Reland "[flang] add option to generate runtime type info as external (llvm#145901)"

Merging upstream PR: llvm#146071.

Reland llvm#145901 with a fix for shared library builds (see second commit).

Lowering cannot directly use cl::opts from lib/Optimizer/Passes/CommandLineOpts.cpp without linking against `flangPasses`.

Instead of adding the linking dependency, I think it is cleaner to use a proper lowering options and let the driver read the cl::opt (I would rather keep the option a cl::opt before doing a bit more testing and making it a proper driver option).

Author: ergawy

flang/include/flang/Evaluate/tools.h

@@ -1585,6 +1585,7 @@ bool IsExtensibleType(const DerivedTypeSpec *);
 bool IsSequenceOrBindCType(const DerivedTypeSpec *);
 bool IsBuiltinDerivedType(const DerivedTypeSpec *derived, const char *name);
 bool IsBuiltinCPtr(const Symbol &);
+bool IsFromBuiltinModule(const Symbol &);
 bool IsEventType(const DerivedTypeSpec *);
 bool IsLockType(const DerivedTypeSpec *);
 bool IsNotifyType(const DerivedTypeSpec *);

flang/include/flang/Lower/LoweringOptions.def

@@ -66,5 +66,9 @@ ENUM_LOWERINGOPT(RepackArraysWhole, unsigned, 1, 0)
 /// If true, CUDA Fortran runtime check is inserted.
 ENUM_LOWERINGOPT(CUDARuntimeCheck, unsigned, 1, 0)
 
+/// If true, do not generate definition for runtime type info global objects of
+/// derived types defined in other compilation units.
+ENUM_LOWERINGOPT(SkipExternalRttiDefinition, unsigned, 1, 0)
+
 #undef LOWERINGOPT
 #undef ENUM_LOWERINGOPT

flang/include/flang/Optimizer/CodeGen/CodeGen.h

@@ -39,6 +39,9 @@ struct FIRToLLVMPassOptions {
   // that such programs would crash at runtime if the derived type descriptors
   // are required by the runtime, so this is only an option to help debugging.
   bool ignoreMissingTypeDescriptors = false;
+  // Similar to ignoreMissingTypeDescriptors, but generate external declaration
+  // for the missing type descriptor globals instead.
+  bool skipExternalRttiDefinition = false;
 
   // Generate TBAA information for FIR types and memory accessing operations.
   bool applyTBAA = false;

flang/include/flang/Optimizer/Passes/CommandLineOpts.h

@@ -32,6 +32,19 @@ extern llvm::cl::opt<std::size_t> arrayStackAllocationThreshold;
 /// generated by the frontend.
 extern llvm::cl::opt<bool> ignoreMissingTypeDescriptors;
 
+/// Shared option in tools to only generate rtti static object definitions for
+/// derived types defined in the current compilation unit. Derived type
+/// descriptor object for types defined in other objects will only be declared
+/// as external. This also changes the linkage of rtti objects defined in the
+/// current compilation unit from linkonce_odr to external so that unused rtti
+/// objects are retained and can be accessed from other compilation units. This
+/// is an experimental option to explore compilation speed improvements and is
+/// an ABI breaking change because of the linkage change.
+/// It will also require linking against module file objects of modules defining
+/// only types (even for trivial types without type bound procedures, which
+/// differs from most compilers).
+extern llvm::cl::opt<bool> skipExternalRttiDefinition;
+
 /// Default optimization level used to create Flang pass pipeline is O0.
 extern llvm::OptimizationLevel defaultOptLevel;
 

flang/include/flang/Optimizer/Support/Utils.h

@@ -35,32 +35,6 @@ inline std::int64_t toInt(mlir::arith::ConstantOp cop) {
       .getSExtValue();
 }
 
-// Reconstruct binding tables for dynamic dispatch.
-using BindingTable = llvm::DenseMap<llvm::StringRef, unsigned>;
-using BindingTables = llvm::DenseMap<llvm::StringRef, BindingTable>;
-
-inline void buildBindingTables(BindingTables &bindingTables,
-                               mlir::ModuleOp mod) {
-
-  // The binding tables are defined in FIR after lowering inside fir.type_info
-  // operations. Go through each binding tables and store the procedure name and
-  // binding index for later use by the fir.dispatch conversion pattern.
-  for (auto typeInfo : mod.getOps<fir::TypeInfoOp>()) {
-    unsigned bindingIdx = 0;
-    BindingTable bindings;
-    if (typeInfo.getDispatchTable().empty()) {
-      bindingTables[typeInfo.getSymName()] = bindings;
-      continue;
-    }
-    for (auto dtEntry :
-         typeInfo.getDispatchTable().front().getOps<fir::DTEntryOp>()) {
-      bindings[dtEntry.getMethod()] = bindingIdx;
-      ++bindingIdx;
-    }
-    bindingTables[typeInfo.getSymName()] = bindings;
-  }
-}
-
 // Translate front-end KINDs for use in the IR and code gen.
 inline std::vector<fir::KindTy>
 fromDefaultKinds(const Fortran::common::IntrinsicTypeDefaultKinds &defKinds) {

flang/include/flang/Semantics/runtime-type-info.h

@@ -38,6 +38,10 @@ RuntimeDerivedTypeTables BuildRuntimeDerivedTypeTables(SemanticsContext &);
 /// to describe other derived types at runtime in flang descriptor.
 constexpr char typeInfoBuiltinModule[]{"__fortran_type_info"};
 
+/// Name of the builtin derived type in __fortran_type_inf that is used for
+/// derived type descriptors.
+constexpr char typeDescriptorTypeName[]{"derivedtype"};
+
 /// Name of the bindings descriptor component in the DerivedType type of the
 /// __Fortran_type_info module
 constexpr char bindingDescCompName[]{"binding"};

flang/lib/Evaluate/tools.cpp

@@ -2334,6 +2334,11 @@ bool IsBuiltinCPtr(const Symbol &symbol) {
   return false;
 }
 
+bool IsFromBuiltinModule(const Symbol &symbol) {
+  const Scope &scope{symbol.GetUltimate().owner()};
+  return IsSameModule(&scope, scope.context().GetBuiltinsScope());
+}
+
 bool IsIsoCType(const DerivedTypeSpec *derived) {
   return IsBuiltinDerivedType(derived, "c_ptr") ||
       IsBuiltinDerivedType(derived, "c_funptr");

flang/lib/Frontend/CompilerInvocation.cpp

@@ -14,6 +14,7 @@
 #include "flang/Frontend/CodeGenOptions.h"
 #include "flang/Frontend/PreprocessorOptions.h"
 #include "flang/Frontend/TargetOptions.h"
+#include "flang/Optimizer/Passes/CommandLineOpts.h"
 #include "flang/Semantics/semantics.h"
 #include "flang/Support/Fortran-features.h"
 #include "flang/Support/OpenMP-features.h"
@@ -1807,6 +1808,7 @@ void CompilerInvocation::setLoweringOptions() {
   // Lower TRANSPOSE as a runtime call under -O0.
   loweringOpts.setOptimizeTranspose(codegenOpts.OptimizationLevel > 0);
   loweringOpts.setUnderscoring(codegenOpts.Underscoring);
+  loweringOpts.setSkipExternalRttiDefinition(skipExternalRttiDefinition);
 
   const Fortran::common::LangOptions &langOptions = getLangOpts();
   loweringOpts.setIntegerWrapAround(langOptions.getSignedOverflowBehavior() ==

flang/lib/Lower/Bridge.cpp

@@ -263,6 +263,7 @@ class TypeInfoConverter {
   }
 
   void createTypeInfo(Fortran::lower::AbstractConverter &converter) {
+    createTypeInfoForTypeDescriptorBuiltinType(converter);
     while (!registeredTypeInfoA.empty()) {
       currentTypeInfoStack = &registeredTypeInfoB;
       for (const TypeInfo &info : registeredTypeInfoA)
@@ -278,10 +279,22 @@ class TypeInfoConverter {
 private:
   void createTypeInfoOpAndGlobal(Fortran::lower::AbstractConverter &converter,
                                  const TypeInfo &info) {
-    Fortran::lower::createRuntimeTypeInfoGlobal(converter, info.symbol.get());
+    if (!converter.getLoweringOptions().getSkipExternalRttiDefinition())
+      Fortran::lower::createRuntimeTypeInfoGlobal(converter, info.symbol.get());
     createTypeInfoOp(converter, info);
   }
 
+  void createTypeInfoForTypeDescriptorBuiltinType(
+      Fortran::lower::AbstractConverter &converter) {
+    if (registeredTypeInfoA.empty())
+      return;
+    auto builtinTypeInfoType = llvm::cast<fir::RecordType>(
+        converter.genType(registeredTypeInfoA[0].symbol.get()));
+    converter.getFirOpBuilder().createTypeInfoOp(
+        registeredTypeInfoA[0].loc, builtinTypeInfoType,
+        /*parentType=*/fir::RecordType{});
+  }
+
   void createTypeInfoOp(Fortran::lower::AbstractConverter &converter,
                         const TypeInfo &info) {
     fir::RecordType parentType{};

flang/lib/Lower/ConvertVariable.cpp

@@ -647,13 +647,19 @@ fir::GlobalOp Fortran::lower::defineGlobal(
 
 /// Return linkage attribute for \p var.
 static mlir::StringAttr
-getLinkageAttribute(fir::FirOpBuilder &builder,
+getLinkageAttribute(Fortran::lower::AbstractConverter &converter,
                     const Fortran::lower::pft::Variable &var) {
+  fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   // Runtime type info for a same derived type is identical in each compilation
   // unit. It desired to avoid having to link against module that only define a
   // type. Therefore the runtime type info is generated everywhere it is needed
-  // with `linkonce_odr` LLVM linkage.
-  if (var.isRuntimeTypeInfoData())
+  // with `linkonce_odr` LLVM linkage (unless the skipExternalRttiDefinition
+  // option is set, in which case one will need to link against objects of
+  // modules defining types). Builtin objects rtti is always generated because
+  // the builtin module is currently not compiled or part of the runtime.
+  if (var.isRuntimeTypeInfoData() &&
+      (!converter.getLoweringOptions().getSkipExternalRttiDefinition() ||
+       Fortran::semantics::IsFromBuiltinModule(var.getSymbol())))
     return builder.createLinkOnceODRLinkage();
   if (var.isModuleOrSubmoduleVariable())
     return {}; // external linkage
@@ -673,7 +679,7 @@ static void instantiateGlobal(Fortran::lower::AbstractConverter &converter,
   fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   std::string globalName = converter.mangleName(sym);
   mlir::Location loc = genLocation(converter, sym);
-  mlir::StringAttr linkage = getLinkageAttribute(builder, var);
+  mlir::StringAttr linkage = getLinkageAttribute(converter, var);
   fir::GlobalOp global;
   if (var.isModuleOrSubmoduleVariable()) {
     // A non-intrinsic module global is defined when lowering the module.
@@ -1265,7 +1271,7 @@ instantiateAggregateStore(Fortran::lower::AbstractConverter &converter,
   if (var.isGlobal()) {
     fir::GlobalOp global;
     auto &aggregate = var.getAggregateStore();
-    mlir::StringAttr linkage = getLinkageAttribute(builder, var);
+    mlir::StringAttr linkage = getLinkageAttribute(converter, var);
     if (var.isModuleOrSubmoduleVariable()) {
       // A module global was or will be defined when lowering the module. Emit
       // only a declaration if the global does not exist at that point.
@@ -2470,8 +2476,7 @@ void Fortran::lower::defineModuleVariable(
     AbstractConverter &converter, const Fortran::lower::pft::Variable &var) {
   // Use empty linkage for module variables, which makes them available
   // for use in another unit.
-  mlir::StringAttr linkage =
-      getLinkageAttribute(converter.getFirOpBuilder(), var);
+  mlir::StringAttr linkage = getLinkageAttribute(converter, var);
   if (!var.isGlobal())
     fir::emitFatalError(converter.getCurrentLocation(),
                         "attempting to lower module variable as local");
@@ -2606,10 +2611,9 @@ void Fortran::lower::createIntrinsicModuleGlobal(
 void Fortran::lower::createRuntimeTypeInfoGlobal(
     Fortran::lower::AbstractConverter &converter,
     const Fortran::semantics::Symbol &typeInfoSym) {
-  fir::FirOpBuilder &builder = converter.getFirOpBuilder();
   std::string globalName = converter.mangleName(typeInfoSym);
   auto var = Fortran::lower::pft::Variable(typeInfoSym, /*global=*/true);
-  mlir::StringAttr linkage = getLinkageAttribute(builder, var);
+  mlir::StringAttr linkage = getLinkageAttribute(converter, var);
   defineGlobal(converter, var, globalName, linkage);
 }