On Sat, May 2, 2020 at 12:51 AM Richard Henderson <
richard.hender...@linaro.org> wrote:
> On 5/1/20 9:29 AM, 罗勇刚(Yonggang Luo) wrote:
> > On Fri, May 1, 2020 at 10:18 PM Richard Henderson <
> richard.hender...@linaro.org
> > Step 1 is to rearrange the fp helpers to eliminate
> helper_reset_fpstatus().
> > I've mentioned this before, that it's possible to leave the
> steady-state of
> > env->fp_status.exception_flags == 0, so there's no need for a
> separate function
> > call. I suspect this is worth a decent speedup by itself.
> >
> > Hi Richard, what kinds of rearrange the fp need to be done? Can you give
> me a
> > more detailed example? I am still not get the idea.
>
> See target/openrisc, helper_update_fpcsr.
>
> This is like target/ppc helper_float_check_status, in that it is called
> after
> the primary fpu helper, after the fpu result is written back to the
> architectural register, to process fpu exceptions.
>
> Note that if get_float_exception_flags returns non-zero, we immediately
> reset
> them to zero. Thus the exception flags are only ever non-zero in between
> the
> primary fpu operation and the update of the fpscr.
>
According to
```
void HELPER(update_fpcsr)(CPUOpenRISCState *env)
{
int tmp = get_float_exception_flags(&env->fp_status);
if (tmp) {
set_float_exception_flags(0, &env->fp_status);
tmp = ieee_ex_to_openrisc(tmp);
if (tmp) {
env->fpcsr |= tmp;
if (env->fpcsr & FPCSR_FPEE) {
helper_exception(env, EXCP_FPE);
}
}
}
}
```
The openrisc also clearing the flags before each fp operation?
>
> Thus, no need for a separate helper_reset_fpstatus.
>
>
> r~
>
--
此致
礼
罗勇刚
Yours
sincerely,
Yonggang Luo
