Make std::match_results::_M_resize more useful

As both callers of match_results::_M_resize(unsigned) immediately follow
it with a loop to update the value of each sub_match, that behaviour can
be moved into _M_resize itself. The first caller fills the container
with unmatched subs, which can be done with vector::assign, and the
second caller clears the container to establish a specific state, which
can be provided by a new member function specific to that purpose.

Tangentially, I also noticed that match_results::max_size() doesn't
account for the three special sub_match objects that are always present
in a fully established result state. This patch also fixes that.

	* include/bits/regex.h (match_results::max_size()): Adjust return
	value to account for prefix/suffix/unmatched subs.
	(match_results::_M_resize(unsigned int)): Use _Base_type::assign to
	reset the contained sub matches.
	(match_results::_M_establish_failed_match(_Bi_iter)): Add new member
	function to set result state following a failed match.
	* include/bits/regex.tcc (__regex_algo_impl): Remove loop to set
	sub_match states after _M_resize. Use _M_establish_failed_match.

From-SVN: r271167

3 files changed, 23 insertions, 10 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 995f2ce..3cfcd06 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,14 @@
 2019-05-14  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/bits/regex.h (match_results::max_size()): Adjust return
+	value to account for prefix/suffix/unmatched subs.
+	(match_results::_M_resize(unsigned int)): Use _Base_type::assign to
+	reset the contained sub matches.
+	(match_results::_M_establish_failed_match(_Bi_iter)): Add new member
+	function to set result state following a failed match.
+	* include/bits/regex.tcc (__regex_algo_impl): Remove loop to set
+	sub_match states after _M_resize. Use _M_establish_failed_match.
+
 	PR libstdc++/69724
 	* include/std/thread (thread::_State_impl, thread::_S_make_state):
 	Replace single _Callable parameter with variadic _Args pack, to
diff --git a/libstdc++-v3/include/bits/regex.h b/libstdc++-v3/include/bits/regex.h
index 76219b5..b30b41a 100644
--- a/libstdc++-v3/include/bits/regex.h
+++ b/libstdc++-v3/include/bits/regex.h
@@ -1707,7 +1707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
       size_type
       max_size() const noexcept
-      { return _Base_type::max_size(); }
+      { return _Base_type::max_size() - 3; }
 
       /**
        * @brief Indicates if the %match_results contains no results.
@@ -1953,9 +1953,20 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 				    const basic_regex<_Cp, _Rp>&,
 				    regex_constants::match_flag_type);
 
+      // Reset contents to __size unmatched sub_match objects
+      // (plus additional objects for prefix, suffix and unmatched sub).
       void
       _M_resize(unsigned int __size)
-      { _Base_type::resize(__size + 3); }
+      { _Base_type::assign(__size + 3, sub_match<_Bi_iter>{}); }
+
+      // Set state to a failed match for the given past-the-end iterator.
+      void
+      _M_establish_failed_match(_Bi_iter __end)
+      {
+	sub_match<_Bi_iter> __sm;
+	__sm.first = __sm.second = __end;
+	_Base_type::assign(3, __sm);
+      }
 
       const_reference
       _M_unmatched_sub() const
diff --git a/libstdc++-v3/include/bits/regex.tcc b/libstdc++-v3/include/bits/regex.tcc
index dbe348d..53cf1ff 100644
--- a/libstdc++-v3/include/bits/regex.tcc
+++ b/libstdc++-v3/include/bits/regex.tcc
@@ -59,8 +59,6 @@ namespace __detail
       typename match_results<_BiIter, _Alloc>::_Base_type& __res = __m;
       __m._M_begin = __s;
       __m._M_resize(__re._M_automaton->_M_sub_count());
-      for (auto& __it : __res)
-	__it.matched = false;
 
       bool __ret;
       if ((__re.flags() & regex_constants::__polynomial)
@@ -111,12 +109,7 @@ namespace __detail
 	}
       else
 	{
-	  __m._M_resize(0);
-	  for (auto& __it : __res)
-	    {
-	      __it.matched = false;
-	      __it.first = __it.second = __e;
-	    }
+	  __m._M_establish_failed_match(__e);
 	}
       return __ret;
     }