On Mon, 6 Nov 2023, Tamar Christina wrote:
> Hi All,
>
> This finishes wiring that didn't fit in any of the other patches.
> Essentially just adding related changes so peeling for early break works.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> * tree-vect-loop-manip.cc (vect_set_loop_condition_normal,
> vect_do_peeling): Support early breaks.
> * tree-vect-loop.cc (vect_need_peeling_or_partial_vectors_p): Likewise.
> * tree-vectorizer.cc (pass_vectorize::execute): Check all exits.
>
> --- inline copy of patch --
> diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
> index
> eef2bb50c1505f5cf802d5d80300affc2cbe69f6..9c1405d79fd8fe8689007df3b7605b7a3d3ecdd7
> 100644
> --- a/gcc/tree-vect-loop-manip.cc
> +++ b/gcc/tree-vect-loop-manip.cc
> @@ -1187,7 +1187,7 @@ vect_set_loop_condition_partial_vectors_avx512 (class
> loop *loop,
> loop handles exactly VF scalars per iteration. */
>
> static gcond *
> -vect_set_loop_condition_normal (loop_vec_info /* loop_vinfo */, edge
> exit_edge,
> +vect_set_loop_condition_normal (loop_vec_info loop_vinfo, edge exit_edge,
> class loop *loop, tree niters, tree step,
> tree final_iv, bool niters_maybe_zero,
> gimple_stmt_iterator loop_cond_gsi)
> @@ -1296,7 +1296,8 @@ vect_set_loop_condition_normal (loop_vec_info /*
> loop_vinfo */, edge exit_edge,
> gsi_insert_before (&loop_cond_gsi, cond_stmt, GSI_SAME_STMT);
>
> /* Record the number of latch iterations. */
> - if (limit == niters)
> + if (limit == niters
> + || LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
> /* Case A: the loop iterates NITERS times. Subtract one to get the
> latch count. */
> loop->nb_iterations = fold_build2 (MINUS_EXPR, niters_type, niters,
> @@ -3242,6 +3243,16 @@ vect_do_peeling (loop_vec_info loop_vinfo, tree
> niters, tree nitersm1,
> bound_epilog += vf - 1;
> if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo))
> bound_epilog += 1;
> +
> + /* For early breaks the scalar loop needs to execute at most VF times
> + to find the element that caused the break. */
> + if (LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
> + {
> + bound_epilog = vf;
> + /* Force a scalar epilogue as we can't vectorize the index finding. */
> + vect_epilogues = false;
This is originally initialized with
bool vect_epilogues = loop_vinfo->epilogue_vinfos.length () > 0;
so I think we should avoid filling that with LOOP_VINFO_EARLY_BREAKS
rather than fixing up after the fact? That is in vect_analyze_loop
adjust
/* Only vectorize epilogues if PARAM_VECT_EPILOGUES_NOMASK is
enabled, SIMDUID is not set, it is the innermost loop and we have
either already found the loop's SIMDLEN or there was no SIMDLEN to
begin with.
TODO: Enable epilogue vectorization for loops with SIMDUID set. */
bool vect_epilogues = (!simdlen
&& loop->inner == NULL
&& param_vect_epilogues_nomask
&& LOOP_VINFO_PEELING_FOR_NITER
(first_loop_vinfo)
&& !loop->simduid);
and add !LOOP_VINFO_EARLY_BREAKS?
> + }
> +
> bool epilog_peeling = maybe_ne (bound_epilog, 0U);
> poly_uint64 bound_scalar = bound_epilog;
>
> @@ -3376,14 +3387,23 @@ vect_do_peeling (loop_vec_info loop_vinfo, tree
> niters, tree nitersm1,
> bound_prolog + bound_epilog)
> : (!LOOP_REQUIRES_VERSIONING (loop_vinfo)
> || vect_epilogues));
> +
> + /* We only support early break vectorization on known bounds at this time.
> + This means that if the vector loop can't be entered then we won't
> generate
> + it at all. So for now force skip_vector off because the additional
> control
> + flow messes with the BB exits and we've already analyzed them. */
> + skip_vector = skip_vector && !LOOP_VINFO_EARLY_BREAKS (loop_vinfo);
> +
bool skip_vector = (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
? maybe_lt (LOOP_VINFO_INT_NITERS (loop_vinfo),
bound_prolog + bound_epilog)
: (!LOOP_REQUIRES_VERSIONING (loop_vinfo)
|| vect_epilogues));
to me that looks like
gcc_assert (!skip_vector || !LOOP_VINFO_EARLY_BREAKS (loop_vinfo));
should work? You are basically relying on cost modeling rejecting
vectorization that doesn't enter the vector loop.
> /* Epilog loop must be executed if the number of iterations for epilog
> loop is known at compile time, otherwise we need to add a check at
> the end of vector loop and skip to the end of epilog loop. */
> bool skip_epilog = (prolog_peeling < 0
> || !LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
> || !vf.is_constant ());
> - /* PEELING_FOR_GAPS is special because epilog loop must be executed. */
> - if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo))
> + /* PEELING_FOR_GAPS and peeling for early breaks are special because epilog
> + loop must be executed. */
> + if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)
> + || LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
> skip_epilog = false;
>
> class loop *scalar_loop = LOOP_VINFO_SCALAR_LOOP (loop_vinfo);
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index
> 55d6aee3d29151e6b528f6fdde15c693e5bdd847..51a054c5b035ac80dfbbf3b5ba2f6da82fda91f6
> 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -1236,6 +1236,14 @@ vect_need_peeling_or_partial_vectors_p (loop_vec_info
> loop_vinfo)
> th = LOOP_VINFO_COST_MODEL_THRESHOLD (LOOP_VINFO_ORIG_LOOP_INFO
> (loop_vinfo));
>
> + /* When we have multiple exits and VF is unknown, we must require partial
> + vectors because the loop bounds is not a minimum but a maximum. That
> is to
> + say we cannot unpredicate the main loop unless we peel or use partial
> + vectors in the epilogue. */
> + if (LOOP_VINFO_EARLY_BREAKS (loop_vinfo)
> + && !LOOP_VINFO_VECT_FACTOR (loop_vinfo).is_constant ())
> + return true;
> +
I don't quite understand the !.is_constant (), early breaks always
require peeling?
> if (LOOP_VINFO_NITERS_KNOWN_P (loop_vinfo)
> && LOOP_VINFO_PEELING_FOR_ALIGNMENT (loop_vinfo) >= 0)
> {
> @@ -3149,7 +3157,8 @@ start_over:
>
> /* If an epilogue loop is required make sure we can create one. */
> if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo)
> - || LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo))
> + || LOOP_VINFO_PEELING_FOR_NITER (loop_vinfo)
> + || LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
> {
> if (dump_enabled_p ())
> dump_printf_loc (MSG_NOTE, vect_location, "epilog loop required\n");
> diff --git a/gcc/tree-vectorizer.cc b/gcc/tree-vectorizer.cc
> index
> d97e2b54c25ac60378935392aa7b73476efed74b..8b495fc7ca137109fc0097c77837233c660e032a
> 100644
> --- a/gcc/tree-vectorizer.cc
> +++ b/gcc/tree-vectorizer.cc
> @@ -1381,7 +1381,9 @@ pass_vectorize::execute (function *fun)
> predicates that need to be shared for optimal predicate usage.
> However reassoc will re-order them and prevent CSE from working
> as it should. CSE only the loop body, not the entry. */
> - bitmap_set_bit (exit_bbs, single_exit (loop)->dest->index);
> + auto_vec<edge> exits = get_loop_exit_edges (loop);
> + for (edge exit : exits)
> + bitmap_set_bit (exit_bbs, exit->dest->index);
>
> edge entry = EDGE_PRED (loop_preheader_edge (loop)->src, 0);
> do_rpo_vn (fun, entry, exit_bbs);
Otherwise OK.
Richard.
