Re: Bit fields

[Richard Henderson <rth@redhat.com>]

On 08/31/2009 01:07 PM, Jean Christophe Beyler wrote:
> If I replace this :
> (define_insn "extzv"
>    [(set (match_operand 0 "register_operand" "")
>          (zero_extract (match_operand 1 "register_operand" "")
>                        (match_operand 2 "const_int_operand" "")
>                        (match_operand 3 "const_int_operand" "")))]
>   ""
>   "")

Well, I can tell you that an insn pattern with no modes
on the non-immediate operands will definitely cause problems.

> (insn 9 8 10 3 struct4.c:24 (set (subreg:DI (reg:QI 76) 0)
>          (zero_extract:DI (reg:DI 75)
>              (const_int 1 [0x1])
>              (const_int 0 [0x0]))) -1 (nil))
>
> (insn 10 9 11 3 struct4.c:24 (set (reg:DI 77)
>          (zero_extend:DI (reg:QI 76))) -1 (nil))
>
> Is there anything I can do to remove that zero_extend?

You could try either using a predicate that disallows
a subreg, or by having your expander rewrite things into

   (set (reg:DI new-scratch))
        (zero_extract:DI ...))
   (set (reg:QI 76 (subreg:QI (reg:DI new scratch)))

and relying on subsequent passes to clean that up.


r~