commit c1f64344793df8b29ccb27d06572ba8d5b51957b
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Sat Feb 23 01:33:02 2019 +0000

    PR libstdc++/89446 fix null pointer dereference in char_traits
    
            PR libstdc++/89446
            * include/bits/char_traits.h (__constant_char_array): Check index is
            in range before dereferencing.
            (char_traits<char>::compare, char_traits<char>::find)
            (char_traits<char8_t>::compare, char_traits<char8_t>::find): Return
            immediately if n is zero.
            (char_traits<wchar_t>::compare, char_traits<wchar_t>::find): Likewise.
            Remove workarounds for PR 67026.
            * testsuite/21_strings/basic_string_view/operators/char/89446.cc:
            New test.
            * testsuite/21_strings/basic_string_view/operators/wchar_t/89446.cc:
            New test.

diff --git a/libstdc++-v3/include/bits/char_traits.h b/libstdc++-v3/include/bits/char_traits.h
index 21099c36c3b..fd9a3c73930 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -260,7 +260,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return __builtin_is_constant_evaluated();
 #else
       size_t __i = 0;
-      while (__builtin_constant_p(__a[__i]) && __i < __n)
+      while (__i < __n && __builtin_constant_p(__a[__i]))
 	__i++;
       return __i == __n;
 #endif
@@ -314,14 +314,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static _GLIBCXX17_CONSTEXPR int
       compare(const char_type* __s1, const char_type* __s2, size_t __n)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus >= 201703L
 	if (__builtin_constant_p(__n)
 	    && __constant_char_array_p(__s1, __n)
 	    && __constant_char_array_p(__s2, __n))
 	  return __gnu_cxx::char_traits<char_type>::compare(__s1, __s2, __n);
 #endif
-	if (__n == 0)
-	  return 0;
 	return __builtin_memcmp(__s1, __s2, __n);
       }
 
@@ -338,14 +338,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static _GLIBCXX17_CONSTEXPR const char_type*
       find(const char_type* __s, size_t __n, const char_type& __a)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus >= 201703L
 	if (__builtin_constant_p(__n)
 	    && __builtin_constant_p(__a)
 	    && __constant_char_array_p(__s, __n))
 	  return __gnu_cxx::char_traits<char_type>::find(__s, __n, __a);
 #endif
-	if (__n == 0)
-	  return 0;
 	return static_cast<const char_type*>(__builtin_memchr(__s, __a, __n));
       }
 
@@ -423,16 +423,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static _GLIBCXX17_CONSTEXPR int
       compare(const char_type* __s1, const char_type* __s2, size_t __n)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus >= 201703L
 	if (__builtin_constant_p(__n)
 	    && __constant_char_array_p(__s1, __n)
 	    && __constant_char_array_p(__s2, __n))
 	  return __gnu_cxx::char_traits<char_type>::compare(__s1, __s2, __n);
 #endif
-	if (__n == 0)
-	  return 0;
-	else
-	  return wmemcmp(__s1, __s2, __n);
+	return wmemcmp(__s1, __s2, __n);
       }
 
       static _GLIBCXX17_CONSTEXPR size_t
@@ -441,24 +440,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #if __cplusplus >= 201703L
 	if (__constant_string_p(__s))
 	  return __gnu_cxx::char_traits<char_type>::length(__s);
-	else
 #endif
-	  return wcslen(__s);
+	return wcslen(__s);
       }
 
       static _GLIBCXX17_CONSTEXPR const char_type*
       find(const char_type* __s, size_t __n, const char_type& __a)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus >= 201703L
 	if (__builtin_constant_p(__n)
 	    && __builtin_constant_p(__a)
 	    && __constant_char_array_p(__s, __n))
 	  return __gnu_cxx::char_traits<char_type>::find(__s, __n, __a);
 #endif
-	if (__n == 0)
-	  return 0;
-	else
-	  return wmemchr(__s, __a, __n);
+	return wmemchr(__s, __a, __n);
       }
 
       static char_type*
@@ -532,14 +529,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static _GLIBCXX17_CONSTEXPR int
       compare(const char_type* __s1, const char_type* __s2, size_t __n)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus > 201402
 	if (__builtin_constant_p(__n)
 	    && __constant_char_array_p(__s1, __n)
 	    && __constant_char_array_p(__s2, __n))
 	  return __gnu_cxx::char_traits<char_type>::compare(__s1, __s2, __n);
 #endif
-	if (__n == 0)
-	  return 0;
 	return __builtin_memcmp(__s1, __s2, __n);
       }
 
@@ -559,14 +556,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       static _GLIBCXX17_CONSTEXPR const char_type*
       find(const char_type* __s, size_t __n, const char_type& __a)
       {
+	if (__n == 0)
+	  return 0;
 #if __cplusplus > 201402
 	if (__builtin_constant_p(__n)
 	    && __builtin_constant_p(__a)
 	    && __constant_char_array_p(__s, __n))
 	  return __gnu_cxx::char_traits<char_type>::find(__s, __n, __a);
 #endif
-	if (__n == 0)
-	  return 0;
 	return static_cast<const char_type*>(__builtin_memchr(__s, __a, __n));
       }
 
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/char/89446.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/char/89446.cc
new file mode 100644
index 00000000000..768ba63ddfe
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/char/89446.cc
@@ -0,0 +1,28 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17 -fexceptions -fnon-call-exceptions -O1" }
+// { dg-do run { target { powerpc*-*-linux* i?86-*-linux* x86_64-*-linux* } } }
+// { dg-require-effective-target c++17 }
+
+#include <string_view>
+
+int main()
+{
+  std::string_view s1, s2;
+  return s1 != s2;
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/wchar_t/89446.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/wchar_t/89446.cc
new file mode 100644
index 00000000000..a0ecbebea92
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operators/wchar_t/89446.cc
@@ -0,0 +1,28 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17 -fexceptions -fnon-call-exceptions -O1" }
+// { dg-do run { target { powerpc*-*-linux* i?86-*-linux* x86_64-*-linux* } } }
+// { dg-require-effective-target c++17 }
+
+#include <string_view>
+
+int main()
+{
+  std::wstring_view s1, s2;
+  return s1 != s2;
+}