[CodeGen] Refactor warn() to use StringRef (NFCI) (#127537)

closes #100064

Author: vortex73

llvm/include/llvm/CGData/CodeGenData.h

@@ -265,7 +265,7 @@ std::unique_ptr<Module> loadModuleForTwoRounds(BitcodeModule &OrigModule,
 Expected<stable_hash> mergeCodeGenData(ArrayRef<StringRef> ObjectFiles);
 
 void warn(Error E, StringRef Whence = "");
-void warn(Twine Message, std::string Whence = "", std::string Hint = "");
+void warn(Twine Message, StringRef Whence = "", StringRef Hint = "");
 
 } // end namespace cgdata
 

llvm/lib/CGData/CodeGenData.cpp

@@ -204,7 +204,7 @@ Expected<Header> Header::readFromBuffer(const unsigned char *Curr) {
 
 namespace cgdata {
 
-void warn(Twine Message, std::string Whence, std::string Hint) {
+void warn(Twine Message, StringRef Whence, StringRef Hint) {
   WithColor::warning();
   if (!Whence.empty())
     errs() << Whence << ": ";
@@ -216,7 +216,7 @@ void warn(Twine Message, std::string Whence, std::string Hint) {
 void warn(Error E, StringRef Whence) {
   if (E.isA<CGDataError>()) {
     handleAllErrors(std::move(E), [&](const CGDataError &IPE) {
-      warn(IPE.message(), Whence.str(), "");
+      warn(IPE.message(), Whence, "");
     });
   }
 }