https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104124
--- Comment #3 from Michael Meissner <meissner at gcc dot gnu.org> --- There are two things going on. 1) There is no vspltisd instruction, so we can't generate a single instruction to load constants other than 0 or -1. Unfortunately, this was not added in either power9 or power10. 2) On the power9 and power10 we have the xxspltib and vecsb2d instructions, and we generate those if -mcpu=power9. To add support for new types of constants, the procedure is: 1) You need to modify easy_altivec_constant and gen_altivec_constant in rs6000.c (or rs6000.cc in GCC 12). Then add new predicates in predicate.md for these new patterns. 2) Look for the predicates "easy_vector_constant_add_self" and so forth in predicates.md and add a new predicate here. 3) Then in altivec.md, look for the define_splits that use the various easy_vector_const_* functions and add a new pattern.
