Always pass a diagnostic handler to the linker.

Before this patch the diagnostic handler was optional. If it was not
passed, the one in the LLVMContext was used.

That is probably not a pattern we want to follow. If each area has an
optional callback, there is a sea of callbacks and it is hard to follow
which one is called.

Doing this also found cases where the callback is a nice addition, like
testing that no errors or warnings are reported.

The other option is to always use the diagnostic handler in the
LLVMContext. That has a few problems

* To implement the C API we would have to set the diag handler and then
  set it back to the original value.
* Code that creates the context might be far away from code that wants
  the diagnostics.

I do have a patch that implements the second option and will send that as
an RFC.

llvm-svn: 254777

llvm/lib/LTO/LTOCodeGenerator.cpp

@@ -65,9 +65,10 @@ const char* LTOCodeGenerator::getVersionString() {
 }
 
 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
-    : Context(Context),
-      MergedModule(new Module("ld-temp.o", Context)),
-      IRLinker(new Linker(*MergedModule)) {
+    : Context(Context), MergedModule(new Module("ld-temp.o", Context)),
+      IRLinker(new Linker(*MergedModule, [this](const DiagnosticInfo &DI) {
+        MergedModule->getContext().diagnose(DI);
+      })) {
   initializeLTOPasses();
 }
 
@@ -123,7 +124,8 @@ void LTOCodeGenerator::setModule(std::unique_ptr<LTOModule> Mod) {
   AsmUndefinedRefs.clear();
 
   MergedModule = Mod->takeModule();
-  IRLinker = make_unique<Linker>(*MergedModule);
+  IRLinker =
+      make_unique<Linker>(*MergedModule, IRLinker->getDiagnosticHandler());
 
   const std::vector<const char*> &Undefs = Mod->getAsmUndefinedRefs();
   for (int I = 0, E = Undefs.size(); I != E; ++I)