Le 28/11/2016 à 15:54, Richard Henderson a écrit :
> On 11/27/2016 11:35 AM, Laurent Vivier wrote:
>>>> + tcg_gen_extr_i64_i32(QREG_CC_N, QREG_CC_C, t64);
>> This does not extract correctly the C flag when the opsize is word or byte.
>> I think we should use a shift instead:
>>
>> - tcg_gen_extr_i64_i32(QREG_CC_N, QREG_CC_C, t64);
>> -
>> - /* Note that C=0 if shift count is 0, and we get that for free. */
>> + if (opsize == OS_LONG) {
>> + tcg_gen_extr_i64_i32(QREG_CC_N, QREG_CC_C, t64);
>> + /* Note that C=0 if shift count is 0, and we get that for
>> free. */
>> + } else {
>> + TCGv zero = tcg_const_i32(0);
>> + tcg_gen_extrl_i64_i32(QREG_CC_N, t64);
>> + tcg_gen_shri_i64(t64, t64, bits);
>> + tcg_gen_extrl_i64_i32(QREG_CC_C, t64);
>> + tcg_gen_movcond_i32(TCG_COND_EQ, QREG_CC_C,
>> + s32, zero, zero, QREG_CC_C);
>> + tcg_temp_free(zero);
>> + }
>>
>> Do you have a better idea?
>
> if (opsize == OS_LONG) {
> tcg_gen_extr_i64_i32(QREG_CC_N, QREG_CC_C, t64);
> } else {
> tcg_gen_extrl_i64_i32(QREG_CC_N, t64);
> tcg_gen_shri_i32(QREG_CC_C, QREG_CC_N, bits);
> }
>
> Since we zero-extend the input from bits, it's still true that a zero shift
> gets C=0 for free.
>
It doesn't work because we work with word/byte where the bit sign has
been extended to the long word. So in the case of 0 shift, with retrieve
C=<original bit sign> and not 0.
Laurent
