[flang][driver] Add support for the `-emit-llvm` option

[awarzynski]

Summary

This patch adds support for the -emit-llvm option in the frontend
driver (i.e. flang-new -fc1). Similarly to Clang, `flang-new -fc1
-emit-llvm file.f` will generate a textual LLVM IR file.

Depends on D118985

[awarzynski]

Rebase, remove trailing "_" from member variable names

[awarzynski]

This has been extracted from fir-dev. Original PR: https://github.com/flang-compiler/f18-llvm-project/pull/1113

[rovka]

flang/include/flang/Frontend/FrontendOptions.h

37

Shouldn't this be .ll?

flang/lib/Frontend/FrontendActions.cpp

422

Nit: Should we assert that mlirModule exists?
Also, why doesn't it already have a triple and a kind mapping?

465

This looks like an obsolete comment.

flang/test/Driver/emit-llvm.f90

2

[awarzynski]

flang/lib/Frontend/FrontendActions.cpp

422

Nit: Should we assert that mlirModule exists?

We could do, yes. However, mlirModule is created in CodeGenAction::BeginSourceFileAction. If that method fails, the driver should stop immediately. So perhaps that would be a better for place for an assert?

On a related note, mlirModule is obtained via LoweringBridge::getModule. But if the corresponding module is nullptr than that getter should probably assert. See https://reviews.llvm.org/D119133.

Also, why doesn't it already have a triple and a kind mapping?

Good catch, this is not needed yet. I didn't notice this when going over tco.

[awarzynski]

Update comments + add an assert

[awarzynski]

Remove the calls to setTargetTriple and setKindMapping.

[rovka]

LGTM, thanks! I just have a minor nit, feel free to ignore it.

flang/lib/Frontend/FrontendActions.cpp

472

Nit: Can this be folded into the above if? (I.e. just write to os if you managed to create it, and add an else branch for the other case)

[kiranchandramohan]

The tests added are failing in the windows CI.

flang/lib/Frontend/FrontendActions.cpp

422

D118985 creates a bridge with an empty triple. The patch here was switching it to "native". Please cross-check what the expected behaviour.

lower::LoweringBridge lb = Fortran::lower::LoweringBridge::create(*mlirCtx,
    defKinds, ci.invocation().semanticsContext().intrinsics(),
    ci.parsing().allCooked(), "", kindMap);

441

Nit: Remove auto.

flang/unittests/Frontend/FrontendActionTest.cpp

176

Nit: Is the size important?

[awarzynski]

I believe that Windows failures are due to the missing support here: https://github.com/llvm/llvm-project/blob/81cde474e2c5a6280cb693b777ddcf473825ae8a/flang/lib/Optimizer/CodeGen/Target.cpp#L290. I can disable the LIT test on Windows, but I'm not sure how to do it for unit tests.

flang/lib/Frontend/FrontendActions.cpp

422

Please cross-check what the expected behaviour.

That's a good point, Kiran! Thanks :)

The constructor for LoweringBridge will call fir::setTargetTriple. This, in turn, will call fir::determineTargetTriple, which (for an empty triple) selects the target as follows:

if (triple.empty() || triple == "default")
  return llvm::sys::getDefaultTargetTriple()

AFAIK, native and default are compatible (I couldn't find any indication otherwise). So, empty triple above and "native" will lead to the same thing. So we are still just using native here.

This made me realise though that we should be explicit in D118985 and set the triple there. I'll update it shortly.

441

Sure! I will also rename this as moduleName.

472

Good suggestion, thanks!

I recall having a good reason to write it like this, but don't remember what it was. Let me simplify!

flang/unittests/Frontend/FrontendActionTest.cpp

176

No, thanks for noting this!

In fact, the generated output is larger than 256 characters.

[awarzynski]

Disable the LIT test on Windows, simplify how output is dumped in EmitLLVMAction::ExecuteAction, remove auto

[awarzynski]

Rebase on top of main

[awarzynski]

Updated fir::CodeGenSpecifics::get to see whether the unit tests pass on Windows. If they do, I'll create a seperate patch with this change.

[awarzynski]

Remove the change from fir::CodeGenSpecifics::get (this was uploaded as a
seperate patch: https://reviews.llvm.org/D119332)

[awarzynski]

Rebase on top of main

[awarzynski]

A believe that all of Kiran's comments have been addressed and pre-merge CI is also passing now (that was one of the concerns). Kiran has not accepted this yet, but he will be away for a few weeks. I will merge this as is to unblock further work. I more than happy to address any post-commit comments, Kiran!

clang/include/clang/Driver/Options.td

 def dylinker__install__name : JoinedOrSeparate<["-"], "dylinker_install_name">;
 def dylinker : Flag<["-"], "dylinker">;
 def dynamiclib : Flag<["-"], "dynamiclib">;
 def dynamic : Flag<["-"], "dynamic">, Flags<[NoArgumentUnused]>;
 def d_Flag : Flag<["-"], "d">, Group<d_Group>;
 def d_Joined : Joined<["-"], "d">, Group<d_Group>;
 def emit_ast : Flag<["-"], "emit-ast">,
   HelpText<"Emit Clang AST files for source inputs">;
-def emit_llvm : Flag<["-"], "emit-llvm">, Flags<[CC1Option]>, Group<Action_Group>,
+def emit_llvm : Flag<["-"], "emit-llvm">, Flags<[CC1Option, FC1Option]>, Group<Action_Group>,
   HelpText<"Use the LLVM representation for assembler and object files">;
 def emit_interface_stubs : Flag<["-"], "emit-interface-stubs">, Flags<[CC1Option]>, Group<Action_Group>,
   HelpText<"Generate Interface Stub Files.">;
 def emit_merged_ifs : Flag<["-"], "emit-merged-ifs">,
   Flags<[CC1Option]>, Group<Action_Group>,
   HelpText<"Generate Interface Stub Files, emit merged text not binary.">;
 def end_no_unused_arguments : Flag<["--"], "end-no-unused-arguments">, Flags<[CoreOption]>,
   HelpText<"Start emitting warnings for unused driver arguments">;

flang/include/flang/Frontend/FrontendActions.h

 //===- FrontendActions.h -----------------------------------------*- C++-*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_FLANG_FRONTEND_FRONTENDACTIONS_H
 #define LLVM_FLANG_FRONTEND_FRONTENDACTIONS_H
 
 #include "flang/Frontend/FrontendAction.h"
 #include "flang/Semantics/semantics.h"
 
 #include "mlir/IR/BuiltinOps.h"
+#include "llvm/IR/Module.h"
 #include <memory>
 
 namespace Fortran::frontend {
 
 // TODO: This is a copy from f18.cpp. It doesn't really belong here and should
 // be moved to a more suitable place in future.
 struct MeasurementVisitor {
   template <typename A> bool Pre(const A &) { return true; }
class CodeGenAction : public FrontendAction {
   bool BeginSourceFileAction() override;
 
 protected:
   /// @name MLIR
   /// {
   std::unique_ptr<mlir::ModuleOp> mlirModule;
   std::unique_ptr<mlir::MLIRContext> mlirCtx;
   /// }
+
+  /// @name LLVM IR
+  std::unique_ptr<llvm::LLVMContext> llvmCtx;
+  std::unique_ptr<llvm::Module> llvmModule;
+
+  /// Generates an LLVM IR module from CodeGenAction::mlirModule and saves it
+  /// in CodeGenAction::llvmModule.
+  void GenerateLLVMIR();
+  /// }
 };
 
 class EmitMLIRAction : public CodeGenAction {
   void ExecuteAction() override;
 };
 
+class EmitLLVMAction : public CodeGenAction {
+  void ExecuteAction() override;
+};
+
 class EmitObjAction : public CodeGenAction {
   void ExecuteAction() override;
 };
 
 } // namespace Fortran::frontend
 
 #endif // LLVM_FLANG_FRONTEND_FRONTENDACTIONS_H

flang/include/flang/Frontend/FrontendOptions.h

enum ActionKind {
   PrintPreprocessedInput,
 
   /// -fsyntax-only
   ParseSyntaxOnly,
 
   /// Emit a .mlir file
   EmitMLIR,
 
+  /// Emit an .ll file
+  EmitLLVM,
+
   /// Emit a .o file.
   EmitObj,
 
   /// Parse, unparse the parse-tree and output a Fortran source file
   DebugUnparse,
 
   /// Parse, unparse the parse-tree and output a Fortran source file, skip the
   /// semantic checks
enum ActionKind {
   /// Parse, run semantics and then dump symbol sources map
   GetSymbolsSources,
 
   /// Only execute frontend initialization
   InitOnly,
 
   /// Run a plugin action
   PluginAction
-
-  /// TODO: RunPreprocessor, EmitLLVM, EmitLLVMOnly,
-  /// EmitCodeGenOnly, EmitAssembly, (...)
 };
 
 /// \param suffix The file extension
 /// \return True if the file extension should be processed as fixed form
 bool isFixedFormSuffix(llvm::StringRef suffix);
 
 /// \param suffix The file extension
 /// \return True if the file extension should be processed as free form

flang/lib/Frontend/CompilerInvocation.cpp

case clang::driver::options::OPT_E:
       opts.programAction = PrintPreprocessedInput;
       break;
     case clang::driver::options::OPT_fsyntax_only:
       opts.programAction = ParseSyntaxOnly;
       break;
     case clang::driver::options::OPT_emit_mlir:
       opts.programAction = EmitMLIR;
       break;
+    case clang::driver::options::OPT_emit_llvm:
+      opts.programAction = EmitLLVM;
+      break;
     case clang::driver::options::OPT_emit_obj:
       opts.programAction = EmitObj;
       break;
     case clang::driver::options::OPT_fdebug_unparse:
       opts.programAction = DebugUnparse;
       break;
     case clang::driver::options::OPT_fdebug_unparse_no_sema:
       opts.programAction = DebugUnparseNoSema;

flang/lib/Frontend/FrontendActions.cpp

 //===--- FrontendActions.cpp ----------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "flang/Frontend/FrontendActions.h"
 #include "flang/Common/default-kinds.h"
 #include "flang/Frontend/CompilerInstance.h"
 #include "flang/Frontend/FrontendOptions.h"
 #include "flang/Frontend/PreprocessorOptions.h"
 #include "flang/Lower/Bridge.h"
 #include "flang/Lower/PFTBuilder.h"
 #include "flang/Lower/Support/Verifier.h"
+#include "flang/Optimizer/Support/FIRContext.h"
 #include "flang/Optimizer/Support/InitFIR.h"
 #include "flang/Optimizer/Support/KindMapping.h"
 #include "flang/Optimizer/Support/Utils.h"
 #include "flang/Parser/dump-parse-tree.h"
 #include "flang/Parser/parsing.h"
 #include "flang/Parser/provenance.h"
 #include "flang/Parser/source.h"
 #include "flang/Parser/unparse.h"
 #include "flang/Semantics/runtime-type-info.h"
 #include "flang/Semantics/semantics.h"
 #include "flang/Semantics/unparse-with-symbols.h"
 
 #include "mlir/IR/Dialect.h"
 #include "mlir/Pass/PassManager.h"
+#include "mlir/Target/LLVMIR/ModuleTranslation.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <clang/Basic/Diagnostic.h>
 #include <memory>
 
 using namespace Fortran::frontend;
 
 //===----------------------------------------------------------------------===//
void GetSymbolsSourcesAction::ExecuteAction() {
   // Report and exit if fatal semantic errors are present
   if (reportFatalSemanticErrors()) {
     return;
   }
 
   ci.semantics().DumpSymbolsSources(llvm::outs());
 }
 
+#include "flang/Tools/CLOptions.inc"
+
+// Lower the previously generated MLIR module into an LLVM IR module
+void CodeGenAction::GenerateLLVMIR() {
+  assert(mlirModule && "The MLIR module has not been generated yet.");
+
+  CompilerInstance &ci = this->instance();
+
+  fir::support::loadDialects(*mlirCtx);
+  fir::support::registerLLVMTranslation(*mlirCtx);
+
+  // Set-up the MLIR pass manager
+  mlir::PassManager pm(mlirCtx.get(), mlir::OpPassManager::Nesting::Implicit);
+
+  pm.addPass(std::make_unique<Fortran::lower::VerifierPass>());
+  pm.enableVerifier(/*verifyPasses=*/true);
+  mlir::PassPipelineCLParser passPipeline("", "Compiler passes to run");
+
+  // Create the pass pipeline
+  fir::createMLIRToLLVMPassPipeline(pm);
+
+  // Run the pass manager
+  if (!mlir::succeeded(pm.run(*mlirModule))) {
+    unsigned diagID = ci.diagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, "Lowering to LLVM IR failed");
+    ci.diagnostics().Report(diagID);
+  }
+
+  // Translate to LLVM IR
+  llvm::Optional<llvm::StringRef> moduleName = mlirModule->getName();
+  llvmCtx = std::make_unique<llvm::LLVMContext>();
+  llvmModule = mlir::translateModuleToLLVMIR(
+      *mlirModule, *llvmCtx, moduleName ? *moduleName : "FIRModule");
+
+  if (!llvmModule) {
+    unsigned diagID = ci.diagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, "failed to create the LLVM module");
+    ci.diagnostics().Report(diagID);
+    return;
+  }
+}
+
+void EmitLLVMAction::ExecuteAction() {
+  CompilerInstance &ci = this->instance();
+  GenerateLLVMIR();
+
+  // If set, use the predefined outupt stream to print the generated module.
+  if (!ci.IsOutputStreamNull()) {
+    llvmModule->print(
+        ci.GetOutputStream(), /*AssemblyAnnotationWriter=*/nullptr);
+    return;
+  }
+
+  // No predefined output stream was set. Create an output file and dump the
+  // generated module there.
+  std::unique_ptr<llvm::raw_ostream> os = ci.CreateDefaultOutputFile(
+      /*Binary=*/false, /*InFile=*/GetCurrentFileOrBufferName(), "ll");
+  if (!os) {
+    unsigned diagID = ci.diagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, "failed to create the output file");
+    ci.diagnostics().Report(diagID);
+    return;
+  }
+  llvmModule->print(*os, /*AssemblyAnnotationWriter=*/nullptr);
+}
+
 void EmitMLIRAction::ExecuteAction() {
   CompilerInstance &ci = this->instance();
 
   // Print the output. If a pre-defined output stream exists, dump the MLIR
   // content there.
   if (!ci.IsOutputStreamNull()) {
     mlirModule->print(ci.GetOutputStream());
     return;

flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
   case InputOutputTest:
     return std::make_unique<InputOutputTestAction>();
   case PrintPreprocessedInput:
     return std::make_unique<PrintPreprocessedAction>();
   case ParseSyntaxOnly:
     return std::make_unique<ParseSyntaxOnlyAction>();
   case EmitMLIR:
     return std::make_unique<EmitMLIRAction>();
+  case EmitLLVM:
+    return std::make_unique<EmitLLVMAction>();
   case EmitObj:
     return std::make_unique<EmitObjAction>();
   case DebugUnparse:
     return std::make_unique<DebugUnparseAction>();
   case DebugUnparseNoSema:
     return std::make_unique<DebugUnparseNoSemaAction>();
   case DebugUnparseWithSymbols:
     return std::make_unique<DebugUnparseWithSymbolsAction>();

flang/test/Driver/driver-help.f90

 !-------------------------------------------------------------
 ! EXPECTED OUTPUT FOR FLANG FRONTEND DRIVER (flang -fc1)
 !-------------------------------------------------------------
 ! HELP-FC1:USAGE: flang
 ! HELP-FC1-EMPTY:
 ! HELP-FC1-NEXT:OPTIONS:
 ! HELP-FC1-NEXT: -cpp                   Enable predefined and command line preprocessor macros
 ! HELP-FC1-NEXT: -D <macro>=<value>     Define <macro> to <value> (or 1 if <value> omitted)
+! HELP-FC1-NEXT: -emit-llvm Use the LLVM representation for assembler and object files
 ! HELP-FC1-NEXT: -emit-mlir Build the parse tree, then lower it to MLIR
 ! HELP-FC1-NEXT: -emit-obj Emit native object files
 ! HELP-FC1-NEXT: -E                     Only run the preprocessor
 ! HELP-FC1-NEXT: -falternative-parameter-statement
 ! HELP-FC1-NEXT: Enable the old style PARAMETER statement
 ! HELP-FC1-NEXT: -fbackslash            Specify that backslash in string introduces an escape character
 ! HELP-FC1-NEXT: -fdebug-dump-all       Dump symbols and the parse tree after the semantic checks
 ! HELP-FC1-NEXT: -fdebug-dump-parse-tree-no-sema

flang/test/Driver/emit-llvm.f90

+! Test the `-emit-llvm` option
+
+! UNSUPPORTED: system-windows
+! Windows is currently not supported in flang/lib/Optimizer/CodeGen/Target.cpp
+
+!------------
+! RUN COMMAND
+!------------
+! RUN: %flang_fc1 -emit-llvm %s -o - | FileCheck %s
+
+!----------------
+! EXPECTED OUTPUT
+!----------------
+! CHECK: ; ModuleID = 'FIRModule'
+! CHECK: define void @_QQmain()
+! CHECK-NEXT:  ret void
+! CHECK-NEXT: }
+
+!------
+! INPUT
+!------
+end program

flang/unittests/Frontend/FrontendActionTest.cpp

TEST_F(FrontendActionTest, ParseSyntaxOnly) {
   // Validate the expected output.
   EXPECT_FALSE(success);
   EXPECT_TRUE(!outputDiagBuffer.empty());
   EXPECT_TRUE(
       llvm::StringRef(outputDiagBuffer.data())
           .contains(
               ":1:14: error: IF statement is not allowed in IF statement\n"));
 }
+
+TEST_F(FrontendActionTest, EmitLLVM) {
+  // Populate the input file with the pre-defined input and flush it.
+  *(inputFileOs_) << "end program";
+  inputFileOs_.reset();
+
+  // Set-up the action kind.
+  compInst_.invocation().frontendOpts().programAction = EmitLLVM;
+  compInst_.invocation().preprocessorOpts().noReformat = true;
+
+  // Set-up the output stream. We are using output buffer wrapped as an output
+  // stream, as opposed to an actual file (or a file descriptor).
+  llvm::SmallVector<char> outputFileBuffer;
+  std::unique_ptr<llvm::raw_pwrite_stream> outputFileStream(
+      new llvm::raw_svector_ostream(outputFileBuffer));
+  compInst_.set_outputStream(std::move(outputFileStream));
+
+  // Execute the action.
+  bool success = ExecuteCompilerInvocation(&compInst_);
+
+  // Validate the expected output.
+  EXPECT_TRUE(success);
+  EXPECT_TRUE(!outputFileBuffer.empty());
+
+  EXPECT_TRUE(llvm::StringRef(outputFileBuffer.data())
+                  .contains("define void @_QQmain()"));
+}
 } // namespace