Re: [Qemu-devel] [PATCH RFC v1 1/3] target/ppc: Emulate LL/SC using cmpxchg helpers

[Richard Henderson]

On 04/06/2017 03:22 AM, Nikunj A Dadhania wrote:
> +    TCGv_i32 tmp = tcg_temp_local_new_i32();
> +    TCGv t0;
>
> +    tcg_gen_movi_i32(tmp, 0);
>      tcg_gen_trunc_tl_i32(cpu_crf[0], cpu_so);
>      l1 = gen_new_label();
>      tcg_gen_brcond_tl(TCG_COND_NE, EA, cpu_reserve, l1);
> -    tcg_gen_ori_i32(cpu_crf[0], cpu_crf[0], CRF_EQ);
> -    tcg_gen_qemu_st_tl(cpu_gpr[reg], EA, ctx->mem_idx, memop);
> +
> +    t0 = tcg_temp_new();
> +    tcg_gen_atomic_cmpxchg_tl(t0, EA, cpu_reserve_val, cpu_gpr[reg],
> +                              ctx->mem_idx, DEF_MEMOP(memop));
> +    tcg_gen_setcond_tl(TCG_COND_EQ, t0, t0, cpu_reserve_val);
> +    tcg_gen_trunc_tl_i32(tmp, t0);
> +
>      gen_set_label(l1);
> +    tcg_gen_shli_i32(tmp, tmp, CRF_EQ_BIT);
> +    tcg_gen_or_i32(cpu_crf[0], cpu_crf[0], tmp);

I encourage you to move these two lines up beside the setcond.
That way you don't need to use a local tmp, which implies a
spill/restore from the stack.


r~