[lld][MachO] Add --lto-emit-llvm command line option

lld/MachO/Config.h

@@ -216,6 +216,7 @@ struct Configuration {
   std::vector<SectionAlign> sectionAlignments;
   std::vector<SegmentProtection> segmentProtections;
   bool ltoDebugPassManager = false;
+  bool emitLLVM = false;
   llvm::StringRef codegenDataGeneratePath;
   bool csProfileGenerate = false;
   llvm::StringRef csProfilePath;

lld/MachO/Driver.cpp

@@ -1999,6 +1999,7 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     config->ignoreAutoLinkOptions.insert(arg->getValue());
   config->strictAutoLink = args.hasArg(OPT_strict_auto_link);
   config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
+  config->emitLLVM = args.hasArg(OPT_lto_emit_llvm);
   config->codegenDataGeneratePath =
       args.getLastArgValue(OPT_codegen_data_generate_path);
   config->csProfileGenerate = args.hasArg(OPT_cs_profile_generate);
@@ -2344,10 +2345,10 @@ bool link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
 
     resolveLCLinkerOptions();
 
-    // If --thinlto-index-only is given, we should create only "index
-    // files" and not object files. Index file creation is already done
-    // in compileBitcodeFiles, so we are done if that's the case.
-    if (config->thinLTOIndexOnly)
+    // If either --thinlto-index-only or --lto-emit-llvm is given, we should
+    // not create object files. Index file creation is already done in
+    // compileBitcodeFiles, so we are done if that's the case.
+    if (config->thinLTOIndexOnly || config->emitLLVM)
       return errorCount() == 0;
 
     // LTO may emit a non-hidden (extern) object file symbol even if the

lld/MachO/LTO.cpp

@@ -64,6 +64,16 @@ static lto::Config createConfig() {
   if (config->saveTemps)
     checkError(c.addSaveTemps(config->outputFile.str() + ".",
                               /*UseInputModulePath=*/true));
+
+  if (config->emitLLVM) {
+    llvm::StringRef outputFile = config->outputFile;
+    c.PreCodeGenModuleHook = [outputFile](size_t task, const Module &m) {
+      if (std::unique_ptr<raw_fd_ostream> os = openLTOOutputFile(outputFile))
+        WriteBitcodeToFile(m, *os, false);
+      return false;
+    };
+  }
+
   return c;
 }
 

lld/MachO/Options.td

@@ -188,6 +188,8 @@ def lto_debug_pass_manager: Flag<["--"], "lto-debug-pass-manager">,
     HelpText<"Debug new pass manager">, Group<grp_lld>;
 def lto_newpm_passes: Joined<["--"], "lto-newpm-passes=">,
     HelpText<"Passes to run during LTO">, Group<grp_lld>;
+def lto_emit_llvm: Flag<["--"], "lto-emit-llvm">,
+    HelpText<"Emit LLVM-IR bitcode">, Group<grp_lld>;
 def load_pass_plugins : Separate<["--"], "load-pass-plugin">, Group<grp_lld>;
 def load_pass_plugins_eq : Joined<["--"], "load-pass-plugin=">,
     Alias<!cast<Separate>(load_pass_plugins)>,

lld/test/MachO/lto-emit-llvm.ll

@@ -0,0 +1,18 @@
+; REQUIRES: x86
+;
+; Check that the --lto-emit-llvm option is handled correctly.
+;
+; RUN: opt %s -o %t.o
+; RUN: ld.lld --lto-emit-llvm %t.o -o %t.out.o
+; RUN: llvm-dis < %t.out.o -o - | FileCheck %s
+;
+; CHECK: define hidden void @main()
+
+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"
+
+@llvm.compiler.used = appending global [1 x ptr] [ptr @main], section "llvm.metadata"
+
+define hidden void @main() {
+  ret void
+}