[clang] NFC: Use compile-time option spelling when generating command line

[jansvoboda11]

Summary

When generating command lines, use the option spelling generated by TableGen (StringLiteral) instead of constructing it at runtime. This saves some needless allocations.

Depends on D157029.

[jansvoboda11]

Rebase

[MaskRay]

Thanks!

clang/lib/Frontend/CompilerInvocation.cpp

static unsigned getOptimizationLevelSize(ArgList &Args) {
   }
   return 0;
 }
 
 static void GenerateArg(SmallVectorImpl<const char *> &Args,
                         llvm::opt::OptSpecifier OptSpecifier,
                         CompilerInvocation::StringAllocator SA) {
   Option Opt = getDriverOptTable().getOption(OptSpecifier);
-  denormalizeSimpleFlag(Args, SA(Opt.getPrefix() + Opt.getName()), SA,
+  denormalizeSimpleFlag(Args, Opt.getSpelling(), SA,
                         Option::OptionClass::FlagClass, 0);
 }
 
 static void GenerateArg(SmallVectorImpl<const char *> &Args,
                         llvm::opt::OptSpecifier OptSpecifier,
                         const Twine &Value,
                         CompilerInvocation::StringAllocator SA) {
   Option Opt = getDriverOptTable().getOption(OptSpecifier);
-  denormalizeString(Args, SA(Opt.getPrefix() + Opt.getName()), SA,
-                    Opt.getKind(), 0, Value);
+  denormalizeString(Args, Opt.getSpelling(), SA, Opt.getKind(), 0, Value);
 }
 
 // Parse command line arguments into CompilerInvocation.
 using ParseFn =
     llvm::function_ref<bool(CompilerInvocation &, ArrayRef<const char *>,
                             DiagnosticsEngine &, const char *)>;
 
 // Generate command line arguments from CompilerInvocation.