diff mbox

Avoid unnecessary block copying in path splitting

Message ID 5679C552.4070401@redhat.com
State New
Headers show

Commit Message

Jeff Law Dec. 22, 2015, 9:49 p.m. UTC 
This is something Richi pointed out.  I didn't think it was a big deal 
and didn't want to unnecessarily complicate the code like I did for jump 
threading to avoid a little bit of block copying.

As it turns out avoiding the copying in path splitting is trivial, so 
trivial we actually get to remove a bit of code.

To ensure this got tested, I put split-paths back into -O2 for my 
bootstrap & regression tested.  It, of course, passed just fine.

Installed on the trunk.

Jeff
commit ed304c35af7050ab30585fd0ad6ed968dfac73c1
Author: Jeff Law <law@redhat.com>
Date:   Tue Dec 22 14:48:12 2015 -0700

    [PATCH] Avoid unnecessary block copying in path splitting
    
    	* gimple-ssa-split-paths.c (split_paths): Avoid unnecessary block
    	copying.
diff mbox

Patch

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 73ab7d4..5e1e819 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@ 
+2015-12-22  Jeff Law  <law@redhat.com>
+
+	* gimple-ssa-split-paths.c (split_paths): Avoid unnecessary block
+	copying.
+
 2015-12-22  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/67376
diff --git a/gcc/gimple-ssa-split-paths.c b/gcc/gimple-ssa-split-paths.c
index 540fdf3..294a1af 100644
--- a/gcc/gimple-ssa-split-paths.c
+++ b/gcc/gimple-ssa-split-paths.c
@@ -192,9 +192,10 @@  split_paths ()
 
       /* BB is the merge point for an IF-THEN-ELSE we want to transform.
 
-	 Essentially we want to create two duplicates of BB and append
-	 a duplicate to the THEN and ELSE clauses.  This will split the
-	 path leading to the latch.  BB will be unreachable and removed.  */
+	 Essentially we want to create a duplicate of bb and redirect the
+	 first predecessor of BB to the duplicate (leaving the second
+	 predecessor as is.  This will split the path leading to the latch
+	 re-using BB to avoid useless copying.  */
       if (bb && is_feasible_trace (bb))
 	{
 	  if (dump_file && (dump_flags & TDF_DETAILS))
@@ -202,9 +203,7 @@  split_paths ()
 		     "Duplicating join block %d into predecessor paths\n",
 		     bb->index);
 	  basic_block pred0 = EDGE_PRED (bb, 0)->src;
-	  basic_block pred1 = EDGE_PRED (bb, 1)->src;
 	  transform_duplicate (pred0, bb);
-	  transform_duplicate (pred1, bb);
 	  changed = true;
 	}
     }