[opt] Report if the provided architecture is invalid.

[fhahn]

Summary

Partly addresses PR15026.

There are a few tests that passed in invalid architectures, which are fixed in: rL355349 and D58931

[efriedma]

LGTM

llvm/tools/opt/opt.cpp

644

I would probably say "unrecognized architecture" or something like that... but that's just nitpicking.

[fhahn]

Thanks Eli! I've updated the message to say unrecognized, which sounds better to me too.

llvm/tools/opt/opt.cpp

#endif
   std::string CPUStr, FeaturesStr;
   TargetMachine *Machine = nullptr;
   const TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
 
   if (ModuleTriple.getArch()) {
     CPUStr = getCPUStr();
     FeaturesStr = getFeaturesStr();
     Machine = GetTargetMachine(ModuleTriple, CPUStr, FeaturesStr, Options);
+  } else if (ModuleTriple.getArchName() != "unknown" &&
+             ModuleTriple.getArchName() != "") {
+    errs() << argv[0] << ": invalid architecture '"
+           << ModuleTriple.getArchName() << "' provided.\n";
+    return 1;
   }
 
   std::unique_ptr<TargetMachine> TM(Machine);
 
   // Override function attributes based on CPUStr, FeaturesStr, and command line
   // flags.
   setFunctionAttributes(CPUStr, FeaturesStr, *M);