[clang][cli] Accept option spelling as `Twine`

[jansvoboda11]

Summary

This will make it possible to accept the spelling as StringLiteral in D157029 and avoid some unnecessary allocations in a later patch.

[benlangmuir]

This code asserts that the Twine is a single stringref, but it's also relying on the fact it's null-terminated; can we check for that as well, or at least document it?

[jansvoboda11]

Assert that spelling is null-terminated

[jansvoboda11]

That's a good point. Updated.

clang/lib/Frontend/CompilerInvocation.cpp

static std::optional<bool> normalizeSimpleNegativeFlag(OptSpecifier Opt,
   return std::nullopt;
 }
 
 /// The tblgen-erated code passes in a fifth parameter of an arbitrary type, but
 /// denormalizeSimpleFlags never looks at it. Avoid bloating compile-time with
 /// unnecessary template instantiations and just ignore it with a variadic
 /// argument.
 static void denormalizeSimpleFlag(SmallVectorImpl<const char *> &Args,
-                                  const char *Spelling,
+                                  const Twine &Spelling,
                                   CompilerInvocation::StringAllocator,
                                   Option::OptionClass, unsigned, /*T*/...) {
-  Args.push_back(Spelling);
+  // Spelling is already allocated or a static string, no need to call SA.
+  Args.push_back(Spelling.getSingleStringRef().data());
 }
 
 template <typename T> static constexpr bool is_uint64_t_convertible() {
   return !std::is_same_v<T, uint64_t> && llvm::is_integral_or_enum<T>::value;
 }
 
 template <typename T,
           std::enable_if_t<!is_uint64_t_convertible<T>(), bool> = false>
return [Value, OtherValue,
     if (const Arg *A = Args.getLastArg(Opt, OtherOpt)) {
       return A->getOption().matches(Opt) ? Value : OtherValue;
     }
     return std::nullopt;
   };
 }
 
 static auto makeBooleanOptionDenormalizer(bool Value) {
-  return [Value](SmallVectorImpl<const char *> &Args, const char *Spelling,
+  return [Value](SmallVectorImpl<const char *> &Args, const Twine &Spelling,
                  CompilerInvocation::StringAllocator, Option::OptionClass,
                  unsigned, bool KeyPath) {
     if (KeyPath == Value)
-      Args.push_back(Spelling);
+      // Spelling is already allocated or a static string, no need to call SA.
+      Args.push_back(Spelling.getSingleStringRef().data());
   };
 }
 
 static void denormalizeStringImpl(SmallVectorImpl<const char *> &Args,
-                                  const char *Spelling,
+                                  const Twine &Spelling,
                                   CompilerInvocation::StringAllocator SA,
                                   Option::OptionClass OptClass, unsigned,
                                   const Twine &Value) {
   switch (OptClass) {
   case Option::SeparateClass:
   case Option::JoinedOrSeparateClass:
   case Option::JoinedAndSeparateClass:
-    Args.push_back(Spelling);
+    // Spelling is already allocated or a static string, no need to call SA.
+    Args.push_back(Spelling.getSingleStringRef().data());
     Args.push_back(SA(Value));
     break;
   case Option::JoinedClass:
   case Option::CommaJoinedClass:
     Args.push_back(SA(Twine(Spelling) + Value));
     break;
   default:
     llvm_unreachable("Cannot denormalize an option with option class "
                      "incompatible with string denormalization.");
   }
 }
 
 template <typename T>
 static void
-denormalizeString(SmallVectorImpl<const char *> &Args, const char *Spelling,
+denormalizeString(SmallVectorImpl<const char *> &Args, const Twine &Spelling,
                   CompilerInvocation::StringAllocator SA,
                   Option::OptionClass OptClass, unsigned TableIndex, T Value) {
   denormalizeStringImpl(Args, Spelling, SA, OptClass, TableIndex, Twine(Value));
 }
 
 static std::optional<SimpleEnumValue>
 findValueTableByName(const SimpleEnumValueTable &Table, StringRef Name) {
   for (int I = 0, E = Table.Size; I != E; ++I)
if (auto MaybeEnumVal = findValueTableByName(Table, ArgValue))
     return MaybeEnumVal->Value;
 
   Diags.Report(diag::err_drv_invalid_value)
       << Arg->getAsString(Args) << ArgValue;
   return std::nullopt;
 }
 
 static void denormalizeSimpleEnumImpl(SmallVectorImpl<const char *> &Args,
-                                      const char *Spelling,
+                                      const Twine &Spelling,
                                       CompilerInvocation::StringAllocator SA,
                                       Option::OptionClass OptClass,
                                       unsigned TableIndex, unsigned Value) {
   assert(TableIndex < SimpleEnumValueTablesSize);
   const SimpleEnumValueTable &Table = SimpleEnumValueTables[TableIndex];
   if (auto MaybeEnumVal = findValueTableByValue(Table, Value)) {
     denormalizeString(Args, Spelling, SA, OptClass, TableIndex,
                       MaybeEnumVal->Name);
   } else {
     llvm_unreachable("The simple enum value was not correctly defined in "
                      "the tablegen option description");
   }
 }
 
 template <typename T>
 static void denormalizeSimpleEnum(SmallVectorImpl<const char *> &Args,
-                                  const char *Spelling,
+                                  const Twine &Spelling,
                                   CompilerInvocation::StringAllocator SA,
                                   Option::OptionClass OptClass,
                                   unsigned TableIndex, T Value) {
   return denormalizeSimpleEnumImpl(Args, Spelling, SA, OptClass, TableIndex,
                                    static_cast<unsigned>(Value));
 }
 
 static std::optional<std::string> normalizeString(OptSpecifier Opt,

 
 static std::optional<std::vector<std::string>>
 normalizeStringVector(OptSpecifier Opt, int, const ArgList &Args,
                       DiagnosticsEngine &) {
   return Args.getAllArgValues(Opt);
 }
 
 static void denormalizeStringVector(SmallVectorImpl<const char *> &Args,
-                                    const char *Spelling,
+                                    const Twine &Spelling,
                                     CompilerInvocation::StringAllocator SA,
                                     Option::OptionClass OptClass,
                                     unsigned TableIndex,
                                     const std::vector<std::string> &Values) {
   switch (OptClass) {
   case Option::CommaJoinedClass: {
     std::string CommaJoinedValue;
     if (!Values.empty()) {