[llvm-commits] Vectors of Pointers and Vector-GEP

Rotem, Nadav nadav.rotem at intel.com
Tue Nov 29 09:35:24 PST 2011


I agree with you, scatter/gather and predication are orthogonal concepts. In theory, you could implement load/store predication using scatter/gather instructions by loading/storing to dedicated 'dead' stack slots. Having said that, I don't know of any architecture which has scatter/gather but does not have predicated instructions. 

Looking onward, I definitely want to see LLVM support predicated architectures. Dan Gohman had some excellent ideas on different way this can be done. As soon as I finish stabilizing the pointer-vector patch, and implement scatter/gather intrinsics, I would like to start a discussion on the implementation of predicated instructions in LLVM. 


-----Original Message-----
From: David A. Greene [mailto:greened at obbligato.org] 
Sent: Tuesday, November 29, 2011 18:18
To: David A. Greene
Cc: Rotem, Nadav; llvm-commits at cs.uiuc.edu; LLVM Developers Mailing List
Subject: Re: [llvm-commits] Vectors of Pointers and Vector-GEP

greened at obbligato.org (David A. Greene) writes:

> "Rotem, Nadav" <nadav.rotem at intel.com> writes:
>> Following the discussion in last week’s LLVM developers conference I
>> started working on support for vectors-of-pointers.  Vectors of
>> pointers are needed for supporting scatter/gather operations and are
>> the first step in the direction of supporting predicated
>> architectures.

I just want to make clear that gather/scatter and prediction are
orthogonal concepts.  You don't need one to do the other.  You can use
scatter/gather to vectorize conditional code but it's not the same as
true predication, which is generally much more efficient.

Intel Israel (74) Limited

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