complexity of matching symbol names to version scripts

[Sean Silva via llvm-commits]

On Mon, May 2, 2016 at 5:26 PM, Rui Ueyama via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> What I'm worrying is this. Let N be the number of symbols in all input
> files and M be the number of symbols that appear in version scripts.
>
> If there's no pattern matching in version symbol script, then the cost of
> setting versions is O(M). We call SymbolTable::find(StringRef) for each
> symbol from version scripts and set a version to the return value.
>
> But if we allow patterns, the cost becomes O(N). Even though is better
> than O(N*M), it is a large number. M is order of hundreds or thousands, but
> N can be as large as order of millions.
>
> So I think we should avoid pattern matching to symbols.
>

What do we do if the user passes a version script that has a pattern match?
Emit an error?

-- Sean Silva


>
>
> On Sat, Apr 30, 2016 at 7:46 PM, Rafael Espíndola <
> rafael.espindola at gmail.com> wrote:
>
>> No idea why this just came to mind, but anyway:
>>
>> I remember you mentioning that one annoying thing about version
>> scripts is the need to match each symbol against multiple possible
>> regular expressions (globs?).
>>
>> But I just remembered that that can be done efficiently. Multiple
>> regular expressions can be tested at once. They are all just NFAs :-)
>>
>> Cheers,
>> Rafael
>>
>
>
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