Use loop->safelen rather than loop->force_vectorize

[Richard Sandiford]

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

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

Richard


2018-03-01  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.

Index: gcc/tree-vect-data-refs.c
===================================================================
--- gcc/tree-vect-data-refs.c	2018-02-10 09:49:47.950776097 +0000
+++ gcc/tree-vect-data-refs.c	2018-03-01 18:17:41.631482331 +0000
@@ -466,7 +466,7 @@ vect_analyze_data_ref_dependence (struct
 	      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 dat
       /* 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,
Index: gcc/testsuite/gcc.dg/vect/vect-alias-check-13.c
===================================================================
--- /dev/null	2018-03-01 08:17:49.562264353 +0000
+++ gcc/testsuite/gcc.dg/vect/vect-alias-check-13.c	2018-03-01 18:17:41.630484279 +0000
@@ -0,0 +1,21 @@
+/* { 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" } } */