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Re: [RFC] Consider lrotate const rotation in vectorizer

On Thu, Jul 18, 2019 at 04:12:48PM +0100, Richard Earnshaw (lists) wrote:
> On 17/07/2019 18:00, Segher Boessenkool wrote:
> >On Wed, Jul 17, 2019 at 12:54:32PM +0200, Jakub Jelinek wrote:
> >>On Wed, Jul 17, 2019 at 12:37:59PM +0200, Richard Biener wrote:
> >>>I'm not sure if it makes sense to have both LROTATE_EXPR and
> >>>RROTATE_EXPR on the GIMPLE level then (that CPUs only
> >>>support one direction is natural though).  So maybe simply get
> >>>rid of one?  Its semantics are also nowhere documented
> >>
> >>A lot of targets support both,
> >
> >Of all the linux targets, we have:
> >
> >No rotate:
> >   alpha microblaze riscv sparc
> >
> >Both directions:
> >   aarch64 c6x ia64 m68k nios2 parisc sh x86 xtensa
> AArch64 is Right only.

This is whether a port has any rotate resp. rotatert in recog, which
generates HAVE_rotate and HAVE_rotatert in insn-config.h .

If the hardware can only do right rotates you should either handle
immediate left rotates everywhere as well, or avoid using left rotates
in define_expand and define_insn.


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