[cfe-dev] [llvm-dev] Unsigned Bitwise Shift for Bit-field Structure

[Liu Hao via cfe-dev]

On 2017/4/20 19:20, Hubert Tong wrote:
> It is hardly clear that the rvalue is of type unsigned long long (and
> not some special bit-field type).
> See http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1260.htm.
> I have been unable to find further discussion of the issue after
> http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1270.pdf.

You are right. Let's assume such an implementation exists, and despite 
that type, the result doesn't change: The (indeterminate) value is 
merely truncated earlier, yielding the same value after it is stored 
into the bit-field member.

I also doubt the existence of such an implementation: 6.7.2.1/4 doesn't 
say bit-field types need exist. Their occurrence also lead to problems: 
Would people benefit from it? What will happen if such an rvalue is 
passed to a function taking variable arguments? What will `sizeof(it+1)` 
where `it` has a bit-field type?


-- 
Best regards,
LH_Mouse