[flang][driver] Add support for the "-init-only" option

Adding the `-init-only` option and corresponding frontend action to
generate a diagnostic.

`-init-only` vs `-test-io`:
`-init-only` ignores the input (it never calls the prescanner)
`-test-io` is similar to `-init-only`, but does read and print the input
without calling the prescanner.

This patch also adds a Driver test to check this action.

Reviewed By: awarzynski, AMDChirag

Differential Revision: https://reviews.llvm.org/D102849

Author: stuellis

clang/include/clang/Driver/Options.td

@@ -5275,8 +5275,6 @@ def analyze : Flag<["-"], "analyze">,
   HelpText<"Run static analysis engine">;
 def dump_tokens : Flag<["-"], "dump-tokens">,
   HelpText<"Run preprocessor, dump internal rep of tokens">;
-def init_only : Flag<["-"], "init-only">,
-  HelpText<"Only execute frontend initialization">;
 def fixit : Flag<["-"], "fixit">,
   HelpText<"Apply fix-it advice to the input source">;
 def fixit_EQ : Joined<["-"], "fixit=">,
@@ -5742,6 +5740,8 @@ let Group = Action_Group in {
 
 def emit_obj : Flag<["-"], "emit-obj">,
   HelpText<"Emit native object files">;
+def init_only : Flag<["-"], "init-only">,
+  HelpText<"Only execute frontend initialization">;
 
 } // let Group = Action_Group
 } // let Flags = [CC1Option, FC1Option, NoDriverOption]

flang/include/flang/Frontend/FrontendActions.h

@@ -38,6 +38,10 @@ class EmitObjAction : public FrontendAction {
   void ExecuteAction() override;
 };
 
+class InitOnlyAction : public FrontendAction {
+  void ExecuteAction() override;
+};
+
 //===----------------------------------------------------------------------===//
 // Prescan Actions
 //===----------------------------------------------------------------------===//

flang/include/flang/Frontend/FrontendOptions.h

@@ -74,7 +74,10 @@ enum ActionKind {
   GetDefinition,
 
   /// Parse, run semantics and then dump symbol sources map
-  GetSymbolsSources
+  GetSymbolsSources,
+
+  /// Only execute frontend initialization
+  InitOnly
 
   /// TODO: RunPreprocessor, EmitLLVM, EmitLLVMOnly,
   /// EmitCodeGenOnly, EmitAssembly, (...)

flang/lib/Frontend/CompilerInvocation.cpp

@@ -165,9 +165,12 @@ static bool ParseFrontendArgs(FrontendOptions &opts, llvm::opt::ArgList &args,
     case clang::driver::options::OPT_fget_definition:
       opts.programAction_ = GetDefinition;
       break;
+    case clang::driver::options::OPT_init_only:
+      opts.programAction_ = InitOnly;
+      break;
 
       // TODO:
-      // case calng::driver::options::OPT_emit_llvm:
+      // case clang::driver::options::OPT_emit_llvm:
       // case clang::driver::options::OPT_emit_llvm_only:
       // case clang::driver::options::OPT_emit_codegen_only:
       // case clang::driver::options::OPT_emit_module:

flang/lib/Frontend/FrontendActions.cpp

@@ -484,3 +484,11 @@ void EmitObjAction::ExecuteAction() {
       clang::DiagnosticsEngine::Error, "code-generation is not available yet");
   ci.diagnostics().Report(DiagID);
 }
+
+void InitOnlyAction::ExecuteAction() {
+  CompilerInstance &ci = this->instance();
+  unsigned DiagID =
+      ci.diagnostics().getCustomDiagID(clang::DiagnosticsEngine::Warning,
+          "Use `-init-only` for testing purposes only");
+  ci.diagnostics().Report(DiagID);
+}

flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

@@ -76,6 +76,9 @@ static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
   case GetSymbolsSources:
     return std::make_unique<GetSymbolsSourcesAction>();
     break;
+  case InitOnly:
+    return std::make_unique<InitOnlyAction>();
+    break;
   default:
     break;
     // TODO:

flang/test/Driver/driver-help.f90

@@ -107,6 +107,7 @@
 ! HELP-FC1-NEXT: -fopenmp               Parse OpenMP pragmas and generate parallel code.
 ! HELP-FC1-NEXT: -fxor-operator         Enable .XOR. as a synonym of .NEQV.
 ! HELP-FC1-NEXT: -help                  Display available options
+! HELP-FC1-NEXT: -init-only             Only execute frontend initialization
 ! HELP-FC1-NEXT: -I <dir>               Add directory to the end of the list of include search paths
 ! HELP-FC1-NEXT: -module-dir <dir>      Put MODULE files in <dir>
 ! HELP-FC1-NEXT: -module-suffix <suffix> Use <suffix> as the suffix for module files (the default value is `.mod`)

flang/test/Driver/init-only.f90

@@ -0,0 +1,7 @@
+! Verify that -init-only flag generates a diagnostic as expected
+
+! REQUIRES: new-flang-driver
+
+! RUN: %flang_fc1 -init-only 2>&1 | FileCheck %s
+
+! CHECK: warning: Use `-init-only` for testing purposes only