[flang][driver] Add support for generating LLVM bytecode files

Support for generating LLVM BC files is added in Flang's compiler and
frontend drivers. This requires the `BitcodeWriterPass` pass to be run
on the input LLVM IR module and is implemented as a dedicated frontend
aciton. The new functionality as seen by the user (compiler driver):
```
flang-new -c -emit-llvm file.90
```
or (frontend driver):
```
flang-new -fc1 -emit-llvm-bc file.f90
```

The new behaviour is consistent with `clang` and `clang -cc1`.

Differential Revision: https://reviews.llvm.org/D123211

clang/include/clang/Driver/Options.td

@@ -5678,8 +5678,6 @@ def emit_header_unit : Flag<["-"], "emit-header-unit">,
   HelpText<"Generate C++20 header units from header files">;
 def emit_pch : Flag<["-"], "emit-pch">,
   HelpText<"Generate pre-compiled header file">;
-def emit_llvm_bc : Flag<["-"], "emit-llvm-bc">,
-  HelpText<"Build ASTs then convert to LLVM, emit .bc file">;
 def emit_llvm_only : Flag<["-"], "emit-llvm-only">,
   HelpText<"Build ASTs and convert to LLVM, discarding output">;
 def emit_codegen_only : Flag<["-"], "emit-codegen-only">,
@@ -6143,6 +6141,8 @@ def emit_obj : Flag<["-"], "emit-obj">,
   HelpText<"Emit native object files">;
 def init_only : Flag<["-"], "init-only">,
   HelpText<"Only execute frontend initialization">;
+def emit_llvm_bc : Flag<["-"], "emit-llvm-bc">,
+  HelpText<"Build ASTs then convert to LLVM, emit .bc file">;
 
 } // let Group = Action_Group
 

flang/include/flang/Frontend/FrontendActions.h

@@ -192,6 +192,10 @@ class EmitLLVMAction : public CodeGenAction {
   void ExecuteAction() override;
 };
 
+class EmitLLVMBitcodeAction : public CodeGenAction {
+  void ExecuteAction() override;
+};
+
 class BackendAction : public CodeGenAction {
 public:
   enum class BackendActionTy {

flang/include/flang/Frontend/FrontendOptions.h

@@ -37,6 +37,9 @@ enum ActionKind {
   /// Emit an .ll file
   EmitLLVM,
 
+  /// Emit a .bc file
+  EmitLLVMBitcode,
+
   /// Emit a .o file.
   EmitObj,
 

flang/lib/Frontend/CMakeLists.txt

@@ -32,6 +32,7 @@ add_flang_library(flangFrontend
   FIRBuilder
   FIRCodeGen
   FIRTransforms
+  LLVMPasses
   MLIRTransforms
   MLIRLLVMToLLVMIRTranslation
   MLIRSCFToControlFlow

flang/lib/Frontend/CompilerInvocation.cpp

@@ -148,6 +148,9 @@ static bool ParseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     case clang::driver::options::OPT_emit_llvm:
       opts.programAction = EmitLLVM;
       break;
+    case clang::driver::options::OPT_emit_llvm_bc:
+      opts.programAction = EmitLLVMBitcode;
+      break;
     case clang::driver::options::OPT_emit_obj:
       opts.programAction = EmitObj;
       break;

flang/lib/Frontend/FrontendActions.cpp

@@ -33,6 +33,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Bitcode/BitcodeWriterPass.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/MC/TargetRegistry.h"
 #include "llvm/Passes/PassBuilder.h"
@@ -472,6 +473,48 @@ void EmitLLVMAction::ExecuteAction() {
   llvmModule->print(*os, /*AssemblyAnnotationWriter=*/nullptr);
 }
 
+void EmitLLVMBitcodeAction::ExecuteAction() {
+  CompilerInstance &ci = this->instance();
+  // Generate an LLVM module if it's not already present (it will already be
+  // present if the input file is an LLVM IR/BC file).
+  if (!llvmModule)
+    GenerateLLVMIR();
+
+  // Create and configure `Target`
+  std::string error;
+  std::string theTriple = llvmModule->getTargetTriple();
+  const llvm::Target *theTarget =
+      llvm::TargetRegistry::lookupTarget(theTriple, error);
+  assert(theTarget && "Failed to create Target");
+
+  // Create and configure `TargetMachine`
+  std::unique_ptr<llvm::TargetMachine> TM(
+      theTarget->createTargetMachine(theTriple, /*CPU=*/"",
+          /*Features=*/"", llvm::TargetOptions(), llvm::None));
+  assert(TM && "Failed to create TargetMachine");
+  llvmModule->setDataLayout(TM->createDataLayout());
+
+  // Generate an output file
+  std::unique_ptr<llvm::raw_ostream> os = ci.CreateDefaultOutputFile(
+      /*Binary=*/true, /*InFile=*/GetCurrentFileOrBufferName(), "bc");
+  if (!os) {
+    unsigned diagID = ci.diagnostics().getCustomDiagID(
+        clang::DiagnosticsEngine::Error, "failed to create the output file");
+    ci.diagnostics().Report(diagID);
+    return;
+  }
+
+  // Set-up the pass manager
+  llvm::ModulePassManager MPM;
+  llvm::ModuleAnalysisManager MAM;
+  llvm::PassBuilder PB(TM.get());
+  PB.registerModuleAnalyses(MAM);
+  MPM.addPass(llvm::BitcodeWriterPass(*os));
+
+  // Run the passes
+  MPM.run(*llvmModule, MAM);
+}
+
 void EmitMLIRAction::ExecuteAction() {
   CompilerInstance &ci = this->instance();
 

flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

@@ -37,6 +37,8 @@ static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
     return std::make_unique<EmitMLIRAction>();
   case EmitLLVM:
     return std::make_unique<EmitLLVMAction>();
+  case EmitLLVMBitcode:
+    return std::make_unique<EmitLLVMBitcodeAction>();
   case EmitObj:
     return std::make_unique<BackendAction>(
         BackendAction::BackendActionTy::Backend_EmitObj);

flang/test/CMakeLists.txt

@@ -55,6 +55,7 @@ set(FLANG_TEST_DEPENDS
   fir-opt
   tco
   bbc
+  llvm-dis
   llvm-objdump
   split-file
 )

flang/test/Driver/driver-help.f90

@@ -71,6 +71,7 @@
 ! 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-bc          Build ASTs then convert to LLVM, emit .bc file
 ! 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

flang/test/Driver/emit-llvm-bc.f90

@@ -0,0 +1,19 @@
+! Test the options for generating LLVM byte-code `-emit-llvm-bc` option
+
+!-------------
+! RUN COMMANDS
+!-------------
+! RUN: %flang -emit-llvm -c %s -o - | llvm-dis -o - | FileCheck %s
+! RUN: %flang_fc1 -emit-llvm-bc %s -o - | llvm-dis -o - | FileCheck %s
+
+!----------------
+! EXPECTED OUTPUT
+!----------------
+! CHECK: define void @_QQmain()
+! CHECK-NEXT:  ret void
+! CHECK-NEXT: }
+
+!------
+! INPUT
+!------
+end program