llvm dev - Dec 2014 - [LLVMdev] Generating code for target with immediate constant?

To generate code for a target which doesn't have immediate constant as
instruction operand, do I (the target specific back-end, XXXTarget) need to
provide code to break up the SDNode with constant (like ISD::ADD $reg1, #1)
to 2 SDNodes (ISD::LOAD $reg2, #1; ISD::ADD $reg1, $reg2) in my
XXXTargetLowering::LowerOperation, or LLVM target-independent framework can
do such transformation automatically with my instruction pattern definition?

Thanks
-Thomson
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Usually what you would do is having load matching the pattern of a constant
or another solution is Custom Selecting (in ISelDAGToDAG) the ISD::Constant
and expanding it to your LoadImmediate instruction that takes as input a
TargetConstant (a kind of constant that skips selection).

You also need to make sure that none of your instructions that shouldn't
accept constants match constants in their patterns/custom selection

Cheers,
Marcello

2014-12-23 19:17 GMT-08:00 Thomson <lilotom at gmail.com>:
> To generate code for a target which doesn't have immediate constant as
> instruction operand, do I (the target specific back-end, XXXTarget) need to
> provide code to break up the SDNode with constant (like ISD::ADD $reg1, #1)
> to 2 SDNodes (ISD::LOAD $reg2, #1; ISD::ADD $reg1, $reg2) in my
> XXXTargetLowering::LowerOperation, or LLVM target-independent framework can
> do such transformation automatically with my instruction pattern
definition?
>
> Thanks
> -Thomson
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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Thanks. Besides the suggestions, is it possible to handle this in Legalize
phase of SelectionDAG? I found that SelectionDAGLegalize could mark an
operation (SDNode) and value type (VT) as custom lowering (morph the
SDNode) via TargetLoweringBase::setOperationAction, but it seems this
doesn't support marking ISD::ADD $reg, #const since it has 2 value types.

-Thomson

On Wed, Dec 24, 2014 at 12:06 PM, Marcello Maggioni <hayarms at gmail.com>
wrote:
> Usually what you would do is having load matching the pattern of a
> constant or another solution is Custom Selecting (in ISelDAGToDAG) the
> ISD::Constant and expanding it to your LoadImmediate instruction that takes
> as input a TargetConstant (a kind of constant that skips selection).
>
> You also need to make sure that none of your instructions that
shouldn't
> accept constants match constants in their patterns/custom selection
>
> Cheers,
> Marcello
>
> 2014-12-23 19:17 GMT-08:00 Thomson <lilotom at gmail.com>:
>
>> To generate code for a target which doesn't have immediate constant
as
>> instruction operand, do I (the target specific back-end, XXXTarget)
need to
>> provide code to break up the SDNode with constant (like ISD::ADD $reg1,
#1)
>> to 2 SDNodes (ISD::LOAD $reg2, #1; ISD::ADD $reg1, $reg2) in my
>> XXXTargetLowering::LowerOperation, or LLVM target-independent framework
can
>> do such transformation automatically with my instruction pattern
definition?
>>
>> Thanks
>> -Thomson
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>
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