RE: [PATCH 4/21]middle-end: update loop peeling code to maintain LCSSA form for early breaks

[Tamar Christina <Tamar.Christina@arm.com>]

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Patch updated to latest trunk,

This splits the part of the function that does peeling for loops at exits to
a different function.  In this new function we also peel for early breaks.

Peeling for early breaks works by redirecting all early break exits to a
single "early break" block and combine them and the normal exit edge together
later in a different block which then goes into the epilog preheader.

This allows us to re-use all the existing code for IV updates, Additionally this
also enables correct linking for multiple vector epilogues.

flush_pending_stmts cannot be used in this scenario since it updates the PHI
nodes in the order that they are in the exit destination blocks.  This means
they are in CFG visit order.  With a single exit this doesn't matter but with
multiple exits with different live values through the different exits the order
usually does not line up.

Additionally the vectorizer helper functions expect to be able to iterate over
the nodes in the order that they occur in the loop header blocks.  This is an
invariant we must maintain.  To do this we just inline the work
flush_pending_stmts but maintain the order by using the header blocks to guide
the work.

Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.

Ok for master?

Thanks,
Tamar

gcc/ChangeLog:

	* tree-vect-loop-manip.cc (vect_is_loop_exit_latch_pred): New.
	(slpeel_tree_duplicate_loop_for_vectorization): New.
	(slpeel_tree_duplicate_loop_to_edge_cfg): use it.
	* tree-vectorizer.h (is_loop_header_bb_p): Drop assert.
	(slpeel_tree_duplicate_loop_to_edge_cfg): Update signature.
	(vect_is_loop_exit_latch_pred): New.

--- inline copy of patch ---

diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index b9161274ce401a7307f3e61ad23aa036701190d7..fafbf924e8db18eb4eec7a4a1906d10f6ce9812f 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1392,6 +1392,153 @@ vect_set_loop_condition (class loop *loop, edge loop_e, loop_vec_info loop_vinfo
 		     (gimple *) cond_stmt);
 }
 
+/* Determine if the exit choosen by the loop vectorizer differs from the
+   natural loop exit.  i.e. if the exit leads to the loop patch or not.
+   When this happens we need to flip the understanding of main and other
+   exits by peeling and IV updates.  */
+
+bool inline
+vect_is_loop_exit_latch_pred (edge loop_exit, class loop *loop)
+{
+  return single_pred (loop->latch) == loop_exit->src;
+}
+
+/* Perform peeling for when the peeled loop is placed after the original loop.
+   This maintains LCSSA and creates the appropriate blocks for multiple exit
+   vectorization.   */
+
+void static
+slpeel_tree_duplicate_loop_for_vectorization (class loop *loop, edge loop_exit,
+					      vec<edge> &loop_exits,
+					      class loop *new_loop,
+					      bool flow_loops,
+					      basic_block new_preheader)
+{
+  bool multiple_exits_p = loop_exits.length () > 1;
+  basic_block main_loop_exit_block = new_preheader;
+  if (multiple_exits_p)
+    {
+      edge loop_entry = single_succ_edge (new_preheader);
+      new_preheader = split_edge (loop_entry);
+    }
+
+  auto_vec <gimple *> new_phis;
+  hash_map <tree, tree> new_phi_args;
+  /* First create the empty phi nodes so that when we flush the
+     statements they can be filled in.   However because there is no order
+     between the PHI nodes in the exits and the loop headers we need to
+     order them base on the order of the two headers.  First record the new
+     phi nodes. Then redirect the edges and flush the changes.  This writes out
+     the new SSA names.  */
+  for (auto gsi_from = gsi_start_phis (loop_exit->dest);
+       !gsi_end_p (gsi_from); gsi_next (&gsi_from))
+    {
+      gimple *from_phi = gsi_stmt (gsi_from);
+      tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
+      gphi *res = create_phi_node (new_res, main_loop_exit_block);
+      new_phis.safe_push (res);
+    }
+
+  for (auto exit : loop_exits)
+    {
+      basic_block dest
+	= exit == loop_exit ? main_loop_exit_block : new_preheader;
+      redirect_edge_and_branch (exit, dest);
+    }
+
+  /* Only fush the main exit, the remaining exits we need to match the order
+     in the loop->header which with multiple exits may not be the same.  */
+  flush_pending_stmts (loop_exit);
+
+  /* Record the new SSA names in the cache so that we can skip materializing
+     them again when we fill in the rest of the LCSSA variables.  */
+  for (auto phi : new_phis)
+    {
+      tree new_arg = gimple_phi_arg (phi, 0)->def;
+
+      if (!SSA_VAR_P (new_arg))
+	continue;
+
+      /* If the PHI MEM node dominates the loop then we shouldn't create
+	 a new LC-SSSA PHI for it in the intermediate block.   */
+      /* A MEM phi that consitutes a new DEF for the vUSE chain can either
+	 be a .VDEF or a PHI that operates on MEM. And said definition
+	 must not be inside the main loop.  Or we must be a parameter.
+	 In the last two cases we may remove a non-MEM PHI node, but since
+	 they dominate both loops the removal is unlikely to cause trouble
+	 as the exits must already be using them.  */
+      if (virtual_operand_p (new_arg)
+	  && (SSA_NAME_IS_DEFAULT_DEF (new_arg)
+	      || !flow_bb_inside_loop_p (loop,
+				gimple_bb (SSA_NAME_DEF_STMT (new_arg)))))
+	{
+	  auto gsi = gsi_for_stmt (phi);
+	  remove_phi_node (&gsi, true);
+	  continue;
+	}
+
+      /* If we decide to remove the PHI node we should also not
+	 rematerialize it later on.  */
+      new_phi_args.put (new_arg, gimple_phi_result (phi));
+
+      if (TREE_CODE (new_arg) != SSA_NAME)
+	continue;
+    }
+
+  /* Copy the current loop LC PHI nodes between the original loop exit
+     block and the new loop header.  This allows us to later split the
+     preheader block and still find the right LC nodes.  */
+  edge loop_entry = single_succ_edge (new_preheader);
+  if (flow_loops)
+    for (auto gsi_from = gsi_start_phis (loop->header),
+	 gsi_to = gsi_start_phis (new_loop->header);
+	 !gsi_end_p (gsi_from) && !gsi_end_p (gsi_to);
+	 gsi_next (&gsi_from), gsi_next (&gsi_to))
+      {
+	gimple *from_phi = gsi_stmt (gsi_from);
+	gimple *to_phi = gsi_stmt (gsi_to);
+	tree new_arg = PHI_ARG_DEF_FROM_EDGE (from_phi, loop_latch_edge (loop));
+	tree *res = NULL;
+
+	/* Check if we've already created a new phi node during edge
+	   redirection.  If we have, only propagate the value downwards.  */
+	if ((res = new_phi_args.get (new_arg)))
+	  new_arg = *res;
+
+	/* All other exits use the previous iters.  */
+	if (multiple_exits_p)
+	  {
+	    tree alt_arg = gimple_phi_result (from_phi);
+	    tree alt_res = copy_ssa_name (alt_arg);
+	    gphi *alt_lcssa_phi = create_phi_node (alt_res, new_preheader);
+	    edge main_e = single_succ_edge (main_loop_exit_block);
+	    for (edge e : loop_exits)
+	      if (e != loop_exit)
+		{
+		  add_phi_arg (alt_lcssa_phi, alt_arg, e, UNKNOWN_LOCATION);
+		  SET_PHI_ARG_DEF (alt_lcssa_phi, main_e->dest_idx, new_arg);
+		}
+	    new_arg = alt_res; /* Push it down to the new_loop header.  */
+	  } else if (!res) {
+	    /* For non-early break we need to keep the possibly live values in
+	       the exit block.  For early break these are kept in the merge
+	       block in the code above.  */
+	    tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
+	    gphi *lcssa_phi = create_phi_node (new_res, new_preheader);
+
+	    /* Main loop exit should use the final iter value.  */
+	    add_phi_arg (lcssa_phi, new_arg, loop_exit, UNKNOWN_LOCATION);
+	    new_arg = new_res;
+	  }
+
+	adjust_phi_and_debug_stmts (to_phi, loop_entry, new_arg);
+    }
+
+  /* Now clear all the redirect maps.  */
+  for (auto exit : loop_exits)
+    redirect_edge_var_map_clear (exit);
+}
+
 /* Given LOOP this function generates a new copy of it and puts it
    on E which is either the entry or exit of LOOP.  If SCALAR_LOOP is
    non-NULL, assume LOOP and SCALAR_LOOP are equivalent and copy the
@@ -1403,13 +1550,16 @@ vect_set_loop_condition (class loop *loop, edge loop_e, loop_vec_info loop_vinfo
    copies remains the same.
 
    If UPDATED_DOMS is not NULL it is update with the list of basic blocks whoms
-   dominators were updated during the peeling.  */
+   dominators were updated during the peeling.  When doing early break vectorization
+   then LOOP_VINFO needs to be provided and is used to keep track of any newly created
+   memory references that need to be updated should we decide to vectorize.  */
 
 class loop *
 slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
 					class loop *scalar_loop,
 					edge scalar_exit, edge e, edge *new_e,
-					bool flow_loops)
+					bool flow_loops,
+					vec<basic_block> *updated_doms)
 {
   class loop *new_loop;
   basic_block *new_bbs, *bbs, *pbbs;
@@ -1526,7 +1676,9 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       }
 
   auto loop_exits = get_loop_exit_edges (loop);
+  bool multiple_exits_p = loop_exits.length () > 1;
   auto_vec<basic_block> doms;
+  class loop *update_loop = NULL;
 
   if (at_exit) /* Add the loop copy at exit.  */
     {
@@ -1536,91 +1688,9 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
 	  flush_pending_stmts (new_exit);
 	}
 
-      auto_vec <gimple *> new_phis;
-      hash_map <tree, tree> new_phi_args;
-      /* First create the empty phi nodes so that when we flush the
-	 statements they can be filled in.   However because there is no order
-	 between the PHI nodes in the exits and the loop headers we need to
-	 order them base on the order of the two headers.  First record the new
-	 phi nodes.  */
-      for (auto gsi_from = gsi_start_phis (scalar_exit->dest);
-	   !gsi_end_p (gsi_from); gsi_next (&gsi_from))
-	{
-	  gimple *from_phi = gsi_stmt (gsi_from);
-	  tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
-	  gphi *res = create_phi_node (new_res, new_preheader);
-	  new_phis.safe_push (res);
-	}
-
-      /* Then redirect the edges and flush the changes.  This writes out the new
-	 SSA names.  */
-      for (edge exit : loop_exits)
-	{
-	  edge temp_e = redirect_edge_and_branch (exit, new_preheader);
-	  flush_pending_stmts (temp_e);
-	}
-      /* Record the new SSA names in the cache so that we can skip materializing
-	 them again when we fill in the rest of the LCSSA variables.  */
-      for (auto phi : new_phis)
-	{
-	  tree new_arg = gimple_phi_arg (phi, 0)->def;
-
-	  if (!SSA_VAR_P (new_arg))
-	    continue;
-	  /* If the PHI MEM node dominates the loop then we shouldn't create
-	      a new LC-SSSA PHI for it in the intermediate block.   */
-	  /* A MEM phi that consitutes a new DEF for the vUSE chain can either
-	     be a .VDEF or a PHI that operates on MEM. And said definition
-	     must not be inside the main loop.  Or we must be a parameter.
-	     In the last two cases we may remove a non-MEM PHI node, but since
-	     they dominate both loops the removal is unlikely to cause trouble
-	     as the exits must already be using them.  */
-	  if (virtual_operand_p (new_arg)
-	      && (SSA_NAME_IS_DEFAULT_DEF (new_arg)
-		  || !flow_bb_inside_loop_p (loop,
-				gimple_bb (SSA_NAME_DEF_STMT (new_arg)))))
-	    {
-	      auto gsi = gsi_for_stmt (phi);
-	      remove_phi_node (&gsi, true);
-	      continue;
-	    }
-	  new_phi_args.put (new_arg, gimple_phi_result (phi));
-
-	  if (TREE_CODE (new_arg) != SSA_NAME)
-	    continue;
-	}
-
-      /* Copy the current loop LC PHI nodes between the original loop exit
-	 block and the new loop header.  This allows us to later split the
-	 preheader block and still find the right LC nodes.  */
-      edge loop_entry = single_succ_edge (new_preheader);
-      if (flow_loops)
-	for (auto gsi_from = gsi_start_phis (loop->header),
-	     gsi_to = gsi_start_phis (new_loop->header);
-	     !gsi_end_p (gsi_from) && !gsi_end_p (gsi_to);
-	     gsi_next (&gsi_from), gsi_next (&gsi_to))
-	  {
-	    gimple *from_phi = gsi_stmt (gsi_from);
-	    gimple *to_phi = gsi_stmt (gsi_to);
-	    tree new_arg = PHI_ARG_DEF_FROM_EDGE (from_phi,
-						  loop_latch_edge (loop));
-
-	    /* Check if we've already created a new phi node during edge
-	       redirection.  If we have, only propagate the value downwards.  */
-	    if (tree *res = new_phi_args.get (new_arg))
-	      {
-		adjust_phi_and_debug_stmts (to_phi, loop_entry, *res);
-		continue;
-	      }
-
-	    tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
-	    gphi *lcssa_phi = create_phi_node (new_res, new_preheader);
-
-	    /* Main loop exit should use the final iter value.  */
-	    add_phi_arg (lcssa_phi, new_arg, loop_exit, UNKNOWN_LOCATION);
-
-	    adjust_phi_and_debug_stmts (to_phi, loop_entry, new_res);
-	  }
+      slpeel_tree_duplicate_loop_for_vectorization (loop, loop_exit, loop_exits,
+						    new_loop, flow_loops,
+						    new_preheader);
 
       set_immediate_dominator (CDI_DOMINATORS, new_preheader, e->src);
 
@@ -1634,6 +1704,21 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       delete_basic_block (preheader);
       set_immediate_dominator (CDI_DOMINATORS, scalar_loop->header,
 			       loop_preheader_edge (scalar_loop)->src);
+
+      /* Finally after wiring the new epilogue we need to update its main exit
+	 to the original function exit we recorded.  Other exits are already
+	 correct.  */
+      if (multiple_exits_p)
+	{
+	  update_loop = new_loop;
+	  for (edge e : get_loop_exit_edges (loop))
+	    doms.safe_push (e->dest);
+	  doms.safe_push (exit_dest);
+
+	  /* Likely a fall-through edge, so update if needed.  */
+	  if (single_succ_p (exit_dest))
+	    doms.safe_push (single_succ (exit_dest));
+	}
     }
   else /* Add the copy at entry.  */
     {
@@ -1681,6 +1766,34 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       delete_basic_block (new_preheader);
       set_immediate_dominator (CDI_DOMINATORS, new_loop->header,
 			       loop_preheader_edge (new_loop)->src);
+
+      if (multiple_exits_p)
+	update_loop = loop;
+    }
+
+  if (multiple_exits_p)
+    {
+      for (edge e : get_loop_exit_edges (update_loop))
+	{
+	  edge ex;
+	  edge_iterator ei;
+	  FOR_EACH_EDGE (ex, ei, e->dest->succs)
+	    {
+	      /* Find the first non-fallthrough block as fall-throughs can't
+		 dominate other blocks.  */
+	      if (single_succ_p (ex->dest))
+		{
+		  doms.safe_push (ex->dest);
+		  ex = single_succ_edge (ex->dest);
+		}
+	      doms.safe_push (ex->dest);
+	    }
+	  doms.safe_push (e->dest);
+	}
+
+      iterate_fix_dominators (CDI_DOMINATORS, doms, false);
+      if (updated_doms)
+	updated_doms->safe_splice (doms);
     }
 
   free (new_bbs);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 76451a7fefe6ff966cecfa2cbc7b11336b038565..b9a71a0b5f5407417e8366b0df132df20c7f60aa 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -1821,7 +1821,7 @@ is_loop_header_bb_p (basic_block bb)
 {
   if (bb == (bb->loop_father)->header)
     return true;
-  gcc_checking_assert (EDGE_COUNT (bb->preds) == 1);
+
   return false;
 }
 
@@ -2212,7 +2212,8 @@ extern bool slpeel_can_duplicate_loop_p (const class loop *, const_edge,
 					 const_edge);
 class loop *slpeel_tree_duplicate_loop_to_edge_cfg (class loop *, edge,
 						    class loop *, edge,
-						    edge, edge *, bool = true);
+						    edge, edge *, bool = true,
+						    vec<basic_block> * = NULL);
 class loop *vect_loop_versioning (loop_vec_info, gimple *);
 extern class loop *vect_do_peeling (loop_vec_info, tree, tree,
 				    tree *, tree *, tree *, int, bool, bool,
@@ -2223,6 +2224,7 @@ extern dump_user_location_t find_loop_location (class loop *);
 extern bool vect_can_advance_ivs_p (loop_vec_info);
 extern void vect_update_inits_of_drs (loop_vec_info, tree, tree_code);
 extern edge vec_init_loop_exit_info (class loop *);
+extern bool vect_is_loop_exit_latch_pred (edge, class loop *);
 
 /* In tree-vect-stmts.cc.  */
 extern tree get_related_vectype_for_scalar_type (machine_mode, tree,

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diff --git a/gcc/tree-vect-loop-manip.cc b/gcc/tree-vect-loop-manip.cc
index b9161274ce401a7307f3e61ad23aa036701190d7..fafbf924e8db18eb4eec7a4a1906d10f6ce9812f 100644
--- a/gcc/tree-vect-loop-manip.cc
+++ b/gcc/tree-vect-loop-manip.cc
@@ -1392,6 +1392,153 @@ vect_set_loop_condition (class loop *loop, edge loop_e, loop_vec_info loop_vinfo
 		     (gimple *) cond_stmt);
 }
 
+/* Determine if the exit choosen by the loop vectorizer differs from the
+   natural loop exit.  i.e. if the exit leads to the loop patch or not.
+   When this happens we need to flip the understanding of main and other
+   exits by peeling and IV updates.  */
+
+bool inline
+vect_is_loop_exit_latch_pred (edge loop_exit, class loop *loop)
+{
+  return single_pred (loop->latch) == loop_exit->src;
+}
+
+/* Perform peeling for when the peeled loop is placed after the original loop.
+   This maintains LCSSA and creates the appropriate blocks for multiple exit
+   vectorization.   */
+
+void static
+slpeel_tree_duplicate_loop_for_vectorization (class loop *loop, edge loop_exit,
+					      vec<edge> &loop_exits,
+					      class loop *new_loop,
+					      bool flow_loops,
+					      basic_block new_preheader)
+{
+  bool multiple_exits_p = loop_exits.length () > 1;
+  basic_block main_loop_exit_block = new_preheader;
+  if (multiple_exits_p)
+    {
+      edge loop_entry = single_succ_edge (new_preheader);
+      new_preheader = split_edge (loop_entry);
+    }
+
+  auto_vec <gimple *> new_phis;
+  hash_map <tree, tree> new_phi_args;
+  /* First create the empty phi nodes so that when we flush the
+     statements they can be filled in.   However because there is no order
+     between the PHI nodes in the exits and the loop headers we need to
+     order them base on the order of the two headers.  First record the new
+     phi nodes. Then redirect the edges and flush the changes.  This writes out
+     the new SSA names.  */
+  for (auto gsi_from = gsi_start_phis (loop_exit->dest);
+       !gsi_end_p (gsi_from); gsi_next (&gsi_from))
+    {
+      gimple *from_phi = gsi_stmt (gsi_from);
+      tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
+      gphi *res = create_phi_node (new_res, main_loop_exit_block);
+      new_phis.safe_push (res);
+    }
+
+  for (auto exit : loop_exits)
+    {
+      basic_block dest
+	= exit == loop_exit ? main_loop_exit_block : new_preheader;
+      redirect_edge_and_branch (exit, dest);
+    }
+
+  /* Only fush the main exit, the remaining exits we need to match the order
+     in the loop->header which with multiple exits may not be the same.  */
+  flush_pending_stmts (loop_exit);
+
+  /* Record the new SSA names in the cache so that we can skip materializing
+     them again when we fill in the rest of the LCSSA variables.  */
+  for (auto phi : new_phis)
+    {
+      tree new_arg = gimple_phi_arg (phi, 0)->def;
+
+      if (!SSA_VAR_P (new_arg))
+	continue;
+
+      /* If the PHI MEM node dominates the loop then we shouldn't create
+	 a new LC-SSSA PHI for it in the intermediate block.   */
+      /* A MEM phi that consitutes a new DEF for the vUSE chain can either
+	 be a .VDEF or a PHI that operates on MEM. And said definition
+	 must not be inside the main loop.  Or we must be a parameter.
+	 In the last two cases we may remove a non-MEM PHI node, but since
+	 they dominate both loops the removal is unlikely to cause trouble
+	 as the exits must already be using them.  */
+      if (virtual_operand_p (new_arg)
+	  && (SSA_NAME_IS_DEFAULT_DEF (new_arg)
+	      || !flow_bb_inside_loop_p (loop,
+				gimple_bb (SSA_NAME_DEF_STMT (new_arg)))))
+	{
+	  auto gsi = gsi_for_stmt (phi);
+	  remove_phi_node (&gsi, true);
+	  continue;
+	}
+
+      /* If we decide to remove the PHI node we should also not
+	 rematerialize it later on.  */
+      new_phi_args.put (new_arg, gimple_phi_result (phi));
+
+      if (TREE_CODE (new_arg) != SSA_NAME)
+	continue;
+    }
+
+  /* Copy the current loop LC PHI nodes between the original loop exit
+     block and the new loop header.  This allows us to later split the
+     preheader block and still find the right LC nodes.  */
+  edge loop_entry = single_succ_edge (new_preheader);
+  if (flow_loops)
+    for (auto gsi_from = gsi_start_phis (loop->header),
+	 gsi_to = gsi_start_phis (new_loop->header);
+	 !gsi_end_p (gsi_from) && !gsi_end_p (gsi_to);
+	 gsi_next (&gsi_from), gsi_next (&gsi_to))
+      {
+	gimple *from_phi = gsi_stmt (gsi_from);
+	gimple *to_phi = gsi_stmt (gsi_to);
+	tree new_arg = PHI_ARG_DEF_FROM_EDGE (from_phi, loop_latch_edge (loop));
+	tree *res = NULL;
+
+	/* Check if we've already created a new phi node during edge
+	   redirection.  If we have, only propagate the value downwards.  */
+	if ((res = new_phi_args.get (new_arg)))
+	  new_arg = *res;
+
+	/* All other exits use the previous iters.  */
+	if (multiple_exits_p)
+	  {
+	    tree alt_arg = gimple_phi_result (from_phi);
+	    tree alt_res = copy_ssa_name (alt_arg);
+	    gphi *alt_lcssa_phi = create_phi_node (alt_res, new_preheader);
+	    edge main_e = single_succ_edge (main_loop_exit_block);
+	    for (edge e : loop_exits)
+	      if (e != loop_exit)
+		{
+		  add_phi_arg (alt_lcssa_phi, alt_arg, e, UNKNOWN_LOCATION);
+		  SET_PHI_ARG_DEF (alt_lcssa_phi, main_e->dest_idx, new_arg);
+		}
+	    new_arg = alt_res; /* Push it down to the new_loop header.  */
+	  } else if (!res) {
+	    /* For non-early break we need to keep the possibly live values in
+	       the exit block.  For early break these are kept in the merge
+	       block in the code above.  */
+	    tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
+	    gphi *lcssa_phi = create_phi_node (new_res, new_preheader);
+
+	    /* Main loop exit should use the final iter value.  */
+	    add_phi_arg (lcssa_phi, new_arg, loop_exit, UNKNOWN_LOCATION);
+	    new_arg = new_res;
+	  }
+
+	adjust_phi_and_debug_stmts (to_phi, loop_entry, new_arg);
+    }
+
+  /* Now clear all the redirect maps.  */
+  for (auto exit : loop_exits)
+    redirect_edge_var_map_clear (exit);
+}
+
 /* Given LOOP this function generates a new copy of it and puts it
    on E which is either the entry or exit of LOOP.  If SCALAR_LOOP is
    non-NULL, assume LOOP and SCALAR_LOOP are equivalent and copy the
@@ -1403,13 +1550,16 @@ vect_set_loop_condition (class loop *loop, edge loop_e, loop_vec_info loop_vinfo
    copies remains the same.
 
    If UPDATED_DOMS is not NULL it is update with the list of basic blocks whoms
-   dominators were updated during the peeling.  */
+   dominators were updated during the peeling.  When doing early break vectorization
+   then LOOP_VINFO needs to be provided and is used to keep track of any newly created
+   memory references that need to be updated should we decide to vectorize.  */
 
 class loop *
 slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
 					class loop *scalar_loop,
 					edge scalar_exit, edge e, edge *new_e,
-					bool flow_loops)
+					bool flow_loops,
+					vec<basic_block> *updated_doms)
 {
   class loop *new_loop;
   basic_block *new_bbs, *bbs, *pbbs;
@@ -1526,7 +1676,9 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       }
 
   auto loop_exits = get_loop_exit_edges (loop);
+  bool multiple_exits_p = loop_exits.length () > 1;
   auto_vec<basic_block> doms;
+  class loop *update_loop = NULL;
 
   if (at_exit) /* Add the loop copy at exit.  */
     {
@@ -1536,91 +1688,9 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
 	  flush_pending_stmts (new_exit);
 	}
 
-      auto_vec <gimple *> new_phis;
-      hash_map <tree, tree> new_phi_args;
-      /* First create the empty phi nodes so that when we flush the
-	 statements they can be filled in.   However because there is no order
-	 between the PHI nodes in the exits and the loop headers we need to
-	 order them base on the order of the two headers.  First record the new
-	 phi nodes.  */
-      for (auto gsi_from = gsi_start_phis (scalar_exit->dest);
-	   !gsi_end_p (gsi_from); gsi_next (&gsi_from))
-	{
-	  gimple *from_phi = gsi_stmt (gsi_from);
-	  tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
-	  gphi *res = create_phi_node (new_res, new_preheader);
-	  new_phis.safe_push (res);
-	}
-
-      /* Then redirect the edges and flush the changes.  This writes out the new
-	 SSA names.  */
-      for (edge exit : loop_exits)
-	{
-	  edge temp_e = redirect_edge_and_branch (exit, new_preheader);
-	  flush_pending_stmts (temp_e);
-	}
-      /* Record the new SSA names in the cache so that we can skip materializing
-	 them again when we fill in the rest of the LCSSA variables.  */
-      for (auto phi : new_phis)
-	{
-	  tree new_arg = gimple_phi_arg (phi, 0)->def;
-
-	  if (!SSA_VAR_P (new_arg))
-	    continue;
-	  /* If the PHI MEM node dominates the loop then we shouldn't create
-	      a new LC-SSSA PHI for it in the intermediate block.   */
-	  /* A MEM phi that consitutes a new DEF for the vUSE chain can either
-	     be a .VDEF or a PHI that operates on MEM. And said definition
-	     must not be inside the main loop.  Or we must be a parameter.
-	     In the last two cases we may remove a non-MEM PHI node, but since
-	     they dominate both loops the removal is unlikely to cause trouble
-	     as the exits must already be using them.  */
-	  if (virtual_operand_p (new_arg)
-	      && (SSA_NAME_IS_DEFAULT_DEF (new_arg)
-		  || !flow_bb_inside_loop_p (loop,
-				gimple_bb (SSA_NAME_DEF_STMT (new_arg)))))
-	    {
-	      auto gsi = gsi_for_stmt (phi);
-	      remove_phi_node (&gsi, true);
-	      continue;
-	    }
-	  new_phi_args.put (new_arg, gimple_phi_result (phi));
-
-	  if (TREE_CODE (new_arg) != SSA_NAME)
-	    continue;
-	}
-
-      /* Copy the current loop LC PHI nodes between the original loop exit
-	 block and the new loop header.  This allows us to later split the
-	 preheader block and still find the right LC nodes.  */
-      edge loop_entry = single_succ_edge (new_preheader);
-      if (flow_loops)
-	for (auto gsi_from = gsi_start_phis (loop->header),
-	     gsi_to = gsi_start_phis (new_loop->header);
-	     !gsi_end_p (gsi_from) && !gsi_end_p (gsi_to);
-	     gsi_next (&gsi_from), gsi_next (&gsi_to))
-	  {
-	    gimple *from_phi = gsi_stmt (gsi_from);
-	    gimple *to_phi = gsi_stmt (gsi_to);
-	    tree new_arg = PHI_ARG_DEF_FROM_EDGE (from_phi,
-						  loop_latch_edge (loop));
-
-	    /* Check if we've already created a new phi node during edge
-	       redirection.  If we have, only propagate the value downwards.  */
-	    if (tree *res = new_phi_args.get (new_arg))
-	      {
-		adjust_phi_and_debug_stmts (to_phi, loop_entry, *res);
-		continue;
-	      }
-
-	    tree new_res = copy_ssa_name (gimple_phi_result (from_phi));
-	    gphi *lcssa_phi = create_phi_node (new_res, new_preheader);
-
-	    /* Main loop exit should use the final iter value.  */
-	    add_phi_arg (lcssa_phi, new_arg, loop_exit, UNKNOWN_LOCATION);
-
-	    adjust_phi_and_debug_stmts (to_phi, loop_entry, new_res);
-	  }
+      slpeel_tree_duplicate_loop_for_vectorization (loop, loop_exit, loop_exits,
+						    new_loop, flow_loops,
+						    new_preheader);
 
       set_immediate_dominator (CDI_DOMINATORS, new_preheader, e->src);
 
@@ -1634,6 +1704,21 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       delete_basic_block (preheader);
       set_immediate_dominator (CDI_DOMINATORS, scalar_loop->header,
 			       loop_preheader_edge (scalar_loop)->src);
+
+      /* Finally after wiring the new epilogue we need to update its main exit
+	 to the original function exit we recorded.  Other exits are already
+	 correct.  */
+      if (multiple_exits_p)
+	{
+	  update_loop = new_loop;
+	  for (edge e : get_loop_exit_edges (loop))
+	    doms.safe_push (e->dest);
+	  doms.safe_push (exit_dest);
+
+	  /* Likely a fall-through edge, so update if needed.  */
+	  if (single_succ_p (exit_dest))
+	    doms.safe_push (single_succ (exit_dest));
+	}
     }
   else /* Add the copy at entry.  */
     {
@@ -1681,6 +1766,34 @@ slpeel_tree_duplicate_loop_to_edge_cfg (class loop *loop, edge loop_exit,
       delete_basic_block (new_preheader);
       set_immediate_dominator (CDI_DOMINATORS, new_loop->header,
 			       loop_preheader_edge (new_loop)->src);
+
+      if (multiple_exits_p)
+	update_loop = loop;
+    }
+
+  if (multiple_exits_p)
+    {
+      for (edge e : get_loop_exit_edges (update_loop))
+	{
+	  edge ex;
+	  edge_iterator ei;
+	  FOR_EACH_EDGE (ex, ei, e->dest->succs)
+	    {
+	      /* Find the first non-fallthrough block as fall-throughs can't
+		 dominate other blocks.  */
+	      if (single_succ_p (ex->dest))
+		{
+		  doms.safe_push (ex->dest);
+		  ex = single_succ_edge (ex->dest);
+		}
+	      doms.safe_push (ex->dest);
+	    }
+	  doms.safe_push (e->dest);
+	}
+
+      iterate_fix_dominators (CDI_DOMINATORS, doms, false);
+      if (updated_doms)
+	updated_doms->safe_splice (doms);
     }
 
   free (new_bbs);
diff --git a/gcc/tree-vectorizer.h b/gcc/tree-vectorizer.h
index 76451a7fefe6ff966cecfa2cbc7b11336b038565..b9a71a0b5f5407417e8366b0df132df20c7f60aa 100644
--- a/gcc/tree-vectorizer.h
+++ b/gcc/tree-vectorizer.h
@@ -1821,7 +1821,7 @@ is_loop_header_bb_p (basic_block bb)
 {
   if (bb == (bb->loop_father)->header)
     return true;
-  gcc_checking_assert (EDGE_COUNT (bb->preds) == 1);
+
   return false;
 }
 
@@ -2212,7 +2212,8 @@ extern bool slpeel_can_duplicate_loop_p (const class loop *, const_edge,
 					 const_edge);
 class loop *slpeel_tree_duplicate_loop_to_edge_cfg (class loop *, edge,
 						    class loop *, edge,
-						    edge, edge *, bool = true);
+						    edge, edge *, bool = true,
+						    vec<basic_block> * = NULL);
 class loop *vect_loop_versioning (loop_vec_info, gimple *);
 extern class loop *vect_do_peeling (loop_vec_info, tree, tree,
 				    tree *, tree *, tree *, int, bool, bool,
@@ -2223,6 +2224,7 @@ extern dump_user_location_t find_loop_location (class loop *);
 extern bool vect_can_advance_ivs_p (loop_vec_info);
 extern void vect_update_inits_of_drs (loop_vec_info, tree, tree_code);
 extern edge vec_init_loop_exit_info (class loop *);
+extern bool vect_is_loop_exit_latch_pred (edge, class loop *);
 
 /* In tree-vect-stmts.cc.  */
 extern tree get_related_vectype_for_scalar_type (machine_mode, tree,