[llvm-dlltool] Remove support for implying output name

[mstorsjo]

Summary

I don't see GNU dlltool supporting doing this; with only a -d option and no -l option, GNU dlltool runs successfully but doesn't output anything.

[mstorsjo]

For the record, while this might look like a surprising patch (removing functionality, why?), I noticed this while looking into the dlltool option -y (for generating a delayload import library). Dlltool has the options -l for specifying the output name of a normal import library, and the option -y for specifying the output name of a delayload import library. If using the -y option only, the current behaviour of implicitly picking an output name and writing to it, if no -l option was specified, seemed odd, and I noticed that GNU dlltool didn't actually have that behaviour.

(I don't have anything upstream-worthy regarding actually implementing the -y option in dlltool; the sole user so far, wine, managed to work around it and use the lld delayload option instead.)

[ruiu]

LGTM

lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

168–169

Nit: you can combine these two if with &&

lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

static MachineTypes getEmulation(StringRef S) {
   return StringSwitch<MachineTypes>(S)
       .Case("i386", IMAGE_FILE_MACHINE_I386)
       .Case("i386:x86-64", IMAGE_FILE_MACHINE_AMD64)
       .Case("arm", IMAGE_FILE_MACHINE_ARMNT)
       .Case("arm64", IMAGE_FILE_MACHINE_ARM64)
       .Default(IMAGE_FILE_MACHINE_UNKNOWN);
 }
 
-static std::string getImplibPath(StringRef Path) {
-  SmallString<128> Out = StringRef("lib");
-  Out.append(Path);
-  sys::path::replace_extension(Out, ".a");
-  return Out.str();
-}
-
 int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
   DllOptTable Table;
   unsigned MissingIndex;
   unsigned MissingCount;
   llvm::opt::InputArgList Args =
       Table.ParseArgs(ArgsArr.slice(1), MissingIndex, MissingCount);
   if (MissingCount) {
     llvm::errs() << Args.getArgString(MissingIndex) << ": missing argument\n";
if (auto *Arg = Args.getLastArg(OPT_D))
     Def->OutputFile = Arg->getValue();
 
   if (Def->OutputFile.empty()) {
     llvm::errs() << "no DLL name specified\n";
     return 1;
   }
 
   std::string Path = Args.getLastArgValue(OPT_l);
-  if (Path.empty())
-    Path = getImplibPath(Def->OutputFile);
 
   if (Machine == IMAGE_FILE_MACHINE_I386 && Args.getLastArg(OPT_k)) {
     for (COFFShortExport& E : Def->Exports) {
       if (!E.AliasTarget.empty() || (!E.Name.empty() && E.Name[0] == '?'))
         continue;
       E.SymbolName = E.Name;
       // Trim off the trailing decoration. Symbols will always have a
       // starting prefix here (either _ for cdecl/stdcall, @ for fastcall
       // or ? for C++ functions). Vectorcall functions won't have any
       // fixed prefix, but the function base name will still be at least
       // one char.
       E.Name = E.Name.substr(0, E.Name.find('@', 1));
       // By making sure E.SymbolName != E.Name for decorated symbols,
       // writeImportLibrary writes these symbols with the type
       // IMPORT_NAME_UNDECORATE.
     }
   }
 
+  if (!Path.empty())
     if (writeImportLibrary(Def->OutputFile, Path, Def->Exports, Machine, true))
       return 1;
   return 0;
 }