Use TargetABI to assign default-target features in getDefaultSubtargetFeatures

It is currently not possible to provide any reasonable
target-features for compiler generated functions (See: #69780)
Having a target-abi will provide a way to add minimal
requirements for target-features like `+d` for RISC-V.

Author: hiraditya

llvm/include/llvm/LTO/legacy/ThinLTOCodeGenerator.h

@@ -40,7 +40,7 @@ struct TargetMachineBuilder {
   std::optional<Reloc::Model> RelocModel;
   CodeGenOptLevel CGOptLevel = CodeGenOptLevel::Aggressive;
 
-  std::unique_ptr<TargetMachine> create() const;
+  std::unique_ptr<TargetMachine> create(const StringRef TargetABI) const;
 };
 
 /// This class define an interface similar to the LTOCodeGenerator, but adapted

llvm/include/llvm/TargetParser/SubtargetFeature.h

@@ -195,7 +195,8 @@ class SubtargetFeatures {
   void dump() const;
 
   /// Adds the default features for the specified target triple.
-  void getDefaultSubtargetFeatures(const Triple& Triple);
+  void getDefaultSubtargetFeatures(const Triple &Triple,
+                                   const StringRef ABIInfo);
 
   /// Determine if a feature has a flag; '+' or '-'
   static bool hasFlag(StringRef Feature) {

llvm/lib/LTO/LTOBackend.cpp

@@ -201,7 +201,12 @@ static std::unique_ptr<TargetMachine>
 createTargetMachine(const Config &Conf, const Target *TheTarget, Module &M) {
   StringRef TheTriple = M.getTargetTriple();
   SubtargetFeatures Features;
-  Features.getDefaultSubtargetFeatures(Triple(TheTriple));
+  StringRef TargetABI = "";
+  if (auto *TargetABIMD =
+          dyn_cast_or_null<MDString>(M.getModuleFlag("target-abi")))
+    TargetABI = TargetABIMD->getString();
+
+  Features.getDefaultSubtargetFeatures(Triple(TheTriple), TargetABI);
   for (const std::string &A : Conf.MAttrs)
     Features.AddFeature(A);
 

llvm/lib/LTO/LTOCodeGenerator.cpp

@@ -402,7 +402,12 @@ bool LTOCodeGenerator::determineTarget() {
   // Construct LTOModule, hand over ownership of module and target. Use MAttr as
   // the default set of features.
   SubtargetFeatures Features(join(Config.MAttrs, ""));
-  Features.getDefaultSubtargetFeatures(Triple);
+  StringRef TargetABI = "";
+  if (auto *TargetABIMD =
+          dyn_cast_or_null<MDString>(MergedModule->getModuleFlag("target-abi")))
+    TargetABI = TargetABIMD->getString();
+
+  Features.getDefaultSubtargetFeatures(Triple, TargetABI);
   FeatureStr = Features.getString();
   if (Config.CPU.empty())
     Config.CPU = lto::getThinLTODefaultCPU(Triple);

llvm/lib/LTO/LTOModule.cpp

@@ -204,7 +204,10 @@ LTOModule::makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
   if (TripleStr.empty())
     TripleStr = sys::getDefaultTargetTriple();
   llvm::Triple Triple(TripleStr);
-
+  StringRef TargetABI = "";
+  if (auto *TargetABIMD =
+          dyn_cast_or_null<MDString>(M->getModuleFlag("target-abi")))
+    TargetABI = TargetABIMD->getString();
   // find machine architecture for this module
   std::string errMsg;
   const Target *march = TargetRegistry::lookupTarget(TripleStr, errMsg);
@@ -213,7 +216,7 @@ LTOModule::makeLTOModule(MemoryBufferRef Buffer, const TargetOptions &options,
 
   // construct LTOModule, hand over ownership of module and target
   SubtargetFeatures Features;
-  Features.getDefaultSubtargetFeatures(Triple);
+  Features.getDefaultSubtargetFeatures(Triple, TargetABI);
   std::string FeatureStr = Features.getString();
   // Set a default CPU for Darwin triples.
   std::string CPU;

llvm/lib/LTO/ThinLTOCodeGenerator.cpp

@@ -578,7 +578,8 @@ void ThinLTOCodeGenerator::crossReferenceSymbol(StringRef Name) {
 }
 
 // TargetMachine factory
-std::unique_ptr<TargetMachine> TargetMachineBuilder::create() const {
+std::unique_ptr<TargetMachine>
+TargetMachineBuilder::create(const StringRef TargetABI) const {
   std::string ErrMsg;
   const Target *TheTarget =
       TargetRegistry::lookupTarget(TheTriple.str(), ErrMsg);
@@ -588,7 +589,7 @@ std::unique_ptr<TargetMachine> TargetMachineBuilder::create() const {
 
   // Use MAttr as the default set of features.
   SubtargetFeatures Features(MAttr);
-  Features.getDefaultSubtargetFeatures(TheTriple);
+  Features.getDefaultSubtargetFeatures(TheTriple, TargetABI);
   std::string FeatureStr = Features.getString();
 
   std::unique_ptr<TargetMachine> TM(
@@ -914,10 +915,13 @@ void ThinLTOCodeGenerator::internalize(Module &TheModule,
  */
 void ThinLTOCodeGenerator::optimize(Module &TheModule) {
   initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
-
+  StringRef TargetABI = "";
+  if (auto *TargetABIMD =
+          dyn_cast_or_null<MDString>(TheModule.getModuleFlag("target-abi")))
+    TargetABI = TargetABIMD->getString();
   // Optimize now
-  optimizeModule(TheModule, *TMBuilder.create(), OptLevel, Freestanding,
-                 DebugPassManager, nullptr);
+  optimizeModule(TheModule, *TMBuilder.create(TargetABI), OptLevel,
+                 Freestanding, DebugPassManager, nullptr);
 }
 
 /// Write out the generated object file, either from CacheEntryPath or from
@@ -992,8 +996,13 @@ void ThinLTOCodeGenerator::run() {
         auto TheModule = loadModuleFromInput(Mod.get(), Context, false,
                                              /*IsImporting*/ false);
 
+        StringRef TargetABI = "";
+        if (auto *TargetABIMD = dyn_cast_or_null<MDString>(
+                TheModule->getModuleFlag("target-abi")))
+          TargetABI = TargetABIMD->getString();
         // CodeGen
-        auto OutputBuffer = codegenModule(*TheModule, *TMBuilder.create());
+        auto OutputBuffer =
+            codegenModule(*TheModule, *TMBuilder.create(TargetABI));
         if (SavedObjectsDirectoryPath.empty())
           ProducedBinaries[count] = std::move(OutputBuffer);
         else
@@ -1181,10 +1190,14 @@ void ThinLTOCodeGenerator::run() {
         saveTempBitcode(*TheModule, SaveTempsDir, count, ".0.original.bc");
 
         auto &ImportList = ImportLists[ModuleIdentifier];
+        StringRef TargetABI = "";
+        if (auto *TargetABIMD = dyn_cast_or_null<MDString>(
+                TheModule->getModuleFlag("target-abi")))
+          TargetABI = TargetABIMD->getString();
         // Run the main process now, and generates a binary
         auto OutputBuffer = ProcessThinLTOModule(
-            *TheModule, *Index, ModuleMap, *TMBuilder.create(), ImportList,
-            ExportList, GUIDPreservedSymbols,
+            *TheModule, *Index, ModuleMap, *TMBuilder.create(TargetABI),
+            ImportList, ExportList, GUIDPreservedSymbols,
             ModuleToDefinedGVSummaries[ModuleIdentifier], CacheOptions,
             DisableCodeGen, SaveTempsDir, Freestanding, OptLevel, count,
             DebugPassManager);

llvm/lib/TargetParser/SubtargetFeature.cpp

@@ -68,7 +68,8 @@ LLVM_DUMP_METHOD void SubtargetFeatures::dump() const {
 }
 #endif
 
-void SubtargetFeatures::getDefaultSubtargetFeatures(const Triple& Triple) {
+void SubtargetFeatures::getDefaultSubtargetFeatures(const Triple &Triple,
+                                                    const StringRef TargetABI) {
   // FIXME: This is an inelegant way of specifying the features of a
   // subtarget. It would be better if we could encode this information
   // into the IR.
@@ -81,5 +82,7 @@ void SubtargetFeatures::getDefaultSubtargetFeatures(const Triple& Triple) {
       AddFeature("64bit");
       AddFeature("altivec");
     }
+  } else if (Triple.isRISCV64() && TargetABI.contains("lp64d")) {
+    AddFeature("+d");
   }
 }