Add a helper for getting the overall alignment of a DR

This combines the information from previous patches to give a guaranteed
alignment for the DR as a whole.  This should be a bit safer than using
base_element_aligned, since that only really took the base into account
(not the init or offset).

2017-07-03  Richard Sandiford  <richard.sandiford@linaro.org>

gcc/
	* tree-data-ref.h (dr_alignment): Declare.
	* tree-data-ref.c (dr_alignment): New function.
	* tree-vectorizer.h (dataref_aux): Remove base_element_aligned.
	* tree-vect-data-refs.c (vect_compute_data_ref_alignment): Don't
	set it.
	* tree-vect-stmts.c (vectorizable_store): Use dr_alignment.

From-SVN: r249917

gcc/ChangeLog

 2017-07-03  Richard Sandiford  <richard.sandiford@linaro.org>
 
+	* tree-data-ref.h (dr_alignment): Declare.
+	* tree-data-ref.c (dr_alignment): New function.
+	* tree-vectorizer.h (dataref_aux): Remove base_element_aligned.
+	* tree-vect-data-refs.c (vect_compute_data_ref_alignment): Don't
+	set it.
+	* tree-vect-stmts.c (vectorizable_store): Use dr_alignment.
+
+2017-07-03  Richard Sandiford  <richard.sandiford@linaro.org>
+
 	* tree-data-ref.h (innermost_loop_behavior): Add base_alignment
 	and base_misalignment fields.
 	(DR_BASE_ALIGNMENT, DR_BASE_MISALIGNMENT): New macros.

gcc/tree-data-ref.c

@@ -4770,6 +4770,30 @@ find_data_references_in_loop (struct loop *loop,
   return NULL_TREE;
 }
 
+/* Return the alignment in bytes that DRB is guaranteed to have at all
+   times.  */
+
+unsigned int
+dr_alignment (innermost_loop_behavior *drb)
+{
+  /* Get the alignment of BASE_ADDRESS + INIT.  */
+  unsigned int alignment = drb->base_alignment;
+  unsigned int misalignment = (drb->base_misalignment
+			       + TREE_INT_CST_LOW (drb->init));
+  if (misalignment != 0)
+    alignment = MIN (alignment, misalignment & -misalignment);
+
+  /* Cap it to the alignment of OFFSET.  */
+  if (!integer_zerop (drb->offset))
+    alignment = MIN (alignment, drb->offset_alignment);
+
+  /* Cap it to the alignment of STEP.  */
+  if (!integer_zerop (drb->step))
+    alignment = MIN (alignment, drb->step_alignment);
+
+  return alignment;
+}
+
 /* Recursive helper function.  */
 
 static bool

gcc/tree-data-ref.h

@@ -405,6 +405,16 @@ extern bool compute_all_dependences (vec<data_reference_p> ,
 				     vec<loop_p>, bool);
 extern tree find_data_references_in_bb (struct loop *, basic_block,
                                         vec<data_reference_p> *);
+extern unsigned int dr_alignment (innermost_loop_behavior *);
+
+/* Return the alignment in bytes that DR is guaranteed to have at all
+   times.  */
+
+inline unsigned int
+dr_alignment (data_reference *dr)
+{
+  return dr_alignment (&DR_INNERMOST (dr));
+}
 
 extern bool dr_may_alias_p (const struct data_reference *,
 			    const struct data_reference *, bool);

gcc/tree-vect-data-refs.c

@@ -731,12 +731,6 @@ vect_compute_data_ref_alignment (struct data_reference *dr)
   unsigned int base_alignment = drb->base_alignment;
   unsigned int base_misalignment = drb->base_misalignment;
   unsigned HOST_WIDE_INT vector_alignment = TYPE_ALIGN_UNIT (vectype);
-  unsigned HOST_WIDE_INT element_alignment
-    = TYPE_ALIGN_UNIT (TREE_TYPE (vectype));
-
-  if (base_alignment >= element_alignment
-      && (base_misalignment & (element_alignment - 1)) == 0)
-    DR_VECT_AUX (dr)->base_element_aligned = true;
 
   if (drb->offset_alignment < vector_alignment
       || !step_preserves_misalignment_p
@@ -797,7 +791,6 @@ vect_compute_data_ref_alignment (struct data_reference *dr)
 
       DR_VECT_AUX (dr)->base_decl = base;
       DR_VECT_AUX (dr)->base_misaligned = true;
-      DR_VECT_AUX (dr)->base_element_aligned = true;
       base_misalignment = 0;
     }
   unsigned int misalignment = (base_misalignment

gcc/tree-vect-stmts.c

@@ -6353,11 +6353,7 @@ vectorizable_store (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
 		misalign = 0;
 	      else if (DR_MISALIGNMENT (first_dr) == -1)
 		{
-		  if (DR_VECT_AUX (first_dr)->base_element_aligned)
-		    align = TYPE_ALIGN_UNIT (elem_type);
-		  else
-		    align = get_object_alignment (DR_REF (first_dr))
-			/ BITS_PER_UNIT;
+		  align = dr_alignment (vect_dr_behavior (first_dr));
 		  misalign = 0;
 		  TREE_TYPE (data_ref)
 		    = build_aligned_type (TREE_TYPE (data_ref),
@@ -7429,11 +7425,7 @@ vectorizable_load (gimple *stmt, gimple_stmt_iterator *gsi, gimple **vec_stmt,
 		      }
 		    else if (DR_MISALIGNMENT (first_dr) == -1)
 		      {
-			if (DR_VECT_AUX (first_dr)->base_element_aligned)
-			  align = TYPE_ALIGN_UNIT (elem_type);
-			else
-			  align = (get_object_alignment (DR_REF (first_dr))
-				   / BITS_PER_UNIT);
+			align = dr_alignment (vect_dr_behavior (first_dr));
 			misalign = 0;
 			TREE_TYPE (data_ref)
 			  = build_aligned_type (TREE_TYPE (data_ref),

gcc/tree-vectorizer.h

@@ -754,8 +754,6 @@ struct dataref_aux {
   int misalignment;
   /* If true the alignment of base_decl needs to be increased.  */
   bool base_misaligned;
-  /* If true we know the base is at least vector element alignment aligned.  */
-  bool base_element_aligned;
   tree base_decl;
 };