[LTO] Support LLVM LTO for IRGen and frontend

This commit adds -lto flag for frontend to enable LTO at LLVM level.
When -lto=llvm given, compiler emits LLVM bitcode file instead of object
file and adds index summary for LTO.
In addition for ELF format, emit llvm.dependent-libraries section to
embed auto linking information

Author: kateinoigakukun

include/swift/AST/IRGenOptions.h

@@ -65,6 +65,12 @@ enum class IRGenDebugInfoFormat : unsigned {
   CodeView
 };
 
+enum class IRGenLLVMLTOKind : unsigned {
+  None,
+  Thin,
+  Full,
+};
+
 enum class IRGenEmbedMode : unsigned {
   None,
   EmbedMarker,
@@ -220,6 +226,8 @@ class IRGenOptions {
   /// Whether we should embed the bitcode file.
   IRGenEmbedMode EmbedMode : 2;
 
+  IRGenLLVMLTOKind LLVMLTOKind : 2;
+
   /// Add names to LLVM values.
   unsigned HasValueNamesSetting : 1;
   unsigned ValueNames : 1;
@@ -320,21 +328,21 @@ class IRGenOptions {
         DebugInfoLevel(IRGenDebugInfoLevel::None),
         DebugInfoFormat(IRGenDebugInfoFormat::None),
         DisableClangModuleSkeletonCUs(false), UseJIT(false),
-        DisableLLVMOptzns(false),
-        DisableSwiftSpecificLLVMOptzns(false), DisableLLVMSLPVectorizer(false),
-        Playground(false), EmitStackPromotionChecks(false),
-        FunctionSections(false), PrintInlineTree(false), EmbedMode(IRGenEmbedMode::None),
-        HasValueNamesSetting(false), ValueNames(false),
-        EnableReflectionMetadata(true), EnableReflectionNames(true),
-        EnableAnonymousContextMangledNames(false), ForcePublicLinkage(false),
-        LazyInitializeClassMetadata(false),
+        DisableLLVMOptzns(false), DisableSwiftSpecificLLVMOptzns(false),
+        DisableLLVMSLPVectorizer(false), Playground(false),
+        EmitStackPromotionChecks(false), FunctionSections(false),
+        PrintInlineTree(false), EmbedMode(IRGenEmbedMode::None),
+        LLVMLTOKind(IRGenLLVMLTOKind::None), HasValueNamesSetting(false),
+        ValueNames(false), EnableReflectionMetadata(true),
+        EnableReflectionNames(true), EnableAnonymousContextMangledNames(false),
+        ForcePublicLinkage(false), LazyInitializeClassMetadata(false),
         LazyInitializeProtocolConformances(false), DisableLegacyTypeInfo(false),
         PrespecializeGenericMetadata(false), UseIncrementalLLVMCodeGen(true),
-        UseSwiftCall(false), UseTypeLayoutValueHandling(true), GenerateProfile(false),
-        EnableDynamicReplacementChaining(false),
+        UseSwiftCall(false), UseTypeLayoutValueHandling(true),
+        GenerateProfile(false), EnableDynamicReplacementChaining(false),
         DisableRoundTripDebugTypes(false), DisableDebuggerShadowCopies(false),
-        DisableConcreteTypeMetadataMangledNameAccessors(false),
-        CmdArgs(), SanitizeCoverage(llvm::SanitizerCoverageOptions()),
+        DisableConcreteTypeMetadataMangledNameAccessors(false), CmdArgs(),
+        SanitizeCoverage(llvm::SanitizerCoverageOptions()),
         TypeInfoFilter(TypeInfoDumpFilter::All) {}
 
   /// Appends to \p os an arbitrary string representing all options which

include/swift/Option/Options.td

@@ -523,6 +523,10 @@ def disable_bridging_pch : Flag<["-"], "disable-bridging-pch">,
   Flags<[HelpHidden]>,
   HelpText<"Disable automatic generation of bridging PCH files">;
 
+def lto : Joined<["-"], "lto=">,
+  Flags<[FrontendOption, NoInteractiveOption]>,
+  HelpText<"Specify the LTO type to either 'llvm-thin' or 'llvm-full'">;
+
 // Experimental feature options
 
 // Note: this flag will be removed when JVP/differential generation in the

lib/Frontend/CompilerInvocation.cpp

@@ -1474,6 +1474,18 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
     }
   }
 
+  if (const Arg *A = Args.getLastArg(options::OPT_lto)) {
+    auto LLVMLTOKind =
+        llvm::StringSwitch<Optional<IRGenLLVMLTOKind>>(A->getValue())
+            .Case("llvm-thin", IRGenLLVMLTOKind::Thin)
+            .Case("llvm-full", IRGenLLVMLTOKind::Full)
+            .Default(llvm::None);
+    if (LLVMLTOKind)
+      Opts.LLVMLTOKind = LLVMLTOKind.getValue();
+    else
+      Diags.diagnose(SourceLoc(), diag::error_invalid_arg_value,
+                     A->getAsString(Args), A->getValue());
+  }
 
   if (const Arg *A = Args.getLastArg(options::OPT_sanitize_coverage_EQ)) {
     Opts.SanitizeCoverage =

lib/IRGen/IRGen.cpp

@@ -548,9 +548,14 @@ bool swift::performLLVM(const IRGenOptions &Opts,
   case IRGenOutputKind::LLVMAssembly:
     EmitPasses.add(createPrintModulePass(*RawOS));
     break;
-  case IRGenOutputKind::LLVMBitcode:
-    EmitPasses.add(createBitcodeWriterPass(*RawOS));
+  case IRGenOutputKind::LLVMBitcode: {
+    if (Opts.LLVMLTOKind == IRGenLLVMLTOKind::Thin) {
+      EmitPasses.add(createWriteThinLTOBitcodePass(*RawOS));
+    } else {
+      EmitPasses.add(createBitcodeWriterPass(*RawOS));
+    }
     break;
+  }
   case IRGenOutputKind::NativeAssembly:
   case IRGenOutputKind::ObjectFile: {
     CodeGenFileType FileType;

lib/IRGen/IRGenModule.cpp

@@ -1108,8 +1108,6 @@ llvm::SmallString<32> getTargetDependentLibraryOption(const llvm::Triple &T,
 }
 
 void IRGenModule::addLinkLibrary(const LinkLibrary &linkLib) {
-  llvm::LLVMContext &ctx = Module.getContext();
-
   // The debugger gets the autolink information directly from
   // the LinkLibraries of the module, so there's no reason to
   // emit it into the IR of debugger expressions.
@@ -1118,10 +1116,7 @@ void IRGenModule::addLinkLibrary(const LinkLibrary &linkLib) {
 
   switch (linkLib.getKind()) {
   case LibraryKind::Library: {
-    llvm::SmallString<32> opt =
-        getTargetDependentLibraryOption(Triple, linkLib.getName());
-    AutolinkEntries.push_back(
-        llvm::MDNode::get(ctx, llvm::MDString::get(ctx, opt)));
+    AutolinkEntries.emplace_back(linkLib);
     break;
   }
   case LibraryKind::Framework: {
@@ -1130,12 +1125,7 @@ void IRGenModule::addLinkLibrary(const LinkLibrary &linkLib) {
     if (std::find(frameworks.begin(), frameworks.end(), linkLib.getName())
           != frameworks.end())
       return;
-
-    llvm::Metadata *args[] = {
-      llvm::MDString::get(ctx, "-framework"),
-      llvm::MDString::get(ctx, linkLib.getName())
-    };
-    AutolinkEntries.push_back(llvm::MDNode::get(ctx, args));
+    AutolinkEntries.emplace_back(linkLib);
     break;
   }
   }
@@ -1205,63 +1195,197 @@ static bool isFirstObjectFileInModule(IRGenModule &IGM) {
   return containingModule->getFiles().front() == file;
 }
 
-void IRGenModule::emitAutolinkInfo() {
-  // Collect the linker options already in the module (from ClangCodeGen).
+static bool
+doesTargetAutolinkUsingAutolinkExtract(const SwiftTargetInfo &TargetInfo,
+                                       const llvm::Triple &Triple) {
+  if (TargetInfo.OutputObjectFormat == llvm::Triple::ELF && !Triple.isPS4())
+    return true;
+
+  if (TargetInfo.OutputObjectFormat == llvm::Triple::Wasm)
+    return true;
+
+  if (Triple.isOSCygMing())
+    return true;
+
+  return false;
+}
+
+namespace {
+
+struct AutolinkKind {
+  enum ValueTy {
+    LLVMLinkerOptions,
+    LLVMDependentLibraries,
+    SwiftAutoLinkExtract,
+  };
+
+  ValueTy Value;
+
+  AutolinkKind(ValueTy value) : Value(value) {}
+  AutolinkKind(const AutolinkKind &kind) : Value(kind.Value) {}
+
+  StringRef getSectionNameMetadata();
+
+  template <typename Vector, typename Set>
+  void collectEntriesFromLibraries(llvm::SetVector<llvm::MDNode *, Vector, Set> &Entries,
+                                   ArrayRef<LinkLibrary> AutolinkEntries,
+                                   IRGenModule &IGM);
+
+  template <typename Vector, typename Set>
+  void writeEntries(llvm::SetVector<llvm::MDNode *, Vector, Set> Entries,
+                    llvm::NamedMDNode *Metadata, IRGenModule &IGM);
+
+  static AutolinkKind create(const SwiftTargetInfo &TargetInfo,
+                             llvm::Triple Triple, IRGenLLVMLTOKind LLVMLTOKind);
+};
+
+} // anonymous namespace
+
+StringRef AutolinkKind::getSectionNameMetadata() {
   // FIXME: This constant should be vended by LLVM somewhere.
-  auto *Metadata = Module.getOrInsertNamedMetadata("llvm.linker.options");
-  for (llvm::MDNode *LinkOption : Metadata->operands())
-    AutolinkEntries.push_back(LinkOption);
-
-  // Remove duplicates.
-  llvm::SmallPtrSet<llvm::MDNode *, 4> knownAutolinkEntries;
-  AutolinkEntries.erase(std::remove_if(AutolinkEntries.begin(),
-                                       AutolinkEntries.end(),
-                                       [&](llvm::MDNode *entry) -> bool {
-                                         return !knownAutolinkEntries.insert(
-                                                   entry).second;
-                                       }),
-                        AutolinkEntries.end());
-
-  const bool AutolinkExtractRequired =
-      (TargetInfo.OutputObjectFormat == llvm::Triple::ELF && !Triple.isPS4()) ||
-      TargetInfo.OutputObjectFormat == llvm::Triple::Wasm ||
-      Triple.isOSCygMing();
-
-  if (!AutolinkExtractRequired) {
+  switch (Value) {
+  case AutolinkKind::LLVMDependentLibraries:
+    return "llvm.dependent-libraries";
+  case AutolinkKind::LLVMLinkerOptions:
+  case AutolinkKind::SwiftAutoLinkExtract:
+    return "llvm.linker.options";
+  }
+
+  llvm_unreachable("Unhandled AutolinkKind in switch.");
+}
+
+template <typename Vector, typename Set>
+void AutolinkKind::collectEntriesFromLibraries(
+    llvm::SetVector<llvm::MDNode *, Vector, Set> &Entries,
+    ArrayRef<LinkLibrary> AutolinkEntries, IRGenModule &IGM) {
+  llvm::LLVMContext &ctx = IGM.getLLVMContext();
+
+  switch (Value) {
+  case AutolinkKind::LLVMLinkerOptions:
+  case AutolinkKind::SwiftAutoLinkExtract: {
+    // On platforms that support autolinking, continue to use the metadata.
+    for (LinkLibrary linkLib : AutolinkEntries) {
+      switch (linkLib.getKind()) {
+      case LibraryKind::Library: {
+        llvm::SmallString<32> opt =
+            getTargetDependentLibraryOption(IGM.Triple, linkLib.getName());
+        Entries.insert(llvm::MDNode::get(ctx, llvm::MDString::get(ctx, opt)));
+        continue;
+      }
+      case LibraryKind::Framework: {
+        llvm::Metadata *args[] = {llvm::MDString::get(ctx, "-framework"),
+                                  llvm::MDString::get(ctx, linkLib.getName())};
+        Entries.insert(llvm::MDNode::get(ctx, args));
+        continue;
+      }
+      }
+      llvm_unreachable("Unhandled LibraryKind in switch.");
+    }
+    return;
+  }
+  case AutolinkKind::LLVMDependentLibraries: {
+    for (LinkLibrary linkLib : AutolinkEntries) {
+      switch (linkLib.getKind()) {
+      case LibraryKind::Library: {
+        Entries.insert(llvm::MDNode::get(
+            ctx, llvm::MDString::get(ctx, linkLib.getName())));
+        continue;
+      }
+      case LibraryKind::Framework: {
+        llvm_unreachable(
+            "llvm.dependent-libraries doesn't support framework dependency");
+      }
+      }
+      llvm_unreachable("Unhandled LibraryKind in switch.");
+    }
+    return;
+  }
+  }
+  llvm_unreachable("Unhandled AutolinkKind in switch.");
+}
+
+template <typename Vector, typename Set>
+void AutolinkKind::writeEntries(llvm::SetVector<llvm::MDNode *, Vector, Set> Entries,
+                                llvm::NamedMDNode *Metadata, IRGenModule &IGM) {
+  switch (Value) {
+  case AutolinkKind::LLVMLinkerOptions:
+  case AutolinkKind::LLVMDependentLibraries: {
     // On platforms that support autolinking, continue to use the metadata.
     Metadata->clearOperands();
-    for (auto *Entry : AutolinkEntries)
+    for (auto *Entry : Entries)
       Metadata->addOperand(Entry);
-  } else {
+    return;
+  }
+  case AutolinkKind::SwiftAutoLinkExtract: {
     // Merge the entries into null-separated string.
     llvm::SmallString<64> EntriesString;
-    for (auto &EntryNode : AutolinkEntries) {
-      const llvm::MDNode *MD = cast<llvm::MDNode>(EntryNode);
+    for (auto EntryNode : Entries) {
+      const auto *MD = cast<llvm::MDNode>(EntryNode);
       for (auto &Entry : MD->operands()) {
         const llvm::MDString *MS = cast<llvm::MDString>(Entry);
         EntriesString += MS->getString();
         EntriesString += '\0';
       }
     }
     auto EntriesConstant = llvm::ConstantDataArray::getString(
-        getLLVMContext(), EntriesString, /*AddNull=*/false);
+        IGM.getLLVMContext(), EntriesString, /*AddNull=*/false);
     // Mark the swift1_autolink_entries section with the SHF_EXCLUDE attribute
     // to get the linker to drop it in the final linked binary.
-    // LLVM doesn't provide an interface to specify section attributs in the IR
-    // so we pass the attribute with inline assembly.
-    if (TargetInfo.OutputObjectFormat == llvm::Triple::ELF)
-      Module.appendModuleInlineAsm(".section .swift1_autolink_entries,"
-                                   "\"0x80000000\"");
+    // LLVM doesn't provide an interface to specify section attributs in the
+    // IR so we pass the attribute with inline assembly.
+    if (IGM.TargetInfo.OutputObjectFormat == llvm::Triple::ELF)
+      IGM.Module.appendModuleInlineAsm(".section .swift1_autolink_entries,"
+                                       "\"0x80000000\"");
     auto var =
-        new llvm::GlobalVariable(*getModule(), EntriesConstant->getType(), true,
-                                 llvm::GlobalValue::PrivateLinkage,
+        new llvm::GlobalVariable(*IGM.getModule(), EntriesConstant->getType(),
+                                 true, llvm::GlobalValue::PrivateLinkage,
                                  EntriesConstant, "_swift1_autolink_entries");
     var->setSection(".swift1_autolink_entries");
-    var->setAlignment(llvm::MaybeAlign(getPointerAlignment().getValue()));
+    var->setAlignment(llvm::MaybeAlign(IGM.getPointerAlignment().getValue()));
 
-    disableAddressSanitizer(*this, var);
-    addUsedGlobal(var);
+    disableAddressSanitizer(IGM, var);
+    IGM.addUsedGlobal(var);
+    return;
   }
+  }
+  llvm_unreachable("Unhandled AutolinkKind in switch.");
+}
+
+AutolinkKind AutolinkKind::create(const SwiftTargetInfo &TargetInfo,
+                                  llvm::Triple Triple,
+                                  IRGenLLVMLTOKind LLVMLTOKind) {
+  // When performing LTO, we always use lld that supports auto linking
+  // mechanism with ELF. So embed dependent libraries names in
+  // "llvm.dependent-libraries" instead of "llvm.linker.options".
+  if (TargetInfo.OutputObjectFormat == llvm::Triple::ELF &&
+      LLVMLTOKind != IRGenLLVMLTOKind::None) {
+    return AutolinkKind::LLVMDependentLibraries;
+  }
+
+  if (doesTargetAutolinkUsingAutolinkExtract(TargetInfo, Triple)) {
+    return AutolinkKind::SwiftAutoLinkExtract;
+  }
+
+  return AutolinkKind::LLVMLinkerOptions;
+}
+
+void IRGenModule::emitAutolinkInfo() {
+  auto Autolink =
+      AutolinkKind::create(TargetInfo, Triple, IRGen.Opts.LLVMLTOKind);
+
+  StringRef AutolinkSectionName = Autolink.getSectionNameMetadata();
+
+  auto *Metadata = Module.getOrInsertNamedMetadata(AutolinkSectionName);
+  llvm::SmallSetVector<llvm::MDNode *, 4> Entries;
+
+  // Collect the linker options already in the module (from ClangCodeGen).
+  for (auto Entry : Metadata->operands()) {
+    Entries.insert(Entry);
+  }
+
+  Autolink.collectEntriesFromLibraries(Entries, AutolinkEntries, *this);
+
+  Autolink.writeEntries(Entries, Metadata, *this);
 
   if (!IRGen.Opts.ForceLoadSymbolName.empty() &&
       (Triple.supportsCOMDAT() || isFirstObjectFileInModule(*this))) {

lib/IRGen/IRGenModule.h

@@ -22,6 +22,7 @@
 #include "SwiftTargetInfo.h"
 #include "TypeLayout.h"
 #include "swift/AST/Decl.h"
+#include "swift/AST/LinkLibrary.h"
 #include "swift/AST/Module.h"
 #include "swift/AST/ReferenceCounting.h"
 #include "swift/AST/SourceFile.h"
@@ -1076,7 +1077,7 @@ class IRGenModule {
   SmallVector<llvm::WeakTrackingVH, 4> LLVMCompilerUsed;
 
   /// Metadata nodes for autolinking info.
-  SmallVector<llvm::MDNode *, 32> AutolinkEntries;
+  SmallVector<LinkLibrary, 32> AutolinkEntries;
 
   /// List of Objective-C classes, bitcast to i8*.
   SmallVector<llvm::WeakTrackingVH, 4> ObjCClasses;

test/IRGen/Inputs/Frameworks/LinkFramework.framework/Headers/LinkFramework.h

@@ -0,0 +1,2 @@
+
+extern int IComeFromLinkFramework;

test/IRGen/Inputs/Frameworks/LinkFramework.framework/LinkFramework

@@ -0,0 +1,4 @@
+framework module LinkFramework {
+  header "LinkFramework.h"
+  export *
+}

test/IRGen/Inputs/Frameworks/LinkFramework.framework/module.map

@@ -0,0 +1 @@
+#pragma comment(lib, "transitive-module")