[gcc r13-6061] Speedup DF dataflow solver

[gcc r13-6061] Speedup DF dataflow solver

[Richard Biener]

https://gcc.gnu.org/g:053d4dda0a205aba6af85fd9662118dd8109df9f

commit r13-6061-g053d4dda0a205aba6af85fd9662118dd8109df9f
Author: Richard Biener <rguenther@suse.de>
Date:   Tue Feb 14 14:46:47 2023 +0100

    Speedup DF dataflow solver
    
    The following makes sure to process blocks that follow the current
    block in the iteration order in the same iteration and only postpone
    blocks that would be visited earlier to the next iteration.
    
    For the all.i testcase in PR26854 at -O2 this shaves off 50% of
    the time to solve the DF RD problem, other problems also improve
    but not as drastically.
    
            PR middle-end/26854
            * df-core.cc (df_worklist_propagate_forward): Put later
            blocks on worklist and only earlier blocks on pending.
            (df_worklist_propagate_backward): Likewise.
            (df_worklist_dataflow_doublequeue): Change the iteration
            to process new blocks in the same iteration if that
            maintains the iteration order.

Diff:
---
 gcc/df-core.cc | 54 +++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 35 insertions(+), 19 deletions(-)

diff --git a/gcc/df-core.cc b/gcc/df-core.cc
index e5ae9ab9348..38f69ac5743 100644
--- a/gcc/df-core.cc
+++ b/gcc/df-core.cc
@@ -874,7 +874,8 @@ make_pass_df_finish (gcc::context *ctxt)
 /* Helper function for df_worklist_dataflow.
    Propagate the dataflow forward.
    Given a BB_INDEX, do the dataflow propagation
-   and set bits on for successors in PENDING
+   and set bits on for successors in PENDING for earlier
+   and WORKLIST for later in bbindex_to_postorder
    if the out set of the dataflow has changed.
 
    AGE specify time when BB was visited last time.
@@ -890,10 +891,11 @@ make_pass_df_finish (gcc::context *ctxt)
 
 static bool
 df_worklist_propagate_forward (struct dataflow *dataflow,
-                               unsigned bb_index,
-                               unsigned *bbindex_to_postorder,
-                               bitmap pending,
-                               sbitmap considered,
+			       unsigned bb_index,
+			       unsigned *bbindex_to_postorder,
+			       bitmap worklist,
+			       bitmap pending,
+			       sbitmap considered,
 			       vec<int> &last_change_age,
 			       int age)
 {
@@ -924,7 +926,13 @@ df_worklist_propagate_forward (struct dataflow *dataflow,
           unsigned ob_index = e->dest->index;
 
           if (bitmap_bit_p (considered, ob_index))
-            bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
+	    {
+	      if (bbindex_to_postorder[bb_index]
+		  < bbindex_to_postorder[ob_index])
+		bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+	      else
+		bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
+	    }
         }
       return true;
     }
@@ -937,10 +945,11 @@ df_worklist_propagate_forward (struct dataflow *dataflow,
 
 static bool
 df_worklist_propagate_backward (struct dataflow *dataflow,
-                                unsigned bb_index,
-                                unsigned *bbindex_to_postorder,
-                                bitmap pending,
-                                sbitmap considered,
+				unsigned bb_index,
+				unsigned *bbindex_to_postorder,
+				bitmap worklist,
+				bitmap pending,
+				sbitmap considered,
 				vec<int> &last_change_age,
 				int age)
 {
@@ -971,7 +980,13 @@ df_worklist_propagate_backward (struct dataflow *dataflow,
           unsigned ob_index = e->src->index;
 
           if (bitmap_bit_p (considered, ob_index))
-            bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
+	    {
+	      if (bbindex_to_postorder[bb_index]
+		  < bbindex_to_postorder[ob_index])
+		bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+	      else
+		bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
+	    }
         }
       return true;
     }
@@ -1021,36 +1036,37 @@ df_worklist_dataflow_doublequeue (struct dataflow *dataflow,
      and pending is for the next. */
   while (!bitmap_empty_p (pending))
     {
-      bitmap_iterator bi;
-      unsigned int index;
-
       std::swap (pending, worklist);
 
-      EXECUTE_IF_SET_IN_BITMAP (worklist, 0, index, bi)
+      do
 	{
+	  unsigned index = bitmap_first_set_bit (worklist);
+	  bitmap_clear_bit (worklist, index);
+
 	  unsigned bb_index;
 	  dcount++;
 
-	  bitmap_clear_bit (pending, index);
 	  bb_index = blocks_in_postorder[index];
 	  prev_age = last_visit_age[index];
 	  if (dir == DF_FORWARD)
 	    changed = df_worklist_propagate_forward (dataflow, bb_index,
 						     bbindex_to_postorder,
-						     pending, considered,
+						     worklist, pending,
+						     considered,
 						     last_change_age,
 						     prev_age);
 	  else
 	    changed = df_worklist_propagate_backward (dataflow, bb_index,
 						      bbindex_to_postorder,
-						      pending, considered,
+						      worklist, pending,
+						      considered,
 						      last_change_age,
 						      prev_age);
 	  last_visit_age[index] = ++age;
 	  if (changed)
 	    last_change_age[index] = age;
 	}
-      bitmap_clear (worklist);
+      while (!bitmap_empty_p (worklist));
     }
 
   BITMAP_FREE (worklist);