[NVPTX] Avoid a crash when 'llc' is called with '-filetype=null'

[ikudrin]

Summary

For -filetype=null, NVPTXTargetStreamer is not created, so the return value of OutStreamer->getTargetStreamer() should be checked before calling the methods.

This fixes a crash in llvm/test/tools/llc/binutils-version.ll when LLVM is built with nvptx64-nvidia-cuda as a default target.

[MaskRay]

Add a regression test in llvm/test/CodeGen/NVPTX like test/tools/llc/filetype-null-stop-after.ll ?

llvm/lib/Target/NVPTX/NVPTXAsmPrinter.cpp

if (!GlobalsEmitted) {
     GlobalsEmitted = true;
   }
 
   // call doFinalization
   bool ret = AsmPrinter::doFinalization(M);
 
   clearAnnotationCache(&M);
 
+  if (auto *TS = static_cast<NVPTXTargetStreamer *>(
+          OutStreamer->getTargetStreamer())) {
     // Close the last emitted section
     if (HasDebugInfo) {
-    static_cast<NVPTXTargetStreamer *>(OutStreamer->getTargetStreamer())
-        ->closeLastSection();
+      TS->closeLastSection();
       // Emit empty .debug_loc section for better support of the empty files.
       OutStreamer->emitRawText("\t.section\t.debug_loc\t{\t}");
     }
 
     // Output last DWARF .file directives, if any.
-  static_cast<NVPTXTargetStreamer *>(OutStreamer->getTargetStreamer())
-      ->outputDwarfFileDirectives();
+    TS->outputDwarfFileDirectives();
+  }
 
   return ret;
 
   //bool Result = AsmPrinter::doFinalization(M);
   // Instead of calling the parents doFinalization, we may
   // clone parents doFinalization and customize here.
   // Currently, we if NVISA out the EmitGlobals() in
   // parent's doFinalization, which is too intrusive.

llvm/test/CodeGen/NVPTX/filetype-null.ll

+; Check that 'llc' does not crash if '-filetype=null' is used.
+
+; RUN: llc %s -filetype=null -march=nvptx -o -
+; RUN: llc %s -filetype=null -march=nvptx64 -o -