Re: [PATCH 1/5] target/mips: Replace GET_OFFSET() macro by get_offset() function

[Richard Henderson]

On 8/18/21 6:43 AM, Philippe Mathieu-Daudé wrote:
> The target endianess information is stored in the BigEndian
> bit of the Config0 register in CP0.
>
> As a first step, replace the GET_OFFSET() macro by an inlined
> get_offset() function, passing CPUMIPSState as argument.
>
> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
> ---
>   target/mips/tcg/ldst_helper.c | 57 +++++++++++++++++++++--------------
>   1 file changed, 35 insertions(+), 22 deletions(-)
>
> diff --git a/target/mips/tcg/ldst_helper.c b/target/mips/tcg/ldst_helper.c
> index d42812b8a6a..97e7ad7d7a4 100644
> --- a/target/mips/tcg/ldst_helper.c
> +++ b/target/mips/tcg/ldst_helper.c
> @@ -52,31 +52,44 @@ HELPER_LD_ATOMIC(lld, ldq, 0x7, (target_ulong))
>   
>   #endif /* !CONFIG_USER_ONLY */
>   
> +static inline bool cpu_is_bigendian(CPUMIPSState *env)
> +{
> +    return extract32(env->CP0_Config0, CP0C0_BE, 1);
> +}
> +
>   #ifdef TARGET_WORDS_BIGENDIAN
>   #define GET_LMASK(v) ((v) & 3)
> -#define GET_OFFSET(addr, offset) (addr + (offset))
>   #else
>   #define GET_LMASK(v) (((v) & 3) ^ 3)
> -#define GET_OFFSET(addr, offset) (addr - (offset))
>   #endif
>   
> +static inline target_ulong get_offset(CPUMIPSState *env,
> +                                      target_ulong addr, int offset)
> +{
> +    if (cpu_is_bigendian(env)) {
> +        return addr + offset;
> +    } else {
> +        return addr - offset;
> +    }
> +}
> +
>   void helper_swl(CPUMIPSState *env, target_ulong arg1, target_ulong arg2,
>                   int mem_idx)
>   {
>       cpu_stb_mmuidx_ra(env, arg2, (uint8_t)(arg1 >> 24), mem_idx, GETPC());
>   
>       if (GET_LMASK(arg2) <= 2) {
> -        cpu_stb_mmuidx_ra(env, GET_OFFSET(arg2, 1), (uint8_t)(arg1 >> 16),
> +        cpu_stb_mmuidx_ra(env, get_offset(env, arg2, 1), (uint8_t)(arg1 >> 16),
>                             mem_idx, GETPC());
>       }
>   
>       if (GET_LMASK(arg2) <= 1) {
> -        cpu_stb_mmuidx_ra(env, GET_OFFSET(arg2, 2), (uint8_t)(arg1 >> 8),
> +        cpu_stb_mmuidx_ra(env, get_offset(env, arg2, 2), (uint8_t)(arg1 >> 8),
>                             mem_idx, GETPC());

So... yes, this is an improvement, but it's now substituting a constant for a runtime 
variable many times over.  I think you should drop get_offset() entirely and replace it with

    int dir = cpu_is_bigendian(env) ? 1 : -1;

    stb(env, arg2 + 1 * dir, data);

    stb(env, arg2 + 2 * dir, data);

Alternately, bite the bullet and split the function(s) into two, explicitly endian 
versions: helper_swl_be, helper_swl_le, etc.


r~