Re: [RFC PATCH 01/43] target/loongarch: Add vector data type vec_t

[Richard Henderson]

On 12/24/22 00:15, Song Gao wrote:
> +#define LSX_LEN   (128)
> +typedef union vec_t vec_t;
> +union vec_t {
> +    int8_t   B[LSX_LEN / 8];
> +    int16_t  H[LSX_LEN / 16];
> +    int32_t  W[LSX_LEN / 32];
> +    int64_t  D[LSX_LEN / 64];
> +    __int128 Q[LSX_LEN / 128];
> +};
> +
> +typedef union fpr_t fpr_t;
> +union fpr_t {
> +    uint64_t d;
> +    vec_t vec;
> +};

You need to think about host endianness with this overlap and indexing.

There are two different models which can be emulated:

(1) target/{arm,s390x}/ has each uint64_t in host-endian order, but the words are indexed 
little-endian.  See, for instance, target/s390x/tcg/vec.h.

(2) target/{ppc,i386}/ has the entire vector in host-endian order.  See, for instance, 
ZMM_* in target/i386/cpu.h.

If you do nothing, I assume this will fail on a big-endian host.


r~