[ClangDiagnostics] Silence warning about fallthrough after PrintFatalError

[xbolva00]

Summary

ClangDiagnosticsEmitter.cpp:1047:57: warning: this statement may fall through [-Wimplicit-fallthrough=]

Builder.PrintFatalError("Unknown modifier type: " + Modifier);
                        ~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~

ClangDiagnosticsEmitter.cpp:1048:5: note: here

case MT_Select: {
              ^

[rtrieu]

Instead of adding a break, you should add a noreturn attribute to the PrintFatalError function. LLVM has the macro LLVM_ATTRIBUTE_NORETURN to do this. You can confirm that PrintFatalError is a noreturn function by seeing that it unconditionally calls llvm::PrintFatalError which itself is attributed with LLVM_ATTRIBUTE_NORETURN.

[xbolva00]

Add correct NORETURN attribute

[xbolva00]

Ok?

[rtrieu]

lgtm

utils/TableGen/ClangDiagnosticsEmitter.cpp

struct DiagnosticTextBuilder {
 
   Piece *getSubstitution(SubstitutionPiece *S) const {
     auto It = Substitutions.find(S->Name);
     if (It == Substitutions.end())
       PrintFatalError("Failed to find substitution with name: " + S->Name);
     return It->second.Root;
   }
 
-  void PrintFatalError(llvm::Twine const &Msg) const {
+  LLVM_ATTRIBUTE_NORETURN void PrintFatalError(llvm::Twine const &Msg) const {
     assert(EvaluatingRecord && "not evaluating a record?");
     llvm::PrintFatalError(EvaluatingRecord->getLoc(), Msg);
   }
 
 private:
   struct DiagText {
     DiagnosticTextBuilder &Builder;
     std::vector<Piece *> AllocatedPieces;