[PATCH]PR tree-optimization/42720 Fixing problematic logic at unswitch-loops pass

[Jing Yu <jingyu at google dot com>]

The patch came out of the discussion to fix the problematic logic at
unswitch-loops pass.
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42720

 2010-04-07? Jing Yu? <jingyu@google.com>
 ??????????? Zdenek Dvorak? <ook@ucw.cz>

 ??????? PR tree-optimization/42720
 ??????? * tree-ssa-loop-unswitch.c (tree_ssa_unswitch_loops): Move one-time
 ??????? loop unswitch conditions here from
 ??????? (tree_unswitch_single_loop).

 I have tested the patch on top of trunk. The empty loop described in
the bugzilla entry is gone.
 The results of dejagnu tests on arm-eabi target do not change with the patch.

 OK for trunk?

 Thanks,
 Jing

Index: gcc/tree-ssa-loop-unswitch.c
===================================================================
--- gcc/tree-ssa-loop-unswitch.c	(revision 158099)
+++ gcc/tree-ssa-loop-unswitch.c	(working copy)
@@ -88,6 +88,26 @@ tree_ssa_unswitch_loops (void)
   /* Go through inner loops (only original ones).  */
   FOR_EACH_LOOP (li, loop, LI_ONLY_INNERMOST)
     {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+        fprintf (dump_file, ";; Considering loop %d\n", loop->num);
+
+      /* Do not unswitch in cold regions. */
+      if (optimize_loop_for_size_p (loop))
+        {
+          if (dump_file && (dump_flags & TDF_DETAILS))
+            fprintf (dump_file, ";; Not unswitching cold loops\n");
+          continue;
+        }
+
+      /* The loop should not be too large, to limit code growth. */
+      if (tree_num_loop_insns (loop, &eni_size_weights)
+          > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
+        {
+          if (dump_file && (dump_flags & TDF_DETAILS))
+            fprintf (dump_file, ";; Not unswitching, loop too big\n");
+          continue;
+        }
+
       changed |= tree_unswitch_single_loop (loop, 0);
     }
 
@@ -189,31 +209,6 @@ tree_unswitch_single_loop (struct loop *
       return false;
     }
 
-  /* Only unswitch innermost loops.  */
-  if (loop->inner)
-    {
-      if (dump_file && (dump_flags & TDF_DETAILS))
-	fprintf (dump_file, ";; Not unswitching, not innermost loop\n");
-      return false;
-    }
-
-  /* Do not unswitch in cold regions.  */
-  if (optimize_loop_for_size_p (loop))
-    {
-      if (dump_file && (dump_flags & TDF_DETAILS))
-	fprintf (dump_file, ";; Not unswitching cold loops\n");
-      return false;
-    }
-
-  /* The loop should not be too large, to limit code growth.  */
-  if (tree_num_loop_insns (loop, &eni_size_weights)
-      > (unsigned) PARAM_VALUE (PARAM_MAX_UNSWITCH_INSNS))
-    {
-      if (dump_file && (dump_flags & TDF_DETAILS))
-	fprintf (dump_file, ";; Not unswitching, loop too big\n");
-      return false;
-    }
-
   i = 0;
   bbs = get_loop_body (loop);