On Thu, Jul 13, 2023 at 12:31 PM Robin Dapp via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Hi,
>
> the recent changes that allowed multi-step conversions for
> "non-packing/unpacking", i.e. modifier == NONE targets included
> promoting to-float and demoting to-int variants. This patch
> adds demoting to-float and promoting to-int handling.
Can you add testcases? Also the current restriction is because
the variants you add are not always correct and I don't see any
checks that the intermediate type doesn't lose significant bits?
Richard.
> Bootstrapped and regtested on x86 and aarch64.
>
> A question that seems related: Why do we require !flag_trapping_math
> for the "NONE" multistep conversion but not for the "NARROW_DST"
> case when both seem to handle float -> int and there are float
> values that do not have an int representation? If a backend
> can guarantee that the conversion traps, should it just implement
> a multistep conversion in a matching expander?
>
> Regards
> Robin
>
>
> gcc/ChangeLog:
>
> * tree-vect-stmts.cc (vectorizable_conversion): Handle
> more demotion/promotion for modifier == NONE.
> ---
> gcc/tree-vect-stmts.cc | 40 +++++++++++++++++++++++++++++-----------
> 1 file changed, 29 insertions(+), 11 deletions(-)
>
> diff --git a/gcc/tree-vect-stmts.cc b/gcc/tree-vect-stmts.cc
> index 10e71178ce7..78e0510be7e 100644
> --- a/gcc/tree-vect-stmts.cc
> +++ b/gcc/tree-vect-stmts.cc
> @@ -5324,28 +5324,46 @@ vectorizable_conversion (vec_info *vinfo,
> break;
> }
>
> - /* For conversions between float and smaller integer types try whether
> we
> - can use intermediate signed integer types to support the
> + /* For conversions between float and larger integer types try whether
> + we can use intermediate signed integer types to support the
> conversion. */
> if ((code == FLOAT_EXPR
> - && GET_MODE_SIZE (lhs_mode) > GET_MODE_SIZE (rhs_mode))
> + && GET_MODE_SIZE (lhs_mode) != GET_MODE_SIZE (rhs_mode))
> || (code == FIX_TRUNC_EXPR
> - && GET_MODE_SIZE (rhs_mode) > GET_MODE_SIZE (lhs_mode)
> - && !flag_trapping_math))
> + && ((GET_MODE_SIZE (rhs_mode) > GET_MODE_SIZE (lhs_mode)
> + && !flag_trapping_math)
> + || GET_MODE_SIZE (rhs_mode) < GET_MODE_SIZE (lhs_mode))))
> {
> + bool demotion = GET_MODE_SIZE (rhs_mode) > GET_MODE_SIZE (lhs_mode);
> bool float_expr_p = code == FLOAT_EXPR;
> - scalar_mode imode = float_expr_p ? rhs_mode : lhs_mode;
> - fltsz = GET_MODE_SIZE (float_expr_p ? lhs_mode : rhs_mode);
> + unsigned short target_size;
> + scalar_mode intermediate_mode;
> + if (demotion)
> + {
> + intermediate_mode = lhs_mode;
> + target_size = GET_MODE_SIZE (rhs_mode);
> + }
> + else
> + {
> + target_size = GET_MODE_SIZE (lhs_mode);
> + tree itype
> + = build_nonstandard_integer_type (GET_MODE_BITSIZE
> + (rhs_mode), 0);
> + intermediate_mode = SCALAR_TYPE_MODE (itype);
> + }
> code1 = float_expr_p ? code : NOP_EXPR;
> codecvt1 = float_expr_p ? NOP_EXPR : code;
> - FOR_EACH_2XWIDER_MODE (rhs_mode_iter, imode)
> + opt_scalar_mode mode_iter;
> + FOR_EACH_2XWIDER_MODE (mode_iter, intermediate_mode)
> {
> - imode = rhs_mode_iter.require ();
> - if (GET_MODE_SIZE (imode) > fltsz)
> + intermediate_mode = mode_iter.require ();
> +
> + if (GET_MODE_SIZE (intermediate_mode) > target_size)
> break;
>
> cvt_type
> - = build_nonstandard_integer_type (GET_MODE_BITSIZE (imode),
> + = build_nonstandard_integer_type (GET_MODE_BITSIZE
> + (intermediate_mode),
> 0);
> cvt_type = get_vectype_for_scalar_type (vinfo, cvt_type,
> slp_node);
> --
> 2.41.0
>
