Re: [C++ PATCH] Fix xvalue COND_EXPR handling (PR c++/88103)

[Jason Merrill <jason@redhat.com>]

On 11/29/18 4:52 PM, Jakub Jelinek wrote:
> Hi!
> 
> On the following testcase, build_conditional_expr_1 tries hard to make sure
> that if both arguments are xvalue_p (or one is and the other throw) the
> result is still xvalue_p.  But, later on we call unary_complex_lvalue,
> which does rationalize_conditional_expr which changes it from
> cond ? x : y to *(cond ? &x : &y) and that change turns something formerly
> xvalue_p into newly lvalue_p.
> 
> Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux,
> ok for trunk?
> 
> 2018-11-29  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/88103
> 	* typeck.c (unary_complex_lvalue): If a COND_EXPR is xvalue_p, make
> 	sure the result is as well.
> 
> 	* g++.dg/cpp0x/rv-cond3.C: New test.
> 
> --- gcc/cp/typeck.c.jj	2018-11-27 09:48:58.506103668 +0100
> +++ gcc/cp/typeck.c	2018-11-29 21:00:33.900636750 +0100
> @@ -6503,7 +6503,16 @@ unary_complex_lvalue (enum tree_code cod
>     /* Handle (a ? b : c) used as an "lvalue".  */
>     if (TREE_CODE (arg) == COND_EXPR
>         || TREE_CODE (arg) == MIN_EXPR || TREE_CODE (arg) == MAX_EXPR)
> -    return rationalize_conditional_expr (code, arg, tf_warning_or_error);
> +    {
> +      tree ret = rationalize_conditional_expr (code, arg, tf_warning_or_error);
> +      /* Preserve xvalue kind.  */
> +      if (xvalue_p (arg))
> +	{
> +	  tree reftype = cp_build_reference_type (TREE_TYPE (arg), true);
> +	  ret = cp_convert (reftype, ret, tf_warning_or_error);

Is there a reason not to use the 'move' function here?

Jason