Re: [PATCH 2/3] target/loongarch: Fix LLSC for LoongArch32

[Philippe Mathieu-Daudé]

On 23/12/24 22:01, Jiaxun Yang wrote:
> 在2024年12月23日十二月 下午3:15，Richard Henderson写道：
> > On 12/22/24 15:40, Jiaxun Yang wrote:
> > > @@ -9,7 +9,7 @@ static bool gen_ll(DisasContext *ctx, arg_rr_i *a, MemOp mop)
> > >        TCGv src1 = gpr_src(ctx, a->rj, EXT_NONE);
> > >        TCGv t0 = make_address_i(ctx, src1, a->imm);
> > ...
> > > @@ -28,7 +28,8 @@ static bool gen_sc(DisasContext *ctx, arg_rr_i *a, MemOp mop)
> > >        TCGLabel *l1 = gen_new_label();
> > >        TCGLabel *done = gen_new_label();
> > >    
> > > -    tcg_gen_addi_tl(t0, src1, a->imm);
> > > +    tcg_gen_mov_tl(t0, src1);
> > > +    t0 = make_address_i(ctx, t0, a->imm);
> >
> > The move before make_address_i is not required.
> > See the similar code just above in gen_ll.
>
> I think it’s necessary, I thought the same and end up spending hours to track 
> down the problem.
>
> make_address_i won’t make a new temp_reg if imm is zero.

Only if va32 = 0, IOW if HW_FLAGS_VA32 is not set. Per is_va32,
VA32 == !LA64 or VA32L[1-3]

Indeed make_address_x() returns the same TCGv if !VA32 and imm=0.

> So when imm is 0 src1 and src2 is the same tcg reg the value will be clobbered 
> by cmpxchg,
> causing a couple of tcg tests to fail.

Missing constraint or mis-designed make_address_x()?
To KISS I'd use a temp in make_address_x() regardless of addend=0.

> I think only way to ensure t0 is a new temp reg is to perform a move here.
>
> Thanks
> > r~