Re: [PATCH] target/arm: Fix sve pred_desc decoding

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

On 1/7/21 8:02 AM, Peter Maydell wrote:
>>  void HELPER(sve_zip_p)(void *vd, void *vn, void *vm, uint32_t pred_desc)
>>  {
>> -    intptr_t oprsz = extract32(pred_desc, 0, SIMD_OPRSZ_BITS) + 2;
>> +    intptr_t oprsz = extract32(pred_desc, 0, SIMD_DATA_SHIFT) + 2;
> 
> Why do we not get oprsz by extracting SIMD_OPRSZ_BITS starting at
> SIMD_OPRSZ_SHIFT ? (or even by calling simd_oprsz(), which
> certainly looks like it ought to be a helper function for
> extracting the oprsz...)

The predicate operations are small -- minimum 2 bytes -- and cannot encode with
the real simd_oprsz (minumum 8, then multiples of 16).

This is shear abuse of the SIMD_* defines.  You're right that I shouldn't have
done this in the first place, and should probably rename everything having to
do with predicates.


r~