libstdc++: Improve tests for constexpr algorithms

These tests just return true without checking that the results of the
algorithms. Although it should be safe to assume that the algorithms
behave the same at compile-time as at run-time, we can use these tests
to verify it.

This replaces each 'return true' statement with a condition that depends
on the basic functionality of the algorithm, such as returning an
iterator to the right position.

libstdc++-v3/ChangeLog:

	* testsuite/25_algorithms/all_of/constexpr.cc: Check result of
	the algorithm.
	* testsuite/25_algorithms/any_of/constexpr.cc: Likewise.
	* testsuite/25_algorithms/binary_search/constexpr.cc: Likewise.
	* testsuite/25_algorithms/copy_backward/constexpr.cc: Likewise.
	* testsuite/25_algorithms/count/constexpr.cc: Likewise.
	* testsuite/25_algorithms/equal/constexpr.cc: Likewise.
	* testsuite/25_algorithms/equal_range/constexpr.cc: Likewise.
	* testsuite/25_algorithms/fill/constexpr.cc: Likewise.
	* testsuite/25_algorithms/find_end/constexpr.cc: Likewise.
	* testsuite/25_algorithms/find_if/constexpr.cc: Likewise.
	* testsuite/25_algorithms/is_partitioned/constexpr.cc: Likewise.
	* testsuite/25_algorithms/is_permutation/constexpr.cc: Likewise.
	* testsuite/25_algorithms/is_sorted_until/constexpr.cc:
	Likewise.
	* testsuite/25_algorithms/lexicographical_compare/constexpr.cc:
	Likewise.
	* testsuite/25_algorithms/lower_bound/constexpr.cc: Likewise.
	* testsuite/25_algorithms/merge/constexpr.cc: Likewise.
	* testsuite/25_algorithms/mismatch/constexpr.cc: Likewise.
	* testsuite/25_algorithms/none_of/constexpr.cc: Likewise.
	* testsuite/25_algorithms/partition_copy/constexpr.cc: Likewise.
	* testsuite/25_algorithms/remove_copy/constexpr.cc: Likewise.
	* testsuite/25_algorithms/remove_copy_if/constexpr.cc: Likewise.
	* testsuite/25_algorithms/remove_if/constexpr.cc: Likewise.
	* testsuite/25_algorithms/replace_if/constexpr.cc: Likewise.
	* testsuite/25_algorithms/reverse/constexpr.cc: Likewise.
	* testsuite/25_algorithms/reverse_copy/constexpr.cc: Likewise.
	* testsuite/25_algorithms/rotate_copy/constexpr.cc: Likewise.
	* testsuite/25_algorithms/search/constexpr.cc: Likewise.
	* testsuite/25_algorithms/set_difference/constexpr.cc: Likewise.
	* testsuite/25_algorithms/set_intersection/constexpr.cc:
	Likewise.
	* testsuite/25_algorithms/set_symmetric_difference/constexpr.cc:
	Likewise.
	* testsuite/25_algorithms/set_union/constexpr.cc: Likewise.
	* testsuite/25_algorithms/unique_copy/constexpr.cc: Likewise.
	* testsuite/25_algorithms/upper_bound/constexpr.cc: Likewise.

libstdc++-v3/testsuite/25_algorithms/all_of/constexpr.cc

@@ -23,13 +23,12 @@
 
 constexpr std::array<int, 6> cae{{0, 2, 4, 6, 8, 10}};
 
-constexpr auto out2 = std::all_of(cae.begin(), cae.end(),
+constexpr auto out1 = std::all_of(cae.begin(), cae.end(),
 			          [](int i){ return i % 2 == 0; });
 
-constexpr bool
-test()
-{
-  return true;
-}
+static_assert(out1);
 
-static_assert(test());
+constexpr auto out2 = std::all_of(cae.begin(), cae.end(),
+			          [](int i){ return i != 8; });
+
+static_assert(!out2);

libstdc++-v3/testsuite/25_algorithms/any_of/constexpr.cc

@@ -29,7 +29,10 @@ test()
   const auto out3 = std::any_of(ca0.begin(), ca0.end(),
 			        [](int i){ return i % 2 == 0; });
 
-  return true;
+  const auto out4 = std::any_of(ca0.begin(), ca0.end(),
+			        [](int i){ return i == -1; });
+
+  return out3 && !out4;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/binary_search/constexpr.cc

@@ -31,7 +31,10 @@ test()
   const auto out5 = std::binary_search(ca0.begin(), ca0.end(), 5,
 				       std::less<int>());
 
-  return true;
+  const auto out6 = std::binary_search(ca0.begin(), ca0.end(), 4.5,
+				       std::less<>());
+
+  return out4 && out5 && !out6;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/copy_backward/constexpr.cc

@@ -30,7 +30,7 @@ test()
   const auto out7 = std::copy_backward(ca0.begin(), ca0.begin() + 8,
 				       ma0.begin() + 10);
 
-  return true;
+  return out7 == ma0.begin() + 2 && ma0[3] == 1;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/count/constexpr.cc

@@ -28,7 +28,9 @@ test()
 
   const auto out8 = std::count(ca0.begin(), ca0.end(), 6);
 
-  return true;
+  const auto out9 = std::count(ca0.begin(), ca0.end(), 16);
+
+  return out8 == 1 && out9 == 0;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/equal/constexpr.cc

@@ -33,7 +33,12 @@ test()
   const auto outb = std::equal(ca0.begin(), ca0.end(), cas.begin(),
 			       [](int i, int j){ return i + 3 == j; });
 
-  return true;
+  auto ca2 = ca0;
+  ca2[5] = -1;
+
+  const auto outc = std::equal(ca0.begin(), ca0.end(), ca2.begin());
+
+  return outa && outb && !outc;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/equal_range/constexpr.cc

@@ -28,7 +28,8 @@ test()
 
   const auto outc = std::equal_range(car.begin(), car.end(), 6);
 
-  return true;
+  return outc.first == (car.begin() + 6)
+    && outc.second == (car.begin() + 8);
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/fill/constexpr.cc

@@ -27,7 +27,7 @@ test()
   std::array<int, 12> ma0{{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}};
   std::fill(ma0.begin(), ma0.end(), 66);
 
-  return true;
+  return ma0[4] == 66 && ma0[7] == 66;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/find_end/constexpr.cc

@@ -24,7 +24,7 @@
 constexpr bool
 test()
 {
-  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5,  6, 7, 8,  9, 10, 11}};
+  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
   constexpr std::array<int, 3> cam{{4, 5, 6}};
   constexpr std::array<int, 3> camm{{-4, -5, -6}};
 
@@ -35,7 +35,7 @@ test()
 				  camm.begin(), camm.end(),
 				  [](int i, int j){ return i + 1 == -j; });
 
-  return true;
+  return outf == (ca0.begin() + 4) && outg == (ca0.begin() + 3);
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/find_if/constexpr.cc

@@ -24,12 +24,12 @@
 constexpr bool
 test()
 {
-  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5,  6, 7, 8,  9, 10, 11}};
+  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
 
   const auto outj = std::find_if(ca0.begin(), ca0.end(),
 				 [](int i){ return i == 6; });
 
-  return true;
+  return outj == (ca0.begin() + 6);
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/is_partitioned/constexpr.cc

@@ -29,7 +29,7 @@ test()
   const auto outs = std::is_partitioned(caeo.begin(), caeo.end(),
 					[](int i){ return i % 2 == 0; });
 
-  return true;
+  return outs;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/is_permutation/constexpr.cc

@@ -29,7 +29,9 @@ test()
 
   const auto outt = std::is_permutation(ca0.begin(), ca0.end(), cap.begin());
 
-  return true;
+  const auto outf = std::is_permutation(ca0.begin() + 1, ca0.end(), cap.begin());
+
+  return outt && !outf;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/is_sorted_until/constexpr.cc

@@ -31,7 +31,10 @@ test()
   const auto outy = std::is_sorted_until(aus.begin(), aus.end(),
 					 std::less<int>());
 
-  return true;
+  const auto outz = std::is_sorted_until(outx - 1, aus.end(),
+					 std::greater<int>());
+
+  return outx == aus.begin() + 7 && outy == outx && outz == (outx + 1);
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/lexicographical_compare/constexpr.cc

@@ -34,7 +34,7 @@ test()
 						   ca1.begin(), ca1.end(),
 						   std::less<int>());
 
-  return true;
+  return outz && outaa;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/lower_bound/constexpr.cc

@@ -31,7 +31,7 @@ test()
   const auto outcc = std::lower_bound(ca0.begin(), ca0.end(), 6,
 				      std::less<int>());
 
-  return true;
+  return outbb == (ca0.begin() + 6) && outcc == outbb;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/merge/constexpr.cc

@@ -31,12 +31,14 @@ test()
 
   const auto outdd = std::merge(ca0.begin(), ca0.end(),
 				cas.begin(), cas.end(), out0.begin());
+  if (outdd != out0.end())
+    return false;
 
   const auto outee = std::merge(ca0.begin(), ca0.end(),
 				camm.begin(), camm.end(), out0.begin(),
 				[](int i, int j){ return i < j; });
 
-  return true;
+  return outee == (out0.begin() + ca0.size() + camm.size());
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/mismatch/constexpr.cc

@@ -32,7 +32,8 @@ test()
   const auto outgg = std::mismatch(ca0.begin(), ca0.end(), cax.begin(),
 				   std::equal_to<int>());
 
-  return true;
+  return outff.first == (ca0.begin() + 6) && outff.second == (cax.begin() + 6)
+    && outgg == outff;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/none_of/constexpr.cc

@@ -29,7 +29,7 @@ test()
   const auto outhh = std::none_of(ca0.begin(), ca0.end(),
 				  [](int i){ return i > 12; });
 
-  return true;
+  return outhh;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/partition_copy/constexpr.cc

@@ -32,7 +32,8 @@ test()
 					 out0.begin(), out1.begin(),
 					 [](int i){ return i % 2 == 0; });
 
-  return true;
+  return outii.first == (out0.begin() + 6) && out0[1] == 2
+    && outii.second == (out1.begin() + 6) && out1[1] == 3;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/remove_copy/constexpr.cc

@@ -24,12 +24,12 @@
 constexpr bool
 test()
 {
-  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5,  6, 7, 8,  9, 10, 11}};
+  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
   std::array<int, 24> out0{{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};
 
   const auto outmm = std::remove_copy(ca0.begin(), ca0.end(), out0.begin(), 6);
 
-  return true;
+  return outmm == out0.begin() + ca0.size() - 1;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/remove_copy_if/constexpr.cc

@@ -30,7 +30,7 @@ test()
   const auto outnn = std::remove_copy_if(ca0.begin(), ca0.end(), out0.begin(),
 					 [](int i){ return i == 7; });
 
-  return true;
+  return outnn == out0.begin() + ca0.size() - 1;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/remove_if/constexpr.cc

@@ -29,7 +29,7 @@ test()
   const auto outll = std::remove_if(ac2.begin(), ac2.end(),
 				    [](int i){ return i == 7; });
 
-  return true;
+  return outll == (ac2.end() - 1) && ac2[7] == 8;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/replace_if/constexpr.cc

@@ -28,7 +28,9 @@ test()
 
   std::replace_if(ar0.begin(), ar0.end(), [](int i){ return i % 2 == 1; }, 42);
 
-  return true;
+  std::array<int, 12> ar1{{0, 42, 2, 42, 4, 42, 6, 6, 8, 42, 42, 42}};
+
+  return ar0 == ar1;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/reverse/constexpr.cc

@@ -23,8 +23,6 @@
 constexpr bool
 test()
 {
-  auto ok = true;
-
   std::array<int, 12> ar0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
 
   std::reverse(ar0.begin() + 2, ar0.begin() + 9);

libstdc++-v3/testsuite/25_algorithms/reverse_copy/constexpr.cc

@@ -29,7 +29,7 @@ test()
 
   const auto outqq = std::reverse_copy(ca0.rbegin(), ca0.rend(), out0.begin());
 
-  return true;
+  return outqq == (out0.begin() + ca0.size()) && out0[3] == 3;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/rotate_copy/constexpr.cc

@@ -30,7 +30,7 @@ test()
   const auto outrr = std::rotate_copy(ca0.begin(), ca0.begin() + 6,
 				      ca0.end(), out0.begin());
 
-  return true;
+  return outrr == (out0.begin() + ca0.size()) && out0[3] == 9 && out0[8] == 2;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/search/constexpr.cc

@@ -24,7 +24,7 @@
 constexpr bool
 test()
 {
-  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5,  6, 7, 8,  9, 10, 11}};
+  constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
   constexpr std::array<int, 3> cam{{4, 5, 6}};
 
   const auto outtt = std::search(ca0.begin(), ca0.end(),
@@ -35,7 +35,7 @@ test()
     = std::search(ca0.begin(), ca0.end(),
 		  std::default_searcher(cam.begin(), cam.end()));
 
-  return true;
+  return outtt == (ca0.begin() + 4) && outtt2 == outtt;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/set_difference/constexpr.cc

@@ -29,13 +29,16 @@ test()
   std::array<int, 24> out0{{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};
 
   const auto outvv = std::set_difference(ca0.begin(), ca0.end(),
-					 cas.begin(), cas.end(), out0.begin());
+					 cas.begin(), cas.end(),
+					 out0.begin());
 
   const auto outww = std::set_difference(ca0.begin(), ca0.end(),
 				         cas.begin(), cas.end(),
-				         out0.begin(), std::less<int>());
+				         outvv,
+					 std::less<int>());
 
-  return true;
+
+  return outvv == (out0.begin() + 3) && outww == (outvv + 3);
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/set_intersection/constexpr.cc

@@ -36,7 +36,7 @@ test()
 					   cas.begin(), cas.end(),
 					   out0.begin(), std::less<int>());
 
-  return true;
+  return outxx == (out0.begin() + 9) && outyy == outxx;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/set_symmetric_difference/constexpr.cc

@@ -25,17 +25,19 @@ constexpr bool
 test()
 {
   constexpr std::array<int, 12> ca0{{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}};
-  constexpr std::array<int, 12> cas{{3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}};
+  constexpr std::array<int, 12> cas{{4, 4, 5, 6, 7, 8, 9, 10, 11, 11, 12, 13}};
   std::array<int, 24> out0{{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};
 
-  const auto outvv = std::set_difference(ca0.begin(), ca0.end(),
-					 cas.begin(), cas.end(), out0.begin());
+  const auto outvv = std::set_symmetric_difference(ca0.begin(), ca0.end(),
+						   cas.begin(), cas.end(),
+						   out0.begin());
 
-  const auto outww = std::set_difference(ca0.begin(), ca0.end(),
-				         cas.begin(), cas.end(),
-				         out0.begin(), std::less<int>());
+  const auto outww = std::set_symmetric_difference(ca0.begin(), ca0.end(),
+						   cas.begin(), cas.end(),
+						   out0.begin(),
+						   std::less<int>());
 
-  return true;
+  return outvv == (out0.begin() + 8) && outww == outvv;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/set_union/constexpr.cc

@@ -29,13 +29,14 @@ test()
   std::array<int, 24> out0{{0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}};
 
   const auto out11 = std::set_union(ca0.begin(), ca0.end(),
-				    cas.begin(), cas.end(), out0.begin());
+				    cas.begin(), cas.end(),
+				    out0.begin());
 
   const auto out22 = std::set_union(ca0.begin(), ca0.end(),
 				    cas.begin(), cas.end(),
 				    out0.begin(), std::less<int>());
 
-  return true;
+  return out11 == (out0.begin() + 15) && out22 == out11;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/unique_copy/constexpr.cc

@@ -29,10 +29,11 @@ test()
 
   const auto out55 = std::unique_copy(ar3.begin(), ar3.end(), out0.begin());
 
-  const auto out66 = std::unique_copy(ar3.begin(), ar3.end(), out0.begin(),
+  const auto out66 = std::unique_copy(ar3.begin(), ar3.end(), out55,
 				      std::equal_to<int>());
 
-  return true;
+  return out55 == (out0.begin() + 10) && out0[7] == 8
+    && out66 == (out55 + 10) ; // && out0[19] == 11;
 }
 
 static_assert(test());

libstdc++-v3/testsuite/25_algorithms/upper_bound/constexpr.cc

@@ -31,7 +31,7 @@ test()
   const auto out88 = std::upper_bound(ca0.begin(), ca0.end(), 6,
 				      std::less<int>());
 
-  return true;
+  return out77 == (ca0.begin() + 7) && out88 == out77;
 }
 
 static_assert(test());