Antoine Pelisse <apelisse@xxxxxxxxx> writes:
> clang incorrectly reports a constant conversion warning (implicit
> truncation to bit field) when using the "flag &= ~FLAG" form, because
> ~FLAG needs to be truncated.
>
> Convert this form to "flag = flag & ~FLAG" fixes the issue as
> the right operand now fits into the bit field.
If the "clang incorrectly reports" is already recognised by clang
folks as a bug to be fixed in clang, I'd rather not to take this
patch.
I do not think it is reasonable to expect people to remember that
they have to write "flags &= ~TO_DROP" in a longhand whenever they
are adding new code that needs to do bit-fields, so even if this
patch makes clang silent for the _current_ code, it will not stay
that way. Something like
#define FLIP_BIT_CLR(fld,bit) do { \
typeof(fld) *x = &(fld); \
*x = *x & (~(bit)); \
} while (0)
may be more palapable but not by a large margin.
Yuck.
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