llvm dev - Jul 2015 - [LLVMdev] Is metadata the right thing to associate one instruction to another?

Background: I am still working on vectorizing (widening) a whole 
instruction tree (from the loads to the stores). I have all scalar loads 
in a SetVector and have created widened version of them (new instructions).

What would be very useful to have is the possibility to get to the 
vector load instruction from the scalar load in constant time. I was 
thinking to somehow add the vector load instruction (pointer) to the 
scalar version as metadata. With that, the traversal of the scalar tree 
can quickly get the vector version of the loads. But metadata seems to 
work with strings of MDNodes. That makes me worry if metadata is what I 
want..

My question: Is metadata the only possibility to 'associate' (in the 
sense of making it quickly accessible) an instruction to another? What 
type of metadata would be recommended ?

Thanks,
Frank

Hi Frank,

Can you just create a hash ScalarInstruction -> WidenedInstruction? This is
the way other vectorizers usually save such data.

I don’t know much about metadata, so I’ll leave this part of the question for
someone else:)

Michael
> On Jul 13, 2015, at 10:39 AM, Frank Winter <fwinter at jlab.org>
wrote:
> 
> Background: I am still working on vectorizing (widening) a whole
instruction tree (from the loads to the stores). I have all scalar loads in a
SetVector and have created widened version of them (new instructions).
> 
> What would be very useful to have is the possibility to get to the vector
load instruction from the scalar load in constant time. I was thinking to
somehow add the vector load instruction (pointer) to the scalar version as
metadata. With that, the traversal of the scalar tree can quickly get the vector
version of the loads. But metadata seems to work with strings of MDNodes. That
makes me worry if metadata is what I want..
> 
> My question: Is metadata the only possibility to 'associate' (in
the sense of making it quickly accessible) an instruction to another? What type
of metadata would be recommended ?
> 
> Thanks,
> Frank
> 
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev

Hi Michael!

Thanks for your reply, I appreciate the info how others do this. I was 
thinking of a hash function but was still hoping for a constant time 
solution :-)
Would be great to attach/store a (user) pointer to/along with an 
instruction..

Thanks,
Frank


On 07/13/2015 03:04 PM, Michael Zolotukhin wrote:
> Hi Frank,
>
> Can you just create a hash ScalarInstruction -> WidenedInstruction? This
is the way other vectorizers usually save such data.
>
> I don’t know much about metadata, so I’ll leave this part of the question
for someone else:)
>
> Michael
>> On Jul 13, 2015, at 10:39 AM, Frank Winter <fwinter at jlab.org>
wrote:
>>
>> Background: I am still working on vectorizing (widening) a whole
instruction tree (from the loads to the stores). I have all scalar loads in a
SetVector and have created widened version of them (new instructions).
>>
>> What would be very useful to have is the possibility to get to the
vector load instruction from the scalar load in constant time. I was thinking to
somehow add the vector load instruction (pointer) to the scalar version as
metadata. With that, the traversal of the scalar tree can quickly get the vector
version of the loads. But metadata seems to work with strings of MDNodes. That
makes me worry if metadata is what I want..
>>
>> My question: Is metadata the only possibility to 'associate'
(in the sense of making it quickly accessible) an instruction to another? What
type of metadata would be recommended ?
>>
>> Thanks,
>> Frank
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev