[Bug c++/67333] [C++11][constexpr] constexpr functions incorrectly prohibit taking references to volatile types

["miyuki at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67333

Mikhail Maltsev <miyuki at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |miyuki at gcc dot gnu.org

--- Comment #1 from Mikhail Maltsev <miyuki at gcc dot gnu.org> ---
EDG accepts the first testcase. The second one is rejected, but presumably due
to incomplete C++14 support.

In potential_constant_expression_1 we have a check:

  if (TREE_THIS_VOLATILE (t))
    {
      if (flags & tf_error)
        error ("expression %qE has side-effects", t);

The comment in tree.h says:
/* Nonzero means this expression is volatile in the C sense:
   its address should be of type `volatile WHATEVER *'.
   In other words, the declared item is volatile qualified.
...
   If this bit is set in an expression, so is TREE_SIDE_EFFECTS.  */

In our case t is:
(gdb) p t
$10 = <var_decl 0x7ffff66a7cf0 meow>
(gdb) pt
warning: Expression is not an assignment (and might have no effect)
 <var_decl 0x7ffff66a7cf0 meow
    type <array_type 0x7ffff6800c78
        type <integer_type 0x7ffff6800a80 int volatile type_6 SI
            size <integer_cst 0x7ffff66bd0a8 constant 32>
            unit size <integer_cst 0x7ffff66bd0c0 constant 4>
            align 32 symtab 0 alias set -1 canonical type 0x7ffff6800a80
precision 32 min <integer_cst 0x7ffff66bd060 -2147483648> max <integer_cst
0x7ffff66bd078 2147483647>
            pointer_to_this <pointer_type 0x7ffff6800d20>>
        TI
        size <integer_cst 0x7ffff669bea0 constant 128>
        unit size <integer_cst 0x7ffff669beb8 constant 16>
        align 32 symtab 0 alias set -1 canonical type 0x7ffff6800c78
        domain <integer_type 0x7ffff6800b28 type <integer_type 0x7ffff669f1f8
sizetype>
            type_6 DI
            size <integer_cst 0x7ffff669be58 constant 64>
            unit size <integer_cst 0x7ffff669be70 constant 8>
            align 64 symtab 0 alias set -1 canonical type 0x7ffff6800b28
precision 64 min <integer_cst 0x7ffff669be88 0> max <integer_cst 0x7ffff680adc8
3>>
        pointer_to_this <pointer_type 0x7ffff68133f0>>
    side-effects addressable volatile used tree_1 decl_5 TI file
/home/miyuki/gcc/test/meow/meow.cc line 15 col 18 size <integer_cst
0x7ffff669bea0 128> unit size <integer_cst 0x7ffff669beb8 16>
    align 32 context <function_decl 0x7ffff67ffe00 main>>

I.e. the condition is probably wrong and we should also check that t is an
expression, not a declaration.