[flang][driver] NFC: Make code more in line with LLVM style

This patch basically implements [1] in ExecuteCompilerInvocation.cpp. It
also:
  * replaces `CreateFrontendBaseAction` with `CreateFrontendAction`
    (only one method is needed ATM, this change removes the extra
    indirection)
  * removes `InvalidAction` from the `ActionKind` enum (I don't think it
    adds much and keeping it would mean adding a new void case in
    `CreateFrontendAction`)
  * sets the default frontend action in FrontendOptions.h to
    `ParseSyntaxOnly` (note that this is still overridden independently
    in `ParseFrontendArg` in CompilerInvocation.cpp)

No new functionality is added, hence no tests.

[1] https://llvm.org/docs/CodingStandards.html#don-t-use-default-labels-in-fully-covered-switches-over-enumerations

Differential Revision: https://reviews.llvm.org/D124245

1 files changed, 3 insertions, 20 deletions

diff --git a/flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp b/flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
index bc2bf1d..8f5b313 100644
--- a/flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
+++ b/flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp
@@ -24,11 +24,10 @@
 
 namespace Fortran::frontend {
 
-static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
+static std::unique_ptr<FrontendAction> CreateFrontendAction(
     CompilerInstance &ci) {
 
-  ActionKind ak = ci.frontendOpts().programAction;
-  switch (ak) {
+  switch (ci.frontendOpts().programAction) {
   case InputOutputTest:
     return std::make_unique<InputOutputTestAction>();
   case PrintPreprocessedInput:
@@ -90,25 +89,9 @@ static std::unique_ptr<FrontendAction> CreateFrontendBaseAction(
     ci.diagnostics().Report(diagID) << ci.frontendOpts().ActionName;
     return nullptr;
   }
-  default:
-    break;
-    // TODO:
-    // case ParserSyntaxOnly:
-    // case EmitLLVM:
-    // case EmitLLVMOnly:
-    // case EmitCodeGenOnly:
-    // (...)
   }
-  return 0;
-}
-
-std::unique_ptr<FrontendAction> CreateFrontendAction(CompilerInstance &ci) {
-  // Create the underlying action.
-  std::unique_ptr<FrontendAction> act = CreateFrontendBaseAction(ci);
-  if (!act)
-    return nullptr;
 
-  return act;
+  llvm_unreachable("Invalid program action!");
 }
 
 bool ExecuteCompilerInvocation(CompilerInstance *flang) {