r209297 - Make the parent-map use significantly less memory.

[Jordan Rose]

On May 21, 2014, at 9:22 , Manuel Klimek <klimek at google.com> wrote:

> On Wed, May 21, 2014 at 6:20 PM, Jordan Rose <jordan_rose at apple.com> wrote:
> 
> On May 21, 2014, at 9:19 , Manuel Klimek <klimek at google.com> wrote:
> 
>> On Wed, May 21, 2014 at 6:10 PM, Jordan Rose <jordan_rose at apple.com> wrote:
>> You might want to bump up the size of the SmallVector too. Right now you're dynamically allocating a SmallVector<T, 1>, and immediately putting two things into it. Alternately, you could use a std::vector, which has a smaller sizeof itself.
>> 
>> I tried the various combinations, and it didn't make a difference, so I went for making the code the simplest, which was reusing the ParentVector typedef.
>> If we change the ParentVector to a SmallVector<T, 2> we'll also use that for getParents() which mostly returns a single element.
>>  
> 
> SmallVector's already too big to fit in registers, so adding another two words to it won't really hurt any uses on the stack, will it?
> 
> So you're proposing to just bump it to 2? I'm happy to do that, but I lack any way to get data that would sway me one way or the other, thus I think it's mostly guesswork (but I trust your guesswork is probably better than mine ;)

Well, we don't have that many matcher-based tools, so I'm not that familiar with how ParentVector is really used in practice. Dynamically allocating a SmallVector that is known to be too small just felt wrong to me, is all.

Jordan

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