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[patch 1/N] std::regex refactoring - _BracketMatcher


I've been looking through the regex code and have a few ideas for
simplifications or optimisations that I'd like to share.

This first patch is for _BracketMatcher. We only use std::bitset when
is_same<_CharT, char> so 8 * sizeof(_CharT) should be __CHAR_BIT__
instead. We also only user _UnsignedCharT when is_same<_CharT, char>
so that can just be simplified to unsigned char.

The contents of _BracketMatcher::_M_char_set are not sorted and can
contain duplicates in the current code. Making that a sorted, unique
list in _BracketMatcher::_M_ready() allows a binary search instead of
linear search. This improves worst case performance for pathological
regular expressions like std::wregex('['+std::wstring(1000, 'a')+"b]")
but I'm not sure if it helps in the common case.

Finally, in the non-char case the _CacheT member is an unused empty
object, so having that as the first member requires 7 bytes of
padding. Re-ordering the members reduces the size of a non-char
_BracketMatcher by 8 bytes (but it's still a whopping 96 bytes).

(For a char _BracketMatcher the bitset cache makes it 128 bytes,
this patch doesn't change that).


diff --git a/libstdc++-v3/include/bits/regex_compiler.h b/libstdc++-v3/include/bits/regex_compiler.h
index f5a198f..a9dd8d3 100644
--- a/libstdc++-v3/include/bits/regex_compiler.h
+++ b/libstdc++-v3/include/bits/regex_compiler.h
+	std::sort(_M_char_set.begin(), _M_char_set.end());
+	auto __end = std::unique(_M_char_set.begin(), _M_char_set.end());
+	_M_char_set.erase(__end, _M_char_set.end());
 	_M_is_ready = true;
       typedef typename is_same<_CharT, char>::type _IsChar;
       struct _Dummy { };
+      static constexpr size_t _S_cache_size() { return 1ul << __CHAR_BIT__; }
       typedef typename conditional<_IsChar::value,
-				   std::bitset<1 << (8 * sizeof(_CharT))>,
+				   std::bitset<_S_cache_size()>,
 				   _Dummy>::type _CacheT;
-      typedef typename make_unsigned<_CharT>::type _UnsignedCharT;
       _M_apply(_CharT __ch, true_type) const
-      { return _M_cache[static_cast<_UnsignedCharT>(__ch)]; }
+      { return _M_cache[static_cast<unsigned char>(__ch)]; }
-	for (int __i = 0; __i < _M_cache.size(); __i++)
-	  _M_cache[static_cast<_UnsignedCharT>(__i)] =
-	    _M_apply(__i, false_type());
+	for (unsigned __i = 0; __i < _S_cache_size(); __i++)
+	  _M_cache[__i] = _M_apply(static_cast<char>(__i), false_type());
       { }
-      _CacheT                                   _M_cache;
       std::vector<_CharT>                       _M_char_set;
       std::vector<_StringT>                     _M_equiv_set;
       std::vector<pair<_StrTransT, _StrTransT>> _M_range_set;
       _CharClassT                               _M_class_set;
       _TransT                                   _M_translator;
       const _TraitsT&                           _M_traits;
+      _CacheT                                   _M_cache;
       bool                                      _M_is_non_matching;
       bool                                      _M_is_ready;
diff --git a/libstdc++-v3/include/bits/regex_compiler.tcc b/libstdc++-v3/include/bits/regex_compiler.tcc
index 128dac1..36edfba 100644
--- a/libstdc++-v3/include/bits/regex_compiler.tcc
+++ b/libstdc++-v3/include/bits/regex_compiler.tcc
     _BracketMatcher<_TraitsT, __icase, __collate>::
     _M_apply(_CharT __ch, false_type) const
-      bool __ret = false;
-      if (std::find(_M_char_set.begin(), _M_char_set.end(),
-		    _M_translator._M_translate(__ch))
-	  != _M_char_set.end())
-	__ret = true;
-      else
+      bool __ret = std::binary_search(_M_char_set.begin(), _M_char_set.end(),
+				      _M_translator._M_translate(__ch));
+      if (!__ret)
 	  auto __s = _M_translator._M_transform(__ch);
 	  for (auto& __it : _M_range_set)

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