On 22/04/2018 21:44, druck wrote:
> On 22/04/2018 12:22, Gareth's Downstairs Computer wrote:
>> For example, due to operator precedence, parentheses might
>> prove to be unnecessary, but you'd be justifiably miffed
>> if they disappeared from the source code, as source code
>> has human understandabilty considerations, and so
>> it becomes necessary to
>> insert a special form of NOP in the compiled code to
>> represent the parentheses; only one NOP for each pair.
>
> No, only the source needs such human readable information, it should not
> appear in compiled code, or even in the output of hand written assembler.

Not wishing to be rude, but may I suggest that you read this
thread from the top, for the discussion, in my terms at least,
is for the source to be the compiled code!

>> So, the reason for wanting the instruction encoding of the A53
>> (now discovered in excelsis) is to seek ambiguous forms of the
>> same instruction to let me effectively insert such NOPs but
>> without unnecessarily slowing down a program.
>
> I couldn't think of a worse way to encode that information, who will
> remember in a years time which ambiguous form mean what?

I repeat my exhortation as above.

> Incidentally; there is only one guaranteed NOP in ARM, and that is ADD
> R0,R0,R0. The 32bit conditional on never instructions (NV) have been
> deprecated and  reused for new instructions, and this may well happen to
> other "non useful with no side effects" instructions such as ADD
> Rx,Rx,Rx where Rx is not 0.

Exhortation repeated, the discussion revolves around the 64bit ARMv8



Nevertheless, thankyou for your contribution

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