[lld-macho] Support parsing of bitcode within archives

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.

Reviewed By: thakis

Differential Revision: https://reviews.llvm.org/D92539

lld/MachO/InputFiles.cpp

@@ -631,15 +631,26 @@ void ArchiveFile::fetch(const object::Archive::Symbol &sym) {
   // to it later.
   const object::Archive::Symbol sym_copy = sym;
 
-  auto file = 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);
 
   // ld64 doesn't demangle sym here even with -demangle. Match that, so
   // intentionally no call to toMachOString() here.
   printArchiveMemberLoad(sym_copy.getName(), file);
-
-  symbols.insert(symbols.end(), file->symbols.begin(), file->symbols.end());
-  subsections.insert(subsections.end(), file->subsections.begin(),
-                     file->subsections.end());
 }
 
 BitcodeFile::BitcodeFile(MemoryBufferRef mbref)

lld/test/MachO/bitcode-nodatalayout.ll

@@ -0,0 +1,13 @@
+; REQUIRES: x86
+; RUN: llvm-as %s -o %t.o
+; RUN: not %lld %t.o -o /dev/null 2>&1 | FileCheck %s
+
+; CHECK: error: input module has no datalayout
+
+; This bitcode file has no datalayout.
+; Check that we error out producing a reasonable diagnostic.
+target triple = "x86_64-apple-macosx10.15.0"
+
+define void @_start() {
+  ret void
+}

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

@@ -0,0 +1,20 @@
+# 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

@@ -0,0 +1,28 @@
+; 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