Hi! On Wed, Apr 14, 2021 at 05:31:23PM +0100, Richard Sandiford wrote: > Jakub Jelinek <ja...@redhat.com> writes: > > +(define_split > > + [(set (match_operand:GPI 0 "register_operand") > > + (LOGICAL:GPI > > + (and:GPI (ashift:GPI (match_operand:GPI 1 "register_operand") > > + (match_operand:QI 2 "aarch64_shift_imm_<mode>")) > > + (match_operand:GPI 4 "const_int_operand")) > > + (zero_extend:GPI (match_operand 3 "register_operand"))))] > > + "can_create_pseudo_p () > > + && REG_P (operands[1]) > > + && REG_P (operands[3]) > > + && REGNO (operands[1]) == REGNO (operands[3]) > > + && ((unsigned HOST_WIDE_INT) > > + trunc_int_for_mode (GET_MODE_MASK (GET_MODE (operands[3])) > > + << INTVAL (operands[2]), <MODE>mode) > > + == UINTVAL (operands[4]))" > > IMO this would be easier to understand as: > > && (trunc_int_for_mode (GET_MODE_MASK (GET_MODE (operands[3])) > << INTVAL (operands[2]), <MODE>mode) > == INTVAL (operands[4])) > > (At first I thought the cast and UINTVAL were trying to escape the > sign-extension canonicalisation.)
Yeah. Or just that with UINTVAL, the implicit conversion is fine (but maybe that warns?) But INTVAL is simpler for sure. > I'm not sure about this one though. The REGNO checks mean that this is > effectively for hard registers only. I thought one of the reasons for > make_more_copies was to avoid combining hard registers like this, so I'm > not sure we should have a pattern that specifically targets them. > > Segher, have I misunderstood? The REGNO checks work fine for pseudos as well. But, why does it do this at all, instead of using match_dup? That should be clearer. The point of make_more_copies is that the hard registers from function arguments are not pushed down by combine into actual instructions. This can be done by RA if it thinks that is a good idea, and not done if it thinks it is a bad idea. Having combine usurp part of the register allocators role is not a good idea. There are other reasons hard regs can still end up in RTL insns in earlier RTL passes of course, but the other changes that went together with make_more_copies stop combine from doing that a lot (the function itself makes sure every hard reg is copied to a new pseudo, because combining that trivial move (from that new pseudo to the pseudo it was copying it to already!) can still be beneficial for other reasons, all strange and pretty unhappy, but important on many targets). Segher
