Don't group gather loads (PR83847)

In the testcase we were trying to group two gather loads, even though
that isn't supported.  Fixed by explicitly disallowing grouping of
gathers and scatters.

This problem didn't show up on SVE because there we convert to
IFN_GATHER_LOAD/IFN_SCATTER_STORE pattern statements, which fail
the can_group_stmts_p check.

2018-01-16  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-vect-data-refs.c (vect_analyze_data_ref_accesses):

gcc/testsuite/
	* gcc.dg/torture/pr83847.c: New test.

From-SVN: r256730

gcc/ChangeLog

+2018-01-16  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* tree-vect-data-refs.c (vect_analyze_data_ref_accesses):
+
 2018-01-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/86620

gcc/testsuite/ChangeLog

+2018-01-16  Richard Sandiford  <richard.sandiford@linaro.org>
+
+	* gcc.dg/torture/pr83847.c: New test.
+
 2018-01-16  Jakub Jelinek  <jakub@redhat.com>
 
 	PR rtl-optimization/86620

gcc/testsuite/gcc.dg/torture/pr83847.c

+/* { dg-do compile } */
+/* { dg-additional-options "-march=bdver4" { target i?86-*-* x86_64-*-* } } */
+
+typedef struct {
+  struct {
+    int a;
+    int b;
+  } c;
+} * d;
+typedef struct {
+  unsigned e;
+  d f[];
+} g;
+g h;
+d *k;
+int i(int j) {
+  if (j) {
+    *k = *h.f;
+    return 1;
+  }
+  return 0;
+}
+int l;
+int m;
+int n;
+d o;
+void p() {
+  for (; i(l); l++) {
+    n += o->c.a;
+    m += o->c.b;
+  }
+}

gcc/tree-vect-data-refs.c

@@ -2923,7 +2923,8 @@ vect_analyze_data_ref_accesses (vec_info *vinfo)
       data_reference_p dra = datarefs_copy[i];
       stmt_vec_info stmtinfo_a = vinfo_for_stmt (DR_STMT (dra));
       stmt_vec_info lastinfo = NULL;
-      if (! STMT_VINFO_VECTORIZABLE (stmtinfo_a))
+      if (!STMT_VINFO_VECTORIZABLE (stmtinfo_a)
+	  || STMT_VINFO_GATHER_SCATTER_P (stmtinfo_a))
 	{
 	  ++i;
 	  continue;
@@ -2932,7 +2933,8 @@ vect_analyze_data_ref_accesses (vec_info *vinfo)
 	{
 	  data_reference_p drb = datarefs_copy[i];
 	  stmt_vec_info stmtinfo_b = vinfo_for_stmt (DR_STMT (drb));
-	  if (! STMT_VINFO_VECTORIZABLE (stmtinfo_b))
+	  if (!STMT_VINFO_VECTORIZABLE (stmtinfo_b)
+	      || STMT_VINFO_GATHER_SCATTER_P (stmtinfo_b))
 	    break;
 
 	  /* ???  Imperfect sorting (non-compatible types, non-modulo