Re: [PATCH v2 03/14] tcg/loongarch64: Lower cmp_vec to vseq/vsle/vslt

[Jiajie Chen]

On 2023/9/2 01:48, Richard Henderson wrote:
> On 9/1/23 10:28, Jiajie Chen wrote:
> > On 2023/9/2 01:24, Richard Henderson wrote:
> > > On 9/1/23 02:30, Jiajie Chen wrote:
> > > > Signed-off-by: Jiajie Chen <c@jia.je>
> > > > ---
> > > >   tcg/loongarch64/tcg-target-con-set.h |  1 +
> > > >   tcg/loongarch64/tcg-target.c.inc     | 60 
> > > > ++++++++++++++++++++++++++++
> > > >   2 files changed, 61 insertions(+)
> > >
> > > Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> > >
> > >
> > > > diff --git a/tcg/loongarch64/tcg-target-con-set.h 
> > > > b/tcg/loongarch64/tcg-target-con-set.h
> > > > index 37b3f80bf9..d04916db25 100644
> > > > --- a/tcg/loongarch64/tcg-target-con-set.h
> > > > +++ b/tcg/loongarch64/tcg-target-con-set.h
> > > > @@ -31,4 +31,5 @@ C_O1_I2(r, 0, rZ)
> > > >   C_O1_I2(r, rZ, ri)
> > > >   C_O1_I2(r, rZ, rJ)
> > > >   C_O1_I2(r, rZ, rZ)
> > > > +C_O1_I2(w, w, wJ)
> > >
> > > Notes for improvement: 'J' is a signed 32-bit immediate.
> >
> >
> > I was wondering about the behavior of 'J' on i128 types: in 
> > tcg_target_const_match(), the argument type is int, so will the 
> > higher bits be truncated?
>
> The argument is int64_t val.
>
> The only constants that we allow for vectors are dupi, so all higher 
> parts are the same as the lower part.


Consider the following scenario:


cmp_vec v128,e32,tmp4,tmp3,v128$0xffffffffffffffff

cmp_vec v128,e32,tmp4,tmp3,v128$0xfffffffefffffffe

cmp_vec v128,e8,tmp4,tmp3,v128$0xfefefefefefefefe


When matching constant constraint, the vector element width is unknown, 
so it cannot decide whether 0xfefefefefefefefe means e8 0xfe or e16 0xfefe.


> > Besides, tcg_target_const_match() does not know the vector element 
> > width.
>
> No, it hadn't been required so far -- there are very few vector 
> instructions that allow immediates.
>
>
> r~