[flang][driver] Add debug options not requiring semantic checks

This patch adds two debugging options in the new Flang driver
(flang-new):
  *fdebug-unparse-no-sema
  *fdebug-dump-parse-tree-no-sema
Each of these options combines two options from the "throwaway" driver
(left: f18, right: flang-new):
  * `-fdebug-uparse -fdebug-no-semantics` --> `-fdebug-unparse-no-sema`
  * `-fdebug-dump-parse-tree -fdebug-no-semantics` -->
    `-fdebug-dump-parse-tree-no-sema`

There are no plans to implement `-fdebug-no-semantics` in the new
driver.  Such option would be too powerful. Also, it would only make
sense when combined with specific frontend actions (`-fdebug-unparse`
and `-fdebug-dump-parse-tree`). Instead, this patch adds 2 specialised
options listed above. Each of these is implemented through a dedicated
FrontendAction (also added).

The new frontend actions are implemented in terms of a new abstract base
action: `PrescanAndSemaAction`. This new base class was required so that
we can have finer control over what steps within the frontend are
executed:
  * `PrescanAction`: run the _prescanner_
  * `PrescanAndSemaAction`: run the _prescanner_ and the _parser_ (new
     in this patch)
  * `PrescanAndSemaAction`: run the _prescanner_, _parser_ and run the
    _semantic checks_

This patch introduces `PrescanAndParseAction::BeginSourceFileAction`.
Apart from the semantic checks removed at the end, it is similar to
`PrescanAndSemaAction::BeginSourceFileAction`.

Differential Revision: https://reviews.llvm.org/D99645

1 files changed, 6 insertions, 0 deletions

diff --git a/flang/lib/Frontend/CompilerInvocation.cpp b/flang/lib/Frontend/CompilerInvocation.cpp
index 43d9d41..d1203c7 100644
--- a/flang/lib/Frontend/CompilerInvocation.cpp
+++ b/flang/lib/Frontend/CompilerInvocation.cpp
@@ -127,6 +127,9 @@ static InputKind ParseFrontendArgs(FrontendOptions &opts,
     case clang::driver::options::OPT_fdebug_unparse:
       opts.programAction_ = DebugUnparse;
       break;
+    case clang::driver::options::OPT_fdebug_unparse_no_sema:
+      opts.programAction_ = DebugUnparseNoSema;
+      break;
     case clang::driver::options::OPT_fdebug_unparse_with_symbols:
       opts.programAction_ = DebugUnparseWithSymbols;
       break;
@@ -136,6 +139,9 @@ static InputKind ParseFrontendArgs(FrontendOptions &opts,
     case clang::driver::options::OPT_fdebug_dump_parse_tree:
       opts.programAction_ = DebugDumpParseTree;
       break;
+    case clang::driver::options::OPT_fdebug_dump_parse_tree_no_sema:
+      opts.programAction_ = DebugDumpParseTreeNoSema;
+      break;
     case clang::driver::options::OPT_fdebug_dump_provenance:
       opts.programAction_ = DebugDumpProvenance;
       break;