Fix setting of call graph node AutoFDO count

We are initializing both the call graph node count and
the entry block count of the function with the head_count value
from the profile.

Count propagation algorithm may refine the entry block count
and we may end up with a case where the call graph node count
is set to zero but the entry block count is non-zero. That becomes
a problem because we have this code in execute_fixup_cfg:

 profile_count num = node->count;
 profile_count den = ENTRY_BLOCK_PTR_FOR_FN (cfun)->count;
 bool scale = num.initialized_p () && !(num == den);

Here if num is 0 but den is not 0, scale becomes true and we
lose the counts in

if (scale)
  bb->count = bb->count.apply_scale (num, den);

This is what happened in the issue reported in PR116743
(a 10% regression in MySQL HAMMERDB tests).
3d9e6767939e9658260e2506e81ec32b37cba041 made an improvement in
AutoFDO count propagation, which caused a mismatch between
the call graph node count (zero) and the entry block count (non-zero)
and subsequent loss of counts as described above.

The fix is to update the call graph node count once we've done count propagation.

Tested on x86_64-pc-linux-gnu.

gcc/ChangeLog:
	PR gcov-profile/116743
	* auto-profile.cc (afdo_annotate_cfg): Fix mismatch between the call graph node count
	and the entry block count.

(cherry picked from commit e683c6b029f809c7a1981b4341c95d9652c22e18)

diff --git a/gcc/auto-profile.cc b/gcc/auto-profile.cc
index 2b34b80b82d26ad2aa0f5f63d886b8f257c2fb8a..89dd05252c2521701462e58d5ef72403776dea2e 100644 (file)
--- a/gcc/auto-profile.cc
+++ b/gcc/auto-profile.cc
@@ -1537,8 +1537,6 @@ afdo_annotate_cfg (const stmt_set &promoted_stmts)
 
   if (s == NULL)
     return;
-  cgraph_node::get (current_function_decl)->count
-     = profile_count::from_gcov_type (s->head_count ()).afdo ();
   ENTRY_BLOCK_PTR_FOR_FN (cfun)->count
      = profile_count::from_gcov_type (s->head_count ()).afdo ();
   EXIT_BLOCK_PTR_FOR_FN (cfun)->count = profile_count::zero ().afdo ();
@@ -1577,6 +1575,8 @@ afdo_annotate_cfg (const stmt_set &promoted_stmts)
       /* Calculate, propagate count and probability information on CFG.  */
       afdo_calculate_branch_prob (&annotated_bb);
     }
+  cgraph_node::get(current_function_decl)->count
+      = ENTRY_BLOCK_PTR_FOR_FN(cfun)->count;
   update_max_bb_count ();
   profile_status_for_fn (cfun) = PROFILE_READ;
   if (flag_value_profile_transformations)