[LTO] Enable module summary emission by default for regular LTO

Summary:
With D33921, we gained the ability to have module summaries in regular
LTO modules without triggering ThinLTO compilation. Module summaries in
regular LTO allow garbage collection (dead stripping) before LTO
compilation and thus open up additional optimization opportunities.

This patch enables summary emission in regular LTO for all targets
except ld64-based ones (which use the legacy LTO API).

Reviewers: pcc, tejohnson, mehdi_amini

Subscribers: inglorion, eraman, cfe-commits

Differential Revision: https://reviews.llvm.org/D34156

llvm-svn: 335284

2 files changed, 29 insertions, 11 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,