AutoFDO: Implement summary information in auto-profile

This patch aims to implement summary support in auto-profile, similar to
LLVM. The summary information stores various information about the
profile being read such as the number of functions, the maximum sample
count, the total number of samples and so on.

It also adds a section called the "detailed summary" which contains a
histogram-based calculation of the minimum execution count for a sample
needed to belong to a specific percentile of samples. This is used to
decide the hot count threshold (which can be controlled with a command
line parameter). The default is any sample belonging to the 99th percentile
being marked as hot.

This patch requires the changes from https://github.com/google/autofdo/pull/251
to work correctly.

Signed-off-by: Dhruv Chawla <dhruvc@nvidia.com>
gcc/ChangeLog:

	* auto-profile.cc (struct summary_info): New struct.
	(summary_info::read): New function.
	(summary_info::get_threshold_count): Likewise.
	(function_instance::read_function_instance): Read
	afdo_profile_info->sum_max directly from summary info.
	(autofdo_source_profile::read): Set afdo_hot_bb_threshold from
	param_hot_bb_count_ws_permille.
	(read_profile): Call summary_info->read.
	(end_auto_profile): Free afdo_summary_info.
	* gcov-io.h (GCOV_TAG_AFDO_SUMMARY): New define.

diff --git a/gcc/auto-profile.cc b/gcc/auto-profile.cc
index 5670b94bb15a5ed5ab526b1bf550c1ba4da87fb6..ad5b0651743c8833c540194a3e932fa131db2bab 100644 (file)
--- a/gcc/auto-profile.cc
+++ b/gcc/auto-profile.cc
@@ -228,6 +228,45 @@ struct string_compare
   }
 };
 
+/* Store the summary information for the profile.  */
+struct summary_info
+{
+  /* There are currently 16 hard-coded percentiles in the GCOV format.  */
+  static constexpr unsigned NUM_PERCENTILES = 16;
+
+  /* The detailed summary is a histogram-based calculation of the minimum
+     execution count required to belong to a certain set of percentile of
+     counts.  */
+  struct detailed_summary
+  {
+    /* The percentile that this represents (multiplied by 1,000,000).  */
+    uint32_t cutoff;
+    /* The minimum execution count required to belong to this percentile.  */
+    uint64_t min_count;
+    /* The number of samples which belong to this percentile.  */
+    uint64_t num_counts;
+  };
+
+  /* The sum of execution counts of all samples.  */
+  uint64_t total_count;
+  /* The maximum individual count.  */
+  uint64_t max_count;
+  /* The maximum head count across all functions.  */
+  uint64_t max_function_count;
+  /* The number of lines that have samples.  */
+  uint64_t num_counts;
+  /* The number of functions that have samples.  */
+  uint64_t num_functions;
+  /* The percentile threshold information.  */
+  detailed_summary detailed_summaries[NUM_PERCENTILES];
+
+  /* Read profile.  Return TRUE on success.  */
+  bool read ();
+
+  /* Get the minimum count required for percentile CUTOFF.  */
+  uint64_t get_threshold_count (uint32_t cutoff);
+};
+
 /* Store a string array, indexed by string position in the array.  */
 class string_table
 {
@@ -672,6 +711,9 @@ private:
   auto_vec <function_instance *> duplicate_functions_;
 };
 
+/* Store the summary information from the GCOV file.  */
+static summary_info *afdo_summary_info;
+
 /* Store the strings read from the profile data file.  */
 static string_table *afdo_string_table;
 
@@ -918,6 +960,47 @@ get_normalized_path (const char *path, bool from_gcov = false)
   return lbasename (path);
 }
 
+/* Member functions for summary_info.  */
+
+bool
+summary_info::read ()
+{
+  if (gcov_read_unsigned () != GCOV_TAG_AFDO_SUMMARY)
+    return false;
+
+  total_count = gcov_read_counter ();
+  max_count = gcov_read_counter ();
+  max_function_count = gcov_read_counter ();
+  num_counts = gcov_read_counter ();
+  num_functions = gcov_read_counter ();
+  uint64_t num_detailed_summaries = gcov_read_counter ();
+  gcc_checking_assert (num_detailed_summaries == NUM_PERCENTILES);
+  for (uint64_t i = 0; i < num_detailed_summaries; i++)
+    {
+      detailed_summaries[i].cutoff = gcov_read_unsigned ();
+      detailed_summaries[i].min_count = gcov_read_counter ();
+      detailed_summaries[i].num_counts = gcov_read_counter ();
+    }
+
+  return !gcov_is_error ();
+}
+
+/* Get the minimum count required for percentile CUTOFF.  */
+
+uint64_t
+summary_info::get_threshold_count (uint32_t cutoff)
+{
+  /* The cutoffs stored in the GCOV are fractions multiplied by 1,000,000.  */
+  gcc_checking_assert (cutoff <= 1'000'000);
+  unsigned idx = 0;
+  /* Find the first cutoff at least as high as CUTOFF.  */
+  for (; idx < NUM_PERCENTILES; idx++)
+    if (detailed_summaries[idx].cutoff >= cutoff)
+      break;
+  idx = std::min (NUM_PERCENTILES - 1, idx);
+  return detailed_summaries[idx].min_count;
+}
+
 /* Member functions for string_table.  */
 
 /* Deconstructor.  */
@@ -2626,8 +2709,6 @@ function_instance::read_function_instance (function_instance_stack *stack,
       unsigned num_targets = gcov_read_unsigned ();
       gcov_type count = gcov_read_counter ();
       s->pos_counts[offset].count = count;
-      afdo_profile_info->sum_max = std::max (afdo_profile_info->sum_max,
-                                            count);
 
       for (unsigned j = 0; j < stack->length (); j++)
         (*stack)[j]->total_count_ += count;
@@ -2907,7 +2988,7 @@ autofdo_source_profile::read ()
                     "auto-profile contains duplicated function instance %s",
                     afdo_string_table->get_symbol_name (s->symbol_name ()));
     }
-  int hot_frac = param_hot_bb_count_fraction;
+  afdo_profile_info->sum_max = afdo_summary_info->max_count;
   /* Scale up the profile, but leave some bits in case some counts gets
      bigger than sum_max eventually.  */
   if (afdo_profile_info->sum_max)
@@ -2915,22 +2996,25 @@ autofdo_source_profile::read ()
       = MAX (((gcov_type)1 << (profile_count::n_bits - 10))
             / afdo_profile_info->sum_max, 1);
   afdo_profile_info->cutoff *= afdo_count_scale;
-  afdo_hot_bb_threshold
-    = hot_frac
-      ? afdo_profile_info->sum_max * afdo_count_scale / hot_frac
-      : (gcov_type)profile_count::max_count;
+  /* Derive the hot count threshold from the profile summary.  */
+  afdo_hot_bb_threshold = afdo_summary_info->get_threshold_count (
+                           param_hot_bb_count_ws_permille * 1000)
+                         * afdo_count_scale;
   set_hot_bb_threshold (afdo_hot_bb_threshold);
   if (dump_file)
-    fprintf (dump_file, "Max count in profile %" PRIu64 "\n"
-                       "Setting scale %" PRIu64 "\n"
-                       "Scaled max count %" PRIu64 "\n"
-                       "Cutoff %" PRIu64 "\n"
-                       "Hot count threshold %" PRIu64 "\n\n",
-            (int64_t)afdo_profile_info->sum_max,
-            (int64_t)afdo_count_scale,
-            (int64_t)(afdo_profile_info->sum_max * afdo_count_scale),
-            (int64_t)afdo_profile_info->cutoff,
-            (int64_t)afdo_hot_bb_threshold);
+    fprintf (dump_file,
+            "Max count in profile %" PRIu64 "\n"
+            "Setting scale %" PRIu64 "\n"
+            "Scaled max count %" PRIu64 "\n"
+            "Cutoff %" PRIu64 "\n"
+            "Unscaled hot count threshold %" PRIu64 "\n"
+            "Hot count threshold %" PRIu64 "\n\n",
+            (int64_t) afdo_profile_info->sum_max, (int64_t) afdo_count_scale,
+            (int64_t) (afdo_profile_info->sum_max * afdo_count_scale),
+            (int64_t) afdo_profile_info->cutoff,
+            (int64_t) afdo_summary_info->get_threshold_count (
+              param_hot_bb_count_ws_permille * 1000),
+            (int64_t) afdo_hot_bb_threshold);
   afdo_profile_info->sum_max *= afdo_count_scale;
   return true;
 }
@@ -3072,6 +3156,14 @@ read_profile (void)
   /* Skip the empty integer.  */
   gcov_read_unsigned ();
 
+  /* summary_info.  */
+  afdo_summary_info = new summary_info ();
+  if (!afdo_summary_info->read ())
+    {
+      error ("cannot read summary information from %s", auto_profile_file);
+      return;
+    }
+
   /* string_table.  */
   afdo_string_table = new string_table ();
   if (!afdo_string_table->read ())
@@ -4512,6 +4604,7 @@ end_auto_profile (void)
 {
   delete autofdo::afdo_source_profile;
   delete autofdo::afdo_string_table;
+  delete autofdo::afdo_summary_info;
   profile_info = NULL;
 }
 

diff --git a/gcc/gcov-io.h b/gcc/gcov-io.h
index 313c15cecbb84798fd275e8b92fbc8571b17c1f9..7b1d93f961d2ccfc254bd295938bb45da71fc92b 100644 (file)
--- a/gcc/gcov-io.h
+++ b/gcc/gcov-io.h
@@ -274,6 +274,8 @@ typedef uint64_t gcov_type_unsigned;
 #define GCOV_TAG_OBJECT_SUMMARY  ((gcov_unsigned_t)0xa1000000)
 #define GCOV_TAG_OBJECT_SUMMARY_LENGTH (2 * GCOV_WORD_SIZE)
 #define GCOV_TAG_PROGRAM_SUMMARY ((gcov_unsigned_t)0xa3000000) /* Obsolete */
+
+#define GCOV_TAG_AFDO_SUMMARY    ((gcov_unsigned_t)0xa8000000)
 #define GCOV_TAG_AFDO_FILE_NAMES ((gcov_unsigned_t)0xaa000000)
 #define GCOV_TAG_AFDO_FUNCTION ((gcov_unsigned_t)0xac000000)
 #define GCOV_TAG_AFDO_WORKING_SET ((gcov_unsigned_t)0xaf000000)