On Thu, Jun 19, 2025 at 05:59:09PM +0800, Yang Yujie wrote:
> In LoongArch psABI, large _BitInt(N) (N > 64) objects are only
> extended to fill the highest 8-byte chunk that contains any used bit,
> but the size of such a large _BitInt type is a multiple of their
> 16-byte alignment. So there may be an entire unused 8-byte
> chunk that is not filled by extension, and this chunk shouldn't be
> checked when testing if the object is properly extended.
>
> The original bitintext.h assumed that all bits within
> sizeof(_BitInt(N)) beyond used bits are filled by extension.
> This patch changes that for LoongArch and possibly
> any future ports with a similar behavior.
>
> P.S. For encoding this test as well as type-generic programming,
> it would be nice to have a builtin function to obtain "N" at
> compile time from _BitInt(N)-typed expressions. But here
> we stick to existing ones (__builtin_clrsbg / __builtin_clzg).
>
> gcc/testsuite/ChangeLog:
>
> * gcc.dg/bitintext.h: Generalize BEXTC to only check extension
> within {S,U}_PROMOTED_SIZE bits.
> * gcc.dg/torture/bitint-82.c: Use the new BEXTC_{U,S} macros.
> ---
> gcc/testsuite/gcc.dg/bitintext.h | 48 +++++++++++++-------
> gcc/testsuite/gcc.dg/torture/bitint-82.c | 56 ++++++++++++------------
> 2 files changed, 60 insertions(+), 44 deletions(-)
>
> diff --git a/gcc/testsuite/gcc.dg/bitintext.h
> b/gcc/testsuite/gcc.dg/bitintext.h
> index 99fedb32a9a..48d5673440f 100644
> --- a/gcc/testsuite/gcc.dg/bitintext.h
> +++ b/gcc/testsuite/gcc.dg/bitintext.h
> @@ -4,26 +4,42 @@ do_copy (void *p, const void *q, __SIZE_TYPE__ r)
> __builtin_memcpy (p, q, r);
> }
>
> +#define S_N(x) (__builtin_clrsbg ((typeof (x)) -1) + 1)
> +#define U_N(x) (__builtin_clzg ((typeof (x)) 1) + 1)
> +#define CEIL(x,y) (((x) + (y) - 1) / (y))
> +
> +/* Promote a _BitInt type to include its padding bits. */
> +#if defined (__s390x__) || defined(__arm__)
> +#define S_PROMOTED_SIZE(x) sizeof (x)
> +#define U_PROMOTED_SIZE(x) sizeof (x)
> +#elif defined(__loongarch__)
> +#define S_PROMOTED_SIZE(x) (sizeof (x) > 8 ? CEIL (S_N (x), 64) * 8: sizeof
> (x))
> +#define U_PROMOTED_SIZE(x) (sizeof (x) > 8 ? CEIL (U_N (x), 64) * 8: sizeof
> (x))
Space before :
More importantly, I really don't like the need to differentiate in the
source code between BEXTC_U and BEXTC_S, the macro should figure that out
automatically and before your changes it did, through the
if ((typeof (x)) -1 < 0)
conditional which folds at compile time to 0 or 1.
#define S(x) \
((typeof (x)) -1 < 0 \
? __builtin_clrsbg (__builtin_choose_expr ((typeof (x)) -1 < 0, \
(typeof (x)) -1, -1)) + 1 \
: __builtin_popcountg (__builtin_choose_expr ((typeof (x)) -1 < 0, \
0U, (typeof (x)) -1)))
macro provides the right _BitInt width for both signed and unsigned values.
But because the BEXTC macro already uses an if ((typeof (x)) -1 < 0)
conditional, you could as well define the S_N and U_N macros as the
second and third subexpressions of ?: above and just use it in the
corresponding parts of the code.
> +#endif
> +
> +#define S_PROMOTED_TYPE(x) _BitInt (S_PROMOTED_SIZE (x) * __CHAR_BIT__)
> +#define U_PROMOTED_TYPE(x) unsigned _BitInt (U_PROMOTED_SIZE (x) *
> __CHAR_BIT__)
> +
> /* Macro to test whether (on targets where psABI requires it) _BitInt
> with padding bits have those filled with sign or zero extension. */
> #if defined(__s390x__) || defined(__arm__) || defined(__loongarch__)
> -#define BEXTC(x) \
> +#define BEXTC_U(x) \
> do { \
> - if ((typeof (x)) -1 < 0) \
> - { \
> - _BitInt(sizeof (x) * __CHAR_BIT__) __x; \
> - do_copy (&__x, &(x), sizeof (__x)); \
> - if (__x != (x)) \
> - __builtin_abort (); \
> - } \
> - else \
> - { \
> - unsigned _BitInt(sizeof (x) * __CHAR_BIT__) __x; \
> - do_copy (&__x, &(x), sizeof (__x)); \
> - if (__x != (x)) \
> - __builtin_abort (); \
> - } \
> + U_PROMOTED_TYPE (x) __x; \
> + do_copy (&__x, &(x), U_PROMOTED_SIZE (x)); \
> + if (__x != (x)) \
> + __builtin_abort (); \
> } while (0)
> +
> +#define BEXTC_S(x) \
> + do { \
> + S_PROMOTED_TYPE (x) __x; \
> + do_copy (&__x, &(x), S_PROMOTED_SIZE (x)); \
> + if (__x != (x)) \
> + __builtin_abort (); \
> + } while (0)
> +
> #else
> -#define BEXTC(x) do { (void) (x); } while (0)
> +#define BEXTC_S(x) do { (void) (x); } while (0)
> +#define BEXTC_U(x) do { (void) (x); } while (0)
> #endif
Jakub
