Re: C++ PATCH to tweak cp_fully_fold (PR c++/84590)

[Jason Merrill <jason at redhat dot com>]

On Thu, Mar 1, 2018 at 2:12 PM, Marek Polacek <polacek@redhat.com> wrote:
> In this testcase we find ourselves in split_nonconstant_init:
>
>        init = cp_fully_fold (init);
>        code = push_stmt_list ();
>        if (split_nonconstant_init_1 (dest, init))
>
> where initially INIT was a CONSTRUCTOR, but cp_fully_fold returned
> a TARGET_EXPR.  This confuses split_nonconstant_init_1 which only expects
> a CONSTRUCTOR or a VECTOR_CST.  Jason suggested stripping TARGET_EXPRs /
> VIEW_CONVERT_EXPRs, so here it is.
>
> Bootstrapped/regtested on x86_64-linux, ok for trunk?
>
> 2018-03-01  Marek Polacek  <polacek@redhat.com>
>
>         PR c++/84590
>         * cp-gimplify.c (cp_fully_fold): Unwrap TARGET_EXPR or a CONSTRUCTOR
>         wrapped in VIEW_CONVERT_EXPR.
>
>         * c-c++-common/ubsan/shift-11.c: New test.
>
> diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
> index 55a9d278dbe..1fa9c466e6b 100644
> --- gcc/cp/cp-gimplify.c
> +++ gcc/cp/cp-gimplify.c
> @@ -2038,7 +2038,18 @@ cp_fully_fold (tree x)
>       have to call both.  */
>    if (cxx_dialect >= cxx11)
>      x = maybe_constant_value (x);
> -  return cp_fold_rvalue (x);
> +  x = cp_fold_rvalue (x);
> +
> +  /* Sometimes we are given a CONSTRUCTOR but cxx_eval_outermost_constant_expr
> +     wraps it into a TARGET_EXPR; undo that here.  */
> +  if (TREE_CODE (x) == TARGET_EXPR)
> +    x = TARGET_EXPR_INITIAL (x);
> +  else if (TREE_CODE (x) == VIEW_CONVERT_EXPR
> +          && TREE_CODE (TREE_OPERAND (x, 0)) == CONSTRUCTOR
> +          && TREE_TYPE (TREE_OPERAND (x, 0)) == TREE_TYPE (x))
> +    x = TREE_OPERAND (x, 0);

I think this should happen in the block with maybe_constant_value;
cp_fold_rvalue doesn't do this.

Jason