[flang][WIP] Add support for -emit-fir

A new parent class for code-gen frontend actions is introduced:
`CodeGenAction`. We will be using this class to encapsulate logic shared
between all code-generation actions but not required otherwise.

For `-emit-fir`, a specialisation of `CodeGenAction` is introduced:
`EmitFIRAction`. The key logic for this class is implemented in
`EmitFirAction::ExecuteAction`.

Author: banach-space

clang/include/clang/Driver/Options.td

@@ -4467,6 +4467,9 @@ def fintrinsic_modules_path : Separate<["-"], "fintrinsic-modules-path">,  Group
   HelpText<"Specify where to find the compiled intrinsic modules">,
   DocBrief<[{This option specifies the location of pre-compiled intrinsic modules, 
   if they are not in the default location expected by the compiler.}]>;
+
+def emit_fir : Flag<["-"], "emit-fir">, Group<Action_Group>,
+  HelpText<"Build the parse tree, then convert to FIR and dump">;
 }
 
 def J : JoinedOrSeparate<["-"], "J">,

clang/lib/Driver/Driver.cpp

@@ -43,6 +43,7 @@
 #include "ToolChains/PS4CPU.h"
 #include "ToolChains/RISCVToolchain.h"
 #include "ToolChains/Solaris.h"
+
 #include "ToolChains/TCE.h"
 #include "ToolChains/VEToolchain.h"
 #include "ToolChains/WebAssembly.h"

flang/include/flang/Frontend/FrontendActions.h

@@ -127,6 +127,19 @@ class ParseSyntaxOnlyAction : public PrescanAndSemaAction {
   void ExecuteAction() override;
 };
 
+//===----------------------------------------------------------------------===//
+// CodeGen Actions
+//===----------------------------------------------------------------------===//
+class CodeGenAction : public FrontendAction {
+
+  void ExecuteAction() override = 0;
+  bool BeginSourceFileAction() override;
+};
+
+class EmitFirAction : public CodeGenAction {
+  void ExecuteAction() override;
+};
+
 } // namespace Fortran::frontend
 
 #endif // LLVM_FLANG_FRONTEND_FRONTENDACTIONS_H

flang/include/flang/Frontend/FrontendOptions.h

@@ -31,6 +31,9 @@ enum ActionKind {
   /// -fsyntax-only
   ParseSyntaxOnly,
 
+  /// Emit a .mlir file
+  EmitFir,
+
   /// Emit a .o file.
   EmitObj,
 

flang/lib/Frontend/CMakeLists.txt

@@ -1,3 +1,5 @@
+get_property(dialect_libs GLOBAL PROPERTY MLIR_DIALECT_LIBS)
+
 add_flang_library(flangFrontend
   CompilerInstance.cpp
   CompilerInvocation.cpp
@@ -19,6 +21,15 @@ add_flang_library(flangFrontend
   FortranLower
   clangBasic
   clangDriver
+  FIRDialect
+  FIRAnalysis
+  FIRSupport
+  FIRTransforms
+  FIRBuilder
+  FIRRuntime
+  ${dialect_libs}
+  MLIRAffineToStandard
+  MLIRSCFToStandard
 
   LINK_COMPONENTS
   Option

flang/lib/Frontend/CompilerInvocation.cpp

@@ -123,6 +123,9 @@ static bool ParseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     case clang::driver::options::OPT_fsyntax_only:
       opts.programAction = ParseSyntaxOnly;
       break;
+    case clang::driver::options::OPT_emit_fir:
+      opts.programAction = EmitFir;
+      break;
     case clang::driver::options::OPT_emit_obj:
       opts.programAction = EmitObj;
       break;

flang/lib/Frontend/FrontendActions.cpp

@@ -11,7 +11,9 @@
 #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/Optimizer/Dialect/FIRType.h"
 #include "flang/Parser/dump-parse-tree.h"
 #include "flang/Parser/parsing.h"
 #include "flang/Parser/provenance.h"
@@ -22,8 +24,16 @@
 #include "flang/Semantics/unparse-with-symbols.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/raw_ostream.h"
 #include <clang/Basic/Diagnostic.h>
 #include <memory>
+#include "mlir/IR/Dialect.h"
+#include "flang/Optimizer/Support/InitFIR.h"
+#include "flang/Optimizer/Support/KindMapping.h"
+#include "flang/Lower/Bridge.h"
+#include "mlir/Pass/PassManager.h"
+#include "mlir/Support/LogicalResult.h"
+#include "flang/Lower/Support/Verifier.h"
 
 using namespace Fortran::frontend;
 
@@ -40,6 +50,10 @@ bool PrescanAndSemaAction::BeginSourceFileAction() {
   return RunPrescan() & RunParse() && RunSemanticChecks();
 }
 
+bool CodeGenAction::BeginSourceFileAction() {
+  return RunPrescan() & RunParse() && RunSemanticChecks();
+}
+
 //===----------------------------------------------------------------------===//
 // Custom ExecuteAction
 //===----------------------------------------------------------------------===//
@@ -351,6 +365,65 @@ void GetSymbolsSourcesAction::ExecuteAction() {
   ci.semantics().DumpSymbolsSources(llvm::outs());
 }
 
+// Translate front-end KINDs for use in the IR and code gen. Extracted from
+// bbc.cpp.
+// TODO: How to share this with bbc.cpp?
+static std::vector<fir::KindTy>
+fromDefaultKinds(const Fortran::common::IntrinsicTypeDefaultKinds &defKinds) {
+  return {static_cast<fir::KindTy>(defKinds.GetDefaultKind(
+              Fortran::common::TypeCategory::Character)),
+          static_cast<fir::KindTy>(
+              defKinds.GetDefaultKind(Fortran::common::TypeCategory::Complex)),
+          static_cast<fir::KindTy>(defKinds.doublePrecisionKind()),
+          static_cast<fir::KindTy>(
+              defKinds.GetDefaultKind(Fortran::common::TypeCategory::Integer)),
+          static_cast<fir::KindTy>(
+              defKinds.GetDefaultKind(Fortran::common::TypeCategory::Logical)),
+          static_cast<fir::KindTy>(
+              defKinds.GetDefaultKind(Fortran::common::TypeCategory::Real))};
+}
+
+void EmitFirAction::ExecuteAction() {
+  CompilerInstance &ci = this->instance();
+
+  // Load the MLIR dialects required by Flang
+  mlir::DialectRegistry registry;
+  mlir::MLIRContext ctx(registry);
+  fir::support::registerNonCodegenDialects(registry);
+  fir::support::loadNonCodegenDialects(ctx);
+
+  // Create a LoweringBridge
+  auto &defKinds = ci.invocation().semanticsContext().defaultKinds();
+  fir::KindMapping kindMap(
+      &ctx, llvm::ArrayRef<fir::KindTy>{fromDefaultKinds(defKinds)});
+  auto lb = Fortran::lower::LoweringBridge::create(ctx, defKinds,
+      ci.invocation().semanticsContext().intrinsics(), ci.parsing().allCooked(),
+      "", kindMap);
+
+  // Create PFT and lower it to FIR
+  auto &parseTree{*ci.parsing().parseTree()};
+  lb.lower(parseTree, ci.invocation().semanticsContext());
+
+  // Run the default passes.
+  mlir::PassManager pm(&ctx, mlir::OpPassManager::Nesting::Implicit);
+  pm.enableVerifier(/*verifyPasses=*/true);
+  pm.addPass(std::make_unique<Fortran::lower::VerifierPass>());
+  mlir::ModuleOp mlirModule = lb.getModule();
+  if (mlir::failed(pm.run(mlirModule))) {
+    // TODO: Replace with a diagnostic
+    llvm::errs() << "FATAL: verification of lowering to FIR failed";
+  }
+
+  // Print the output
+  auto os{ci.CreateDefaultOutputFile(
+          /*Binary=*/true, /*InFile=*/GetCurrentFileOrBufferName(), "mlir")};
+  if (!os) {
+    return;
+  }
+
+  mlirModule.print(*os);
+  }
+
 void EmitObjAction::ExecuteAction() {
   CompilerInstance &ci = this->instance();
   unsigned DiagID = ci.diagnostics().getCustomDiagID(

flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

@@ -32,6 +32,10 @@ static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
     return std::make_unique<PrintPreprocessedAction>();
   case ParseSyntaxOnly:
     return std::make_unique<ParseSyntaxOnlyAction>();
+    break;
+  case EmitFir:
+    return std::make_unique<EmitFirAction>();
+    break;
   case EmitObj:
     return std::make_unique<EmitObjAction>();
   case DebugUnparse:

flang/test/Driver/driver-help-hidden.f90

@@ -22,6 +22,7 @@
 ! CHECK-NEXT: -cpp      Enable predefined and command line preprocessor macros
 ! CHECK-NEXT: -c        Only run preprocess, compile, and assemble steps
 ! CHECK-NEXT: -D <macro>=<value>     Define <macro> to <value> (or 1 if <value> omitted)
+! CHECK-NEXT: -emit-fir              Build the parse tree, then convert to FIR and dump
 ! CHECK-NEXT: -E        Only run the preprocessor
 ! CHECK-NEXT: -falternative-parameter-statement
 ! CHECK-NEXT: Enable the old style PARAMETER statement

flang/test/Driver/driver-help.f90

@@ -22,6 +22,7 @@
 ! HELP-NEXT: -cpp                   Enable predefined and command line preprocessor macros
 ! HELP-NEXT: -c                     Only run preprocess, compile, and assemble steps
 ! HELP-NEXT: -D <macro>=<value>     Define <macro> to <value> (or 1 if <value> omitted)
+! HELP-NEXT: -emit-fir              Build the parse tree, then convert to FIR and dump
 ! HELP-NEXT: -E                     Only run the preprocessor
 ! HELP-NEXT: -falternative-parameter-statement
 ! HELP-NEXT: Enable the old style PARAMETER statement
@@ -65,6 +66,7 @@
 ! 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-fir              Build the parse tree, then convert to FIR and dump
 ! HELP-FC1-NEXT: -emit-obj Emit native object files
 ! HELP-FC1-NEXT: -E                     Only run the preprocessor
 ! HELP-FC1-NEXT: -falternative-parameter-statement