Re: Bit fields

[Jean Christophe Beyler <jean dot christophe dot beyler at gmail dot com>]

Sorry, you are correct. That line is the :
  gcc_assert (outermode != VOIDmode);
of the simplify_subreg function.

However, I've played around with it and saw that I made a mistake when
writing up this question, I simplified what I had put in my MD file,
and actually made a mistake. I apologize.

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" "")))]
 ""
 "")

into :
(define_expand "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" "")))]
 ""
 "")

I do not get any errors. I don't know if it's handled but it seems to
no longer have issues anymore.

However, if I consider this code:
typedef struct stest {
    uint64_t a:1;
    uint64_t b:1;
}STest;

void
goo (STest *t, uint64_t *a, uint64_t *b)
{
    *a = t->a;
}

At the expand phase, I see:

(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?

Thanks,
Jc