[lld-macho] Avoid force-loading the same archive twice

We need to dedup archive loads (similar to what we do for dylib
loads).

I noticed this issue after building some Swift stuff that used
`-force_load_swift_libs`, as it caused some Swift archives to be loaded
many times.

Reviewed By: #lld-macho, thakis, MaskRay

Differential Revision: https://reviews.llvm.org/D104353

lld/MachO/Driver.cpp

@@ -235,6 +235,8 @@ static std::vector<ArchiveMember> getArchiveMembers(MemoryBufferRef mb) {
   return v;
 }
 
+static DenseMap<StringRef, ArchiveFile *> loadedArchives;
+
 static InputFile *addFile(StringRef path, bool forceLoadArchive,
                           bool isExplicit = true,
                           bool isBundleLoader = false) {
@@ -247,6 +249,13 @@ static InputFile *addFile(StringRef path, bool forceLoadArchive,
   file_magic magic = identify_magic(mbref.getBuffer());
   switch (magic) {
   case file_magic::archive: {
+    // Avoid loading archives twice. If the archives are being force-loaded,
+    // loading them twice would create duplicate symbol errors. In the
+    // non-force-loading case, this is just a minor performance optimization.
+    ArchiveFile *&cachedFile = loadedArchives[path];
+    if (cachedFile)
+      return cachedFile;
+
     std::unique_ptr<object::Archive> file = CHECK(
         object::Archive::create(mbref), path + ": failed to parse archive");
 
@@ -286,7 +295,7 @@ static InputFile *addFile(StringRef path, bool forceLoadArchive,
       }
     }
 
-    newFile = make<ArchiveFile>(std::move(file));
+    newFile = cachedFile = make<ArchiveFile>(std::move(file));
     break;
   }
   case file_magic::macho_object:

lld/test/MachO/archive.s

@@ -32,6 +32,11 @@
 # ALL-LOAD: T _main
 # ALL-LOAD: T _unused
 
+## Multiple archives defining the same symbols aren't an issue, due to lazy
+## loading
+# RUN: cp %t/test.a %t/test2.a
+# RUN: %lld %t/test.a %t/test2.a %t/main.o -o /dev/null
+
 #--- 2.s
 .globl _boo
 _boo:

lld/test/MachO/force-load.s

@@ -1,23 +1,48 @@
 # REQUIRES: x86
 # RUN: rm -rf %t; split-file %s %t
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/archive-foo.s -o %t/archive-foo.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/archive-baz.s -o %t/archive-baz.o
 # RUN: llvm-ar rcs %t/foo.a %t/archive-foo.o
+# RUN: llvm-ar rcs %t/baz.a %t/archive-baz.o
 # 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 -force_load %t/foo.a %t/foo.o %t/test.o -o %t/test-force-load-first
+# RUN: %lld -lSystem -force_load %t/foo.a %t/foo.o %t/test.o -o %t/test-force-load-first
 # FORCE-LOAD-FIRST:  __TEXT,archive _foo
 # RUN: llvm-objdump --syms %t/test-force-load-first | FileCheck %s --check-prefix=FORCE-LOAD-FIRST
 
-# RUN: %lld %t/foo.o -force_load %t/foo.a %t/test.o -o %t/test-force-load-second
+# RUN: %lld %t/foo.o -lSystem -force_load %t/foo.a %t/test.o -o %t/test-force-load-second
 # RUN: llvm-objdump --syms %t/test-force-load-second | FileCheck %s --check-prefix=FORCE-LOAD-SECOND
 # FORCE-LOAD-SECOND: __TEXT,obj _foo
 
+## Force-loading the same path twice is fine
+# RUN: %lld -lSystem %t/foo.o -force_load %t/foo.a -force_load %t/foo.a %t/test.o -o /dev/null
+
+## Note that we do not call realpath() before dedup'ing the force-load
+## arguments, so this is an error.
+# RUN: cd %t; not %lld -lSystem %t/foo.o -force_load %t/foo.a -force_load foo.a \
+# RUN:   %t/test.o -o /dev/null 2>&1
+
+# DUP: error: duplicate symbol: _bar
+
+## Force-loading two different paths w/o conflicting symbols is fine
+# RUN: %lld -lSystem -force_load %t/foo.a -force_load %t/baz.a %t/test.o -o %t/test-two-force-loads
+# RUN: llvm-objdump --syms %t/test-two-force-loads | FileCheck %s --check-prefix=TWICE
+# TWICE-DAG: __TEXT,archive _foo
+# TWICE-DAG: __TEXT,archive _bar
+# TWICE-DAG: __TEXT,archive _baz
+
 #--- archive-foo.s
 .section __TEXT,archive
-.globl _foo
+.globl _foo, _bar
 .weak_definition _foo
 _foo:
+_bar:
+
+#--- archive-baz.s
+.section __TEXT,archive
+.globl _baz
+_baz:
 
 #--- foo.s
 .section __TEXT,obj