c++: P2865R5, Remove Deprecated Array Comparisons from C++26 [PR117788]

This patch implements P2865R5 by promoting the warning to permerror in
C++26 only.

In C++20 we should warn even without -Wall.  Jason fixed this in r15-5713
but let's add a test that doesn't use -Wall.

This caused a FAIL in conditionally_borrowed.cc because we end up
comparing two array types in equality_comparable_with ->
__weakly_eq_cmp_with.  That could be fixed in libstc++, perhaps by
adding std::decay in the appropriate place.

	PR c++/117788

gcc/c-family/ChangeLog:

	* c-warn.cc (do_warn_array_compare): Emit a permerror in C++26.

gcc/cp/ChangeLog:

	* typeck.cc (cp_build_binary_op) <case EQ_EXPR>: Don't check
	warn_array_compare.  Check tf_warning_or_error instead of just
	tf_warning.  Maybe return an error_mark_node in C++26.
	<case LE_EXPR>: Likewise.

gcc/testsuite/ChangeLog:

	* c-c++-common/Warray-compare-1.c: Expect an error in C++26.
	* c-c++-common/Warray-compare-3.c: Likewise.
	* c-c++-common/Warray-compare-4.c: New test.
	* c-c++-common/Warray-compare-5.c: New test.
	* g++.dg/warn/Warray-compare-1.C: New test.

libstdc++-v3/ChangeLog:

	* testsuite/std/ranges/adaptors/conditionally_borrowed.cc: Add a
	FIXME, adjust.

Reviewed-by: Jason Merrill <jason@redhat.com>

diff --git a/gcc/c-family/c-warn.cc b/gcc/c-family/c-warn.cc
index 140d97a00d8a20df1ebea08ae267fdbcabaa00eb..0b71842e48dc6a1299824a91807bcde35a0db857 100644 (file)
--- a/gcc/c-family/c-warn.cc
+++ b/gcc/c-family/c-warn.cc
@@ -3820,8 +3820,9 @@ maybe_warn_sizeof_array_div (location_t loc, tree arr, tree arr_type,
 
 /* Warn about C++20 [depr.array.comp] array comparisons: "Equality
    and relational comparisons between two operands of array type are
-   deprecated."  We also warn in C and earlier C++ standards.  CODE is
-   the code for this comparison, OP0 and OP1 are the operands.  */
+   deprecated."  In C++26 this is a permerror.  We also warn in C and earlier
+   C++ standards.  CODE is the code for this comparison, OP0 and OP1 are
+   the operands.  */
 
 void
 do_warn_array_compare (location_t location, tree_code code, tree op0, tree op1)
@@ -3834,10 +3835,22 @@ do_warn_array_compare (location_t location, tree_code code, tree op0, tree op1)
     op1 = TREE_OPERAND (op1, 0);
 
   auto_diagnostic_group d;
-  if (warning_at (location, OPT_Warray_compare,
-                 (c_dialect_cxx () && cxx_dialect >= cxx20)
-                 ? G_("comparison between two arrays is deprecated in C++20")
-                 : G_("comparison between two arrays")))
+  diagnostic_t kind = DK_WARNING;
+  const char *msg;
+  if (c_dialect_cxx () && cxx_dialect >= cxx20)
+    {
+      /* P2865R5 made this comparison ill-formed in C++26.  */
+      if (cxx_dialect >= cxx26)
+       {
+         msg = G_("comparison between two arrays is not allowed in C++26");
+         kind = DK_PERMERROR;
+       }
+      else
+       msg = G_("comparison between two arrays is deprecated in C++20");
+    }
+  else
+    msg = G_("comparison between two arrays");
+  if (emit_diagnostic (kind, location, OPT_Warray_compare, msg))
     {
       /* C doesn't allow +arr.  */
       if (c_dialect_cxx ())

diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc
index adc711327217716b681f4a3728b33488027be916..964e549a61228c415d53cb2a39bae27d496213b8 100644 (file)
--- a/gcc/cp/typeck.cc
+++ b/gcc/cp/typeck.cc
@@ -5830,23 +5830,28 @@ cp_build_binary_op (const op_location_t &location,
        warning_at (location, OPT_Wfloat_equal,
                    "comparing floating-point with %<==%> "
                    "or %<!=%> is unsafe");
-      if (complain & tf_warning)
-       {
-         tree stripped_orig_op0 = tree_strip_any_location_wrapper (orig_op0);
-         tree stripped_orig_op1 = tree_strip_any_location_wrapper (orig_op1);
-         if ((TREE_CODE (stripped_orig_op0) == STRING_CST
-              && !integer_zerop (cp_fully_fold (op1)))
-             || (TREE_CODE (stripped_orig_op1) == STRING_CST
-                 && !integer_zerop (cp_fully_fold (op0))))
-           warning_at (location, OPT_Waddress,
-                       "comparison with string literal results in "
-                       "unspecified behavior");
-         else if (warn_array_compare
-                  && TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE
-                  && TREE_CODE (TREE_TYPE (orig_op1)) == ARRAY_TYPE)
-           do_warn_array_compare (location, code, stripped_orig_op0,
-                                  stripped_orig_op1);
-       }
+      {
+       tree stripped_orig_op0 = tree_strip_any_location_wrapper (orig_op0);
+       tree stripped_orig_op1 = tree_strip_any_location_wrapper (orig_op1);
+       if ((complain & tf_warning_or_error)
+           && ((TREE_CODE (stripped_orig_op0) == STRING_CST
+                && !integer_zerop (cp_fully_fold (op1)))
+               || (TREE_CODE (stripped_orig_op1) == STRING_CST
+                   && !integer_zerop (cp_fully_fold (op0)))))
+         warning_at (location, OPT_Waddress,
+                     "comparison with string literal results in "
+                     "unspecified behavior");
+       else if (TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE
+                && TREE_CODE (TREE_TYPE (orig_op1)) == ARRAY_TYPE)
+         {
+           /* P2865R5 made array comparisons ill-formed in C++26.  */
+           if (complain & tf_warning_or_error)
+             do_warn_array_compare (location, code, stripped_orig_op0,
+                                    stripped_orig_op1);
+           else if (cxx_dialect >= cxx26)
+             return error_mark_node;
+         }
+      }
 
       build_type = boolean_type_node;
       if ((code0 == INTEGER_TYPE || code0 == REAL_TYPE
@@ -6125,14 +6130,17 @@ cp_build_binary_op (const op_location_t &location,
                        "comparison with string literal results "
                        "in unspecified behavior");
        }
-      else if (warn_array_compare
-              && TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE
+      else if (TREE_CODE (TREE_TYPE (orig_op0)) == ARRAY_TYPE
               && TREE_CODE (TREE_TYPE (orig_op1)) == ARRAY_TYPE
-              && code != SPACESHIP_EXPR
-              && (complain & tf_warning))
-       do_warn_array_compare (location, code,
-                              tree_strip_any_location_wrapper (orig_op0),
-                              tree_strip_any_location_wrapper (orig_op1));
+              && code != SPACESHIP_EXPR)
+       {
+         if (complain & tf_warning_or_error)
+           do_warn_array_compare (location, code,
+                                  tree_strip_any_location_wrapper (orig_op0),
+                                  tree_strip_any_location_wrapper (orig_op1));
+         else if (cxx_dialect >= cxx26)
+           return error_mark_node;
+       }
 
       if (gnu_vector_type_p (type0) && gnu_vector_type_p (type1))
        {

diff --git a/gcc/testsuite/c-c++-common/Warray-compare-1.c b/gcc/testsuite/c-c++-common/Warray-compare-1.c
index 922396c0a1a02699e2ead49cfcc90411c2536c6e..90191ecd05653898ab15d25b48f24830289ff186 100644 (file)
--- a/gcc/testsuite/c-c++-common/Warray-compare-1.c
+++ b/gcc/testsuite/c-c++-common/Warray-compare-1.c
@@ -14,12 +14,18 @@ int arr4[2][2];
 bool
 g ()
 {
-  bool b = arr1 == arr2; /* { dg-warning "comparison between two arrays" } */
-  b &= arr1 != arr2; /* { dg-warning "comparison between two arrays" } */
-  b &= arr1 > arr2; /* { dg-warning "comparison between two arrays" } */
-  b &= arr1 >= arr2; /* { dg-warning "comparison between two arrays" } */
-  b &= arr1 < arr2; /* { dg-warning "comparison between two arrays" } */
-  b &= arr1 <= arr2; /* { dg-warning "comparison between two arrays" } */
+  bool b = arr1 == arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 != arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 > arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 >= arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 < arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 <= arr2; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
 #ifdef __cplusplus
   b &= +arr1 == +arr2;
   b &= +arr1 != +arr2;
@@ -35,7 +41,8 @@ g ()
   b &= &arr1[0] < &arr2[0];
   b &= &arr1[0] <= &arr2[0];
 
-  b &= arr3 == arr4; /* { dg-warning "comparison between two arrays" } */
+  b &= arr3 == arr4; /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
 
 #if defined(__cplusplus) && __cplusplus > 201703L
   auto cmp = arr1 <=> arr2; /* { dg-error "invalid operands" "" { target c++20 } } */

diff --git a/gcc/testsuite/c-c++-common/Warray-compare-3.c b/gcc/testsuite/c-c++-common/Warray-compare-3.c
index 4725aa2b38bf4dca01e2de9dc2d1140fd53a57c5..afcc934010e4ae8db440f691fe5523aecb33bb23 100644 (file)
--- a/gcc/testsuite/c-c++-common/Warray-compare-3.c
+++ b/gcc/testsuite/c-c++-common/Warray-compare-3.c
@@ -7,7 +7,8 @@ int a[32][32], b[32][32];
 int
 foo (int x, int y)
 {
-  return (x ? a : b) == (y ? a : b); /* { dg-warning "comparison between two arrays" } */
-/* { dg-message "use '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c } .-1 } */
-/* { dg-message "use unary '\\\+' which decays operands to pointers or '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c++ } .-2 } */
+  return (x ? a : b) == (y ? a : b); /* { dg-warning "comparison between two arrays" "" { target { c || c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+/* { dg-message "use '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c } .-2 } */
+/* { dg-message "use unary '\\\+' which decays operands to pointers or '&\\\(\[^\n\r]*\\\)\\\[0\\\] == &\\\(\[^\n\r]*\\\)\\\[0\\\]' to compare the addresses" "" { target c++ } .-3 } */
 }

diff --git a/gcc/testsuite/c-c++-common/Warray-compare-4.c b/gcc/testsuite/c-c++-common/Warray-compare-4.c
new file mode 100644 (file)
index 0000000..8cfb4b2
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Warray-compare-4.c
@@ -0,0 +1,50 @@
+/* PR c++/97573 */
+/* { dg-do compile } */
+
+#ifndef __cplusplus
+# define bool _Bool
+#endif
+
+int arr1[5];
+int arr2[5];
+int arr3[2][2];
+int arr4[2][2];
+
+bool
+g ()
+{
+  bool b = arr1 == arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 != arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 > arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 >= arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 < arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+  b &= arr1 <= arr2; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+#ifdef __cplusplus
+  b &= +arr1 == +arr2;
+  b &= +arr1 != +arr2;
+  b &= +arr1 > +arr2;
+  b &= +arr1 >= +arr2;
+  b &= +arr1 < +arr2;
+  b &= +arr1 <= +arr2;
+#endif
+  b &= &arr1[0] == &arr2[0];
+  b &= &arr1[0] != &arr2[0];
+  b &= &arr1[0] > &arr2[0];
+  b &= &arr1[0] >= &arr2[0];
+  b &= &arr1[0] < &arr2[0];
+  b &= &arr1[0] <= &arr2[0];
+
+  b &= arr3 == arr4; /* { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } } */
+/* { dg-error "comparison between two arrays" "" { target c++26 } .-1 } */
+
+#if defined(__cplusplus) && __cplusplus > 201703L
+  auto cmp = arr1 <=> arr2; /* { dg-error "invalid operands" "" { target c++20 } } */
+#endif
+  return b;
+}

diff --git a/gcc/testsuite/c-c++-common/Warray-compare-5.c b/gcc/testsuite/c-c++-common/Warray-compare-5.c
new file mode 100644 (file)
index 0000000..eab00d6
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Warray-compare-5.c
@@ -0,0 +1,44 @@
+/* PR c++/97573 */
+/* { dg-do compile } */
+/* { dg-options "-Wall -Wno-error=array-compare" } */
+
+#ifndef __cplusplus
+# define bool _Bool
+#endif
+
+int arr1[5];
+int arr2[5];
+int arr3[2][2];
+int arr4[2][2];
+
+bool
+g ()
+{
+  bool b = arr1 == arr2; /* { dg-warning "comparison between two arrays" } */
+  b &= arr1 != arr2; /* { dg-warning "comparison between two arrays" } */
+  b &= arr1 > arr2; /* { dg-warning "comparison between two arrays" } */
+  b &= arr1 >= arr2; /* { dg-warning "comparison between two arrays" } */
+  b &= arr1 < arr2; /* { dg-warning "comparison between two arrays" } */
+  b &= arr1 <= arr2; /* { dg-warning "comparison between two arrays" } */
+#ifdef __cplusplus
+  b &= +arr1 == +arr2;
+  b &= +arr1 != +arr2;
+  b &= +arr1 > +arr2;
+  b &= +arr1 >= +arr2;
+  b &= +arr1 < +arr2;
+  b &= +arr1 <= +arr2;
+#endif
+  b &= &arr1[0] == &arr2[0];
+  b &= &arr1[0] != &arr2[0];
+  b &= &arr1[0] > &arr2[0];
+  b &= &arr1[0] >= &arr2[0];
+  b &= &arr1[0] < &arr2[0];
+  b &= &arr1[0] <= &arr2[0];
+
+  b &= arr3 == arr4; /* { dg-warning "comparison between two arrays" } */
+
+#if defined(__cplusplus) && __cplusplus > 201703L
+  auto cmp = arr1 <=> arr2; /* { dg-error "invalid operands" "" { target c++20 } } */
+#endif
+  return b;
+}

diff --git a/gcc/testsuite/g++.dg/warn/Warray-compare-1.C b/gcc/testsuite/g++.dg/warn/Warray-compare-1.C
new file mode 100644 (file)
index 0000000..3241329
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Warray-compare-1.C
@@ -0,0 +1,26 @@
+// PR c++/117788
+// { dg-do compile { target c++11 } }
+
+constexpr int arr1[5]{};
+constexpr int arr2[5]{};
+
+template<int I>
+void f1 (int(*)[arr1 == arr2 ? I : I]) = delete;  // { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } }
+// { dg-error "comparison between two arrays" "" { target c++26 } .-1 }
+
+template<int>
+void f1 (...) { }
+
+template<int I>
+void f2 (int(*)[arr1 > arr2 ? I : 1]) = delete; // { dg-warning "comparison between two arrays" "" { target { c++20 && c++23_down } } }
+// { dg-error "comparison between two arrays" "" { target c++26 } .-1 }
+
+template<int>
+void f2 (...) { }
+
+void
+g ()
+{
+  f1<0>(nullptr);
+  f2<0>(nullptr);
+}

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/conditionally_borrowed.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/conditionally_borrowed.cc
index 4a0d1ff001a190c945524e5bb82e1461c6207d3d..4bc0d2da9e0777324e0ce304dfcf44cb107463e4 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/conditionally_borrowed.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/conditionally_borrowed.cc
@@ -61,7 +61,10 @@ void
 test02()
 {
   std::pair<int, std::string_view> a[2]{ {1,"two"}, {3,"four"}};
-  auto pos = ranges::find(a | views::values, "four");
+  // FIXME: We should be able to get rid of the decay via the + here.
+  // But we'd end up comparing two array types in equality_comparable_with
+  // -> __weakly_eq_cmp_with which is ill-formed in C++26 due to P2865.
+  auto pos = ranges::find(a | views::values, +"four");
   VERIFY( *pos == "four" );
 
   static_assert( ranges::borrowed_range<decltype(a | views::keys)> );