Add a pass to convert aggregate loads/stores into scalar load stores

[Hal Finkel]

----- Original Message -----
> From: "deadal nix" <deadalnix at gmail.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Chandler Carruth" <chandlerc at google.com>, "llvm-commits" <llvm-commits at cs.uiuc.edu>, "Philip Reames"
> <listmail at philipreames.com>
> Sent: Thursday, October 30, 2014 11:58:21 PM
> Subject: Re: Add a pass to convert aggregate loads/stores into scalar load stores
> 
> 2014-10-30 21:52 GMT-07:00 Hal Finkel < hfinkel at anl.gov > :
> 
> 
> ----- Original Message -----
> > From: "deadal nix" < deadalnix at gmail.com >
> > To: "Philip Reames" < listmail at philipreames.com >
> > Cc: "Chandler Carruth" < chandlerc at google.com >, "Hal Finkel" <
> > hfinkel at anl.gov >, "llvm-commits"
> > < llvm-commits at cs.uiuc.edu >
> > Sent: Thursday, October 30, 2014 11:45:12 PM
> > Subject: Re: Add a pass to convert aggregate loads/stores into
> > scalar load stores
> > 
> > Option 4 - Transform to series of smaller integer loads
> > - This appears to be what this patch implements. Not entirely sure
> > why this was chosen.
> > 
> > 
> > Yes, this is what this diff is doing.
> > 
> > 
> > This option allow to keep pointerness of load/stores (it could be
> > refined in this patch, but the idea is there). It also avoid to
> > generate a bunch of small load when a big load would suffice.
> > 
> > 
> > Making a big load of iN (option 2) is also reasonable, but in this
> > case, the load won't respect the target alignment's constraints. I
> > thought it was a problem so I went for the option 3 instead.
> 
> You can manually set the alignment on the load to be whatever you
> need (down to align 1).
> 
> -Hal
> 
> I wasn't sure how well it is supported and wanted to avoid to open a
> new can of worms. If you think this is a better approach, I can
> update the diff in that direction.

It is well supported. I think it is a better approach, and I'll comment on why shortly.

 -Hal

> 

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