Hi! On Fri, Feb 10, 2023 at 10:59:52AM +0800, Xionghu Luo via Gcc-patches wrote: > The native RTL expression for vec_mrghw should be same for BE and LE as > they are register and endian-independent.
This isn't so obvious at all. All elements of these constructs are very much not endian-independent, because of very unfortunate choices in the meaning of some RTL constructs. It is possible all things in this negate all other things, but please show that then. > So both BE and LE need > generate exactly same RTL with index [0 4 1 5] when expanding vec_mrghw > with vec_select and vec_concat. > > (set (reg:V4SI 141) (vec_select:V4SI (vec_concat:V8SI > (subreg:V4SI (reg:V16QI 139) 0) > (subreg:V4SI (reg:V16QI 140) 0)) > [const_int 0 4 1 5])) With BE, if the source vecs are ABCD and EFGH, the vec_concat gives ABCDEFGH, and the vec_select than gives AEBF. What happens for LE? Segher
