switch (Type) {
+  case sys::fs::file_magic::bitcode:
+    return Object;
+  case sys::fs::file_magic::elf_relocatable:
+  case sys::fs::file_magic::macho_object:
+  case sys::fs::file_magic::coff_object: {
+    ErrorOr<std::unique_ptr<ObjectFile>> ObjFile =
+        ObjectFile::createObjectFile(Object, Type);
+    if (!ObjFile)
+      return ObjFile.getError();
+    return findBitcodeInObject(*ObjFile->get());
+  }
+  default:
+    return object_error::invalid_file_type;
+  }
+}
+
 ErrorOr<std::unique_ptr<IRObjectFile>>
 llvm::object::IRObjectFile::createIRObjectFile(MemoryBufferRef Object,
                                                LLVMContext &Context) {
+  ErrorOr<MemoryBufferRef> BCOrErr = findBitcodeInMemBuffer(Object);
+  if (!BCOrErr)
+    return BCOrErr.getError();
 
-  std::unique_ptr<MemoryBuffer> Buff(MemoryBuffer::getMemBuffer(Object, false));
+  std::unique_ptr<MemoryBuffer> Buff(
+      MemoryBuffer::getMemBuffer(BCOrErr.get(), false));
 
   ErrorOr<Module *> MOrErr = getLazyBitcodeModule(std::move(Buff), Context);
   if (std::error_code EC = MOrErr.getError())

lib/Object/SymbolicFile.cpp

@@ -40,11 +40,9 @@ ErrorOr<std::unique_ptr<SymbolicFile>> SymbolicFile::createSymbolicFile(
   case sys::fs::file_magic::macho_universal_binary:
   case sys::fs::file_magic::windows_resource:
     return object_error::invalid_file_type;
-  case sys::fs::file_magic::elf_relocatable:
   case sys::fs::file_magic::elf_executable:
   case sys::fs::file_magic::elf_shared_object:
   case sys::fs::file_magic::elf_core:
-  case sys::fs::file_magic::macho_object:
   case sys::fs::file_magic::macho_executable:
   case sys::fs::file_magic::macho_fixed_virtual_memory_shared_lib:
   case sys::fs::file_magic::macho_core:
@@ -54,10 +52,26 @@ ErrorOr<std::unique_ptr<SymbolicFile>> SymbolicFile::createSymbolicFile(
   case sys::fs::file_magic::macho_bundle:
   case sys::fs::file_magic::macho_dynamically_linked_shared_lib_stub:
   case sys::fs::file_magic::macho_dsym_companion:
-  case sys::fs::file_magic::coff_object:
   case sys::fs::file_magic::coff_import_library:
   case sys::fs::file_magic::pecoff_executable:
     return ObjectFile::createObjectFile(Object, Type);
+  case sys::fs::file_magic::elf_relocatable:
+  case sys::fs::file_magic::macho_object:
+  case sys::fs::file_magic::coff_object: {
+    ErrorOr<std::unique_ptr<ObjectFile>> Obj =
+        ObjectFile::createObjectFile(Object, Type);
+    if (!Obj || !Context)
+      return std::move(Obj);
+
+    ErrorOr<MemoryBufferRef> BCData =
+        IRObjectFile::findBitcodeInObject(*Obj->get());
+    if (!BCData)
+      return std::move(Obj);
+
+    return IRObjectFile::createIRObjectFile(
+        MemoryBufferRef(BCData->getBuffer(), Object.getBufferIdentifier()),
+        *Context);
+  }
   }
   llvm_unreachable("Unexpected Binary File Type");
 }