On 01/21/2015 11:52 PM, Richard Biener wrote: > On January 21, 2015 10:23:56 PM CET, Richard Henderson <r...@redhat.com> > wrote: >> On 12/29/2014 06:04 AM, Thomas Preud'homme wrote: >>> Since 16bit byteswap can be done via an 8 bit rotation (and it is the >> canonical form), >>> the check for an optab only serves to prevent the bswap optimization >> for >>> targets that don't have a 16bit byteswap (but do have a rotation >> instruction). See >>> PR63259 (comments 6 and onwards) for more details. >> >> I question the choice to have rotate be the canonical form. >> >> Doesn't this make things more complicated for targets that >> don't have rotate? Or, equivalently, no 16-bit rotate? >> That would seem to cover 99% of all 32-bit risc machines. > > I was asking for the generic expander to consider bswapHI. Rotates are > certainly more likely to get combined with sth else.
Maybe. Alternately, don't we canonicalize byte-swapping memory ops as (set (reg:HI) (bswap:HI (mem:HI))) (set (mem:HI) (bswap:HI (reg:HI))) Certainly this is true for powerpc. (It appears that both sparc and s390 are missing similar patterns, despite having instructions that can perform this operation...) r~ r~
