tree-vect-loop-manip.c assumes there is an alias if: ((store_ptr_0 + store_segment_length_0) < load_ptr_0) || (load_ptr_0 + load_segment_length_0) < store_ptr_0))
which means that contiguous arrays are unnecessarily considered to alias. This patch changes the "<" to "<=". Tested on x86_64-linux-gnu (all languages). OK to install? Richard gcc/ * tree-vect-loop-manip.c (vect_create_cond_for_alias_checks): Tighten overlap check. Index: gcc/tree-vect-loop-manip.c =================================================================== --- gcc/tree-vect-loop-manip.c 2011-06-22 16:46:34.000000000 +0100 +++ gcc/tree-vect-loop-manip.c 2011-07-13 11:12:06.000000000 +0100 @@ -2409,13 +2409,13 @@ vect_create_cond_for_alias_checks (loop_ tree part_cond_expr, length_factor; /* Create expression - ((store_ptr_0 + store_segment_length_0) < load_ptr_0) - || (load_ptr_0 + load_segment_length_0) < store_ptr_0)) + ((store_ptr_0 + store_segment_length_0) <= load_ptr_0) + || (load_ptr_0 + load_segment_length_0) <= store_ptr_0)) && ... && - ((store_ptr_n + store_segment_length_n) < load_ptr_n) - || (load_ptr_n + load_segment_length_n) < store_ptr_n)) */ + ((store_ptr_n + store_segment_length_n) <= load_ptr_n) + || (load_ptr_n + load_segment_length_n) <= store_ptr_n)) */ if (VEC_empty (ddr_p, may_alias_ddrs)) return; @@ -2484,8 +2484,8 @@ vect_create_cond_for_alias_checks (loop_ part_cond_expr = fold_build2 (TRUTH_OR_EXPR, boolean_type_node, - fold_build2 (LT_EXPR, boolean_type_node, seg_a_max, seg_b_min), - fold_build2 (LT_EXPR, boolean_type_node, seg_b_max, seg_a_min)); + fold_build2 (LE_EXPR, boolean_type_node, seg_a_max, seg_b_min), + fold_build2 (LE_EXPR, boolean_type_node, seg_b_max, seg_a_min)); if (*cond_expr) *cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,