[LLVMdev] Inserting a custom switch instruction implementation in backend

[Marcello Maggioni]

Thanks Hal, I take this into consideration in case I decide to go for a 
custom lowering in the IR.

Il 21/09/2013 23:28, Hal Finkel ha scritto:
> ----- Original Message -----
>> Hello
>>
>> Probably the easiest way for you is to lower switch instructions via
>> IR-to-IR pass in the way you want.
> In case it helps, lib/Transforms/Utils/LowerSwitch.cpp does generic switch lowering. You might be able to use that as a base for what you need to do.
>
>   -Hal
>
>> On Sat, Sep 21, 2013 at 3:43 PM, Marcello Maggioni
>> <marcello at codeplay.com> wrote:
>>> Hi,
>>>
>>> in implementing a backend for a target we work on, I ended up
>>> needing to
>>> lower the switch instruction in a very specific way that is quite
>>> different
>>> from the standard llvm way with the decision trees.
>>>
>>> The custom implementation wants to get rid of the decision blocks
>>> that llvm
>>> generates between the actual cases basic blocks and the switch root
>>> block.
>>> What I do currently is basically deleting these blocks manually and
>>> moving
>>> all the successors (updating the PHIs) to the switch root block and
>>> splicing
>>> the instructions in the decision blocks into the switch root block
>>> manually
>>> and then proceed to the removal of these blocks.
>>>
>>> This seems to work fine, but is a solution that I not like very
>>> much. I
>>> would prefer being able to lower the switch instructions in my own
>>> way
>>> directly instead of having to let llvm do it its own way and
>>> "morph" the
>>> result into my own.
>>>
>>> There is a clean way to custom lower the switch instruction in the
>>> backend
>>> without substituting the entire SelectionDAGBuilder?
>>>
>>> Cheers,
>>> Marcello
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>
>>
>> --
>> With best regards, Anton Korobeynikov
>> Faculty of Mathematics and Mechanics, Saint Petersburg State
>> University
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