[patch][IRA] Really record loop exits

[Steven Bosscher]

Hello,

IRA uses record_loop_exits() to cache the loop exit edges, but due to
a code ordering bug the edges are not actually recorded.
record_loop_exits() starts with:

  if (!current_loops)
    return;

So ira.c should set current_loops before calling record_loop_exits.
With the current order, the exists are not actually recorded. Also,
ira.c should release recorded exits and loops, this releases a
considerable amount of GC memory that can be re-used in the next IRA
iteration.

It's not clear to me why IRA has to re-compute the cfgloop tree from
scratch, though, so I've added a "???" comment for that.

Bootstrapped&tested (with and without checking) on
powerpc64-unknown-linux-gnu. OK for trunk?

Ciao!
Steven

        * ira.c (ira): Set current_loops to &ira_loops before recording
        loop exits.  Release recorded exits and loops early.

Index: ira.c
===================================================================
--- ira.c       (revision 192377)
+++ ira.c       (working copy)
@@ -4233,8 +4233,8 @@ ira (FILE *f)
   if (flag_ira_region == IRA_REGION_ALL || flag_ira_region == IRA_REGION_MIXED)
     {
       flow_loops_find (&ira_loops);
+      current_loops = &ira_loops;
       record_loop_exits ();
-      current_loops = &ira_loops;
     }

   if (internal_flag_ira_verbose > 0 && ira_dump_file != NULL)
@@ -4277,9 +4277,14 @@ ira (FILE *f)
             info.  */
          df_analyze ();

+         /* ??? Rebuild the loop tree, but why?  Does the loop tree
+            change if new insns were generated?  Can that be handled
+            by updating the loop tree incrementally?  */
+         release_recorded_exits ();
+         flow_loops_free (&ira_loops);
          flow_loops_find (&ira_loops);
+         current_loops = &ira_loops;
          record_loop_exits ();
-         current_loops = &ira_loops;

          setup_allocno_assignment_flags ();
          ira_initiate_assign ();
@@ -4363,6 +4368,7 @@ do_reload (void)

   if (current_loops != NULL)
     {
+      release_recorded_exits ();
       flow_loops_free (&ira_loops);
       free_dominance_info (CDI_DOMINATORS);
     }