Subject: Re: [PATCH 0/9] bitfield: tidy up bitfield.h

From: David Laight <[email-masked]>
Date: Thu, 11 Dec 2025 10:51:07 +0000

On Wed, 10 Dec 2025 13:20:16 -0500
Yury Norov <[email-masked]> wrote:

> On Tue, Dec 09, 2025 at 10:03:04AM +0000, [email-masked] wrote:
> > From: David Laight <[email-masked]>
...
> > I noticed some very long (18KB) error messages from the compiler.
> > Turned out they were errors on lines that passed GENMASK() to FIELD_PREP().
> > Since most of the #defines are already statement functions the values
> > can be copied to locals so the actual parameters only get expanded once.
> > 
> > The 'bloat' is reduced further by using a simple test to ensure 'reg'
> > is large enough, slightly simplifying the test for constant 'val' and
> > only checking 'reg' and 'val' when the parameters are present.  
> 
> So, can you share the before/after?

Not that hard to generate since the kernel makefiles will create foo.i

I would have fed the .i file though xargs - but someone broke it
(there is no option to ignore quotes, and -s70 isn't allowed).
So I used:
tr ' ' '\n' foo.i | (ll=; while read -r l; do ll1="$ll $l"; [ ${#l} = 0 -o ${#ll1} -ge 70 ] && { echo "$ll"; ll="$l";} || ll="$ll1"; done; echo "$ll")

GENMASK(hi, lo)
    ((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))

A chunk of that would be removed by changing type_max() to do
2 * (n - 1) + 1 instead of (n - 1) + n, but for unsigned types
it isn't needed.
Changing type_max(t) to (t)-1 GENMASK(hi, lo) becomes
(patch not posted...)
    ((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) + ((unsigned long)-1
    << (lo) & (unsigned long)-1 >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))
There are still four expansions of both lo and hi - but they are
usually trivial. 

You asked for this one :-)
old FIELD_GET(GENMASK(hi, lo), reg)
    ({ do { __attribute__((__noreturn__)) extern void
    __compiletime_assert_769(void) __attribute__((__error__("FIELD_GET: "
    "type of reg too small for mask"))); if (!(!(((typeof(
    _Generic((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))), char: (unsigned
    char)0, unsigned char: (unsigned char)0, signed char: (unsigned
    char)0, unsigned short: (unsigned short)0, signed short: (unsigned
    short)0, unsigned int: (unsigned int)0, signed int: (unsigned int)0,
    unsigned long: (unsigned long)0, signed long: (unsigned long)0,
    unsigned long long: (unsigned long long)0, signed long long:
    (unsigned long long)0, default: (((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))))))(((unsigned
    long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi))))))) > ((typeof(
    _Generic((reg), char: (unsigned char)0, unsigned char: (unsigned
    char)0, signed char: (unsigned char)0, unsigned short: (unsigned
    short)0, signed short: (unsigned short)0, unsigned int: (unsigned
    int)0, signed int: (unsigned int)0, unsigned long: (unsigned long)0,
    signed long: (unsigned long)0, unsigned long long: (unsigned long
    long)0, signed long long: (unsigned long long)0, default:
    (reg))))(~0ull))))) __compiletime_assert_769(); } while (0); ({ ({ do
    { __attribute__((__noreturn__)) extern void
    __compiletime_assert_770(void) __attribute__((__error__("FIELD_GET: "
    "mask is not constant"))); if (!(!(!__builtin_constant_p(((unsigned
    long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))))))
    __compiletime_assert_770(); } while (0); do {
    __attribute__((__noreturn__)) extern void
    __compiletime_assert_771(void) __attribute__((__error__("FIELD_GET: "
    "mask is zero"))); if (!(!((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) == 0)))
    __compiletime_assert_771(); } while (0); do {
    __attribute__((__noreturn__)) extern void
    __compiletime_assert_772(void) __attribute__((__error__("FIELD_GET: "
    "value too large for the field"))); if (!(!(__builtin_constant_p(0U)
    ? ~((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) >>
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1)) & (0 + (0U)) :
    0))) __compiletime_assert_772(); } while (0); do {
    __attribute__((__noreturn__)) extern void
    __compiletime_assert_773(void) __attribute__((__error__("BUILD_BUG_ON
    failed: " "(((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), \"const_true((lo) > (hi))\" \" is true\");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) + (1ULL <<
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), \"const_true((lo) > (hi))\" \" is true\");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1))) &
    (((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), \"const_true((lo) > (hi))\" \" is true\");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) + (1ULL <<
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), \"const_true((lo) > (hi))\" \" is true\");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1))) - 1)) !=
    0"))); if (!(!((((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) + (1ULL <<
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1))) &
    (((((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) + (1ULL <<
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1))) - 1)) != 0)))
    __compiletime_assert_773(); } while (0); }); (typeof(((unsigned
    long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))))(((reg) & (((unsigned
    long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi))))))) >>
    (__builtin_ffsll(((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi)))))) - 1)); }); })

new FIELD_GET(GENMASK(hi, lo), reg)
    ({ __auto_type _mask = ((unsigned long)(((int)sizeof(struct
    {_Static_assert(!(__builtin_choose_expr((sizeof(int) == sizeof(*(8 ?
    ((void *)((long)((lo) > (hi)) * 0l)) : (int *)8))), (lo) > (hi),
    false)), "const_true((lo) > (hi))" " is true");})) +
    (((typeof(unsigned long))((((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))) - 1) + ((typeof(unsigned long))1 <<
    (8*sizeof(typeof(unsigned long)) - 1 - (((typeof(unsigned long))(-1))
    < ( typeof(unsigned long))1))))) << (lo) & ((typeof(unsigned
    long))((((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long))
    - 1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1))) -
    1) + ((typeof(unsigned long))1 << (8*sizeof(typeof(unsigned long)) -
    1 - (((typeof(unsigned long))(-1)) < ( typeof(unsigned long))1)))))
    >> ((sizeof(unsigned long) * 8) - 1 - (hi))))); __auto_type _reg =
    reg; ({ do { do { __attribute__((__noreturn__)) extern void
    __compiletime_assert_697(void) __attribute__((__error__("FIELD_GET: "
    "mask is not constant"))); if (!(!(!__builtin_constant_p(_mask))))
    __compiletime_assert_697(); } while (0); do {
    __attribute__((__noreturn__)) extern void
    __compiletime_assert_698(void) __attribute__((__error__("FIELD_GET: "
    "mask is zero or not contiguous"))); if (!(!((!(_mask) || ((_mask) &
    ((_mask) + ((_mask) & -(_mask)))))))) __compiletime_assert_698(); }
    while (0); } while (0); do { __attribute__((__noreturn__)) extern
    void __compiletime_assert_699(void)
    __attribute__((__error__("FIELD_GET: " "type of reg too small for
    mask"))); if (!(!(_mask + 0U + 0UL + 0ULL > ~0ULL >> (64 - 8 * sizeof
    (_reg))))) __compiletime_assert_699(); } while (0); ((_reg) &
    (_mask)) >> (__builtin_ffsll(_mask) - 1); }); })

	David