Re: [PATCH 2/2] util/bufferiszero: Add simd acceleration for loongarch64

[Richard Henderson]

On 6/5/24 20:36, maobibo wrote:
static biz_accel_fn const accel_table[] = {
     buffer_is_zero_int_ge256,
#ifdef __loongarch_sx
     buffer_is_zero_lsx,
#endif
#ifdef __loongarch_asx
     buffer_is_zero_lasx,
#endif
};
static unsigned best_accel(void)
{
#ifdef __loongarch_asx
     /* lasx may be index 1 or 2, but always last */
     return ARRAY_SIZE(accel_table) - 1;
#else
     /* lsx is always index 1 */
     return 1;
#endif
}
size of accel_table is decided at compile-time, will it be better if runtime checking is 
added also?  something like this:

  unsigned info = cpuinfo_init();

  #ifdef __loongarch_asx
  if (info & CPUINFO_LASX) {
       /* lasx may be index 1 or 2, but always last */
       return ARRAY_SIZE(accel_table) - 1;
  }
  #endif

No, because the ifdef checks that the *compiler* is prepared to use LASX/LSX instructions 
itself without further checks.  There's no point in qemu checking further.


r~