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From: "marc.glisse at normalesup dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/51033] generic vector subscript and shuffle support was not added to C++
Date: Sun, 22 Apr 2012 13:22:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51033

--- Comment #20 from Marc Glisse <marc.glisse at normalesup dot org> 2012-04-22 13:21:14 UTC ---
(In reply to comment #19)
> Created attachment 27217 [details]
> shuffle

Doesn't work with -std=c++11, which requires:

--- semantics.c    (revision 186667)
+++ semantics.c    (working copy)
@@ -5603,11 +5603,12 @@ float_const_decimal64_p (void)

 bool
 literal_type_p (tree t)
 {
   if (SCALAR_TYPE_P (t)
-      || TREE_CODE (t) == REFERENCE_TYPE)
+      || TREE_CODE (t) == REFERENCE_TYPE
+      || TREE_CODE (t) == VECTOR_TYPE)
     return true;
   if (CLASS_TYPE_P (t))
     {
       t = complete_type (t);
       gcc_assert (COMPLETE_TYPE_P (t) || errorcount);
@@ -8487,10 +8488,11 @@ potential_constant_expression_1 (tree t,
                           want_rval, flags))
       return false;
       return true;

     case FMA_EXPR:
+    case VEC_PERM_EXPR:
      for (i = 0; i < 3; ++i)
       if (!potential_constant_expression_1 (TREE_OPERAND (t, i),
                         true, flags))
     return false;
      return true;


And then I still need to write a cxx_eval_vec_perm function so the result of
__builtin_shuffle can be constexpr. I haven't seen how the C front-end handles
shuffles of constants. Maybe a "sorry" would do for now.