[DebugInfo] Make children iterator bidirectional

Make the DIE iterator bidirectional so we can move to the previous
sibling of a DIE.

Differential revision: https://reviews.llvm.org/D49173

llvm-svn: 336823
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
index 0ef65c2..904ceab 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFDie.cpp
@@ -555,12 +555,24 @@
   return DWARFDie();
 }
 
+DWARFDie DWARFDie::getPreviousSibling() const {
+  if (isValid())
+    return U->getPreviousSibling(Die);
+  return DWARFDie();
+}
+
 DWARFDie DWARFDie::getFirstChild() const {
   if (isValid())
     return U->getFirstChild(Die);
   return DWARFDie();
 }
 
+DWARFDie DWARFDie::getLastChild() const {
+  if (isValid())
+    return U->getLastChild(Die);
+  return DWARFDie();
+}
+
 iterator_range<DWARFDie::attribute_iterator> DWARFDie::attributes() const {
   return make_range(attribute_iterator(*this, false),
                     attribute_iterator(*this, true));