[PATCH] Improve rotation by mode bitsize - 1 (take 2)

[Uros Bizjak]

On Mon, May 13, 2013 at 6:43 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Fri, May 10, 2013 at 07:15:38PM +0200, Jan Hubicka wrote:
>> It seems to me that it is not different from normalizing reg-10 into reg+(-10)
>> we do for years (and for good reason).  It is still target preference when use
>> add and when sub to perform the arithmetic, but it makes sense to keep single
>> canonical form of the expression both in RTL and Gimple.
>>
>> For example we may want to be able to prove that
>>   (rotate reg 31) == (rotatert reg 1)
>> is true or
>>   (rotate reg 30) == (rotatert reg 2)
>> is also true or cross jump both variants into one instruction.
>
> Ok, this patch reverts my earlier patch and does the canonicalization, for
> now for RTL only.  Bootstrapped/regtested on x86_64-linux and i686-linux, ok
> for trunk?
>
> 2013-05-13  Jakub Jelinek  <jakub@redhat.com>
>
>         * expmed.c (expand_shift_1): Canonicalize rotates by
>         constant bitsize / 2 to bitsize - 1.
>         * simplify-rt.x (simplify_binary_operation_1) <case ROTATE,
>         case ROTATERT>: Likewise.
>
>         Revert:
>         2013-05-10  Jakub Jelinek  <jakub@redhat.com>
>
>         * config/i386/i386.md (rotateinv): New code attr.
>         (*<rotate_insn><mode>3_1, *<rotate_insn>si3_1_zext,
>         *<rotate_insn>qi3_1_slp): Emit rorl %eax instead of
>         roll $31, %eax, etc.

You can revert your own patch without approval, so the patch approval
depends solely on the approval from ME maintainer.

Thanks,
Uros.