Re: [PATCH] rs6000: Don't ICE when we disassemble an MMA variable [PR101322]

["Kewen.Lin" <linkw@linux.ibm.com>]

>>>> +      if (TREE_TYPE (TREE_TYPE (src_ptr)) != src_type)
>>>
>>> This line looks unexpected, the former is type char while the latter is type __vector_pair *.
>>>
>>> I guess you meant to compare the type of pointer type like: 
>>>    
>>>    TREE_TYPE (TREE_TYPE (src_ptr)) != TREE_TYPE (src_type)
>>
>> Maybe?  However, if that is the case, how can it be working for me?
>> Let me throw this in the debugger and verify the types and I'll report
>> back with what I find.
> 
> Ok, you are correct.  Thanks for catching that!  I don't think we need
> those matching outer TREE_TYPE() uses.  I think just a simple:
> 
> 	if (TREE_TYPE (src_ptr) != src_type)
> 
> ...should suffice.
> 

Yeah, it's enough for the associated test case.  :)

> 
>>> or even with mode like:
>>>
>>>    TYPE_MODE (TREE_TYPE (TREE_TYPE (src_ptr))) != TYPE_MODE (TREE_TYPE (src_type))
> 
> I'd rather not look at the mode here, since OOmode/XOmode doesn't necessarily
> mean __vector_{pair,quad}, so I'll go with the modified test above.

Good point.  I thought the cv qualifier can affect the type equality check and
assumed for test case like:

void
foo (char *resp, const __vector_pair *vpp)
{
  __builtin_vsx_disassemble_pair (resp, (__vector_pair *) vpp);
}

, we don't want to have the conversion there and the ICE seems related to the
underlying mode, so I thought maybe you wanted to use TYPE_MODE.


>>>> +	src_ptr = build1 (VIEW_CONVERT_EXPR, src_type, src_ptr);
>>>
>>> Nit: NOP_EXPR seems to be better suited here for pointer conversion.
> 
> Ok, this works too, so code changed to use it.  Thanks!
> 
> Question for my own education, when would you use VIEW_CONVERT_EXPR over NOP_EXPR?

tree.def has some note about VIEW_CONVERT_EXPR, it quite matches what Segher replied.
In my experience, VIEW_CONVERT_EXPR are used a lot for vector type conversion.

BR,
Kewen