Use loop->safelen rather than loop->force_vectorize

...since the latter doesn't guarantee independence by itself.

2018-03-02  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence)
	(vect_analyze_data_ref_access): Use loop->safe_len rather than
	loop->force_vectorize to check whether there is no alias.

gcc/testsuite/
	* gcc.dg/vect/vect-alias-check-13.c: New test.

From-SVN: r258130

gcc/ChangeLog

+2018-03-02  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* tree-vect-data-refs.c (vect_analyze_data_ref_dependence)
+	(vect_analyze_data_ref_access): Use loop->safe_len rather than
+	loop->force_vectorize to check whether there is no alias.
+
 2018-03-02  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/84614

gcc/testsuite/ChangeLog

+2018-03-02  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* gcc.dg/vect/vect-alias-check-13.c: New test.
+
 2018-03-02  Jakub Jelinek  <jakub@redhat.com>
 
 	PR target/84614

gcc/testsuite/gcc.dg/vect/vect-alias-check-13.c

+/* { dg-do compile } */
+/* { dg-require-effective-target vect_int } */
+
+void
+f1 (int *x, long step1, int n)
+{
+  for (int i = 0; i < n; ++i)
+    x[i * step1] += 1;
+}
+
+void
+f2 (int *x, long step2, int n)
+{
+#pragma GCC ivdep
+  for (int i = 0; i < n; ++i)
+    x[i * step2] += 2;
+}
+
+/* { dg-final { scan-tree-dump {need run-time check that [^\n]*step1[^\n]* is nonzero} "vect" } } */
+/* { dg-final { scan-tree-dump-not {need run-time check that [^\n]*step2[^\n]* is nonzero} "vect" } } */
+/* { dg-final { scan-tree-dump-times {LOOP VECTORIZED} 2 "vect" } } */

gcc/tree-vect-data-refs.c

@@ -466,7 +466,7 @@ vect_analyze_data_ref_dependence (struct data_dependence_relation *ddr,
 	      return true;
 	    }
 
-	  if (!loop->force_vectorize)
+	  if (loop->safelen < 2)
 	    {
 	      tree indicator = dr_zero_step_indicator (dra);
 	      if (TREE_CODE (indicator) != INTEGER_CST)
@@ -2720,7 +2720,7 @@ vect_analyze_data_ref_access (struct data_reference *dr)
       /* Allow references with zero step for outer loops marked
 	 with pragma omp simd only - it guarantees absence of
 	 loop-carried dependencies between inner loop iterations.  */
-      if (!loop->force_vectorize)
+      if (loop->safelen < 2)
 	{
 	  if (dump_enabled_p ())
 	    dump_printf_loc (MSG_NOTE, vect_location,