Re: [PATCH v8] target/ppc: Fix bugs in VSX_CVT_FP_TO_INT and VSX_CVT_FP_TO_INT2 macros

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

On 11/11/23 09:36, Cédric Le Goater wrote:
> Adding Richard,
> 
> Thanks,
> 
> C.
> 
> 
> On 11/10/23 19:41, John Platts wrote:
>> The patch below fixes a bug in the VSX_CVT_FP_TO_INT and VSX_CVT_FP_TO_INT2
>> macros in target/ppc/fpu_helper.c where a non-NaN floating point value from the
>> source vector is incorrectly converted to 0, 0x80000000, or 0x8000000000000000
>> instead of the expected value if a preceding source floating point value from
>> the same source vector was a NaN.
>>
>> The bug in the VSX_CVT_FP_TO_INT and VSX_CVT_FP_TO_INT2 macros in
>> target/ppc/fpu_helper.c was introduced with commit c3f24257e3c0.
>>
>> This patch also adds a new vsx_f2i_nan test in tests/tcg/ppc64 that checks that
>> the VSX xvcvspsxws, xvcvspuxws, xvcvspsxds, xvcvspuxds, xvcvdpsxws, xvcvdpuxws,
>> xvcvdpsxds, and xvcvdpuxds instructions correctly convert non-NaN floating point
>> values to integer values if the source vector contains NaN floating point values.
>>
>> Fixes: c3f24257e3c0 ("target/ppc: Clear fpstatus flags on helpers missing it")
>> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1941
>> Signed-off-by: John Platts <john_platts@hotmail.com>
>> ---
>>   target/ppc/fpu_helper.c         |  12 +-
>>   tests/tcg/ppc64/Makefile.target |   5 +
>>   tests/tcg/ppc64/vsx_f2i_nan.c   | 300 ++++++++++++++++++++++++++++++++
>>   3 files changed, 313 insertions(+), 4 deletions(-)
>>   create mode 100644 tests/tcg/ppc64/vsx_f2i_nan.c
>>
>> diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c
>> index 03150a0f10..4b3dcad5d1 100644
>> --- a/target/ppc/fpu_helper.c
>> +++ b/target/ppc/fpu_helper.c
>> @@ -2880,20 +2880,22 @@ uint64_t helper_XSCVSPDPN(uint64_t xb)
>>   #define VSX_CVT_FP_TO_INT(op, nels, stp, ttp, sfld, tfld, sfi, rnan)         \
>>   void helper_##op(CPUPPCState *env, ppc_vsr_t *xt, ppc_vsr_t *xb)             \
>>   {                                                                            \
>> +    int all_flags = 0;                                                       \
>>       ppc_vsr_t t = { };                                                       \
>>       int i, flags;                                                            \
>>                                                                                \
>> -    helper_reset_fpstatus(env);                                              \
>> -                                                                             \
>>       for (i = 0; i < nels; i++) {                                             \
>> +        helper_reset_fpstatus(env);                                          \
>>           t.tfld = stp##_to_##ttp##_round_to_zero(xb->sfld, &env->fp_status);  \
>>           flags = env->fp_status.float_exception_flags;                        \
>> +        all_flags |= flags;                                                  \
>>           if (unlikely(flags & float_flag_invalid)) {                          \
>>               t.tfld = float_invalid_cvt(env, flags, t.tfld, rnan, 0, GETPC());\
>>           }                                                                    \
>>       }                                                                        \
>>                                                                                \
>>       *xt = t;                                                                 \
>> +    env->fp_status.float_exception_flags = all_flags;                        \
>>       do_float_check_status(env, sfi, GETPC());    


Looks reasonable.  Each lane wants to check for snan, and it needs a clean set of flags to 
do that.  Merge all lane flags to pass to do_float_check_status.  So,

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>


r~