On Sun, May 1, 2022 at 2:15 PM Aldy Hernandez via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> We are ICEing in set_range_info_raw because value_range_kind cannot be
> VR_VARYING, since SSA_NAME_RANGE_TYPE can only hold VR_RANGE /
> VR_ANTI_RANGE. Most of the time setting a VR_VARYING as a global
> range makes no sense. However, we can have a range spanning the
> entire domain (VR_RANGE of [MIN,MAX] which is essentially a
> VR_VARYING), if the nonzero bits are set.
>
> This was working before because set_range_info_raw allows setting
> VR_RANGE of [MIN, MAX]. However, when going through an irange, we
> normalize this to a VR_VARYING, thus causing the ICE. It's
> interesting that other calls to set_range_info with an irange haven't
> triggered this.
>
> One solution would be to just ignore VR_VARYING and bail, since
> set_range_info* is really an update of the current range semantic
> wise. After all, we keep the nonzero bits which provide additional
> info. But this would be a change in behavior, so not suitable until
> after GCC 12 is released. So in order to keep with current behavior
> we can just denormalize the varying to VR_RANGE.
But there's no point in storing such info - shouldn't the function simply
clear the range and return? Or at least avoid allocating a new range
-info and just return if none is associated with the SSA name at the moment?
> Tested on x86-64 Linux.
>
> PR tree-optimization/105432
>
> gcc/ChangeLog:
>
> * tree-ssanames.cc (set_range_info): Denormalize VR_VARYING to
> VR_RANGE before passing a piecewise range to set_range_info_raw.
> ---
> gcc/tree-ssanames.cc | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-ssanames.cc b/gcc/tree-ssanames.cc
> index c957597af4f..05536cd2f74 100644
> --- a/gcc/tree-ssanames.cc
> +++ b/gcc/tree-ssanames.cc
> @@ -395,8 +395,17 @@ set_range_info (tree name, enum value_range_kind
> range_type,
> {
> gcc_assert (!POINTER_TYPE_P (TREE_TYPE (name)));
>
> - /* A range of the entire domain is really no range at all. */
> tree type = TREE_TYPE (name);
> + if (range_type == VR_VARYING)
> + {
> + /* SSA_NAME_RANGE_TYPE can only hold a VR_RANGE or
> + VR_ANTI_RANGE. Denormalize VR_VARYING to VR_RANGE. */
> + range_type = VR_RANGE;
> + gcc_checking_assert (min == wi::min_value (type));
> + gcc_checking_assert (max == wi::max_value (type));
> + }
> +
> + /* A range of the entire domain is really no range at all. */
> if (min == wi::min_value (TYPE_PRECISION (type), TYPE_SIGN (type))
> && max == wi::max_value (TYPE_PRECISION (type), TYPE_SIGN (type)))
> {
> --
> 2.35.1
>
