--- a/gcc/tree-ssa-loop-prefetch.c	Fri Oct 27 22:46:09 2017 +0900
+++ b/gcc/tree-ssa-loop-prefetch.c	Thu Oct 25 07:37:49 2018 +0900
@@ -1,5 +1,5 @@
 /* Array prefetching.
-   Copyright (C) 2005-2017 Free Software Foundation, Inc.
+   Copyright (C) 2005-2018 Free Software Foundation, Inc.
 
 This file is part of GCC.
 
@@ -992,6 +992,33 @@
 static bool
 should_issue_prefetch_p (struct mem_ref *ref)
 {
+  /* Do we want to issue prefetches for non-constant strides?  */
+  if (!cst_and_fits_in_hwi (ref->group->step) && PREFETCH_DYNAMIC_STRIDES == 0)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file,
+		 "Skipping non-constant step for reference %u:%u\n",
+		 ref->group->uid, ref->uid);
+      return false;
+    }
+
+  /* Some processors may have a hardware prefetcher that may conflict with
+     prefetch hints for a range of strides.  Make sure we don't issue
+     prefetches for such cases if the stride is within this particular
+     range.  */
+  if (cst_and_fits_in_hwi (ref->group->step)
+      && abs_hwi (int_cst_value (ref->group->step))
+	  < (HOST_WIDE_INT) PREFETCH_MINIMUM_STRIDE)
+    {
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	fprintf (dump_file,
+		 "Step for reference %u:%u (" HOST_WIDE_INT_PRINT_DEC
+		 ") is less than the mininum required stride of %d\n",
+		 ref->group->uid, ref->uid, int_cst_value (ref->group->step),
+		 PREFETCH_MINIMUM_STRIDE);
+      return false;
+    }
+
   /* For now do not issue prefetches for only first few of the
      iterations.  */
   if (ref->prefetch_before != PREFETCH_ALL)