--- a/utils/gdb-scripts/prettyprinters.py	Fri Nov 25 19:14:25 2016 +0900
+++ b/utils/gdb-scripts/prettyprinters.py	Fri Oct 27 17:07:41 2017 +0900
@@ -103,9 +103,218 @@
   def display_hint (self):
     return 'array'
 
+class OptionalPrinter:
+  """Print an llvm::Optional object."""
+
+  def __init__(self, value):
+    self.value = value
+
+  class _iterator:
+    def __init__(self, member, empty):
+      self.member = member
+      self.done = empty
+
+    def __iter__(self):
+      return self
+
+    def next(self):
+      if self.done:
+        raise StopIteration
+      self.done = True
+      return ('value', self.member.dereference())
+
+  def children(self):
+    if not self.value['hasVal']:
+      return self._iterator('', True)
+    return self._iterator(self.value['storage']['buffer'].address.cast(self.value.type.template_argument(0).pointer()), False)
+
+  def to_string(self):
+    return 'llvm::Optional is %sinitialized' % ('' if self.value['hasVal'] else 'not ')
+
+class DenseMapPrinter:
+  "Print a DenseMap"
+
+  class _iterator:
+    def __init__(self, key_info_t, begin, end):
+      self.key_info_t = key_info_t
+      self.cur = begin
+      self.end = end
+      self.advancePastEmptyBuckets()
+      self.first = True
+
+    def __iter__(self):
+      return self
+
+    def advancePastEmptyBuckets(self):
+      # disabled until the comments below can be addressed
+      # keeping as notes/posterity/hints for future contributors
+      return
+      n = self.key_info_t.name
+      is_equal = gdb.parse_and_eval(n + '::isEqual')
+      empty = gdb.parse_and_eval(n + '::getEmptyKey()')
+      tombstone = gdb.parse_and_eval(n + '::getTombstoneKey()')
+      # the following is invalid, GDB fails with:
+      #   Python Exception <class 'gdb.error'> Attempt to take address of value
+      #   not located in memory.
+      # because isEqual took parameter (for the unsigned long key I was testing)
+      # by const ref, and GDB
+      # It's also not entirely general - we should be accessing the "getFirst()"
+      # member function, not the 'first' member variable, but I've yet to figure
+      # out how to find/call member functions (especially (const) overloaded
+      # ones) on a gdb.Value.
+      while self.cur != self.end and (is_equal(self.cur.dereference()['first'], empty) or is_equal(self.cur.dereference()['first'], tombstone)):
+        self.cur = self.cur + 1
+
+    def next(self):
+      if self.cur == self.end:
+        raise StopIteration
+      cur = self.cur
+      v = cur.dereference()['first' if self.first else 'second']
+      if not self.first:
+        self.cur = self.cur + 1
+        self.advancePastEmptyBuckets()
+        self.first = True
+      else:
+        self.first = False
+      return 'x', v
+
+  def __init__(self, val):
+    self.val = val
+
+  def children(self):
+    t = self.val.type.template_argument(3).pointer()
+    begin = self.val['Buckets'].cast(t)
+    end = (begin + self.val['NumBuckets']).cast(t)
+    return self._iterator(self.val.type.template_argument(2), begin, end)
+
+  def to_string(self):
+    return 'llvm::DenseMap with %d elements' % (self.val['NumEntries'])
+
+  def display_hint(self):
+    return 'map'
+
+class TwinePrinter:
+  "Print a Twine"
+
+  def __init__(self, val):
+    self._val = val
+
+  def display_hint(self):
+    return 'string'
+
+  def string_from_pretty_printer_lookup(self, val):
+    '''Lookup the default pretty-printer for val and use it.
+
+    If no pretty-printer is defined for the type of val, print an error and
+    return a placeholder string.'''
+
+    pp = gdb.default_visualizer(val)
+    if pp:
+      s = pp.to_string()
+
+      # The pretty-printer may return a LazyString instead of an actual Python
+      # string.  Convert it to a Python string.  However, GDB doesn't seem to
+      # register the LazyString type, so we can't check
+      # "type(s) == gdb.LazyString".
+      if 'LazyString' in type(s).__name__:
+        s = s.value().address.string()
+
+    else:
+      print(('No pretty printer for {} found. The resulting Twine ' +
+             'representation will be incomplete.').format(val.type.name))
+      s = '(missing {})'.format(val.type.name)
+
+    return s
+
+  def is_twine_kind(self, kind, expected):
+    if not kind.endswith(expected):
+      return False
+    # apparently some GDB versions add the NodeKind:: namespace
+    # (happens for me on GDB 7.11)
+    return kind in ('llvm::Twine::' + expected,
+                    'llvm::Twine::NodeKind::' + expected)
+
+  def string_from_child(self, child, kind):
+    '''Return the string representation of the Twine::Child child.'''
+
+    if self.is_twine_kind(kind, 'EmptyKind') or self.is_twine_kind(kind, 'NullKind'):
+      return ''
+
+    if self.is_twine_kind(kind, 'TwineKind'):
+      return self.string_from_twine_object(child['twine'].dereference())
+
+    if self.is_twine_kind(kind, 'CStringKind'):
+      return child['cString'].string()
+
+    if self.is_twine_kind(kind, 'StdStringKind'):
+      val = child['stdString'].dereference()
+      return self.string_from_pretty_printer_lookup(val)
+
+    if self.is_twine_kind(kind, 'StringRefKind'):
+      val = child['stringRef'].dereference()
+      pp = StringRefPrinter(val)
+      return pp.to_string()
+
+    if self.is_twine_kind(kind, 'SmallStringKind'):
+      val = child['smallString'].dereference()
+      pp = SmallStringPrinter(val)
+      return pp.to_string()
+
+    if self.is_twine_kind(kind, 'CharKind'):
+      return chr(child['character'])
+
+    if self.is_twine_kind(kind, 'DecUIKind'):
+      return str(child['decUI'])
+
+    if self.is_twine_kind(kind, 'DecIKind'):
+      return str(child['decI'])
+
+    if self.is_twine_kind(kind, 'DecULKind'):
+      return str(child['decUL'].dereference())
+
+    if self.is_twine_kind(kind, 'DecLKind'):
+      return str(child['decL'].dereference())
+
+    if self.is_twine_kind(kind, 'DecULLKind'):
+      return str(child['decULL'].dereference())
+
+    if self.is_twine_kind(kind, 'DecLLKind'):
+      return str(child['decLL'].dereference())
+
+    if self.is_twine_kind(kind, 'UHexKind'):
+      val = child['uHex'].dereference()
+      return hex(int(val))
+
+    print(('Unhandled NodeKind {} in Twine pretty-printer. The result will be '
+           'incomplete.').format(kind))
+
+    return '(unhandled {})'.format(kind)
+
+  def string_from_twine_object(self, twine):
+    '''Return the string representation of the Twine object twine.'''
+
+    lhs_str = ''
+    rhs_str = ''
+
+    lhs = twine['LHS']
+    rhs = twine['RHS']
+    lhs_kind = str(twine['LHSKind'])
+    rhs_kind = str(twine['RHSKind'])
+
+    lhs_str = self.string_from_child(lhs, lhs_kind)
+    rhs_str = self.string_from_child(rhs, rhs_kind)
+
+    return lhs_str + rhs_str
+
+  def to_string(self):
+    return self.string_from_twine_object(self._val)
+
 pp = gdb.printing.RegexpCollectionPrettyPrinter("LLVMSupport")
 pp.add_printer('llvm::SmallString', '^llvm::SmallString<.*>$', SmallStringPrinter)
 pp.add_printer('llvm::StringRef', '^llvm::StringRef$', StringRefPrinter)
 pp.add_printer('llvm::SmallVectorImpl', '^llvm::SmallVector(Impl)?<.*>$', SmallVectorPrinter)
 pp.add_printer('llvm::ArrayRef', '^llvm::(Const)?ArrayRef<.*>$', ArrayRefPrinter)
+pp.add_printer('llvm::Optional', '^llvm::Optional<.*>$', OptionalPrinter)
+pp.add_printer('llvm::DenseMap', '^llvm::DenseMap<.*>$', DenseMapPrinter)
+pp.add_printer('llvm::Twine', '^llvm::Twine$', TwinePrinter)
 gdb.printing.register_pretty_printer(gdb.current_objfile(), pp)