llvm dev - May 2019 - Assigning custom information to IR instruction and passing it to its correspondent in Selection DAG

Hello,



I’m looking for the best approach which would allow for marking given LLVM
IR instruction during IR custom pass and later utilizing that information
during DAG Instruction Selection in order to match given pattern based on
this marking.



I’m wondering if marking IR instruction utilizing Metadata is good idea.

But how later pass that information to DAG and appropriately mark in
DAGBuilder SDNode, which represents the earlier marked instruction in IR?



Any suggestion how to implement the most efficiently?

I’m expecting there are already similar solutions – maybe someone would be
able to indicate the exact example?



Thanks in advance,

Przemek
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Hi,
as I wrote in mu previous post I wanted to somehow mark one IR instruction
(in this particular case it would be 'load') during dedicated pass,
which
will set the marking based on neighboring instructions. Next I wanted to
somehow to convey this marking from 'load' IR instruction to
'load' SDNode
in order to use it during DAG Instruction Selection - information stored in
this marking would 'enable' or 'disable' particular pattern... I
was
thinking about usage metadata for it, but I didn't get any feedback.
So now I'm wondering if solution with metadata is the best one or it maybe
it doesn't make any sense an something else would be better.

I don't have big experience with metadata, but what I've read it would
allow for customizing IR instruction without modifying the instruction. Or
maybe I'm unnecessarily thinking about metadata, because 'load'
instruction
has already some fields which could be used for storing 'flags', which
might represent any custom information. Obviously I don't want to modify
'load'.
Any suggestions?

Thanks,
Przemek



On Thu, Apr 25, 2019 at 11:54 AM Przemyslaw Ossowski <
przemyslaw.ossowski at googlemail.com> wrote:
> Hello,
>
>
>
> I’m looking for the best approach which would allow for marking given LLVM
> IR instruction during IR custom pass and later utilizing that information
> during DAG Instruction Selection in order to match given pattern based on
> this marking.
>
>
>
> I’m wondering if marking IR instruction utilizing Metadata is good idea.
>
> But how later pass that information to DAG and appropriately mark in
> DAGBuilder SDNode, which represents the earlier marked instruction in IR?
>
>
>
> Any suggestion how to implement the most efficiently?
>
> I’m expecting there are already similar solutions – maybe someone would be
> able to indicate the exact example?
>
>
>
> Thanks in advance,
>
> Przemek
>
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On Tue, Apr 30, 2019 at 3:51 PM Przemyslaw Ossowski via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
> as I wrote in mu previous post I wanted to somehow mark one IR instruction
> (in this particular case it would be 'load') during dedicated pass,
which
> will set the marking based on neighboring instructions. Next I wanted to
> somehow to convey this marking from 'load' IR instruction to
'load' SDNode
> in order to use it during DAG Instruction Selection - information stored in
> this marking would 'enable' or 'disable' particular
pattern... I was
> thinking about usage metadata for it, but I didn't get any feedback.
> So now I'm wondering if solution with metadata is the best one or it
maybe
> it doesn't make any sense an something else would be better.
>
> I don't have big experience with metadata, but what I've read it
would
> allow for customizing IR instruction without modifying the instruction. Or
> maybe I'm unnecessarily thinking about metadata, because 'load'
instruction
> has already some fields which could be used for storing 'flags',
which
> might represent any custom information. Obviously I don't want to
modify
> 'load'.
> Any suggestions?
>
In general metadata aren't recommended for carrying semantically important
information as they can be dropped at any time.

What about using a target specific intrinsic? Your pass could convert the
instructions to your intrinsic that you can then easily match in
SelectionDAG.

-- 
Mehdi


>
>
>
> On Thu, Apr 25, 2019 at 11:54 AM Przemyslaw Ossowski <
> przemyslaw.ossowski at googlemail.com> wrote:
>
>> Hello,
>>
>>
>>
>> I’m looking for the best approach which would allow for marking given
>> LLVM IR instruction during IR custom pass and later utilizing that
>> information during DAG Instruction Selection in order to match given
>> pattern based on this marking.
>>
>>
>>
>> I’m wondering if marking IR instruction utilizing Metadata is good
idea.
>>
>> But how later pass that information to DAG and appropriately mark in
>> DAGBuilder SDNode, which represents the earlier marked instruction in
IR?
>>
>>
>>
>> Any suggestion how to implement the most efficiently?
>>
>> I’m expecting there are already similar solutions – maybe someone would
>> be able to indicate the exact example?
>>
>>
>>
>> Thanks in advance,
>>
>> Przemek
>>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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