RE: [PATCH 4/9] Hexagon (target/hexagon) Mark has_pred_dest in trans functions

[<ltaylorsimpson@gmail.com>]

> -----Original Message-----
> From: Matheus Tavares Bernardino <quic_mathbern@quicinc.com>
> Sent: Tuesday, February 27, 2024 8:21 AM
> To: Taylor Simpson <ltaylorsimpson@gmail.com>
> Cc: qemu-devel@nongnu.org; bcain@quicinc.com;
> quic_mathbern@quicinc.com; sidneym@quicinc.com;
> quic_mliebel@quicinc.com; richard.henderson@linaro.org;
> philmd@linaro.org; ale@rev.ng; anjo@rev.ng
> Subject: Re: [PATCH 4/9] Hexagon (target/hexagon) Mark has_pred_dest in
> trans functions
> 
> On Mon, 26 Feb 2024 13:17:17 -0700 Taylor Simpson
> <ltaylorsimpson@gmail.com> wrote:
> >
> > diff --git a/target/hexagon/gen_trans_funcs.py
> > b/target/hexagon/gen_trans_funcs.py
> > index 07292e0170..f1972fd2dd 100755
> > --- a/target/hexagon/gen_trans_funcs.py
> > +++ b/target/hexagon/gen_trans_funcs.py
> > @@ -86,6 +86,7 @@ def gen_trans_funcs(f):
> >
> >          new_read_idx = -1
> >          dest_idx = -1
> > +        has_pred_dest = "false"
> >          for regno, regstruct in enumerate(regs):
> >              reg_type, reg_id, _, _ = regstruct
> >              reg = hex_common.get_register(tag, reg_type, reg_id) @@
> > -96,6 +97,8 @@ def gen_trans_funcs(f):
> >                  new_read_idx = regno
> >              if reg.is_written() and dest_idx == -1:
> >                  dest_idx = regno
> > +            if reg_type == "P" and not reg.is_read():
> > +                has_pred_dest = "true"
> 
> I got a bit confused here. Why do we use "not reg.is_read()"? I though
this
> would be "reg.is_written()".

The original C code is
            if ((strstr(opcode_wregs[opcode], "Pd4") ||
                 strstr(opcode_wregs[opcode], "Pe4")) &&
Checking for reg.is_written() would also match Px4, which is read-write.

Would it be more clear if we checked for reg.is_written() and non
reg.is_read()?

Thanks,
Taylor