[PATCH] [arm] Implement Armv8.1-M low overhead loops

[Kyrill Tkachov]

Hi Roman,

On 2/21/20 3:49 PM, Roman Zhuykov wrote:
> 11.02.2020 14:00, Richard Earnshaw (lists) wrote:
>> +(define_insn "*doloop_end"
>> +Â  [(parallel [(set (pc)
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (if_then_else
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (ne (reg:SI LR_REGNUM) (const_int 1))
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (label_ref (match_operand 0 "" ""))
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (pc)))
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â  (set (reg:SI LR_REGNUM)
>> +Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  (plus:SI (reg:SI LR_REGNUM) (const_int -1)))])]
>> +Â  "TARGET_32BIT && TARGET_HAVE_LOB && !flag_modulo_sched"
>> +Â  "le\tlr, %l0")
>>
>> Is it deliberate that this pattern name has a '*' prefix?  doloop_end
>> is a named expansion pattern according to md.texi.
>>
>> R.
> 21.02.2020 18:30, Kyrill Tkachov wrote:
>> +;; Originally expanded by 'doloop_end'.
>> +(define_insn "doloop_end_internal"
>>
>> We usually prefer to name these patterns with a '*' in front to
>> prevent the gen* machinery from generating gen_* unneeded expanders
>> for them if they're not used.
>>
> It seems you and Richard asking Andrea to do the opposite things.
> :) LOL.patch


Almost, but not exactly incompatible things ;)

doloop_end is a standard name and if we wanted to use it directly it 
cannot have a '*', which Richard is right to point out.

Once "doloop_end" is moved to its own expander and the define_insn is 
doloop_end_internal, there is no reason for it to not have a '*' as its 
gen_* form is never called.

Thanks,

Kyrill


> Roman
>
> PS. I don't have an idea what approach is correct.