[gcc(refs/users/tnfchris/heads/gcc-14-early-break)] middle-end: Add remaining changes to peeling and vectorizer to support early breaks

[gcc(refs/users/tnfchris/heads/gcc-14-early-break)] middle-end: Add remaining changes to peeling and vectorizer to support early breaks

[Tamar Christina]

https://gcc.gnu.org/g:e049151fd3fc653055ac87ed88718c4efa163fc6

commit e049151fd3fc653055ac87ed88718c4efa163fc6
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Thu Nov 2 17:04:37 2023 +0000

    middle-end: Add remaining changes to peeling and vectorizer to support early breaks

Diff:
---
 gcc/tree-vect-loop-manip.cc | 28 ++++++++++++++++++++++++----
 gcc/tree-vect-loop.cc       | 11 ++++++++++-
 gcc/tree-vectorizer.cc      |  4 +++-
 3 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index 44f70965528..d00765c39bd 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1200,7 +1200,7 @@ 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)
@@ -1308,7 +1308,8 @@ 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,
@@ -3051,6 +3052,16 @@ 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;
 
@@ -3185,14 +3196,23 @@ 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 2476e59ef48..f406c59c2c3 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)
     {
@@ -3151,7 +3159,8 @@ 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 d97e2b54c25..8b495fc7ca1 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);