[PATCH] Improvde code quality of vselect

[Michael Liao]

Thanks. Committed in r179267.

- Michael

On Wed, 2013-04-10 at 22:08 -0700, Nadav Rotem wrote:
> Oh yes, I see. I read the code and it LGTM.  Thanks Michael.
> 
> On Apr 10, 2013, at 9:17 PM, Michael Liao <michael.liao at intel.com>
> wrote:
> 
> > Hi Nadav
> > 
> > This patch addresses different issue from simplify-demanded-bits,
> > where
> > condition in vselect is simplified regarding to BLEND* only takes
> > the
> > highest bit. This patch address the issue regarding to the value
> > being
> > selected not the selector. Says, V := select Cond, A, B. When A, or
> > B or
> > both of them are all 0s or all 1s. We could exploit the fact that
> > packed
> > comparison will generated all 0s or 1s in each SIMD lane. Such
> > select
> > could be reduced to an AND/OR or simply removed.
> > 
> > Yours
> > - Michael
> > 
> > 
> > 
> > On Wed, 2013-04-10 at 17:30 -0700, Nadav Rotem wrote:
> > > Michael, 
> > > 
> > > 
> > > I think that the best way to handle the redundant sign-extending
> > > is to
> > > improve the simplify-demanded-bits optimization.  Last year I
> > > added
> > > some code to optimize the X86::VSELECT using
> > > simplify-demanded-bits.
> > > Do you know why it does not work ?
> > > 
> > > 
> > > Thanks,
> > > Nadav
> > > 
> > > On Apr 10, 2013, at 4:48 PM, Michael Liao <michael.liao at intel.com>
> > > wrote:
> > > 
> > > > Hi,
> > > > 
> > > > As we canonicalize sext from i1 to select in instcomb, it
> > > > generates
> > > > redundant code to prepare all 0s and all 1s if we don't take it
> > > > into
> > > > account that, in SSE/AVX, packed comparisons output all 0s or 1s
> > > > in
> > > > SIMD lanes. The attached patch adds optimization for those cases
> > > > and
> > > > transforms select into AND/OR to reduce BLEND pressure when
> > > > profitable.
> > > > 
> > > > Thanks for review
> > > > - Michael
> > > > 
> > > > <0001-Add-optimization-to-leverage-all-0s-1s-produced-by-p.patch>_______________________________________________
> > > > llvm-commits mailing list
> > > > llvm-commits at cs.uiuc.edu
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> 
>