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[pf3gnuchains/gcc-fork.git] / gcc / tree-vect-loop-manip.c
index 72b9056..70c4f89 100644 (file)
@@ -1,6 +1,6 @@
 /* Vectorizer Specific Loop Manipulations
-   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Free Software
-   Foundation, Inc.
+   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012
+   Free Software Foundation, Inc.
    Contributed by Dorit Naishlos <dorit@il.ibm.com>
    and Ira Rosen <irar@il.ibm.com>
 
@@ -27,13 +27,13 @@ along with GCC; see the file COPYING3.  If not see
 #include "ggc.h"
 #include "tree.h"
 #include "basic-block.h"
-#include "diagnostic.h"
+#include "tree-pretty-print.h"
+#include "gimple-pretty-print.h"
 #include "tree-flow.h"
 #include "tree-dump.h"
 #include "cfgloop.h"
 #include "cfglayout.h"
-#include "expr.h"
-#include "toplev.h"
+#include "diagnostic-core.h"
 #include "tree-scalar-evolution.h"
 #include "tree-vectorizer.h"
 #include "langhooks.h"
@@ -513,7 +513,7 @@ slpeel_update_phi_nodes_for_guard1 (edge guard_edge, struct loop *loop,
        !gsi_end_p (gsi_orig) && !gsi_end_p (gsi_update);
        gsi_next (&gsi_orig), gsi_next (&gsi_update))
     {
-      source_location loop_locus, guard_locus;;
+      source_location loop_locus, guard_locus;
       orig_phi = gsi_stmt (gsi_orig);
       update_phi = gsi_stmt (gsi_update);
 
@@ -1037,7 +1037,7 @@ slpeel_verify_cfg_after_peeling (struct loop *first_loop,
 
 static void
 set_prologue_iterations (basic_block bb_before_first_loop,
-                        tree first_niters,
+                        tree *first_niters,
                         struct loop *loop,
                         unsigned int th)
 {
@@ -1100,12 +1100,11 @@ set_prologue_iterations (basic_block bb_before_first_loop,
   newphi = create_phi_node (var, bb_before_first_loop);
   add_phi_arg (newphi, prologue_after_cost_adjust_name, e_fallthru,
               UNKNOWN_LOCATION);
-  add_phi_arg (newphi, first_niters, e_false, UNKNOWN_LOCATION);
+  add_phi_arg (newphi, *first_niters, e_false, UNKNOWN_LOCATION);
 
-  first_niters = PHI_RESULT (newphi);
+  *first_niters = PHI_RESULT (newphi);
 }
 
-
 /* Function slpeel_tree_peel_loop_to_edge.
 
    Peel the first (last) iterations of LOOP into a new prolog (epilog) loop
@@ -1159,7 +1158,7 @@ set_prologue_iterations (basic_block bb_before_first_loop,
 
 static struct loop*
 slpeel_tree_peel_loop_to_edge (struct loop *loop,
-                              edge e, tree first_niters,
+                              edge e, tree *first_niters,
                               tree niters, bool update_first_loop_count,
                               unsigned int th, bool check_profitability,
                               tree cond_expr, gimple_seq cond_expr_stmt_list)
@@ -1172,6 +1171,7 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
   basic_block bb_before_first_loop;
   basic_block bb_between_loops;
   basic_block new_exit_bb;
+  gimple_stmt_iterator gsi;
   edge exit_e = single_exit (loop);
   LOC loop_loc;
   tree cost_pre_condition = NULL_TREE;
@@ -1185,6 +1185,40 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
    the function tree_duplicate_bb is called.  */
   gimple_register_cfg_hooks ();
 
+  /* If the loop has a virtual PHI, but exit bb doesn't, create a virtual PHI
+     in the exit bb and rename all the uses after the loop.  This simplifies
+     the *guard[12] routines, which assume loop closed SSA form for all PHIs
+     (but normally loop closed SSA form doesn't require virtual PHIs to be
+     in the same form).  Doing this early simplifies the checking what
+     uses should be renamed.  */
+  for (gsi = gsi_start_phis (loop->header); !gsi_end_p (gsi); gsi_next (&gsi))
+    if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
+      {
+       gimple phi = gsi_stmt (gsi);
+       for (gsi = gsi_start_phis (exit_e->dest);
+            !gsi_end_p (gsi); gsi_next (&gsi))
+         if (!is_gimple_reg (gimple_phi_result (gsi_stmt (gsi))))
+           break;
+       if (gsi_end_p (gsi))
+         {
+           gimple new_phi = create_phi_node (SSA_NAME_VAR (PHI_RESULT (phi)),
+                                             exit_e->dest);
+           tree vop = PHI_ARG_DEF_FROM_EDGE (phi, EDGE_SUCC (loop->latch, 0));
+           imm_use_iterator imm_iter;
+           gimple stmt;
+           tree new_vop = make_ssa_name (SSA_NAME_VAR (PHI_RESULT (phi)),
+                                         new_phi);
+           use_operand_p use_p;
+
+           add_phi_arg (new_phi, vop, exit_e, UNKNOWN_LOCATION);
+           gimple_phi_set_result (new_phi, new_vop);
+           FOR_EACH_IMM_USE_STMT (stmt, imm_iter, vop)
+             if (stmt != new_phi && gimple_bb (stmt) != loop->header)
+               FOR_EACH_IMM_USE_ON_STMT (use_p, imm_iter)
+                 SET_USE (use_p, new_vop);
+         }
+       break;
+      }
 
   /* 1. Generate a copy of LOOP and put it on E (E is the entry/exit of LOOP).
         Resulting CFG would be:
@@ -1329,8 +1363,8 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
   if (!update_first_loop_count)
     {
       pre_condition =
-       fold_build2 (LE_EXPR, boolean_type_node, first_niters,
-                    build_int_cst (TREE_TYPE (first_niters), 0));
+       fold_build2 (LE_EXPR, boolean_type_node, *first_niters,
+                    build_int_cst (TREE_TYPE (*first_niters), 0));
       if (check_profitability)
        {
          tree scalar_loop_iters
@@ -1361,8 +1395,8 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
                                 loop, th);
 
       pre_condition =
-       fold_build2 (LE_EXPR, boolean_type_node, first_niters,
-                    build_int_cst (TREE_TYPE (first_niters), 0));
+       fold_build2 (LE_EXPR, boolean_type_node, *first_niters,
+                    build_int_cst (TREE_TYPE (*first_niters), 0));
     }
 
   skip_e = slpeel_add_loop_guard (bb_before_first_loop, pre_condition,
@@ -1403,7 +1437,7 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
   bb_after_second_loop = split_edge (single_exit (second_loop));
 
   pre_condition =
-       fold_build2 (EQ_EXPR, boolean_type_node, first_niters, niters);
+       fold_build2 (EQ_EXPR, boolean_type_node, *first_niters, niters);
   skip_e = slpeel_add_loop_guard (bb_between_loops, pre_condition, NULL,
                                   bb_after_second_loop, bb_before_first_loop);
   slpeel_update_phi_nodes_for_guard2 (skip_e, second_loop,
@@ -1412,13 +1446,13 @@ slpeel_tree_peel_loop_to_edge (struct loop *loop,
   /* 4. Make first-loop iterate FIRST_NITERS times, if requested.
    */
   if (update_first_loop_count)
-    slpeel_make_loop_iterate_ntimes (first_loop, first_niters);
-
-  adjust_vec_debug_stmts ();
+    slpeel_make_loop_iterate_ntimes (first_loop, *first_niters);
 
   BITMAP_FREE (definitions);
   delete_update_ssa ();
 
+  adjust_vec_debug_stmts ();
+
   return new_loop;
 }
 
@@ -1516,7 +1550,7 @@ vect_generate_tmps_on_preheader (loop_vec_info loop_vinfo,
   edge pe;
   basic_block new_bb;
   gimple_seq stmts;
-  tree ni_name;
+  tree ni_name, ni_minus_gap_name;
   tree var;
   tree ratio_name;
   tree ratio_mult_vf_name;
@@ -1533,9 +1567,39 @@ vect_generate_tmps_on_preheader (loop_vec_info loop_vinfo,
   ni_name = vect_build_loop_niters (loop_vinfo, cond_expr_stmt_list);
   log_vf = build_int_cst (TREE_TYPE (ni), exact_log2 (vf));
 
+  /* If epilogue loop is required because of data accesses with gaps, we
+     subtract one iteration from the total number of iterations here for
+     correct calculation of RATIO.  */
+  if (LOOP_VINFO_PEELING_FOR_GAPS (loop_vinfo))
+    {
+      ni_minus_gap_name = fold_build2 (MINUS_EXPR, TREE_TYPE (ni_name),
+                                      ni_name,
+                                      build_one_cst (TREE_TYPE (ni_name)));
+      if (!is_gimple_val (ni_minus_gap_name))
+       {
+         var = create_tmp_var (TREE_TYPE (ni), "ni_gap");
+          add_referenced_var (var);
+
+          stmts = NULL;
+          ni_minus_gap_name = force_gimple_operand (ni_minus_gap_name, &stmts,
+                                                   true, var);
+          if (cond_expr_stmt_list)
+            gimple_seq_add_seq (&cond_expr_stmt_list, stmts);
+          else
+            {
+              pe = loop_preheader_edge (loop);
+              new_bb = gsi_insert_seq_on_edge_immediate (pe, stmts);
+              gcc_assert (!new_bb);
+            }
+        }
+    }
+  else
+    ni_minus_gap_name = ni_name;
+
   /* Create: ratio = ni >> log2(vf) */
 
-  ratio_name = fold_build2 (RSHIFT_EXPR, TREE_TYPE (ni_name), ni_name, log_vf);
+  ratio_name = fold_build2 (RSHIFT_EXPR, TREE_TYPE (ni_minus_gap_name),
+                           ni_minus_gap_name, log_vf);
   if (!is_gimple_val (ratio_name))
     {
       var = create_tmp_var (TREE_TYPE (ni), "bnd");
@@ -1790,9 +1854,7 @@ vect_update_ivs_after_vectorizer (loop_vec_info loop_vinfo, tree niters,
                         fold_convert (TREE_TYPE (step_expr), niters),
                         step_expr);
       if (POINTER_TYPE_P (TREE_TYPE (init_expr)))
-       ni = fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (init_expr),
-                         init_expr,
-                         fold_convert (sizetype, off));
+       ni = fold_build_pointer_plus (init_expr, off);
       else
        ni = fold_build2 (PLUS_EXPR, TREE_TYPE (init_expr),
                          init_expr,
@@ -1898,7 +1960,7 @@ vect_do_peeling_for_loop_bound (loop_vec_info loop_vinfo, tree *ratio,
     }
 
   new_loop = slpeel_tree_peel_loop_to_edge (loop, single_exit (loop),
-                                            ratio_mult_vf_name, ni_name, false,
+                                            &ratio_mult_vf_name, ni_name, false,
                                             th, check_profitability,
                                            cond_expr, cond_expr_stmt_list);
   gcc_assert (new_loop);
@@ -1975,31 +2037,27 @@ vect_gen_niters_for_prolog_loop (loop_vec_info loop_vinfo, tree loop_niters)
   tree vectype = STMT_VINFO_VECTYPE (stmt_info);
   int vectype_align = TYPE_ALIGN (vectype) / BITS_PER_UNIT;
   tree niters_type = TREE_TYPE (loop_niters);
-  int step = 1;
-  int element_size = GET_MODE_SIZE (TYPE_MODE (TREE_TYPE (DR_REF (dr))));
   int nelements = TYPE_VECTOR_SUBPARTS (vectype);
 
-  if (STMT_VINFO_STRIDED_ACCESS (stmt_info))
-    step = DR_GROUP_SIZE (vinfo_for_stmt (DR_GROUP_FIRST_DR (stmt_info)));
-
   pe = loop_preheader_edge (loop);
 
   if (LOOP_PEELING_FOR_ALIGNMENT (loop_vinfo) > 0)
     {
-      int byte_misalign = LOOP_PEELING_FOR_ALIGNMENT (loop_vinfo);
-      int elem_misalign = byte_misalign / element_size;
+      int npeel = LOOP_PEELING_FOR_ALIGNMENT (loop_vinfo);
 
       if (vect_print_dump_info (REPORT_DETAILS))
-        fprintf (vect_dump, "known alignment = %d.", byte_misalign);
+        fprintf (vect_dump, "known peeling = %d.", npeel);
 
-      iters = build_int_cst (niters_type,
-                     (((nelements - elem_misalign) & (nelements - 1)) / step));
+      iters = build_int_cst (niters_type, npeel);
     }
   else
     {
       gimple_seq new_stmts = NULL;
+      bool negative = tree_int_cst_compare (DR_STEP (dr), size_zero_node) < 0;
+      tree offset = negative
+         ? size_int (-TYPE_VECTOR_SUBPARTS (vectype) + 1) : NULL_TREE;
       tree start_addr = vect_create_addr_base_for_vector_ref (dr_stmt,
-                                               &new_stmts, NULL_TREE, loop);
+                                               &new_stmts, offset, loop);
       tree ptr_type = TREE_TYPE (start_addr);
       tree size = TYPE_SIZE (ptr_type);
       tree type = lang_hooks.types.type_for_size (tree_low_cst (size, 1), 1);
@@ -2016,14 +2074,18 @@ vect_gen_niters_for_prolog_loop (loop_vec_info loop_vinfo, tree loop_niters)
 
       /* Create:  byte_misalign = addr & (vectype_size - 1)  */
       byte_misalign =
-        fold_build2 (BIT_AND_EXPR, type, fold_convert (type, start_addr), vectype_size_minus_1);
+        fold_build2 (BIT_AND_EXPR, type, fold_convert (type, start_addr), 
+                     vectype_size_minus_1);
 
       /* Create:  elem_misalign = byte_misalign / element_size  */
       elem_misalign =
         fold_build2 (RSHIFT_EXPR, type, byte_misalign, elem_size_log);
 
       /* Create:  (niters_type) (nelements - elem_misalign)&(nelements - 1)  */
-      iters = fold_build2 (MINUS_EXPR, type, nelements_tree, elem_misalign);
+      if (negative)
+       iters = fold_build2 (MINUS_EXPR, type, elem_misalign, nelements_tree);
+      else
+       iters = fold_build2 (MINUS_EXPR, type, nelements_tree, elem_misalign);
       iters = fold_build2 (BIT_AND_EXPR, type, iters, nelements_minus_1);
       iters = fold_convert (niters_type, iters);
     }
@@ -2096,7 +2158,7 @@ vect_update_inits_of_drs (loop_vec_info loop_vinfo, tree niters)
   if (vect_print_dump_info (REPORT_DETAILS))
     fprintf (vect_dump, "=== vect_update_inits_of_dr ===");
 
-  for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
+  FOR_EACH_VEC_ELT (data_reference_p, datarefs, i, dr)
     vect_update_init_of_dr (dr, niters);
 }
 
@@ -2115,6 +2177,7 @@ vect_do_peeling_for_alignment (loop_vec_info loop_vinfo)
   struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
   tree niters_of_prolog_loop, ni_name;
   tree n_iters;
+  tree wide_prolog_niters;
   struct loop *new_loop;
   unsigned int th = 0;
   int min_profitable_iters;
@@ -2125,8 +2188,8 @@ vect_do_peeling_for_alignment (loop_vec_info loop_vinfo)
   initialize_original_copy_tables ();
 
   ni_name = vect_build_loop_niters (loop_vinfo, NULL);
-  niters_of_prolog_loop = vect_gen_niters_for_prolog_loop (loop_vinfo, ni_name);
-
+  niters_of_prolog_loop = vect_gen_niters_for_prolog_loop (loop_vinfo,
+                                                          ni_name);
 
   /* Get profitability threshold for vectorized loop.  */
   min_profitable_iters = LOOP_VINFO_COST_MODEL_MIN_ITERS (loop_vinfo);
@@ -2136,7 +2199,7 @@ vect_do_peeling_for_alignment (loop_vec_info loop_vinfo)
   /* Peel the prolog loop and iterate it niters_of_prolog_loop.  */
   new_loop =
     slpeel_tree_peel_loop_to_edge (loop, loop_preheader_edge (loop),
-                                  niters_of_prolog_loop, ni_name, true,
+                                  &niters_of_prolog_loop, ni_name, true,
                                   th, true, NULL_TREE, NULL);
 
   gcc_assert (new_loop);
@@ -2149,8 +2212,27 @@ vect_do_peeling_for_alignment (loop_vec_info loop_vinfo)
   LOOP_VINFO_NITERS (loop_vinfo) = fold_build2 (MINUS_EXPR,
                TREE_TYPE (n_iters), n_iters, niters_of_prolog_loop);
 
+  if (types_compatible_p (sizetype, TREE_TYPE (niters_of_prolog_loop)))
+    wide_prolog_niters = niters_of_prolog_loop;
+  else
+    {
+      gimple_seq seq = NULL;
+      edge pe = loop_preheader_edge (loop);
+      tree wide_iters = fold_convert (sizetype, niters_of_prolog_loop);
+      tree var = create_tmp_var (sizetype, "prolog_loop_adjusted_niters");
+      add_referenced_var (var);
+      wide_prolog_niters = force_gimple_operand (wide_iters, &seq, false,
+                                                 var);
+      if (seq)
+       {
+         /* Insert stmt on loop preheader edge.  */
+          basic_block new_bb = gsi_insert_seq_on_edge_immediate (pe, seq);
+          gcc_assert (!new_bb);
+        }
+    }
+
   /* Update the init conditions of the access functions of all data refs.  */
-  vect_update_inits_of_drs (loop_vinfo, niters_of_prolog_loop);
+  vect_update_inits_of_drs (loop_vinfo, wide_prolog_niters);
 
   /* After peeling we have to reset scalar evolution analyzer.  */
   scev_reset ();
@@ -2218,18 +2300,24 @@ vect_create_cond_for_align_checks (loop_vec_info loop_vinfo,
   /* Create expression (mask & (dr_1 || ... || dr_n)) where dr_i is the address
      of the first vector of the i'th data reference. */
 
-  for (i = 0; VEC_iterate (gimple, may_misalign_stmts, i, ref_stmt); i++)
+  FOR_EACH_VEC_ELT (gimple, may_misalign_stmts, i, ref_stmt)
     {
       gimple_seq new_stmt_list = NULL;
       tree addr_base;
       tree addr_tmp, addr_tmp_name;
       tree or_tmp, new_or_tmp_name;
       gimple addr_stmt, or_stmt;
+      stmt_vec_info stmt_vinfo = vinfo_for_stmt (ref_stmt);
+      tree vectype = STMT_VINFO_VECTYPE (stmt_vinfo);
+      bool negative = tree_int_cst_compare
+       (DR_STEP (STMT_VINFO_DATA_REF (stmt_vinfo)), size_zero_node) < 0;
+      tree offset = negative
+       ? size_int (-TYPE_VECTOR_SUBPARTS (vectype) + 1) : NULL_TREE;
 
       /* create: addr_tmp = (int)(address_of_first_vector) */
       addr_base =
        vect_create_addr_base_for_vector_ref (ref_stmt, &new_stmt_list,
-                                             NULL_TREE, loop);
+                                             offset, loop);
       if (new_stmt_list != NULL)
        gimple_seq_add_seq (cond_expr_stmt_list, new_stmt_list);
 
@@ -2296,26 +2384,32 @@ vect_create_cond_for_align_checks (loop_vec_info loop_vinfo,
 
    Input:
      DR: The data reference.
-     VECT_FACTOR: vectorization factor.
+     LENGTH_FACTOR: segment length to consider.
 
    Return an expression whose value is the size of segment which will be
    accessed by DR.  */
 
 static tree
-vect_vfa_segment_size (struct data_reference *dr, tree vect_factor)
+vect_vfa_segment_size (struct data_reference *dr, tree length_factor)
 {
-  tree segment_length = fold_build2 (MULT_EXPR, integer_type_node,
-                                    DR_STEP (dr), vect_factor);
+  tree segment_length;
+
+  if (!compare_tree_int (DR_STEP (dr), 0))
+    segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr)));
+  else
+    segment_length = size_binop (MULT_EXPR,
+                                 fold_convert (sizetype, DR_STEP (dr)),
+                                 fold_convert (sizetype, length_factor));
 
-  if (vect_supportable_dr_alignment (dr) == dr_explicit_realign_optimized)
+  if (vect_supportable_dr_alignment (dr, false)
+        == dr_explicit_realign_optimized)
     {
       tree vector_size = TYPE_SIZE_UNIT
                          (STMT_VINFO_VECTYPE (vinfo_for_stmt (DR_STMT (dr))));
 
-      segment_length = fold_build2 (PLUS_EXPR, integer_type_node,
-                                   segment_length, vector_size);
+      segment_length = size_binop (PLUS_EXPR, segment_length, vector_size);
     }
-  return fold_convert (sizetype, segment_length);
+  return segment_length;
 }
 
 
@@ -2349,36 +2443,37 @@ vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo,
   struct loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
   VEC (ddr_p, heap) * may_alias_ddrs =
     LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
-  tree vect_factor =
-    build_int_cst (integer_type_node, LOOP_VINFO_VECT_FACTOR (loop_vinfo));
+  int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
+  tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
 
   ddr_p ddr;
   unsigned int i;
-  tree part_cond_expr;
+  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;
 
-  for (i = 0; VEC_iterate (ddr_p, may_alias_ddrs, i, ddr); i++)
+  FOR_EACH_VEC_ELT (ddr_p, may_alias_ddrs, i, ddr)
     {
       struct data_reference *dr_a, *dr_b;
       gimple dr_group_first_a, dr_group_first_b;
       tree addr_base_a, addr_base_b;
       tree segment_length_a, segment_length_b;
       gimple stmt_a, stmt_b;
+      tree seg_a_min, seg_a_max, seg_b_min, seg_b_max;
 
       dr_a = DDR_A (ddr);
       stmt_a = DR_STMT (DDR_A (ddr));
-      dr_group_first_a = DR_GROUP_FIRST_DR (vinfo_for_stmt (stmt_a));
+      dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
       if (dr_group_first_a)
         {
          stmt_a = dr_group_first_a;
@@ -2387,7 +2482,7 @@ vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo,
 
       dr_b = DDR_B (ddr);
       stmt_b = DR_STMT (DDR_B (ddr));
-      dr_group_first_b = DR_GROUP_FIRST_DR (vinfo_for_stmt (stmt_b));
+      dr_group_first_b = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_b));
       if (dr_group_first_b)
         {
          stmt_b = dr_group_first_b;
@@ -2401,8 +2496,12 @@ vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo,
         vect_create_addr_base_for_vector_ref (stmt_b, cond_expr_stmt_list,
                                              NULL_TREE, loop);
 
-      segment_length_a = vect_vfa_segment_size (dr_a, vect_factor);
-      segment_length_b = vect_vfa_segment_size (dr_b, vect_factor);
+      if (!operand_equal_p (DR_STEP (dr_a), DR_STEP (dr_b), 0))
+       length_factor = scalar_loop_iters;
+      else
+       length_factor = size_int (vect_factor);
+      segment_length_a = vect_vfa_segment_size (dr_a, length_factor);
+      segment_length_b = vect_vfa_segment_size (dr_b, length_factor);
 
       if (vect_print_dump_info (REPORT_DR_DETAILS))
        {
@@ -2413,19 +2512,20 @@ vect_create_cond_for_alias_checks (loop_vec_info loop_vinfo,
          print_generic_expr (vect_dump, DR_REF (dr_b), TDF_SLIM);
        }
 
+      seg_a_min = addr_base_a;
+      seg_a_max = fold_build_pointer_plus (addr_base_a, segment_length_a);
+      if (tree_int_cst_compare (DR_STEP (dr_a), size_zero_node) < 0)
+       seg_a_min = seg_a_max, seg_a_max = addr_base_a;
+
+      seg_b_min = addr_base_b;
+      seg_b_max = fold_build_pointer_plus (addr_base_b, segment_length_b);
+      if (tree_int_cst_compare (DR_STEP (dr_b), size_zero_node) < 0)
+       seg_b_min = seg_b_max, seg_b_max = addr_base_b;
 
       part_cond_expr =
        fold_build2 (TRUTH_OR_EXPR, boolean_type_node,
-         fold_build2 (LT_EXPR, boolean_type_node,
-           fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (addr_base_a),
-             addr_base_a,
-             segment_length_a),
-           addr_base_b),
-         fold_build2 (LT_EXPR, boolean_type_node,
-           fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (addr_base_b),
-             addr_base_b,
-             segment_length_b),
-           addr_base_a));
+         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,