[DWARF] Emit a split line table only if there are split type units.

A .debug_info.dwo section doesn't use the .debug_line.dwo section.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@326395 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -2105,6 +2105,8 @@ void DwarfDebug::emitDebugAbbrevDWO() {
 
 void DwarfDebug::emitDebugLineDWO() {
   assert(useSplitDwarf() && "No split dwarf?");
+  if (!HasSplitTypeUnits)
+    return;
   Asm->OutStreamer->SwitchSection(
       Asm->getObjFileLowering().getDwarfLineDWOSection());
   SplitTypeUnitFileTable.Emit(*Asm->OutStreamer, MCDwarfLineTableParams());
@@ -2220,6 +2222,7 @@ void DwarfDebug::addDwarfTypeUnitType(DwarfCompileUnit &CU,
       InfoHolder.computeSizeAndOffsetsForUnit(TU.first.get());
       InfoHolder.emitUnit(TU.first.get(), useSplitDwarf());
     }
+    HasSplitTypeUnits = useSplitDwarf();
   }
   CU.addDIETypeSignature(RefDie, Signature);
 }

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -274,6 +274,10 @@ class DwarfDebug : public DebugHandlerBase {
   /// a monolithic sequence of string offsets.
   bool UseSegmentedStringOffsetsTable;
 
+  /// Whether we have emitted any type units with split DWARF (and therefore
+  /// need to emit a line table to the .dwo file).
+  bool HasSplitTypeUnits = false;
+
   /// Separated Dwarf Variables
   /// In general these will all be for bits that are left in the
   /// original object file, rather than things that are meant

test/DebugInfo/Generic/empty.ll

@@ -16,7 +16,9 @@
 ; CHECK: contents:
 
 ; Don't emit DW_AT_addr_base when there are no addresses.
+; Also don't emit a split line table when there are no type units.
 ; FISSION-NOT: DW_AT_GNU_addr_base [DW_FORM_sec_offset]
+; FISSION-NOT: .debug_line.dwo contents:
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!5}