Use base inequality for some vector alias checks

[Richard Sandiford <richard.sandiford@linaro.org>]

This patch checks whether two data references x and y cannot
partially overlap and so are independent whenever &x != &y.
We can then use this in the vectoriser to optimise alias checks.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

Thanks,
Richard


gcc/
2016-05-03  Richard Sandiford  <richard.sandiford@linaro.org>

	* hash-traits.h (pair_hash): New struct.
	* tree-data-ref.h (data_dependence_relation): Add object_a and
	object_b fields.
	(DDR_OBJECT_A, DDR_OBJECT_B): New macros.
	* tree-data-ref.c (initialize_data_dependence_relation): Initialize
	DDR_OBJECT_A and DDR_OBJECT_B.
	* tree-vectorizer.h (vec_object_pair): New type.
	(_loop_vec_info): Add a check_unequal_addrs field.
	(LOOP_VINFO_CHECK_UNEQUAL_ADDRS): New macro.
	(LOOP_REQUIRES_VERSIONING_FOR_ALIAS): Return true if there is an
	entry in check_unequal_addrs.  Check comp_alias_ddrs instead of
	may_alias_ddrs.
	* tree-vect-loop.c (destroy_loop_vec_info): Release
	LOOP_VINFO_CHECK_UNEQUAL_ADDRS.
	(vect_analyze_loop_2): Likewise, when restarting.
	(vect_estimate_min_profitable_iters): Estimate the cost of
	LOOP_VINFO_CHECK_UNEQUAL_ADDRS.
	* tree-vect-data-refs.c: Include tree-hash-traits.h.
	(vect_prune_runtime_alias_test_list): Try to handle conflicts
	using LOOP_VINFO_CHECK_UNEQUAL_ADDRS, if the data dependence allows.
	Count such tests in the final summary.
	* tree-vect-loop-manip.c (chain_cond_expr): New function.
	(vect_create_cond_for_align_checks): Use it.
	(vect_create_cond_for_alias_checks): Likewise.
	(vect_create_cond_for_unequal_addrs): New function.
	(vect_loop_versioning): Call it.

gcc/testsuite/
	* gcc.dg/vect/vect-alias-check-6.c: New test.

Index: gcc/hash-traits.h
===================================================================
--- gcc/hash-traits.h	2017-02-23 19:54:15.000000000 +0000
+++ gcc/hash-traits.h	2017-05-03 08:48:53.312035228 +0100
@@ -301,6 +301,76 @@ struct ggc_cache_ptr_hash : pointer_hash
 
 struct nofree_string_hash : string_hash, typed_noop_remove <const char *> {};
 
+/* Traits for pairs of values, using the first to record empty and
+   deleted slots.  */
+
+template <typename T1, typename T2>
+struct pair_hash
+{
+  typedef std::pair <typename T1::value_type,
+		     typename T2::value_type> value_type;
+  typedef std::pair <typename T1::compare_type,
+		     typename T2::compare_type> compare_type;
+
+  static inline hashval_t hash (const value_type &);
+  static inline bool equal (const value_type &, const compare_type &);
+  static inline void remove (value_type &);
+  static inline void mark_deleted (value_type &);
+  static inline void mark_empty (value_type &);
+  static inline bool is_deleted (const value_type &);
+  static inline bool is_empty (const value_type &);
+};
+
+template <typename T1, typename T2>
+inline hashval_t
+pair_hash <T1, T2>::hash (const value_type &x)
+{
+  return iterative_hash_hashval_t (T1::hash (x.first), T2::hash (x.second));
+}
+
+template <typename T1, typename T2>
+inline bool
+pair_hash <T1, T2>::equal (const value_type &x, const compare_type &y)
+{
+  return T1::equal (x.first, y.first) && T2::equal (x.second, y.second);
+}
+
+template <typename T1, typename T2>
+inline void
+pair_hash <T1, T2>::remove (value_type &x)
+{
+  T1::remove (x.first);
+  T2::remove (x.second);
+}
+
+template <typename T1, typename T2>
+inline void
+pair_hash <T1, T2>::mark_deleted (value_type &x)
+{
+  T1::mark_deleted (x.first);
+}
+
+template <typename T1, typename T2>
+inline void
+pair_hash <T1, T2>::mark_empty (value_type &x)
+{
+  T1::mark_empty (x.first);
+}
+
+template <typename T1, typename T2>
+inline bool
+pair_hash <T1, T2>::is_deleted (const value_type &x)
+{
+  return T1::is_deleted (x.first);
+}
+
+template <typename T1, typename T2>
+inline bool
+pair_hash <T1, T2>::is_empty (const value_type &x)
+{
+  return T1::is_empty (x.first);
+}
+
 template <typename T> struct default_hash_traits : T {};
 
 template <typename T>
Index: gcc/tree-data-ref.h
===================================================================
--- gcc/tree-data-ref.h	2017-05-03 08:48:48.737038502 +0100
+++ gcc/tree-data-ref.h	2017-05-03 08:48:53.313041828 +0100
@@ -240,6 +240,13 @@ struct data_dependence_relation
        but the analyzer cannot be more specific.  */
   tree are_dependent;
 
+  /* If nonnull, COULD_BE_INDEPENDENT_P is true and the accesses are
+     independent when the runtime addresses of OBJECT_A and OBJECT_B
+     are different.  The addresses of both objects are invariant in the
+     loop nest.  */
+  tree object_a;
+  tree object_b;
+
   /* For each subscript in the dependence test, there is an element in
      this array.  This is the attribute that labels the edge A->B of
      the data_dependence_relation.  */
@@ -303,6 +310,8 @@ #define DDR_A(DDR) (DDR)->a
 #define DDR_B(DDR) (DDR)->b
 #define DDR_AFFINE_P(DDR) (DDR)->affine_p
 #define DDR_ARE_DEPENDENT(DDR) (DDR)->are_dependent
+#define DDR_OBJECT_A(DDR) (DDR)->object_a
+#define DDR_OBJECT_B(DDR) (DDR)->object_b
 #define DDR_SUBSCRIPTS(DDR) (DDR)->subscripts
 #define DDR_SUBSCRIPT(DDR, I) DDR_SUBSCRIPTS (DDR)[I]
 #define DDR_NUM_SUBSCRIPTS(DDR) DDR_SUBSCRIPTS (DDR).length ()
Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c	2017-05-03 08:48:48.737038502 +0100
+++ gcc/tree-data-ref.c	2017-05-03 08:48:53.313041828 +0100
@@ -1715,6 +1715,15 @@ initialize_data_dependence_relation (str
 	}
 
       DDR_COULD_BE_INDEPENDENT_P (res) = true;
+      if (!loop_nest.exists ()
+	  || (object_address_invariant_in_loop_p (loop_nest[0],
+						  struct_ref_a)
+	      && object_address_invariant_in_loop_p (loop_nest[0],
+						     struct_ref_b)))
+	{
+	  DDR_OBJECT_A (res) = struct_ref_a;
+	  DDR_OBJECT_B (res) = struct_ref_b;
+	}
     }
 
   DDR_AFFINE_P (res) = true;
Index: gcc/tree-vectorizer.h
===================================================================
--- gcc/tree-vectorizer.h	2017-05-03 08:48:48.738045102 +0100
+++ gcc/tree-vectorizer.h	2017-05-03 08:48:53.315055028 +0100
@@ -174,6 +174,10 @@ struct dr_with_seg_len_pair_t
 
 
 
+/* Describes two objects whose addresses must be unequal for the vectorized
+   loop to be valid.  */
+typedef std::pair<tree, tree> vec_object_pair;
+
 /* Vectorizer state common between loop and basic-block vectorization.  */
 struct vec_info {
   enum { bb, loop } kind;
@@ -270,6 +274,9 @@ typedef struct _loop_vec_info : public v
      lengths from which the run-time aliasing check is built.  */
   vec<dr_with_seg_len_pair_t> comp_alias_ddrs;
 
+  /* Check that the addresses of each pair of objects is unequal.  */
+  vec<vec_object_pair> check_unequal_addrs;
+
   /* Statements in the loop that have data references that are candidates for a
      runtime (loop versioning) misalignment check.  */
   vec<gimple *> may_misalign_stmts;
@@ -364,6 +371,7 @@ #define LOOP_VINFO_UNALIGNED_DR(L)
 #define LOOP_VINFO_MAY_MISALIGN_STMTS(L)   (L)->may_misalign_stmts
 #define LOOP_VINFO_MAY_ALIAS_DDRS(L)       (L)->may_alias_ddrs
 #define LOOP_VINFO_COMP_ALIAS_DDRS(L)      (L)->comp_alias_ddrs
+#define LOOP_VINFO_CHECK_UNEQUAL_ADDRS(L)  (L)->check_unequal_addrs
 #define LOOP_VINFO_GROUPED_STORES(L)       (L)->grouped_stores
 #define LOOP_VINFO_SLP_INSTANCES(L)        (L)->slp_instances
 #define LOOP_VINFO_SLP_UNROLLING_FACTOR(L) (L)->slp_unrolling_factor
@@ -383,7 +391,8 @@ #define LOOP_VINFO_ORIG_LOOP_INFO(L)
 #define LOOP_REQUIRES_VERSIONING_FOR_ALIGNMENT(L)	\
   ((L)->may_misalign_stmts.length () > 0)
 #define LOOP_REQUIRES_VERSIONING_FOR_ALIAS(L)		\
-  ((L)->comp_alias_ddrs.length () > 0)
+  ((L)->comp_alias_ddrs.length () > 0 \
+   || (L)->check_unequal_addrs.length () > 0)
 #define LOOP_REQUIRES_VERSIONING_FOR_NITERS(L)		\
   (LOOP_VINFO_NITERS_ASSUMPTIONS (L))
 #define LOOP_REQUIRES_VERSIONING(L)			\
Index: gcc/tree-vect-loop.c
===================================================================
--- gcc/tree-vect-loop.c	2017-04-18 19:52:35.059158859 +0100
+++ gcc/tree-vect-loop.c	2017-05-03 08:48:53.315055028 +0100
@@ -1275,6 +1275,8 @@ destroy_loop_vec_info (loop_vec_info loo
   destroy_cost_data (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo));
   loop_vinfo->scalar_cost_vec.release ();
 
+  LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).release ();
+
   free (loop_vinfo);
   loop->aux = NULL;
 }
@@ -2299,6 +2301,7 @@ vect_analyze_loop_2 (loop_vec_info loop_
     }
   /* Free optimized alias test DDRS.  */
   LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo).release ();
+  LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).release ();
   /* Reset target cost data.  */
   destroy_cost_data (LOOP_VINFO_TARGET_COST_DATA (loop_vinfo));
   LOOP_VINFO_TARGET_COST_DATA (loop_vinfo)
@@ -3261,6 +3264,11 @@ vect_estimate_min_profitable_iters (loop
       unsigned len = LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo).length ();
       (void) add_stmt_cost (target_cost_data, len, vector_stmt, NULL, 0,
 			    vect_prologue);
+      len = LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).length ();
+      if (len)
+	/* Count LEN - 1 ANDs and LEN comparisons.  */
+	(void) add_stmt_cost (target_cost_data, len * 2 - 1, scalar_stmt,
+			      NULL, 0, vect_prologue);
       dump_printf (MSG_NOTE,
                    "cost model: Adding cost of checks for loop "
                    "versioning aliasing.\n");
Index: gcc/tree-vect-data-refs.c
===================================================================
--- gcc/tree-vect-data-refs.c	2017-05-03 08:48:48.738045102 +0100
+++ gcc/tree-vect-data-refs.c	2017-05-03 08:48:53.314048428 +0100
@@ -50,6 +50,7 @@ Software Foundation; either version 3, o
 #include "expr.h"
 #include "builtins.h"
 #include "params.h"
+#include "tree-hash-traits.h"
 
 /* Return true if load- or store-lanes optab OPTAB is implemented for
    COUNT vectors of type VECTYPE.  NAME is the name of OPTAB.  */
@@ -3085,10 +3086,14 @@ dependence_distance_ge_vf (data_dependen
 bool
 vect_prune_runtime_alias_test_list (loop_vec_info loop_vinfo)
 {
-  vec<ddr_p> may_alias_ddrs =
-    LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
-  vec<dr_with_seg_len_pair_t>& comp_alias_ddrs =
-    LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
+  typedef pair_hash <tree_operand_hash, tree_operand_hash> tree_pair_hash;
+  hash_set <tree_pair_hash> compared_objects;
+
+  vec<ddr_p> may_alias_ddrs = LOOP_VINFO_MAY_ALIAS_DDRS (loop_vinfo);
+  vec<dr_with_seg_len_pair_t> &comp_alias_ddrs
+    = LOOP_VINFO_COMP_ALIAS_DDRS (loop_vinfo);
+  vec<vec_object_pair> &check_unequal_addrs
+    = LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo);
   int vect_factor = LOOP_VINFO_VECT_FACTOR (loop_vinfo);
   tree scalar_loop_iters = LOOP_VINFO_NITERS (loop_vinfo);
 
@@ -3151,6 +3156,24 @@ vect_prune_runtime_alias_test_list (loop
       if (dependence_distance_ge_vf (ddr, loop_depth, vect_factor))
 	continue;
 
+      if (DDR_OBJECT_A (ddr))
+	{
+	  vec_object_pair new_pair (DDR_OBJECT_A (ddr), DDR_OBJECT_B (ddr));
+	  if (!compared_objects.add (new_pair))
+	    {
+	      if (dump_enabled_p ())
+		{
+		  dump_printf_loc (MSG_NOTE, vect_location, "checking that ");
+		  dump_generic_expr (MSG_NOTE, TDF_SLIM, new_pair.first);
+		  dump_printf (MSG_NOTE, " and ");
+		  dump_generic_expr (MSG_NOTE, TDF_SLIM, new_pair.second);
+		  dump_printf (MSG_NOTE, " have different addresses\n");
+		}
+	      LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo).safe_push (new_pair);
+	    }
+	  continue;
+	}
+
       dr_a = DDR_A (ddr);
       stmt_a = DR_STMT (DDR_A (ddr));
       dr_group_first_a = GROUP_FIRST_ELEMENT (vinfo_for_stmt (stmt_a));
@@ -3346,11 +3369,12 @@ vect_prune_runtime_alias_test_list (loop
 	}
     }
 
+  unsigned int count = (comp_alias_ddrs.length ()
+			+ check_unequal_addrs.length ());
   dump_printf_loc (MSG_NOTE, vect_location,
 		   "improved number of alias checks from %d to %d\n",
-		   may_alias_ddrs.length (), comp_alias_ddrs.length ());
-  if ((int) comp_alias_ddrs.length () >
-      PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
+		   may_alias_ddrs.length (), count);
+  if ((int) count > PARAM_VALUE (PARAM_VECT_MAX_VERSION_FOR_ALIAS_CHECKS))
     {
       if (dump_enabled_p ())
 	dump_printf_loc (MSG_MISSED_OPTIMIZATION, vect_location,
Index: gcc/tree-vect-loop-manip.c
===================================================================
--- gcc/tree-vect-loop-manip.c	2017-04-18 19:52:34.027608884 +0100
+++ gcc/tree-vect-loop-manip.c	2017-05-03 08:48:53.314048428 +0100
@@ -1926,6 +1926,20 @@ vect_create_cond_for_niters_checks (loop
     *cond_expr = part_cond_expr;
 }
 
+/* Set *COND_EXPR to a tree that is true when both the original *COND_EXPR
+   and PART_COND_EXPR are true.  Treat a null *COND_EXPR as "true".  */
+
+static void
+chain_cond_expr (tree *cond_expr, tree part_cond_expr)
+{
+  if (*cond_expr)
+    *cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
+			      *cond_expr, part_cond_expr);
+  else
+    *cond_expr = part_cond_expr;
+}
+
+
 /* Function vect_create_cond_for_align_checks.
 
    Create a conditional expression that represents the alignment checks for
@@ -2037,13 +2051,32 @@ vect_create_cond_for_align_checks (loop_
   ptrsize_zero = build_int_cst (int_ptrsize_type, 0);
   part_cond_expr = fold_build2 (EQ_EXPR, boolean_type_node,
 				and_tmp_name, ptrsize_zero);
-  if (*cond_expr)
-    *cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
-			      *cond_expr, part_cond_expr);
-  else
-    *cond_expr = part_cond_expr;
+  chain_cond_expr (cond_expr, part_cond_expr);
 }
 
+
+/* If LOOP_VINFO_CHECK_UNEQUAL_ADDRS contains <A1, B1>, ..., <An, Bn>,
+   create a tree representation of: (&A1 != &B1) && ... && (&An != &Bn).
+   Set *COND_EXPR to a tree that is true when both the original *COND_EXPR
+   and this new condition are true.  Treat a null *COND_EXPR as "true".  */
+
+static void
+vect_create_cond_for_unequal_addrs (loop_vec_info loop_vinfo, tree *cond_expr)
+{
+  vec<vec_object_pair> pairs = LOOP_VINFO_CHECK_UNEQUAL_ADDRS (loop_vinfo);
+  unsigned int i;
+  vec_object_pair *pair;
+  FOR_EACH_VEC_ELT (pairs, i, pair)
+    {
+      tree addr1 = build_fold_addr_expr (pair->first);
+      tree addr2 = build_fold_addr_expr (pair->second);
+      tree part_cond_expr = fold_build2 (NE_EXPR, boolean_type_node,
+					 addr1, addr2);
+      chain_cond_expr (cond_expr, part_cond_expr);
+    }
+}
+
+
 /* Given two data references and segment lengths described by DR_A and DR_B,
    create expression checking if the two addresses ranges intersect with
    each other based on index of the two addresses.  This can only be done
@@ -2280,11 +2313,7 @@ vect_create_cond_for_alias_checks (loop_
 
       /* Create condition expression for each pair data references.  */
       create_intersect_range_checks (loop_vinfo, &part_cond_expr, dr_a, dr_b);
-      if (*cond_expr)
-	*cond_expr = fold_build2 (TRUTH_AND_EXPR, boolean_type_node,
-				  *cond_expr, part_cond_expr);
-      else
-	*cond_expr = part_cond_expr;
+      chain_cond_expr (cond_expr, part_cond_expr);
     }
 
   if (dump_enabled_p ())
@@ -2353,7 +2382,10 @@ vect_loop_versioning (loop_vec_info loop
 				       &cond_expr_stmt_list);
 
   if (version_alias)
-    vect_create_cond_for_alias_checks (loop_vinfo, &cond_expr);
+    {
+      vect_create_cond_for_unequal_addrs (loop_vinfo, &cond_expr);
+      vect_create_cond_for_alias_checks (loop_vinfo, &cond_expr);
+    }
 
   cond_expr = force_gimple_operand_1 (cond_expr, &gimplify_stmt_list,
 				      is_gimple_condexpr, NULL_TREE);
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-6.c
===================================================================
--- /dev/null	2017-05-03 08:16:26.972699664 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-6.c	2017-05-03 08:48:53.312035228 +0100
@@ -0,0 +1,23 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_int } */
+
+#define N 16
+
+struct s { int x[N]; };
+
+void
+f1 (struct s *a, struct s *b)
+{
+  for (int i = 0; i < N - 1; ++i)
+    a->x[i + 1] += b->x[i];
+}
+
+void
+f2 (struct s *a, struct s *b)
+{
+  for (int i = 0; i < N; ++i)
+    a->x[i] += b->x[N - i - 1];
+}
+
+/* { dg-final { scan-tree-dump-times {checking that [^\n]* and [^\n]* have different addresses} 2 "vect" } } */
+/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 2 "vect" } } */