[libc++] Add regression test for std::hash implementation in ABI v1

Differential Revision: https://reviews.llvm.org/D144107

Author: ldionne

libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v1.pass.cpp

@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03
+
+// Test that the CityHash implementation returns the results we expect.
+//
+// Note that this implementation is technically incorrect, however changing it is
+// an ABI break. This test ensures that we don't unintentionally break the ABI v1
+// by "fixing" the hash implementation.
+// REQUIRES: libcpp-abi-version=1
+
+#include <cassert>
+#include <string>
+#include <utility>
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#  define CHOOSE_BY_ENDIANESS(little, big) (little)
+#else
+#  define CHOOSE_BY_ENDIANESS(little, big) (big)
+#endif
+
+std::string CityHash[] = {
+    {/* "abcdefgh" */ "\x61\x62\x63\x64\x65\x66\x67\x68"},
+    {/* "abcDefgh" */ "\x61\x62\x63\x44\x65\x66\x67\x68"},
+    {/* "CityHash" */ "\x43\x69\x74\x79\x48\x61\x73\x68"},
+    {/* "CitYHash" */ "\x43\x69\x74\x59\x48\x61\x73\x68"},
+};
+
+int main(int, char**) {
+  const std::pair<std::string, uint64_t> TestCases[] = {
+      {CityHash[0], CHOOSE_BY_ENDIANESS(0x87c69099911bab7eULL, 0x297621d7fa436a3ULL)},
+      {CityHash[1], CHOOSE_BY_ENDIANESS(0x87c69099911bab7eULL, 0xb17be531dde56e57ULL)},
+      {CityHash[2], CHOOSE_BY_ENDIANESS(0x85322632e188694aULL, 0xe14f578b688e266dULL)},
+      {CityHash[3], CHOOSE_BY_ENDIANESS(0x85322632e188694aULL, 0xca5a764a0450eac6ULL)},
+  };
+
+  std::__murmur2_or_cityhash<uint64_t> h64;
+  for (const auto& test_case : TestCases) {
+    assert(h64(test_case.first.data(), test_case.first.size()) == test_case.second);
+  }
+
+  return 0;
+}

libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.pass.cpp renamed to libcxx/test/libcxx/utilities/utility/__murmur2_or_cityhash.abi-v2.pass.cpp

@@ -6,10 +6,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-// Test the CityHash implementation is correct.
-
 // UNSUPPORTED: c++03
 
+// Test that the CityHash implementation is correct.
+//
 // In ABI v1, our CityHash implementation is incorrect and fixing it would
 // be an ABI break.
 // REQUIRES: libcpp-abi-version=2