Don't use __glibcxx_assert to check class invariants

Assertions should be used to check preconditions that users must meet,
not to check whether the implementation is correct.

	* include/bits/regex_automaton.tcc (_StateSeq<_TraitsT>::_M_clone()):
	Remove __glibcxx_assert statements and use map::find instead of
	map::operator[].

From-SVN: r264422

libstdc++-v3/ChangeLog

+2018-09-19  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/regex_automaton.tcc (_StateSeq<_TraitsT>::_M_clone()):
+	Remove __glibcxx_assert statements and use map::find instead of
+	map::operator[].
+
 2018-09-18  François Dumont  <fdumont@gcc.gnu.org>
 
 	PR libstdc++/87135

libstdc++-v3/include/bits/regex_automaton.tcc

@@ -220,16 +220,9 @@ namespace __detail
 	  auto __v = __it.second;
 	  auto& __ref = _M_nfa[__v];
 	  if (__ref._M_next != _S_invalid_state_id)
-	    {
-	      __glibcxx_assert(__m.count(__ref._M_next) > 0);
-	      __ref._M_next = __m[__ref._M_next];
-	    }
-	  if (__ref._M_has_alt())
-	    if (__ref._M_alt != _S_invalid_state_id)
-	      {
-		__glibcxx_assert(__m.count(__ref._M_alt) > 0);
-		__ref._M_alt = __m[__ref._M_alt];
-	      }
+	    __ref._M_next = __m.find(__ref._M_next)->second;
+	  if (__ref._M_has_alt() && __ref._M_alt != _S_invalid_state_id)
+	    __ref._M_alt = __m.find(__ref._M_alt)->second;
 	}
       return _StateSeq(_M_nfa, __m[_M_start], __m[_M_end]);
     }