Re: [PATCH] New switch optimization pass (PR tree-optimization/54742)

[Steve Ellcey <sellcey at imgtec dot com>]

On Wed, 2013-05-15 at 10:44 +0200, Richard Biener wrote:

> Indeed.  I'd rather have a flag to the SESE copier that tells it the region
> is SEME and in that case make it not update dominators but leave that
> to the caller (which means, recompute them).  It seems the code already
> handles ME regions if the other exits are "not important" (we don't have
> to insert/update PHI nodes in those exit blocks), so it may be that there
> are even more constraints on those unimportant exits due to the
> iterative dominator update - I think that the entry block of the region
> needs to dominate all exit destinations, otherwise get_dominated_by_region
> is not working correctly.  In your case one exit is a back-edge?  We should
> be able to add checking to the code to verify unimportant edges are
> unimportant "enough".
> 
> I'm sure Zdenek knows the limitations best.
> 
> Richard.

Here is a patch that adds a flag to gimple_duplicate_sese_region to tell
it whether or not to update the dominator information.  I had to add the
same flag to copy_bbs to make it all work.  How does this look?  I
tested it with a bootstrap and test on x86 (with my optimization
enabled) and got no regressions.

2013-05-15  Steve Ellcey  <sellcey@imgtec.com>

	* cfghooks.c (copy_bbs): Add update_dominance argument.
	* cfghooks.h (copy_bbs): Update prototype.
	* tree-cfg.c (gimple_duplicate_sese_region):
	Add update_dominance argument.
	* tree-flow.h (gimple_duplicate_sese_region): Update prototype.
	* tree-ssa-loop-ch.c (copy_loop_headers): Update
	gimple_duplicate_sese_region call.
	* tree-vect-loop-manip.c (slpeel_tree_duplicate_loop_to_edge_cfg):
	Update copy_bbs call.
	* cfgloopmanip.c (duplicate_loop_to_header_edge): Ditto.
	* trans-mem.c (ipa_uninstrument_transaction): Ditto.

diff --git a/gcc/cfghooks.c b/gcc/cfghooks.c
index 22b962b..18af38b 100644
--- a/gcc/cfghooks.c
+++ b/gcc/cfghooks.c
@@ -1287,7 +1287,8 @@ end:
    function assigns bbs into loops (copy of basic block bb is assigned to
    bb->loop_father->copy loop, so this must be set up correctly in advance)
    and updates dominators locally (LOOPS structure that contains the information
-   about dominators is passed to enable this).
+   about dominators is passed to enable this) if update_dominance is set to
+   true.
 
    BASE is the superloop to that basic block belongs; if its header or latch
    is copied, we do not set the new blocks as header or latch.
@@ -1301,7 +1302,7 @@ end:
 void
 copy_bbs (basic_block *bbs, unsigned n, basic_block *new_bbs,
 	  edge *edges, unsigned num_edges, edge *new_edges,
-	  struct loop *base, basic_block after)
+	  struct loop *base, basic_block after, bool update_dominance)
 {
   unsigned i, j;
   basic_block bb, new_bb, dom_bb;
@@ -1327,16 +1328,19 @@ copy_bbs (basic_block *bbs, unsigned n, basic_block *new_bbs,
     }
 
   /* Set dominators.  */
-  for (i = 0; i < n; i++)
+  if (update_dominance)
     {
-      bb = bbs[i];
-      new_bb = new_bbs[i];
-
-      dom_bb = get_immediate_dominator (CDI_DOMINATORS, bb);
-      if (dom_bb->flags & BB_DUPLICATED)
+      for (i = 0; i < n; i++)
 	{
-	  dom_bb = get_bb_copy (dom_bb);
-	  set_immediate_dominator (CDI_DOMINATORS, new_bb, dom_bb);
+	  bb = bbs[i];
+	  new_bb = new_bbs[i];
+
+	  dom_bb = get_immediate_dominator (CDI_DOMINATORS, bb);
+	  if (dom_bb->flags & BB_DUPLICATED)
+	    {
+	      dom_bb = get_bb_copy (dom_bb);
+	      set_immediate_dominator (CDI_DOMINATORS, new_bb, dom_bb);
+	    }
 	}
     }
 
diff --git a/gcc/cfghooks.h b/gcc/cfghooks.h
index bff0a0c..ec595a5 100644
--- a/gcc/cfghooks.h
+++ b/gcc/cfghooks.h
@@ -201,7 +201,7 @@ extern void lv_add_condition_to_bb (basic_block, basic_block, basic_block,
 extern bool can_copy_bbs_p (basic_block *, unsigned);
 extern void copy_bbs (basic_block *, unsigned, basic_block *,
 		      edge *, unsigned, edge *, struct loop *,
-		      basic_block);
+		      basic_block, bool);
 
 void account_profile_record (struct profile_record *, int);
 
diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c
index 9581677..bc87755 100644
--- a/gcc/cfgloopmanip.c
+++ b/gcc/cfgloopmanip.c
@@ -1300,7 +1300,7 @@ duplicate_loop_to_header_edge (struct loop *loop, edge e,
 
       /* Copy bbs.  */
       copy_bbs (bbs, n, new_bbs, spec_edges, 2, new_spec_edges, loop,
-		place_after);
+		place_after, true);
       place_after = new_spec_edges[SE_LATCH]->src;
 
       if (flags & DLTHE_RECORD_COPY_NUMBER)
diff --git a/gcc/trans-mem.c b/gcc/trans-mem.c
index 5cb8286..c66278c 100644
--- a/gcc/trans-mem.c
+++ b/gcc/trans-mem.c
@@ -3978,7 +3978,8 @@ ipa_uninstrument_transaction (struct tm_region *region,
   int n = queue.length ();
   basic_block *new_bbs = XNEWVEC (basic_block, n);
 
-  copy_bbs (queue.address (), n, new_bbs, NULL, 0, NULL, NULL, transaction_bb);
+  copy_bbs (queue.address (), n, new_bbs, NULL, 0, NULL, NULL, transaction_bb,
+	    true);
   edge e = make_edge (transaction_bb, new_bbs[0], EDGE_TM_UNINSTRUMENTED);
   add_phi_args_after_copy (new_bbs, n, e);
 
diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
index a08a737..d492903 100644
--- a/gcc/tree-cfg.c
+++ b/gcc/tree-cfg.c
@@ -5686,16 +5686,17 @@ add_phi_args_after_copy (basic_block *region_copy, unsigned n_region,
    inside region is live over the other exit edges of the region.  All entry
    edges to the region must go to ENTRY->dest.  The edge ENTRY is redirected
    to the duplicate of the region.  Dominance and loop information is
-   updated, but not the SSA web.  The new basic blocks are stored to
-   REGION_COPY in the same order as they had in REGION, provided that
-   REGION_COPY is not NULL.
+   updated if update_dominance is true, but not the SSA web.  The new basic
+   blocks are stored to REGION_COPY in the same order as they had in REGION,
+   provided that REGION_COPY is not NULL.
    The function returns false if it is unable to copy the region,
    true otherwise.  */
 
 bool
 gimple_duplicate_sese_region (edge entry, edge exit,
 			    basic_block *region, unsigned n_region,
-			    basic_block *region_copy)
+			    basic_block *region_copy,
+			    bool update_dominance)
 {
   unsigned i;
   bool free_region_copy = false, copying_header = false;
@@ -5749,12 +5750,15 @@ gimple_duplicate_sese_region (edge entry, edge exit,
       free_region_copy = true;
     }
 
-  /* Record blocks outside the region that are dominated by something
-     inside.  */
-  doms.create (0);
   initialize_original_copy_tables ();
 
-  doms = get_dominated_by_region (CDI_DOMINATORS, region, n_region);
+  /* Record blocks outside the region that are dominated by something
+     inside.  */
+  if (update_dominance)
+    {
+      doms.create (0);
+      doms = get_dominated_by_region (CDI_DOMINATORS, region, n_region);
+    }
 
   if (entry->dest->count)
     {
@@ -5778,7 +5782,7 @@ gimple_duplicate_sese_region (edge entry, edge exit,
     }
 
   copy_bbs (region, n_region, region_copy, &exit, 1, &exit_copy, loop,
-	    split_edge_bb_loc (entry));
+	    split_edge_bb_loc (entry), update_dominance);
   if (total_count)
     {
       scale_bbs_frequencies_gcov_type (region, n_region,
@@ -5809,10 +5813,13 @@ gimple_duplicate_sese_region (edge entry, edge exit,
      for entry block and its copy.  Anything that is outside of the
      region, but was dominated by something inside needs recounting as
      well.  */
-  set_immediate_dominator (CDI_DOMINATORS, entry->dest, entry->src);
-  doms.safe_push (get_bb_original (entry->dest));
-  iterate_fix_dominators (CDI_DOMINATORS, doms, false);
-  doms.release ();
+  if (update_dominance)
+    {
+      set_immediate_dominator (CDI_DOMINATORS, entry->dest, entry->src);
+      doms.safe_push (get_bb_original (entry->dest));
+      iterate_fix_dominators (CDI_DOMINATORS, doms, false);
+      doms.release ();
+    }
 
   /* Add the other PHI node arguments.  */
   add_phi_args_after_copy (region_copy, n_region, NULL);
@@ -5944,7 +5951,7 @@ gimple_duplicate_sese_tail (edge entry ATTRIBUTE_UNUSED, edge exit ATTRIBUTE_UNU
     }
 
   copy_bbs (region, n_region, region_copy, exits, 2, nexits, orig_loop,
-	    split_edge_bb_loc (exit));
+	    split_edge_bb_loc (exit), true);
   if (total_count)
     {
       scale_bbs_frequencies_gcov_type (region, n_region,
diff --git a/gcc/tree-flow.h b/gcc/tree-flow.h
index 01fe363..24fcfbf 100644
--- a/gcc/tree-flow.h
+++ b/gcc/tree-flow.h
@@ -395,7 +395,7 @@ extern void verify_gimple_in_cfg (struct function *);
 extern tree gimple_block_label (basic_block);
 extern void extract_true_false_edges_from_block (basic_block, edge *, edge *);
 extern bool gimple_duplicate_sese_region (edge, edge, basic_block *, unsigned,
-					basic_block *);
+					basic_block *, bool);
 extern bool gimple_duplicate_sese_tail (edge, edge, basic_block *, unsigned,
 				      basic_block *);
 extern void gather_blocks_in_sese_region (basic_block entry, basic_block exit,
diff --git a/gcc/tree-ssa-loop-ch.c b/gcc/tree-ssa-loop-ch.c
index a1d0299..ff17c7e 100644
--- a/gcc/tree-ssa-loop-ch.c
+++ b/gcc/tree-ssa-loop-ch.c
@@ -197,7 +197,8 @@ copy_loop_headers (void)
       entry = loop_preheader_edge (loop);
 
       propagate_threaded_block_debug_into (exit->dest, entry->dest);
-      if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs))
+      if (!gimple_duplicate_sese_region (entry, exit, bbs, n_bbs, copied_bbs,
+					 true))
 	{
 	  fprintf (dump_file, "Duplication failed.\n");
 	  continue;
diff --git a/gcc/tree-vect-loop-manip.c b/gcc/tree-vect-loop-manip.c
index bff5c22..d1a1f06 100644
--- a/gcc/tree-vect-loop-manip.c
+++ b/gcc/tree-vect-loop-manip.c
@@ -735,7 +735,7 @@ slpeel_tree_duplicate_loop_to_edge_cfg (struct loop *loop, edge e)
 
   copy_bbs (bbs, loop->num_nodes + 1, new_bbs,
 	    &exit, 1, &new_exit, NULL,
-	    e->src);
+	    e->src, true);
   basic_block new_preheader = new_bbs[loop->num_nodes];
 
   add_phi_args_after_copy (new_bbs, loop->num_nodes + 1, NULL);