Il mer 23 apr 2025, 15:54 Ben Dooks <ben.do...@codethink.co.uk> ha scritto:
> > Leaving aside your patch I think you can improve the density of the
> > tbflags a bit too:
> >
> > - PM_MASK_ENABLED, PM_BASE_ENABLED and AXL are unused, which gives you
> > back 4 bits.
>
> Hmm, the PM_MASK_ENABLED, PM_BASE_ENABLED are also used by VMA and VTA
>
Ah, indeed they were reused without removing the old ones. So those are
out...
> - VLMUL == 4 is invalid, and you can use that to get rid of VILL
> - SEW reserves 3 bits, but TCG only supports 8/16/32/64; that could be
> > one more bit if you can live with the limitation
>
... and any of these two is the easiest in the short term if you need to
recoup one bit.
Paolo
> This is already 6 bits, but for FS and VS it may be efficient enough to
> > have just one bit (dirty vs. everything else): for all cases other than
> > dirty, REQUIRE_FPU and require_rv* can call a helper to look at the
> > actual MSTATUS and generate the exception if the extension is disabled;
> > then the caller always proceeds with translation into TCG ops(*). The
> > overhead for the DISABLED/INITIAL/CLEAN cases is minimal and it gives
> > back 2 more bits.
> >
> > Finally, in many cases it makes sense to do a full TB flush when CSRs
> > change. However I am not sure if this could be done for RISC-V, maybe
> > for the CFI enabled bits?
>
> I'll have a look at those, but for now I'm going back to 9.1
>
>
> > Thanks,
> >
> > Paolo
> >
> > (*) that is:
> >
> > static bool require_rvv(DisasContext *s)
> > {
> > REQUIRE_EXT(s, RVV);
> > if (!s->mstatus_vs_dirty) {
> > gen_helper_require_rvv(tcg_env);
> > }
> > return true;
> > }
> >
> > static bool require_rvf(DisasContext *s)
> > {
> > switch (s->sew) {
> > case MO_16:
> > if (!s->cfg_ptr->ext_zvfh) {
> > return false;
> > }
> > break;
> > case MO_32:
> > if (s->cfg_ptr->ext_zve32f) {
> > return false;
> > }
> > break;
> > case MO_64:
> > if (s->cfg_ptr->ext_zve64d) {
> > return false;
> > }
> > break;
> > default:
> > return false;
> > }
> >
> > if (!s->mstatus_fs_dirty) {
> > gen_helper_require_rvf(tcg_env);
> > }
> > return true;
> > }
> >
> >
>
>
> --
> Ben Dooks http://www.codethink.co.uk/
> Senior Engineer Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html
>
>
