[LLD] [COFF] Require an explicit -implib option for creating implibs in mingw mode

[mstorsjo]

Summary

GNU ld doesn't produce implibs unless explicitly requested.

Is the test command ok to use in lit tests, is that one of the commands that can be assumed to be available for all users, or is there a better way for testing whether a file exists? (I guess some other dummy command that inspects the file also would work...)

[ruiu]

LGTM

COFF/Driver.cpp

1852 ↗

(On Diff #215670)

... In MinGW mode, we do that only when -implib option is explicitly given for compatibility with GNU ld.

test/COFF/implib-name-mingw.test

13 ↗

(On Diff #215670)

I believe using test command is OK, as we are already using some other basic commands such as tar.

[rnk]

I checked, and the test command is in Chromium's gnuwin tools package. There must be an existing test that uses it, since we wouldn't have added it for any other reason. :)

[mstorsjo]

COFF/Driver.cpp

1862 ↗

(On Diff #215670)

Committed this with a minor twek here; we still need to run fixupExports and assignExportOrdinals, even if we aren't writing the import library.

lld/trunk/COFF/Driver.cpp

for (auto i = ObjFile::instances.begin(), e = ObjFile::instances.end();
         ObjFile::instances.erase(i);
         ObjFile::instances.push_back(file);
         break;
       }
     }
   }
 
   // Windows specific -- when we are creating a .dll file, we also
-  // need to create a .lib file.
+  // need to create a .lib file. In MinGW mode, we only do that when the
+  // -implib option is given explicitly, for compatibility with GNU ld.
   if (!config->exports.empty() || config->dll) {
     fixupExports();
+    if (!config->mingw || !config->implib.empty())
       createImportLibrary(/*asLib=*/false);
     assignExportOrdinals();
   }
 
   // Handle /output-def (MinGW specific).
   if (auto *arg = args.getLastArg(OPT_output_def))
     writeDefFile(arg->getValue());
 
   // Set extra alignment for .comm symbols

lld/trunk/test/COFF/implib-name-mingw.test

+REQUIRES: x86
+RUN: mkdir -p %t-out
+RUN: llvm-mc -triple x86_64-windows-gnu -filetype obj -o %t-out/object.obj %S/Inputs/object.s
+
+Check that linking without an explicit -implib doesn't produce any implib.
+
+First test that linking without -lldmingw does produce an implib, but when
+adding -lldmingw, it no longer is produced. And when it is explicitly named,
+it is created.
+
+RUN: rm -f %t-out/library.lib
+RUN: lld-link -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console
+RUN: test -f %t-out/library.lib
+
+RUN: rm -f %t-out/library.lib
+RUN: lld-link -lldmingw -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console
+RUN: not test -f %t-out/library.lib
+
+RUN: lld-link -lldmingw -dll -machine:x64 -def:%S/Inputs/named.def -out:%t-out/library.dll %t-out/object.obj -entry:f -subsystem:console -implib:%t-out/library.lib
+RUN: test -f %t-out/library.lib