https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65368
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> --- (In reply to Uroš Bizjak from comment #5) > (In reply to Jakub Jelinek from comment #3) > > For zero_extract RTL we require that the POS and LEN arguments are in the > > right ranges, while bextr allows any values, and either uses 0 for bits > > outside of the original operand and for LEN uses umin (len, <bitsize>). > > Ah, thanks, this explains my question from Comment #4. > > Speculating a bit further, is BZHI just a special case of BEXTR, where start > = 0 (I'm referring to [1]). It would be nice to make these insn as general > as possible, so combine will have a chance here. > > [1] http://en.wikipedia.org/wiki/Bit_Manipulation_Instruction_Sets To some extent BZHI is a special case of BEXTR, but I'm afraid any generalization is much harder due to the weirdo encoding of the operands, unless both the START and LEN are CONST_INTs (and if they are constants, it is questionable if BEXTR or BZHI are the best instructions to use, because both take just register for the LEN or START/LEN pair, so one would need to set some register to a constant and then perform BEXTR/BZHI, so two instructions, while there is always the option to perform AND and right shift (or right shift and AND).
