[7/7] Add negative and zero strides to vect_memory_access_type

This patch uses the vect_memory_access_type from patch 6 to represent
the effect of a negative contiguous stride or a zero stride.  The latter
is valid only for loads.

Tested on aarch64-linux-gnu and x86_64-linux-gnu.

gcc/
	* tree-vectorizer.h (vect_memory_access_type): Add
	VMAT_INVARIANT, VMAT_CONTIGUOUS_DOWN and VMAT_CONTIGUOUS_REVERSED.
	* tree-vect-stmts.c (compare_step_with_zero): New function.
	(perm_mask_for_reverse): Move further up file.
	(get_group_load_store_type): Stick to VMAT_ELEMENTWISE if the
	step is negative.
	(get_negative_load_store_type): New function.
	(get_load_store_type): Call it.  Add an ncopies argument.
	(vectorizable_mask_load_store): Update call accordingly and
	remove tests for negative steps.
	(vectorizable_store, vectorizable_load): Likewise.  Handle new
	memory_access_types.

From-SVN: r238039

gcc/ChangeLog

 2016-07-06  Richard Sandiford  <richard.sandiford@arm.com>
 
+	* tree-vectorizer.h (vect_memory_access_type): Add
+	VMAT_INVARIANT, VMAT_CONTIGUOUS_DOWN and VMAT_CONTIGUOUS_REVERSED.
+	* tree-vect-stmts.c (compare_step_with_zero): New function.
+	(perm_mask_for_reverse): Move further up file.
+	(get_group_load_store_type): Stick to VMAT_ELEMENTWISE if the
+	step is negative.
+	(get_negative_load_store_type): New function.
+	(get_load_store_type): Call it.  Add an ncopies argument.
+	(vectorizable_mask_load_store): Update call accordingly and
+	remove tests for negative steps.
+	(vectorizable_store, vectorizable_load): Likewise.  Handle new
+	memory_access_types.
+
+2016-07-06  Richard Sandiford  <richard.sandiford@arm.com>
+
 	* tree-vectorizer.h (vect_memory_access_type): New enum.
 	(_stmt_vec_info): Add a memory_access_type field.
 	(STMT_VINFO_MEMORY_ACCESS_TYPE): New macro.

gcc/tree-vectorizer.h

@@ -484,14 +484,26 @@ enum slp_vect_type {
 /* Describes how we're going to vectorize an individual load or store,
    or a group of loads or stores.  */
 enum vect_memory_access_type {
+  /* An access to an invariant address.  This is used only for loads.  */
+  VMAT_INVARIANT,
+
   /* A simple contiguous access.  */
   VMAT_CONTIGUOUS,
 
+  /* A contiguous access that goes down in memory rather than up,
+     with no additional permutation.  This is used only for stores
+     of invariants.  */
+  VMAT_CONTIGUOUS_DOWN,
+
   /* A simple contiguous access in which the elements need to be permuted
      after loading or before storing.  Only used for loop vectorization;
      SLP uses separate permutes.  */
   VMAT_CONTIGUOUS_PERMUTE,
 
+  /* A simple contiguous access in which the elements need to be reversed
+     after loading or before storing.  */
+  VMAT_CONTIGUOUS_REVERSE,
+
   /* An access that uses IFN_LOAD_LANES or IFN_STORE_LANES.  */
   VMAT_LOAD_STORE_LANES,