Re: [RFC PATCH 2/8] riscv: Generate payload scripts

[LIU Zhiwei]

On 2020/5/20 13:41, Richard Henderson wrote:
> On 5/19/20 7:37 PM, LIU Zhiwei wrote:
> > On 2020/5/12 1:40, Richard Henderson wrote:
> > > On 4/30/20 12:21 AM, LIU Zhiwei wrote:
> > > > +    # sequence of li rd, 0x1234567887654321
> > > > +    #
> > > > +    #  0:   002471b7                lui     rd,0x247
> > > > +    #  4:   8ad1819b                addiw   rd,rd,-1875
> > > > +    #  8:   00c19193                slli    rd,rd,0xc
> > > > +    #  c:   f1118193                addi    rd,rd,-239 # 0x246f11
> > > > +    # 10:   00d19193                slli    rd,rd,0xd
> > > > +    # 14:   d9518193                addi    rd,rd,-619
> > > > +    # 18:   00e19193                slli    rd,rd,0xe
> > > > +    # 1c:   32118193                addi    rd,rd,801
> > > You don't really need to use addiw.  Removing that special case would really
> > > simplify this.
> > I think I don't get it. Do you mean that the immediate will not be 64 bit?
> Well, mostly the immediate will be small, actually.  But the interface must
> support 64-bit immediates.
>
> I'm saying that for this computation,
>
>         lui
>         addi
>         slli
>         addi
>         ...
>
> is the same.  You don't *have* to use addiw.
I see addiw is not good, as it is a RV64 only instruction. I think addi 
is right and better.

But I'm afraid I don't get

"Removing that special case would really
simplify this."

Do you mean I need not the decode_li function if I use addi instead of 
addiw?

Zhiwei
> r~