[LLD][MinGW] Support --allow-multiple-definition

[Ericson2314]

Summary

We want the Clang CrossWindows toolchain to work with ld.lld and ld.bfd
alike, and it uses this, so we need to support this.

[mstorsjo]

Looks nice in general, but a couple minor details

lld/MinGW/Options.td

29

Nit: Stray empty line added here

lld/test/MinGW/driver.test

44

The newly added option in Options.td is for --allow-multiple-definition without a trailing s, but here you're testing with a trailing s. I presume it should be without s, as that's what ld.bfd supports, and that's what Clang's CrossWindows driver supports.

Two notes though: ld.bfd supports this option with both one and two leading dashes, and we try to match that as far as possible. (Previously lld was quite inconsistent wrt which options happened to handle both cases, but I tried cleaning it up some months ago.)

Secondly, ld.bfd doesn't seem to support the negative form. We can still add support for that (since it makes sense to have both forms), but do add a comment somewhere noting that only the nonnegated form matches ld.bfd.

lld/MinGW/Driver.cpp

if (args.hasArg(OPT_major_os_version, OPT_minor_os_version,
     StringRef minor = minOSVer ? minOSVer->getValue()
                                : minSubSysVer ? minSubSysVer->getValue() : "";
     StringRef sep = minor.empty() ? "" : ".";
     add("-subsystem:" + subSys + "," + major + sep + minor);
   } else if (auto *a = args.getLastArg(OPT_subs)) {
     add("-subsystem:" + StringRef(a->getValue()));
   }
 
+  if (args.hasFlag(OPT_allow_multiple_definition, OPT_no_allow_multiple_definition, false))
+    add("-force:multiple");
   if (auto *a = args.getLastArg(OPT_out_implib))
     add("-implib:" + StringRef(a->getValue()));
   if (auto *a = args.getLastArg(OPT_stack))
     add("-stack:" + StringRef(a->getValue()));
   if (auto *a = args.getLastArg(OPT_output_def))
     add("-output-def:" + StringRef(a->getValue()));
   if (auto *a = args.getLastArg(OPT_image_base))
     add("-base:" + StringRef(a->getValue()));

lld/MinGW/Options.td

multiclass EqLong<string name, string help> {
   def NAME # _eq: Joined<["--"], name # "=">, Alias<!cast<Separate>(NAME)>,
     HelpText<help>;
 }
 
 def L: JoinedOrSeparate<["-"], "L">, MetaVarName<"<dir>">,
   HelpText<"Add a directory to the library search path">;
 def Bdynamic: F<"Bdynamic">, HelpText<"Link against shared libraries">;
 def Bstatic: F<"Bstatic">, HelpText<"Do not link against shared libraries">;
+
+defm allow_multiple_definition: B<"allow-multiple-definition",
+    "Allow multiple definitions",
+    "Do not allow multiple definitions (default)">;
+
 def dynamicbase: F<"dynamicbase">, HelpText<"Enable ASLR">;
+
 defm entry: Eq<"entry", "Name of entry point symbol">, MetaVarName<"<entry>">;
 def exclude_all_symbols: F<"exclude-all-symbols">,
     HelpText<"Don't automatically export any symbols">;
 def export_all_symbols: F<"export-all-symbols">,
     HelpText<"Export all symbols even if a def file or dllexport attributes are used">;
 def gc_sections: F<"gc-sections">, HelpText<"Remove unused sections">;
 def help: F<"help">, HelpText<"Print option help">;
 def icf: J<"icf=">, HelpText<"Identical code folding">;

lld/test/MinGW/driver.test

 
 RUN: ld.lld -### foo.o -m i386pep -shared FOO.DEF | FileCheck -check-prefix=DEF2 %s
 DEF2: -def:FOO.DEF
 
 RUN: ld.lld -### foo.o -m i386pep -obar.exe | FileCheck -check-prefix=OUT %s
 RUN: ld.lld -### foo.o -m i386pep -o bar.exe | FileCheck -check-prefix=OUT %s
 OUT: -out:bar.exe
 
+RUN: ld.lld -### foo.o -m i386pep --allow-multiple-definitions | FileCheck -check-prefix=FORCE_MULTIPLE %s
+RUN: ld.lld -### foo.o -m i386pep --no-allow-multiple-definitions --allow-multiple-definitions | FileCheck -check-prefix=FORCE_MULTIPLE %s
+FORCE_MULTIPLE: -force:multiple
+
+RUN: ld.lld -### foo.o -m i386pep --no-allow-multiple-definitions | FileCheck -check-prefix=NO_FORCE_MULTIPLE %s
+RUN: ld.lld -### foo.o -m i386pep --allow-multiple-definitions --no-allow-multiple-definitions | FileCheck -check-prefix=NO_FORCE_MULTIPLE %s
+NO_FORCE_MULTIPLE-NOT: -force:multiple
+
 RUN: ld.lld -### foo.o -m i386pep --out-implib bar | FileCheck -check-prefix=IMPLIB %s
 RUN: ld.lld -### foo.o -m i386pep --out-implib=bar | FileCheck -check-prefix=IMPLIB %s
 RUN: ld.lld -### foo.o -m i386pep -out-implib bar | FileCheck -check-prefix=IMPLIB %s
 RUN: ld.lld -### foo.o -m i386pep -out-implib=bar | FileCheck -check-prefix=IMPLIB %s
 IMPLIB: -implib:bar
 
 RUN: ld.lld -### foo.o -m i386pep -e bar | FileCheck -check-prefix=ENTRY %s
 RUN: ld.lld -### foo.o -m i386pep -ebar | FileCheck -check-prefix=ENTRY %s