[patch] change specific int128 -> generic intN

[Marc Glisse]

(Adding libstdc++@ in Cc: so they see the patch at
https://gcc.gnu.org/ml/gcc-patches/2014-06/msg01655.html )

On Sat, 21 Jun 2014, DJ Delorie wrote:

> New version of https://gcc.gnu.org/ml/gcc-patches/2014-04/msg00723.html
>
> This is a big patch, but it includes all the features/changes/support
> requested since the initial patch.  Tested with identical results
> before/after on x86-64 EXCEPT for g++.dg/ext/int128-1.C, which assumes
> __int128 is not supported with -std= but as per previous discussion,
> it now is (because __intN might be used for size_t, which is
> required).  Tested on msp430 with significant improvements but a few
> regressions (expected).
>
> This patch replaces the current int128 support with a generic intN
> support, which happens to provide int128 as well as up to three
> additional intN types per target.  I will post a separate patch for
> the msp430 backend demonstrating the use of this new feature for
> __int20, as well as a third to fix some problems with PSImode in
> general.
>
> The general idea is that genmodes has a new macro INT_N() for
> <tm>-modes.def, which gives the mode and precision to use for
> target-specific intN types.  These types are always created, but the
> parser will error with "unsupported" if the target does not support
> that mode for that compile (i.e. because of command line switches,
> etc).  There's an INT_N(TI,128) in the common sources.
>
> If the target defines any types larger than "long long", those types
> (like int128 before) will be used for type promotion, but types
> smaller than "long long" will not, to avoid confusing the C type
> promotion rules.  Otherwise, it's up to the source being compiled to
> specific __intN types as desired.

Nice. A couple quick comments on the parts I understand while
maintainers are resting for the week-end.

> Index: libstdc++-v3/src/c++11/limits.cc
> ===================================================================
[...]
> +#if !defined(__STRICT_ANSI__)

Since the test on __STRICT_ANSI__ is removed for all other uses, it would 
seem consistent to me to remove this one as well. Besides, you are already 
testing __GLIBCXX_USE_INT_N_0, which as far as I understand is protected 
by !flag_iso (with the exception of size_t).

> -#if !defined(__STRICT_ANSI__) && defined(_GLIBCXX_USE_INT128)
> +  // Conditionalizing on __STRICT_ANSI__ here will break any port that
> +  // uses one of these types for size_t.
> +#if defined(__GLIBCXX_USE_INT_N_0)
>   template<>
> -    struct __is_integral_helper<__int128>
> +    struct __is_integral_helper<__GLIBCXX_TYPE_INT_N_0>

Since the check for __STRICT_ANSI__ is removed, do we need to add
__extension__ in front of __GLIBCXX_TYPE_INT_N_0 to avoid warning with
-Wsystem-headers?

> --- gcc/cp/rtti.c	(revision 211858)
> +++ gcc/cp/rtti.c	(working copy)
> @@ -1506,31 +1506,44 @@ emit_support_tinfo_1 (tree bltn)
>
> void
> emit_support_tinfos (void)
> {
>   /* Dummy static variable so we can put nullptr in the array; it will be
>      set before we actually start to walk the array.  */
> -  static tree *const fundamentals[] =
> +  static tree * fundamentals[] =
>   {
>     &void_type_node,
>     &boolean_type_node,
>     &wchar_type_node, &char16_type_node, &char32_type_node,
>     &char_type_node, &signed_char_type_node, &unsigned_char_type_node,
>     &short_integer_type_node, &short_unsigned_type_node,
>     &integer_type_node, &unsigned_type_node,
>     &long_integer_type_node, &long_unsigned_type_node,
>     &long_long_integer_type_node, &long_long_unsigned_type_node,
> -    &int128_integer_type_node, &int128_unsigned_type_node,
>     &float_type_node, &double_type_node, &long_double_type_node,
>     &dfloat32_type_node, &dfloat64_type_node, &dfloat128_type_node,
> +#define FUND_INT_N_IDX 22
> +    // These eight are for intN_t nodes
> +    &nullptr_type_node, &nullptr_type_node, &nullptr_type_node, &nullptr_type_node,
> +    &nullptr_type_node, &nullptr_type_node, &nullptr_type_node, &nullptr_type_node,
>     &nullptr_type_node,
>     0
>   };
> -  int ix;
> +  int ix, i;
>   tree bltn_type, dtor;
>
> +  ix = FUND_INT_N_IDX;
> +  for (i = 0; i < NUM_INT_N_ENTS; i ++)
> +    if (int_n_enabled_p[i])
> +      {
> +	fundamentals [ix++] = &int_n_trees[i].signed_type;
> +	fundamentals [ix++] = &int_n_trees[i].unsigned_type;
> +      }
> +  fundamentals [ix++] = &nullptr_type_node;
> +  fundamentals [ix++] = 0;
> +
>   push_abi_namespace ();
>   bltn_type = xref_tag (class_type,
> 			get_identifier ("__fundamental_type_info"),
> 			/*tag_scope=*/ts_current, false);
>   pop_abi_namespace ();
>   if (!COMPLETE_TYPE_P (bltn_type))

That seems complicated. You just need to call emit_support_tinfo_1 on
each of the types (see how fundamentals is used at the end of the
function), no need to put everything in the array.

-- 
Marc Glisse