Re: [PATCH v4] Generalize get_most_common_single_value to return k_th value & count

[luoxhu <luoxhu@linux.ibm.com>]

Currently get_most_common_single_value could only return the max hist
<value, count>, add sort after reading from disk, then it return nth value
in later use.  Rename it to get_nth_most_common_value.

Hi Martin,
Thanks for your review, v4 Changes as below:
 1. Use decrease bubble sort.
BTW, I have a question about hist->hvalue.counters[2], when will it become
 -1, please? Thanks.  Currently, if it is -1, the function will return false.

gcc/ChangeLog:

	2019-07-15  Xiong Hu Luo  <luoxhu@linux.ibm.com>

	* ipa-profile.c (get_most_common_single_value): Use
	get_nth_most_common_value.
	* profile.c (sort_hist_value): New function.
	(compute_value_histograms): Call sort_hist_value to sort the
	values after loading from disk.
	* value-prof.c (get_most_common_single_value): Rename to ...
	get_nth_most_common_value.  Add input params n, return
	the n_th value and count.
	(gimple_divmod_fixed_value_transform): Use
	get_nth_most_common_value.
	(gimple_ic_transform): Likewise.
	(gimple_stringops_transform): Likewise.
	* value-prof.h (get_most_common_single_value): Add input params
	n, default to 0.
---
 gcc/ipa-profile.c |  4 ++--
 gcc/profile.c     | 44 +++++++++++++++++++++++++++++++++++++++
 gcc/value-prof.c  | 53 ++++++++++++++++++++---------------------------
 gcc/value-prof.h  |  9 ++++----
 4 files changed, 73 insertions(+), 37 deletions(-)

diff --git a/gcc/ipa-profile.c b/gcc/ipa-profile.c
index 1fb939b73d0..970dba39c80 100644
--- a/gcc/ipa-profile.c
+++ b/gcc/ipa-profile.c
@@ -192,8 +192,8 @@ ipa_profile_generate_summary (void)
 		  if (h)
 		    {
 		      gcov_type val, count, all;
-		      if (get_most_common_single_value (NULL, "indirect call",
-							h, &val, &count, &all))
+		      if (get_nth_most_common_value (NULL, "indirect call", h,
+						     &val, &count, &all))
 			{
 			  struct cgraph_edge * e = node->get_edge (stmt);
 			  if (e && !e->indirect_unknown_callee)
diff --git a/gcc/profile.c b/gcc/profile.c
index 441cb8eb183..ae21b1192a0 100644
--- a/gcc/profile.c
+++ b/gcc/profile.c
@@ -743,6 +743,44 @@ compute_branch_probabilities (unsigned cfg_checksum, unsigned lineno_checksum)
   free_aux_for_blocks ();
 }
 
+  /* Sort the histogram value and count for TOPN and INDIR_CALL type.  */
+
+static bool
+sort_hist_value (histogram_value hist)
+{
+
+  if (hist->hvalue.counters[2] == -1)
+    return false;
+
+  gcc_assert (hist->type == HIST_TYPE_TOPN_VALUES
+	      || hist->type == HIST_TYPE_INDIR_CALL);
+
+  gcc_assert (hist->n_counters == GCOV_TOPN_VALUES_COUNTERS);
+
+  unsigned i, j;
+  bool swapped = true;
+  /* Hist value is organized as:
+     [counter0 value1 counter1 value2 counter2 value3 counter3 value4 counter4]
+     Use decrese bubble sort to rearrange it.  The sort starts from <value1,
+     counter1> and compares counter first, If counter is same, compares the
+     value, exchange it if small to keep stable.  */
+  for (i = 0; i < GCOV_TOPN_VALUES - 1 && swapped; i++)
+    {
+      swapped = false;
+      for (j = 0; j < GCOV_TOPN_VALUES - 1 - i; j++)
+	{
+	  gcov_type *p = &hist->hvalue.counters[2 * j + 1];
+	  if (p[1] < p[3] || (p[1] == p[3] && p[0] < p[2]))
+	    {
+	      std::swap (p[0], p[2]);
+	      std::swap (p[1], p[3]);
+	      swapped = true;
+	    }
+	}
+    }
+
+  return true;
+}
 /* Load value histograms values whose description is stored in VALUES array
    from .gcda file.  
 
@@ -808,6 +846,12 @@ compute_value_histograms (histogram_values values, unsigned cfg_checksum,
         else
           hist->hvalue.counters[j] = 0;
 
+      if (hist->type == HIST_TYPE_TOPN_VALUES
+	  || hist->type == HIST_TYPE_INDIR_CALL)
+	{
+	  sort_hist_value (hist);
+	}
+
       /* Time profiler counter is not related to any statement,
          so that we have to read the counter and set the value to
          the corresponding call graph node.  */
diff --git a/gcc/value-prof.c b/gcc/value-prof.c
index 32e6ddd8165..759458868a8 100644
--- a/gcc/value-prof.c
+++ b/gcc/value-prof.c
@@ -713,45 +713,38 @@ gimple_divmod_fixed_value (gassign *stmt, tree value, profile_probability prob,
   return tmp2;
 }
 
-/* Return most common value of TOPN_VALUE histogram.  If
-   there's a unique value, return true and set VALUE and COUNT
+/* Return the n-th value count of TOPN_VALUE histogram.  If
+   there's a value, return true and set VALUE and COUNT
    arguments.  */
 
 bool
-get_most_common_single_value (gimple *stmt, const char *counter_type,
-			      histogram_value hist,
-			      gcov_type *value, gcov_type *count,
-			      gcov_type *all)
+get_nth_most_common_value (gimple *stmt, const char *counter_type,
+			   histogram_value hist, gcov_type *value,
+			   gcov_type *count, gcov_type *all, unsigned n)
 {
   if (hist->hvalue.counters[2] == -1)
     return false;
 
+  gcc_assert (n < GCOV_TOPN_VALUES);
+
   *count = 0;
   *value = 0;
 
   gcov_type read_all = hist->hvalue.counters[0];
 
-  for (unsigned i = 0; i < GCOV_TOPN_VALUES; i++)
-    {
-      gcov_type v = hist->hvalue.counters[2 * i + 1];
-      gcov_type c = hist->hvalue.counters[2 * i + 2];
-
-      /* Indirect calls can't be vereified.  */
-      if (stmt && check_counter (stmt, counter_type, &c, &read_all,
-				 gimple_bb (stmt)->count))
-	return false;
+  gcov_type v = hist->hvalue.counters[2 * n + 1];
+  gcov_type c = hist->hvalue.counters[2 * n + 2];
 
-      *all = read_all;
+  /* Indirect calls can't be verified.  */
+  if (stmt
+      && check_counter (stmt, counter_type, &c, &read_all,
+			gimple_bb (stmt)->count))
+    return false;
 
-      if (c > *count)
-	{
-	  *value = v;
-	  *count = c;
-	}
-      else if (c == *count && v > *value)
-	*value = v;
-    }
+  *all = read_all;
 
+  *value = v;
+  *count = c;
   return true;
 }
 
@@ -784,8 +777,8 @@ gimple_divmod_fixed_value_transform (gimple_stmt_iterator *si)
   if (!histogram)
     return false;
 
-  if (!get_most_common_single_value (stmt, "divmod", histogram, &val, &count,
-				     &all))
+  if (!get_nth_most_common_value (stmt, "divmod", histogram, &val, &count,
+				  &all))
     return false;
 
   value = histogram->hvalue.value;
@@ -1439,8 +1432,8 @@ gimple_ic_transform (gimple_stmt_iterator *gsi)
   if (!histogram)
     return false;
 
-  if (!get_most_common_single_value (NULL, "indirect call", histogram, &val,
-				     &count, &all))
+  if (!get_nth_most_common_value (NULL, "indirect call", histogram, &val,
+				  &count, &all))
     return false;
 
   if (4 * count <= 3 * all)
@@ -1658,8 +1651,8 @@ gimple_stringops_transform (gimple_stmt_iterator *gsi)
   if (!histogram)
     return false;
 
-  if (!get_most_common_single_value (stmt, "stringops", histogram, &val,
-				     &count, &all))
+  if (!get_nth_most_common_value (stmt, "stringops", histogram, &val, &count,
+				  &all))
     return false;
 
   gimple_remove_histogram_value (cfun, stmt, histogram);
diff --git a/gcc/value-prof.h b/gcc/value-prof.h
index ca846d08cbd..1078722163b 100644
--- a/gcc/value-prof.h
+++ b/gcc/value-prof.h
@@ -89,11 +89,10 @@ void free_histograms (function *);
 void stringop_block_profile (gimple *, unsigned int *, HOST_WIDE_INT *);
 gcall *gimple_ic (gcall *, struct cgraph_node *, profile_probability);
 bool check_ic_target (gcall *, struct cgraph_node *);
-bool get_most_common_single_value (gimple *stmt, const char *counter_type,
-				   histogram_value hist,
-				   gcov_type *value, gcov_type *count,
-				   gcov_type *all);
-
+bool get_nth_most_common_value (gimple *stmt, const char *counter_type,
+				histogram_value hist, gcov_type *value,
+				gcov_type *count, gcov_type *all,
+				unsigned n = 0);
 
 /* In tree-profile.c.  */
 extern void gimple_init_gcov_profiler (void);
-- 
2.22.0.428.g6d5b264208