[LLVMdev] Legalizing truncating store using atomic load.

[Lei Mou]

Hi Ivan,

Thank you for your suggestion. I'll try that!

Regards,
Lei Mou

On Thu, May 31, 2012 at 5:30 PM, Ivan Llopard <ivanllopard at gmail.com> wrote:
> Hi Lei,
>
> Le 31/05/2012 03:44, Lei Mou a écrit :
>
>> Problem solved by returning the second result of the ATOMIC_LOAD_OR
>> node...
>
>
> You got the chain instead of the loaded value.
>
> IMHO, a better solution would have been to add a Pat<> rule to match
> truncstores and expand them into target store/load/and/or.
> Pat : <(truncstore16 GPR:$val, MEM:$mem),
>    (store MEM:$mem,
>        (or
>            (and (load MEM:$mem), (i32 0xffff0000))
>            , GPR:$val
>        )
>    )>;
>
> And you can also write a custom rule for truncstore8 if necessary. See other
> target BE's for examples.
>
> Ivan
>
>>
>> On Wed, May 30, 2012 at 9:38 PM, Lei Mou<lei.mou.uu at gmail.com>  wrote:
>>>
>>> Hi,
>>>
>>> Our target only has native support for i32 and f32 types. For data
>>> types smaller than these, I have to custom lowering truncating store
>>> using two atomic load instruction (which have the same semantics as
>>> ISD::ATOMIC_LOAD_AND and ATOMIC_LOAD_OR, respectively). I run into a
>>> problem during the legalization process, where the legalizer complains
>>> that ISD::STORE and ISD::ATOMIC_LOAD_OR (generated at step 3 in the
>>> following list) has different types.
>>>
>>> Here is the lowering steps:
>>> 1. Calculate a bitmask (e.g. 0xFFFF0000 for i16) indicating where to
>>> write the data;
>>> 2. Using atomic_load_and and the negated bitmask to clear the bits to
>>> be written;
>>> 3. Using atomic_load_or and the bitmask writing the result into the
>>> corresponding position.
>>>
>>> I'm not sure whether this could be done using custom lowering, so I'm
>>> writing to ask whether I'm on the right track:
>>> 1. If so, how to solve the type difference problem mentioned above;
>>> 2. If not, what is the right approach to solve this kind of problem.
>>>
>>> Any pointers and guidance are welcomed and appreciated. Thanks!
>>>
>>> Regards,
>>> Lei Mou
>>
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