2012-08-22 Richard Guenther <rguenther@suse.de>

	PR tree-optimization/46590
	* tree-ssa-alias.h (get_continuation_for_phi): Add alias query
	counter output argument.
	(walk_non_aliased_vuses): Add alias query counter argument
	to the walker callback.
	* tree-ssa-alias.c (maybe_skip_until): Add alias query counter
	output argument and count alias queries.
	(get_continuation_for_phi_1): Likewise.
	(get_continuation_for_phi): Likewise.
	(walk_non_aliased_vuses): Add alias query counter argument
	to the walker callback and allow it to abort the walk by
	returning -1.
	* tree-ssa-pre.c (translate_vuse_through_block): Adjust.
	* tree-ssa-sccvn.c (vn_reference_lookup_2): Add alias query
	counter parmeter, abort walk if that is bigger than
	--param sccvn-max-alias-queries-per-access.
	* params.def (sccvn-max-alias-queries-per-access): New param.
	* doc/invoke.texi (sccvn-max-alias-queries-per-access): Document.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@190594 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 8 insertions, 1 deletions

diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index 216d3f647e9..5d5a91cef7c 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -1330,12 +1330,19 @@ static vn_lookup_kind default_vn_walk_kind;
    with the current VUSE and performs the expression lookup.  */
 
 static void *
-vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse, void *vr_)
+vn_reference_lookup_2 (ao_ref *op ATTRIBUTE_UNUSED, tree vuse,
+		       unsigned int cnt, void *vr_)
 {
   vn_reference_t vr = (vn_reference_t)vr_;
   void **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;