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[12/21] middle-end: Add remaining changes to peeling and vectorizer to support early breaks

Message ID ZUiYcOPCGYeyht2/@arm.com
State Unresolved
Headers
Series None |

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Commit Message

Tamar Christina Nov. 6, 2023, 7:40 a.m. UTC 
  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




--
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;
+    }
+
   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);
+
   /* 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;
+
   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);

Comments

Richard Biener Dec. 6, 2023, 8:31 a.m. UTC | #1 
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.
Richard Biener Dec. 6, 2023, 9:27 a.m. UTC | #2 
On Wed, 6 Dec 2023, Tamar Christina wrote:

> > -----Original Message-----
> > From: Richard Biener <rguenther@suse.de>
> > Sent: Wednesday, December 6, 2023 8:32 AM
> > To: Tamar Christina <Tamar.Christina@arm.com>
> > Cc: gcc-patches@gcc.gnu.org; nd <nd@arm.com>; jlaw@ventanamicro.com
> > Subject: Re: [PATCH 12/21]middle-end: Add remaining changes to peeling and
> > vectorizer to support early breaks
> > 
> > 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..9c1405d79fd8fe8689007df3b7
> > 605b7a3d3ecdd7 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..51a054c5b035ac80dfbbf3b5
> > ba2f6da82fda91f6 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?
> 
> It's mostly to force the use of an unpredicated main loop, since this
> forces LOOP_VINFO_PEELING_FOR_NITER.  I can alternatively not
> set it and then mask the individual comparisons in
> vectorizable_early_break.  Both work equally,  I guess that may be
> better since the assumption is that the break is not taken.

That might be easier to understand, yes.  But why not

  if (LOOP_VINFO_EARLY_BREAKS (loop_vinfo))
    return true;

?  Because even with constant VF we can predicate the main loop
(with AVX512, --param vect-partial-vector-usage=2)

> Any preference?
> 
> Thanks,
> Tamar
> 
> > 
> > >    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..8b495fc7ca137109fc0097c7
> > 7837233c660e032a 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.
>
diff mbox series

Patch

--- 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;
+    }
+
   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);
+
   /* 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;
+
   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);