From: Vincent Mailhol
> Sent: 13 November 2024 17:19
>
> In GENMASK_INPUT_CHECK(),
>
> __builtin_choose_expr(__is_constexpr((l) > (h)), (l) > (h), 0)
>
> is the exact expansion of:
>
> const_true((l) > (h))
>
> Apply const_true() to simplify GENMASK_INPUT_CHECK().
Wouldn't statically_true() give better coverage ?
I wouldn't have though that GENMASK() got used anywhere where a constant
integer expression was needed.
More interesting would be to get it to pass a W=1 build for
any place where 'l' is 0u.
David
>
> Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
> ---
> This change passes the unit tests from CONFIG_BITS_TEST, including the
> extra negative tests provided under #ifdef TEST_GENMASK_FAILURES [1].
>
> [1] commit 6d511020e13d ("lib/test_bits.c: add tests of GENMASK")
> Link: https://git.kernel.org/torvalds/c/6d511020e13d
> ---
> include/linux/bits.h | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 60044b608817..61a75d3f294b 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -20,9 +20,8 @@
> */
> #if !defined(__ASSEMBLY__)
> #include <linux/build_bug.h>
> -#define GENMASK_INPUT_CHECK(h, l) \
> - (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> - __is_constexpr((l) > (h)), (l) > (h), 0)))
> +#include <linux/compiler.h>
> +#define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h)))
> #else
> /*
> * BUILD_BUG_ON_ZERO is not available in h files included from asm files,
> --
> 2.45.2
>
-
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