Re: [PATCH] c++: Ensure !!var is not an lvalue [PR107065]

[Jason Merrill <jason@redhat.com>]

On 12/10/22 04:33, Jakub Jelinek wrote:
> Hi!
> 
> The TRUTH_NOT_EXPR case in cp_build_unary_op is one of the spots where
> we somewhat fold immediately using invert_truthvalue_loc.
> I've tried using
>    return build1_loc (location, TRUTH_NOT_EXPR, boolean_type_node, arg);
> in there instead, but unfortunately that regressed
> Wlogical-not-parentheses-*.c pr49706.c pr62199.c pr65120.c sequence-pt-1.C
> tests, so at least for backporting that doesn't seem to be a way to go.
> 
> So, this patch instead wraps it into NON_LVALUE_EXPR if needed (which also
> need a tweak for some tests in the pr47906.c test, but nothing major),
> with the intent to make it backportable, and later I'll try to do further
> steps to avoid folding here prematurely.  Most of the problems with
> build1 TRUTH_NOT_EXPR are that it doesn't even invert comparisons as most
> common case and lots of warning code isn't able to deal with ! around
> comparisons; so perhaps one way to do this would be fold by hand only
> invertable comparisons and for the rest create TRUTH_NOT_EXPR.
> 
> Anyway, bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk
> (for now) and for release branches (after a while on the trunk)?

OK.

> 2022-12-10  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/107065
> gcc/cp/
> 	* typeck.cc (cp_build_unary_op) <case TRUTH_NOT_EXPR>: If
> 	invert_truthvalue_loc returns obvalue_p, wrap it into NON_LVALUE_EXPR.
> 	* parser.cc (cp_parser_binary_expression): Don't call
> 	warn_logical_not_parentheses if current.lhs is a NON_LVALUE_EXPR
> 	of a decl with boolean type.
> gcc/testsuite/
> 	* g++.dg/cpp0x/pr107065.C: New test.
> 
> --- gcc/cp/typeck.cc.jj	2022-11-30 10:29:42.024701797 +0100
> +++ gcc/cp/typeck.cc	2022-12-09 17:47:54.132856233 +0100
> @@ -7396,9 +7396,13 @@ cp_build_unary_op (enum tree_code code,
>   				   build_zero_cst (TREE_TYPE (arg)), complain);
>         arg = perform_implicit_conversion (boolean_type_node, arg,
>   					 complain);
> -      val = invert_truthvalue_loc (location, arg);
>         if (arg != error_mark_node)
> -	return val;
> +	{
> +	  val = invert_truthvalue_loc (location, arg);
> +	  if (obvalue_p (val))
> +	    val = non_lvalue_loc (location, val);
> +	  return val;
> +	}
>         errstring = _("in argument to unary !");
>         break;
>   
> --- gcc/cp/parser.cc.jj	2022-12-09 11:02:35.871444993 +0100
> +++ gcc/cp/parser.cc	2022-12-09 19:14:26.698847734 +0100
> @@ -10224,7 +10224,10 @@ cp_parser_binary_expression (cp_parser*
>   		      || (TREE_CODE (TREE_TYPE (TREE_OPERAND (current.lhs, 0)))
>   			  != BOOLEAN_TYPE))))
>   	  /* Avoid warning for !!b == y where b is boolean.  */
> -	  && (!DECL_P (tree_strip_any_location_wrapper (current.lhs))
> +	  && (!(DECL_P (tree_strip_any_location_wrapper (current.lhs))
> +		|| (TREE_CODE (current.lhs) == NON_LVALUE_EXPR
> +		    && DECL_P (tree_strip_any_location_wrapper
> +					    (TREE_OPERAND (current.lhs, 0)))))
>   	      || TREE_TYPE (current.lhs) == NULL_TREE
>   	      || TREE_CODE (TREE_TYPE (current.lhs)) != BOOLEAN_TYPE))
>   	warn_logical_not_parentheses (current.loc, current.tree_type,
> --- gcc/testsuite/g++.dg/cpp0x/pr107065.C.jj	2022-12-09 16:22:59.686548071 +0100
> +++ gcc/testsuite/g++.dg/cpp0x/pr107065.C	2022-12-09 16:22:59.686548071 +0100
> @@ -0,0 +1,14 @@
> +// PR c++/107065
> +// { dg-do compile { target c++11 } }
> +
> +template<class, class> struct is_same { static constexpr bool value = false; };
> +template<class T> struct is_same<T, T> { static constexpr bool value = true; };
> +
> +int
> +main ()
> +{
> +  bool b = true;
> +  static_assert (is_same<decltype (!(!b)), bool>::value, "");
> +  auto bb = (!(!b));
> +  static_assert (is_same<decltype (bb), bool>::value, "");
> +}
> 
> 	Jakub
>