2018-03-19  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/84946
	* gimple-ssa-store-merging.c (mem_valid_for_store_merging): Compute
	bitsize + bitsize in poly_uint64 rather than poly_int64.

--- gcc/gimple-ssa-store-merging.c.jj	2018-02-22 09:28:07.000000000 +0100
+++ gcc/gimple-ssa-store-merging.c	2018-03-19 17:55:22.486472527 +0100
@@ -3948,7 +3948,8 @@ mem_valid_for_store_merging (tree mem, p
   if (known_eq (bitregion_end, 0U))
     {
       bitregion_start = round_down_to_byte_boundary (bitpos);
-      bitregion_end = round_up_to_byte_boundary (bitpos + bitsize);
+      bitregion_end = bitpos;
+      bitregion_end = round_up_to_byte_boundary (bitregion_end + bitsize);
     }
 
   if (offset != NULL_TREE)