[OpenMP] Make default OpenMP library (the one selected with just -fopenmp) configurable in the CMake build. There shouldn't be any change in default behavior.

[klimek]

CMakeLists.txt

447–448

Add comment explaining the space in the end.

[djasper]

CMakeLists.txt

447–448

Removed. I don't think it is necessary.

[rsmith]

lib/Driver/Tools.cpp

6294–6309

It seems bad to silently not link against any OpenMP library if the value for OPENMP_DEFAULT_LIB is unknown. Maybe either OPENMP_DEFAULT_LIB should be a lib name that we blindly add to the link line ("-l" #OPENMP_DEFAULT_LIB), or we should check the value is valid in CMakeLists.txt.

6295

Hm, are you expecting the -D value to already include the double-quotes? If not, this looks wrong. And if so, you should not be adding a trailing space in CMakeLists.txt.

[rsmith]

I switched to specifying a library name in OPENMP_DEFAULT_LIB (to support cases where people ship libiomp5 under a different name) and commited as r237850.

CMakeLists.txt

 if(CLANG_ENABLE_ARCMT)
   add_definitions(-DCLANG_ENABLE_ARCMT)
   add_definitions(-DCLANG_ENABLE_OBJC_REWRITER)
 endif()
 if(CLANG_ENABLE_STATIC_ANALYZER)
   add_definitions(-DCLANG_ENABLE_STATIC_ANALYZER)
 endif()
 
+set(OPENMP_DEFAULT_LIB "" CACHE STRING
+  "OpenMP library used with -fopenmp.")
+
+if( OPENMP_DEFAULT_LIB )
+  add_definitions( -DOPENMP_DEFAULT_LIB="${OPENMP_DEFAULT_LIB} " )
+endif()
+
 # Clang version information
 set(CLANG_EXECUTABLE_VERSION
      "${CLANG_VERSION_MAJOR}.${CLANG_VERSION_MINOR}" CACHE STRING
     "Version number that will be placed into the clang executable, in the form XX.YY")
 set(LIBCLANG_LIBRARY_VERSION
      "${CLANG_VERSION_MAJOR}.${CLANG_VERSION_MINOR}" CACHE STRING
     "Version number that will be placed into the libclang library , in the form XX.YY")
 mark_as_advanced(CLANG_EXECUTABLE_VERSION LIBCLANG_LIBRARY_VERSION)

lib/Driver/Tools.cpp

void darwin::Link::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (!Args.hasArg(options::OPT_nostdlib) &&
       !Args.hasArg(options::OPT_nostartfiles))
     getMachOToolChain().addStartObjectFileArgs(Args, CmdArgs);
 
   Args.AddAllArgs(CmdArgs, options::OPT_L);
 
   LibOpenMP UsedOpenMPLib = LibUnknown;
-  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
-    UsedOpenMPLib = llvm::StringSwitch<LibOpenMP>(A->getValue())
+  auto OpenMPStringToVersion = [](StringRef OpenMPString) {
+    return llvm::StringSwitch<LibOpenMP>(OpenMPString)
         .Case("libgomp",  LibGOMP)
         .Case("libiomp5", LibIOMP5)
         .Default(LibUnknown);
+  };
+  if (const Arg *A = Args.getLastArg(options::OPT_fopenmp_EQ)) {
+    UsedOpenMPLib = OpenMPStringToVersion(A->getValue());
     if (UsedOpenMPLib == LibUnknown)
       getToolChain().getDriver().Diag(diag::err_drv_unsupported_option_argument)
         << A->getOption().getName() << A->getValue();
   } else if (Args.hasArg(options::OPT_fopenmp)) {
+#if defined(OPENMP_DEFAULT_LIB)
+    UsedOpenMPLib = OpenMPStringToVersion(OPENMP_DEFAULT_LIB);
+#else
     UsedOpenMPLib = LibIOMP5;
+#endif
   }
   switch (UsedOpenMPLib) {
   case LibGOMP:
     CmdArgs.push_back("-lgomp");
     break;
   case LibIOMP5:
     CmdArgs.push_back("-liomp5");
     break;
   case LibUnknown:
     break;
   }
 
   AddLinkerInputs(getToolChain(), Inputs, Args, CmdArgs);
   // Build the input file for -filelist (list of linker input files) in case we
   // need it later
   for (const auto &II : Inputs) {
     if (!II.isFilename()) {
       // This is a linker input argument.
       // We cannot mix input arguments and file names in a -filelist input, thus