[PATCH V11] : tree-ssa-sink: Improve code sinking pass

[Ajit Agarwal <aagarwa1@linux.ibm.com>]

Hello Richard:

Currently, code sinking will sink code at the use points with loop having same
nesting depth. The following patch improves code sinking by placing the sunk
code in immediate dominator with same loop nest depth.

Review comments are incorporated.

For example :

void bar();
int j;
void foo(int a, int b, int c, int d, int e, int f)
{
  int l;
  l = a + b + c + d +e + f;
  if (a != 5)
    {
      bar();
      j = l;
    }
}

Code Sinking does the following:

void bar();
int j;
void foo(int a, int b, int c, int d, int e, int f)
{
  int l;

  if (a != 5)
    {
      l = a + b + c + d +e + f;
      bar();
      j = l;
    }
}

Bootstrapped regtested on powerpc64-linux-gnu.

Thanks & Regards
Ajit


tree-ssa-sink: Improve code sinking pass

Currently, code sinking will sink code at the use points with loop having same
nesting depth. The following patch improves code sinking by placing the sunk
code in immediate dominator with same loop nest depth.

2023-10-30  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>

gcc/ChangeLog:

        PR tree-optimization/81953
        * tree-ssa-sink.cc (statement_sink_location): Move statements with
        same loop nest depth.
        (select_best_block): Add heuristics to select the best blocks in the
        immediate dominato for same loop nest depthr.

gcc/testsuite/ChangeLog:

        PR tree-optimization/81953
        * gcc.dg/tree-ssa/ssa-sink-21.c: New test.
        * gcc.dg/tree-ssa/ssa-sink-22.c: New test.
---
 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c | 15 +++++++++++++++
 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c | 19 +++++++++++++++++++
 gcc/tree-ssa-sink.cc                        | 21 ++++++++++++++-------
 3 files changed, 48 insertions(+), 7 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
new file mode 100644
index 00000000000..d3b79ca5803
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-21.c
@@ -0,0 +1,15 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-stats" } */
+void bar();
+int j;
+void foo(int a, int b, int c, int d, int e, int f)
+{
+  int l;
+  l = a + b + c + d +e + f;
+  if (a != 5)
+    {
+      bar();
+      j = l;
+    }
+}
+/* { dg-final { scan-tree-dump {l_12\s+=\s+_4\s+\+\s+f_11\(D\);\n\s+bar\s+\(\)} sink1 } } */
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
new file mode 100644
index 00000000000..84e7938c54f
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-22.c
@@ -0,0 +1,19 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-stats" } */
+void bar();
+int j, x;
+void foo(int a, int b, int c, int d, int e, int f)
+{
+  int l;
+  l = a + b + c + d +e + f;
+  if (a != 5)
+    {
+      bar();
+      if (b != 3)
+        x = 3;
+      else
+        x = 5;
+      j = l;
+    }
+}
+/* { dg-final { scan-tree-dump {l_13\s+=\s+_4\s+\+\s+f_12\(D\);\n\s+bar\s+\(\)} sink1 } } */
diff --git a/gcc/tree-ssa-sink.cc b/gcc/tree-ssa-sink.cc
index a360c5cdd6e..0b823b81309 100644
--- a/gcc/tree-ssa-sink.cc
+++ b/gcc/tree-ssa-sink.cc
@@ -176,6 +176,9 @@ nearest_common_dominator_of_uses (def_operand_p def_p, bool *debug_stmts)
    tree, return the best basic block between them (inclusive) to place
    statements.
 
+   The best basic block should be an immediate dominator of
+   best basic block if we've moved to same loop nest.
+
    We want the most control dependent block in the shallowest loop nest.
 
    If the resulting block is in a shallower loop nest, then use it.  Else
@@ -201,14 +204,13 @@ select_best_block (basic_block early_bb,
     {
       /* If we've moved into a lower loop nest, then that becomes
 	 our best block.  */
-      if (bb_loop_depth (temp_bb) < bb_loop_depth (best_bb))
+      if (bb_loop_depth (temp_bb) <= bb_loop_depth (best_bb))
 	best_bb = temp_bb;
 
       /* Walk up the dominator tree, hopefully we'll find a shallower
  	 loop nest.  */
       temp_bb = get_immediate_dominator (CDI_DOMINATORS, temp_bb);
     }
-
   /* Placing a statement before a setjmp-like function would be invalid
      (it cannot be reevaluated when execution follows an abnormal edge).
      If we selected a block with abnormal predecessors, just punt.  */
@@ -250,7 +252,14 @@ select_best_block (basic_block early_bb,
       /* If result of comparsion is unknown, prefer EARLY_BB.
 	 Thus use !(...>=..) rather than (...<...)  */
       && !(best_bb->count * 100 >= early_bb->count * threshold))
-    return best_bb;
+    {
+     /* Avoid sinking to immediate dominator if the statement to be moved
+	 has memory operand and same loop nest.  */
+      if (best_bb != late_bb && gimple_vuse (stmt))
+	return late_bb;
+
+      return best_bb;
+    }
 
   /* No better block found, so return EARLY_BB, which happens to be the
      statement's original block.  */
@@ -430,6 +439,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 	    continue;
 	  break;
 	}
+
       use = USE_STMT (one_use);
 
       if (gimple_code (use) != GIMPLE_PHI)
@@ -439,10 +449,7 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 	  if (sinkbb == frombb)
 	    return false;
 
-	  if (sinkbb == gimple_bb (use))
-	    *togsi = gsi_for_stmt (use);
-	  else
-	    *togsi = gsi_after_labels (sinkbb);
+	  *togsi = gsi_after_labels (sinkbb);
 
 	  return true;
 	}
-- 
2.39.3