Bitwidth attribute

Clang Frontend
1

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.

Thank you
   Adam Husar

2

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

3

Hi;

4

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.

This was the custom attribute added to llvm-gcc during the arbitrary
width integer project. Though even in llvm-gcc is was not
working always properly and right now noone is interested in it.