[LLVMdev] LLVM Loop Vectorizer

[Hal Finkel]

----- Original Message -----
> From: "Micah Villmow" <Micah.Villmow at amd.com>
> To: "Dibyendu Das" <Dibyendu.Das at amd.com>, "Nadav Rotem" <nrotem at apple.com>, "llvmdev at cs.uiuc.edu Mailing List"
> <llvmdev at cs.uiuc.edu>
> Sent: Friday, October 5, 2012 10:32:17 AM
> Subject: Re: [LLVMdev] LLVM Loop Vectorizer
> 
> Why not just have a hook into the TargetInstrInfo to query for the
> cost of an instruction? This is already used in many places
> throughout the optimizers.

Makes sense to me.

 -Hal

> 
> > -----Original Message-----
> > From: llvmdev-bounces at cs.uiuc.edu
> > [mailto:llvmdev-bounces at cs.uiuc.edu]
> > On Behalf Of Das, Dibyendu
> > Sent: Friday, October 05, 2012 2:00 AM
> > To: Nadav Rotem; llvmdev at cs.uiuc.edu Mailing List
> > Subject: Re: [LLVMdev] LLVM Loop Vectorizer
> > 
> > I think we should try to abstract the costs of instructions of
> > various
> > targets instead of trying to replicate them exactly. The coarser
> > the
> > costing infrastructure the more robust will be the vectorization
> > pass.
> > Also this eliminates/reduces the need of updating the costing
> > infrastructure as and when new h/w reduces the cost(s) of existing
> > instructions.
> > - Dibyendu
> > 
> > -----Original Message-----
> > From: llvmdev-bounces at cs.uiuc.edu
> > [mailto:llvmdev-bounces at cs.uiuc.edu]
> > On Behalf Of Nadav Rotem
> > Sent: Friday, October 05, 2012 11:45 AM
> > To: llvmdev at cs.uiuc.edu Mailing List
> > Subject: [LLVMdev] LLVM Loop Vectorizer
> > 
> > Hi,
> > 
> > We are starting to work on an LLVM loop vectorizer. There's number
> > of
> > different projects that already vectorize LLVM IR. For example
> > Hal's
> > BB-Vectorizer, Intel's OpenCL Vectorizer, Polly, ISPC, AnySL, just
> > to
> > name a few. I think that it would be great if we could collaborate
> > on
> > the areas that are shared between the different projects. I think
> > that
> > refactoring LLVM in away that would expose target information to
> > IR-
> > level transformations would be a good way to start. Vectorizers, as
> > well as other IR-level transformations, require target-specific
> > information, such as the cost of different instruction or the
> > availability of certain features. Currently, llvm-based vectorizers
> > do
> > not make use of this information, or just hard-code target
> > information.
> > A loop vectorizer would need target information. After we have some
> > basic target information infrastructure in place we can start
> > discussing the vectorizer itself.
> > 
> > I think that the first step would be to expose Target Lowering
> > Interface (TLI) to OPT's IR-level passes. Currently TLI is only
> > available in LLC. I suggest that we merge LLC and OPT into a single
> > tool that will drive both IR-level passes and the codegen. LLC and
> > OPT
> > can remain as wrappers around the new tool. Please let me know if
> > you
> > can think of a good name for the new tool. I was thinking that
> > "llvm-
> > cli" may be a good name (cli = command line interface). OPT and LLC
> > are
> > only used by LLVM developers, so the impact of this change on the
> > user
> > community would be small.
> > 
> > Thanks,
> > Nadav
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> > 
> > 
> > 
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> 
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-- 
Hal Finkel
Postdoctoral Appointee
Leadership Computing Facility
Argonne National Laboratory