Re: About hardfloat in ppc

[Richard Henderson]

On 5/1/20 9:29 AM, 罗勇刚(Yonggang Luo) wrote:
> On Fri, May 1, 2020 at 10:18 PM Richard Henderson <address@hidden
>     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.

Thus, no need for a separate helper_reset_fpstatus.


r~