Re: [RFC PATCH 2/3] tcg/riscv: Fix tcg_out_opc_imm when imm exceeds

[Richard Henderson <richard.henderson@linaro.org>]

On 10/20/22 20:41, LIU Zhiwei wrote:
> TYPE-I immediate can only represent a signed 12-bit value. If immediate
> exceed, mov it to an register.
> 
> Signed-off-by: LIU Zhiwei <zhiwei_liu@linux.alibaba.com>
> ---
>   tcg/riscv/tcg-target.c.inc | 28 +++++++++++++++++++++++-----
>   1 file changed, 23 insertions(+), 5 deletions(-)
> 
> diff --git a/tcg/riscv/tcg-target.c.inc b/tcg/riscv/tcg-target.c.inc
> index 32f4bc7bfc..bfdf2bea69 100644
> --- a/tcg/riscv/tcg-target.c.inc
> +++ b/tcg/riscv/tcg-target.c.inc
> @@ -668,7 +668,12 @@ static void tcg_out_addsub2(TCGContext *s,
>       if (!cbh) {
>           tcg_out_opc_reg(s, (is_sub ? opc_sub : opc_add), th, ah, bh);
>       } else if (bh != 0 || ah == rl) {
> -        tcg_out_opc_imm(s, opc_addi, th, ah, (is_sub ? -bh : bh));
> +        if (bh == sextract(bh, 0, 12)) {
> +            tcg_out_opc_imm(s, opc_addi, th, ah, (is_sub ? -bh : bh));
> +        } else {
> +            tcg_out_movi(s, TCG_TYPE_TL, th, (is_sub ? -bh : bh));
> +            tcg_out_opc_reg(s, opc_add, th, ah, th);
> +        }

This value is currently constrained by 'M': +/- 0xfff.
You're suggesting that the fix should be to use 'I', which is signed 12-bit.

But this fix is definitely in the wrong place.


r~