[PATCH] PowerPC - ilogb[f|l] optimization for POWER7

[Richard Henderson]

On 05/08/12 05:33, Adhemerval Zanella wrote:
> +#if defined(_ARCH_PWR7)
> +
> +/* Optimized double to word cast for POWER7: the 'ori 2,2,0'
> +   instructions between the store double / load integer is
> +   to force a new dispatch group.  */
> +#undef DOUBLE_TO_WORDS
> +#define DOUBLE_TO_WORDS(d, i)				\
> +  do {							\
> +    double d__ = d;					\
> +    int32_t i__;					\
> +    ieee_double_shape_type iw_u;			\
> +    __asm (						\
> +      "fctiwz  %1,%1\n"					\
> +      "stfd    %1,%2\n"					\
> +      "ori     2,2,0\n"					\
> +      "lwz     %0,%3\n"					\
> +      : "=r" (i__)					\
> +      : "f" (d__), "m" (iw_u.value), "m" (iw_u.word));	\
> +    i = i__;						\
> +  } while (0)
> +
> +#endif /* __ARCH_PWR7  */

Is this really so much better than what the compiler can generate?
If the dispatch group split is that critical, you ought to fix it
in the scheduler -- it's not like these are the only two double->int
conversions in the entire library.

The documentation for this macro is sorely lacking too.  At first I
thought you meant EXTRACT_WORDS64 but hadn't known what the macro
was supposed to be called.



r~