[cfe-commits] r49570 - in /cfe/trunk/lib/Sema: IdentifierResolver.cpp IdentifierResolver.h

[Argiris Kirtzidis]

Chris Lattner wrote:
>> +  if (CurIndex == VECTOR_SIZE) {
>> +    // Add a IdDeclInfo vector 'pool'
>> +    IDIVecs.resize(IDIVecs.size() + 1);
>
> I believe this is O(n) on some std::list's.  I'd just use 
> IDIVecs.push_back(std::vector<t>());  This is guaranteed constant time 
> and is more idiomatic.

Done.

>
>> +    // Fill the vector
>> +    IDIVecs.back().resize(VECTOR_SIZE);
>
> If you're using std::vector, why not just make this 
> 'reserve(VECTOR_SIZE)' and then use push_back when adding elements.  
> This way, the vector keeps track of the size, instead of having to 
> maintain CurIndex in parallel?
>
>>   }
>> +  IdDeclInfo *IDI = &IDIVecs.back()[CurIndex];
>
> If you do that, this can just be push_back() + back().

I had tested both ways and found the 'resize and initialize all at once' 
to be a tiny bit more efficient. This was on msvc though. I attached the 
'reserve' way in case you'd like to test it yourself.
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