[gcc(refs/users/tnfchris/heads/gcc-14-early-break)] middle-end: support multiple exits in loop versioning

[gcc(refs/users/tnfchris/heads/gcc-14-early-break)] middle-end: support multiple exits in loop versioning

[Tamar Christina]

https://gcc.gnu.org/g:249a10e231eb5ebed38536a75d9e90259a687061

commit 249a10e231eb5ebed38536a75d9e90259a687061
Author: Tamar Christina <tamar.christina@arm.com>
Date:   Thu Nov 2 15:42:21 2023 +0000

    middle-end: support multiple exits in loop versioning
    
    Reviewed at https://reviewboard.gnu.aws.arm.com/r/17966/

Diff:
---
 gcc/tree-vect-loop-manip.cc | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index a5a612dc6b4..d3fa8699271 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -4016,12 +4016,23 @@ vect_loop_versioning (loop_vec_info loop_vinfo,
 	 If loop versioning wasn't done from loop, but scalar_loop instead,
 	 merge_bb will have already just a single successor.  */
 
-      merge_bb = single_exit (loop_to_version)->dest;
+      /* When the loop has multiple exits then we can only version itself.
+	 This is denoted by loop_to_version == loop.  In this case we can
+	 do the versioning by selecting the exit edge the vectorizer is
+	 currently using.  */
+      edge exit_edge;
+      if (loop_to_version == loop)
+	exit_edge = LOOP_VINFO_IV_EXIT (loop_vinfo);
+      else
+	exit_edge = single_exit (loop_to_version);
+
+      gcc_assert (exit_edge);
+      merge_bb = exit_edge->dest;
       if (EDGE_COUNT (merge_bb->preds) >= 2)
 	{
 	  gcc_assert (EDGE_COUNT (merge_bb->preds) >= 2);
-	  new_exit_bb = split_edge (single_exit (loop_to_version));
-	  new_exit_e = single_exit (loop_to_version);
+	  new_exit_bb = split_edge (exit_edge);
+	  new_exit_e = exit_edge;
 	  e = EDGE_SUCC (new_exit_bb, 0);
 
 	  for (gsi = gsi_start_phis (merge_bb); !gsi_end_p (gsi);