[fpc-devel] Inlining problem and LEB128

[Florian Klämpfl]

Am 23. Juni 2019 16:05:05 schrieb Jonas Maebe <jonas at freepascal.org>:

> On 23/06/2019 01:10, J. Gareth Moreton wrote:
>
>> Currently, you can get away with specifying the "inline" directive for a
>> function in just the implementation section of a unit, and the function
>> will be inlined.  However, in some situations, this can cause compiler
>> crashes which I believe is due to a mixture of the function no longer
>> being inlined and the internal CRCs not changing, possibly due to a
>> collision.
>
> While possible, I don't think the issue is CRC collisions. It's more
> likely to be stale pointers somewhere.
>
>> My solution to this is as follows... ALWAYS attempt to create a node
>> tree (unless "noinline" is specified).  This is effectively
>> auto-inlining, but routines are not inlined unless the explicit
>> directive instructs the compiler to do so (or something like -O4 is
>> specified and the compiler determines that a function should be inlined
>> due to its shortness, say).  This would help mitigate the problem of the
>> null node tree by causing the compiler to check said node tree and set
>> the "cannot inline" flag when appropriate.
>>
>> This isn't ideal though, as it would have two notable side-effects:
>>
>> - General compilation will be slightly slower because of extra analysis
>> on the node trees and copying them into the "inlined nodes" pointer.
>> - The compiled PPU files will increase in size significantly.
>
> The main issue is that loading PPUs would become a lot slower in this
> case: the entire node tree of all of those functions would then also be
> reconstructed while loading the PPUs -> tons of class instantiations.
> That would also significantly increase the compiler's memory usage.
>
>
> Jonas
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Not to forget that it would be very easy to reconstruct the source code from PPU. Some users might not like this ...