3 files changed, 31 insertions, 13 deletions
diff --git a/clang/lib/CodeGen/BackendUtil.cpp b/clang/lib/CodeGen/BackendUtil.cpp
index 4125d507a1e..b06c68fe742 100644
--- a/clang/lib/CodeGen/BackendUtil.cpp
+++ b/clang/lib/CodeGen/BackendUtil.cpp
@@ -524,7 +524,7 @@ void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
     PMBuilder.Inliner = createFunctionInliningPass(
         CodeGenOpts.OptimizationLevel, CodeGenOpts.OptimizeSize,
         (!CodeGenOpts.SampleProfileFile.empty() &&
-         CodeGenOpts.EmitSummaryIndex));
+         CodeGenOpts.PrepareForThinLTO));
   }
 
   PMBuilder.OptLevel = CodeGenOpts.OptimizationLevel;
@@ -534,7 +534,7 @@ void EmitAssemblyHelper::CreatePasses(legacy::PassManager &MPM,
 
   PMBuilder.DisableUnrollLoops = !CodeGenOpts.UnrollLoops;
   PMBuilder.MergeFunctions = CodeGenOpts.MergeFunctions;
-  PMBuilder.PrepareForThinLTO = CodeGenOpts.EmitSummaryIndex;
+  PMBuilder.PrepareForThinLTO = CodeGenOpts.PrepareForThinLTO;
   PMBuilder.PrepareForLTO = CodeGenOpts.PrepareForLTO;
   PMBuilder.RerollLoops = CodeGenOpts.RerollLoops;
 
@@ -776,7 +776,7 @@ void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
     break;
 
   case Backend_EmitBC:
-    if (CodeGenOpts.EmitSummaryIndex) {
+    if (CodeGenOpts.PrepareForThinLTO) {
       if (!CodeGenOpts.ThinLinkBitcodeFile.empty()) {
         ThinLinkOS = openOutputFile(CodeGenOpts.ThinLinkBitcodeFile);
         if (!ThinLinkOS)
@@ -784,10 +784,20 @@ void EmitAssemblyHelper::EmitAssembly(BackendAction Action,
       }
       PerModulePasses.add(createWriteThinLTOBitcodePass(
           *OS, ThinLinkOS ? &ThinLinkOS->os() : nullptr));
-    }
-    else
+    } else {
+      // Emit a module summary by default for Regular LTO except for ld64
+      // targets
+      bool EmitLTOSummary =
+          (CodeGenOpts.PrepareForLTO &&
+           llvm::Triple(TheModule->getTargetTriple()).getVendor() !=
+               llvm::Triple::Apple);
+      if (EmitLTOSummary && !TheModule->getModuleFlag("ThinLTO"))
+        TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
+
       PerModulePasses.add(
-          createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists));
+          createBitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
+                                  EmitLTOSummary));
+    }
     break;
 
   case Backend_EmitLL:
@@ -935,7 +945,7 @@ void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
   ModulePassManager MPM(CodeGenOpts.DebugPassManager);
 
   if (!CodeGenOpts.DisableLLVMPasses) {
-    bool IsThinLTO = CodeGenOpts.EmitSummaryIndex;
+    bool IsThinLTO = CodeGenOpts.PrepareForThinLTO;
     bool IsLTO = CodeGenOpts.PrepareForLTO;
 
     if (CodeGenOpts.OptimizationLevel == 0) {
@@ -996,7 +1006,7 @@ void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
     break;
 
   case Backend_EmitBC:
-    if (CodeGenOpts.EmitSummaryIndex) {
+    if (CodeGenOpts.PrepareForThinLTO) {
       if (!CodeGenOpts.ThinLinkBitcodeFile.empty()) {
         ThinLinkOS = openOutputFile(CodeGenOpts.ThinLinkBitcodeFile);
         if (!ThinLinkOS)
@@ -1005,9 +1015,17 @@ void EmitAssemblyHelper::EmitAssemblyWithNewPassManager(
       MPM.addPass(ThinLTOBitcodeWriterPass(*OS, ThinLinkOS ? &ThinLinkOS->os()
                                                            : nullptr));
     } else {
+      // Emit a module summary by default for Regular LTO except for ld64
+      // targets
+      bool EmitLTOSummary =
+          (CodeGenOpts.PrepareForLTO &&
+           llvm::Triple(TheModule->getTargetTriple()).getVendor() !=
+               llvm::Triple::Apple);
+      if (EmitLTOSummary && !TheModule->getModuleFlag("ThinLTO"))
+        TheModule->addModuleFlag(Module::Error, "ThinLTO", uint32_t(0));
+
       MPM.addPass(BitcodeWriterPass(*OS, CodeGenOpts.EmitLLVMUseLists,
-                                    CodeGenOpts.EmitSummaryIndex,
-                                    CodeGenOpts.EmitSummaryIndex));
+                                    EmitLTOSummary));
     }
     break;
 
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 3ca6459a6a3..a0d5fd62360 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -578,7 +578,7 @@ void CGDebugInfo::CreateCompileUnit() {
                           CSInfo,
                           getSource(SM, SM.getMainFileID())),
       CGOpts.EmitVersionIdentMetadata ? Producer : "",
-      LO.Optimize || CGOpts.PrepareForLTO || CGOpts.EmitSummaryIndex,
+      LO.Optimize || CGOpts.PrepareForLTO || CGOpts.PrepareForThinLTO,
       CGOpts.DwarfDebugFlags, RuntimeVers,
       CGOpts.EnableSplitDwarf ? "" : CGOpts.SplitDwarfFile, EmissionKind,
       0 /* DWOid */, CGOpts.SplitDwarfInlining, CGOpts.DebugInfoForProfiling,
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 1f9d6b0d7f5..60ed5fdf708 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -749,11 +749,11 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   Opts.ProfileSampleAccurate = Args.hasArg(OPT_fprofile_sample_accurate);
 
   Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
-  Opts.EmitSummaryIndex = false;
+  Opts.PrepareForThinLTO = false;
   if (Arg *A = Args.getLastArg(OPT_flto_EQ)) {
     StringRef S = A->getValue();
     if (S == "thin")
-      Opts.EmitSummaryIndex = true;
+      Opts.PrepareForThinLTO = true;
     else if (S != "full")
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << S;
   }