Re: __int256

[Mike Stump <mikestump at comcast dot net>]

On Jul 13, 2012, at 1:57 AM, Richard Guenther wrote:
>> I have put the patch through the C test suite, and it doesn't show any failures.
>> 
>> Do you have any examples of bugs that are _introduced_ by my patch?  I'd be happy to fix any that arise.
> 
> No.  Just you expose the users to those bugs by exposing __int256 ;)  Docs
> should have a pretty big fat warning on it.

Ah, ok, thanks.  Now, the problem, OImode I believe is _already_ exposed to the user:

int __attribute__((mode(SI))) a;
int __attribute__((mode(OI))) b;

This just changes the exposure slightly to be higher visibility and a prettier interface in my opinion.  Also, notice, that exposure I believe is limited to ports that do this:

my_scalar_mode_supported_p (enum machine_mode mode)
{
  switch (mode)
    {
    case OImode:
      return true;
    default:
      return default_scalar_mode_supported_p (mode);
    }
}

_exclusively_.  As, in my code, it does this:

+    if (targetm.scalar_mode_supported_p (OImode))
+      {
+        int256_integer_type_node = make_signed_type (256);
+        int256_unsigned_type_node = make_unsigned_type (256);
+      }


and this:

+           case RID_INT256:
+             if (int256_integer_type_node == NULL_TREE)
+               {
+                 error_at (loc, "%<__int256%> is not supported for this target");
+                 return specs;
+               }

and this:

+  if (explicit_int256)
+    {
+      if (int256_integer_type_node == NULL_TREE)
+       {
+         error ("%<__int256%> is not supported by this target");
+         explicit_int256 = false;
+       }

so, I'm having a really hard time with the notion that this actually creates any new problems for anyone, even those that support OImode already.  I just checked all in tree gcc targets, and none claim OImode support.  Do you have any example of a testcase that shows a regression?  Any that shows a regression on any in tree port?  I can easily test, as I have compilers that don't have any OI support, compilers that have OI support, and compilers that have __int256 support.

As for documenting bugs, generally we don't do that.  Our intention is to actually spend time to fix all bugs, so, documenting them I don't feel is necessary.