tree-optimization/108353 - copyprop iteration order

After recent improvements to copyprop to catch more constants
it shows that the current iteration order prefering forward
progress over iterating doesn't make much sense for an SSA
propagator.  The following instead first iterates cycles which
makes sure to not start with optimistically constant PHIs out
of cycles that optimistically do not exit.

	PR tree-optimization/108353
	* tree-ssa-propagate.cc (cfg_blocks_back, ssa_edge_worklist_back):
	Remove.
	(add_ssa_edge): Simplify.
	(add_control_edge): Likewise.
	(ssa_prop_init): Likewise.
	(ssa_prop_fini): Likewise.
	(ssa_propagation_engine::ssa_propagate): Likewise.

	* gcc.dg/tree-ssa/ssa-copyprop-3.c: New testcase.

gcc/testsuite/gcc.dg/tree-ssa/ssa-copyprop-3.c

@@ -0,0 +1,38 @@
+/* { dg-do link } */
+/* { dg-require-effective-target int32plus } */
+/* { dg-options "-O -fdump-tree-copyprop2" } */
+
+#include <limits.h>
+enum { a } b();
+int d;
+int e;
+int f;
+void foo();
+[[gnu::noipa]]
+void bar49_(void){}
+[[gnu::noipa]]
+void(c)(void){}
+static short g(int h, int i) {
+  int j = -1420678603, k = 1;
+  if (h)
+    for (; j < INT_MAX-18; j = j + 9) {
+      f = 0;
+      for (; f <= 1; c())
+        k = 90;
+    }
+  i = k;
+  for (; e; ++e) {
+    if (i)
+      continue;
+    foo();
+    i = b();
+  }
+  return 4;
+}
+int l() {
+  bar49_();
+  return 1;
+}
+int main() { d = d || g(d, l()); }
+
+/* { dg-final { scan-tree-dump-not "foo" "copyprop2" } } */

gcc/tree-ssa-propagate.cc

@@ -113,7 +113,6 @@
    order by visiting in bit-order.  We use two worklists to
    first make forward progress before iterating.  */
 static bitmap cfg_blocks;
-static bitmap cfg_blocks_back;
 static int *bb_to_cfg_order;
 static int *cfg_order_to_bb;
 
@@ -123,7 +122,6 @@ static int *cfg_order_to_bb;
    UID in a bitmap.  UIDs order stmts in execution order.  We use
    two worklists to first make forward progress before iterating.  */
 static bitmap ssa_edge_worklist;
-static bitmap ssa_edge_worklist_back;
 static vec<gimple *> uid_to_stmt;
 
 /* Current RPO index in the iteration.  */
@@ -159,12 +157,7 @@ add_ssa_edge (tree var)
 	       & EDGE_EXECUTABLE))
 	continue;
 
-      bitmap worklist;
-      if (bb_to_cfg_order[gimple_bb (use_stmt)->index] < curr_order)
-	worklist = ssa_edge_worklist_back;
-      else
-	worklist = ssa_edge_worklist;
-      if (bitmap_set_bit (worklist, gimple_uid (use_stmt)))
+      if (bitmap_set_bit (ssa_edge_worklist, gimple_uid (use_stmt)))
 	{
 	  uid_to_stmt[gimple_uid (use_stmt)] = use_stmt;
 	  if (dump_file && (dump_flags & TDF_DETAILS))
@@ -193,10 +186,7 @@ add_control_edge (edge e)
   e->flags |= EDGE_EXECUTABLE;
 
   int bb_order = bb_to_cfg_order[bb->index];
-  if (bb_order < curr_order)
-    bitmap_set_bit (cfg_blocks_back, bb_order);
-  else
-    bitmap_set_bit (cfg_blocks, bb_order);
+  bitmap_set_bit (cfg_blocks, bb_order);
 
   if (dump_file && (dump_flags & TDF_DETAILS))
     fprintf (dump_file, "Adding destination of edge (%d -> %d) to worklist\n",
@@ -380,9 +370,7 @@ ssa_prop_init (void)
 
   /* Worklists of SSA edges.  */
   ssa_edge_worklist = BITMAP_ALLOC (NULL);
-  ssa_edge_worklist_back = BITMAP_ALLOC (NULL);
   bitmap_tree_view (ssa_edge_worklist);
-  bitmap_tree_view (ssa_edge_worklist_back);
 
   /* Worklist of basic-blocks.  */
   bb_to_cfg_order = XNEWVEC (int, last_basic_block_for_fn (cfun) + 1);
@@ -392,7 +380,6 @@ ssa_prop_init (void)
   for (int i = 0; i < n; ++i)
     bb_to_cfg_order[cfg_order_to_bb[i]] = i;
   cfg_blocks = BITMAP_ALLOC (NULL);
-  cfg_blocks_back = BITMAP_ALLOC (NULL);
 
   /* Initially assume that every edge in the CFG is not executable.
      (including the edges coming out of the entry block).  Mark blocks
@@ -430,11 +417,9 @@ static void
 ssa_prop_fini (void)
 {
   BITMAP_FREE (cfg_blocks);
-  BITMAP_FREE (cfg_blocks_back);
   free (bb_to_cfg_order);
   free (cfg_order_to_bb);
   BITMAP_FREE (ssa_edge_worklist);
-  BITMAP_FREE (ssa_edge_worklist_back);
   uid_to_stmt.release ();
 }
 
@@ -453,8 +438,7 @@ ssa_propagation_engine::ssa_propagate (void)
   curr_order = 0;
 
   /* Iterate until the worklists are empty.  We iterate both blocks
-     and stmts in RPO order, using sets of two worklists to first
-     complete the current iteration before iterating over backedges.
+     and stmts in RPO order, prioritizing backedge processing.
      Seed the algorithm by adding the successors of the entry block to the
      edge worklist.  */
   edge e;
@@ -471,18 +455,7 @@ ssa_propagation_engine::ssa_propagate (void)
       int next_stmt_uid = (bitmap_empty_p (ssa_edge_worklist)
 			   ? -1 : bitmap_first_set_bit (ssa_edge_worklist));
       if (next_block_order == -1 && next_stmt_uid == -1)
-	{
-	  if (bitmap_empty_p (cfg_blocks_back)
-	      && bitmap_empty_p (ssa_edge_worklist_back))
-	    break;
-
-	  if (dump_file && (dump_flags & TDF_DETAILS))
-	    fprintf (dump_file, "Regular worklists empty, now processing "
-		     "backedge destinations\n");
-	  std::swap (cfg_blocks, cfg_blocks_back);
-	  std::swap (ssa_edge_worklist, ssa_edge_worklist_back);
-	  continue;
-	}
+	break;
 
       int next_stmt_bb_order = -1;
       gimple *next_stmt = NULL;