Re: [PATCH, rs6000] Correct programmer access to vperm for little endian

[David Edelsohn <dje dot gcc at gmail dot com>]

On Fri, Nov 15, 2013 at 12:45 PM, Bill Schmidt
<wschmidt@linux.vnet.ibm.com> wrote:
> Hi,
>
> A previous patch of mine was misguided.  It modified the altivec_vperm_*
> patterns to use the little endian conversion trick of reversing the
> input operands and complementing the permute control vector.
>
> Looking at the Altivec manual, we really can't do this.  These patterns
> need to be direct pass-throughs to the vperm instruction, as shown in
> Figure 4-95 on page 130 of
> http://www.freescale.com/files/32bit/doc/ref_manual/ALTIVECPIM.pdf.
> Section 4.2 on page 49 confirms that big-endian byte ordering is to be
> used with the Altivec instruction descriptions.
>
> This patch reverts that specific change, cleans up some associated
> commentary in another part, and modifies the one test case affected by
> the change.  gcc.dg/vmx/3b-15.c performs the argument reversal and
> control vector complementing in the source code, as all users will need
> to do when porting code containing vec_perm calls to little endian.
>
> Bootstrapped and tested on powerpc64{,le}-unknown-linux-gnu with no
> regressions.  Is this ok for trunk?
>
> Thanks,
> Bill
>
>
> gcc:
>
> 2013-11-15  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
>
>         * config/rs6000/altivec.md (UNSPEC_VPERM_X, UNSPEC_VPERM_UNS_X):
>         Remove.
>         (altivec_vperm_<mode>): Revert earlier little endian change.
>         (*altivec_vperm_<mode>_internal): Remove.
>         (altivec_vperm_<mode>_uns): Revert earlier little endian change.
>         (*altivec_vperm_<mode>_uns_internal): Remove.
>         * config/rs6000/vector.md (vec_realign_load_<mode>): Revise
>         commentary.
>
> gcc/testsuite:
>
> 2013-11-15  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>
>
>         * gcc.dg/vmx/3b-15.c: Revise for little endian.

Okay.

Thanks, David