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

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

On 8/18/21 6:56 PM, Richard Henderson wrote:
> 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.

Oops indeed.

>  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.

I'll go for the easier path ;)