[Bug tree-optimization/61559] FAIL: gcc.dg/builtin-bswap-8.c on i686 with -mmovbe

[rguenther at suse dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61559

--- Comment #14 from rguenther at suse dot de <rguenther at suse dot de> ---
On Thu, 4 Sep 2014, ubizjak at gmail dot com wrote:

> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61559
> 
> --- Comment #12 from Uroš Bizjak <ubizjak at gmail dot com> ---
> (In reply to Uroš Bizjak from comment #11)
> 
> > This one should be:
> > 
> >     (simplify
> >       (bswap (bitop (bswap @0) (bswap @1)))
> >       (bitop @0 @1))
> 
> Oh, we already have this. Please disregard this message.

Not sure - we don't exactly have it.  OTOH I think
that

    (simplify
      (bitop (bswap @0) (bswap @1))
      (bswap (bitop @0 @1)))

is profitable in most cases (not only when wrapped inside another
bswap).  Jakubs concern applies though.

OTOH

    (simplify
      (bswap (bitop (bswap @0) INTEGER_CST@1))
      (bitop @0 (bswap @1)))))

may generally apply (not only to INTEGER_CST 2nd operand to bitop).
The argument would be that one bswap goes away.  But again if
@0 was a memory and @1 is not then this isn't always profitable(?)
(well, the outer bswap goes away).

So merge the restricted first one and this to

   (simplify
     (bswap (bitop:c (bswap @0) @1))
     (bitop @0 (bswap @1)))

?  Thus only one operand of the bitop needs to be a bswap if
there is an outer bswap.  For constant @1 the inner bswap
will be folded away as well as if @1 is a bswap itself.


/* PR61559.  Transforms for gcc.dg/builtin-bswap-8.c  */
(for bswap in BUILT_IN_BSWAP16 BUILT_IN_BSWAP32 BUILT_IN_BSWAP64
  (simplify
    (bswap (bswap @0))
    @0)
  (simplify
    (bswap (bit_not (bswap @0)))
    (bit_not @0))
  (for bitop in bit_xor bit_ior bit_and
    /* This might not be profitable if the inner bswaps are
       free because @0 and @1 are memory operands and the
       target has an instruction for load+bswap.  */
    (simplify
      (bitop (bswap @0) (bswap @1))
      (bswap (bitop @0 @1)))
    (simplify
      (bswap (bitop:c (bswap @0) @1))
      (bitop @0 (bswap @1)))))