[Sema][OpenCL] Improve diagnostics for not viable overloadable function candidates

Summary:
Allowed extension name (that ought to be disabled) printing in the note message.

This diagnostic was proposed here: https://reviews.llvm.org/D51341

Reviewers: Anastasia, yaxunl

Reviewed By: Anastasia

Subscribers: cfe-commits, asavonic, bader

Differential Revision: https://reviews.llvm.org/D52292

llvm-svn: 344246
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index a9c5f7d..916f23c 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -1914,6 +1914,34 @@
   setOpenCLExtensionForDecl(D, CurrOpenCLExtension);
 }
 
+std::string Sema::getOpenCLExtensionsFromDeclExtMap(FunctionDecl *FD) {
+  if (!OpenCLDeclExtMap.empty())
+    return getOpenCLExtensionsFromExtMap(FD, OpenCLDeclExtMap);
+
+  return "";
+}
+
+std::string Sema::getOpenCLExtensionsFromTypeExtMap(FunctionType *FT) {
+  if (!OpenCLTypeExtMap.empty())
+    return getOpenCLExtensionsFromExtMap(FT, OpenCLTypeExtMap);
+
+  return "";
+}
+
+template <typename T, typename MapT>
+std::string Sema::getOpenCLExtensionsFromExtMap(T *FDT, MapT &Map) {
+  std::string ExtensionNames = "";
+  auto Loc = Map.find(FDT);
+
+  for (auto const& I : Loc->second) {
+    ExtensionNames += I;
+    ExtensionNames += " ";
+  }
+  ExtensionNames.pop_back();
+
+  return ExtensionNames;
+}
+
 bool Sema::isOpenCLDisabledDecl(Decl *FD) {
   auto Loc = OpenCLDeclExtMap.find(FD);
   if (Loc == OpenCLDeclExtMap.end())