[cfe-dev] Bitwidth attribute

Douglas Gregor dgregor at apple.com
Fri Jan 14 07:49:02 PST 2011

On Jan 12, 2011, at 3:13 AM, ihusar wrote:

> Hello,
>   I would like to ask, whether there are any plan to support the bitwidth attribute.
> In llvm-test-2.8 in SingleSource/UnitTests/Integer/bits.h, there is the attribute used:
> typedef unsigned int __attribute__((bitwidth(1))) uint1;
> ...
> However, when I try to compile it with clang 2.8, I get this message:
> test.c:2:37: warning: unknown attribute 'bitwidth' ignored [-Wunknown-attributes]
>   I did not try the latest llvm-gcc, but last time i tried, it did not work either.
> So, I would like to ask, whether you plan to include support for the bitwidth attribute in the close future, or if
> you would be willing to accept a patch that implements this support.
>   We need this to describe hardware using C and I think that we are not the only ones that
> would find this useful.

Where does this attribute come from? I don't see it in GCC's list of attributes, nor do I recall seeing it in other compilers.

We try to add attributes when we need to for compatibility or when there's a strong benefit and a solid implementation for that attribute.

	- Doug

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