On Mon, Dec 19, 2022 at 9:12 AM Kewen.Lin <li...@linux.ibm.com> wrote:
>
> Hi,
>
> In function fold_convert_const_real_from_real, when the modes of
> two types involved in fp conversion are the same, we can simply
> take it as copy, rebuild with the exactly same TREE_REAL_CST and
> the target type. It is more efficient and helps to avoid possible
> unexpected signalling bit clearing in [1].
>
> Bootstrapped and regtested on x86_64-redhat-linux, aarch64-linux-gnu
> and powerpc64{,le}-linux-gnu.
>
> Is it ok for trunk?
But shouldn't
double x = (double) __builtin_nans("sNAN");
result in a quiet NaN?
> [1] https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608533.html
>
> gcc/ChangeLog:
>
> * fold-const.cc (fold_convert_const_real_from_real): Treat floating
> point conversion to a type with same mode as copy instead of normal
> convertFormat.
> ---
> gcc/fold-const.cc | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/gcc/fold-const.cc b/gcc/fold-const.cc
> index 114258fa182..eb4b6ca8820 100644
> --- a/gcc/fold-const.cc
> +++ b/gcc/fold-const.cc
> @@ -2178,6 +2178,15 @@ fold_convert_const_real_from_real (tree type,
> const_tree arg1)
> REAL_VALUE_TYPE value;
> tree t;
>
> + /* If the underlying modes are the same, simply treat it as
> + copy and rebuild with TREE_REAL_CST information and the
> + given type. */
> + if (TYPE_MODE (type) == TYPE_MODE (TREE_TYPE (arg1)))
> + {
> + t = build_real (type, TREE_REAL_CST (arg1));
> + return t;
> + }
> +
> /* Don't perform the operation if flag_signaling_nans is on
> and the operand is a signaling NaN. */
> if (HONOR_SNANS (arg1)
> --
> 2.27.0
