[fpc-devel] Progress on reviewing x86_64 optimizer overhaul and node semantic pass

[J. Gareth Moreton]

Sorry, I meant a "repeat... until False;" loop, using "Break" or "Exit" 
statements when I actually want to leave it, and "Continue" for the 
'not-a-goto' statement!

On 26/10/2019 15:47, J. Gareth Moreton wrote:
> Hi Florian,
>
> That seems like a fair assessment.  I'll see what I can do, especially 
> as I have a design spec to go by, so maybe there's stuff to salvage 
> and re-implement.
>
> If I recall, there was a similar TODO in the current code and it just 
> got moved, but I'll double-check that.
>
> I've seen 'goto' used a few times in the code but wasn't sure what the 
> policy was on that.  Generally I use a "repeat... until True;" loop 
> with a "Continue;" - is that an okay substitution?
>
> Since you're suggesting more bite-sized chunks, I think the first 
> thing I'll do is overhaul the jump optimisations, since they caused 
> significant improvements in places that are independent of reducing 
> the optimiser passes.
>
> Gareth aka. Kit
>
> On 26/10/2019 13:26, Florian Klämpfl wrote:
>> Am 18.10.19 um 18:07 schrieb J. Gareth Moreton:
>>> Hi everyone,
>>>
>>> How is everyone doing?  Sorry for my silence - been a bit tied up 
>>> with things in life.  Anyway, that aside, has there been any further 
>>> progress on reviewing the x86_64 optimizer overhaul over at 
>>> https://bugs.freepascal.org/view.php?id=34628? I ask because I've 
>>> sort-of blocked myself in any further improvements to the peephole 
>>> optimizer.
>>
>> I had meanwhile a look at it and to be honest, I am against applying 
>> the remainders in its current form.
>> - First, the patches are inter-winded and the single patches do not 
>> cover one single topic. Today, using e.g. TortoiseGit on Windows 
>> (sorry, on Linux there is no tool which comes close) such patches can 
>> be re-arranged without too much hazzle.
>> - Breaking the principle of the multiple optimizer passes is 
>> reasonable on the one hand, on the other hand it makes complicated 
>> code even more complicated and in particular as only the optimizer 
>> benefits, I see no reason to do so. In particular in combination with 
>> using gotos, the price being payed regarding maintainability is very 
>> high.
>> - Also things like ConditionalJumpShortcut in aoptx86.pas containing 
>> arm and aarch64 defines does not convince me regarding the patches.
>> - Patches contains open todo: "TODO: FIXME removing the first 
>> instruction fails"
>>
>> I would really like to see parts of the patch applied, but this 
>> requires that it is re-arranged in small, oversee-able changes.
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>>
>

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