[gcc r14-11219] Fix setting of call graph node AutoFDO count

[Eugene Rozenfeld]

https://gcc.gnu.org/g:802771f22815157cce8643e54e6810ed80079f13

commit r14-11219-g802771f22815157cce8643e54e6810ed80079f13
Author: Eugene Rozenfeld <erozen@microsoft.com>
Date:   Fri Jan 10 19:48:52 2025 -0800

    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:
---
 gcc/auto-profile.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/gcc/auto-profile.cc b/gcc/auto-profile.cc
index de59b94bcb33..216ea7fecc04 100644
--- a/gcc/auto-profile.cc
+++ b/gcc/auto-profile.cc
@@ -1538,8 +1538,6 @@ 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 ();
@@ -1578,6 +1576,8 @@ 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)