[lld-macho] Support parsing of bitcode within archives

[int3]

Summary

Also error out if we find anything other than an object or bitcode file
in the archive.

Note that we were previously inserting the symbols and sections of the
unpacked ObjFile into the containing ArchiveFile. This was actually
unnecessary -- we can just insert the ObjectFile (or BitcodeFile) into
the inputFiles vector. This is the approach taken by LLD-ELF.

[int3]

update

[thakis]

Conceptually lg, but I think it'd be good if we try to keep the various ports looking alike (in this case, probably like COFF/InputFiles.cpp).

lld/MachO/InputFiles.cpp

623

nit: other ports have a isBitcode() in InputFiles.h instead and call that here and assume obj if that returns false

[int3]

lld/MachO/InputFiles.cpp

623

Isn't it better to have more precise error handling though?

lld/MachO/InputFiles.cpp

if (tar && c.getParent()->isThin())
     tar->append(relativeToRoot(CHECK(c.getFullName(), this)), mb.getBuffer());
 
   uint32_t modTime = toTimeT(
       CHECK(c.getLastModified(), toString(this) +
                                      ": could not get the modification time "
                                      "for the member defining symbol " +
                                      toMachOString(sym)));
 
-  inputFiles.push_back(make<ObjFile>(mb, modTime, getName()));
+  InputFile *file;
+  switch (identify_magic(mb.getBuffer())) {
+  case file_magic::macho_object:
+    file = make<ObjFile>(mb, modTime, getName());
+    break;
+  case file_magic::bitcode:
+    file = make<BitcodeFile>(mb);
+    break;
+  default:
+    StringRef bufname =
+        CHECK(c.getName(), toString(this) + ": could not get buffer name");
+    error(toString(this) + ": archive member " + bufname +
+          " has unhandled file type");
+    return;
+  }
+  inputFiles.push_back(file);
 }
 
 BitcodeFile::BitcodeFile(MemoryBufferRef mbref)
     : InputFile(BitcodeKind, mbref) {
   obj = check(lto::InputFile::create(mbref));
 }

lld/test/MachO/invalid/bad-archive-member.s

+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/foo.s -o %t/foo.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+# RUN: %lld -dylib -lSystem %t/foo.o -o %t/foo.dylib
+# RUN: rm -f %t/foo.a
+# RUN: llvm-ar rcs %t/foo.a %t/foo.dylib
+# RUN: not %lld %t/test.o %t/foo.a -o /dev/null 2>&1 | FileCheck %s -DFILE=%t/foo.a
+# CHECK: error: [[FILE]]: archive member foo.dylib has unhandled file type
+
+#--- foo.s
+.globl _foo
+_foo:
+  ret
+
+#--- test.s
+.globl _main
+_main:
+  callq _foo
+  ret

lld/test/MachO/lto-archive.ll

+; REQUIRES: x86
+; RUN: split-file %s %t
+; RUN: llvm-as %t/foo.ll -o %t/foo.o
+; RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+; RUN: rm -f %t/foo.a
+; RUN: llvm-ar rcs %t/foo.a %t/foo.o
+; RUN: %lld -save-temps -lSystem %t/test.o %t/foo.a -o %t/test
+; RUN: llvm-objdump -d --macho --no-show-raw-insn %t/test | FileCheck %s
+
+; CHECK:      _main:
+; CHECK-NEXT: callq _foo
+; CHECK-NEXT: retq
+
+;--- foo.ll
+
+target triple = "x86_64-apple-macosx10.15.0"
+target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @foo() {
+  ret void
+}
+
+;--- test.s
+
+.globl _main
+_main:
+  callq _foo
+  ret