Index: gcc/tree-data-ref.c
===================================================================
--- gcc/tree-data-ref.c	2019-11-11 18:30:53.863170161 +0000
+++ gcc/tree-data-ref.c	2019-11-11 18:30:57.167147102 +0000
@@ -1453,6 +1453,54 @@ comp_dr_with_seg_len_pair (const void *p
   return 0;
 }
 
+/* Dump information about ALIAS_PAIR, indenting each line by INDENT.  */
+
+static void
+dump_alias_pair (dr_with_seg_len_pair_t *alias_pair, const char *indent)
+{
+  dump_printf (MSG_NOTE, "%sreference:      %T vs. %T\n", indent,
+	       DR_REF (alias_pair->first.dr),
+	       DR_REF (alias_pair->second.dr));
+
+  dump_printf (MSG_NOTE, "%ssegment length: %T", indent,
+	       alias_pair->first.seg_len);
+  if (!operand_equal_p (alias_pair->first.seg_len,
+			alias_pair->second.seg_len, 0))
+    dump_printf (MSG_NOTE, " vs. %T", alias_pair->second.seg_len);
+
+  dump_printf (MSG_NOTE, "\n%saccess size:    ", indent);
+  dump_dec (MSG_NOTE, alias_pair->first.access_size);
+  if (maybe_ne (alias_pair->first.access_size, alias_pair->second.access_size))
+    {
+      dump_printf (MSG_NOTE, " vs. ");
+      dump_dec (MSG_NOTE, alias_pair->second.access_size);
+    }
+
+  dump_printf (MSG_NOTE, "\n%salignment:      %d", indent,
+	       alias_pair->first.align);
+  if (alias_pair->first.align != alias_pair->second.align)
+    dump_printf (MSG_NOTE, " vs. %d", alias_pair->second.align);
+
+  dump_printf (MSG_NOTE, "\n%sflags:         ", indent);
+  if (alias_pair->flags & DR_ALIAS_RAW)
+    dump_printf (MSG_NOTE, " RAW");
+  if (alias_pair->flags & DR_ALIAS_WAR)
+    dump_printf (MSG_NOTE, " WAR");
+  if (alias_pair->flags & DR_ALIAS_WAW)
+    dump_printf (MSG_NOTE, " WAW");
+  if (alias_pair->flags & DR_ALIAS_ARBITRARY)
+    dump_printf (MSG_NOTE, " ARBITRARY");
+  if (alias_pair->flags & DR_ALIAS_SWAPPED)
+    dump_printf (MSG_NOTE, " SWAPPED");
+  if (alias_pair->flags & DR_ALIAS_UNSWAPPED)
+    dump_printf (MSG_NOTE, " UNSWAPPED");
+  if (alias_pair->flags & DR_ALIAS_MIXED_STEPS)
+    dump_printf (MSG_NOTE, " MIXED_STEPS");
+  if (alias_pair->flags == 0)
+    dump_printf (MSG_NOTE, " <none>");
+  dump_printf (MSG_NOTE, "\n");
+}
+
 /* Merge alias checks recorded in ALIAS_PAIRS and remove redundant ones.
    FACTOR is number of iterations that each data reference is accessed.
 
@@ -1656,6 +1704,8 @@ prune_runtime_alias_test_list (vec<dr_wi
      dr_with_seg_len_pair_t.  If we ended up combining swapped and
      unswapped pairs into the same check, we have to invalidate any
      RAW, WAR and WAW information for it.  */
+  if (dump_enabled_p ())
+    dump_printf (MSG_NOTE, "merged alias checks:\n");
   FOR_EACH_VEC_ELT (*alias_pairs, i, alias_pair)
     {
       unsigned int swap_mask = (DR_ALIAS_SWAPPED | DR_ALIAS_UNSWAPPED);
@@ -1665,6 +1715,8 @@ prune_runtime_alias_test_list (vec<dr_wi
       else if (swapped != DR_ALIAS_UNSWAPPED)
 	alias_pair->flags |= DR_ALIAS_ARBITRARY;
       alias_pair->flags &= ~swap_mask;
+      if (dump_enabled_p ())
+	dump_alias_pair (alias_pair, "  ");
     }
 }
 
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-8.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/vect-alias-check-8.c	2019-03-08 18:15:02.280871184 +0000
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-8.c	2019-11-11 18:30:57.167147102 +0000
@@ -58,3 +58,5 @@ main (void)
   FOR_EACH_TYPE (DO_TEST)
   return 0;
 }
+
+/* { dg-final { scan-tree-dump {flags: *WAR\n} "vect" { target vect_int } } } */
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-9.c
===================================================================
--- gcc/testsuite/gcc.dg/vect/vect-alias-check-9.c	2019-03-08 18:15:02.244871320 +0000
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-9.c	2019-11-11 18:30:57.167147102 +0000
@@ -17,7 +17,7 @@ #define FOR_EACH_TYPE(M) \
   M (sll) M (ull) \
   M (float) M (double)
 
-#define TEST_VALUE(I) ((I) * 5 / 2)
+#define TEST_VALUE(I) ((I) * 17 / 2)
 
 #define ADD_TEST(TYPE)				\
   void __attribute__((noinline, noclone))	\
@@ -51,3 +51,5 @@ main (void)
   FOR_EACH_TYPE (DO_TEST)
   return 0;
 }
+
+/* { dg-final { scan-tree-dump {flags: [^\n]*ARBITRARY\n} "vect" { target vect_int } } } */
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-14.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-14.c	2019-11-11 18:30:57.167147102 +0000
@@ -0,0 +1,62 @@
+#define N 200
+#define M 4
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define TEST_VALUE(I) ((I) * 17 / 2)
+
+#define ADD_TEST(TYPE)				\
+  void __attribute__((noinline, noclone))	\
+  test_##TYPE (TYPE *a, TYPE *b)		\
+  {						\
+    for (int i = 0; i < N; i += 2)		\
+      {						\
+	TYPE b0 = b[i + 0];			\
+	TYPE b1 = b[i + 1];			\
+	a[i + 0] = b0 + 2;			\
+	a[i + 1] = b1 + 3;			\
+      }						\
+  }
+
+#define DO_TEST(TYPE)						\
+  for (int j = 0; j < M; ++j)					\
+    {								\
+      TYPE a[N + M];						\
+      for (int i = 0; i < N + M; ++i)				\
+	a[i] = TEST_VALUE (i);					\
+      test_##TYPE (a + j, a);					\
+      for (int i = 0; i < N; i += 2)				\
+	{							\
+	  TYPE base1 = j == 0 ? TEST_VALUE (i) : a[i];		\
+	  TYPE base2 = j <= 1 ? TEST_VALUE (i + 1) : a[i + 1];	\
+	  if (a[i + j] != (TYPE) (base1 + 2)			\
+	      || a[i + j + 1] != (TYPE) (base2 + 3))		\
+	    __builtin_abort ();					\
+	}							\
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *WAR\n} "vect" { target vect_int } } } */
+/* { dg-final { scan-tree-dump-not {flags: [^\n]*ARBITRARY\n} "vect" } } */
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-15.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-15.c	2019-11-11 18:30:57.167147102 +0000
@@ -0,0 +1,59 @@
+#define N 200
+#define DIST 32
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define ADD_TEST(TYPE)				\
+  void __attribute__((noinline, noclone))	\
+  test_##TYPE (TYPE *x, TYPE *y)		\
+  {						\
+    for (int i = 0; i < N; ++i)			\
+      {						\
+	x[i] = i;				\
+	y[i] = 42 - i * 2;			\
+      }						\
+  }
+
+#define DO_TEST(TYPE)						\
+  for (int i = 0; i < DIST * 2; ++i)				\
+    {								\
+      TYPE a[N + DIST * 2] = {};				\
+      test_##TYPE (a + DIST, a + i);				\
+      for (int j = 0; j < N + DIST * 2; ++j)			\
+	{							\
+	  TYPE expected = 0;					\
+	  if (i > DIST && j >= i && j < i + N)			\
+	    expected = 42 - (j - i) * 2;			\
+	  if (j >= DIST && j < DIST + N)			\
+	    expected = j - DIST;				\
+	  if (i <= DIST && j >= i && j < i + N)			\
+	    expected = 42 - (j - i) * 2;			\
+	  if (expected != a[j])					\
+	    __builtin_abort ();					\
+	}							\
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *WAW\n} "vect" { target vect_int } } } */
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-16.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-16.c	2019-11-11 18:30:57.167147102 +0000
@@ -0,0 +1,64 @@
+#define N 200
+#define DIST 32
+
+typedef signed char sc;
+typedef unsigned char uc;
+typedef signed short ss;
+typedef unsigned short us;
+typedef int si;
+typedef unsigned int ui;
+typedef signed long long sll;
+typedef unsigned long long ull;
+
+#define FOR_EACH_TYPE(M) \
+  M (sc) M (uc) \
+  M (ss) M (us) \
+  M (si) M (ui) \
+  M (sll) M (ull) \
+  M (float) M (double)
+
+#define TEST_VALUE(I) ((I) * 13 / 2)
+
+#define ADD_TEST(TYPE)				\
+  TYPE __attribute__((noinline, noclone))	\
+  test_##TYPE (TYPE *x, TYPE *y)		\
+  {						\
+    TYPE res = 0;				\
+    for (int i = 0; i < N; ++i)			\
+      {						\
+	x[i] = i;				\
+	res += y[i];				\
+      }						\
+    return res;					\
+  }
+
+#define DO_TEST(TYPE)						\
+  for (int i = 0; i < DIST * 2; ++i)				\
+    {								\
+      TYPE a[N + DIST * 2];					\
+      for (int j = 0; j < N + DIST * 2; ++j)			\
+	a[j] = TEST_VALUE (j);					\
+      TYPE res = test_##TYPE (a + DIST, a + i);			\
+      for (int j = 0; j < N; ++j)				\
+	if (a[j + DIST] != (TYPE) j)				\
+	  __builtin_abort ();					\
+      TYPE expected_res = 0;					\
+      for (int j = i; j < i + N; ++j)				\
+	if (i <= DIST && j >= DIST && j < DIST + N)		\
+	  expected_res += j - DIST;				\
+	else							\
+	  expected_res += TEST_VALUE (j);			\
+      if (expected_res != res)					\
+	__builtin_abort ();					\
+    }
+
+FOR_EACH_TYPE (ADD_TEST)
+
+int
+main (void)
+{
+  FOR_EACH_TYPE (DO_TEST)
+  return 0;
+}
+
+/* { dg-final { scan-tree-dump {flags: *RAW\n} "vect" { target vect_int } } } */
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-17.c
===================================================================
--- /dev/null	2019-09-17 11:41:18.176664108 +0100
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-17.c	2019-11-11 18:30:57.167147102 +0000
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-require-effective-target vect_load_lanes } */
+
+struct s { int x[100]; };
+
+void
+f (struct s *s1, int a, int b)
+{
+  for (int i = 0; i < 32; ++i)
+    s1->x[a + i] = s1->x[b + i * 2] + s1->x[b + i * 3];
+}
+
+/* { dg-final { scan-tree-dump {flags: *[^\n]*MIXED_STEPS} "vect" } } */
