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[GOOGLE] Fix a bug when profile propagation handles infinite loop.


If the propagation finds an infinite look, if the in-edge count is
non-zero, then it will cause compiler go into infinite loop when
building with AutoFDO.

Bootstrapped and regression test on-going.

OK for google-4_8 branch?

Thanks,
Dehao

Index: gcc/auto-profile.c
===================================================================
--- gcc/auto-profile.c (revision 204027)
+++ gcc/auto-profile.c (working copy)
@@ -1287,6 +1287,7 @@ afdo_propagate (void)
 {
   basic_block bb;
   bool changed = true;
+  int i = 0;

   FOR_ALL_BB (bb)
     {
@@ -1295,7 +1296,7 @@ afdo_propagate (void)
  bb->flags |= BB_ANNOTATED;
     }

-  while (changed)
+  while (changed && i++ < PARAM_VALUE (PARAM_AUTOFDO_MAX_PROPAGATE_ITERATIONS))
     {
       changed = false;

Index: gcc/params.def
===================================================================
--- gcc/params.def (revision 204027)
+++ gcc/params.def (working copy)
@@ -460,6 +460,14 @@ DEFPARAM(PARAM_MAX_PREDICTED_ITERATIONS,
  "The maximum number of loop iterations we predict statically",
  100, 0, 0)

+/* This parameter controls the maximum iterations that AutoFDO profile
+   prpagation algorithm will run for a specific CFG.  */
+
+DEFPARAM(PARAM_AUTOFDO_MAX_PROPAGATE_ITERATIONS,
+         "max-autofdo-max-propagate-iterations",
+         "The maximum number of AutoFDO profile propagation iterations",
+         1000, 0, 0)
+
 /* This parameter controls the probability of builtin_expect. The default
    value is 90%. This empirical value is obtained through the weighted
    probability of FDO counters (with the FDO count value as the weight)


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