[12/13] Use ssizetype selectors for autovectorised VEC_PERM_EXPRs

[Richard Sandiford]

The previous patches mean that there's no reason that constant
VEC_PERM_EXPRs need to have the same shape as the data inputs.
This patch makes the autovectoriser use ssizetype elements instead,
so that indices don't get truncated for large or variable-length vectors.


2017-12-09  Richard Sandiford  <richard.sandif...@linaro.org>

gcc/
        * tree-cfg.c (verify_gimple_assign_ternary): Allow the size of
        the selector elements to be different from the data elements
        if the selector is a VECTOR_CST.
        * tree-vect-stmts.c (vect_gen_perm_mask_any): Use a vector of
        ssizetype for the selector.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c      2017-12-09 22:47:07.103588314 +0000
+++ gcc/tree-cfg.c      2017-12-09 22:48:58.259216407 +0000
@@ -4300,8 +4300,11 @@ verify_gimple_assign_ternary (gassign *s
        }
 
       if (TREE_CODE (TREE_TYPE (rhs3_type)) != INTEGER_TYPE
-         || GET_MODE_BITSIZE (SCALAR_INT_TYPE_MODE (TREE_TYPE (rhs3_type)))
-            != GET_MODE_BITSIZE (SCALAR_TYPE_MODE (TREE_TYPE (rhs1_type))))
+         || (TREE_CODE (rhs3) != VECTOR_CST
+             && (GET_MODE_BITSIZE (SCALAR_INT_TYPE_MODE
+                                   (TREE_TYPE (rhs3_type)))
+                 != GET_MODE_BITSIZE (SCALAR_TYPE_MODE
+                                      (TREE_TYPE (rhs1_type))))))
        {
          error ("invalid mask type in vector permute expression");
          debug_generic_expr (lhs_type);
Index: gcc/tree-vect-stmts.c
===================================================================
--- gcc/tree-vect-stmts.c       2017-12-09 22:48:52.268015910 +0000
+++ gcc/tree-vect-stmts.c       2017-12-09 22:48:58.259216407 +0000
@@ -6518,11 +6518,12 @@ vectorizable_store (gimple *stmt, gimple
 tree
 vect_gen_perm_mask_any (tree vectype, const vec_perm_indices &sel)
 {
-  tree mask_elt_type, mask_type;
+  tree mask_type;
 
-  mask_elt_type = lang_hooks.types.type_for_mode
-    (int_mode_for_mode (TYPE_MODE (TREE_TYPE (vectype))).require (), 1);
-  mask_type = get_vectype_for_scalar_type (mask_elt_type);
+  unsigned int nunits = sel.length ();
+  gcc_assert (nunits == TYPE_VECTOR_SUBPARTS (vectype));
+
+  mask_type = build_vector_type (ssizetype, nunits);
   return vec_perm_indices_to_tree (mask_type, sel);
 }