DebugLabelFolder ruthlessly deletes redundant labels. However, sometimes the redundant labels is referenced by debug info somewhere else. This patch provies a way so that dwarf writer can mark labels as used.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@68813 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/MachineModuleInfo.h

@@ -37,6 +37,7 @@
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/UniqueVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/CodeGen/MachineLocation.h"
 #include "llvm/GlobalValue.h"
@@ -115,6 +116,9 @@ private:
   // searchable format.
   SmallPtrSet<const Function *, 32> UsedFunctions;
 
+  /// UsedDbgLabels - labels are used by debug info entries.
+  SmallSet<unsigned, 8> UsedDbgLabels;
+
   bool CallsEHReturn;
   bool CallsUnwindInit;
  
@@ -195,6 +199,19 @@ public:
     return LabelID ? LabelIDList[LabelID - 1] : 0;
   }
 
+  /// isDbgLabelUsed - Return true if label with LabelID is used by
+  /// DwarfWriter.
+  bool isDbgLabelUsed(unsigned LabelID) {
+    return UsedDbgLabels.count(LabelID);
+  }
+  
+  /// RecordUsedDbgLabel - Mark label with LabelID as used. This is used
+  /// by DwarfWriter to inform DebugLabelFolder that certain labels are
+  /// not to be deleted.
+  void RecordUsedDbgLabel(unsigned LabelID) {
+    UsedDbgLabels.insert(LabelID);
+  }
+
   /// getFrameMoves - Returns a reference to a list of moves done in the current
   /// function's prologue.  Used to construct frame maps for debug and exception
   /// handling comsumers.