middle-end/117932 - speed up DF solver

The following addresses slow bitmap operations for maintaining the
iteration order of df_worklist_dataflow_doublequeue for large number
of basic-blocks.  The main complexity change is switching the
worklist and pending bitmaps to tree view, a secondary change is
avoiding the fully populated initial bitmap for the first iteration
and instead special-casing that plus avoiding all forward worklist
bitmap sets in that iteration.  Usually second or later iterations
are sparse, so optimizing the first iteration seems worthwhile.

For PR117932 when isolating from ext-dce and fold-mem-offset issues
this results in a 10% compile-time reduction.

	PR middle-end/117932
	* df-core.cc (df_worklist_propagate_forward): When WORKLIST
	is NULL, do not set bits there.
	(df_worklist_propagate_backward): Likewise.
	(df_worklist_dataflow_doublequeue): Separate first pass
	over all blocks with NULL worklist.
	(df_worklist_dataflow): Do not initialize pending and adjust.

1 files changed, 48 insertions, 22 deletions

diff --git a/gcc/df-core.cc b/gcc/df-core.cc
index 0f27bd2..99fe466 100644
--- a/gcc/df-core.cc
+++ b/gcc/df-core.cc
@@ -872,7 +872,8 @@ make_pass_df_finish (gcc::context *ctxt)
    Given a BB_INDEX, do the dataflow propagation
    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.
+   if the out set of the dataflow has changed.  When WORKLIST
+   is NULL we are processing all later blocks.
 
    AGE specify time when BB was visited last time.
    AGE of 0 means we are visiting for first time and need to
@@ -925,7 +926,10 @@ df_worklist_propagate_forward (struct dataflow *dataflow,
 	    {
 	      if (bbindex_to_postorder[bb_index]
 		  < bbindex_to_postorder[ob_index])
-		bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+		{
+		  if (worklist)
+		    bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+		}
 	      else
 		bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
 	    }
@@ -979,7 +983,10 @@ df_worklist_propagate_backward (struct dataflow *dataflow,
 	    {
 	      if (bbindex_to_postorder[bb_index]
 		  < bbindex_to_postorder[ob_index])
-		bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+		{
+		  if (worklist)
+		    bitmap_set_bit (worklist, bbindex_to_postorder[ob_index]);
+		}
 	      else
 		bitmap_set_bit (pending, bbindex_to_postorder[ob_index]);
 	    }
@@ -1010,26 +1017,55 @@ df_worklist_propagate_backward (struct dataflow *dataflow,
 
 static void
 df_worklist_dataflow_doublequeue (struct dataflow *dataflow,
-			  	  bitmap pending,
                                   sbitmap considered,
                                   int *blocks_in_postorder,
 				  unsigned *bbindex_to_postorder,
-				  int n_blocks)
+				  unsigned n_blocks)
 {
   enum df_flow_dir dir = dataflow->problem->dir;
   int dcount = 0;
-  bitmap worklist = BITMAP_ALLOC (&df_bitmap_obstack);
   int age = 0;
   bool changed;
   vec<int> last_visit_age = vNULL;
   vec<int> last_change_age = vNULL;
   int prev_age;
 
+  bitmap worklist = BITMAP_ALLOC (&df_bitmap_obstack);
+  bitmap_tree_view (worklist);
+
   last_visit_age.safe_grow_cleared (n_blocks, true);
   last_change_age.safe_grow_cleared (n_blocks, true);
 
-  /* Double-queueing. Worklist is for the current iteration,
-     and pending is for the next. */
+  /* We start with processing all blocks, populating pending for the
+     next iteration.  */
+  bitmap pending = BITMAP_ALLOC (&df_bitmap_obstack);
+  bitmap_tree_view (pending);
+  for (unsigned index = 0; index < n_blocks; ++index)
+    {
+      unsigned bb_index = blocks_in_postorder[index];
+      dcount++;
+      prev_age = last_visit_age[index];
+      if (dir == DF_FORWARD)
+	changed = df_worklist_propagate_forward (dataflow, bb_index,
+						 bbindex_to_postorder,
+						 NULL, pending,
+						 considered,
+						 last_change_age,
+						 prev_age);
+      else
+	changed = df_worklist_propagate_backward (dataflow, bb_index,
+						  bbindex_to_postorder,
+						  NULL, pending,
+						  considered,
+						  last_change_age,
+						  prev_age);
+      last_visit_age[index] = ++age;
+      if (changed)
+	last_change_age[index] = age;
+    }
+
+  /* Double-queueing.  Worklist is for the current iteration,
+     and pending is for the next.  */
   while (!bitmap_empty_p (pending))
     {
       std::swap (pending, worklist);
@@ -1037,11 +1073,8 @@ df_worklist_dataflow_doublequeue (struct dataflow *dataflow,
       do
 	{
 	  unsigned index = bitmap_clear_first_set_bit (worklist);
-
-	  unsigned bb_index;
+	  unsigned bb_index = blocks_in_postorder[index];
 	  dcount++;
-
-	  bb_index = blocks_in_postorder[index];
 	  prev_age = last_visit_age[index];
 	  if (dir == DF_FORWARD)
 	    changed = df_worklist_propagate_forward (dataflow, bb_index,
@@ -1091,7 +1124,6 @@ df_worklist_dataflow (struct dataflow *dataflow,
                       int *blocks_in_postorder,
                       int n_blocks)
 {
-  bitmap pending = BITMAP_ALLOC (&df_bitmap_obstack);
   bitmap_iterator bi;
   unsigned int *bbindex_to_postorder;
   int i;
@@ -1118,21 +1150,15 @@ df_worklist_dataflow (struct dataflow *dataflow,
 
   /* Initialize the mapping of block index to postorder.  */
   for (i = 0; i < n_blocks; i++)
-    {
-      bbindex_to_postorder[blocks_in_postorder[i]] = i;
-      /* Add all blocks to the worklist.  */
-      bitmap_set_bit (pending, i);
-    }
+    bbindex_to_postorder[blocks_in_postorder[i]] = i;
 
   /* Initialize the problem. */
   if (dataflow->problem->init_fun)
     dataflow->problem->init_fun (blocks_to_consider);
 
   /* Solve it.  */
-  df_worklist_dataflow_doublequeue (dataflow, pending, considered,
-				    blocks_in_postorder,
-				    bbindex_to_postorder,
-				    n_blocks);
+  df_worklist_dataflow_doublequeue (dataflow, considered, blocks_in_postorder,
+				    bbindex_to_postorder, n_blocks);
   free (bbindex_to_postorder);
 }