[Bug middle-end/70434] [5/6 Regression] adding an extraneous cast to vector type results in inferior code

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70434

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot 
gnu.org

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Index: gcc/c-family/c-common.c
===================================================================
--- gcc/c-family/c-common.c     (revision 234517)
+++ gcc/c-family/c-common.c     (working copy)
@@ -12456,46 +12456,11 @@ convert_vector_to_pointer_for_subscript
             || tree_to_uhwi (index) >= TYPE_VECTOR_SUBPARTS (type))
           warning_at (loc, OPT_Warray_bounds, "index value is out of bound");

-      if (ret)
-       {
-         tree tmp = create_tmp_var_raw (type);
-         DECL_SOURCE_LOCATION (tmp) = loc;
-         *vecp = c_save_expr (*vecp);
-         if (TREE_CODE (*vecp) == C_MAYBE_CONST_EXPR)
-           {
-             bool non_const = C_MAYBE_CONST_EXPR_NON_CONST (*vecp);
-             *vecp = C_MAYBE_CONST_EXPR_EXPR (*vecp);
-             *vecp
-               = c_wrap_maybe_const (build4 (TARGET_EXPR, type, tmp,
-                                             *vecp, NULL_TREE, NULL_TREE),
-                                     non_const);
-           }
-         else
-           *vecp = build4 (TARGET_EXPR, type, tmp, *vecp,
-                           NULL_TREE, NULL_TREE);
-         SET_EXPR_LOCATION (*vecp, loc);
-         c_common_mark_addressable_vec (tmp);
-       }
-      else
-       c_common_mark_addressable_vec (*vecp);
-      type = build_qualified_type (TREE_TYPE (type), TYPE_QUALS (type));
-      type1 = build_pointer_type (TREE_TYPE (*vecp));
-      bool ref_all = TYPE_REF_CAN_ALIAS_ALL (type1);
-      if (!ref_all
-         && !DECL_P (*vecp))
-       {
-         /* If the original vector isn't declared may_alias and it
-            isn't a bare vector look if the subscripting would
-            alias the vector we subscript, and if not, force ref-all.  */
-         alias_set_type vecset = get_alias_set (*vecp);
-         alias_set_type sset = get_alias_set (type);
-         if (!alias_sets_must_conflict_p (sset, vecset)
-             && !alias_set_subset_of (sset, vecset))
-           ref_all = true;
-       }
-      type = build_pointer_type_for_mode (type, ptr_mode, ref_all);
-      *vecp = build1 (ADDR_EXPR, type1, *vecp);
-      *vecp = convert (type, *vecp);
+      *vecp = build1 (VIEW_CONVERT_EXPR,
+                     build_array_type_nelts (TREE_TYPE (type),
+                                             TYPE_VECTOR_SUBPARTS (type)),
+                     *vecp);
+      c_common_mark_addressable_vec (*vecp);
     }
   return ret;
 }


but note we fail to re-write v into SSA and thus generated code is worse
(but the same for both cases).  .optimized has

bar4 (int x, v4si v)
{
  int _2;
  int _3;
  int _4;
  int _7;

  <bb 2>:
  _2 = VIEW_CONVERT_EXPR<int[4]>(v)[0];
  _3 = VIEW_CONVERT_EXPR<int[4]>(v)[1];
  _4 = _2 ^ _3;
  VIEW_CONVERT_EXPR<int[4]>(v)[0] = _4;
  _7 = VIEW_CONVERT_EXPR<int[4]>(v)[x_6(D)];
  return _7;

where you can see we miss foldings for V_C_E<array>(x)[CST] into
BIT_FIELD_REFs.  It at least avoids taking the address of 'v'.
With a BIT_FIELD_INSERT we could re-write 'v' into SSA.