libstdc++: Fix bogus use of memcmp in ranges::lexicographical_compare (PR 93972)

We were enabling the memcmp optimization in ranges::lexicographical_compare for
signed integral types and for integral types wider than a byte.  But memcmp
gives the wrong answer for arrays of such types.  This patch fixes this issue by
refining the condition that enables the memcmp optimization.  It's now
consistent with the corresponding condition used in
std::lexicographical_compare.

libstdc++-v3/ChangeLog:

	PR libstdc++/93972
	* include/bits/ranges_algo.h (__lexicographical_compare_fn::operator()):
	Fix condition for when to use memcmp, making it consistent with the
	corresponding condition used in std::lexicographical_compare.
	* testsuite/25_algorithms/lexicographical_compare/93972.cc: New test.

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 6484e499b963998257dc499e8de9985b78c482a2..efbe1dafdf5f4469871e3e60654af7a4bfc7d3d4 100644 (file)
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,11 @@
 2020-02-28  Patrick Palka  <ppalka@redhat.com>
 
+       PR libstdc++/93972
+       * include/bits/ranges_algo.h (__lexicographical_compare_fn::operator()):
+       Fix condition for when to use memcmp, making it consistent with the
+       corresponding condition used in std::lexicographical_compare.
+       * testsuite/25_algorithms/lexicographical_compare/93972.cc: New test.
+
        * testsuite/26_numerics/headers/numeric/synopsis.cc: Add signatures for
        functions introduced in C++11, C++17 and C++2a.  Add 'constexpr' to
        existing signatures for C++2a.

diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index 05c0851d41158b7603a5fdde1d41b476cd9f0b6b..8fa4a8a91610fa3f4d724ea5053a9ab73bb49a1e 100644 (file)
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -3466,9 +3466,13 @@ namespace ranges
              {
                using _ValueType1 = iter_value_t<_Iter1>;
                using _ValueType2 = iter_value_t<_Iter2>;
+               // This condition is consistent with the one in
+               // __lexicographical_compare_aux in <bits/stl_algobase.h>.
                constexpr bool __use_memcmp
-                 = ((is_integral_v<_ValueType1> || is_pointer_v<_ValueType1>)
-                    && is_same_v<_ValueType1, _ValueType2>
+                 = (__is_byte<_ValueType1>::__value
+                    && __is_byte<_ValueType2>::__value
+                    && !__gnu_cxx::__numeric_traits<_ValueType1>::__is_signed
+                    && !__gnu_cxx::__numeric_traits<_ValueType2>::__is_signed
                     && is_pointer_v<_Iter1>
                     && is_pointer_v<_Iter2>
                     && (is_same_v<_Comp, ranges::less>

diff --git a/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/93972.cc b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/93972.cc
new file mode 100644 (file)
index 0000000..53c4e0d
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/93972.cc
@@ -0,0 +1,169 @@
+// Copyright (C) 2020 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++2a" }
+// { dg-do run { target c++2a } }
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+using std::signed_integral;
+
+namespace ranges = std::ranges;
+
+template<signed_integral T>
+void
+test01()
+{
+  T i[] = { -1 };
+  T j[] = { 1 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+template<signed_integral T>
+void
+test02()
+{
+  T i[] = { -5 };
+  T j[] = { -5, 3 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( !ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+template<signed_integral T>
+void
+test03()
+{
+  T i[] = { -10 };
+  T j[] = { -5, 3 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+template<signed_integral T>
+void
+test04()
+{
+  T i[] = { -2 };
+  T j[] = { -5, 3 };
+
+  VERIFY( !ranges::lexicographical_compare(i, j) );
+  VERIFY( ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( ranges::lexicographical_compare(j, i) );
+  VERIFY( !ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+void
+test05()
+{
+  unsigned i[] = { 1 };
+  unsigned j[] = { 256 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+void
+test06()
+{
+  signed char i[] = { 100, 1 };
+  unsigned char j[] = { 100 };
+
+  VERIFY( !ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+void
+test07()
+{
+  char i[] = { 95, 1 };
+  unsigned char j[] = { 100 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+void
+test08()
+{
+  signed char i[] = { 112, 1 };
+  signed char j[] = { 87 };
+
+  VERIFY( !ranges::lexicographical_compare(i, j) );
+  VERIFY( ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( ranges::lexicographical_compare(j, i) );
+  VERIFY( !ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+void
+test09()
+{
+  char i[] = { 1 };
+  unsigned char j[] = { 100 };
+
+  VERIFY( ranges::lexicographical_compare(i, j) );
+  VERIFY( !ranges::lexicographical_compare(i, j, ranges::greater{}) );
+
+  VERIFY( !ranges::lexicographical_compare(j, i) );
+  VERIFY( ranges::lexicographical_compare(j, i, ranges::greater{}) );
+}
+
+int
+main()
+{
+  test01<signed char>();
+  test01<int>();
+
+  test02<signed char>();
+  test02<int>();
+
+  test03<signed char>();
+  test03<int>();
+
+  test04<signed char>();
+  test04<int>();
+
+  test05();
+  test06();
+  test07();
+  test08();
+  test09();
+}