re PR tree-optimization/90316 (large compile time increase in opt / alias stmt walking for Go example)

2019-05-07  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/90316
	* tree-ssa-alias.h (get_continuation_for_phi): Take walking
	limit by reference.
	(walk_non_aliased_vuses): Take walking limit argument.
	* tree-ssa-alias.c (maybe_skip_until): Take limit and abort
	walking if it is reached instead of just counting.
	(get_continuation_for_phi): Likewise.
	(walk_non_aliased_vuses): Likewise, instead of leaving counter
	limiting to the callback.
	* tree-ssa-sccvn.c (vn_reference_lookup_2): Adjust.
	(vn_reference_lookup_3): Likewise.
	(vn_reference_lookup_pieces): Likewise.
	(vn_reference_lookup): Likewise.
	* tree-ssa-pre.c (translate_vuse_through_block): Limit walking.
	* tree-ssa-scopedtables.c (vuse_eq): Adjust.
	(avail_exprs_stack::lookup_avail_expr): Likewise.

From-SVN: r270940

6 files changed, 61 insertions, 43 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index ac9a600..20586bf 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,4 +1,23 @@
-2019-05-03  Jan Hubicka  <hubicka@ucw.cz>
+2019-05-07  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/90316
+	* tree-ssa-alias.h (get_continuation_for_phi): Take walking
+	limit by reference.
+	(walk_non_aliased_vuses): Take walking limit argument.
+	* tree-ssa-alias.c (maybe_skip_until): Take limit and abort
+	walking if it is reached instead of just counting.
+	(get_continuation_for_phi): Likewise.
+	(walk_non_aliased_vuses): Likewise, instead of leaving counter
+	limiting to the callback.
+	* tree-ssa-sccvn.c (vn_reference_lookup_2): Adjust.
+	(vn_reference_lookup_3): Likewise.
+	(vn_reference_lookup_pieces): Likewise.
+	(vn_reference_lookup): Likewise.
+	* tree-ssa-pre.c (translate_vuse_through_block): Limit walking.
+	* tree-ssa-scopedtables.c (vuse_eq): Adjust.
+	(avail_exprs_stack::lookup_avail_expr): Likewise.
+
+2019-05-07  Jan Hubicka  <hubicka@ucw.cz>
 
 	* tree-ssa-alias.c (aliasing_component_refs_p): Continue looking
 	for comparaible types in the second direction even if first one
diff --git a/gcc/tree-ssa-alias.c b/gcc/tree-ssa-alias.c
index 1947710..619cc89 100644
--- a/gcc/tree-ssa-alias.c
+++ b/gcc/tree-ssa-alias.c
@@ -2601,7 +2601,7 @@ stmt_kills_ref_p (gimple *stmt, tree ref)
 
 static bool
 maybe_skip_until (gimple *phi, tree &target, basic_block target_bb,
-		  ao_ref *ref, tree vuse, unsigned int *cnt, bitmap *visited,
+		  ao_ref *ref, tree vuse, unsigned int &limit, bitmap *visited,
 		  bool abort_on_visited,
 		  void *(*translate)(ao_ref *, tree, void *, bool *),
 		  void *data)
@@ -2636,7 +2636,7 @@ maybe_skip_until (gimple *phi, tree &target, basic_block target_bb,
 	  /* An already visited PHI node ends the walk successfully.  */
 	  if (bitmap_bit_p (*visited, SSA_NAME_VERSION (PHI_RESULT (def_stmt))))
 	    return !abort_on_visited;
-	  vuse = get_continuation_for_phi (def_stmt, ref, cnt,
+	  vuse = get_continuation_for_phi (def_stmt, ref, limit,
 					   visited, abort_on_visited,
 					   translate, data);
 	  if (!vuse)
@@ -2648,7 +2648,9 @@ maybe_skip_until (gimple *phi, tree &target, basic_block target_bb,
       else
 	{
 	  /* A clobbering statement or the end of the IL ends it failing.  */
-	  ++*cnt;
+	  if ((int)limit <= 0)
+	    return false;
+	  --limit;
 	  if (stmt_may_clobber_ref_p_1 (def_stmt, ref))
 	    {
 	      bool disambiguate_only = true;
@@ -2676,12 +2678,13 @@ maybe_skip_until (gimple *phi, tree &target, basic_block target_bb,
 /* Starting from a PHI node for the virtual operand of the memory reference
    REF find a continuation virtual operand that allows to continue walking
    statements dominating PHI skipping only statements that cannot possibly
-   clobber REF.  Increments *CNT for each alias disambiguation done.
+   clobber REF.  Decrements LIMIT for each alias disambiguation done
+   and aborts the walk, returning NULL_TREE if it reaches zero.
    Returns NULL_TREE if no suitable virtual operand can be found.  */
 
 tree
 get_continuation_for_phi (gimple *phi, ao_ref *ref,
-			  unsigned int *cnt, bitmap *visited,
+			  unsigned int &limit, bitmap *visited,
 			  bool abort_on_visited,
 			  void *(*translate)(ao_ref *, tree, void *, bool *),
 			  void *data)
@@ -2723,7 +2726,7 @@ get_continuation_for_phi (gimple *phi, ao_ref *ref,
       arg1 = PHI_ARG_DEF (phi, i);
       if (arg1 == arg0)
 	;
-      else if (! maybe_skip_until (phi, arg0, dom, ref, arg1, cnt, visited,
+      else if (! maybe_skip_until (phi, arg0, dom, ref, arg1, limit, visited,
 				   abort_on_visited,
 				   /* Do not translate when walking over
 				      backedges.  */
@@ -2759,18 +2762,22 @@ get_continuation_for_phi (gimple *phi, ao_ref *ref,
    implement optimistic value-numbering for example.  Note that the
    VUSE argument is assumed to be valueized already.
 
+   LIMIT specifies the number of alias queries we are allowed to do,
+   the walk stops when it reaches zero and NULL is returned.  LIMIT
+   is decremented by the number of alias queries (plus adjustments
+   done by the callbacks) upon return.
+
    TODO: Cache the vector of equivalent vuses per ref, vuse pair.  */
 
 void *
 walk_non_aliased_vuses (ao_ref *ref, tree vuse,
-			void *(*walker)(ao_ref *, tree, unsigned int, void *),
+			void *(*walker)(ao_ref *, tree, void *),
 			void *(*translate)(ao_ref *, tree, void *, bool *),
 			tree (*valueize)(tree),
-			void *data)
+			unsigned &limit, void *data)
 {
   bitmap visited = NULL;
   void *res;
-  unsigned int cnt = 0;
   bool translated = false;
 
   timevar_push (TV_ALIAS_STMT_WALK);
@@ -2780,7 +2787,7 @@ walk_non_aliased_vuses (ao_ref *ref, tree vuse,
       gimple *def_stmt;
 
       /* ???  Do we want to account this to TV_ALIAS_STMT_WALK?  */
-      res = (*walker) (ref, vuse, cnt, data);
+      res = (*walker) (ref, vuse, data);
       /* Abort walk.  */
       if (res == (void *)-1)
 	{
@@ -2804,11 +2811,15 @@ walk_non_aliased_vuses (ao_ref *ref, tree vuse,
       if (gimple_nop_p (def_stmt))
 	break;
       else if (gimple_code (def_stmt) == GIMPLE_PHI)
-	vuse = get_continuation_for_phi (def_stmt, ref, &cnt,
+	vuse = get_continuation_for_phi (def_stmt, ref, limit,
 					 &visited, translated, translate, data);
       else
 	{
-	  cnt++;
+	  if ((int)limit <= 0)
+	    {
+	      res = NULL;
+	      break;
+	    }
 	  if (stmt_may_clobber_ref_p_1 (def_stmt, ref))
 	    {
 	      if (!translate)
diff --git a/gcc/tree-ssa-alias.h b/gcc/tree-ssa-alias.h
index a5293cd..cee8449 100644
--- a/gcc/tree-ssa-alias.h
+++ b/gcc/tree-ssa-alias.h
@@ -132,15 +132,13 @@ extern bool call_may_clobber_ref_p_1 (gcall *, ao_ref *);
 extern bool stmt_kills_ref_p (gimple *, tree);
 extern bool stmt_kills_ref_p (gimple *, ao_ref *);
 extern tree get_continuation_for_phi (gimple *, ao_ref *,
-				      unsigned int *, bitmap *, bool,
+				      unsigned int &, bitmap *, bool,
 				      void *(*)(ao_ref *, tree, void *, bool *),
 				      void *);
 extern void *walk_non_aliased_vuses (ao_ref *, tree,
-				     void *(*)(ao_ref *, tree,
-					       unsigned int, void *),
+				     void *(*)(ao_ref *, tree, void *),
 				     void *(*)(ao_ref *, tree, void *, bool *),
-				     tree (*)(tree),
-				     void *);
+				     tree (*)(tree), unsigned &, void *);
 extern int walk_aliased_vdefs (ao_ref *, tree,
 			       bool (*)(ao_ref *, tree, void *),
 			       void *, bitmap *,
diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index e1c75f8e..646feb6 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -1151,6 +1151,7 @@ translate_vuse_through_block (vec<vn_reference_op_s> operands,
   if (gimple_bb (phi) != phiblock)
     return vuse;
 
+  unsigned int cnt = PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS);
   use_oracle = ao_ref_init_from_vn_reference (&ref, set, type, operands);
 
   /* Use the alias-oracle to find either the PHI node in this block,
@@ -1159,8 +1160,10 @@ translate_vuse_through_block (vec<vn_reference_op_s> operands,
   if (gimple_code (phi) == GIMPLE_PHI)
     e = find_edge (block, phiblock);
   else if (use_oracle)
-    while (!stmt_may_clobber_ref_p_1 (phi, &ref))
+    while (cnt > 0
+	   && !stmt_may_clobber_ref_p_1 (phi, &ref))
       {
+	--cnt;
 	vuse = gimple_vuse (phi);
 	phi = SSA_NAME_DEF_STMT (vuse);
 	if (gimple_bb (phi) != phiblock)
@@ -1179,10 +1182,9 @@ translate_vuse_through_block (vec<vn_reference_op_s> operands,
       if (use_oracle)
 	{
 	  bitmap visited = NULL;
-	  unsigned int cnt;
 	  /* Try to find a vuse that dominates this phi node by skipping
 	     non-clobbering statements.  */
-	  vuse = get_continuation_for_phi (phi, &ref, &cnt, &visited, false,
+	  vuse = get_continuation_for_phi (phi, &ref, cnt, &visited, false,
 					   NULL, NULL);
 	  if (visited)
 	    BITMAP_FREE (visited);
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index a174f18..219fb9e 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -1671,19 +1671,12 @@ vn_reference_lookup_1 (vn_reference_t vr, vn_reference_t *vnresult)
    with the current VUSE and performs the expression lookup.  */
 
 static void *
-vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse,
-		       unsigned int cnt, void *vr_)
+vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *vr_)
 {
   vn_reference_t vr = (vn_reference_t)vr_;
   vn_reference_s **slot;
   hashval_t hash;
 
-  /* This bounds the stmt walks we perform on reference lookups
-     to O(1) instead of O(N) where N is the number of dominating
-     stores.  */
-  if (cnt > (unsigned) PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS))
-    return (void *)-1;
-
   if (last_vuse_ptr)
     *last_vuse_ptr = vuse;
 
@@ -2023,8 +2016,7 @@ vn_reference_lookup_3 (ao_ref *ref, tree vuse, void *vr_,
 	  last_vuse_ptr = NULL;
 	  tree saved_vuse = vr->vuse;
 	  hashval_t saved_hashcode = vr->hashcode;
-	  void *res = vn_reference_lookup_2 (ref,
-					     gimple_vuse (def_stmt), 0, vr);
+	  void *res = vn_reference_lookup_2 (ref, gimple_vuse (def_stmt), vr);
 	  /* Need to restore vr->vuse and vr->hashcode.  */
 	  vr->vuse = saved_vuse;
 	  vr->hashcode = saved_hashcode;
@@ -2671,13 +2663,14 @@ vn_reference_lookup_pieces (tree vuse, alias_set_type set, tree type,
       && vr1.vuse)
     {
       ao_ref r;
+      unsigned limit = PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS);
       vn_walk_kind = kind;
       if (ao_ref_init_from_vn_reference (&r, set, type, vr1.operands))
 	*vnresult =
 	  (vn_reference_t)walk_non_aliased_vuses (&r, vr1.vuse,
 						  vn_reference_lookup_2,
 						  vn_reference_lookup_3,
-						  vuse_valueize, &vr1);
+						  vuse_valueize, limit, &vr1);
       gcc_checking_assert (vr1.operands == shared_lookup_references);
     }
 
@@ -2720,6 +2713,7 @@ vn_reference_lookup (tree op, tree vuse, vn_lookup_kind kind,
     {
       vn_reference_t wvnresult;
       ao_ref r;
+      unsigned limit = PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS);
       /* Make sure to use a valueized reference if we valueized anything.
          Otherwise preserve the full reference for advanced TBAA.  */
       if (!valuezied_anything
@@ -2733,7 +2727,7 @@ vn_reference_lookup (tree op, tree vuse, vn_lookup_kind kind,
 	(vn_reference_t)walk_non_aliased_vuses (&r, vr1.vuse,
 						vn_reference_lookup_2,
 						vn_reference_lookup_3,
-						vuse_valueize, &vr1);
+						vuse_valueize, limit, &vr1);
       gcc_checking_assert (vr1.operands == shared_lookup_references);
       if (wvnresult)
 	{
diff --git a/gcc/tree-ssa-scopedtables.c b/gcc/tree-ssa-scopedtables.c
index 2f3ba18..0614afc 100644
--- a/gcc/tree-ssa-scopedtables.c
+++ b/gcc/tree-ssa-scopedtables.c
@@ -100,19 +100,12 @@ avail_exprs_stack::record_expr (class expr_hash_elt *elt1,
    the desired memory state.  */
 
 static void *
-vuse_eq (ao_ref *, tree vuse1, unsigned int cnt, void *data)
+vuse_eq (ao_ref *, tree vuse1, void *data)
 {
   tree vuse2 = (tree) data;
   if (vuse1 == vuse2)
     return data;
 
-  /* This bounds the stmt walks we perform on reference lookups
-     to O(1) instead of O(N) where N is the number of dominating
-     stores leading to a candidate.  We re-use the SCCVN param
-     for this as it is basically the same complexity.  */
-  if (cnt > (unsigned) PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS))
-    return (void *)-1;
-
   return NULL;
 }
 
@@ -299,13 +292,14 @@ avail_exprs_stack::lookup_avail_expr (gimple *stmt, bool insert, bool tbaa_p)
 	 up the virtual use-def chain using walk_non_aliased_vuses.
 	 But don't do this when removing expressions from the hash.  */
       ao_ref ref;
+      unsigned limit = PARAM_VALUE (PARAM_SCCVN_MAX_ALIAS_QUERIES_PER_ACCESS);
       if (!(vuse1 && vuse2
 	    && gimple_assign_single_p (stmt)
 	    && TREE_CODE (gimple_assign_lhs (stmt)) == SSA_NAME
 	    && (ao_ref_init (&ref, gimple_assign_rhs1 (stmt)),
 		ref.base_alias_set = ref.ref_alias_set = tbaa_p ? -1 : 0, true)
-	    && walk_non_aliased_vuses (&ref, vuse2,
-				       vuse_eq, NULL, NULL, vuse1) != NULL))
+	    && walk_non_aliased_vuses (&ref, vuse2, vuse_eq, NULL, NULL,
+				       limit, vuse1) != NULL))
 	{
 	  if (insert)
 	    {