Re: [PATCH] [RFC, PGO+LTO] Missed function specialization + partial devirtualization

["Martin Liška" <mliska@suse.cz>]

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Hi.

So the first part is about support of N tracked values to be supported.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

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From f3e361fb6d799acf538bc76a91bfcc8e265b7cbe Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Wed, 19 Jun 2019 14:15:14 +0200
Subject: [PATCH 1/2] Support N values in libgcov for single value counter
 type.

gcc/testsuite/ChangeLog:

2019-06-20  Martin Liska  <mliska@suse.cz>

	* gcc.dg/tree-prof/val-prof-2.c: Update scanned pattern
	as we do now better.

libgcc/ChangeLog:

2019-06-20  Martin Liska  <mliska@suse.cz>

	* libgcov-merge.c (merge_single_value_set): Support N values.
	* libgcov-profiler.c (__gcov_one_value_profiler_body): Likewise.
---
 gcc/testsuite/gcc.dg/tree-prof/val-prof-2.c |  5 +--
 libgcc/libgcov-merge.c                      | 48 +++++++++++----------
 libgcc/libgcov-profiler.c                   | 42 ++++++++++++++----
 3 files changed, 60 insertions(+), 35 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-prof/val-prof-2.c b/gcc/testsuite/gcc.dg/tree-prof/val-prof-2.c
index 8cb3c64fd17..b3bbadfeb40 100644
--- a/gcc/testsuite/gcc.dg/tree-prof/val-prof-2.c
+++ b/gcc/testsuite/gcc.dg/tree-prof/val-prof-2.c
@@ -25,8 +25,5 @@ main ()
   return 0;
 }
 /* autofdo does not do value profiling so far */
-/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: mod power of 2" "profile" } } */
-/* This is part of code checking that n is power of 2, so we are sure that the transformation
-   didn't get optimized out.  */
-/* { dg-final-use-not-autofdo { scan-tree-dump "n_\[0-9\]* \\+ (4294967295|0x0*ffffffff)" "optimized"} } */
+/* { dg-final-use-not-autofdo { scan-ipa-dump "Transformation done: div/mod by constant 256" "profile" } } */
 /* { dg-final-use { scan-tree-dump-not "Invalid sum" "optimized"} } */
diff --git a/libgcc/libgcov-merge.c b/libgcc/libgcov-merge.c
index f778cc4b6b7..84367005663 100644
--- a/libgcc/libgcov-merge.c
+++ b/libgcc/libgcov-merge.c
@@ -89,49 +89,53 @@ __gcov_merge_time_profile (gcov_type *counters, unsigned n_counters)
 static void
 merge_single_value_set (gcov_type *counters)
 {
-  unsigned j;
-  gcov_type value, counter;
-
   /* First value is number of total executions of the profiler.  */
   gcov_type all = gcov_get_counter_ignore_scaling (-1);
   counters[0] += all;
   ++counters;
 
+  /* Read all part values.  */
+  gcov_type read_counters[2 * GCOV_DISK_SINGLE_VALUES];
+
   for (unsigned i = 0; i < GCOV_DISK_SINGLE_VALUES; i++)
     {
-      value = gcov_get_counter_target ();
-      counter = gcov_get_counter_ignore_scaling (-1);
+      read_counters[2 * i] = gcov_get_counter_target ();
+      read_counters[2 * i + 1] = gcov_get_counter_ignore_scaling (-1);
+    }
 
-      if (counter == -1)
-	{
-	  counters[1] = -1;
-	  /* We can't return as we need to read all counters.  */
-	  continue;
-	}
-      else if (counter == 0 || counters[1] == -1)
-	{
-	  /* We can't return as we need to read all counters.  */
-	  continue;
-	}
+  if (read_counters[1] == -1)
+    {
+      counters[1] = -1;
+      return;
+    }
+
+  for (unsigned i = 0; i < GCOV_DISK_SINGLE_VALUES; i++)
+    {
+      if (read_counters[2 * i + 1] == 0)
+	return;
 
+      unsigned j;
       for (j = 0; j < GCOV_DISK_SINGLE_VALUES; j++)
 	{
-	  if (counters[2 * j] == value)
+	  if (counters[2 * j] == read_counters[2 * i])
 	    {
-	      counters[2 * j + 1] += counter;
+	      counters[2 * j + 1] += read_counters[2 * i + 1];
 	      break;
 	    }
 	  else if (counters[2 * j + 1] == 0)
 	    {
-	      counters[2 * j] = value;
-	      counters[2 * j + 1] = counter;
+	      counters[2 * j] += read_counters[2 * i];
+	      counters[2 * j + 1] += read_counters[2 * i + 1];
 	      break;
 	    }
 	}
 
-      /* We haven't found a free slot for the value, mark overflow.  */
+      /* We haven't found a slot, bail out.  */
       if (j == GCOV_DISK_SINGLE_VALUES)
-	counters[1] = -1;
+	{
+	  counters[1] = -1;
+	  return;
+	}
     }
 }
 
diff --git a/libgcc/libgcov-profiler.c b/libgcc/libgcov-profiler.c
index 9ba65b90df3..04d6f9c0e40 100644
--- a/libgcc/libgcov-profiler.c
+++ b/libgcc/libgcov-profiler.c
@@ -118,20 +118,44 @@ static inline void
 __gcov_one_value_profiler_body (gcov_type *counters, gcov_type value,
 				int use_atomic)
 {
-  if (value == counters[1])
-    counters[2]++;
-  else if (counters[2] == 0)
+  if (use_atomic)
+    __atomic_fetch_add (&counters[0], 1, __ATOMIC_RELAXED);
+  else
+    counters[0]++;
+
+  ++counters;
+
+  /* We have GCOV_DISK_SINGLE_VALUES as we can keep multiple values
+     next to each other.  */
+  unsigned sindex = 0;
+
+  for (unsigned i = 0; i < GCOV_DISK_SINGLE_VALUES; i++)
     {
-      counters[2] = 1;
-      counters[1] = value;
+      if (value == counters[2 * i])
+	{
+	  if (use_atomic)
+	    __atomic_fetch_add (&counters[2 * i + 1], 1, __ATOMIC_RELAXED);
+	  else
+	    counters[2 * i + 1]++;
+	  return;
+	}
+      else if (counters[2 * i + 1] == 0)
+	{
+	  /* We found an empty slot.  */
+	  counters[2 * i] = value;
+	  counters[2 * i + 1] = 1;
+	  return;
+	}
+
+      if (counters[2 * i + 1] < counters[2 * sindex + 1])
+	sindex = i;
     }
-  else
-    counters[2]--;
 
+  /* We haven't found an empty slot, then decrement the smallest.  */
   if (use_atomic)
-    __atomic_fetch_add (&counters[0], 1, __ATOMIC_RELAXED);
+    __atomic_fetch_sub (&counters[2 * sindex + 1], 1, __ATOMIC_RELAXED);
   else
-    counters[0]++;
+    counters[2 * sindex + 1]--;
 }
 
 #ifdef L_gcov_one_value_profiler_v2
-- 
2.21.0