[LLVMdev] Is metadata the right thing to associate one instruction to another? (original) (raw)

Hal Finkel hfinkel at anl.gov
Tue Jul 21 20:08:58 PDT 2015

----- Original Message -----

From: "Frank Winter" <fwinter at jlab.org> To: "Michael Zolotukhin" <mzolotukhin at apple.com> Cc: llvmdev at cs.uiuc.edu Sent: Monday, July 13, 2015 2:37:00 PM Subject: Re: [LLVMdev] Is metadata the right thing to associate one instruction to another?

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 :-)

Hash tables give you average O(1) lookups, and I think that's as good as you're going to get. We have to guard the size of Instruction objects pretty carefully.

Would be great to attach/store a (user) pointer to/along with an instruction..

The metadata entries are not stored in the Instruction object either (except for debug metadata, but that's a hard-coded special case). For everything else, you're going through a hash table.

-Hal

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

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-- Hal Finkel Assistant Computational Scientist Leadership Computing Facility Argonne National Laboratory

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