[fpc-devel] extend "unreachable code" warning for more cases?

Sven Barth pascaldragon at googlemail.com
Wed Feb 26 10:28:15 CET 2014

Am 26.02.2014 09:41, schrieb Sergei Gorelkin:
> 26.02.2014 12:09, Sven Barth пишет:
>> Hello together!
>> In context of Apple's recent security bug where a "goto fail;" at the 
>> wrong place disabled
>> certificate checking or something along that lines I've thought 
>> whether it would 1) be worthwhile to
>> extend FPC with the capability to detect such cases as well and 2) to 
>> see whether it would be
>> currently feasible at all.
>> So, how hard would it be to let the compiler detect cases like these:
>> === code begin ===
>> procedure Test1;
>> begin
>>    Writeln('Test1');
>>    Exit;
>>    Writeln('Test1');
>> end;
>> procedure Test2;
>> label
>>    stop;
>> begin
>>    Writeln('Test2');
>>    goto stop;
>>    Writeln('Test2');
>> stop:
>> end;
>> === code end ===
>> and of course potentially more complex ones...
>> Also would you think it would be worthwhile to spend time on this?
> The definite assignment analysis ported by me four years ago 
> (http://bugs.freepascal.org/view.php?id=15523) detects all cases of 
> unreachable code, except backward goto's. Everything but backward 
> goto's is almost trivial, backward goto's are more complicated because 
> they require multiple iterations over code tree, but are certainly 
> feasible.
Nice... does that code still work with current trunk? How does it look 
in light of Florian's recent work on SSA? (though it's not yet fully in 
trunk AFAIK) Could your DFA be combined combined with the current DFA so 
that we would have both definite assignment analysis and live variable 
analysis? [ok, after reading your first comment it should be possible] 
Since you now have write access to SVN you could finally use a branch 
for this. :)


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