[lld-macho] Implement -force_load_swift_libs

It causes libraries whose names start with "swift" to be force-loaded.
Note that unlike the more general `-force_load`, this flag only applies
to libraries specified via LC_LINKER_OPTIONS, and not those passed on
the command-line. This is what ld64 does.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D103709

lld/MachO/Config.h

@@ -89,6 +89,7 @@ struct Configuration {
   bool hasReexports = false;
   bool allLoad = false;
   bool forceLoadObjC = false;
+  bool forceLoadSwift = false;
   bool staticLink = false;
   bool implicitDylibs = false;
   bool isPic = false;

lld/MachO/Driver.cpp

@@ -327,10 +327,10 @@ static InputFile *addFile(StringRef path, bool forceLoadArchive,
 }
 
 static void addLibrary(StringRef name, bool isNeeded, bool isWeak,
-                       bool isReexport, bool isExplicit) {
+                       bool isReexport, bool isExplicit, bool forceLoad) {
   if (Optional<StringRef> path = findLibrary(name)) {
     if (auto *dylibFile = dyn_cast_or_null<DylibFile>(
-            addFile(*path, /*forceLoadArchive=*/false, isExplicit))) {
+            addFile(*path, forceLoad, isExplicit))) {
       if (isNeeded)
         dylibFile->forceNeeded = true;
       if (isWeak)
@@ -386,10 +386,14 @@ void macho::parseLCLinkerOption(InputFile *f, unsigned argc, StringRef data) {
 
   for (const Arg *arg : args) {
     switch (arg->getOption().getID()) {
-    case OPT_l:
-      addLibrary(arg->getValue(), /*isNeeded=*/false, /*isWeak=*/false,
-                 /*isReexport=*/false, /*isExplicit=*/false);
+    case OPT_l: {
+      StringRef name = arg->getValue();
+      bool forceLoad =
+          config->forceLoadSwift ? name.startswith("swift") : false;
+      addLibrary(name, /*isNeeded=*/false, /*isWeak=*/false,
+                 /*isReexport=*/false, /*isExplicit=*/false, forceLoad);
       break;
+    }
     case OPT_framework:
       addFramework(arg->getValue(), /*isNeeded=*/false, /*isWeak=*/false,
                    /*isReexport=*/false, /*isExplicit=*/false);
@@ -916,7 +920,7 @@ void createFiles(const InputArgList &args) {
     case OPT_weak_l:
       addLibrary(arg->getValue(), opt.getID() == OPT_needed_l,
                  opt.getID() == OPT_weak_l, opt.getID() == OPT_reexport_l,
-                 /*isExplicit=*/true);
+                 /*isExplicit=*/true, /*forceLoad=*/false);
       break;
     case OPT_framework:
     case OPT_needed_framework:
@@ -1032,6 +1036,7 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   config->runtimePaths = args::getStrings(args, OPT_rpath);
   config->allLoad = args.hasArg(OPT_all_load);
   config->forceLoadObjC = args.hasArg(OPT_ObjC);
+  config->forceLoadSwift = args.hasArg(OPT_force_load_swift_libs);
   config->deadStripDylibs = args.hasArg(OPT_dead_strip_dylibs);
   config->demangle = args.hasArg(OPT_demangle);
   config->implicitDylibs = !args.hasArg(OPT_no_implicit_dylibs);

lld/MachO/Options.td

@@ -193,6 +193,9 @@ def force_load : Separate<["-"], "force_load">,
     MetaVarName<"<path>">,
     HelpText<"Load all members static archive library at <path>">,
     Group<grp_libs>;
+def force_load_swift_libs : Flag<["-"], "force_load_swift_libs">,
+    HelpText<"Apply -force_load to libraries listed in LC_LINKER_OPTIONS whose names start with 'swift'">,
+    Group<grp_libs>;
 
 def grp_content : OptionGroup<"content">, HelpText<"ADDITIONAL CONTENT">;
 
@@ -1193,10 +1196,6 @@ def flto_codegen_only : Flag<["-"], "flto-codegen-only">,
     HelpText<"This option is undocumented in ld64">,
     Flags<[HelpHidden]>,
     Group<grp_undocumented>;
-def force_load_swift_libs : Flag<["-"], "force_load_swift_libs">,
-    HelpText<"This option is undocumented in ld64">,
-    Flags<[HelpHidden]>,
-    Group<grp_undocumented>;
 def force_symbol_not_weak : Flag<["-"], "force_symbol_not_weak">,
     HelpText<"This option is undocumented in ld64">,
     Flags<[HelpHidden]>,

lld/test/MachO/force-load-swift-libs.ll

@@ -0,0 +1,43 @@
+; REQUIRES: x86
+; RUN: rm -rf %t; split-file %s %t
+
+; RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/swift-foo.s -o %t/swift-foo.o
+; RUN: llvm-ar rcs %t/libswiftFoo.a %t/swift-foo.o
+; RUN: llvm-as %t/lc-linker-opt.ll -o %t/lc-linker-opt.o
+; RUN: llvm-as %t/no-lc-linker-opt.ll -o %t/no-lc-linker-opt.o
+
+; RUN: %lld -lSystem -force_load_swift_libs -L%t %t/lc-linker-opt.o -o %t/lc-linker-opt
+; RUN: llvm-objdump --macho --syms %t/lc-linker-opt | FileCheck %s --check-prefix=HAS-SWIFT
+
+; RUN: %lld -lSystem -L%t %t/lc-linker-opt.o -o %t/lc-linker-opt-no-force
+; RUN: llvm-objdump --macho --syms %t/lc-linker-opt-no-force | FileCheck %s --check-prefix=NO-SWIFT
+
+;; Swift libraries passed on the CLI don't get force-loaded!
+; RUN: %lld -lSystem -force_load_swift_libs -lswiftFoo -L%t %t/no-lc-linker-opt.o -o %t/no-lc-linker-opt
+; RUN: llvm-objdump --macho --syms %t/no-lc-linker-opt | FileCheck %s --check-prefix=NO-SWIFT
+
+; HAS-SWIFT: _swift_foo
+; NO-SWIFT-NOT: _swift_foo
+
+;--- lc-linker-opt.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"
+
+!0 = !{!"-lswiftFoo"}
+!llvm.linker.options = !{!0}
+
+define void @main() {
+  ret void
+}
+
+;--- no-lc-linker-opt.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 @main() {
+  ret void
+}
+
+;--- swift-foo.s
+.globl _swift_foo
+_swift_foo: