llvm dev - Nov 2007 - [LLVMdev] Two labels around one instruction in Codegen

Hi Evan,

Evan Cheng wrote:
>
> One way to solve this right now is to use flag value. But that means  
> ISD::LABEL, ISD::{S|U}DIV, ISD::LOAD, ISD::STORE will be marked  
> SDNPOutFlag and SDNPOptInFlag. But that's just yucky. Perhaps we need  
> to add new variants of these nodes and leave the current opcodes as  
> non-faulting. But I am not certain that's a very clean solution either.
>
>   
I think having variants (1) or differentiating ISD::{S|U}DIV from other
binary instructions (2) is what we would like to avoid.

Following what we discussed with Duncan, what if we generate the labels
around a basic block? Is there a way then to ensure that the begin and
end labels will actually bracket the instructions in the block? I've
found that currently it's not the case, but perhaps it can trigger an
easier solution than (1) or (2).

Thanks,
Nicolas
> Evan
>
>   
>> Thanks,
>> Nicolas
>>
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>>     
>
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>

On Nov 7, 2007, at 9:07 AM, Nicolas Geoffray wrote:
> Hi Evan,
>
> Evan Cheng wrote:
>>
>> One way to solve this right now is to use flag value. But that means
>> ISD::LABEL, ISD::{S|U}DIV, ISD::LOAD, ISD::STORE will be marked
>> SDNPOutFlag and SDNPOptInFlag. But that's just yucky. Perhaps we
need
>> to add new variants of these nodes and leave the current opcodes as
>> non-faulting. But I am not certain that's a very clean solution  
>> either.
>>
>>
>
> I think having variants (1) or differentiating ISD::{S|U}DIV from  
> other
> binary instructions (2) is what we would like to avoid.
>
> Following what we discussed with Duncan, what if we generate the  
> labels
> around a basic block? Is there a way then to ensure that the begin and
> end labels will actually bracket the instructions in the block? I've
> found that currently it's not the case, but perhaps it can trigger an
> easier solution than (1) or (2).
Ok, so it turns out the labels do not have to be just before / after  
the divide. So we don't have to use the MVT::Flag hackery. However,  
the second label must be after the divide. I think the solution is to  
add a trapping version of DIV (and others) and the second label can  
use its chain value as operand.

Evan
>
>
> Thanks,
> Nicolas
>
>> Evan
>>
>>
>>> Thanks,
>>> Nicolas
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

> Ok, so it turns out the labels do not have to be just before / after  
> the divide. So we don't have to use the MVT::Flag hackery. However,  
> the second label must be after the divide. I think the solution is to  
> add a trapping version of DIV (and others) and the second label can  
> use its chain value as operand.
How about a new "trapping" SDNode, which you can wrap trapping sdiv
and other instructions in?

D.