RE: [PATCH] Hexagon (target/hexagon) TCG generation cleanup

[Taylor Simpson]

> -----Original Message-----
> From: Richard Henderson <richard.henderson@linaro.org>
> Sent: Monday, March 15, 2021 8:40 AM
> To: Taylor Simpson <tsimpson@quicinc.com>; qemu-devel@nongnu.org
> Cc: philmd@redhat.com
> Subject: Re: [PATCH] Hexagon (target/hexagon) TCG generation cleanup
>
> On 3/14/21 10:54 PM, Taylor Simpson wrote:
> > Simplify TCG generation of hex_reg_written
> >
> > Address feedback from Richard Henderson
> <<richard.henderson@linaro.org>
> >
> > Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
> > ---
> >   target/hexagon/genptr.c | 12 +++++++++---
> >   1 file changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/target/hexagon/genptr.c b/target/hexagon/genptr.c
> > index 7481f4c..0ad63fe 100644
> > --- a/target/hexagon/genptr.c
> > +++ b/target/hexagon/genptr.c
> > @@ -43,9 +43,15 @@ static inline void gen_log_predicated_reg_write(int
> rnum, TCGv val, int slot)
> >       tcg_gen_movcond_tl(TCG_COND_EQ, hex_new_value[rnum],
> slot_mask, zero,
> >                              val, hex_new_value[rnum]);
> >   #if HEX_DEBUG
> > -    /* Do this so HELPER(debug_commit_end) will know */
> > -    tcg_gen_movcond_tl(TCG_COND_EQ, hex_reg_written[rnum],
> slot_mask, zero,
> > -                       one, hex_reg_written[rnum]);
> > +    /*
> > +     * Do this so HELPER(debug_commit_end) will know
> > +     *
> > +     * Note that slot_mask indicates the value is not written
> > +     * (i.e., slot was cancelled), so we negate the value before
> > +     * or'ing with hex_reg_written[rnum].
> > +     */
> > +    tcg_gen_xori_tl(slot_mask, slot_mask, 1 << slot);
> > +    tcg_gen_or_tl(hex_reg_written[rnum], hex_reg_written[rnum],
> slot_mask);
>
> reg_written appears to be a boolean, not a mask of any kind.
> I think you want
>
>      tcg_gen_setcond_i32(TCG_COND_EQ, slot_mask, slot_mask, zero);
>
> and not the xor.

I'm treating it as a zero/non-zero value.  The change works because the usage 
in op_helper.c is
    if (env->reg_written[i]) ...

I'll change the xor to setcond to make it more clear.


Thanks,
Taylor