[gomp4, committed] Insert new exit block only when needed in transform_to_exit_first_loop_alt

[Tom de Vries <Tom_deVries at mentor dot com>]

Hi,

while testing the (now committed) fix for PR66642 (Add empty loop exit 
block in transform_to_exit_first_loop_alt) on the gomp-4_0-branch I ran 
into an ICE for the kernels-reduction.c testcase.

For oacc kernels, we don't generate a low iteration count loop, so the 
exit block of the loop already may have a single predecessor, so there's 
no need to add an empty loop exit block.

This patch conditionalizes the fix for PR66642 and fixes the ICE.

Bootstrapped and reg-tested on x86_64 on top of gomp-4_0-branch, and 
committed.

Thanks,
- Tom

Insert new exit block only when needed in transform_to_exit_first_loop_alt

2015-06-30  Tom de Vries  <tom@codesourcery.com>

	* tree-parloops.c (transform_to_exit_first_loop_alt): Insert new exit
	block only when needed.
---
 gcc/tree-parloops.c | 42 ++++++++++++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 14 deletions(-)

diff --git a/gcc/tree-parloops.c b/gcc/tree-parloops.c
index 9c04308..04708c0 100644
--- a/gcc/tree-parloops.c
+++ b/gcc/tree-parloops.c
@@ -1734,10 +1734,15 @@ transform_to_exit_first_loop_alt (struct loop *loop,
   /* Set the latch arguments of the new phis to ivtmp/sum_b.  */
   flush_pending_stmts (post_inc_edge);
 
-  /* Create a new empty exit block, inbetween the new loop header and the old
-     exit block.  The function separate_decls_in_region needs this block to
-     insert code that is active on loop exit, but not any other path.  */
-  basic_block new_exit_block = split_edge (exit);
+
+  basic_block new_exit_block = NULL;
+  if (!single_pred_p (exit->dest))
+    {
+      /* Create a new empty exit block, inbetween the new loop header and the
+	 old exit block.  The function separate_decls_in_region needs this block
+	 to insert code that is active on loop exit, but not any other path.  */
+      new_exit_block = split_edge (exit);
+    }
 
   /* Insert and register the reduction exit phis.  */
   for (gphi_iterator gsi = gsi_start_phis (exit_block);
@@ -1745,17 +1750,24 @@ transform_to_exit_first_loop_alt (struct loop *loop,
        gsi_next (&gsi))
     {
       gphi *phi = gsi.phi ();
+      gphi *nphi = NULL;
       tree res_z = PHI_RESULT (phi);
+      tree res_c;
 
-      /* Now that we have a new exit block, duplicate the phi of the old exit
-	 block in the new exit block to preserve loop-closed ssa.  */
-      edge succ_new_exit_block = single_succ_edge (new_exit_block);
-      edge pred_new_exit_block = single_pred_edge (new_exit_block);
-      tree res_y = copy_ssa_name (res_z, phi);
-      gphi *nphi = create_phi_node (res_y, new_exit_block);
-      tree res_c = PHI_ARG_DEF_FROM_EDGE (phi, succ_new_exit_block);
-      add_phi_arg (nphi, res_c, pred_new_exit_block, UNKNOWN_LOCATION);
-      add_phi_arg (phi, res_y, succ_new_exit_block, UNKNOWN_LOCATION);
+      if (new_exit_block != NULL)
+	{
+	  /* Now that we have a new exit block, duplicate the phi of the old
+	     exit block in the new exit block to preserve loop-closed ssa.  */
+	  edge succ_new_exit_block = single_succ_edge (new_exit_block);
+	  edge pred_new_exit_block = single_pred_edge (new_exit_block);
+	  tree res_y = copy_ssa_name (res_z, phi);
+	  nphi = create_phi_node (res_y, new_exit_block);
+	  res_c = PHI_ARG_DEF_FROM_EDGE (phi, succ_new_exit_block);
+	  add_phi_arg (nphi, res_c, pred_new_exit_block, UNKNOWN_LOCATION);
+	  add_phi_arg (phi, res_y, succ_new_exit_block, UNKNOWN_LOCATION);
+	}
+      else
+	res_c = PHI_ARG_DEF_FROM_EDGE (phi, exit);
 
       if (virtual_operand_p (res_z))
 	continue;
@@ -1763,7 +1775,9 @@ transform_to_exit_first_loop_alt (struct loop *loop,
       gimple reduc_phi = SSA_NAME_DEF_STMT (res_c);
       struct reduction_info *red = reduction_phi (reduction_list, reduc_phi);
       if (red != NULL)
-	red->keep_res = nphi;
+	red->keep_res = (nphi != NULL
+			 ? nphi
+			 : phi);
     }
 
   /* We're going to cancel the loop at the end of gen_parallel_loop, but until
-- 
1.9.1