On Fri, Nov 14, 2025 at 3:03 PM Robin Dapp <[email protected]> wrote:
>
> Hi,
>
> Currently select_vl is a direct optab with its mode always Xmode/Pmode.
> This does not give us sufficient freedom to enable/disable vsetvl
> (=SELECT_VL) depending on the vector mode.
>
> This patch makes select_vl a convert optab and adjusts the associated IFN
> functions as well as the query/emit code in the vectorizer.
>
> With this patch nothing new is actually exercised yet. This is going to
> happen in a separate riscv patch that enables "VLS" select_vl.
>
> Bootstrapped on x86 and power10. Regtested on riscv64 (with and without
> follow-up patches).
OK.
Thanks,
Richard.
> Regards
> Robin
>
> gcc/ChangeLog:
>
> * config/riscv/autovec.md (select_vl<mode>): Rename to...
> (select_vl<V:mode><P:mode>): ...this.
> * doc/md.texi: Document new behavior.
> * internal-fn.cc (select_vl_direct): Make
> (expand_select_vl_optab_fn): Adjust for convert optab.
> (direct_select_vl_optab_supported_p): Ditto.
> * internal-fn.def (SELECT_VL): Ditto.
> * optabs.def (OPTAB_CD): Add select_vl.
> (OPTAB_D): Remove select_vl.
> * tree-vect-loop-manip.cc (vect_set_loop_controls_directly):
> Adjust for convert select_vl optab.
> * tree-vect-loop.cc: Ditto.
> ---
> gcc/config/riscv/autovec.md | 5 +++--
> gcc/doc/md.texi | 17 +++++++++--------
> gcc/internal-fn.cc | 5 +++++
> gcc/internal-fn.def | 2 +-
> gcc/optabs.def | 2 +-
> gcc/tree-vect-loop-manip.cc | 4 +++-
> gcc/tree-vect-loop.cc | 15 ++++++++++++---
> 7 files changed, 34 insertions(+), 16 deletions(-)
>
> diff --git a/gcc/config/riscv/autovec.md b/gcc/config/riscv/autovec.md
> index 60beab98e03..bb66afad30b 100644
> --- a/gcc/config/riscv/autovec.md
> +++ b/gcc/config/riscv/autovec.md
> @@ -1334,10 +1334,11 @@ (define_insn_and_split "fnms<mode>4"
> ;; == SELECT_VL
> ;; =========================================================================
>
> -(define_expand "select_vl<mode>"
> +(define_expand "select_vl<V:mode><P:mode>"
> [(match_operand:P 0 "register_operand")
> (match_operand:P 1 "vector_length_operand")
> - (match_operand:P 2 "immediate_operand")]
> + (match_operand:P 2 "immediate_operand")
> + (match_operand:V 3)]
> "TARGET_VECTOR"
> {
> riscv_vector::expand_select_vl (operands);
> diff --git a/gcc/doc/md.texi b/gcc/doc/md.texi
> index ae5d709bd47..6dedca225ae 100644
> --- a/gcc/doc/md.texi
> +++ b/gcc/doc/md.texi
> @@ -5273,13 +5273,14 @@ for (i = 1; i < operand3; i++)
> operand0[i] = operand0[i - 1] && (operand1 + i < operand2);
> @end smallexample
>
> -@cindex @code{select_vl@var{m}} instruction pattern
> -@item @code{select_vl@var{m}}
> -Set operand 0 to the number of scalar iterations that should be handled
> -by one iteration of a vector loop. Operand 1 is the total number of
> -scalar iterations that the loop needs to process and operand 2 is a
> -maximum bound on the result (also known as the maximum ``vectorization
> -factor'').
> +@cindex @code{select_vl@var{m}@var{n}} instruction pattern
> +@item @code{select_vl@var{m}@var{n}}
> +Set operand 0 (of mode @var{n}) to the number of scalar iterations that
> +should be handled by one iteration of a vector loop. Operand 1 is the
> +total number of scalar iterations that the loop needs to process and
> +operand 2 is a maximum bound on the result (also known as the
> +maximum ``vectorization factor''). Operand 3 (of mode @var{m}) is
> +a dummy parameter to pass the vector mode to be used.
>
> The maximum value of operand 0 is given by:
> @smallexample
> @@ -5293,7 +5294,7 @@ this, it is generally not useful to define this
> instruction if it will
> always calculate the maximum value.
>
> This optab is only useful on targets that implement @samp{len_load_@var{m}}
> -and/or @samp{len_store_@var{m}}.
> +and/or @samp{len_store_@var{m}} or the associated @samp{_len} variants.
>
> @cindex @code{check_raw_ptrs@var{m}} instruction pattern
> @item @samp{check_raw_ptrs@var{m}}
> diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
> index 514fe98f40d..13fbd2ce788 100644
> --- a/gcc/internal-fn.cc
> +++ b/gcc/internal-fn.cc
> @@ -195,6 +195,7 @@ init_internal_fns ()
> #define check_ptrs_direct { 0, 0, false }
> #define crc_direct { 1, -1, true }
> #define reduc_sbool_direct { 0, 0, true }
> +#define select_vl_direct { 2, 0, false }
>
> const direct_internal_fn_info direct_internal_fn_array[IFN_LAST + 1] = {
> #define DEF_INTERNAL_FN(CODE, FLAGS, FNSPEC) not_direct,
> @@ -4183,6 +4184,9 @@ expand_reduc_sbool_optab_fn (internal_fn fn, gcall
> *stmt, direct_optab optab)
> #define expand_check_ptrs_optab_fn(FN, STMT, OPTAB) \
> expand_direct_optab_fn (FN, STMT, OPTAB, 4)
>
> +#define expand_select_vl_optab_fn(FN, STMT, OPTAB) \
> + expand_convert_optab_fn (FN, STMT, OPTAB, 3)
> +
> /* Expanders for optabs that can use expand_convert_optab_fn. */
>
> #define expand_unary_convert_optab_fn(FN, STMT, OPTAB) \
> @@ -4299,6 +4303,7 @@ multi_vector_optab_supported_p (convert_optab optab,
> tree_pair types,
> #define direct_vec_set_optab_supported_p direct_optab_supported_p
> #define direct_vec_extract_optab_supported_p convert_optab_supported_p
> #define direct_reduc_sbool_optab_supported_p direct_optab_supported_p
> +#define direct_select_vl_optab_supported_p convert_optab_supported_p
>
> /* Return the optab used by internal function FN. */
>
> diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
> index 7874fcfb3df..4e83a59880e 100644
> --- a/gcc/internal-fn.def
> +++ b/gcc/internal-fn.def
> @@ -250,7 +250,7 @@ DEF_INTERNAL_OPTAB_FN (LEN_STORE, 0, len_store, len_store)
> DEF_INTERNAL_OPTAB_FN (MASK_LEN_STORE, 0, mask_len_store, mask_len_store)
>
> DEF_INTERNAL_OPTAB_FN (WHILE_ULT, ECF_CONST | ECF_NOTHROW, while_ult, while)
> -DEF_INTERNAL_OPTAB_FN (SELECT_VL, ECF_CONST | ECF_NOTHROW, select_vl, binary)
> +DEF_INTERNAL_OPTAB_FN (SELECT_VL, ECF_CONST | ECF_NOTHROW, select_vl,
> select_vl)
> DEF_INTERNAL_OPTAB_FN (CHECK_RAW_PTRS, ECF_CONST | ECF_NOTHROW,
> check_raw_ptrs, check_ptrs)
> DEF_INTERNAL_OPTAB_FN (CHECK_WAR_PTRS, ECF_CONST | ECF_NOTHROW,
> diff --git a/gcc/optabs.def b/gcc/optabs.def
> index b6f290a9513..5218b6d6ec0 100644
> --- a/gcc/optabs.def
> +++ b/gcc/optabs.def
> @@ -116,6 +116,7 @@ OPTAB_CD (udot_prod_optab, "udot_prod$I$a$b")
> OPTAB_CD (usdot_prod_optab, "usdot_prod$I$a$b")
>
> OPTAB_CD (while_ult_optab, "while_ult$a$b")
> +OPTAB_CD (select_vl_optab, "select_vl$a$b")
>
> OPTAB_NL(add_optab, "add$P$a3", PLUS, "add", '3', gen_int_fp_fixed_libfunc)
> OPTAB_NX(add_optab, "add$F$a3")
> @@ -553,6 +554,5 @@ OPTAB_D (len_load_optab, "len_load_$a")
> OPTAB_D (len_store_optab, "len_store_$a")
> OPTAB_D (mask_len_strided_load_optab, "mask_len_strided_load_$a")
> OPTAB_D (mask_len_strided_store_optab, "mask_len_strided_store_$a")
> -OPTAB_D (select_vl_optab, "select_vl$a")
> OPTAB_D (andn_optab, "andn$a3")
> OPTAB_D (iorn_optab, "iorn$a3")
> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> index 3e121a96ddf..9e5a00f3fc6 100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -574,8 +574,10 @@ vect_set_loop_controls_directly (class loop *loop,
> loop_vec_info loop_vinfo,
> {
> create_iv (nitems_total, MINUS_EXPR, step, NULL_TREE, loop,
> &incr_gsi,
> insert_after, &index_before_incr, &index_after_incr);
> + tree vectype = build_zero_cst (rgc->type);
> tree len = gimple_build (header_seq, IFN_SELECT_VL, iv_type,
> - index_before_incr, nitems_step);
> + index_before_incr, nitems_step,
> + vectype);
> gimple_seq_add_stmt (header_seq, gimple_build_assign (step, len));
> }
> else
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 576a69c82d2..65cf0d42995 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -2428,14 +2428,23 @@ start_over:
> if (LOOP_VINFO_USING_DECREMENTING_IV_P (loop_vinfo))
> {
> tree iv_type = LOOP_VINFO_RGROUP_IV_TYPE (loop_vinfo);
> - if (direct_internal_fn_supported_p (IFN_SELECT_VL, iv_type,
> - OPTIMIZE_FOR_SPEED)
> - && LOOP_VINFO_LENS (loop_vinfo).length () == 1
> + if (LOOP_VINFO_LENS (loop_vinfo).length () == 1
> && LOOP_VINFO_LENS (loop_vinfo)[0].factor == 1
> && (!LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
> || !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ()))
> LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo) = true;
>
> + if (LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo))
> + for (auto rgc : LOOP_VINFO_LENS (loop_vinfo))
> + if (rgc.type
> + && !direct_internal_fn_supported_p (IFN_SELECT_VL,
> + rgc.type, iv_type,
> + OPTIMIZE_FOR_SPEED))
> + {
> + LOOP_VINFO_USING_SELECT_VL_P (loop_vinfo) = false;
> + break;
> + }
> +
> /* If any of the SLP instances cover more than a single lane
> we cannot use .SELECT_VL at the moment, even if the number
> of lanes is uniform throughout the SLP graph. */
> --
> 2.51.0
>
