[LLVMdev] Modularizing LICM

[Nema, Ashutosh]

Thanks Philip and Bruno.

I agree with Bruno’s suggestion, we can expose LICM core functionality(i.e. SinkRegion, HoistRegion, PromoteAliasSet) in LoopUtils.

Below are high level changes identified for it:

1) Expose SinkRegion, HoistRegion, PromoteAliasSet functions in LoopUtils.h
These functions will be accepting all the required analysis and pre-requisite.
i.e.:  AliasAnalysis* , LoopInfo *, DominatorTree *, DataLayout *, TargetLibraryInfo *, Loop * , AliasSetTracker *

2) Implementation of SinkRegion, HoistRegion, PromoteAliasSet & supporting functions will be in a new file inside Utils.
(i.e.: /llvm/lib/Transforms/Utils/LICMCore.cpp)
These functions will first ensure the pre-requisite then only perform actions.
If any pre-requisite is un-available then the simply return.
LICM will no more have implementation for SinkRegion, HoistRegion, PromoteAliasSet and supporting functions.

3) LoopPromoter will be moved to Utils (i.e. LICMCore.cpp)

4) Who ever makes call to SinkRegion, HoistRegion, PromoteAliasSet has responsibility to pass required analysis and pre-requisites.

5) LICM pass will became more like a wrapper pass, calling SinkRegion, HoistRegion, PromoteAliasSet defined in Utils.

Suggestions are welcome.

Regards,
Ashutosh

-----Original Message-----
From: Bruno Cardoso Lopes [mailto:bruno.cardoso at gmail.com] 
Sent: Tuesday, December 23, 2014 4:25 AM
To: Philip Reames
Cc: LLVM Developers Mailing List; Nema, Ashutosh
Subject: Re: [LLVMdev] Modularizing LICM

One way you could go is to expose the interface in include/llvm/Transforms/Utils/LoopUtils.h. There's a similar approach in the LCSSA and LoopSimplify passes, both define functions used by other passes (e.g LoopUnroll and LICM).

On Fri, Dec 19, 2014 at 10:58 PM, Philip Reames <listmail at philipreames.com> wrote:
> I've come across similar use cases recently.  In particular, there are 
> some cases where I'd like run HoistRegion on a particular basic block 
> after loop unswitching.
>
> I would be open to reviewing patches if you wanted to send them.  I 
> may get around to doing so myself eventually, but it's fairly low on 
> my priority list.
>
> Philip
>
>
> On 12/15/2014 04:16 AM, Nema, Ashutosh wrote:
>
> Hi,
>
>
>
> I’m writing a new loop pass, and has a need to call LICM(Loop 
> Invariant Code
> Motion) ‘PromoteAliasSet’ on modified loop.
>
>
>
> For now I didn’t found any why to call ‘PromoteAliasSet’ from my pass 
> explicitly.
>
>
>
> The only way is to schedule LICM pass after my pass.
>
>
>
> For some reason my pass need more control and preferring to call LICM 
> ‘PromoteAliasSet’ instead running full LICM as next pass.
>
>
>
> Can LICM be more modular by exposing wrapper functions for its core 
> functionalities (i.e. SinkRegion, HoistRegion, PromoteAliasSet) ?
>
>
>
> These wrappers will check pre-requisite(i.e. AliasAnalysis, LoopInfo 
> availability ) and call appropriate functions.
>
>
>
> Regards,
>
> Ashutosh
>
>
>
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--
Bruno Cardoso Lopes
http://www.brunocardoso.cc