[PATCH][1/2] Alternate fix for PR81403

[Richard Biener <rguenther@suse.de>]

I had the need to analyze the PR81403 failure again and figured the real
cause and prepared a patch for this (the original fix still keeps some
issues latent I think).

This is cleanups that make it easier to debug PRE issues.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied.

Richard.

2017-11-22  Richard Biener  <rguenther@suse.de>

	* gimple-iterator.c (gimple_find_edge_insert_loc): Ignore
	fake edges to exit when looking for a place to insert.
	* tree-ssa-pre.c (clear_expression_ids): Inline into callers
	and remove.
	(insert_into_preds_of_block): Commit edge insertion immediately,
	assert that doesn't require new BBs.
	(fini_pre): Release expressions.
	(pass_pre::execute): Shuffle things around a bit, if the fn
	is too large do not compute AVAIL either as this is really the
	quadratic bit.

Index: gcc/gimple-iterator.c
===================================================================
--- gcc/gimple-iterator.c	(revision 254995)
+++ gcc/gimple-iterator.c	(working copy)
@@ -763,7 +763,12 @@ gimple_find_edge_insert_loc (edge e, gim
      Except for the entry block.  */
   src = e->src;
   if ((e->flags & EDGE_ABNORMAL) == 0
-      && single_succ_p (src)
+      && (single_succ_p (src)
+	  /* Do not count a fake edge as successor as added to infinite
+	     loops by connect_infinite_loops_to_exit.  */
+	  || (EDGE_COUNT (src->succs) == 2
+	      && (EDGE_SUCC (src, 0)->flags & EDGE_FAKE
+		  || EDGE_SUCC (src, 1)->flags & EDGE_FAKE)))
       && src != ENTRY_BLOCK_PTR_FOR_FN (cfun))
     {
       *gsi = gsi_last_bb (src);
Index: gcc/tree-ssa-pre.c
===================================================================
--- gcc/tree-ssa-pre.c	(revision 254995)
+++ gcc/tree-ssa-pre.c	(working copy)
@@ -400,15 +400,6 @@ expression_for_id (unsigned int id)
   return expressions[id];
 }
 
-/* Free the expression id field in all of our expressions,
-   and then destroy the expressions array.  */
-
-static void
-clear_expression_ids (void)
-{
-  expressions.release ();
-}
-
 static object_allocator<pre_expr_d> pre_expr_pool ("pre_expr nodes");
 
 /* Given an SSA_NAME NAME, get or create a pre_expr to represent it.  */
@@ -1331,7 +1322,6 @@ get_representative_for (const pre_expr e
 }
 
 
-
 static pre_expr
 phi_translate (pre_expr expr, bitmap_set_t set1, bitmap_set_t set2,
 	       basic_block pred, basic_block phiblock);
@@ -3004,7 +2994,8 @@ insert_into_preds_of_block (basic_block
       gcc_assert (!(pred->flags & EDGE_ABNORMAL));
       if (!gimple_seq_empty_p (stmts))
 	{
-	  gsi_insert_seq_on_edge (pred, stmts);
+	  basic_block new_bb = gsi_insert_seq_on_edge_immediate (pred, stmts);
+	  gcc_assert (! new_bb);
 	  insertions = true;
 	}
       if (!builtexpr)
@@ -4127,6 +4118,7 @@ static void
 fini_pre ()
 {
   value_expressions.release ();
+  expressions.release ();
   BITMAP_FREE (inserted_exprs);
   bitmap_obstack_release (&grand_bitmap_obstack);
   bitmap_set_pool.release ();
@@ -4181,22 +4173,21 @@ pass_pre::execute (function *fun)
      loop_optimizer_init may create new phis, etc.  */
   loop_optimizer_init (LOOPS_NORMAL);
   split_critical_edges ();
+  scev_initialize ();
 
   run_scc_vn (VN_WALK);
 
   init_pre ();
-  scev_initialize ();
-
-  /* Collect and value number expressions computed in each basic block.  */
-  compute_avail ();
 
   /* Insert can get quite slow on an incredibly large number of basic
      blocks due to some quadratic behavior.  Until this behavior is
      fixed, don't run it when he have an incredibly large number of
      bb's.  If we aren't going to run insert, there is no point in
-     computing ANTIC, either, even though it's plenty fast.  */
+     computing ANTIC, either, even though it's plenty fast nor do
+     we require AVAIL.  */
   if (n_basic_blocks_for_fn (fun) < 4000)
     {
+      compute_avail ();
       compute_antic ();
       insert ();
     }
@@ -4211,19 +4202,19 @@ pass_pre::execute (function *fun)
      not keeping virtual operands up-to-date.  */
   gcc_assert (!need_ssa_update_p (fun));
 
-  /* Remove all the redundant expressions.  */
-  todo |= vn_eliminate (inserted_exprs);
-
   statistics_counter_event (fun, "Insertions", pre_stats.insertions);
   statistics_counter_event (fun, "PA inserted", pre_stats.pa_insert);
   statistics_counter_event (fun, "HOIST inserted", pre_stats.hoist_insert);
   statistics_counter_event (fun, "New PHIs", pre_stats.phis);
 
-  clear_expression_ids ();
+  /* Remove all the redundant expressions.  */
+  todo |= vn_eliminate (inserted_exprs);
 
-  scev_finalize ();
   remove_dead_inserted_code ();
+
   fini_pre ();
+
+  scev_finalize ();
   loop_optimizer_finalize ();
 
   /* Restore SSA info before tail-merging as that resets it as well.  */