[fpc-devel] More peephole

[Martin Frb]

On 22/01/2014 21:29, Florian Klämpfl wrote:
> Am 22.01.2014 04:06, schrieb Martin Frb:
>> On 21/01/2014 21:28, Florian Klämpfl wrote:
>>> Can you post some example code? It might be worth to think about
>>> improving this already in at the node level.
>>>
>> While getting examples, another issue:
>>
>>
>> with -O2 , -O3 or -O4
>>
>> Note the
>>      movl    %eax,%edx
>>      movl    %edx,%eax
>>
>> with -O1 it is
>>      movl    %eax,-4(%ebp)
>>      movl    -4(%ebp),%eax
> Well, -O1 can be neglected ...
>

Ok.

There is another idea, I had in that context, and like to bring up. 
Though maybe this is already solved in a different way.

One of the optimizations you said it where better avoided to be created 
in first. I agree.
Only, even if that is archived at some time, who guarantees that it will 
not be back (and unnoticed)?

Are there tests, that can detect this?
Of course all generated assembler could be parsed back, and analysed. 
But that is rather a lot of work.

Or the code could be added, and asserted not to be triggered. Of course 
adding actual test code to the compiler is not a good way either. Unless 
assert style / Only compiled in if -Sa or -dXXX is given.

Would anything in that direction make sense?
Then the code could work in real live, until no longer needed, at which 
time it was still useful for assertion.

Just an idea.