[AIX] llvm-link support big archive.

[DiggerLin]

Summary

Use object::Archive::create so that the returned archive object has a dynamic type of either Archive or BigArchive.

[MaskRay]

It's unclear why the old code doesn't support big archives while the new code supports big archives. Can you explain it in the summary and the comment?

[DiggerLin]

In D124940#3491557, @MaskRay wrote:

It's unclear why the old code doesn't support big archives while the new code supports big archives. Can you explain it in the summary and the comment?

I have explained it in the sumary @MaskRay

[MaskRay]

[AIX] llvm-link support big archive.

You can say [AIX] Make llvm-link support big archives

[MaskRay]

The summary can probably be made clearer with something like

Use object::Archive::create so that the returned archive object has a dynamic type of either Archive or BigArchive.

[jhenderson]

LGTM, with @MaskRay's summary change suggestion.

Would it make sense to make the object::Archive constructor private, to stop code from directly using it instead of using the create function? Could be a follow-up patch, if you want.

llvm/test/tools/llvm-link/archivell.ll

-# XFAIL: system-aix
 # RUN: llvm-ar cr %t.fg.a %S/Inputs/f.ll %S/Inputs/g.ll
 # RUN: not llvm-link %S/Inputs/h.ll %t.fg.a -o %t.linked.bc 2>&1 | FileCheck %s
 
 # RUN: rm -f %t.fg.a
 # RUN: rm -f %t.linked.bc
 
 # CHECK: error: member of archive is not a bitcode file

llvm/tools/llvm-link/llvm-link.cpp

 static std::unique_ptr<Module> loadArFile(const char *Argv0,
                                           std::unique_ptr<MemoryBuffer> Buffer,
                                           LLVMContext &Context) {
   std::unique_ptr<Module> Result(new Module("ArchiveModule", Context));
   StringRef ArchiveName = Buffer->getBufferIdentifier();
   if (Verbose)
     errs() << "Reading library archive file '" << ArchiveName
            << "' to memory\n";
-  Error Err = Error::success();
-  object::Archive Archive(*Buffer, Err);
-  ExitOnErr(std::move(Err));
+  Expected<std::unique_ptr<object::Archive>> ArchiveOrError =
+      object::Archive::create(Buffer->getMemBufferRef());
+  if (!ArchiveOrError)
+    ExitOnErr(ArchiveOrError.takeError());
+
+  std::unique_ptr<object::Archive> Archive = std::move(ArchiveOrError.get());
+
   Linker L(*Result);
-  for (const object::Archive::Child &C : Archive.children(Err)) {
+  Error Err = Error::success();
+  for (const object::Archive::Child &C : Archive->children(Err)) {
     Expected<StringRef> Ename = C.getName();
     if (Error E = Ename.takeError()) {
       errs() << Argv0 << ": ";
       WithColor::error() << " failed to read name of archive member"
                          << ArchiveName << "'\n";
       return nullptr;
     }
     std::string ChildName = Ename.get().str();