[PATCH] Fix the LOOP_BRANCH prediction

[Dehao Chen]

Hi,

This patch fixed the problem when a LOOP_EXIT edge for the inner loop
happened to target at the LOOP_LATCH of the outer loop. As the outer
loop is processed first, the LOOP_BRANCH heuristic is honored
(first_match), thus the inner loop's trip count is 0. (The attached
unittest demonstrates this).

Bootstrapped and passed gcc regression test.

Is it ok for trunk?

Thanks,
Dehao

gcc/ChangeLog

2012-07-30  Dehao Chen  <de...@google.com>

        * predict.c (predict_loops): Fix the prediction of LOOP_BRANCH.

gcc/testsuite/ChangeLog

2012-07-31  Dehao Chen  <de...@google.com>

        * gcc.dg/predict-7.c: New test.

Index: gcc/testsuite/gcc.dg/predict-7.c
===================================================================
--- gcc/testsuite/gcc.dg/predict-7.c    (revision 0)
+++ gcc/testsuite/gcc.dg/predict-7.c    (revision 0)
@@ -0,0 +1,17 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
+
+extern int global;
+
+int bar (int);
+
+void foo (int base)
+{
+  int i;
+  while (global < 10)
+    for (i = base; i < 10; i++)
+      bar (i);
+}
+
+/* { dg-final { scan-tree-dump-times "loop branch heuristics" 0
"profile_estimate"} } */
+/* { dg-final { cleanup-tree-dump "profile_estimate" } } */
Index: gcc/predict.c
===================================================================
--- gcc/predict.c       (revision 189835)
+++ gcc/predict.c       (working copy)
@@ -1404,7 +1404,7 @@

          /* Loop branch heuristics - predict an edge back to a
             loop's head as taken.  */
-         if (bb == loop->latch)
+         if (bb == loop->latch && bb->loop_father == loop)
            {
              e = find_edge (loop->latch, loop->header);
              if (e)