Re: [PATCH] Pr 68805, Fix PowerPC little endian -mvsx-timode

[David Edelsohn <dje.gcc@gmail.com>]

On Wed, Dec 16, 2015 at 6:20 PM, Michael Meissner
<meissner@linux.vnet.ibm.com> wrote:
> My first mail did not seem to be delivered, so I'm trying again.
>
> This fixes a bug with the debug switch -mvsx-timode that we would eventually
> like to enable by default on PowerPC little endian server systems.  The bug is
> that the load with rotate or rotate with store instructions needed on power8
> little endian systems used VEC_SELECT to swap the 64-bit words.  This patch
> uses ROTATE for TImode, just like I did for KFmode.
>
> Without this patch, 10 of the 30 spec 2006 benchmarks fail to compile on a
> little endian PowerPC system with -mvsx-timode.  With the patch, all 30
> benchmarks compile and do the spec verification.
>
> In developing the patch, I noticed that the generic swap optimizations that are
> done for vector types are not done for TImode, since we don't split the TImoves
> until after register allocation when we discover a vector register was used
> instead of a GPR register.  So, I added a peephole2 to catch the common case of
> store followed by load, eliminating the pair of ROTATE insns.
>
> I bootstrapped it on both a big endian power7 and a little endian power8 system
> with no regressions.  Is it ok to install on the trunk?
>
> At the current time, I don't see the need to back port it to GCC 5 (though the
> backport is fairly simple), because it isn't on by default in GCC 5, and we
> don't plan to eventually have -mvsx-timode and -mlra on by default in that
> branch.
>
> [gcc]
> 2015-12-15  Michael Meissner  <meissner@linux.vnet.ibm.com>
>
>         PR target/68805
>         * config/rs6000/rs6000.c (rs6000_gen_le_vsx_permute): Use ROTATE
>         instead of VEC_SELECT for TImode.
>
>         * config/rs6000/vsx.md (VSX_LE): Move TImode from VSX_LE to
>         VSX_LE_128, so that we use ROTATE to swap the 64-bit words instead
>         of using VEC_SELECT.
>         (VSX_LE_128): Likewise.
>         (define_peephole2): Add peephole to eliminate double xxpermdi when
>         copying TImode.
>
> [gcc/testsuite]
> 2015-12-15  Michael Meissner  <meissner@linux.vnet.ibm.com>
>
>         PR target/68805
>         * gcc.target/powerpc/pr68805.c: New test.

Okay.

Thanks, David