[GOOGLE] recalculate dominance before update_ssa in AutoFDO pass

[Dehao Chen]

This patch recalculates dominance info before update_ssa call in
AutoFDO. This fixes bug when dominance info is out-of-date and causes
segfaults during update_ssa.

Bootstrapped and regression test on-going.

OK for google-4_9 branch?

Thanks,
Dehao

Index: gcc/auto-profile.c
===================================================================
--- gcc/auto-profile.c (revision 216278)
+++ gcc/auto-profile.c (working copy)
@@ -1756,6 +1756,11 @@ auto_profile (void)
       early_inline ();
       autofdo::afdo_annotate_cfg (promoted_stmts);
       compute_function_frequency ();
+
+      free_dominance_info (CDI_DOMINATORS);
+      free_dominance_info (CDI_POST_DOMINATORS);
+      calculate_dominance_info (CDI_POST_DOMINATORS);
+      calculate_dominance_info (CDI_DOMINATORS);
       update_ssa (TODO_update_ssa);

       /* Local pure-const may imply need to fixup the cfg.  */