On 11/18/18 8:44 AM, Michael Eager wrote:
> On 11/16/18 14:50, Segher Boessenkool wrote:
>> Hi!
>>
>> On Wed, Nov 14, 2018 at 11:22:58AM -0800, Michael Eager wrote:
>>> The (mem:SI) is converted to (mem:QI).
>>>
>>> The return from make_extract() is
>>> (zero_extract:SI (mem:QI (reg/v/f:SI 50 [ gp ]))
>>> (const_int 1 [0x1])
>>> (const_int 2 [0x2]))
>>>
>>> The target has an instruction pattern for zero_extract, but it matches
>>> SI values, not QI. So the instruction which implements a test of a bit
>>> flag is never generated.
>>
>> The RTL documentation says:
>>
>> If @var{loc} is in memory, its mode must be a single-byte integer
>> mode.
>>
>> But obviously various ports use other modes, too. I wonder if that ever
>> worked well.
>
> Thanks. I hadn't noticed this.
>
> Does anyone have any idea why there is a restriction on the mode?
> Other instruction patterns don't place arbitrary restriction on the
> memory access mode.
Not offhand. BUt it's been around for a long time (at least since the
early 90s). I stumbled over it several times through the years. It
could well be an artifact of the m68k or the vax.
Jeff
