[OpenMP] Don't set rpath for system paths

[tstellar]

Summary

Suggested in https://reviews.llvm.org/D118493#3402001

[tstellar]

clang/lib/Driver/ToolChains/CommonArgs.cpp

799

I wasn't sure exactly how to determine if something is a system path, so I'm open to other ideas here.

[JonChesterfield]

I'm happy with this but agree that "what might be a system path?" is a tricky heuristic. What we want is to exclude the places that the application will search anyway, but that's OS dependent. I'm mostly worried about toolchains installed under /opt or under $HOME so this is good for me. It's also easy to pull later if we reconsider.

[MaskRay]

In D142174#4171731, @JonChesterfield wrote:

I'm happy with this but agree that "what might be a system path?" is a tricky heuristic. What we want is to exclude the places that the application will search anyway, but that's OS dependent. I'm mostly worried about toolchains installed under /opt or under $HOME so this is good for me. It's also easy to pull later if we reconsider.

Thank you for being considerate the use case. But I don't think we should base the decision on whether /usr/lib or /usr/lib64 is used and make directories different. We should unconditionally disable rpath, regardless of the directory path.

[tstellar]

-fopenmp-add-rpath has been removed.

clang/lib/Driver/ToolChains/CommonArgs.cpp

#endif
 
   // Handle remarks hotness/threshold related options.
   renderRemarksHotnessOptions(Args, CmdArgs, PluginOptPrefix);
 
   addMachineOutlinerArgs(D, Args, CmdArgs, ToolChain.getEffectiveTriple(),
                          /*IsLTO=*/true, PluginOptPrefix);
 }
 
+static bool isSystemPath(const StringRef &path) {
+  return llvm::StringSwitch<bool>(path)
+    .Case("/usr/lib", true)
+    .Case("/usr/lib64", true)
+    .Default(false);
+}
+
 void tools::addOpenMPRuntimeSpecificRPath(const ToolChain &TC,
                                           const ArgList &Args,
                                           ArgStringList &CmdArgs) {
 
   if (Args.hasFlag(options::OPT_fopenmp_implicit_rpath,
                    options::OPT_fno_openmp_implicit_rpath, true)) {
     // Default to clang lib / lib64 folder, i.e. the same location as device
     // runtime
     SmallString<256> DefaultLibPath =
         llvm::sys::path::parent_path(TC.getDriver().Dir);
     llvm::sys::path::append(DefaultLibPath, CLANG_INSTALL_LIBDIR_BASENAME);
+
+    // If clang is installed to a 'system path' there is no reason to add rpath.
+    if (isSystemPath(DefaultLibPath))
+      return;
+
     CmdArgs.push_back("-rpath");
     CmdArgs.push_back(Args.MakeArgString(DefaultLibPath));
   }
 }
 
 void tools::addOpenMPRuntimeLibraryPath(const ToolChain &TC,
                                         const ArgList &Args,
                                         ArgStringList &CmdArgs) {