Fix incorrect loop exit edge probability [PR103270]

r12-4526 cancelled jump thread path rotates loop. It exposes a issue in
profile-estimate when predict_extra_loop_exits, outer loop's exit edge
is marked as inner loop's extra loop exit and set with incorrect
prediction, then a hot inner loop will become cold loop finally through
optimizations, this patch add loop check when searching extra exit edges
to avoid unexpected predict_edge from predict_paths_for_bb.

Regression tested on P8LE.

gcc/ChangeLog:

2021-12-21  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR middle-end/103270
	* predict.c (predict_extra_loop_exits): Add loop parameter.
	(predict_loops): Call with loop argument.

gcc/testsuite/ChangeLog:

2021-12-21  Xionghu Luo  <luoxhu@linux.ibm.com>

	PR middle-end/103270
	* gcc.dg/pr103270.c: New test.

diff --git a/gcc/predict.c b/gcc/predict.c
index 1a1da7e8360b89592fe2d2810c67c6a11b8e5093..1316ca88e204f1cfea46469b6c735edd414d7a77 100644 (file)
--- a/gcc/predict.c
+++ b/gcc/predict.c
@@ -1859,7 +1859,7 @@ predict_iv_comparison (class loop *loop, basic_block bb,
    exits to predict them using PRED_LOOP_EXTRA_EXIT.  */
 
 static void
-predict_extra_loop_exits (edge exit_edge)
+predict_extra_loop_exits (class loop *loop, edge exit_edge)
 {
   unsigned i;
   bool check_value_one;
@@ -1912,12 +1912,14 @@ predict_extra_loop_exits (edge exit_edge)
        continue;
       if (EDGE_COUNT (e->src->succs) != 1)
        {
-         predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
+         predict_paths_leading_to_edge (e, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
+                                        loop);
          continue;
        }
 
       FOR_EACH_EDGE (e1, ei, e->src->preds)
-       predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN);
+       predict_paths_leading_to_edge (e1, PRED_LOOP_EXTRA_EXIT, NOT_TAKEN,
+                                      loop);
     }
 }
 
@@ -2008,7 +2010,7 @@ predict_loops (void)
                         ex->src->index, ex->dest->index);
              continue;
            }
-         predict_extra_loop_exits (ex);
+         predict_extra_loop_exits (loop, ex);
 
          if (number_of_iterations_exit (loop, ex, &niter_desc, false, false))
            niter = niter_desc.niter;

diff --git a/gcc/testsuite/gcc.dg/pr103270.c b/gcc/testsuite/gcc.dg/pr103270.c
new file mode 100644 (file)
index 0000000..819310e
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr103270.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-profile_estimate" } */
+
+void test(int a, int* i)
+{
+  for (; a < 5; ++a)
+    {
+      int b = 0;
+      int c = 0;
+      for (; b != -11; b--)
+       for (int d = 0; d ==0; d++)
+         {
+           *i += c & a;
+           c = b;
+         }
+    }
+}
+
+/* { dg-final { scan-tree-dump-not "extra loop exit heuristics of edge\[^:\]*:" "profile_estimate"} } */