On 2022/10/20 19:22, Richard Henderson wrote:
> 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.
I don't know why we need 'M'. Can I just use the constraint
C_O2_I4(r, r, rZ, rZ, rS, rS);
I see the problem now. Look at the top of tcg_out_addsub2, where we (conditionally) negate the constant.
We want to constrain the constant to be representable either positive or negative, i.e not -4096..4095 but -4095..4095. But we got the endpoints wrong in tcg_target_const_match: 0xfff instead of 0x7ff.
r~