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Re: locating unsigned type for non-standard precision

by Georg-Johann Lay-2 :: Rate this Message:

Richard Guenther wrote:

> Georg-Johann Lay wrote:
>> Georg-Johann Lay wrote:
>>> Richard Guenther wrote:
>>>> Georg-Johann Lay wrote:
>>>>> [...]
>>>>>
>>>>> http://gcc.gnu.org/PR51527
>>>>>
>>>>> It works with 4.8 trunk but crashes with 4.7.
>>>>> Did not yet track what changes made it work with 4.8, though.
>>>>> Unfortunately, noone remembers :-(
>>>>>
>>>>> http://gcc.gnu.org/ml/gcc/2012-03/msg00440.html
>>>> I have done changes in this area, trying to remove the type_for_size langhook.
>>>>
>>>> Richard.
>>> One apparent change is tree.c:signed_or_unsigned_type_for
>>>
>>> that changed [...] at 2012-03-12
>>>
>>> http://gcc.gnu.org/viewcvs?view=revision&revision=185226
>>>
>>> Is this appropriate to backport?
>
> No, it's not.
>
>>> Or is the preferred solution to override lang_hooks.types.type_for_size in the
>>> backend, if applicable?
>
> Neither. It is a "lang"-hook, not a target-hook after all.
>
> I already told you what the right fix is - the callers of
> type_for_size have to cater
> for the returned type to be of different precision. Btw, I already see it does
>
> /* But now perhaps TYPEX is as wide as INPREC.
> In that case, do nothing special here.
> (Otherwise would recurse infinitely in convert. */
> if (TYPE_PRECISION (typex) != inprec)
>
> Richard

Would you help me with the code? It's almost impossible to understand the
convert stuff for a noob. I tried TARGET_CONVERT_TO_TYPE

static tree
avr_convert_to_type (tree type, tree expr)
{
tree xtype = TREE_TYPE (expr);

/* convert enters infinite recursion for __int24 -> unsigned long
convertsions. */

if (/* From __int24 ... */
TREE_CODE (xtype) == INTEGER_TYPE
&& TYPE_PRECISION (xtype) == 24
&& !TYPE_UNSIGNED (xtype)
/* ... to unsigned long. */
&& TREE_CODE (type) == INTEGER_TYPE
&& TYPE_PRECISION (type) > 24
&& TYPE_UNSIGNED (type))
{
/* Perform an intermediate conversion:
__int24 -> long -> unsigned long */

/* Signed variant of type */
tree stype = lang_hooks.types.type_for_mode (TYPE_MODE (type), 0);

expr = convert (stype, expr);
// expr = build1 (CONVERT_EXPR, stype, expr);
expr = build1 (NOP_EXPR, type, expr);

return expr;
}

return NULL_TREE;
}

#undef TARGET_CONVERT_TO_TYPE
#define TARGET_CONVERT_TO_TYPE avr_convert_to_type

but with no avail. The explicit, intermediate conversion from __int24 to long
does not prevent the infinite recursion.

Johann

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