[C++ PATCH] Fix lval {REAL,IMAG}PART_EXPR constexpr evaluation (PR c++/71828)

[Jason Merrill]

OK.

On Mon, Jul 11, 2016 at 4:08 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> Hi!
>
> REALPART_EXPR and IMAGPART_EXPR are handled like unary expressions, even
> though they are references.  For !lval that makes no difference, but for
> lval it means we can get ADDR_EXPR of INTEGER_CST etc., or trying to store
> into an INTEGER_CST.
>
> Fixed by doing roughly what we do for other references like COMPONENT_REF,
> ARRAY_REF etc. in that case.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/6.2?
>
> 2016-07-11  Jakub Jelinek  <jakub@redhat.com>
>
>         PR c++/71828
>         * constexpr.c (cxx_eval_constant_expression) <case REALPART_EXPR>:
>         For lval don't use cxx_eval_unary_expression and instead recurse
>         and if needed rebuild the reference.
>
>         * g++.dg/cpp0x/constexpr-71828.C: New test.
>
> --- gcc/cp/constexpr.c.jj       2016-07-11 11:14:28.000000000 +0200
> +++ gcc/cp/constexpr.c  2016-07-11 13:30:17.333065119 +0200
> @@ -3790,6 +3790,19 @@ cxx_eval_constant_expression (const cons
>
>      case REALPART_EXPR:
>      case IMAGPART_EXPR:
> +      if (lval)
> +       {
> +         r = cxx_eval_constant_expression (ctx, TREE_OPERAND (t, 0), lval,
> +                                           non_constant_p, overflow_p);
> +         if (r == error_mark_node)
> +           ;
> +         else if (r == TREE_OPERAND (t, 0))
> +           r = t;
> +         else
> +           r = fold_build1 (TREE_CODE (t), TREE_TYPE (t), r);
> +         break;
> +       }
> +      /* FALLTHRU */
>      case CONJ_EXPR:
>      case FIX_TRUNC_EXPR:
>      case FLOAT_EXPR:
> --- gcc/testsuite/g++.dg/cpp0x/constexpr-71828.C.jj     2016-07-11 13:39:31.635423827 +0200
> +++ gcc/testsuite/g++.dg/cpp0x/constexpr-71828.C        2016-07-11 13:39:02.000000000 +0200
> @@ -0,0 +1,5 @@
> +// PR c++/71828
> +// { dg-do compile { target c++11 } }
> +
> +constexpr _Complex int a { 1, 2 };
> +static_assert (& __imag a != &__real a, "");
>
>         Jakub