[PATCH] minor FDO profile related fixes

[Indu Bhagat]

I have been looking at -fdump-ipa-profile dump with an intention to sanitize
bits of information so that one may use it to judge the "quality of a profile"
in FDO.

The overall question I want to address is - are there ways to know which
functions were not run in the training run, i.e. have ZERO profile ?
(This patch corrects some dumped info; in a subsequent patch I would like to add
some more explicit information/diagnostics.)

Towards that end, I noticed that there are a couple of misleading bits of
information (so I think) in the symbol table dump listing all functions in the
compilation unit :
    --- "globally 0" appears even when profile data has not been fed by feedback
         profile (not the intent as the documentation of profile_guessed_global0
          in profile-count.h suggests).
    --- "unlikely_executed" should appear only when there is profile feedback or
        a function attribute is specified (as per documentation of
        node_frequency in coretypes.h). "unlikely_executed" in case of STALE or
        NO profile is misleading in my opinion.

Summary of changes :

1. This patch makes some adjustments around how x_profile_status of a function
is set - x_profile_status should be set to PROFILE_READ only when there is a
profile for a function read from the .gcda file. So, instead of relying on
profile_info (set whenever the gcda feedback file is present, even if the
function does not have a profile available in the file), use exec_counts
(non null when function has a profile (the latter may or may not be zero)). In
essence, x_profile_status and profile_count::m_quality
are set consistent to the stated intent (in code comments.)

2. A minor change in coverage.c is for more precise location of the message

Following -fdump-ipa-profile dump excerpts show the effect :

------------------------------------------------
      -O1, -O2, -O3
------------------------------------------------

0. APPLICABLE PROFILE
Trunk : Function flags: count:224114269 body hot
After Patch : Function flags: count:224114269 (precise) body hot

1. STALE PROFILE
(i.e., those cases covered by Wcoverage-mismatch; when control flow changes
  between profile-generate and profile-use)
Trunk : Function flags: count:224114269 body hot
After Patch : Function flags: count:224114269 (precise) body hot

2. NO PROFILE
(i.e., those cases covered by Wmissing-profile; when function has no profile
  available in the .gcda file)
Trunk (missing .gcda file) : Function flags: count:1073741824 (estimated locally) body
Trunk (missing function) : Function flags: count: 1073741824 (estimated locally, globally 0) body unlikely_executed
After Patch (missing .gcda file) : Function flags: count:1073741824 (estimated locally) body
After Patch (missing function) : Function flags: count:1073741824 (estimated locally) body

3. ZERO PROFILE (functions not run in training run)
Trunk : Function flags: count: 1073741824 (estimated locally, globally 0) body unlikely_executed
After Patch (remains the same) : count: 1073741824 (estimated locally, globally 0) body unlikely_executed

--------------------------------------------------
     O0
--------------------------------------------------
In O0, flag_guess_branch_prob is not set. This makes the profile_quality set to
(precise) for most of the above cases.

0. APPLICABLE PROFILE
Trunk : Function flags: count:224114269 body hot
After Patch : Function flags: count:224114269 (precise) body hot

1. STALE PROFILE
(i.e., those cases covered by Wcoverage-mismatch; when control flow changes
  between profile-generate and profile-use)
Trunk : Function flags: count:224114269 body hot
After Patch : Function flags: count:224114269 (precise) body hot

2. NO PROFILE
(i.e., those cases covered by Wmissing-profile; when function has no profile
  available in the .gcda file)
Trunk (missing file) : Function flags: body
Trunk (missing function) : Function flags: count:0 body unlikely_executed
After Patch (missing file) :  Function flags: body
*** After Patch (missing function) : Function flags: count:0 (precise) body
(*** This remains misleading, and I do not have a solution for this; as use of heuristics
  to guess branch probability is not allowed in O0)

3. ZERO PROFILE (functions not run in training run)
Trunk : Function flags: count:0 body unlikely_executed
After Patch : Function flags: count:0 (precise) body

--------------------------------------------------

make check-gcc on x86_64 shows no new failures.

(A related PR was https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86957 where we added diagnostics for the NO PROFILE case.)

-------------- next part --------------
diff --git a/gcc/coverage.c b/gcc/coverage.c
index 599a3bb..7595e6c 100644
--- a/gcc/coverage.c
+++ b/gcc/coverage.c
@@ -358,7 +358,7 @@ get_coverage_counts (unsigned counter, unsigned cfg_checksum,
       if (warning_printed && dump_enabled_p ())
 	{
 	  dump_user_location_t loc
-	    = dump_user_location_t::from_location_t (input_location);
+	    = dump_user_location_t::from_function_decl (current_function_decl);
           dump_printf_loc (MSG_MISSED_OPTIMIZATION, loc,
                            "use -Wno-error=coverage-mismatch to tolerate "
                            "the mismatch but performance may drop if the "
diff --git a/gcc/profile-count.c b/gcc/profile-count.c
index f4ab244..90f4feb 100644
--- a/gcc/profile-count.c
+++ b/gcc/profile-count.c
@@ -83,6 +83,8 @@ profile_count::dump (FILE *f) const
 	fprintf (f, " (auto FDO)");
       else if (m_quality == profile_guessed)
 	fprintf (f, " (guessed)");
+      else if (m_quality == profile_precise)
+	fprintf (f, " (precise)");
     }
 }
 
diff --git a/gcc/profile.c b/gcc/profile.c
index 2130319..57e3f3c 100644
--- a/gcc/profile.c
+++ b/gcc/profile.c
@@ -698,6 +698,11 @@ compute_branch_probabilities (unsigned cfg_checksum, unsigned lineno_checksum)
 	}
     }
 
+  if (exec_counts)
+    {
+      profile_status_for_fn (cfun) = PROFILE_READ;
+    }
+
   /* If we have real data, use them!  */
   if (bb_gcov_count (ENTRY_BLOCK_PTR_FOR_FN (cfun))
       || !flag_guess_branch_prob)
@@ -705,7 +710,7 @@ compute_branch_probabilities (unsigned cfg_checksum, unsigned lineno_checksum)
       bb->count = profile_count::from_gcov_type (bb_gcov_count (bb));
   /* If function was not trained, preserve local estimates including statically
      determined zero counts.  */
-  else
+  else if (profile_status_for_fn (cfun) == PROFILE_READ)
     FOR_ALL_BB_FN (bb, cfun)
       if (!(bb->count == profile_count::zero ()))
         bb->count = bb->count.global0 ();
@@ -718,6 +723,11 @@ compute_branch_probabilities (unsigned cfg_checksum, unsigned lineno_checksum)
 
   if (dump_file)
     {
+      fprintf (dump_file, " Profile feedback for function");
+      fprintf (dump_file, ((profile_status_for_fn (cfun) == PROFILE_READ)
+			   ? " is available \n"
+			   : " is not available \n"));
+
       fprintf (dump_file, "%d branches\n", num_branches);
       if (num_branches)
 	for (i = 0; i < 10; i++)
@@ -1317,12 +1327,12 @@ branch_prob (void)
   values.release ();
   free_edge_list (el);
   coverage_end_function (lineno_checksum, cfg_checksum);
-  if (flag_branch_probabilities && profile_info)
+  if (flag_branch_probabilities
+      && (profile_status_for_fn (cfun) == PROFILE_READ))
     {
       struct loop *loop;
       if (dump_file && (dump_flags & TDF_DETAILS))
 	report_predictor_hitrates ();
-      profile_status_for_fn (cfun) = PROFILE_READ;
 
       /* At this moment we have precise loop iteration count estimates.
 	 Record them to loop structure before the profile gets out of date. */