[GCC][PATCH v2][Aarch64] Exploiting BFXIL when OR-ing two AND-operations with appropriate bitmasks

[Sam Tebbs]

On 08/28/2018 11:53 PM, James Greenhalgh wrote:
> Hm, I'm not very sure about the naming here; "left consecutive" isn't a
> common phrase to denote the mask you're looking for (exact_log2 (-i) != -1
> if I'm reading right), and is misleading 0x0000ffff is 'left consecutive'
> too, just with zeroes rather than ones.
>
I think you're right about it not being the best naming. Do you have any 
suggestions for a better name?
>> diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
>> index af5db9c595385f7586692258f750b6aceb3ed9c8..01d9e1bd634572fcfa60208ba4dc541805af5ccd 100644
>> --- a/gcc/config/aarch64/aarch64-protos.h
>> +++ b/gcc/config/aarch64/aarch64-protos.h
>> @@ -574,4 +574,6 @@ rtl_opt_pass *make_pass_fma_steering (gcc::context *ctxt);
>>   
>>   poly_uint64 aarch64_regmode_natural_size (machine_mode);
>>   
>> +bool aarch64_is_left_consecutive (HOST_WIDE_INT);
>> +
>>   #endif /* GCC_AARCH64_PROTOS_H */
>> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
>> index fa01475aa9ee579b6a3b2526295b622157120660..3cfa51b15af3e241672f1383cf881c12a44494a5 100644
>> --- a/gcc/config/aarch64/aarch64.c
>> +++ b/gcc/config/aarch64/aarch64.c
>> @@ -1454,6 +1454,14 @@ aarch64_hard_regno_caller_save_mode (unsigned regno, unsigned,
>>       return SImode;
>>   }
>>   
>> +/* Implement IS_LEFT_CONSECUTIVE.  Check if I's bits are consecutive
> What is IS_LEFT_CONSECUTIVE - I don't see it elsewhere in the GCC code, so
> what does the comment refer to implementing?
Thanks for pointing out this mistake, it should read 
"AARCH64_IS_LEFT_CONSECUTIVE" to refer to the function definition in 
aarch64-protos.h. This will of course change once a better name is 
thought of.

Thanks,
Sam