[gcc r12-5817] Improve AutoFDO count propagation algorithm

[gcc r12-5817] Improve AutoFDO count propagation algorithm

[Eugene Rozenfeld]

https://gcc.gnu.org/g:3d9e6767939e9658260e2506e81ec32b37cba041

commit r12-5817-g3d9e6767939e9658260e2506e81ec32b37cba041
Author: Eugene Rozenfeld <erozen@microsoft.com>
Date:   Thu Dec 2 18:37:09 2021 -0800

    Improve AutoFDO count propagation algorithm
    
    When a basic block A has been annotated with a count and it has only one
    successor (or predecessor) B, we can propagate the A's count to B.
    The algoritm without this change could leave B without an annotation if B had
    other unannotated predecessors (or successors). For example, in the test case I added,
    the loop header block was left unannotated, which prevented loop unrolling.
    
    gcc/ChangeLog:
            * auto-profile.c (afdo_propagate_edge): Improve count propagation algorithm.
    
    gcc/testsuite/ChangeLog:
            * gcc.dg/tree-prof/init-array.c: New test for unrolling inner loops.

Diff:
---
 gcc/auto-profile.c                          | 20 ++++++++++++--
 gcc/testsuite/gcc.dg/tree-prof/init-array.c | 43 +++++++++++++++++++++++++++++
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/gcc/auto-profile.c b/gcc/auto-profile.c
index 4c1fc6b536b..dfcd68113aa 100644
--- a/gcc/auto-profile.c
+++ b/gcc/auto-profile.c
@@ -1192,7 +1192,8 @@ afdo_find_equiv_class (bb_set *annotated_bb)
 /* If a basic block's count is known, and only one of its in/out edges' count
    is unknown, its count can be calculated. Meanwhile, if all of the in/out
    edges' counts are known, then the basic block's unknown count can also be
-   calculated.
+   calculated. Also, if a block has a single predecessor or successor, the block's
+   count can be propagated to that predecessor or successor.
    IS_SUCC is true if out edges of a basic blocks are examined.
    Update ANNOTATED_BB accordingly.
    Return TRUE if any basic block/edge count is changed.  */
@@ -1208,6 +1209,7 @@ afdo_propagate_edge (bool is_succ, bb_set *annotated_bb)
     edge e, unknown_edge = NULL;
     edge_iterator ei;
     int num_unknown_edge = 0;
+    int num_edge = 0;
     profile_count total_known_count = profile_count::zero ().afdo ();
 
     FOR_EACH_EDGE (e, ei, is_succ ? bb->succs : bb->preds)
@@ -1217,6 +1219,7 @@ afdo_propagate_edge (bool is_succ, bb_set *annotated_bb)
 	  num_unknown_edge++, unknown_edge = e;
 	else
 	  total_known_count += AFDO_EINFO (e)->get_count ();
+	num_edge++;
       }
 
     /* Be careful not to annotate block with no successor in special cases.  */
@@ -1230,7 +1233,20 @@ afdo_propagate_edge (bool is_succ, bb_set *annotated_bb)
     else if (num_unknown_edge == 1 && is_bb_annotated (bb, *annotated_bb))
       {
 	if (bb->count > total_known_count)
-	  AFDO_EINFO (unknown_edge)->set_count (bb->count - total_known_count);
+	  {
+	      profile_count new_count = bb->count - total_known_count;
+	      AFDO_EINFO(unknown_edge)->set_count(new_count);
+	      if (num_edge == 1)
+		{
+		  basic_block succ_or_pred_bb = is_succ ? unknown_edge->dest : unknown_edge->src;
+		  if (new_count > succ_or_pred_bb->count)
+		    {
+		      succ_or_pred_bb->count = new_count;
+		      if (!is_bb_annotated (succ_or_pred_bb, *annotated_bb))
+			set_bb_annotated (succ_or_pred_bb, annotated_bb);
+		    }
+		}
+	   }
 	else
 	  AFDO_EINFO (unknown_edge)->set_count (profile_count::zero().afdo ());
 	AFDO_EINFO (unknown_edge)->set_annotated ();
diff --git a/gcc/testsuite/gcc.dg/tree-prof/init-array.c b/gcc/testsuite/gcc.dg/tree-prof/init-array.c
new file mode 100644
index 00000000000..0f7a5c84481
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-prof/init-array.c
@@ -0,0 +1,43 @@
+/* { dg-options "-O3 -fdump-tree-cunrolli-details" } */
+
+static int s[10][10][10];
+static int d[10][10][10];
+
+__attribute__((noipa)) 
+int array()
+{
+	int i;
+	register int j, k;
+	for (i = 0; i < 10; i++)
+		for (j = 0; j < 10; j++)
+			for (k = 0; k < 10; k++)
+				d[i][j][k] = s[i][j][k];
+
+	return(0);
+}
+
+__attribute__((noipa)) 
+void TestBench()
+{
+	for (int i = 0; i < 150000; ++i)
+	{ 
+	   array();
+	}
+}
+
+int main(int argc, char *argv[])
+{
+
+	TestBench();
+
+	if (d[9][9][9] == 0 && s[9][9][9] == 0)
+	{
+		return 0;
+	}
+	else
+	{
+		return -1;
+	}	
+}
+
+/* { dg-final-use { scan-tree-dump-times "loop with 10 iterations completely unrolled" 2 "cunrolli"} } */