[PATCH] Fix PR bootstrap/57154

[tejohnson, 2013-05-03 16:23:59]

This patch fixes PR bootstrap/57154.

Bootstrapped on powerpc64-linux to ensure it fixes the bootstrap problem
reported
for that architecture, and also the test case attached to the bug report.
Also bootstrapped and regtested on x86_64-unknown-linux-gnu.

Ok for trunk?

Thanks,
Teresa

2013-05-03  Teresa Johnson  <tejohnson@google.com>

        PR bootstrap/57154
	* sched-rgn.c (compute_dom_prob_ps): Ensure accumulated probabilities
        do not exceed REG_BR_PROB_BASE.

Index: sched-rgn.c
===================================================================
--- sched-rgn.c	(revision 198532)
+++ sched-rgn.c	(working copy)
@@ -1442,6 +1442,12 @@ compute_dom_prob_ps (int bb)
 	bitmap_set_bit (pot_split[bb], EDGE_TO_BIT (out_edge));
 
       prob[bb] += combine_probabilities (prob[pred_bb], in_edge->probability);
+      // The rounding divide in combine_probabilities can result in an extra
+      // probability increment propagating along 50-50 edges. Eventually when
+      // the edges re-merge, the accumulated probability can go slightly above
+      // REG_BR_PROB_BASE.
+      if (prob[bb] > REG_BR_PROB_BASE)
+        prob[bb] = REG_BR_PROB_BASE;
     }
 
   bitmap_set_bit (dom[bb], bb);

--
This patch is available for review at http://codereview.appspot.com/9179043

[law_redhat.com, 2013-05-03 16:40:25]

On 05/03/2013 10:23 AM, Teresa Johnson wrote:
> This patch fixes PR bootstrap/57154.
>
> Bootstrapped on powerpc64-linux to ensure it fixes the bootstrap problem
reported
> for that architecture, and also the test case attached to the bug report.
> Also bootstrapped and regtested on x86_64-unknown-linux-gnu.
>
> Ok for trunk?
>
> Thanks,
> Teresa
>
> 2013-05-03  Teresa Johnson  <tejohnson@google.com>
>
>          PR bootstrap/57154
> 	* sched-rgn.c (compute_dom_prob_ps): Ensure accumulated probabilities
>          do not exceed REG_BR_PROB_BASE.
This is fine as it's the standard way to clamp probabilities.

jeff