[Flang][Driver] Add warning support for invalid R_Group options

With the R_Group options, invalid values e.g. '-Rpa' will not emit
a warning like clang. This patch enables warning reporting, as
well as suggestions on what option the user intended to select.

Depends on D158174 and D158436. The former, adds backend
support to R_Group options while the latter, implements
regex support with some tests refactoring that cause a merge
conflict.

Reviewed By: awarzynski

Differential Revision: https://reviews.llvm.org/D158593

flang/lib/FrontendTool/ExecuteCompilerInvocation.cpp

@@ -101,6 +101,18 @@ createFrontendAction(CompilerInstance &ci) {
   llvm_unreachable("Invalid program action!");
 }
 
+static void emitUnknownDiagWarning(clang::DiagnosticsEngine &diags,
+                                   clang::diag::Flavor flavor,
+                                   llvm::StringRef prefix,
+                                   llvm::StringRef opt) {
+  llvm::StringRef suggestion =
+      clang::DiagnosticIDs::getNearestOption(flavor, opt);
+  diags.Report(clang::diag::warn_unknown_diag_option)
+      << (flavor == clang::diag::Flavor::WarningOrError ? 0 : 1)
+      << (prefix.str() += std::string(opt)) << !suggestion.empty()
+      << (prefix.str() += std::string(suggestion));
+}
+
 // Remarks are ignored by default in Diagnostic.td, hence, we have to
 // enable them here before execution. Clang follows same idea using
 // ProcessWarningOptions in Warnings.cpp
@@ -123,6 +135,13 @@ updateDiagEngineForOptRemarks(clang::DiagnosticsEngine &diagsEng,
     if (!isPositive)
       remarkOpt = remarkOpt.substr(3);
 
+    // Verify that this is a valid optimization remarks option
+    if (diagIDs->getDiagnosticsInGroup(flavor, remarkOpt, diags)) {
+      emitUnknownDiagWarning(diagsEng, flavor, isPositive ? "-R" : "-Rno-",
+                             remarkOpt);
+      return;
+    }
+
     diagsEng.setSeverityForGroup(flavor, remarkOpt,
                                  isPositive ? clang::diag::Severity::Remark
                                             : clang::diag::Severity::Ignored);

flang/test/Driver/optimization-remark-invalid.f90

@@ -5,8 +5,15 @@
 ! Check error on invalid regex -Rpass message is emitted
 ! RUN: not %flang %s -O1 -Rpass=[ -c 2>&1 | FileCheck %s --check-prefix=REGEX-INVALID
 
+! Check "unknown remark option" warning
+! RUN: %flang %s -O1 -R -c 2>&1 | FileCheck %s --check-prefix=WARN
+
+! Check "unknown remark option" warning with suggestion
+! RUN: %flang %s -O1 -Rpas -c 2>&1 | FileCheck %s --check-prefix=WARN-SUGGEST
 
 ! REGEX-INVALID: error: in pattern '-Rpass=[': brackets ([ ]) not balanced
+! WARN: warning: unknown remark option '-R'
+! WARN-SUGGEST: warning: unknown remark option '-Rpas'; did you mean '-Rpass'?
 
 program forttest
 end program forttest