[lld-macho] Run ObjCContractPass during LTO

Run the ObjCARCContractPass during LTO. The legacy LTO backend (under
LTO/ThinLTOCodeGenerator.cpp) already does this; this diff just adds that
behavior to the new LTO backend. Without that pass, the objc.clang.arc.use
intrinsic will get passed to the instruction selector, which doesn't know how to
handle it.

In order to test both the new and old pass managers, I've also added support for
the `--[no-]lto-legacy-pass-manager` flags.

P.S. Not sure if the ordering of the pass within the pipeline matters...

Reviewed By: fhahn

Differential Revision: https://reviews.llvm.org/D94547

lld/MachO/Config.h

@@ -47,6 +47,7 @@ struct Configuration {
   bool implicitDylibs = false;
   bool isPic = false;
   bool headerPadMaxInstallNames = false;
+  bool ltoNewPassManager = LLVM_ENABLE_NEW_PASS_MANAGER;
   bool printEachFile = false;
   bool printWhyLoad = false;
   bool searchDylibsFirst = false;

lld/MachO/Driver.cpp

@@ -733,6 +733,9 @@ bool macho::link(ArrayRef<const char *> argsArr, bool canExitEarly,
   config->printWhyLoad = args.hasArg(OPT_why_load);
   config->outputType = getOutputType(args);
   config->ltoObjPath = args.getLastArgValue(OPT_object_path_lto);
+  config->ltoNewPassManager =
+      args.hasFlag(OPT_no_lto_legacy_pass_manager, OPT_lto_legacy_pass_manager,
+                   LLVM_ENABLE_NEW_PASS_MANAGER);
   config->runtimePaths = args::getStrings(args, OPT_rpath);
   config->allLoad = args.hasArg(OPT_all_load);
   config->forceLoadObjC = args.hasArg(OPT_ObjC);

lld/MachO/LTO.cpp

@@ -18,6 +18,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/ObjCARC.h"
 
 using namespace lld;
 using namespace lld::macho;
@@ -30,6 +31,10 @@ static lto::Config createConfig() {
   c.CodeModel = getCodeModelFromCMModel();
   c.CPU = getCPUStr();
   c.MAttrs = getMAttrs();
+  c.UseNewPM = config->ltoNewPassManager;
+  c.PreCodeGenPassesHook = [](legacy::PassManager &pm) {
+    pm.add(createObjCARCContractPass());
+  };
   return c;
 }
 

lld/MachO/Options.td

@@ -29,6 +29,12 @@ def reproduce_eq: Joined<["--"], "reproduce=">,
 def version: Flag<["--"], "version">,
     HelpText<"Display the version number and exit">,
     Group<grp_lld>;
+def lto_legacy_pass_manager: Flag<["--"], "lto-legacy-pass-manager">,
+    HelpText<"Use the legacy pass manager in LLVM">,
+    Group<grp_lld>;
+def no_lto_legacy_pass_manager : Flag<["--"], "no-lto-legacy-pass-manager">,
+    HelpText<"Use the new pass manager in LLVM">,
+    Group<grp_lld>;
 
 
 // This is a complete Options.td compiled from Apple's ld(1) manpage

lld/test/MachO/objc-arc-contract.ll

@@ -0,0 +1,30 @@
+; REQUIRES: x86
+
+;; Verify that we run the ObjCARCContractPass during LTO. Without that, the
+;; objc.clang.arc.use intrinsic will get passed to the instruction selector,
+;; which doesn't know how to handle it.
+
+; RUN: llvm-as %s -o %t.o
+; RUN: %lld -dylib -lSystem %t.o -o %t --lto-legacy-pass-manager
+; RUN: llvm-objdump -d %t | FileCheck %s
+; RUN: %lld -dylib -lSystem %t.o -o %t --no-lto-legacy-pass-manager
+; RUN: llvm-objdump -d %t | FileCheck %s
+
+; RUN: opt -module-summary %s -o %t.o
+; RUN: %lld -dylib -lSystem %t.o -o %t --lto-legacy-pass-manager
+; RUN: llvm-objdump -d %t | FileCheck %s
+; RUN: %lld -dylib -lSystem %t.o -o %t --no-lto-legacy-pass-manager
+; RUN: llvm-objdump -d %t | FileCheck %s
+
+; CHECK:      <_foo>:
+; CHECK-NEXT: retq
+
+target triple = "x86_64-apple-darwin"
+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(i8* %a, i8* %b) {
+  call void (...) @llvm.objc.clang.arc.use(i8* %a, i8* %b) nounwind
+  ret void
+}
+
+declare void @llvm.objc.clang.arc.use(...) nounwind

llvm/include/llvm/LTO/Config.h

@@ -19,6 +19,7 @@
 #include "llvm/IR/DiagnosticInfo.h"
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/LegacyPassManager.h"
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Target/TargetOptions.h"
@@ -43,6 +44,8 @@ struct Config {
   TargetOptions Options;
   std::vector<std::string> MAttrs;
   std::vector<std::string> PassPlugins;
+  /// For adding passes that run right before codegen.
+  std::function<void(legacy::PassManager &)> PreCodeGenPassesHook;
   Optional<Reloc::Model> RelocModel = Reloc::PIC_;
   Optional<CodeModel::Model> CodeModel = None;
   CodeGenOpt::Level CGOptLevel = CodeGenOpt::Default;

llvm/lib/LTO/LTOBackend.cpp

@@ -428,6 +428,8 @@ static void codegen(const Config &Conf, TargetMachine *TM,
   legacy::PassManager CodeGenPasses;
   CodeGenPasses.add(
       createImmutableModuleSummaryIndexWrapperPass(&CombinedIndex));
+  if (Conf.PreCodeGenPassesHook)
+    Conf.PreCodeGenPassesHook(CodeGenPasses);
   if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS,
                               DwoOut ? &DwoOut->os() : nullptr,
                               Conf.CGFileType))